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  • Springer  (73,368)
  • American Chemical Society  (59,270)
  • American Geophysical Union  (8,649)
  • Annual Reviews
  • 2020-2023  (124)
  • 2020-2022  (142,051)
  • 1980-1984
  • 2020  (142,175)
  • 2020  (142,175)
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  • 2020-2023  (124)
  • 2020-2022  (142,051)
  • 1980-1984
  • 2020-2024  (129)
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  • 1
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    Millimeter wave spectroscopic measurements over the South Pole: 5. Morphology and evolution of HNO3vertical distribution, 1993 versus 1995 (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground‐based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range ∼16–48 km, and cover the fall‐winter‐spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occurring about 20 days before sunset, which appears to be the result of higher altitude heterogeneous conversion of NOx as photolysis diminishes. Both years show a strong increase in HNO3 beginning about polar sunset, in a layer peaking at about 25 km, as additional NOx is heterogeneously converted to nitric acid. When temperatures drop to the polar stratospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduced in the lower stratosphere, although at least 2–3 weeks of temperatures ≤192 K appear to be required to complete most of the gas‐phase removal at the upper end of the depletion range (22–25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinatubo, there appears to be little gross difference in the timing and effects of PSC formation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs appears to be nearly complete up to ∼25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynamical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion‐based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High‐altitude HNO3 production peaks during a period of ∼20 days, but appears to persist for up to ∼40 days in the 40–45 km range, ceasing well before sunrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reappearance of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to ∼1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from ∼25 km as temperatures rise during the late winter. There is a delay of ∼15 days after sunrise before photolysis causes significant depletion in the altitude range below ∼30 km, where subsidence has carried virtually all higher‐altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixing ratios less than ∼5 ppbv below 30 km until the final breakdown of the vortex in November brings larger amounts of HNO3 with air from lower latitudes.
    Description: Published
    Description: 17739-17750
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: ozone depletion ; HNO3 ; Antarctic stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Reliability of the automatic procedures for locating earthquakes in southwestern Alps and northern Apennines (Italy) (2020)
    Springer
    Details
    Publication Date: 2020-10-16
    Description: Reliable automatic procedure for locating earthquake in quasi-real time is strongly needed for seismic warning system, earthquake preparedness, and producing shaking maps. The reliability of an automatic location algorithm is influenced by several factors such as errors in picking seismic phases, network geometry, and velocity model uncertainties. The main purpose of this work is to investigate the performances of different automatic procedures to choose the most suitable one to be applied for the quasi-real-time earthquake locations in northwestern Italy. The reliability of two automatic-picking algorithms (one based on the Characteristic Function (CF) analysis, CF picker, and the other one based on the Akaike Information Criterion (AIC), AIC picker) and two location methods (“Hypoellipse” and “NonLinLoc” codes) is analysed by comparing the automatically determined hypocentral coordinates with reference ones. Reference locations are computed by the “Hypoellipse” code considering manually revised data and tested using quarry blasts. The comparison is made on a dataset composed by 575 seismic events for the period 2000–2007 as recorded by the Regional Seismic network of Northwestern Italy. For P phases, similar results, in terms of both amount of detected picks and magnitude of travel time differences with respect to manual picks, are obtained applying the AIC and the CF picker; on the contrary, for S phases, the AIC picker seems to provide a significant greater number of readings than the CF picker. Furthermore, the “NonLin- Loc” software (applied to a 3D velocity model) is proved to be more reliable than the “Hypoellipse” code (applied to layered 1D velocity models), leading to more reliable automatic locations also when outliers (wrong picks) are present.
    Description: Published
    Description: 393–411
    Description: 8T. Sismologia in tempo reale
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Application of monitoring guidelines to induced seismicity in Italy (2020)
    Springer
    Details
    Publication Date: 2020-11-12
    Description: Public concern about anthropogenic seismic- ity in Italy first arose in the aftermath of the deadly M ≈ 6 earthquakes that hit the Emilia-Romagna region (northern Italy) in May 2012. As these events occurred in a (tectonically active) region of oil and gas production and storage, the question was raised, whether stress perturbations due to underground industrial activities could have induced or triggered the shocks. Following expert recommendations, in 2014, the Italian Oil & Gas Safety Authority (DGS-UNMIG, Ministry of Economic Development) published guidelines (ILG - Indirizzi e linee guida per il monitoraggio della sismicità, delle deformazioni del suolo e delle pressioni di poro nell’ambito delle attività antropiche), describing regula- tions regarding hydrocarbon extraction, waste-water in- jection and gas storage that could also be adapted to other technologies, such as dams, geothermal systems, CO2 storage, and mining. The ILG describe the frame- work for the different actors involved in monitoring activities, their relationship and responsibilities, the procedure to be followed in case of variations of mon- itored parameters, the need for in-depth scientific anal- yses, the definition of different alert levels, their mean- ing and the parameters to be used to activate such alerts. Four alert levels are defined, the transition among which follows a decision to be taken jointly by relevant au- thorities and industrial operator on the basis of evalua- tion of several monitored parameters (micro-seismicity, ground deformation, pore pressure) carried on by a scientific-technical agency. Only in the case of liquid reinjection, the alert levels are automatically activated on the basis of exceedance of thresholds for earthquake magnitude and ground shaking – in what is generally known as a Traffic Light System (TLS). Istituto Nazionale di Geofisica e Vulcanologia has been charged by the Italian oil and gas safety authority (DGS- UNMIG) to apply the ILG in three test cases (two oil extraction and one gas storage plants). The ILG indeed represent a very important and positive innovation, as they constitute official guidelines to coherently regulate monitoring activity on a national scale. While pilot studies are still mostly under way, we may point out merits of the whole framework, and a few possible critical issues, requiring special care in the implementa- tion. Attention areas of adjacent reservoirs, possibly licenced to different operators, may overlap, hence mak- ing the point for joint monitoring, also in view of the possible interaction between stress changes related to the different reservoirs. The prescribed initial blank- level monitoring stage, aimed at assessing background seismicity, may lose significance in case of nearby ac- tive production. Magnitude – a critical parameter used to define a possible step-up in activation levels – has inherent uncertainty and can be evaluated using differ- ent scales. A final comment considers the fact that relevance of TLS, most frequently used in hydraulic fracturing operations, may not be high in case of trig- gered tectonic events.
    Description: Published
    Description: 1015–1028
    Description: 1IT. Reti di monitoraggio e sorveglianza
    Description: JCR Journal
    Keywords: Anthropogenic seismicity ; Alert system ; Monitoring guidelines ; 04.06. Seismology ; 05.04. Instrumentation and techniques of general interest
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Geochemistry of gas and water discharge from the magmatic-hydrothermal system of Guallatiri volcano, northern Chile (2020)
    Springer
    Details
    Publication Date: 2020-11-09
    Description: This work presents the first chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O, and δD) data for fluid discharges fromGuallatiri volcano, a remote and massive stratovolcano, which is considered as the second most active volcano of the Central Volcanic Zone (CVZ) in northern Chile. Fumarolic gases had outlet temperatures of between 80.2 and 265 °C, and showed a significant magmatic fluid contribution marked by the occurrence of SO2, HCl, and HF that are partially scrubbed by a hydrothermal aquifer. The helium isotope ratios (〈 3.2) were relatively low compared to those of other active volcanoes in CVZ, possibly due to contamination of the magmatic source by 4He-rich crust and/or crustal fluid addition to the hydrothermal reservoir. Geothermometry in the H2O-CO2-CO-H2-CH4 system suggests equilibrium temperatures of up to 320 °C attained in a vapor phase at redox conditions intermediate between those typical of hydrothermal and magmatic environments. Thermal springs located 12 km northwest of the volcano’s summit had outlet temperatures of up to 50.1 °C, neutral to slightly basic pH, and a sodium bicarbonate composition, typical of distal fluid discharges in volcanic systems. Cold springs at the base of the volcanic edifice, showing a calcium sulfate composition, were likely produced by interaction of shallow meteoric water with CO2- andH2S-rich gases. A geochemical conceptual model was constructed to graphically represent these results, which can be used as an indication for future geochemical monitoring and volcanic hazard assessment.
    Description: Published
    Description: id 57
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Total grain size distribution of components of fallout deposits and implications for magma fragmentation mechanisms: examples from Campi Flegrei caldera (Italy) (2020)
    Springer
    Details
    Publication Date: 2020-12-18
    Description: In this paper, we present results of the reconstruction of the total grain size distribution (TGSD) of the material erupted during explosive volcanic eruptions at Campi Flegrei (Italy) considering all components (juvenile, lithic and crystal clasts). To date, the few TGSDs made available have been mostly reconstructed by assuming that the tephra deposits consisted of only one component. This simplification can introduce substantial bias in the interpretation of magma fragmentation mechanisms and significantly affect ash dispersion forecasts, since each tephra component has specific aerodynamic characteristics. By means of field investigations and laboratory analyses on samples collected from deposits of the Agnano-Monte Spina and Astroni eruptions, we reconstructed the TGSDs of juvenile, lithic and crystal components via the Voronoi tessellation method. Our results show how the systematic reconstruction of a TGSD, from the component-specific to the bulk TGSD, can provide important information on magma fragmentation mechanisms and wall-rock erosion processes. Results confirm that the bulk TGSD is the combination of the merging of different component subpopulations, according to their own TGSD, density and relative mass proportions. In addition, the integration of component analysis, TGSD and settling velocity data allowed characterization of the aerodynamic behaviour of each component at variable distances from the vent, which can be related to their own parent grain size distribution. The integration of new data from distal tephra deposits for the considered eruptions has thus allowed a reassessment of the erupted volumes of eruptions considered in this research, which are now 3.17 and 0.63 km3, for Agnano-Monte Spina and Astroni, respectively.
    Description: Published
    Description: id 31
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Cross-Correlation Analysis of Seismic Noise Data in the Fucino Plain (Central Appennines, Italy) (2020)
    Springer
    Details
    Publication Date: 2020-10-01
    Description: Several months of ambient seismic noise recordings are used for investigating the distribution of elastic properties in the Fucino Plain, one of the largest intermontane tectonic depressions of the Italian Apennine chain (Central Italy). The Plain is characterized by a low level of seismicity but the presence of several active faults makes it an Italian area of high seismic hazard. The most recent and strongest seismic event in Fucino Plain occurred in the 1915 (Avezzano earthquake) and it represents one of the most energetic events (Ms = 7.0) happened in central Apennines. Inter-stations Green’s functions are reconstructed by the cross-correlation of continuous ambient noise data recorded from twelve seismic velocimeters deployed around the Avezzano city, and organized in two different temporally sub-networks. The aim of cross-correlation analysis is to extract surface waves from Green’s functions for investigating the dispersive response of the structure. We analyzed the temporal stability of the cross-correlated signals that is used as an indicator of reliability of measurements and as criteria to select the Green’s functions to analyze
    Description: Published
    Description: 1173-1176
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Cross correlation ; Noise ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 7
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    Pyrite and Organic Compounds Coexisting in Intrusive Mafic Xenoliths (Hyblean Plateau, Sicily): Implications for Subsurface Abiogenesis (2020)
    Springer
    Details
    Publication Date: 2020-10-20
    Description: Pyrite and organic matter closely coexist in some hydrothermally-altered gabbroic xenoliths from the Hyblean Plateau, Sicily. The representative sample consists of plagioclase, Fe-oxides, clinopyroxene, pyrite and minor amounts of many other minerals. Plagioclase displays incipient albitization, clinopyroxene is deeply corroded. Pyrite grains are widely replaced by spongy-textured magnetite, which locally hosts Ca-(and Fe-)sulfate micrograins and blebs of condensed organic matter. Whole-rock trace element distribution evidences that incompatible elements, particularly the fluid-mobile Ba, U and Pb, are significantly enriched with respect to N-MORB values. The mineralogical and geochemical characteristics of the sample, and its U-Pb zircon age of 216.9 ± 6.7 MA, conform to the xenolith-based viewpoint that the unexposed Hyblean basement is a relict of the Ionian Tethys lithospheric domain, mostly consisting of abyssal-type serpentinized peridotites with small gabbroic intrusions. Circulating hydrothermal fluids there favored the formation of hydrocarbons trough Fischer-Tropsch-type organic synthesis, giving also rise to sulfidization episodes. Subsequent variations in temperature and redox conditions of the system induced partial de-sulfidization, Fe-oxides precipitation and sulfate-forming reactions, also promoting poly-condensation and aromatization of the already-formed hydrocarbons. Here we show organic matter adhering to a crystal face of a microscopic pyrite grain. Pyrite surfaces, as abiotic analogues of enzymes, can adsorb and concentrate organic molecules, also acting as catalysts for a broad range of proto-biochemical reactions. The present data therefore may support established abiogenesis models suggesting that pyrite surfaces carried out primitive metabolic cycles in suitable environments of the early Earth, such as endolithic recesses in mafic rocks permeated by hydrothermal fluids.
    Description: Published
    Description: 19-47
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: Abiogenesis ; FTT synthesis ; Hydrothermal system ; Pyrite ; Sicily ; Xenoliths
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    Promoting Geo-awareness to Make Citizens the First Watchers of the Territory (2020)
    Springer
    Details
    Publication Date: 2020-10-22
    Description: The earthquake occured in Tohoku (Japan) in 2011 showed that no matter how outstanding is the model of the mitigation of natural hazard, an earthquake can always surprise any studied attempt to contain a tsunami. I report this extreme example to draw the reader attention on how strong should be the commitment of the society in producing the optimal conditions to face natural hazard. Every country has a peculiar social context. If in the past we considered this as a secondary aspect, now we are obliged to recognize that the social context is of main importance when promoting mitigation of natural hazard. In this occasion I would like to refer to my experience as an educator in my country. Italy is a country where it is difficult to promote a dialogue between the Institutions and the citizens. The dialogue is difficult also among the communities of engineers, geologists and politicians. There is still a great confusion on the attribution of tasks and a lot of problems of difficult solution are related to corruption. In this context, education can play a crucial role and should be intensively addressed to promote geo-awareness in the citizens. People should learn about the geological site where their houses are built and get all the info necessary to understand if it has been done according to the law. Only in this way citizens become an active agent in promoting those changes without which an efficacious mitigation of natural hazard is impossible.
    Description: Published
    Description: 85-88
    Description: 3TM. Comunicazione
    Keywords: Risk communication, Earth Education, Public Awareness ; 05.03. Educational, History of Science, Public Issues
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 9
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    Local Seismic Response in a Large Intra-mountain Basin as Observed from Earthquakes and Microtremor Recordings: The Avezzano Area (Central Italy) (2020)
    Springer
    Details
    Publication Date: 2020-11-30
    Description: Buildings close to each other can perform different behaviour despite its similar seismic vulnerability. This effect is mainly due to the local seismic response connected to the characteristics of the shallow soil layers, especially when we move away from the epicentral area and the near field motion reduces its importance among the total amount of shaking. In this paper we show some results of the microzonation project of the Avezzano municipality, a town located in the southwestern portion of the Abruzzi region, which experienced the severe effects of the January 13th, 1915 M 7.0 earthquake. Starting from a particularly detailed knowledge of the geological characteristics of outcropping lithologies and inferring the trend of subsoil geometries, we explored the role played by the near-surface geology in causing variability of the ground motion by analysing a large database of earthquakes and microtremor recordings acquired by temporary seismological networks using classical site-reference and non-reference spectral techniques. Based on the obtained results we can seismically characterize all the municipal territory not only in terms of fundamental resonance frequency, useful in drawing maps of seismic microzonation and design geological sections, but also of amplification factors helpful in verifying numerical modelling of seismic response as required by national microzonation guidelines. We have also found many criticisms that need a more detailed analysis in order to establish the cause of these anomalies.
    Description: Published
    Description: 1153-1157
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Microzonation ; Site response ; Spectral techniques ; Seismic amplification ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 10
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    Using ground motion prediction equations to monitor variations in quality factor due to induced seismicity: a feasibility study (2020)
    Springer
    Details
    Publication Date: 2020-12-15
    Description: Sub-surface operations for energy production such as gas storage, fluid reinjection or hydraulic fracking may modify the physical properties of the rocks, in particular the seismic velocity and the anelastic attenuation. The aim of the present study is to investigate, through a synthetic test, the possibility of using empirical ground-motion prediction equations (GMPEs) to observe the variations in the reservoir. In the synthetic test, we reproduce the expected seismic activity (in terms of rate, focal mechanisms, stress drop and the b value of the Gutenberg-Richter) and the variation of medium properties in terms of the quality factor Q induced by a fluid injection experiment. In practice, peak-ground velocity data of the simulated earthquakes during the field operations are used to update the coefficients of a reference GMPE in order to test whether the coefficients are able to capture the medium properties variation. The results of the test show that the coefficients of the GMPE vary during the simulated field operations revealing their sensitivity to the variation of the anelastic attenuation. The proposed approach is suggested as a promising tool that, if confirmed by real data analysis, could be used for monitoring and interpreting induced seismicity in addition to more conventional techniques.
    Description: for Clean Energy) project, which received funding from the European Union’s Horizon 2020 research and innovation action, under grant agreement No 764810, and was partially funded by the PRIN Project MATISSE (Bando 2017, Prot. 20177EPPN2).
    Description: Published
    Description: 723–735
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Keywords: Induced seismicity ; Anelastic attenuation ; Ground motion predictive equations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 11
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    Probabilistic Seismic Hazard Analysis at Regional and National Scales: State of the Art and Future Challenges (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-01
    Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.
    Description: Published
    Description: e2019RG000653
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 12
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    The state of the art of gravimetry in Italy (2020)
    Springer
    Details
    Publication Date: 2020-11-25
    Description: Relative and absolute gravimetric measurements are carried out for metrological, geodetic and geophysical (structural and dynamic) studies. Gravimetry is largely used in Italy since long time for vast set of studies. Both relative and absolute measurements are carried out in several fields of geodesy, geophysics and geodynamic with different approaches. After a brief historical excursus, the paper presents the State of the Art of “Modern” Gravimetry in Italy in its various applications, together the main available results and products, with particular attention to: - Development of modern gravimetry in Italy: from relative to absolute measurements. - Italian Reference Gravity Networks: state of the art - The Italian gravimetric map: its evolution over time, data, the present-day status and related products. - Dynamic gravimetry: examples of applications in geodynamical areas. Finally, suggestions for future perspectives for gravimetry in Italy are outlined.
    Description: Published
    Description: 35–48
    Description: 1IT. Reti di monitoraggio e sorveglianza
    Description: JCR Journal
    Keywords: Gravimetria ; Reti di riferimento e monitoraggio
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  • 13
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    Unsupervised Geochemical Analysis of the Eruptive Products of Ischia, Vesuvius and Campi Flegrei (2020)
    Springer
    Details
    Publication Date: 2020-11-30
    Description: This work aimed to study geochemical data, composed of major and trace elements describing volcanic rocks collected from the Campanian active volcanoes of Vesuvius, Campi Flegrei and Ischia Island. The data were analyzed through the Self-Organizing Map (SOM) unsupervised neural net. SOM is able to group the input data into clusters according to their intrinsic similarities without using any information derived from previous geochemical-petrological considerations. The net was trained on a dataset of 276 geochemical patterns of which 96 belonged to Ischia, 94 to Vesuvius and 86 to Campi Flegrei volcanoes. Two investigations were carried out. The first one aimed to cluster geochemical data mainly characterizing the type of volcanic rocks of the three volcanic areas. The SOM clustering well grouped the oldest volcanic products of Ischia, Vesuvius and Campi Flegrei identifying a similar behaviour for the rocks emplaced in the oldest activity periods (〉19 ka), and showing their different evolution over time. In the second test, devoted to inferring information on the magmatic source, the ratios of significant trace elements and K2O/Na2O have been used as input data. The SOM results highlighted a high degree of affinity between the geochemical element ratios of Vesuvius and Campi Flegrei that were separated from the products of Ischia. This result was also evidenced through isotope ratios by using traditional two-dimensional diagrams.
    Description: Published
    Description: 175-184
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 14
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    Measurements of volcanic SO2 and CO2 fluxes by combined DOAS, Multi-GAS and FTIR observations: a case study from Turrialba and Telica volcanoes (2020)
    Springer
    Details
    Publication Date: 2020-11-25
    Description: Over the past few decades, substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic SO2 emissions. However, measurements of CO2 emissions still present many difficulties, partly due to the lack of instruments that can directly measure CO2 emissions and partly due to its strong atmospheric background. In order to overcome these difficulties, a commonly taken approach is to combine differential optical absorption spectroscopy (DOAS) by using NOVAC scan-DOAS instruments for continuous measurements of crateric SO2 emissions, and electrochemical/NDIR multi-component gas analyser system (multi-GAS) instruments for measuring CO2/SO2 ratios of excerpts of the volcanic plume. This study aims to quantify the representativeness of excerpts of CO2/SO2 ratios measured by Multi-GAS as a fraction of the whole plume composition, by comparison with simultaneously measured CO2/SO2 ratios using cross-crater Fourier transform infrared spectroscopy (FTIR). Two study cases are presented: Telica volcano (Nicaragua), with a homogenous plume, quiescent degassing from a deep source and ambient temperature, and Turrialba volcano (Costa Rica), which has a non-homogeneous plume from three main sources with different compositions and temperatures. Our comparison shows that in our “easier case” (Telica), FTIR and Multi-GAS CO2/SO2 ratios agree within a factor about 3 %. In our “complicated case” (Turrialba), Multi-GAS and FTIR yield CO2/SO2 ratios differing by approximately 13–25 % at most. These results suggest that a fair estimation of volcanic CO2 emissions can be provided by the combination of DOAS and Multi-GAS instruments for volcanoes with similar degassing conditions as Telica or Turrialba. Based on the results of this comparison, we report that by the time our measurements were made, Telica and Turrialba were emitting approximately 100 and 1,000 t day−1 of CO2, respectively.
    Description: This work was supported by the Swedish International Development Agency (SIDA), and the DECADE initiative in coordination with OVSICORI-UNA and INETER. The research leading to these results received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007/2013)/ERC grant agreement n1305377 (PI Aiuppa)
    Description: Published
    Description: 2335–2347
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: volcanic degassing ; Multi-GAS ; UV spectroscopy ; FTIR
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 15
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    Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain) (2020)
    Springer
    Details
    Publication Date: 2020-12-14
    Description: Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (includ- ing structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and paleomagnetism, and paleo- thermometry) is used to define thrusting conditions, defor- mation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal dis- placement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analy- sis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside stria- tions) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direc- tion onto the kmax/kint plane in sites with strong shear defor- mation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong defor- mation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multi- disciplinary approach is useful when dealing with thrusts at shallow crustal levels.
    Description: Published
    Description: 1023–1055
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Keywords: Intraplate thrusting ; Fault rock ; Cameros–Demanda thrust ; Transport direction ; Magnetic techniques ; Paleothermometry ; Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    A probabilistic approach for the classification of earthquakes as ‘triggered’ or ‘not triggered’ (2020)
    Springer
    Details
    Publication Date: 2020-12-15
    Description: The occurrence time of earthquakes can be anticipated or delayed by external phenomena that induce strain energy changes on the faults. ‘Anticipated’ earthquakes are generally called ‘triggered’; however, it can be controversial to label a specific earthquake as such, mostly because of the stochastic nature of earthquake occurrence and of the large uncertainties usually associated to stress modelling. Here we introduce a combined statistical and physical approach to quantify the probability that a given earthquake was triggered by a given stress-inducing phenomenon. As an example, we consider an earthquake that was likely triggered by a natural event: the M = 6.2 13 Jan 1976 Kópasker earthquake on the Grímsey lineament (Tjörnes Fracture Zone, Iceland), which occurred about 3 weeks after a large dike injection in the nearby Krafla fissure swarm. By using Coulomb stress calculations and the rate-and-state earthquake nucleation theory, we calculate the likelihood of the earthquake in a scenario that contains only the tectonic background and excludes the dike and in a scenario that includes the dike but excludes the background. Applying the Bayes’ theorem, we obtain that the probability that the earthquake was indeed triggered by the dike, rather than purely due to the accumulation of tectonic strain, is about 60 to 90 %. This methodology allows us to assign quantitative probabilities to different scenarios and can help in classifying earthquakes as triggered or not triggered by natural or human-induced changes of stress in the crust.
    Description: Published
    Description: 165–187
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Natural blue zircon from Vesuvius (2020)
    Springer
    Details
    Publication Date: 2021-01-20
    Description: Zircon from syenitic ejecta of Vesuvius (Campania, Italy) is unusually blue, a property shared with gem zircon from Ratanakiri province (Cambodia), which turns from natural reddish-brown to blue when heated under reducing conditions. Here, the origins of these unusual crystals were traced through geochronology, trace elements, and O-Hf isotopic compositions. The causes of its colour were investigated through optical and electron microscopy, optical absorption spectroscopy, and Raman microspectroscopy. Colour stability upon heating and ultraviolet light (UV) exposure was tested using Ratanakiri zircon as a control. Vesuvius zircon contains vesiculated zones with abundant inclusions ~2.5 μm to 〈100 nm in diameter (mostly U-rich thorianite and pyrochlore-group minerals), while homogeneous zircon domains are high in Th and U (up to 5.9 and 1.8 wt%, respectively). Its blue colouration is stable under UV radiation, as well as heat-treatment under reducing conditions (1000 °C; 〉15 h). Turbid domains rich in large inclusions change to yellow-brown after heating under oxidizing conditions, while transparent domains remain pale blue or colourless. Optical absorption spectra display sharp absorption lines attributed to U4+, and slightly elevated absorption towards shorter wavelengths. The ~1007 cm−1 ν3(SiO4) Raman band is broadened due to lattice distortion by non-stoichiometric elements in high-Th/-U zircon, whereas narrow bands in inclusion-rich domains indicate a decrease in lattice strain due to inclusion precipitation. Blue colouration in Vesuvius zircon is explained by the effect of light scattering (Rayleigh and/or Mie scattering) on highly refractive actinide-rich inclusions ranging in size from 〈1/10 to few multiples of the wavelengths of visible light. Inclusions likely formed during fluid-mediated coupled dissolution-reprecipitation that locally transformed lattice-strained actinide-rich zircon within several hundreds of years prior to eruption.
    Description: Published
    Description: 21–36
    Description: 1V. Storia eruttiva
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: 5V. Processi eruttivi e post-eruttivi
    Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio
    Description: JCR Journal
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    Effect of Shallow Slip Amplification Uncertainty on Probabilistic Tsunami Hazard Analysis in Subduction Zones: Use of Long-Term Balanced Stochastic Slip Models (2020)
    Springer
    Details
    Publication Date: 2021-04-20
    Description: The complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic k−2 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model ~ 150,000 earthquakes with 𝑀𝑤 from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depth-independent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world.
    Description: Published
    Description: 1497–1520
    Description: 3T. Sorgente sismica
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 19
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    Assessment of earthquake locations in 3D deterministic velocity models: a case study from the Altotiberina Near Fault Observatory (Italy) (2020)
    American Geophysical Union
    Details
    Publication Date: 2021-07-14
    Description: An edited version of this paper was published by AGU. Copyright (2016) American Geophysical Union.
    Description: The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high-resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three-dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, 6 deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P- and S-wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a non-linear, global-search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher-quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.
    Description: Published
    Description: 8113-8135
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: deterministic velocity model ; earthquakes ; nonlinear hypocenter location ; lithological control on seismicity ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    The Simplified Ionospheric Regional Model (SIRM) for HF Prediction: Basic Theory, Its Evolution and Applications (2020)
    Springer
    Details
    Publication Date: 2020-09-01
    Description: This paper is a final review of the Simplified Ionospheric Regional Model (SIRM) devel- oped as a prototype in the early 1990s and improved in the following years. By means of an algorithm based on the Fourier synthesis, the SIRM model in its prototype version pro- vides predicted monthly median values of the main ionospheric characteristics such as: the ordinary wave critical frequencies (foE, foF1, and foF2) of the E, F1, and F2 ionospheric layers; the lowest virtual height (h’F) of the ordinary trace of the F region; the obliquity factor for a distance of 3000 km (M(3000)F2). Instead, the improved version focuses only on foF2 and M(3000)F2. The SIRM model has been largely employed in the framework of different international research projects as the climatological reference to output foF2 and M(3000)F2 monthly median predictions, but in its SIRMUP version is used also as a nowcasting model and as an intermediate step of complex procedures for a near real- time three-dimensional representation of the ionospheric electron density. In this regard, some results provided by both SIRM and SIRMUP for telecommunication applications are shown. Moreover, the mathematical treatment concerning both the phase correction of the Fourier synthesis and the fundamental steps carried out to define the SIRM algorithm in its final version, never published so far, will be described in detail in dedicated Appendices. Finally, for the first time the SIRM code is now downloadable for the benefit of users.
    Description: Published
    Description: 1143-1178
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Keywords: SIRM ; SIRMUP ; foF2 ; M(3000)F2 ; Regional modelling ; 01.02. Ionosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Intercomparison of stratospheric HNO3measurements over Antarctica: Ground-based millimeter-wave versus UARS/MLS Version 5 retrievals (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: [1] We present the first intercomparison between the two most comprehensive records of gas‐phase HNO3 profiles in the Antarctic stratosphere, covering the greater part of 1993 and 1995. We compare measurements by the Stony Brook Ground‐Based Millimeter‐wave Spectrometer (GBMS) at the South Pole with Version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite. Trajectory tracing was used to select MLS measurements in the 70°–80°S latitude band that sampled air observed by the GBMS during passage over the Pole. When temperatures were near the HNO3 condensation range, additional screening was performed to select MLS measurements that sampled air parcels within 1.5 K of the temperature they experienced over the Pole. Quantitative comparisons are given at 7 different potential temperature levels spanning the range ∼19–30 km. Agreement between the data sets is quite good between 465 and 655 K (∼20–25 km) during a large fraction of the year. Agreement is best during winter and spring, when seasonally averaged differences are generally within 1 ppbv below ∼25 km. At higher altitudes, and during summer and fall, the agreement becomes worse, and GBMS measurements can exceed MLS values by more than 3 ppbv. We provide evidence that differences occurring in the lower stratosphere during fall are due to lack of colocation between the two data sets during a period of strong poleward gradients in HNO3. Remaining discrepancies between GBMS and MLS V5 HNO3 measurements are thought to be due to instrumental or retrieval biases.
    Description: Published
    Description: id 4809
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: MLS ; Nitric acid ; polar stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 22
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    Analyzing Complex Models Using Data and Statistics (2020)
    Springer
    Details
    Publication Date: 2020-10-21
    Description: Complex systems (e.g., volcanoes, debris flows, climate) commonly have many models advocated by different modelers and incorporating different modeling assumptions. Limited and sparse data on the modeled phenomena does not permit a clean discrimination among models for fitness of purpose, and, heuristic choices are usually made, especially for critical predictions of behavior that has not been experienced. We advocate here for characterizing models and the modeling assumptions they represent using a statistical approach over the full range of applicability of the models. Such a characterization may then be used to decide the appropriateness of a model for use, and, perhaps as needed weighted compositions of models for better predictive power. We use the example of dense granular representations of natural mass flows in volcanic debris avalanches, to illustrate our approach.
    Description: Published
    Description: 724-736
    Description: 5V. Processi eruttivi e post-eruttivi
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 23
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    Editorial: Flank dynamics, sector collapses, lahars, and rockfalls: analysis, monitoring, and modelling of small to large scale volcanic slope instability (2020)
    Springer
    Details
    Publication Date: 2020-11-12
    Description: Slope dynamics in volcanic environments comprise a wide spectrum of phenomena, from large lateral collapse to shallow debris remobilization, which may represent a major threat for human communities and infrastructures. Many volcanos built up from the ocean floor and large portions of the volcano edifice are submerged. In these settings, only the edifice’s summit can be investigated by terrestrial remote sensing and in-situ approaches. Growth and destruction, including tectonics and gravitational phenomena, affect entire volcano flanks and are not limited to the physical boundary of the sea level but could comprise their subaqueous parts.
    Description: Published
    Description: 2615–2618
    Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio
    Description: JCR Journal
    Keywords: volcanoes ; flanks ; volcano-tectonics ; structure ; collapse ; stability ; 04.08. Volcanology ; 05.08. Risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 24
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    Geochemical and Sr–Nd isotopic features of the Zaro volcanic complex: insights on the magmatic processes triggering a small-scale prehistoric eruption at Ischia island (south Italy) (2020)
    Springer
    Details
    Publication Date: 2020-11-16
    Description: The prehistoric (〈7 ka) Zaro eruption at Ischia island (Southern Italy) produced a lava complex overlaying a pyroclastic deposit. Although being of low energy, the Zaro eruption might have caused casualties among the neolithic population that inhabited that area of Ischia, and damages to their settlements. A similar eruption at Ischia with its present-day population would turn into a disaster. Therefore, understanding the magmatic processes that triggered the Zaro eruption would be important for volcanic hazard assessment and risk mitigation, so as to improve a knowledge that can be applied to other active volcanic areas worldwide. The main Zaro lava body is trachyte and hosts abundant mafc and felsic enclaves. Here all juvenile facies have been fully characterized from petrographic, geochemical and isotopic viewpoints. The whole dataset (major and trace element contents; Sr–Nd isotopic composition) leads to rule out a genetic link by fractional crystallization among the variable facies. Thus, we suggest that the Zaro mafc enclaves could represent a deep-origin mafc magma that mingled/mixed with the main trachytic one residing in the Ischia shallow magmatic system. The intrusion of such a mafc magma into a shallow reservoir flled by partly crystallized, evolved magma could have destabilized the magmatic system presumably acting as a rapid eruption trigger. The resulting processes of convection, mixing and rejuvenation have possibly played an important role in pre- and syn-eruptive phases also in several eruptions of diferent sizes in the Neapolitan area and elsewhere in the world.
    Description: Published
    Description: 2829–2849
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: Ischia island ; Zaro volcanic complex ; Mineral chemistry ; Isotope geochemistry ; Mafic enclaves
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    Spatial analysis for an evaluation of monitoring networks: examples from the Italian seismic and accelerometric networks (2020)
    Springer
    Details
    Publication Date: 2020-12-21
    Description: In this work, we propose a statistical approach to evaluate the coverage of a network based on the spatial distribution of its nodes and the target information, including all those data related to the final objectives of the network itself. This statistical approach encompasses descriptive spatial statistics in combination with point pattern techniques. As case studies, we evaluate the spatial arrangements of the stations within the Italian National Seismic Network and the Italian Strong Motion Network. Seismic networks are essential tools for observing earthquakes and assessing seismic hazards, while strong motion (accelerometric) networks allow us to describe seismic shaking and to measure the expected effects on buildings and infrastructures. The capability of both networks is a function of an adequate number of optimally distributed stations. We compare the seismic network with the spatial distributions of historical and instrument seismicity and with the distribution of well-known seismogenic sources, and we compare the strong motion station distribution with seismic hazard maps and the population distribution. This simple and reliable methodological approach is able to provide quantitative information on the coverage of any type of network and is able to identify critical areas that require optimization and therefore address areas of future development.
    Description: Published
    Description: 1045–1061
    Description: 1IT. Reti di monitoraggio e sorveglianza
    Description: JCR Journal
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    Hybrid Broadband Seismograms for Seismic Shaking Scenarios: An Application to the Po Plain Sedimentary Basin (Northern Italy) (2020)
    Springer
    Details
    Publication Date: 2021-06-22
    Description: The densely populated Po Plain, a very deep sedi- mentary basin in northern Italy, is prone to heavy shaking during earthquakes. Seismic hazard assessment must account for local variation in wave amplification. Standard ground motion prediction equations may fail to picture the complexity of strong lateral gradients in seismic response, due to sharp structural heterogeneity. For this reason, there is an increasing demand for full waveform predictions for engineering applications. Here, we present an implementation of a hybrid broadband simulation based on the method of Mai et al. (Bull Seismol Soc Am 100(6):3338–3339, 2010), to obtain complete broadband seismograms of 0.1–10 Hz. With this method, low frequency (〈1 Hz) and high frequency (1–10 Hz) seismograms are simulated separately using a deter- ministic and a stochastic method, respectively. We apply the method to four events recorded within the Po basin, with magnitude ranging from Mw = 4.4 to Mw = 5.6. The low frequency (LF) simulation is performed using SPECFEM3D on a few test sub- surface velocity models. The three-dimensional velocity model MAMBo (Molinari et al. in Bull Seismol Soc Am 105(2A):753–764, 2015)—consisting of a detailed structural description of the basin, based on extensive active-source data, embedded within a regional 3D crustal model—provided the best results for broadband simulations that most closely corresponded with the observations. It performed better than an ambient noise tomography model with more accurate S-wave velocities but less well defined layer topographies, emphasizing the importance of first order velocity discontinuities. The high frequency (HF) seis- mograms are simulated using the multiple scattering approach of Zeng et al. (J Geophys Res Solid Earth 96(B1):607–619, 1991). The scattering coefficients are obtained by performing a non linear inversion for each station to find best fitting synthetic envelopes. HF energy is then combined at 1 Hz to match the amplitude and phase spectra of the LF signal. We are able to simulate full waveforms throughout the Po Plain, of which shaking duration matches observed data for stations located in the basin. Shaking amplitudes are generally overestimated in the low frequency simulation by the MAMBo velocity model. Updating the MAMBo velocity model with more accurate S-wave velocity information of the ambient noise tomography model should improve the fit in future simulations.
    Description: Published
    Description: 2181–2198
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Ground motion ; hybrid method ; sedimentary basin ; Seismic shaking scenario ; 04. Solid Earth
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    Tropical Rains Controlling Deposition of Saharan Dust Across the North Atlantic Ocean (2020)
    American Geophysical Union
    In:  EPIC3Geophysical Research Letters, American Geophysical Union, 47(5), ISSN: 0094-8276
    Details
    Publication Date: 2020-05-13
    Description: Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of the oceans.
    Repository Name: EPIC Alfred Wegener Institut
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    Spread of the invasive shell-boring annelid Polydora websteri (Polychaeta, Spionidae) into naturalised oyster reefs in the European Wadden Sea (2020)
    Springer
    In:  EPIC3Marine Biodiversity, Springer, 50(5), pp. 63, ISSN: 1867-1616
    Details
    Publication Date: 2020-08-06
    Description: With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea (Magallana) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri, a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.
    Repository Name: EPIC Alfred Wegener Institut
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    Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin (2020)
    American Geophysical Union
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union, 34(8), ISSN: 0886-6236
    Details
    Publication Date: 2020-09-02
    Repository Name: EPIC Alfred Wegener Institut
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  • 30
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    Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica (2020)
    Springer
    In:  EPIC3Advances in Atmospheric Sciences, Springer, 37(5), pp. 455-476, ISSN: 0256-1530
    Details
    Publication Date: 2020-07-13
    Description: Atmospheric rivers (ARs) are an important component of the hydrological cycle linking moisture sources in lowerlatitudes to the Antarctic surface mass balance. We investigate AR signatures in the atmospheric vertical profiles at theDronning Maud Land coast, East Antarctica, using regular and extra radiosonde measurements conducted during the Yearof Polar Prediction Special Observing Period November 2018 to February 2019. Prominent AR events affecting thelocations of Neumayer and Syowa cause a strong increase in specific humidity extending through the mid-troposphere anda strong low-level jet (LLJ). At Neumayer, the peak in the moisture inversion (up to 4 g kg−1) is observed between 800 and900 hPa, while the LLJ (up to 32 m s−1) is concentrated below 900 hPa. At Syowa the increase in humidity is lesspronounced and peaks near the surface, while there is a substantial increase in wind speed (up to 40 m s−1) between 825 and925 hPa. Moisture transport (MT) within the vertical profile during the ARs attains a maximum of 100 g kg−1 m s−1 at bothlocations, and is captured by both ERA-Interim and ERA5 reanalysis data at Neumayer, but is strongly underestimated atSyowa. Composites of the enhanced MT events during 2009−19 show that these events represent an extreme state of thelower-tropospheric profile compared to its median values with respect to temperature, humidity, wind speed and,consequently, MT. High temporal- and vertical-resolution radiosonde observations are important for understanding thecontribution of these rare events to the total MT towards Antarctica and improving their representation in models.
    Repository Name: EPIC Alfred Wegener Institut
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    YOUMARES 9 - The Oceans: Our Research, Our Future (2020)
    Springer
    In:  EPIC3Cham, Springer, 378 p., ISBN: 978-3-030-20389-4
    Details
    Publication Date: 2020-06-12
    Description: This open access book summarizes peer-reviewed articles and the abstracts of oral and poster presentations given during the YOUMARES 9 conference which took place in Oldenburg, Germany, in September 2018. The aims of this book are to summarize state-of-the-art knowledge in marine sciences and to inspire scientists of all career stages in the development of further research. These conferences are organized by and for young marine researchers. Qualified early-career researchers, who moderated topical sessions during the conference, contributed literature reviews on specific topics within their research field.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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    Deglacial to Holocene variability in surface water characteristics and major floods in the Beaufort Sea (2020)
    Springer
    In:  EPIC3Communications Earth & Environment, Springer, 1(25), pp. 1-12
    Details
    Publication Date: 2020-10-15
    Description: Surface water characteristics of the Beaufort Sea have global climate implications during the last deglaciation and the Holocene, as (1) sea ice is a critical component of the climate system and (2) Laurentide Ice Sheet meltwater discharges via the Mackenzie River to the Arctic Ocean and further, to its outflow near the deep-water source area of the Atlantic Meridional Overturning Circulation. Here we present high-resolution biomarker records from the southern Beaufort Sea. Multi-proxy biomarker reconstruction suggests that the southern Beaufort Sea was nearly ice-free during the deglacial to Holocene transition, and a seasonal sea-ice cover developed during the mid-late Holocene. Superimposed on the long-term change, two events of high sediment flux were documented at ca. 13 and 11 kyr BP, respectively. The first event can be attributed to the Younger Dryas flood and the second event is likely related to a second flood and/or coastal erosion.
    Repository Name: EPIC Alfred Wegener Institut
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
    Repository Name: EPIC Alfred Wegener Institut
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    Rapid Identification and Quantification of Microplastics in the Environment by Quantum Cascade Laser-Based Hyperspectral Infrared Chemical Imaging (2020)
    American Chemical Society
    In:  EPIC3Environmental Science & Technology, American Chemical Society, 54(24), pp. 15893-15903, ISSN: 0013-936X
    Details
    Publication Date: 2021-04-08
    Repository Name: EPIC Alfred Wegener Institut
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    Simulated Thermohaline Fingerprints in Response to Different Greenland‐Scotland Ridge and Fram Strait Subsidence Histories (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-16
    Description: Changes in ocean gateway configuration can induce basin‐scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland‐Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.
    Repository Name: EPIC Alfred Wegener Institut
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    Dynamical processes in the Arctic atmosphere (2020)
    Springer
    In:  EPIC3Physics and Chemistry of the Arctic Atmosphere, Physics and Chemistry of the Arctic Atmosphere, Springer, pp. 1-51, ISBN: 978-3-030-33566-3
    Details
    Publication Date: 2020-02-05
    Description: This book presents current knowledge on chemistry and physics of Arctic atmosphere. Special attention is given to studies of the Arctic haze phenomenon, Arctic tropospheric clouds, Arctic fog, polar stratospheric and mesospheric clouds, atmospheric dynamics, thermodynamics and radiative transfer as related to the polar environment. The atmosphere-cryosphere feedbacks and atmospheric remote sensing techniques are presented in detail. The problems of climate change in the Arctic are also addressed.
    Repository Name: EPIC Alfred Wegener Institut
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    Planet Microbe: An Ontology-Enriched Cyberinfrastructure System for FAIR Marine ‘Omics Data (2020)
    American Geophysical Union
    In:  EPIC3Ocean Sciences Meeting 2020, 2020-02-16-2020-02-21American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Repository Name: EPIC Alfred Wegener Institut
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    How Different Analysis and Interpolation Methods Affect the Accuracy of Ice Surface Elevation Changes Inferred from Satellite Altimetry (2020)
    Springer
    In:  EPIC3Mathematical Geosciences, Springer, 52, pp. 499-525, ISSN: 1874-8961
    Details
    Publication Date: 2020-05-11
    Description: Satellite altimetry has been widely used to determine surface elevation changes in polar ice sheets. The original height measurements are irregularly distributed in space and time. Gridded surface elevation changes are commonly derived by repeat altimetry analysis (RAA) and subsequent spatial interpolation of height change estimates. This article assesses how methodological choices related to those two steps affect the accuracy of surface elevation changes, and how well this accuracy is represented by formal uncertainties. In a simulation environment resembling CryoSat-2 measurements acquired over a region in northeast Greenland between December 2010 and January 2014, different local topography modeling approaches and different cell sizes for RAA, and four interpolation approaches are tested. Among the simulated cases, the choice of either favorable or unfavorable RAA affects the accuracy of results by about a factor of 6, and the different accuracy levels are propagated into the results of interpolation. For RAA, correcting local topography by an external digital elevation model (DEM) is best, if a very precise DEM is available, which is not always the case. Yet the best DEM-independent local topography correction (nine-parameter model within a 3,000 m diameter cell) is comparable to the use of a perfect DEM, which exactly represents the ice sheet topography, on the same cell size. Interpolation by heterogeneous measurement-error-filtered kriging is significantly more accurate (on the order of 50% error reduction) than interpolation methods, which do not account for heterogeneous errors.
    Repository Name: EPIC Alfred Wegener Institut
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    Successional processes in Antarctic benthic algae (2020)
    Springer
    In:  EPIC3Antarctic Seaweeds Diversity, Adaptation and Ecosystem Services, Antarctic Seaweeds, Cham, Switzerland, Springer, 397 p., pp. 241-264, ISBN: 978-3-030-39447-9
    Details
    Publication Date: 2020-06-10
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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    Antarctic Circumpolar Current Dynamics at the Pacific Entrance to the Drake Passage Over the Past 1.3 Million Years (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35(7), pp. e2019PA003773, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-01
    Description: The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, "Sortable Silt") and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending for at least the last 1.3 Ma. The orbital‐scale cyclicity follows well‐known global climate changes from prevailing ca. 41‐kyr cycles in the early part of the record (1.3 Ma to 850 ka; marine isotope stage 21) across the mid‐Pleistocene transition into the middle and late Pleistocene 100‐kyr world. A comparison to a bottom water flow record from the deep western boundary current off New Zealand (Ocean Drilling Program Site 1123) reveals anti‐phased changes between the two sites. The enhanced supply of deep water along the DP and into the Atlantic Ocean during interglacials corresponds to a weakened flow of the SW Pacific deep western boundary current.
    Repository Name: EPIC Alfred Wegener Institut
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    Late Quaternary sedimentation dynamics in the Beenchime‑Salaatinsky Crater, Northern Yakutia (2020)
    Springer
    In:  EPIC3arctos, Springer, ISSN: 2364-9461
    Details
    Publication Date: 2021-05-21
    Description: The Beenchime-Salaatinsky Crater (BSC) is located west of the Olenyok River in Northern Yakutia, ~ 260 km south-west of Tiksi and the Lena Delta. The age and origin (volcanic versus meteoritic) of this crater is poorly understood. The key scientific interest in re-visiting the BSC is the reappraisal of the Quaternary sedimentation dynamics for a better understanding of the sediment history and thickness in the basin. This aides for an assessment, if the site is prospective for a deeper drilling of a Quaternary (or Cenozoic) sediment archive. Soil pits and auger cores from slopes and lowland terrain in the basin were sampled and studied to infer sediment ages and transport dynamics. This also included a thermokarst lake placed in the centre of the basin. Studied properties include grain-size distribution, organic carbon and nitrogen contents (TOC and TN), heavy mineral compositions, δ13C of organic carbon, 14C ages from sediment, δ18O and δD from ground ice and waters, and lake bathymetry from GPR profiling, in addition. We conclude that the crater floor in the BSC is underlain by fluvial/alluvial sediments from the MIS 3 period. Thermokarst lake formation took place during the Holocene Thermal Maximum between 7600 and 6100 cal yr BP. The lake has been shrinking hereafter. Fluvial/alluvial sedimentation along the drainage pattern was active again between 5700 to 1500 cal yr BP, and it was flanked by the accumulation of peaty and organic-rich sediments and the formation of ice-wedge polygons.
    Repository Name: EPIC Alfred Wegener Institut
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    Estimation of information loss when maskingconditional dependence and categorizingcontinuous data: further experiments on adatabase for spatial prediction modelling innorthern Italy (2020)
    Springer | Springer
    Details
    Publication Date: 2020-02-11
    Description: Prediction patterns are generated using different data sets from a database for landslides hazard in northern Italy. A direct supporting pattern of the distribution of 28 complex landslides was previously used to obtain their spatial relationships with five categorical indirect supporting patterns representing the spatial context of the landslides: geology, land use, and permeability in addition to internal relief and slope, the latter two categorized into five classes. The five indirect supporting patterns were selected to minimize the effects of conditional dependence on prediction patterns by a Weight-of-Evidence model. The same set of patterns is reanalysed applying the Empirical Likelihood Ratio model using also uncategorized continuous supporting patterns: aspect, curvature, and digital elevation, in addition to internal relief and slope. The resulting prediction patterns are compared in terms of prediction rates and target-uncertainty patterns.
    Description: Published
    Description: 291-294
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: N/A or not JCR
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    Tsunamis: Bayesian Probabilistic Hazard Analysis (2020)
    Springer
    Details
    Publication Date: 2020-02-20
    Description: Tsunamis are low-frequency high-consequences major natural threats, rare events devastating vast coastal regions near and far from their generation areas. They may be caused by coseismic seafloor motions, subaerial and submarine mass movements, volcanic activities (like explosions, pyroclastic flows and caldera collapses), meteorological phenomena and meteorite ocean impacts. The probability of tsunami occurrence and/or impact on a given coast may be treated formally by combining calculations based on empirical observations and on models; this probability can be updated in light of new/independent information. This is the general concept of the Bayesian method applied to tsunami probabilistic hazard analysis, which also provides a direct quantification of forecast uncertainties. This entry presents a critical overview of Bayesian procedures with a primary focus on their appropriate and relevant applicability to tsunami hazard analyses.
    Description: Published
    Description: 6T. Studi di pericolosità sismica e da maremoto
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    Computational Tools for Relaxing the Fault Segmentation in Probabilistic Seismic Hazard Modelling in Complex Fault Systems (2020)
    Springer
    Details
    Publication Date: 2020-06-10
    Description: Use of faults in seismic hazard models allows us to capture the recurrence of large-magnitude events and therefore improve the reliability of probabilistic seismic hazard assessment (PSHA). In the past decades, fault segmentation provided an important framework for quantifying fault-based PSHA. Recent complex coseismic ruptures (e.g., 2010 Mw 7.1 Canterbury, 2012 Mw 8.6 Sumatra, 2016 Mw 7.8 Kaikōura, 2016 Mw 6.5 central Italy) have shown the need to consider different possible combinations of rupture scenarios in PSHA. Here we present two new methodologies that model rates of ruptures along complex fault systems, one based on a floating rupture approach (FRESH) and another one based on assumed rupture scenarios (SUNFISH). They represent alternatives to a recently proposed approach (SHERIFS), and further step to overcome the segmented and un-segmented approaches commonly used in PSHA in Europe. Differences among SHERIFS, SUNFiSH and FRESH are related to the way slip rate, rupture geometries and magnitude–frequency distributions are modelled. To quantify the differences between these three methodologies, we compared PSHA results based on geometries and slip rates of a fault system located in northeastern Italy, assuming a given maximum magnitude and the same seismic moment rate target. Differences up to 20–30% in the peak ground acceleration at 2% and 10% in 50 years are observed. Finally, we show that the three methodologies are able to solve for the long-term rate of ruptures with resulting PSHA that reflect the fault system geometry and slip rates, without any assumption on segment boundaries. Using fault-based approaches in PSHA requires collecting as much local geological information as possible. Now that multi-fault rupture approaches are available, simplifying assumptions often made to model complex fault systems (uniform slip rate, segmentation hypothesis) are no longer necessary. On the other hand, local data collection should be strongly encouraged to better characterize the actual fault slip rate variability and the complex 3D geometrie
    Description: Published
    Description: 1855–1877
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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    Blind source separation problem in GPS time series (2020)
    Springer
    Details
    Publication Date: 2020-03-03
    Description: A critical point in the analysis of ground dis- placement time series, as those recorded by space geodetic techniques, is the development of data-driven methods that allow the different sources of deformation to be discerned and characterized in the space and time domains. Multivariate statistic includes several approaches that can be considered as a part of data-driven methods. A widely used technique is the principal component analysis (PCA), which allows us to reduce the dimensionality of the data space while maintain- ing most of the variance of the dataset explained. However, PCA does not perform well in finding the solution to the so-called blind source separation (BSS) problem, i.e., in recovering and separating the original sources that gener- ate the observed data. This is mainly due to the fact that PCA minimizes the misfit calculated using an L 2 norm (χ 2 ), look- ing for a new Euclidean space where the projected data are uncorrelated. The independent component analysis (ICA) is a popular technique adopted to approach the BSS problem. However, the independence condition is not easy to impose, and it is often necessary to introduce some approximations. To work around this problem, we test the use of a modi- fied variational Bayesian ICA (vbICA) method to recover the multiple sources of ground deformation even in the presence of missing data. The vbICA method models the probability density function (pdf) of each source signal using a mix of Gaussian distributions, allowing for more flexibility in the description of the pdf of the sources with respect to standard ICA, and giving a more reliable estimate of them. Here we present its application to synthetic global positioning system (GPS) position time series, generated by simulating deforma- tion near an active fault, including inter-seismic, co-seismic, and post-seismic signals, plus seasonal signals and noise, and an additional time-dependent volcanic source. We evaluate the ability of the PCA and ICA decomposition techniques in explaining the data and in recovering the original (known) sources. Using the same number of components, we find that the vbICA method fits the data almost as well as a PCA method, since the χ 2 increase is less than 10 % the value cal- culated using a PCA decomposition. Unlike PCA, the vbICA algorithm is found to correctly separate the sources if the correlation of the dataset is low (〈0.67) and the geodetic network is sufficiently dense (ten continuous GPS stations within a box of side equal to two times the locking depth of a fault where an earthquake of Mw 〉 6 occurred). We also provide a cookbook for the use of the vbICA algorithm in analyses of position time series for tectonic and non-tectonic applications.
    Description: Published
    Description: 323–341
    Description: 1T. Struttura della Terra
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: 04. Solid Earth ; 04.03. Geodesy
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    Time-dependent Sr and Nd isotope variations during the evolution of the ultrapotassic Sabatini Volcanic District (Roman province, Central Italy) (2020)
    Springer
    Details
    Publication Date: 2020-03-04
    Description: The SabatiniVolcanicDistrict (SVD), active between 0.8 and 0.07 Ma, is a volcanic field in the Roman province (Central Italy) located along the Tyrrhenian margin of the Italian peninsula. In this volcanic region, high-K magmas originated from a metasomatised phlogopite-bearing peridotite mantle recording subduction-related fluids and/or melting processes. Here, we investigate magma evolution during the six main eruptive phases of the SVD by means of chemical and isotopic (Sr and Nd) analyses. Specifically, we analyzed clinopyroxene crystals from juvenile pumice and scoria clasts and lavas, from 40 major SVD eruptive units chronologically well constrained by 40Ar/39Ar dating. 87Sr/86Sr and 144Nd/143Nd ratios in SVDclinopyroxene range 0.7095–0.7115 and 0.51210- 0.51214, respectively. The mean Sr and Nd isotope compositions of each eruptive phases show a gradual, long-term decrease over the entire SVD eruptive history. However, when considering the distinct temporal windows of the individual eruptive phases, a significant variability of the Sr-Nd isotope ratios emerges, thus highlighting a more complex, time-dependent geochemical trend for the erupted magmas,with respect to a previously described trend at the nearby Colli AlbaniVolcanic District (0.6–0.04 Ma). Geochemical features of clinopyroxene in lavas and juvenile pyroclasts suggest that magma differentiation occurred in an open system due to assimilation of siliciclastic sedimentary rocks. Moreover, a critical review of the available geochemical data, in light of 40Ar/39Ar ages, allows the recognition of the SVD as the source of widespread tephra markers recorded in the central Mediterranean area by previous works.
    Description: Published
    Description: id 67
    Description: 1V. Storia eruttiva
    Description: JCR Journal
    Keywords: Sabatini Volcanic District ; Roman province ; Sr and Nd isotopes
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    Disentangling ionospheric refraction and diffraction effects in GNSS raw phase through fast iterative filtering technique (2020)
    Springer
    Details
    Publication Date: 2020-07-02
    Description: We contribute to the debate on the identification of phase scintillation induced by the ionosphere on the Global Navigation Satellite System (GNSS) by introducing a phase detrending method able to provide realistic values of the phase scintillation index at high latitude. It is based on the Fast Iterative Filtering (FIF) signal decomposition technique, which is a recently developed fast implementation of the well-established Adaptive Local Iterative Filtering (ALIF) algorithm. FIF has been conceived to decompose nonstationary signals efficiently and providing a discrete set of oscillating functions, each of them having its frequency. It overcomes most of the problems that arise when using traditional time-frequency analysis techniques and relies on a consolidated mathematical basis since its a priori convergence and stability have been proved. By relying on the capability of FIF to efficiently identify the frequencies embedded in the GNSS raw phase, we define a method based on the FIF-derived spectral features to identify the proper cutoff frequency for phase detrending. To test such a method, we analyze the data acquired from GPS and Galileo signals over Antarctica during the September 2017 storm by the Ionospheric Scintillation Monitor Receiver (ISMR) located in Concordia Station (75.10°S, 123.33°E). Different cases of diffraction and refraction effects are provided, showing the capability of the method in deriving a more accurate determination of the SigmaPhi index. We found values of cutoff frequency in the range of 0.73 to 0.83 Hz, providing further evidence of the inadequacy of the choice of 0.1 Hz, which is often used when dealing with ionospheric scintillation monitoring at high latitudes.
    Description: This research is supported by TREASURE, a project funded by the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Actions grant agreement n.722023 (http://ww.treasure-gnss.eu).
    Description: Published
    Description: id 85
    Description: 2TM. Divulgazione Scientifica
    Description: JCR Journal
    Keywords: ionospheric scintillation · plasma drift velocity · scintillation indices · refractive and diffractive effects · Galileo and GPS signals · data detrending ; Disentangling ionospheric refraction and diffraction effects in GNSS raw phase through fast iterative filtering technique
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    A case study of correspondence between Pc1 activity and ionospheric irregularities at polar latitudes (2020)
    Springer
    Details
    Publication Date: 2020-07-13
    Description: A possible driver of precipitation of magnetospheric energetic electrons in the high-latitude atmosphere is represented by electromagnetic ion-cyclotron (EMIC) magnetospheric waves. The precipitating particles produce variations, by collision, in the ionized component of the atmosphere, altering its chemistry and electrical conductivity, with a significant impact on the atmospheric processes. In this framework, it would be significant to find experimental evidence of a correspondence between ionospheric electron density irregularities and the occurrence of Ultra-Low-Frequency (ULF) Pc1 geomagnetic pulsations, i.e., the ground signatures of EMIC waves, at high latitudes. In this work, we face this subject by considering a specific case study occurred on 22 February 2007 during quiet magnetospheric conditions. The study is based on the analysis of simultaneous ULF geomagnetic field and Total Electron Content (TEC) measurements recorded at Mario Zucchelli Station in Antarctica. We show that Pc1 pulsations occur in correspondence to solar wind pressure increases and that, at the same time, the ionosphere is characterized by the presence of ionospheric irregularities. We suggest that a possible link between the Pc1 activity and the ionospheric irregularities may be energetic electron precipitations, driven by EMIC waves generated in the compressed magnetosphere, which produce density variations in the ionized component of the atmosphere.
    Description: Published
    Description: id 59
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
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    Our PET project: an unlimited supply of big and small water sample vials for the assay of radon in water (2020)
    Springer
    Details
    Publication Date: 2020-02-10
    Description: RAD7 and BigBottle system has been developed, using large glass bottles, but these are fragile and awkward to carry around. In searching for a better solution, we tested polyethylene terephthalate (PET) bottles for water samples storage to estimate radon loss over time. Two sets of experiments with 0.355 and 1.75 L bottles demonstrated that PET is a suitable material for storage. If correction for 226Ra content in water is applied, we can also calculate the rate of radon loss (0.03 ± 0.08 % day-1).
    Description: Published
    Description: 2277-2280
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: Polyethylene terephthalate ; Radon loss from water during storage ; RAD7 ; BigBottle RADH2O ; 05.04. Instrumentation and techniques of general interest
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    Vp/Vs ratio of incoming sediments off Cascadia subduction zone from analysis of controlled-source multicomponent OBS records (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(6), (2020): e2019JB019239, doi:10.1029/2019JB019239.
    Description: P‐to‐S‐converted waves observed in controlled‐source multicomponent ocean bottom seismometer (OBS) records were used to derive the Vp/Vs structure of Cascadia Basin sediments. We used P‐to‐S waves converted at the basement to derive an empirical function describing the average Vp/Vs of Cascadia sediments as a function of sediment thickness. We derived one‐dimensional interval Vp/Vs functions from semblance velocity analysis of S‐converted intrasediment and basement reflections, which we used to define an empirical Vp/Vs versus burial depth compaction trend. We find that seaward from the Cascadia deformation front, Vp/Vs structure offshore northern Oregon and Washington shows little variability along strike, while the structure of incoming sediments offshore central Oregon is more heterogeneous and includes intermediate‐to‐deep sediment layers of anomalously elevated Vp/Vs. These zones with elevated Vp/Vs are likely due to elevated pore fluid pressures, although layers of high sand content intercalated within a more clayey sedimentary sequence, and/or a higher content of coarser‐grained clay minerals relative to finer‐grained smectite could be contributing factors. We find that the proto‐décollement offshore central Oregon develops within the incoming sediments at a low‐permeability boundary that traps fluids in a stratigraphic level where fluid overpressure exceeds 50% of the differential pressure between the hydrostatic pressure and the lithostatic pressure. Incoming sediments with the highest estimated fluid overpressures occur offshore central Oregon where deformation of the accretionary prism is seaward vergent. Conversely, landward vergence offshore northern Oregon and Washington correlates with more moderate pore pressures and laterally homogeneous Vp/Vs functions of Cascadia Basin sediments.
    Description: This research was funded by National Science Foundation (NSF) Grant OCE‐1657237 to J. P. C, OCE‐1657839 to A. F. A. and S. H., and OCE‐1657737 to S. M. C. Data used in this study were acquired with funding from NSF Grants OCE‐1029305 and OCE‐1249353. Data used in this research were provided by instruments from the Ocean Bottom Seismic Instrument Center (http://obsic.whoi.edu, formerly OBSIP), which is funded by the NSF. OBSIC/OBSIP data are archived at the IRIS Data Management Center (http://www.iris.edu) under network code X6 (https://doi.org/10.7914/SN/X6_2012). Data processing was conducted with Emerson‐Paradigm Software package Echos licensed to Woods Hole Oceanographic Institution under Paradigm Academic Software Program and MATLAB package SeismicLab of the University of Alberta, Canada (http://seismic-lab.physics.ualberta.ca), under GNU General Public License (MATLAB® is a registered trademark of MathWorks).
    Description: 2020-11-28
    Keywords: Vp/Vs ; sediments ; ocean bottom seismometer ; Juan de Fuca plate ; Cascadia
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    Labrador Sea Water transport across the Charlie-Gibbs Fracture Zone (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016068, doi:10.1029/2020JC016068.
    Description: Labrador Sea Water (LSW) is a major component of the deep limb of the Atlantic Meridional Overturning Circulation, yet LSW transport pathways and their variability lack a complete description. A portion of the LSW exported from the subpolar gyre is advected eastward along the North Atlantic Current and must contend with the Mid‐Atlantic Ridge before reaching the eastern basins of the North Atlantic. Here, we analyze observations from a mooring array and satellite altimetry, together with outputs from a hindcast ocean model simulation, to estimate the mean transport of LSW across the Charlie‐Gibbs Fracture Zone (CGFZ), a primary gateway for the eastward transport of the water mass. The LSW transport estimated from the 25‐year altimetry record is 5.3 ± 2.9 Sv, where the error represents the combination of observational variability and the uncertainty in the projection of the surface velocities to the LSW layer. Current velocities modulate the interannual to higher‐frequency variability of the LSW transport at the CGFZ, while the LSW thickness becomes important on longer time scales. The modeled mean LSW transport for 1993–2012 is higher than the estimate from altimetry, at 8.2 ± 4.1 Sv. The modeled LSW thickness decreases substantially at the CGFZ between 1996 and 2009, consistent with an observed decline in LSW volume in the Labrador Sea after 1994. We suggest that satellite altimetry and continuous hydrographic measurements in the central Labrador Sea, supplemented by profiles from Argo floats, could be sufficient to quantify the LSW transport at the CGFZ.
    Description: A. G. N. appreciates conversations with Kathy Donohue, Tom Rossby and Lisa Beal, which helped to interpret the results. J. B. P. acknowledges support from NSF through Grant OCE‐1947829. The authors thank all colleagues and ship crew involved in the R/V Meteor cruise M‐82/2 and Maria S. Merian cruise MSM‐21/2. The mooring data presented in this paper were funded by NSF through Grant OCE‐0926656.
    Description: 2021-01-03
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  • 52
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    Are elevation and open-water conversion of salt marshes connected? (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(3), (2020): e2019GL086703, doi:10.1029/2019GL086703.
    Description: Salt marsh assessments focus on vertical metrics such as accretion or lateral metrics such as open‐water conversion, without exploration of how the dimensions are related. We exploited a novel geospatial data set to explore how elevation is related to the unvegetated‐vegetated marsh ratio (UVVR), a lateral metric, across individual marsh “units” within four estuarine‐marsh systems. We find that elevation scales consistently with the UVVR across systems, with lower elevation units demonstrating more open‐water conversion and higher UVVRs. A normalized elevation‐UVVR relationship converges across systems near the system‐mean elevation and a UVVR of 0.1, a critical threshold identified by prior studies. This indicates that open‐water conversion becomes a dominant lateral instability process at a relatively conservative elevation threshold. We then integrate the UVVR and elevation to yield lifespan estimates, which demonstrate that higher elevation marshes are more resilient to internal deterioration, with an order‐of‐magnitude longer lifespan than predicted for lower elevation marshes.
    Description: This study was supported by the USGS through the Coastal Marine Hazards/Resources Program, the National Park Service through the Natural Resource Preservation Program, and the U.S. Fish and Wildlife Service through the Science Support Partnership. Erika Lentz, Elizabeth Pendleton, Meagan Gonneea, Joel Carr, and two anonymous reviewers provided constructive advice on the study. S.F. was partly supported by US National Science Foundation award 1637630 (PIE LTER), 1832221 (VCR LTER). The geospatial data used in this study are published in the Coastal Wetlands Synthesis Products catalog on ScienceBase (https://www.sciencebase.gov/catalog/item/5b73325ee4b0f5d5787c5ff3).
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  • 53
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    Decreased soil organic matter in a long-term soil warming experiment lowers soil water holding capacity and affects soil thermal and hydrological buffering (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research- Biogeosciences 125(4), (2020): e2019JG005158, doi:10.1029/2019JG005158.
    Description: Long‐term soil warming can decrease soil organic matter (SOM), resulting in self‐reinforcing feedback to the global climate system. We investigated additional consequences of SOM reduction for soil water holding capacity (WHC) and soil thermal and hydrological buffering. At a long‐term soil warming experiment in a temperate forest in the northeastern United States, we suspended the warming treatment for 104 days during the summer of 2017. The formerly heated plot remained warmer (+0.39 °C) and drier (−0.024 cm3 H2O cm−3 soil) than the control plot throughout the suspension. We measured decreased SOM content (−0.184 g SOM g−1 for O horizon soil, −0.010 g SOM g−1 for A horizon soil) and WHC (−0.82 g H2O g−1 for O horizon soil, −0.18 g H2O g−1 for A horizon soil) in the formerly heated plot relative to the control plot. Reduced SOM content accounted for 62% of the WHC reduction in the O horizon and 22% in the A horizon. We investigated differences in SOM composition as a possible explanation for the remaining reductions with Fourier transform infrared (FTIR) spectra. We found FTIR spectra that correlated more strongly with WHC than SOM, but those particular spectra did not differ between the heated and control plots, suggesting that SOM composition affects WHC but does not explain treatment differences in this study. We conclude that SOM reductions due to soil warming can reduce WHC and hydrological and thermal buffering, further warming soil and decreasing SOM. This feedback may operate in parallel, and perhaps synergistically, with carbon cycle feedbacks to climate change.
    Description: We would like to acknowledge Jeffery Blanchard, Priya Chowdhury, Kristen DeAngelis, Luiz Dominguez‐Horta, Kevin Geyer, Rachelle Lacroix, Xaiojun Liu, William Rodriguez, and Alexander Truchonand and for assistance with field sampling. We would like to acknowledge Michael Bernard for assistance with field sampling and lab work. We would like to acknowledge Aaron Ellison for statistical consultation. This research was financially supported by the U.S. National Science Foundation's Long Term Ecological Research Program (NSF‐DEB‐0620443 and NSF‐DEB‐1237491), the Long Term Research in Environmental Biology Program (NSF DEB‐1456528) , and the U.S. Department of Energy (DOE‐DE‐SC0005421 and DOE‐DE‐SC0010740). Data used in this study are available from the Harvard Forest Data Archive (Datasets HF018‐03, HF018‐04, and HF018‐13), accessible at https://harvardforest.fas.harvard.edu/harvard‐forest‐data‐archive.
    Description: 2020-10-04
    Repository Name: Woods Hole Open Access Server
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    Interannual variability of the Mid-Atlantic bight cold pool (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016445, doi:10.1029/2020JC016445.
    Description: The Mid‐Atlantic Bight (MAB) Cold Pool is a bottom‐trapped, cold (temperature below 10°C) and fresh (practical salinity below 34) water mass that is isolated from the surface by the seasonal thermocline and is located over the midshelf and outer shelf of the MAB. The interannual variability of the Cold Pool with regard to its persistence time, volume, temperature, and seasonal along‐shelf propagation is investigated based on a long‐term (1958–2007) high‐resolution regional model of the northwest Atlantic Ocean. A Cold Pool Index is defined and computed in order to quantify the strength of the Cold Pool on the interannual timescale. Anomalous strong, weak, and normal years are categorized and compared based on the Cold Pool Index. A detailed quantitative study of the volume‐averaged heat budget of the Cold Pool region (CPR) has been examined on the interannual timescale. Results suggest that the initial temperature and abnormal warming/cooling due to advection are the primary drivers in the interannual variability of the near‐bottom CPR temperature anomaly during stratified seasons. The long persistence of temperature anomalies from winter to summer in the CPR also suggests a potential for seasonal predictability.
    Description: This work was funded by the National Oceanic and Atmospheric Administration through Awards NOAA‐NA‐15OAR4310133 and NOAA‐NA‐13OAR4830233 and the National Science Foundation Awards OCE‐1049088, OCE‐1419584, and OCE‐0961545.
    Description: 2021-02-03
    Keywords: Mid‐Atlantic Bight ; Cold Pool ; continental shelf ; temperature balance ; interannual variability ; near‐bottom temperature
    Repository Name: Woods Hole Open Access Server
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  • 55
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    The Atlantic Water boundary current in the Chukchi Borderland and Southern Canada Basin (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016197, doi:10.1029/2020JC016197.
    Description: Synoptic shipboard measurements, together with historical hydrographic data and satellite data, are used to elucidate the detailed structure of the Atlantic Water (AW) boundary current system in the southern Canada Basin and its connection to the upstream source of AW in the Chukchi Borderland. Nine high‐resolution occupations of a transect extending from the Beaufort shelf to the deep basin near 152°W, taken between 2003 and 2018, reveal that there are two branches of the AW boundary current that flow beneath and counter to the Beaufort Gyre. Each branch corresponds to a warm temperature core and transports comparable amounts of Fram Strait Branch Water between roughly 200–700 m depth, although they are characterized by a different temperature/salinity (T/S) structure. The mean volume flux of the combined branches is 0.87 ± 0.13 Sv. Using the historical hydrographic data, the two branches are tracked upstream by their temperature cores and T/S signatures. This sheds new light on how the AW negotiates the Chukchi Borderland and why two branches emerge from this region. Lastly, the propagation of warm temperature anomalies through the region is quantified and shown to be consistent with the deduced circulation scheme.
    Description: This work was funded by the following sources: National Science Foundation Grants PLR‐1504333, OPP‐1733564, and OPP‐1504394; National Oceanic and Atmospheric Administration Grant NA14OAR4320158; and National Aeronautics and Space Administration Grant NNX10AF42G.
    Description: 2021-01-27
    Repository Name: Woods Hole Open Access Server
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    Understanding How Microplastics Affect Marine Biota on the Cellular Level Is Important for Assessing Ecosystem Function: A Review (2020)
    Springer
    In:  EPIC3Cham, Springer, 19 p., ISBN: 978-3-030-20388-7
    Details
    Publication Date: 2020-03-09
    Description: Plastic has become indispensable for human life. When plastic debris is discarded into waterways, these items can interact with organisms. Of particular concern are microscopic plastic particles (microplastics) which are subject to ingestion by several taxa. This review summarizes the results of cutting-edge research about the interactions between a range of aquatic species and microplastics, including effects on biota physiology and secondary ingestion. Uptake pathways via digestive or ventilatory systems are discussed, including (1) the physical penetration of microplastic particles into cellular structures, (2) leaching of chemical additives or adsorbed persistent organic pollutants (POPs), and (3) consequences of bacterial or viral microbiota contamination associated with microplastic ingestion. Following uptake, a number of individual-level effects have been observed, including reduction of feeding activities, reduced growth and reproduction through cellular modifications, and oxidative stress. Microplastic-associated effects on marine biota have become increasingly investigated with growing concerns regarding human health through trophic transfer. We argue that research on the cellular interactions with microplastics provide an understanding of their impact to the organisms’ fitness and, therefore, its ability to sustain their functional role in the ecosystem. The review summarizes information from 236 scientific publications. Of those, only 4.6% extrapolate their research of microplastic intake on individual species to the impact on ecosystem functioning. We emphasize the need for risk evaluation from organismal effects to an ecosystem level to effectively evaluate the effect of microplastic pollution on marine environments. Further studies are encouraged to investigate sublethal effects in the context of environmentally relevant microplastic pollution conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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    Holocene variability in sea ice and primary productivity in the northeastern Baffin Bay (2020)
    Springer
    In:  EPIC3arktos, Springer, 6, ISSN: 2364-9461
    Details
    Publication Date: 2020-03-13
    Description: Arctic sea ice is a critical component of the climate system, known to in uence ocean circulation, earth’s albedo, and ocean–atmosphere heat and gas exchange. Current developments in the use of IP25 (a sea ice proxy with 25 carbon atoms only synthesized by Arctic sea ice diatoms) have proven it to be a suitable proxy for paleo-sea ice reconstructions over hundreds of thousands to even millions of years. In the NE Baffin Bay, off NW Greenland, Melville Bugt is a climate-sensitive region characterized by strong seasonal sea ice variability and strong melt-water discharge from the Greenland Ice Sheet (GIS). Here, we present a centennial-scale resolution Holocene sea ice record, based on IP25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III) using core GeoB19927-3 (73° 35.26′ N, 58° 05.66′ W). Seasonal to ice-edge conditions near the core site are documented for most of the Holocene period with some significant variability. In the lower-most part, a cold interval characterized by extensive sea ice cover and very low local productivity is succeeded by an interval (~ 9.4–8.5 ka BP) with reduced sea ice cover, enhanced GIS spring melting, and strong in uence of the West Greenland Current (WGC). From ~ 8.5 until ~ 7.8 ka BP, a cooling event is recorded by ice algae and phytoplankton biomarkers. They indicate an extended sea ice cover, possibly related to the opening of Nares Strait, which may have led to an increased influx of Polar Water into NE-Baffin Bay. The interval between ~ 7.8 and ~ 3.0 ka BP is characterized by generally reduced sea ice cover with millennial-scale variability of the (late winter/early spring) ice-edge limit, increased open-water conditions (polynya type), and a dominant WGC carrying warm waters at least as far as the Melville Bugt area. During the last ~ 3.0 ka BP, our biomarker records do not reflect the late Holocene ‘Neoglacial cooling’ observed elsewhere in the Northern Hemisphere, possibly due to the persistent influence of the WGC and interactions with the adjacent fjords. Peaks in HBI III at about ~ 2.1 and ~ 1.3 ka BP, interpreted as persistent ice-edge situations, might correlate with the Roman Warm Period (RWP) and Medieval Climate Anomaly (MCA), respectively, in-phase with the North Atlantic Oscillation (NAO) mode. When integrated with marine and terrestrial records from other circum-Baffin Bay areas (Disko Bay, the Canadian Arctic, the Labrador Sea), the Melville Bugt biomarker records point to close ties with high Arctic and Northern Hemispheric climate conditions, driven by solar and oceanic circulation forcings.
    Repository Name: EPIC Alfred Wegener Institut
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    In situ sounding of radiative flux profiles through the Arctic lower troposphere (2020)
    Springer
    In:  EPIC3Bulletin of Atmospheric Science and Technology, Springer, ISSN: 2662-1495
    Details
    Publication Date: 2020-05-27
    Description: In situ profiles and fixed-altitude time series of all four components of net radiation were obtained at Ny-Ålesund, Svalbard (78.9° N, 11.9° E), in the period May 04–21, 2015. Measurements were performed using adapted high-quality instrumentation classified as “secondary standard” carried by a tethered balloon system. Balloon-lifted measurements of albedo under clear-sky conditions demonstrate the local dependence on altitude and on the surface inhomogeneity of this parameter over coastal terrain of Ny-Ålesund. Depending on the surface composition within the sensor’s footprint near the coastline, the albedo over predominantly snow-covered surfaces was found to decrease to 0.548 and 0.452 at 494 m and 881 m altitude compared with 0.731 and 0.788 measured with near-surface references, respectively. Albedo profiles show an all-sky maximum at 150 m above surface level due to local surface inhomogeneity, and an averaged vertical change rate of − 0.040/100 up to 750 m aboveground level (clear sky) and − 0.034/100 m (overcast). Profiling of arctic low-level clouds reveals distinct vertical gradients in all radiative fluxes but longwave upward at the cloud top. Observed radiative cooling at the top of a partly dissolving stratus cloud with heating rates of − 40.4 to − 62.1 Kd−1 in subsequent observations is exemplified.
    Repository Name: EPIC Alfred Wegener Institut
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  • 59
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    Attenuation tomography of the Southern Apennines (Italy) (2020)
    Springer
    Details
    Publication Date: 2021-11-09
    Description: The aim of this study is to improve our knowledge of the attenuation structure in the Southern Apennines using a new amplitude ratio tomography method (Phillips et al., Geophys Res Lett 32(21): L21301, 2005) applied on both direct and coda envelope measurements derived from 150 events recorded by 47 stations of the Istituto Nazionale di Geofisica e Vulcanologia National Seismic Network (Rete Sismica Nazionale Centralizzata). The twodimensional (2-D) analysis allows us to take into account lateral crustal variations and heterogeneities of this region. Using the same event and station distribution, we also applied a simple 1-D methodology, and the performance of the 1-D and 2-D path assumptions is tested by comparing the average interstation variance for the path-corrected amplitudes using coda and direct waves. In general, coda measurement results are more stable than using direct waves when the same methodology is applied. Using the 2-D approach, we observe more stable results for both waves. However, the improvement is quite small, probably because the crustal heterogeneity is weak. This means that, for this region, the 1-D path assumption is a good approximation of the attenuation characteristics of the region. A comparison between Q tomography images obtained using direct and coda amplitudes shows similar results, consistent with the geology of the region. In fact, we observe low Q along the Apennine chain toward the Tyrrhenian Sea and higher values to the east, in correspondence with the Gargano zone that is related to the Apulia Carbonate Platform. Finally, we compared our results with the coda Q values proposed by Bianco et al. (Geophys J Int 150:10–22, 2002) for the same region. The good agreement validates our results as the authors used a completely independent methodology.
    Description: Published
    Description: 355–365
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: coda Q tomography
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 60
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    Volcanic Hazard Assessment of Poás (Costa Rica) Based on the 1834, 1910, 1953–1955 and 2017 Historical Eruptions (2020)
    Springer
    Details
    Publication Date: 2021-12-13
    Description: Poás is a complex stratovolcano with an altitude of 2,708 m asl, located in the Cordillera Volcánica Central of Costa Rica. Prior to 2017, the last three historical eruptions occurred on 7 February 1834, between January and May 1910 and during the period 1953-1955. Very few literature exists on the 1834 eruption. The only references state that it was an important event, that ash reached 〉53 km W-SW of Poás, and that it harmed the grasslands around the volcano. Related deposits of this eruption suggest phreatic activity, which launched bombs and blocks. Moreover, there is evidence of pyroclastic flow deposits near the crater. The 1910 eruption is better described. Despite the fact that ash fall is only reported near the volcano, a volume of the deposit of 1.6 x 107 m3 is estimated. Deposits of the eruption are white in color with many hydrothermally altered, and minor presence of juvenile fragments (vesicular lapilli). The eruption is classified as vulcanian, with deposits of ash fall and pyroclastic flows close to the crater. A Volcano Explosivity Index 3 (VEI 3) is estimated. The eruption affected agriculture. The 1953-1955 eruptions had a longer duration. Various ash fall deposits at several sites are reported. Deposits of this eruption, easily distinguished in the field, are black scoria lapilli, bombs with, sometimes fusiform, bread crust textures. In the eastern sector of the crater bombs can reach meters in size; such large bombs near the eruption centre at one side suggest the inclination of the eruptive conduct, or an asymmetrical vent-crater system. Inside the crater a 40 m-high dome and a lava flow were extruded during the eruption. Towards the east side of the current Laguna Caliente crater lake, relicts of a 8.5 m thick lava pool are found. During the entire eruptive episode, the acid lake presumably lacked. The eruption is described to be of a mixed type: strombolian, phreatomagmatic, vulcanian and dome extrusion eruptions. Considering the characteristics of this eruption, the height of the eruption column, ejected volume (2.1 x 107  m3), and its presumed duration, a VEI 3 is estimated. The eruptions damaged agricultural activity (including cattle), and forced the spontaneous evacuation of some people. In April 2017 magmatic eruptions followed a decade-long period of intense phreatic activity. These eruptions destroyed the 1953-1955 Dome and led to the complete dry out of Laguna Caliente. Pyroclastic cones and sulphur volcanism manifested at the bottom of the former crater lake bottom. The 2017 eruption severely affected touristic activities at and near Poás, with an estimated economic loss of 20 million dollars. By May-August 2018 Laguna Caliente reappeared. The volcanic hazards related to the three studied historical eruptions are: pyroclastic flows (at least 1 km from the eruptive centre, including reaching the current mirador sector), ballistics (bomb ejections up to 2 km from the emission centre), dispersion and fall of pyroclasts (tens of kms), gas emission and acid rain, dispersed by WSW dominant winds, and lahars in most of the river canyons SW of the volcano.  
    Description: Published
    Description: 261-299
    Description: 1V. Storia eruttiva
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 61
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    Climate change impacts on the atmospheric circulation, ocean, and fisheries in the southwest South Atlantic Ocean: a review (2020)
    Springer
    In:  EPIC3Climatic Change, Springer, 162(4), pp. 2359-2377
    Details
    Publication Date: 2022-07-13
    Description: We present an interdisciplinary review of the observed and projected variations in atmospheric and oceanic circulation within the southwestern South Atlantic focused on basin-scale processes driven by climate change, and their potential impact on the regional fisheries. The observed patterns of atmospheric circulation anomalies are consistent with anthropogenic climate change. There is strong scientific evidence suggesting that the Brazil Current is intensifying and shifting southwards during the past decades in response to changes in near-surface wind patterns, leading to intense ocean warming along the path of the Brazil Current, the South Brazil Bight, and in the Río de la Plata. These changes are presumably responsible for the poleward shift of commercially important pelagic species in the region and the long-term shift from cold-water to warm-water species in industrial fisheries of Uruguay. Scientific and traditional knowledge shows that climate change is also affecting small-scale fisheries. Long-term records suggest that mass mortalities decimated harvested clam populations along coastal ecosystems of the region, leading to prolonged shellfishery closures. More frequent and intense harmful algal blooms together with unfavorable environmental conditions driven by climate change stressors affect coastal shellfisheries, impact economic revenues, and damage the livelihood of local communities. We identify future modelling needs to reduce uncertainty in the expected effects of climate change on marine fisheries. However, the paucity of fisheries data prevents a more effective assessment of the impact of climate change on fisheries and hampers the ability of governments and communities to adapt to these changes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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    Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ruppel, C. D., & Waite, W. F. Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems. Journal of Geophysical Research: Solid Earth, 125(8), (2020): e2018JB016459, doi:10.1029/2018JB016459.
    Description: Gas hydrate is an ice‐like form of water and low molecular weight gas stable at temperatures of roughly −10°C to 25°C and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one sixth of Earth's methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean‐atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean‐atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth's near‐surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some field studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems.
    Description: Both authors have received nearly two decades of support from the U.S. Geological Survey's (USGS's) Energy Resources Program and the Coastal/Marine Hazards and Resources Program and from numerous DOE‐USGS Interagency Agreements, most recently DE‐FE0023495. C. R. acknowledges support from NOAA's Office of Ocean Exploration and Research (OER) under NOAA‐USGS Interagency Agreement 16‐01118.
    Keywords: Gas hydrate ; Hydrate breakdown ; Hydrate formation ; Permafrost hydrate ; Geologic systems ; Marine hydrate
    Repository Name: Woods Hole Open Access Server
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    Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Rheuban, J. E., Doney, S. C., McCorkle, D. C., & Jakuba, R. W. Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification. Journal of Geophysical Research-Oceans, 124, (2019): 9085-9100, doi: 10.1029/2019JC015556.
    Description: The U.S. Northeast is vulnerable to ocean and coastal acidification because of low alkalinity freshwater discharge that naturally acidifies the region, and high anthropogenic nutrient loads that lead to eutrophication in many estuaries. This study describes a combined nutrient and carbonate chemistry monitoring program in five embayments of Buzzards Bay, Massachusetts to quantify the effects of nutrient loading and freshwater discharge on aragonite saturation state (Ω). Monitoring occurred monthly from June 2015 to September 2017 with higher frequency at two embayments (Quissett and West Falmouth Harbors) and across nitrogen loading and freshwater discharge gradients. The more eutrophic stations experienced seasonal aragonite undersaturation, and at one site, nearly every measurement collected was undersaturated. We present an analytical framework to decompose variability in aragonite Ω into components driven by temperature, salinity, freshwater endmember mixing, and biogeochemical processes. We observed strong correlations between apparent oxygen utilization and the portion of aragonite Ω variation that we attribute to biogeochemistry. The regression slopes were consistent with Redfield ratios of dissolved inorganic carbon and total alkalinity to dissolved oxygen. Total nitrogen and the contribution of biogeochemical processes to aragonite Ω were highly correlated, and this relationship was used to estimate the likely effects of nitrogen loading improvements on aragonite Ω. Under nitrogen loading reduction scenarios, aragonite Ω in the most eutrophic estuaries could be raised by nearly 0.6 units, potentially increasing several stations above the critical threshold of 1. This analysis provides a quantitative framework for incorporating ocean and coastal acidification impacts into regulatory and management discussions.
    Description: We thank Kelly Luis, Michaela Fendrock, Will Oesterich, Sheron Luk, Marti Jeglinksi, and Tony Williams for their help with field sample collection and logistical support and Chris Neill, Lindsay Scott, Rich McHorney, and Paul Henderson for laboratory sample analysis. We also thank the Waquoit Bay National Estuarine Research Reserve for loaning their handheld water quality meters and two anonymous reviewers for their feedback on this manuscript. Financial support for this work was provided by the John D. and Catherine T. MacArthur Foundation (grant no. 14‐106159‐000‐CFP), MIT Sea Grant (subaward 5710004045) and the West Wind Foundation. The data used in this analysis can be found in the NOAA NCEI repository for carbonate chemistry measurements, the Ocean Carbon Data System at the following link: https://www.nodc.noaa.gov/ocads/data/0206206.xml.
    Keywords: Coastal Acidification ; Eutrophication
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    Selective preservation of coccolith calcite in Ontong-Java Plateau sediments (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology, 34, (2019): 2141-2157, doi: 10.1029/2019PA003731.
    Description: Dissolution of calcite in deep ocean sediments, which is required to balance global marine CaCO3 production and burial fluxes, is still a poorly understood process. In order to assess the mechanisms of dissolution in sediments, we analyzed four multicore tops taken along a depth transect on the Ontong‐Java Plateau. These cores were taken directly on the equator, and span water column calcite saturation states from ∼0.93 to ∼0.74, allowing us to assess the effect of dissolution on carbonate sediment composition. The top 2 cm of each multicore was sectioned and sieved to separate coccolith from foraminiferal calcite, and the %CaCO3, δ13C, Δ14C, and Mg/Ca were evaluated. The mass ratio of coccoliths to foraminifera increases by a factor of 3 as a function of water depth, reflecting the preferential dissolution of foraminifera. Carbon isotope (δ13C and Δ14C) data suggest that most dissolution takes place at the sediment‐water interface and primarily affects foraminifera. Mg/Ca analyses indicate that the Mg content of the entire foraminiferal assemblage decreases as a function of dissolution. In contrast, coccolith dissolution takes place within the sediments, rather than at the interface. Together these two processes cause coccoliths to be up to 1,000 radiocarbon years younger than foraminifera from the same depth horizon. Despite this within‐sediment coccolith dissolution flux, sediments below the calcite saturation horizon remain enriched in coccolith calcite. Combined with global seafloor hypsometry and calcium carbonate content, this enrichment suggests that globally, coccoliths may outweigh foraminifera in deep ocean sediments by a factor of 1.8.
    Description: A. V. S. thanks the NOSAMS facility and the WHOI/NOSAMS postdoc scholar program, James Funds, and the Bessette family for funding and support. A. Q. acknowledges Williams College research and travel funds. We thank the Stanley W. Watson Director's Discretionary Fund for the Picarro‐Automate analyzer. We thank Ellen Roosen at the WHOI core repository for help with sample identification and sectioning. Thanks to Gretchen Swarr and the WHOI plasma mass spectrometry facility. Finally, we thank Bill Martin and Wally Broecker for enlightening discussions on dissolution and radiocarbon dating of deep ocean sediments. All data are included as supporting information files and are archived with NOAA's World Data Service for Paleoceanography (WDS Paleo; https://www.ncdc.noaa.gov/paleo/study/28150).
    Description: 2020-05-15
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    Evaluating the performance of past climate model projections (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(1), (2020): e2019GL085378, doi:10.1029/2019GL085378.
    Description: Retrospectively comparing future model projections to observations provides a robust and independent test of model skill. Here we analyze the performance of climate models published between 1970 and 2007 in projecting future global mean surface temperature (GMST) changes. Models are compared to observations based on both the change in GMST over time and the change in GMST over the change in external forcing. The latter approach accounts for mismatches in model forcings, a potential source of error in model projections independent of the accuracy of model physics. We find that climate models published over the past five decades were skillful in predicting subsequent GMST changes, with most models examined showing warming consistent with observations, particularly when mismatches between model‐projected and observationally estimated forcings were taken into account.
    Description: Z. H. conceived the project, Z. H. and H. F. D. created the figures, and Z. H., H. F. D., T. A., and G. S. helped gather data and wrote the article text. A public GitHub repository with code used to analyze the data and generate figures and csv files containing the data shown in the figures is available online (https://github.com/hausfath/OldModels). Additional information on the code and data used in the analysis can be found in the supporting information. We would like to thank Piers Forster for providing the ensemble of observationally‐informed radiative forcing estimates. No dedicated funding from any of the authors supported this project.
    Description: 2020-06-04
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    Quantification of the arctic sea ice-driven atmospheric circulation variability in coordinated large ensemble simulations (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Liang, Y., Kwon, Y., Frankignoul, C., Danabasoglu, G., Yeager, S., Cherchi, A., Gao, Y., Gastineau, G., Ghosh, R., Matei, D., Mecking, J., V., Peano, D., Suo, L., & Tian, T. Quantification of the arctic sea ice-driven atmospheric circulation variability in coordinated large ensemble simulations. Geophysical Research Letters, 47(1), (2020): e2019GL085397, doi:10.1029/2019GL085397.
    Description: A coordinated set of large ensemble atmosphere‐only simulations is used to investigate the impacts of observed Arctic sea ice‐driven variability (SIDV) on the atmospheric circulation during 1979–2014. The experimental protocol permits separating Arctic SIDV from internal variability and variability driven by other forcings including sea surface temperature and greenhouse gases. The geographic pattern of SIDV is consistent across seven participating models, but its magnitude strongly depends on ensemble size. Based on 130 members, winter SIDV is ~0.18 hPa2 for Arctic‐averaged sea level pressure (~1.5% of the total variance), and ~0.35 K2 for surface air temperature (~21%) at interannual and longer timescales. The results suggest that more than 100 (40) members are needed to separate Arctic SIDV from other components for dynamical (thermodynamical) variables, and insufficient ensemble size always leads to overestimation of SIDV. Nevertheless, SIDV is 0.75–1.5 times as large as the variability driven by other forcings over northern Eurasia and Arctic.
    Description: The authors thank Editor Christina Patricola and two anonymous reviewers for their comprehensive and insightful comments, which have led to improved presentation of this manuscript. We acknowledge support by the Blue‐Action Project (European Union's Horizon 2020 research and innovation program, 727852, http://www.blue‐action.eu/index.php?id = 3498). The WHOI‐NCAR group is also supported by the US National Science Foundation (NSF) Office of Polar Programs Grants 1736738 and 1737377, and their computing and data storage resources, including the Cheyenne supercomputer (doi:10.5065/D6RX99HX), were provided by the Computational and Information Systems Laboratory at NCAR. NCAR is a major facility sponsored by the U.S. NSF under Cooperative Agreement 1852977. The LOCEAN‐IPSL group was granted access to the HPC resources of TGCC under the Allocation A5‐017403 made by GENCI. The SST and SIC data were downloaded from the U.K. Met Office Hadley Centre Observations Datasets (http://www.metoffice.gov.uk/hadobs/hadisst).
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    What can we learn from X-ray fluorescence core scanning data? A paleomonsoon case study (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(2), (2020): e2019GC008414, doi:10.1029/2019GC008414.
    Description: X‐ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF‐derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly a function of changes in median grain size of lithogenic particles and often covary with changes in Ca concentrations that reflect changes in biogenic calcium carbonate production. This suggests that a common process (i.e., sea level) influences both records. The interpretation of lighter element data (e.g., Si and Al) based on low XRF counts is complicated as variations in mean grain size and water content result in systematic artifacts and signal intensities not related to the Al or Si content of the sediments. This highlights the need for calibration of XRF core scanning data based on discrete sample analyses and careful examination of sediment properties such as porosity/water content for reliably disentangling environmental signals from other physical properties. In the case of the Andaman Sea, reliable extraction of a monsoon signal requires accounting for the sea level influence on the XRF data.
    Description: The staff at the Bremen Core Repository is thanked for their help with core handling and Sam Müller at the University of Kiel provided technical assistance with the XRF scanner. We thank two anonymous reviewers for their insightful comments that improved the manuscript significantly. This work was partially funded through DFG Grant HA 5751/3. P. A. and K. N.‐K. acknowledge support from UK‐IODP and Natural and Environment Research Council, UK. The authors express their thanks to all those who contributed to the success of the National Gas Hydrate Program Expedition 01 (NGHP01) and Expedition 353. The data set supporting the conclusions of this article is available in the PANGEA repository (doi: https://doi.pangaea.de/10.1594/PANGAEA.910533).
    Description: 2020-07-10
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    Characterization of sea surface temperature and air-sea heat flux anomalies associated with mesoscale eddies in the South China Sea (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(4), (2020): e2019JC015470, doi:10.1029/2019JC015470.
    Description: This study is to quantify the effects of mesoscale eddies on air‐sea heat fluxes and related air‐sea variables in the South China Sea. Using satellite observations of sea surface temperature (SST) and sea surface height anomaly and a high‐resolution air‐sea heat flux product for the 16‐year period from 2000 to 2015, we conducted the composite patterns of air‐sea fluxes and variables associated with anticyclonic eddies (AEs) and cyclonic eddies (CEs). It is found that the SST‐sea surface height correlations over eddies are not always positive. Only 56% of AEs are corresponded with positive SST anomalies (SSTA), that is, SST+ AEs, and 58% of CEs with negative SSTA, that is, SST− CEs. The percentage of these eddies increases with eddy amplitude and shows slight seasonal variations, higher in winter and lower in summer. Composites of SSTA, air‐sea variables, and fluxes are constructed over all eddies, including both SST+ eddies and SST− eddies. All composites show asymmetric patterns, showing that the centers (where the extrema are located) of the fluxes and variables shift westward and poleward (equatorward) relative to the AEs (CEs) cores. Besides, composites of latent heat flux (LHF), sensible heat flux (SHF), and air temperature show monopole patterns, while composites of wind speed and specific humidity show dipole patterns. For SST+ AEs, the coupling strength is 39.6 ± 6.5 W/m2 (7.2 ± 1.7 W/m2) per degree increase of SSTA for LHF (SHF). For SST− CEs, the coupling strength is 39.0 ± 2.0 W/m2 (9.0 ± 0.96 W/m2) per degree decrease of SSTA for LHF (SHF).
    Description: This research was conducted while Y. Liu was a visiting graduate student at Woods Hole Oceanographic Institution (WHOI). She sincerely thanks the WHOI Academic Programs Office for hosting her visit and is grateful to the support from China Scholarship Council (CSC). This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDA19060101), the Key R & D project of Shandong Province (Grant 2019JZZY010102), the Key deployment project of Center for Ocean Mega‐Science, CAS (Grant COMS2019R02), the CAS Program (Grant Y9KY04101L), and the National Natural Science Foundation of China (Grant 41776183 and 41906157). Dr. Xiangze Jin is acknowledged for providing the OAFluxHR analysis and for his programming support and guidance to this study. Heat flux data used in this paper can be downloaded (from https://figshare.com/articles/Eddy‐induced_heat_flux_in_the_South_China_Sea/11949735). AVISO SSH data are downloaded from the website (http://www.aviso.altimetry.fr), OISST from the ftp://eclipse.ncdc.noaa.gov/ site, and OAFluxHR analysis will be available from the project website (http://oaflux.whoi.edu).
    Description: 2020-09-16
    Keywords: mesoscale eddies ; air‐sea coupling ; South China Sea
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    Eddies in the Hawaiian archipelago region: formation, characterization, and potential implications on larval retention of reef fish (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC015348, doi:10.1029/2019JC015348.
    Description: Here we present an assessment of eddy activity in a 3,500 × 2,000 km region of the North Pacific. Eddies were identified and tracked within a numerical simulation that used the Massachusetts Institute of Technology general circulation model and an eddy characterization algorithm. Spatially, eddy births were more frequent: (1) nearshore (cyclones) and offshore (anticyclones) on the windward side of the main Hawai‘ian Islands; (2) in patches of cyclones and anticyclones that resembled the dipole structure of wind stress curl along the islands’ leeward side; and (3) in zonal patches of eddies of both polarities west and north of the islands. Temporally, high eddy activities occurred in spring. There was a meridional distribution of eddy lifespans, which increased northward. Cyclones were more abundant, longer‐lived, smaller, and more nonlinear. Reef fish spawning locations in Hawai‘i coincide with the regions of high eddy activity, with nonlinear eddies responsible for high larval retention.
    Description: This work was supported by the National Ocean and Atmospheric Administration (NOAA) Fisheries And The Environment (FATE) Award WE133F17SE1020. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation Grant NSF‐OCE170005.
    Description: 2020-10-29
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    Basin-width dependence of northern deep convection (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(15), (2020): e2020GL089135, doi:10.1029/2020GL089135.
    Description: Convection penetrates to the ocean bottom in the North Atlantic but not in the North Pacific. This study examines the role of basin width in shutting down high‐latitude ocean convection. Deep convection is triggered by polar cooling, but it is opposed by precipitation. A two‐layer analytical model illustrates that the overturning circulation acts to mitigate the effect of precipitation by advecting salty, dense water from subtropical latitudes to polar latitudes. The nonlinear dependence of the overturning strength on basin width makes it more efficient in a narrow basin, resulting in a convection shutdown at a stronger freshwater forcing. These predictions are confirmed by simulations with a general circulation model configured with a single closed basin to the north and a reentrant channel to the south. This suggests that basin width may play a role in suppressing convection in the North Pacific but not in the North Atlantic.
    Description: M. K. Y. and R. F. acknowledge support through National Science Foundation (NSF) Awards OCE‐1536515 and AGS‐1835576. M. K. Y. acknowledges funding from the National Defense Science and Engineering Graduate Fellowship and the American Meteorological Society Graduate Student Fellowship. G. R. F. was supported by NSF OCE‐1459702.
    Description: 2020-01-2021
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    Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schultz, C., Doney, S. C., Zhang, W. G., Regan, H., Holland, P., Meredith, M. P., & Stammerjohn, S. Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula. Journal of Geophysical Research: Oceans, 125(8), (2020): e2020JC016109, doi:10.1029/2020JC016109.
    Description: The Southern Ocean is chronically undersampled due to its remoteness, harsh environment, and sea ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data; however, they often underestimate surface mixed layer depth (MLD), with consequences for surface water‐column temperature, salinity, and nutrient concentration. In this study, a coupled circulation and sea ice model was implemented for the region adjacent to the West Antarctic Peninsula, a climatically sensitive region which has exhibited decadal trends towards higher ocean temperature, shorter sea ice season, and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air‐ice drag coefficients and Langmuir circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air‐ice drag coefficient also increased modeled MLD by similar amounts and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for biases towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the West Antarctic Peninsula during late summer and suggests that areas of intense summertime sea ice melt can still show net annual freezing due to high sea ice formation during the winter.
    Description: C. Schultz and S. Doney acknowledge support by the U.S. National Science Foundation (grant PLR‐1440435 to the Palmer Long Term Ecological Research program) and support from the University of Virginia. W. G. Zhang acknowledge support by the U.S. National Science Foundation (grant OPP‐1643901). The MITgcm model is an open source model (mitgcm.org). The version used in this study, with added parameterizations and specific configurations, is on C. Schultz’s github (https://github.com/crisoceano/WAP_MITgcm). A copy of the files with specific configurations for this study, the forcing files needed for the simulations, and a copy of the files used for the KPP package are in three separate records on zenodo.org, under DOIs 10.5281/zenodo.3627365, 10.5281/zenodo.3627564, and 10.5281/zenodo.3627742.
    Keywords: West Antarctic Peninsula ; sea ice ; Langmuir circulation ; mixed layer depth ; glacial runoff
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    Introduction to special issue on gas hydrate in porous media: linking laboratory and field-scale phenomena (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(8), (2019): 7525-7537, doi: 10.1029/2019JB018186.
    Description: The proliferation of drilling expeditions focused on characterizing natural gas hydrate as a potential energy resource has spawned widespread interest in gas hydrate reservoir properties and associated porous media phenomena. Between 2017 and 2019, a Special Section of this journal compiled contributed papers elucidating interactions between gas hydrate and sediment based on laboratory, numerical modeling, and field studies. Motivated mostly by field observations in the northern Gulf of Mexico and offshore Japan, several papers focus on the mechanisms for gas hydrate formation and accumulation, particularly with vapor phase gas, not dissolved gas, as the precursor to hydrate. These studies rely on numerical modeling or laboratory experiments using sediment packs or benchtop micromodels. A second focus of the Special Section is the role of fines in inhibiting production of gas from methane hydrate, controlling the distribution of hydrate at a pore scale, and influencing the bulk behavior of seafloor sediments. Other papers fill knowledge gaps related to the physical properties of hydrate‐bearing sediments and advance new approaches in coupled thermal‐mechanical modeling of these sediments during hydrate dissociation. Finally, one study addresses the long‐standing question about the fate of methane hydrate at the molecular level when CO2 is injected into natural reservoirs under hydrate‐forming conditions.
    Description: C. R. was supported by the U.S. Geological Survey's Energy Resources Program and the Coastal/Marine Hazards and Resources Program, as well as by DOE Interagency Agreement DE‐FE0023495. C. R. thanks W. Waite and J. Jang for discussions and suggestions that improved this paper and L. Stern for a helpful review. J. Y. Lee was supported by the Ministry of Trade, Industry, and Energy (MOTIE) through the Project “Gas Hydrate Exploration and Production Study (19‐1143)” under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM). Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    Keywords: Gas hydrate ; Methane ; Reservoir properties ; Multiphase flow
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    Surface methane concentrations along the mid-Atlantic bight driven by aerobic subsurface production rather than seafloor gas seeps. (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC015989, doi:10.1029/2019JC015989.
    Description: Relatively minor amounts of methane, a potent greenhouse gas, are currently emitted from the oceans to the atmosphere, but such methane emissions have been hypothesized to increase as oceans warm. Here, we investigate the source, distribution, and fate of methane released from the upper continental slope of the U.S. Mid‐Atlantic Bight, where hundreds of gas seeps have been discovered between the shelf break and ~1,600 m water depth. Using physical, chemical, and isotopic analyses, we identify two main sources of methane in the water column: seafloor gas seeps and in situ aerobic methanogenesis which primarily occurs at 100–200 m depth in the water column. Stable isotopic analyses reveal that water samples collected at all depths were significantly impacted by aerobic methane oxidation, the dominant methane sink in this region, with the average fraction of methane oxidized being 50%. Due to methane oxidation in the deeper water column, below 200 m depth, surface concentrations of methane are influenced more by methane sources found near the surface (0–10 m depth) and in the subsurface (10–200 m depth), rather than seafloor emissions at greater depths.
    Description: This research was supported by DOE Grant (DE‐FE0028980) to J. K. and by DOE‐USGS Interagency Agreement DE‐FE0026195.
    Description: 2020-10-04
    Keywords: Methane ; Ocean ; Isotopes ; Gas seeps ; Mid Atlantic bight ; Oxidation
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    Enhanced carbon uptake and reduced methane emissions in a newly restored wetland (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 125(1), (2020): e2019JG005222, doi:10.1029/2019JG005222.
    Description: Wetlands play an important role in reducing global warming potential in response to global climate change. Unfortunately, due to the effects of human disturbance and natural erosion, wetlands are facing global extinction. It is essential to implement engineering measures to restore damaged wetlands. However, the carbon sink capacity of restored wetlands is unclear. We examined the seasonal change of greenhouse gas emissions in both restored wetland and natural wetland and then evaluated the carbon sequestration capacity of the restored wetland. We found that (1) the carbon sink capacity of the restored wetland showed clear daily and seasonal change, which was affected by light intensity, air temperature, and vegetation growth, and (2) the annual daytime (8–18 hr) sustained‐flux global warming potential was −11.23 ± 4.34 kg CO2 m−2 y−1, representing a much larger carbon sink than natural wetland (−5.04 ± 3.73 kg CO2 m−2 y−1) from April to December. In addition, the results showed that appropriate tidal flow management may help to reduce CH4 emission in wetland restoration. Thus, we proposed that the restored coastal wetland, via effective engineering measures, reliably acted as a large net carbon sink and has the potential to help mitigate climate change.
    Description: We would like to thank Yangtze Delta Estuarine Wetland Ecosystem Ministry of Education & Shanghai Observation and Research Station for providing sites during our research. This research was supported by the National Key Research and Development Program of China (Grant 2017YFC0506002), the National Natural Science Foundation of China Overseas and Hong Kong‐Macao Scholars Collaborative Research Fund (Grant 31728003), the China Postdoctoral Science Foundation (Grant 2018M640362), the Shanghai University Distinguished Professor (Oriental Scholars) Program (Grant JZ2016006), the Open Fund of Shanghai Key Lab for Urban Ecological Processes and Eco‐Restoration (Grant SHUES2018B06), and the Scientific Projects of Shanghai Municipal Oceanic Bureau (Grant 2018‐03). The complete data set is available at https://data.4tu.nl/repository/uuid:536b2614‐c4ca‐43d2‐84dd‐6180fd859544.
    Keywords: Blue carbon ; Restored wetland ; Sustained‐flux global warming potential (SGWP) ; Greenhouse gas (GHG) ; Carbon sequestration capacity
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    Sediment delivery to a tidal marsh platform is minimized by source decoupling and flux convergence (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 125(8),(2020): e2020JF005558, doi:10.1029/2020JF005558.
    Description: Sediment supply is a primary factor in determining marsh response to sea level rise and is typically approximated through high‐resolution measurements of suspended sediment concentrations (SSCs) from adjacent tidal channels. However, understanding sediment transport across the marsh itself remains limited by discontinuous measurements of SSC over individual tidal cycles. Here, we use an array of optical turbidity sensors to build a long‐term, continuous record of SSC across a marsh platform and adjacent tidal channel. We find that channel and marsh concentrations are correlated (i.e., coupled) within tidal cycles but are largely decoupled over longer time scales. We also find that net sediment fluxes decline to near zero within 10 m of the marsh edge. Together, these results suggest that large sections of the marsh platform receive minimal sediment independent of flooding frequency or channel sediment supply. Marsh‐centric, as opposed to channel‐centric, measures of sediment supply may better characterize marsh platform vulnerability.
    Description: This work was funded by NSF Awards 1529245, 1654374, 1426981, 1637630, and 1832221, the NSF Graduate Research Fellowship Program, and the USGS Climate and Land Use Research and Development program. We thank D. Walters, J. Himmelstein, D. Nicks, R. Walker, T. Messerschmidt, and the Plum Island Ecosystems LTER, especially S. Kelsey for laboratory and field assistance. Additionally, we thank C. Friedrichs, G. Guntenspergen, and O. Duran Vinent for contributing ideas that helped develop the work, and the reviewers who helped improve the manuscript. This work is Contribution Number 3928 of the Virginia Institute of Marine Science. In memoriam of David Nicks.
    Description: 2021-01-27
    Keywords: Salt marsh ; Sediment transport ; Turbidity ; Flux convergence ; Decoupling
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  • 76
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    Focused fluid flow along the Nootka fault zone and continental slope, explorer-Juan de Fuca Plate Boundary (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Riedel, M., Rohr, K. M. M., Spence, G. D., Kelley, D., Delaney, J., Lapham, L., Pohlman, J. W., Hyndman, R. D., & Willoughby, E. C. Focused fluid flow along the Nootka fault zone and continental slope, explorer-Juan de Fuca Plate Boundary. Geochemistry Geophysics Geosystems, 21(8), (2020): e2020GC009095, doi:10.1029/2020GC009095.
    Description: Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from 〉20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios 〈500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate‐related bottom‐simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.
    Description: This study represents data from numerous cruises acquired over more than two decades. We would like to thank all the scientific personnel and technical staff involved in data acquisition, processing of samples, and making observations during the ROV dives, as well as the crews and captains of the various research vessels involved. This is contribution #5877 from the University of Maryland Center for Environmental Science. This is NRCan contribution number / Numéro de contribution de RNCan: 20200324.
    Keywords: Fluid flow ; Nootka transform fault ; Gas hydrate ; Intrusion ; Heat flow
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  • 77
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    Recent contributions of theory to our understanding of the Atlantic Meridional Overturning Circulation (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Johnson, H. L., Cessi, P., Marshall, D. P., Schloesser, F., & Spall, M. A. Recent contributions of theory to our understanding of the Atlantic Meridional Overturning Circulation. Journal of Geophysical Research-Oceans, 124(8), (2019): 5376-5399, doi: 10.1029/2019JC015330.
    Description: Revolutionary observational arrays, together with a new generation of ocean and climate models, have provided new and intriguing insights into the Atlantic Meridional Overturning Circulation (AMOC) over the last two decades. Theoretical models have also changed our view of the AMOC, providing a dynamical framework for understanding the new observations and the results of complex models. In this paper we review recent advances in conceptual understanding of the processes maintaining the AMOC. We discuss recent theoretical models that address issues such as the interplay between surface buoyancy and wind forcing, the extent to which the AMOC is adiabatic, the importance of mesoscale eddies, the interaction between the middepth North Atlantic Deep Water cell and the abyssal Antarctic Bottom Water cell, the role of basin geometry and bathymetry, and the importance of a three‐dimensional multiple‐basin perspective. We review new paradigms for deep water formation in the high‐latitude North Atlantic and the impact of diapycnal mixing on vertical motion in the ocean interior. And we discuss advances in our understanding of the AMOC's stability and its scaling with large‐scale meridional density gradients. Along with reviewing theories for the mean AMOC, we consider models of AMOC variability and discuss what we have learned from theory about the detection and meridional propagation of AMOC anomalies. Simple theoretical models remain a vital and powerful tool for articulating our understanding of the AMOC and identifying the processes that are most critical to represent accurately in the next generation of numerical ocean and climate models.
    Description: H. L. J. and D. P. M. are grateful for funding from the U.K. Natural Environment Research Council under the UK‐OSNAP project (NE/K010948/1). P. C. gratefully acknowledges support by the National Science Foundation through OCE‐1634128. M. A. S. was supported by the National Science Foundation Grants OCE‐1558742 and OCE‐1634468. We are also grateful to Eli Tziperman and an anonymous reviewer whose comments helped us to improve the manuscript. The Estimating the Circulation and Climate of the Ocean state estimate (ECCO version 4 release 3) used to produce Figure 2 is available online (https://ecco.jpl.nasa.gov). Please refer to the original papers reviewed here for access to any other data discussed.
    Keywords: Atlantic ; Overturning circulation
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  • 78
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    Effects of oceanic mesoscale and submesoscale frontal processes on the vertical transport of phytoplankton (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(8), (2019): 5999-6014, doi: 10.1029/2019JC015034.
    Description: Oceanic fronts are dynamically active regions of the global ocean that support upwelling and downwelling with significant implications for phytoplankton production and export. However (on time scales urn:x-wiley:jgrc:media:jgrc23568:jgrc23568-math-0001 the inertial time scale), the vertical velocity is 103–104 times weaker than the horizontal velocity and is difficult to observe directly. Using intensive field observations in conjunction with a process study ocean model, we examine vertical motion and its effect on phytoplankton fluxes at multiple spatial horizontal scales in an oligotrophic region in the Western Mediterranean Sea. The mesoscale ageostrophic vertical velocity (∼10 m/day) inferred from our observations shapes the large‐scale phytoplankton distribution but does not explain the narrow (1–10 km wide) features of high chlorophyll content extending 40–60 m downward from the deep chlorophyll maximum. Using modeling, we show that downwelling submesoscale features concentrate 80% of the downward vertical flux of phytoplankton within just 15% of the horizontal area. These submesoscale spatial structures serve as conduits between the surface mixed layer and pycnocline and can contribute to exporting carbon from the sunlit surface layers to the ocean interior.
    Description: The AlborEx experiment was conducted in the framework of PERSEUS EU‐funded project (Grant 287600) and was led by the Spanish National Research Council (CSIC) and involved other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy); and Woods Hole Oceanographic Institution (WHOI, ONR Grant N00014‐16‐1‐3130). Glider operations were partially funded by JERICO FP7 project. Part of this work has been carried out as part of the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. CMEMS is implemented by Mercator Ocean in the framework of a delegation agreement with the European Union. S. R. and A. P. acknowledge support from WHOI Subcontract A101339. Data available from authors: Ship CTDs, glider and VM‐ADCP data files are available in the SOCIB data catalog (https://doi.org/10.25704/z5y2-qpye); model data are available at IMEDEA data catalog https://ide.imedea.uib-csic.es/thredds/catalog/data/projects/alborex/catalog.html. We thank all the crew and participants on board R/V SOCIB for their collaboration and Marc Torner and the SOCIB glider Facility for their efficient cooperation. We also thank B. Mourre for numerical data from the Western Mediterranean Operational Model to initialize the Process Study Ocean Model. Figures were created using the cmocean colormaps package (Thyng et al., 2016).
    Keywords: Vertical motion ; Ocean front ; Mesoscale ; Submesoscale ; Transport ; Phytoplankton
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  • 79
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    The relationship between U.S. East Coast sea level and the Atlantic Meridional Overturning Circulation: a review (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Little, C. M., Hu, A., Hughes, C. W., McCarthy, G. D., Piecuch, C. G., Ponte, R. M., & Thomas, M. D. The relationship between U.S. East Coast sea level and the Atlantic Meridional Overturning Circulation: a review. Journal of Geophysical Research-Oceans, 124(9), (2019): 6435-6458, doi:10.1029/2019JC015152.
    Description: Scientific and societal interest in the relationship between the Atlantic Meridional Overturning Circulation (AMOC) and U.S. East Coast sea level has intensified over the past decade, largely due to (1) projected, and potentially ongoing, enhancement of sea level rise associated with AMOC weakening and (2) the potential for observations of U.S. East Coast sea level to inform reconstructions of North Atlantic circulation and climate. These implications have inspired a wealth of model‐ and observation‐based analyses. Here, we review this research, finding consistent support in numerical models for an antiphase relationship between AMOC strength and dynamic sea level. However, simulations exhibit substantial along‐coast and intermodel differences in the amplitude of AMOC‐associated dynamic sea level variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of ageostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections.
    Description: The authors acknowledge funding support from NSF Grant OCE‐1805029 (C. M. L.) and NASA Contract NNH16CT01C (C. M. L. and R. M. P.), the Regional and Global Model Analysis (RGMA) component of the Earth and Environmental System Modeling Program of the U.S. Department of Energy's Office of Biological & Environmental Research Cooperative Agreement DE‐FC02‐97ER62402 (A. H.), Natural Environment Research Council NE/K012789/1 (C. W. H.), Irish Marine Institute Project A4 PBA/CC/18/01 (G. D. M.), and NSF Awards OCE‐1558966 and OCE‐1834739 (C. G. P.). The National Center for Atmospheric Research is sponsored by National Science Foundation. The authors thank the two reviewers for their comments, and CLIVAR and the U.S. AMOC Science Team for inspiration and patience. All CMIP5 data used in Figures 4-6 are available at http://pcmdi9.llnl.gov/ website; the AMOC strength fields were digitized from Chen et al. (2018, supporting information Figure S3).
    Keywords: Sea level ; AMOC ; United States ; Coastal ; Climate model ; Review
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  • 80
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    Long-term evolution of nontransform discontinuities at the Mid-Atlantic Ridge, 24°N–27°30′N (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124 (2019): 10023–10055, doi: 10.1029/2019JB017648.
    Description: We studied long‐term evolution of nontransform discontinuities (NTDs) on the Mid‐Atlantic Ridge from 0‐ to ~20‐ to 25‐Ma crust using plate reconstructions of multibeam bathymetry, long‐range HMR1 sidescan sonar, residual mantle Bouguer gravity anomaly (RMBA), and gravity‐derived crustal thickness. NTDs have propagated north and south with respect to flowlines of relative plate motion and both rapidly and slowly compared to the half spreading rate; at times they have been quasi‐stable. Fast, short‐term (〈2 Myr) propagation is driven by reduced magma supply (increased tectonic extension) in the propagating ridge tip when NTD ridge‐axis offsets are small (≲5 km). Propagation at larger offsets generally is slower and longer term. These NTDs can show classic structures of rift propagation including inner and outer pseudofaults and crustal blocks transferred between ridge flanks by discontinuous jumps of the propagating ridge tip. In all cases crustal transfer occurs within the NTD valley. Aside from ridge‐axis offset, the evolution of NTDs appears to be controlled by three factors: (1) gross volume and distribution of magma supplied to ridge segments as controlled by 3‐D heterogeneities in mantle fertility and/or dynamic upwelling; this controls fundamental ridge segmentation. (2) The lithospheric plumbing system through which magma is delivered to the crust. (3) The consequent focusing of tectonic extension in magma‐poor parts of spreading segments, typically at segment ends, which can drive propagation. We also observe long‐wavelength (5‐10 Myr) RMBA asymmetry between the conjugate ridge flanks, and we attribute this to asymmetric distribution of density anomalies in the upper mantle.
    Description: We thank Tingting Wang for providing plate‐reconstruction codes, Ross Parnell‐Turner for technical support, and Anouk Beniest and an anonymous reviewer for comments that helped to improve the manuscript. We benefited greatly from discussion with the Deep Sea Geodynamics Group of the South China Sea Institute of Oceanology. Figures were drawn using the GMT software of Wessel and Smith (1998). This study was supported by National Natural Science Foundation of China (91628301, 41890813, and U1606401), Chinese Academy of Sciences (Y4SL021001, QYZDY‐SSW‐DQC005, and 133244KYSB20180029), Chinese National 985 Project (1350141509), International Exchange Program for Graduate Students of Tongji University (2016020006), China Scholarship Council (201706260034), and Woods Hole Oceanographic Institution. We thank the crews and science parties of the ARSRP, MAREAST, MODE94, and MODE98 expeditions for their contributions to data acquisition. ARSRP and MAREAST data acquisition was funded by Office of Naval Research grant N00014‐90‐J‐6121 and by U.S. National Science Foundation grant OCE‐9503561, respectively. Access to the original data used in this study is available at https://doi.org/10.26025/z2z7‐kd89.
    Description: 2020-03-11
    Keywords: Mid‐Atlantic Ridge ; Nontransform discontinuity ; Plate reconstruction ; Propagating rift
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  • 81
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    Shelfbreak downwelling in the Alaskan Beaufort Sea (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124 (2019): 7201-7225, doi: 10.1029/2019JC015520.
    Description: The oceanographic response and atmospheric forcing associated with downwelling along the Alaskan Beaufort Sea shelf/slope is described using mooring data collected from August 2002 to September 2004, along with meteorological time series, satellite data, and reanalysis fields. In total, 55 downwelling events are identified with peak occurrence in July and August. Downwelling is initiated by cyclonic low‐pressure systems displacing the Beaufort High and driving westerly winds over the region. The shelfbreak jet responds by accelerating to the east, followed by a depression of isopycnals along the outer shelf and slope. The storms last 3.25 ± 1.80 days, at which point conditions relax toward their mean state. To determine the effect of sea ice on the oceanographic response, the storms are classified into four ice seasons: open water, partial ice, full ice, and fast ice (immobile). For a given wind strength, the largest response occurs during partial ice cover, while the most subdued response occurs in the fast ice season. Over the two‐year study period, the winds were strongest during the open water season; thus, the shelfbreak jet intensified the most during this period and the cross‐stream Ekman flow was largest. During downwelling, the cold water fluxed off the shelf ventilates the upper halocline of the Canada Basin. The storms approach the Beaufort Sea along three distinct pathways: a northerly route from the high Arctic, a westerly route from northern Siberia, and a southerly route from south of Bering Strait. Differences in the vertical structure of the storms are presented as well.
    Description: The authors thank Paula Fratantoni and Dan Torres for processing the moored profiler and ADCP data, respectively. Data from the SBI mooring array can be found at https://archive.eol.ucar.edu/projects/sbi/all_data.shtml. Funding for the analysis was provided by the following grants: National Science Foundation Grants OCE‐1259618 (N. F. and R. P.), OCE‐1756361 (N. F.), and PLR‐1504333 (N. F. and R. P.); National Oceanic and Atmospheric Administration Grant NA14‐OAR4320158 (R. P. and P. L.); and the Natural Sciences and Engineering Research Council of Canada (K. M.).
    Description: 2020-04-16
    Keywords: Downwelling ; Beaufort Sea ; Shelfbreak ; North Slope ; Arctic cyclone
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  • 82
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    Magnetic mineral populations in lower oceanic crustal gabbros (Atlantis Bank, SW Indian Ridge): implications for marine magnetic anomalies (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(3), (2020): e2019GC008847, doi:10.1029/2019GC008847.
    Description: To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly 〈1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank.
    Description: This work used samples and data provided by the International Ocean Discovery Program. Funding was provided by the U.S. Science Support Program (J.B.). I.L. has benefited from a Smithsonian Edward and Helen Hintz Secretarial Scholarship. We thank the members of the IODP Expedition 360 Science Party, and the captain and crew of the JOIDES Resolution. Part of this work was done as a Visiting Fellow at the Institute for Rock Magnetism (IRM) at the University of Minnesota. The IRM is made possible through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. We would like to thank IRM staff M. Jackson, P. Solheid, and D. Bilardello for their generous assistance. Many thanks to A. Butula, K. Vernon, and J. Marquardt for their assistance with rock magnetic measurements at UWM and to L. McHenry for assistance with XRD. We also thank two anonymous reviewers for their thoughtful comments that improved the manuscript. Magnetic data associated with this manuscript are available in the Magnetics Information Consortium (MagIC) database at https://www.earthref.org/MagIC/doi/10.1029/2019GC008847. XRD data are available at https://zenodo.org/record/3611642.
    Description: 2020-08-28
    Keywords: Marine magnetic anomalies ; Ocean crust magnetization ; Magnetic mineralogy ; IODP ; Expedition 360 ; JOIDES Resolution
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  • 83
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    Impact of current-wind interaction on vertical processes in the Southern Ocean (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(4), (2020): e2020JC016046, doi:10.1029/2020JC016046.
    Description: Momentum input from westerly winds blowing over the Southern Ocean can be modulated by mesoscale surface currents and result in changes in large‐scale ocean circulation. Here, using an eddy‐resolving 1/20 degree ocean model configured near Drake Passage, we evaluate the impact of current‐wind interaction on vertical processes. We find a reduction in momentum input from the wind, reduced eddy kinetic energy, and a modification of Ekman pumping rates. Wind stress curl resulting from current‐wind interaction leads to net upward motion, while the nonlinear Ekman pumping term associated with horizontal gradients of relative vorticity induces net downward motion. The spatially averaged mixed layer depth estimated using a density criteria is shoaled slightly by current‐wind interaction. Current‐wind interaction, on the other hand, enhances the stratification in the thermocline below the mixed layer. Such changes have the potential to alter biogeochemical processes including nutrient supply, biological productivity, and air‐sea carbon dioxide exchange.
    Description: The MITgcm can be obtained online (http://mitgcm.org). The geostrophic current product derived from the sea level anomaly can be downloaded in the Copernicus Marine and Environment Monitoring Service of Ssalto/Duacs gridded “allsat” series and along‐track Sea Level Anomalies, Absolute Dynamic Topographies and Geostrophic velocities over the Global Ocean, Mediterranean Sea, Black Sea, European Seas and Acrtic Ocean areas, in Delayed‐Time and in Near‐Real‐Time. Resources supporting this work were provided by the NASA High‐End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center with the award number SMD‐15‐5752. H. S., J. M., and D. J. M. were supported by the NSF MOBY project (OCE‐1048926 and OCE‐1048897). H. S. acknowledges the support by National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF‐2019R1C1C1003663) and Yonsei University Research Fund of 2018‐22‐0053. D. J. M. also gratefully acknowledges NSF and NASA support, along with the Holger W. Jannasch and Columbus O'Donnell Iselin shared chairs for Excellence in Oceanography. H. Seo acknowledges the support from the ONR (N00014‐17‐1‐2398), NOAA (NA10OAR4310376), and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research at WHOI. We also thank two anonymous referees whose comments significantly improved the presentation of results.
    Description: 2020-09-17
    Keywords: Southern Ocean ; Eddy-wind interaction ; Ekman pumping ; Stratification ; Eddy kinetic energy ; Mixed layer depth
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    What caused recent shifts in tropical pacific decadal sea-level trends? (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124 (2019): 7575-7590, doi: 10.1029/2019JC015339.
    Description: Satellite altimetry reveals substantial decadal variability in sea level 𝜁 across the tropical Pacific during 1993–2015. An ocean state estimate that faithfully reproduces the observations is used to elucidate the origin of these low-frequency tropical Pacific 𝜁 variations. Analysis of the hydrostatic equation reveals that recent decadal 𝜁 changes in the tropical Pacific are mainly hermosteric in nature, related to changes in upper-ocean heat content. A forcing experiment performed with the numerical model suggests that anomalous wind stress was an important driver of the relevant heat storage and thermosteric variation. Closed budget diagnostics further clarify that the wind-stress-related thermosteric 𝜁 variation resulted from the joint actions of large-scale ocean advection and local surface heat flux, such that advection controlled the budget over shorter, intraseasonal to interannual time scales, and local surface heat flux became increasingly influential at longer decadal periods. In particular, local surface heat flux was important in contributing to a recent reversal of decadal 𝜁 trends in the tropical Pacific. Contributions from local surface heat flux partly reflect damping latent heat flux tied to wind-stress-driven sea-surface-temperature variations.
    Description: This work was supported by NSF Awards OCE‐1558966 and OCE‐1834739. Support of the ECCO project by the NASA Physical Oceanography, Cryospheric Science, and Modeling, Analysis and Prediction programs is also acknowledged. We thank Ou Wang (NASA JPL) for performing the forcing perturbation experiment. Comments from two anonymous reviewers were helpful. Altimetry observations used in Figures 1 and 2 were downloaded from CSIRO (http://www.cmar.csiro.au/sealevel/sl_data_cmar.html). ECCOv4 output is available on the group website (https://ecco.jpl.nasa.gov/).
    Description: 2020-04-30
    Keywords: Sea‐level change ; Sea‐level variability ; Decadal variability ; Tropical Pacific ; State estimation
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    Coral records of temperature and salinity in the tropical western Pacific reveal influence of the Pacific Decadal Oscillation since the late nineteenth century (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ramos, R. D., Goodkin, N. F., Siringan, F. P., & Hughen, K. A. Coral records of temperature and salinity in the tropical western Pacific reveal influence of the Pacific Decadal Oscillation since the late nineteenth century. Paleoceanography and Paleoclimatology, 34(8), (2019): 1344-1358, doi: 10.1029/2019PA003684.
    Description: The Pacific Decadal Oscillation (PDO) is a complex aggregate of different atmospheric and oceanographic forcings spanning the extratropical and tropical Pacific. The PDO has widespread climatic and societal impacts, thus understanding the processes contributing to PDO variability is critical. Distinguishing PDO‐related variability is particularly challenging in the tropical Pacific due to the dominance of the El Niño–Southern Oscillation and influence of anthropogenic warming signals. Century‐long western Pacific records of subannual sea surface temperature (SST) and sea surface salinity (SSS), derived from coral Sr/Ca and δ18O profiles, respectively, allow for evaluating different climatic sensitivities and identifying PDO‐related variability in the region. The summer Sr/Ca‐SST record provides evidence of a significant SST increase, likely tied to greenhouse gas emissions. Anthropogenic warming is masked in the winter Sr/Ca‐SST record by interannual to multidecadal scale changes driven by the East‐Asian Winter Monsoon and the PDO. Decadal climate variability during winter is strongly correlated to the PDO, in agreement with other PDO records in the region. The PDO also exerts influence on the SSS difference between the dry and wet season coral δ18O (δ18Oc)‐SSS records through water advection. The PDO and El Niño–Southern Oscillation constructively combine to enhance/reduce advection of saline Kuroshio waters at our site. Overall, we are able to demonstrate that climate records from a tropical reef environment significantly capture PDO variability and related changes over the period of a century. This implies that the tropical western Pacific is a key site in understanding multifrequency climate variability, including its impact on tropical climate at longer timescales.
    Description: The authors would like to thank J. Ossolinski, J. Aggangan, J. Quevedo, R. Lloren, G. Albano, J. Perez, and A. Bolton for their help in acquiring core samples in the field. The detailed comments and suggestions of two anonymous reviewers significantly improved the original manuscript. This research was funded by the National Research Foundation Singapore under its Singapore NRF Fellowship scheme awarded to N. F. Goodkin (National Research Fellow award NRF‐RF2012‐03), as administered by the Earth Observatory of Singapore and the Singapore Ministry of Education under the Research Centers of Excellence initiative and by the Ministry of Education, Singapore through its Academic Research Fund Tier 2 (Project MOE2016‐T2‐1‐016). The coral Sr/Ca and δ18O data generated in this study are available in the supporting information Data Set S1 and are archived at the NOAA NCDC World Data Center for Paleoclimatology (https://www.ncdc.noaa.gov/paleo/study/27271). Other data and resources used in this study were sourced from the following sites: PDO index (http://research.jisao.washington.edu/pdo/PDO.latest); IPO index (https://www.esrl.noaa.gov/psd/data/timeseries/IPOTPI/ipotpi.hadisst2.data); NP index (https://www.esrl.noaa.gov/psd/data/correlation/np.data); PDO and North Pacific SST reconstructions (https://www.ncdc.noaa.gov/data‐access/paleoclimatology‐data); and MTM coherence and phase analysis MATLAB® code (https://www.mathworks.com/matlabcentral/fileexchange/22551‐multi‐taper‐coherence‐method‐with‐bias‐correction).
    Keywords: Coral proxies ; PDO ; ENSO ; EAWM ; Western Pacific
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    Silica-rich vein formation in an evolving stress field, Atlantis Bank Oceanic Core Complex (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ma, Q., Dick, H. J. B., Urann, B., & Zhou, H. Silica-rich vein formation in an evolving stress field, Atlantis Bank Oceanic Core Complex. Geochemistry Geophysics Geosystems, 21(7), (2020): e2019GC008795, doi:10.1029/2019GC008795.
    Description: Drilling 809‐m Hole U1473A in the gabbro batholith at the Atlantis Bank Oceanic Core Complex (OCC) found two felsic vein generations: late magmatic fractionates, rich in deuteric water, hosted by oxide gabbros, and anatectic veins associated with dike intrusion and introduction of seawater‐derived volatiles. Microtextures show a change from compressional to tensional stress during vein formation. Temperatures and oxidation state were obtained from amphibole‐plagioclase and oxide pairs in the adjacent gabbros. Type I veins generally have reverse shear‐sense, with restricted ΔFMQ, high Mt/Ilm ratios, and low‐amphibole Cl/F indicating deuteric fluids. They formed during percolation and fractionation of Fe‐Ti‐rich melts into the primary olivine gabbro. Type II veins are usually hosted by olivine gabbro, occur at dike contacts and the margins of normal‐sense shear zones. They are undeformed or weakly deformed, with highly variable ΔFMQ, low Mt/Ilm ratios, and high‐amphibole Cl/F, indicating seawater‐derived fluids. The detachment fault on which the gabbro massif was emplaced rooted near the base of the dike‐gabbro transition beneath the rift valley. The ingress of seawater volatiles began at 〉800°C and penetrated at least ~590 m into the lower crust during extensional faulting in the rift valley and adjacent rift mountains. The sequence of the felsic vein formation likely reflects asymmetric diapiric flow, with a reversal of the stress regime, and a transition from juvenile to seawater‐derived volatiles. This, in turn, is consistent with fault capture leading to the large asymmetries in spreading rates during OCC formations and heat flow beneath the rift mountains.
    Description: This study was supported by the Chinese National Key Basic Research Program (Grant 2012CB417300). H. Dick and B. Urann were supported by U.S. National Science Foundation (Grant OCE‐MG&G 8371300). Emmanuel Codillo provided numerous useful comments and moral support. We thank N. Chatterjee for assistance in analyzing major element mineral composition in the MIT Electron Microprobe Laboratory. The great contributions of 360 Scientific Party for their initial shipboard description and interpretations of the Hole U1473A cores made this work possible. Special thanks go to C. J. MacLeod, Expedition cochief scientist, and Peter Blum, staff scientist, Stephen Midgley, IODP operations superintendent, and Siem Offshore James Samuel McLelland, offshore installation manager, ship's master Terry Skinner, and the crew and drillers on the JOIDES Resolution.
    Keywords: Felsic veins ; Magma chambers ; Ocean ridge ; Geothermometry ; Flourine‐chlorine ; Dynamics
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  • 87
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    Exceptional 20th century ocean circulation in the Northeast Atlantic (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spooner, P. T., Thornalley, D. J. R., Oppo, D. W., Fox, A. D., Radionovskaya, S., Rose, N. L., Mallett, R., Cooper, E., & Roberts, J. M. Exceptional 20th century ocean circulation in the Northeast Atlantic. Geophysical Research Letters, 47(10), (2020): e2020GL087577, doi:10.1029/2020GL087577.
    Description: The North Atlantic subpolar gyre (SPG) connects tropical and high‐latitude waters, playing a leading role in deep‐water formation, propagation of Atlantic water into the Arctic, and as habitat for many ecosystems. Instrumental records spanning recent decades document significant decadal variability in SPG circulation, with associated hydrographic and ecological changes. Emerging longer‐term records provide circumstantial evidence that the North Atlantic also experienced centennial trends during the 20th century. Here, we use marine sediment records to show that there has been a long‐term change in SPG circulation during the industrial era, largely during the 20th century. Moreover, we show that the shift and late 20th century SPG configuration were unprecedented in the last 10,000 years. Recent SPG dynamics resulted in an expansion of subtropical ecosystems into new habitats and likely also altered the transport of heat to high latitudes.
    Description: We thank Janet Hope and UCL laboratory staff, colleagues who sailed on EN539, Kathryn Pietro‐Rose, Sean O'Keefe and Henry Abrams, Sara Chipperton, Tanya Monica, Laura Thrower and Kitty Green for sediment processing, Miles Irving for artwork assistance, James Rolfe for nitrogen isotope measurement, Maryline Vautravers and Michael Kucera for guidance, Arne Biastoch and Christian Mohn for discussion of VIKING20, and Chris Brierley, Meric Srokosz, and Jon Robson for comments. Funding was provided by National Science Foundation (NSF) grant OCE‐1304291 to D.W.O. and D.J.R.T., the Leverhulme Trust, National Environment Research Council (NERC) grant NE/S009736/1, and the ATLAS project to D.J.R.T. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement 678760 (ATLAS). This paper reflects only the authors views and the European Union cannot be held responsible for any use that may be made of the information contained herein.
    Keywords: Foraminifera ; Subpolar gyre ; North Atlantic ; Ocean circulation ; Industrial era
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  • 88
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    Equatorial circulation in the western Indian Ocean during onset of the 2018 summer monsoon and links to the Bay of Bengal (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(10), (2020): e2020GL087215, doi:10.1029/2020GL087215.
    Description: Cross‐equator transects occupied by an underwater glider and a research vessel in the western Indian Ocean captured the evolution of equatorial circulation during onset of the boreal summer monsoon in 2018. At the end of the winter monsoon in March, surface currents were westward, while the equatorial undercurrent carried salty Arabian Sea High‐Salinity Water eastward. As winds transitioned from westward to eastward during April, an eastward near‐surface Wyrtki Jet developed, while the equatorial undercurrent weakened, vanishing by May. A first‐mode baroclinic Kelvin wave propagated through the survey region after westward winds relaxed. However, the vertical structure of the evolving circulation was inconsistent with the first baroclinic mode, suggesting the influence of higher modes in setting observed vertical structure. The strong equatorial undercurrent at the end of the winter monsoon allowed high‐salinity waters from the western equatorial Indian Ocean to reach the southern Bay of Bengal in summer 2018.
    Description: This work was supported by the Office of Naval Research as part of the NASCar DRI under Grant N000141512632 and as part of the MISO‐BOB DRI under Grant N000141712968.
    Keywords: Monsoon ; Indian Ocean ; Equatorial ; Underwater glider ; Equatorial undercurrent
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  • 89
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    Observations and a model of net calcification declines in Palau's largest coral reef lagoon between 1992 and 2015 (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016147, doi:10.1029/2020JC016147.
    Description: Net ecosystem calcification (NEC) rates of Palau's largest lagoon and barrier reef system between 1992 and 2015 are estimated from sparse total alkalinity (TA) and salinity measurements and a tidal exchange model in which surface lagoon water transported offshore on the ebb tide is replaced by saltier (denser) ocean water that sinks to the bottom after entering the lagoon on the flood tide. Observed lagoon salinities are accurately reproduced by the model with no adjustable parameters. To accurately reproduce observed lagoon TA, NEC for the lagoon‐barrier reef system was 70 mmols m−2 day−1 from 1992 to 1998, 35 mmols m−2 day−1 from 1999 to 2012, and 25 mmols m−2 day−1 from 2013 to 2015. This indicates that Palau's largest lagoon and barrier reef system has not recovered, as of 2015, from the 50% decline in NEC in 1998 caused by the loss of coral cover following a severe bleaching event. The cause of the further decline in NEC in 2012–2013 is unclear. Lagoon residence times vary from 8 days during spring tides to 14 days during neap tides and drive substantial spring‐neap variations in lagoon TA (~25% of the mean salinity‐normalized ocean‐lagoon TA difference). Sparse measurements that do not resolve these spring‐neap variations can exhibit apparent long‐term variations in alkalinity that are not due to changes in NEC.
    Description: This work was partially supported by NSF award 1220529 to A.L.C., S.J.L., and K.E.F.S and NSF award 1737311 to A.L.C. and the Oceanography Department, Texas A&M University K.E.F.S.
    Description: 2021-01-06
    Keywords: Coral reef ; Calcification ; Bleaching ; Residence time ; Net ecosystem calcification ; Palau
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  • 90
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    Intercomparison of XRF core scanning results from seven labs and approaches to practical calibration (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dunlea, A. G., Murray, R. W., Tada, R., Alvarez-Zarikian, C. A., Anderson, C. H., Gilli, A., Giosan, L., Gorgas, T., Hennekam, R., Irino, T., Murayama, M., Peterson, L. C., Reichart, G., Seki, A., Zheng, H., & Ziegler, M. Intercomparison of XRF core scanning results from seven labs and approaches to practical calibration. Geochemistry Geophysics Geosystems, 21(9), (2020): e2020GC009248, doi:10.1029/2020GC009248.
    Description: X‐ray fluorescence (XRF) scanning of marine sediment has the potential to yield near‐continuous and high‐resolution records of elemental abundances, which are often interpreted as proxies for paleoceanographic processes over different time scales. However, many other variables also affect scanning XRF measurements and convolute the quantitative calibrations of element abundances and comparisons of data from different labs. Extensive interlab comparisons of XRF scanning results and calibrations are essential to resolve ambiguities and to understand the best way to interpret the data produced. For this study, we sent a set of seven marine sediment sections (1.5 m each) to be scanned by seven XRF facilities around the world to compare the outcomes amidst a myriad of factors influencing the results. Results of raw element counts per second (cps) were different between labs, but element ratios were more comparable. Four of the labs also scanned a set of homogenized sediment pellets with compositions determined by inductively coupled plasma‐optical emission spectrometry (ICP‐OES) and ICP‐mass spectrometry (MS) to convert the raw XRF element cps to concentrations in two ways: a linear calibration and a log‐ratio calibration. Although both calibration curves are well fit, the results show that the log‐ratio calibrated data are significantly more comparable between labs than the linearly calibrated data. Smaller‐scale (higher‐resolution) features are often not reproducible between the different scans and should be interpreted with caution. Along with guidance on practical calibrations, our study recommends best practices to increase the quality of information that can be derived from scanning XRF to benefit the field of paleoceanography.
    Description: Funding for this research was provided by the U.S. National Science Foundation to R. W. M. (Grant 1130531). USSSP postcruise support was provided to Expedition 346 shipboard participants A. G. D., R. W. M., L. G., C. A. Z., and L. P. Portions of this material are based upon work supported while R. W. M. was serving at the National Science Foundation.
    Keywords: XRF scanning ; Quantitative XRF ; Paleoceanography ; Sedimentary geochemistry ; XRF calibration ; XRF intercomparison
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  • 91
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    Enormous lithium isotopic variations of abyssal peridotites reveal fast cooling and Melt/Fluid-rock interactions (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(9),(2020): e2020JB020393, doi:10.1029/2020JB020393.
    Description: Fast diffusing Li isotopes provide important insights into the “recent” transient events or processes for both modern and ancient times, but questions remain concerning the large Li isotopic variations of mantle peridotites, which greatly hampers their usage as a geochemical tracer. This study investigates in situ Li content and isotopic profiles of the constituent minerals of abyssal peridotites from the Gakkel Ridge and Southwest Indian Ridge. The complicated and large variations of Li isotopic profiles in Clinopyroxene (Cpx) and Orthopyroxene (Opx) indicate Li isotopic disequilibrium at millimeter scale. The negative correlations of a wide range of Li contents (0.5 to 6.5 ppm) and δ7Li values (−10 to +20‰) of olivine, Opx and Cpx grains/relicts, trace element zoning of Cpx, the occurrence of plagioclase, olivine serpentinization along cracks, together with numerical modeling demonstrate the observed Li characteristics to be a manifestation of high‐temperature mineral‐melt Li diffusion during melt impregnation overprinted by low‐temperature mineral‐fluid Li diffusion during dissolution and serpentinization. The preservation of the Li isotopic diffusion profiles requires rapid cooling of 0.3–5°C/year after final‐stage melt impregnation at the Moho boundary, which is consistent with the low temperature at very slow spreadin g ridges caused by conductive cooling. Compared with the well‐studied melt‐rock interaction process, our study indicates that low‐temperature fluid‐rock interaction can induce Li diffusion even in the visibly unaltered mineral relicts of partially altered rocks.
    Description: This study was financially supported by the National Science Foundation of China (grant no. 41872058) and the U.S. National Science Foundation grant.
    Description: 2021-03-07
    Keywords: Li isotope ; Abyssal peridotite ; Isotope diffusion ; Melt‐rock interaction ; Fluid‐rock interaction
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  • 92
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    Ocean circulation and variability beneath Nioghalvfjerdsbrae (79 North Glacier) ice tongue (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016091, doi:10.1029/2020JC016091.
    Description: The floating ice tongue of 79 North Glacier, a major outlet glacier of the Northeast Greenland Ice Stream, has thinned by 30% since 1999. Earlier studies have indicated that long‐term warming of Atlantic Intermediate Water (AIW) is likely driving increased basal melt, causing the observed thinning. Still, limited ocean measurements in 79 North Fjord beneath the ice tongue have made it difficult to test this hypothesis. Here we use data from an Ice Tethered Mooring (ITM) deployed in a rift in the ice tongue from August 2016 to July 2017 to show that the subannual AIW temperature variability is smaller than the observed interannual variability, supporting the conclusion that AIW has warmed over the period of ice tongue thinning. In July 2017, the AIW at 500 m depth in the ice tongue cavity reached a maximum recorded temperature of 1.5°C. Velocity measurements reveal weak tides and a mean overturning circulation, which is likely seasonally enhanced by subglacial runoff discharged at the grounding line. Deep inflow of AIW and shallow export of melt‐modified water persist throughout the record, indicating year‐round basal melting of the ice tongue. Comparison with a mooring outside of the cavity suggests a rapid exchange between the cavity and continental shelf. Warming observed during 2016–2017 is estimated to drive a 33 ± 20% increase in basal melt rate near the ice tongue terminus and a 14 ± 2% increase near the grounding line if sustained.
    Description: Funding for the ITM was provided by the Grossman Family Foundation through the WHOI Development Office. M. R. L. is supported by a National Defense Science and Engineering Graduate Fellowship. N. L. B. is supported by a grant from the National Science Foundation (NSF OCE‐1536856).
    Description: 2021-02-10
    Keywords: 79 North ; Basal melt ; Fjord ; Greenland ; Ice ocean interaction ; Ice shelf
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    The air-sea response during Hurricane Irma's (2017) rapid intensification over the Amazon-Orinoco River plume as measured by atmospheric and oceanic observations (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 125(18), (2020): e2019JD032368, doi:10.1029/2019JD032368.
    Description: Hurricane Irma (2017) underwent rapid intensification (RI) while passing over the Amazon‐Orinoco River plume in the tropical Atlantic. The freshwater discharge from the plume creates a vertical salinity gradient that suppresses turbulent heat flux from the cool, ocean subsurface. The stability within the plume reduces sea surface temperature (SST) cooling and promotes energetic air‐sea fluxes. Hence, it is hypothesized that this ocean feature may have facilitated Irma's RI through favorable upper ocean conditions. This hypothesis is validated using a collection of atmospheric and oceanic observations to quantify how the ocean response influences surface flux and atmospheric boundary layer thermodynamics during Hurricane Irma's RI over the river plume. Novel aircraft‐deployed oceanic profiling floats highlight the detailed evolution of the ocean response during Irma's passage over the river plume. Analyses include quantifying the ocean response and identifying how it influenced atmospheric boundary layer temperature, moisture, and equivalent potential temperature (θE). An atmospheric boundary layer recovery analysis indicates that surface fluxes were sufficient to support the enhanced boundary layer θE (moist entropy) observed, which promotes inner‐core convection and facilitates TC intensification. The implicit influence of salinity stratification on Irma's intensity during RI is assessed using theoretical intensity frameworks. Overall, the findings suggest that the salinity stratification sustained SST during Irma's passage, which promoted energetic air‐sea fluxes that aided in boundary layer recovery and facilitated Irma's intensity during RI. Examination of the air‐sea coupling over this river plume, corresponding atmospheric boundary layer response, and feedback on TC intensity was previously absent in literature.
    Description: This research was performed while the corresponding author held an NRC Research Associateship Award at the U.S. Naval Research Lab, Monterey. Chen is supported by Office of Naval Research (ONR) grant N0001416WX00470. Sanabia is sponsored by ONR grants N0001416WX01384 and N0001416WX01262. Jayne is supported by National Oceanic and Atmospheric Administration (NOAA) grant NA13OAR4830233.The authors gratefully acknowledge the HRD scientists, NOAA AOC crews, U.S. Air Force crews, and U.S. Navy crews who were involved in the collection of both atmospheric and oceanic data. This research would not be possible without your efforts. We are thankful for helpful discussion and pre‐RI AXBT data provided by Jun Zhang (NOAA/HRD).
    Description: 2020-12-12
    Keywords: Hurricane Irma ; Air-sea interaction ; Atmospheric boundary layer ; River plume ; Tropical cyclone ; Upper ocean response
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    Understanding of contemporary regional sea-level change and the implications for the future (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Reviews of Geophysics 58(3), (2020): e2019RG000672, doi:10.1029/2019RG000672.
    Description: Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea‐level observing system, the knowledge of regional sea‐level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea‐level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea‐level change. Here we review the individual processes which lead to sea‐level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea‐level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea‐level observation network—particularly as related to satellite observations—in the improved scientific understanding of the contributors to regional sea‐level change.
    Description: The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The authors acknowledge support from the National Aeronautics and Space Administration under Grants 80NSSC17K0565, 80NSSC170567, 80NSSC17K0566, 80NSSC17K0564, and NNX17AB27G. A. A. acknowledges support under GRACE/GRACEFO Science Team Grant (NNH15ZDA001N‐GRACE). T. W. acknowledges support by the National Aeronautics and Space Administration (NASA) under the New (Early Career) Investigator Program in Earth Science (Grant: 80NSSC18K0743). C. G. P was supported by the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists at the Woods Hole Oceanographic Institution.
    Keywords: Sea level ; Satellite observations ; Remote sensing
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  • 95
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    Fate of internal waves on a shallow shelf (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC015377, doi:10.1029/2019JC015377.
    Description: Internal waves strongly influence the physical and chemical environment of coastal ecosystems worldwide. We report novel observations from a distributed temperature sensing (DTS) system that tracked the transformation of internal waves from the shelf break to the surf zone over a narrow shelf slope region in the South China Sea. The spatially continuous view of temperature fields provides a perspective of physical processes commonly available only in laboratory settings or numerical models, including internal wave reflection off a natural slope, shoreward transport of dense fluid within trapped cores, and observations of internal rundown (near‐bed, offshore‐directed jets of water preceding a breaking internal wave). Analysis shows that the fate of internal waves on this shelf—whether transmitted into shallow waters or reflected back offshore—is mediated by local water column density structure and background currents set by the previous shoaling internal waves, highlighting the importance of wave‐wave interactions in nearshore internal wave dynamics.
    Description: We are grateful for the support of the Dongsha Atoll Research Station (DARS) and the Dongsha Atoll Marine National Park, whose efforts made this research possible. The authors would also like to thank A. Hall, S. Tyler, and J. Selker from the Center for Transformative Environmental Monitoring Programs (CTEMPs) funded by the National Science Foundation (EAR awards 1440596 and 1440506), G. Lohmann from WHOI, A. Safaie from UC Irvine, G. Wong, L. Hou, F. Shiah, and K. Lee from Academia Sinica for providing logistical and field support, as well as E. Pawlak, S. Lentz, B. Sanders, and S. Grant for equipment, and B. Raubenheimer, S. Elgar, R. Walter and D. Lucas for informative discussions that improved this work. We acknowledge the US Army Research Laboratory DoD Supercomputing Resource Center for computer time on Excalibur, which was used for the numerical simulations in this work. Funding for this work supported by Academia Sinica and for K.D. and E.R. from NSF‐OCE 1753317 and for O.F., J.R., and R.A. from ONR Grant 1182789‐1‐TDZZM. A portion of this work (R.A.) was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE‐AC52‐07NA27344.
    Description: 2020-10-21
    Keywords: Internal waves ; Distributed temperature sensing ; Coral reef ; Internal wave reflection
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  • 96
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    From Andes to Amazon: assessing branched tetraether lipids as tracers for soil organic carbon in the Madre de Dios River system (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Kirkels, F. M. S. A., Ponton, C., Galy, V., West, A. J., Feakins, S. J., & Peterse, F. From Andes to Amazon: assessing branched tetraether lipids as tracers for soil organic carbon in the Madre de Dios River system. Journal of Geophysical Research-Biogeosciences, 125(1), (2020): e2019JG005270, doi:10.1029/2019JG005270.
    Description: We investigate the implications of upstream processes and hydrological seasonality on the transfer of soil organic carbon (OC) from the Andes mountains to the Amazon lowlands by the Madre de Dios River (Peru), using branched glycerol dialkyl glycerol tetraether (brGDGT) lipids. The brGDGT signal in Andean soils (0.5 to 3.5 km elevation) reflects air temperature, with a lapse rate of −6.0 °C/km elevation (r 2 = 0.89, p 〈 0.001) and −5.6 °C/km elevation (r 2 = 0.89, p 〈 0.001) for organic and mineral horizons, respectively. The same compounds are present in river suspended particulate matter (SPM) with a lapse rate of −4.1 °C/km elevation (r 2 = 0.82, p 〈 0.001) during the wet season, where the offset in intercept between the temperature lapse rates for soils and SPM indicates upstream sourcing of brGDGTs. The lapse rate for SPM appears insensitive to an increasing relative contribution of 6‐methyl isomer brGDGTs produced within the river. River depth profiles show that brGDGTs are well mixed in the river and are not affected by hydrodynamic sorting. The brGDGTs accumulate relative to OC downstream, likely due to the transition of particulate OC to the dissolved phase and input of weathered soils toward the lowlands. The temperature‐altitude correlation of brGDGTs in Madre de Dios SPM contrasts with the Lower Amazon River, where the initial soil signature is altered by changes in seasonal in‐river production and variable provenance of brGDGTs. Our study indicates that brGDGTs in the Madre de Dios River system are initially soil derived and highlights their use to study OC sourcing in mountainous river systems.
    Description: The brGDGT analyses were supported by NWO‐Veni grant 863.13.016 to F.P. This material is based upon work supported by the US National Science Foundation under grant EAR‐1227192 to A. J. W. and S. J. F. for the river fieldwork and lipid purification. In Perú, we thank the Servicio Nacional de Áreas Naturales Protegidas por el Estado (SERNANP) and personnel of Manu and Tambopata National Parks for logistical assistance and permission to work in the protected areas. We thank the Explorers' Inn and the Pontifical Catholic University of Perú (PUCP), as well as the Amazon Conservation Association for the use of the Tambopata and Wayqecha Research Stations, respectively. For river fieldwork assistance, we thank M. Torres, A. Robles, and A. Cachuana. Soil samples were contributed by Andrew Nottingham and Patrick Meir. Logistical support was provided by Y. Malhi, J. Huaman, W. Huaraca Huasco, and other collaborators as part of the Andes Biodiversity and Ecosystems Research Group ABERG (www.andesresearch.org). We thank Dominika Kasjaniuk for technical support at Utrecht. Two anonymous reviewers have provided valuable comments that have helped to improve this manuscript. Geochemical and brGDGT data are available in the PANGAEA Data Repository (Kirkels et al., 2019) and can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.906170
    Keywords: Bacterial membrane lipids (brGDGTs) ; Altitude‐temperature relations ; Amazon headwaters ; Soil‐river connectivity ; Riverine organic carbon transport, brGDGT proxy signal
    Repository Name: Woods Hole Open Access Server
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  • 97
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    How does viscosity contrast influence phase mixing and strain localization? (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125 (2020): e2020JB020323, doi: 10.1029/2020JB020323.
    Description: Ultramylonites—intensely deformed rocks with fine grain sizes and well‐mixed mineral phases—are thought to be a key component of Earth‐like plate tectonics, because coupled phase mixing and grain boundary pinning enable rocks to deform by grain‐size‐sensitive, self‐softening creep mechanisms over long geologic timescales. In isoviscous two‐phase composites, “geometric” phase mixing occurs via the sequential formation, attenuation (stretching), and disaggregation of compositional layering. However, the effects of viscosity contrast on the mechanisms and timescales for geometric mixing are poorly understood. Here, we describe a series of high‐strain torsion experiments on nonisoviscous calcite‐fluorite composites (viscosity contrast, ηca/ηfl ≈ 200) at 500°C, 0.75 GPa confining pressure, and 10−6–10−4 s−1 shear strain rate. At low to intermediate shear strains (γ ≤ 10), polycrystalline domains of the individual phases become sheared and form compositional layering. As layering develops, strain localizes into the weaker phase, fluorite. Strain partitioning impedes mixing by reducing the rate at which the stronger (calcite) layers deform, attenuate, and disaggregate. Even at very large shear strains (γ ≥ 50), grain‐scale mixing is limited, and thick compositional layers are preserved. Our experiments (1) demonstrate that viscosity contrasts impede mechanical phase mixing and (2) highlight the relative inefficiency of mechanical mixing. Nevertheless, by employing laboratory flow laws, we show that “ideal” conditions for mechanical phase mixing may be found in the wet middle to lower continental crust and in the dry mantle lithosphere, where quartz‐feldspar and olivine‐pyroxene viscosity contrasts are minimized, respectively.
    Description: This work was funded through a National Science Foundation grant (EAR‐1352306) awarded to P. S., with additional support for A. J. C. provided by the McDonnell Center for the Space Sciences (Washington University in St. Louis), the J. Lamar Worzel Assistant Scientist Fund (WHOI), and the Penzance Endowed Fund in Support of Assistant Scientists (WHOI). Partial support for electron microscopy was provided by the Institute of Materials Science and Engineering (Washington University in St. Louis).
    Description: 2021-02-04
    Keywords: Ultramylonite ; Geometric mixing ; Strain partitioning ; Shear zone ; Calcite ; Torsion
    Repository Name: Woods Hole Open Access Server
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  • 98
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    Changes in the arctic ocean carbon cycle with diminishing ice cover (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DeGrandpre, M., Evans, W., Timmermans, M., Krishfield, R., Williams, B., & Steele, M. Changes in the arctic ocean carbon cycle with diminishing ice cover. Geophysical Research Letters, 47(12), (2020): e2020GL088051, doi:10.1029/2020GL088051.
    Description: Less than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO2 measurements collected over a 6‐year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO2 levels are significantly higher during low ice years. The pCO2 increase is likely driven by ocean surface heating and uptake of atmospheric CO2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice‐free periods will further increase sea surface pCO2, reducing the Canada Basin's current role as a net sink of atmospheric CO2.
    Description: This research was made possible by grants from the NSF Arctic Observing Network program (ARC‐1107346, PLR‐1302884, PLR‐1504410, and OPP‐1723308). In addition, M. S. was supported by ONR (Grant 00014‐17‐1‐2545), NASA (Grant NNX16AK43G), and NSF (Grants PLR‐1503298 and OPP‐1751363).
    Keywords: Arctic Ocean ; Ice concentration ; Seawater CO2 ; Interannual variability ; Canada Basin ; Shipboard CO2 measurements
    Repository Name: Woods Hole Open Access Server
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  • 99
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    Using the sigma-pi diagram to analyze water masses in the northern South China Sea in spring (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(7), (2020): e2019JC015676, doi:10.1029/2019JC015676.
    Description: The temperature‐salinity (T‐S) diagram is widely used in water mass analysis, but the boundaries between water masses are vaguely distinguished by conventional T‐S‐based methods. Herein, we propose a new method based on the potential density‐potential spicity (sigma‐pi) diagram. The new method has been applied to the conductivity‐temperature‐depth data collected in the northern South China Sea during a spring cruise in 2011. The water masses in the study region are classified into 13 types according to both the standard deviation of potential spicity in each potential density layer and the water volumetric distribution in the sigma‐pi space. The results suggest that this new method is reasonable and robust for classifying water masses in the sigma‐pi space as compared to previous methods based on the traditional T‐S space. In addition, the westward intrusion of the West Pacific Ocean water to the northern South China Sea can be clearly detected by the tongue‐like potential spicity structure and relatively high potential spicity patches on potential density layers, further verifying the robustness and efficiency of our method in the water mass analysis.
    Description: This work was supported by the National Natural Science Foundation of China (91958203, 41776027, and 11732010) and the National Basic Research Program of China (2015CB954004 and 2009CB421208). Funding of Y.G.'s cotutelle doctoral research project by Région Hauts‐de‐France and Xiamen University is acknowledged. All the cruise participants are appreciated. We also thank the editor and anonymous reviewers for their valuable comments.
    Description: 2020-12-20
    Keywords: Water mass ; Spicity ; Northern South China Sea
    Repository Name: Woods Hole Open Access Server
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  • 100
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    Sea-level rise will drive divergent sediment transport patterns on fore reefs and reef flats, potentially causing erosion on Atoll Islands (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 125 (2020): e2019JF005446, doi: 10.1029/2019JF005446.
    Description: Atoll reef islands primarily consist of unconsolidated sediment, and their ocean‐facing shorelines are maintained by sediment produced and transported across their reefs. Changes in incident waves can alter cross‐shore sediment exchange and, thus, affect the sediment budget and morphology of atoll reef islands. Here we investigate the influence of sea level rise and projected wave climate change on wave characteristics and cross‐shore sediment transport across an atoll reef at Kwajalein Island, Republic of the Marshall Islands. Using a phase‐resolving model, we quantify the influence on sediment transport of quantities not well captured by wave‐averaged models, namely, wave asymmetry and skewness and flow acceleration. Model results suggest that for current reef geometry, sea level, and wave climate, potential bedload transport is directed onshore, decreases from the fore reef to the beach, and is sensitive to the influence of flow acceleration. We find that a projected 12% decrease in annual wave energy by 2100 CE has negligible influence on reef flat hydrodynamics. However, 0.5–2.0 m of sea level rise increases wave heights, skewness, and shear stress on the reef flat and decreases wave skewness and shear stress on the fore reef. These hydrodynamic changes decrease potential sediment inputs onshore from the fore reef where coral production is greatest but increase potential cross‐reef sediment transport from the outer reef flat to the beach. Assuming sediment production on the fore reef remains constant or decreases due to increasing ocean temperatures and acidification, these processes have the potential to decrease net sediment delivery to atoll islands, causing erosion.
    Description: This study was supported by the Strategic Environmental Research and Development Program through awards SERDP: RC‐2334, and RC‐2336. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    Description: 2021-03-25
    Keywords: Coral atolls ; Fringing reefs ; Sediment transport ; Wave model ; Wave climate ; Sea level rise
    Repository Name: Woods Hole Open Access Server
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