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  • Wiley  (39,427)
  • Copernicus  (5,836)
  • MDPI Publishing
  • 2020-2023  (111)
  • 2020-2022  (45,152)
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  • 1
    Publication Date: 2020-12-22
    Description: Globally, thermodynamics explains an increase in atmospheric water vapor with warming of around 7%/°C near to the surface. In contrast, global precipitation and evaporation are constrained by the Earth's energy balance to increase at ∼2-3%/°C. However, this rate of increase is suppressed by rapid atmospheric adjustments in response to greenhouse gases and absorbing aerosols that directly alter the atmospheric energy budget. Rapid adjustments to forcings, cooling effects from scattering aerosol, and observational uncertainty can explain why observed global precipitation responses are currently difficult to detect but are expected to emerge and accelerate as warming increases and aerosol forcing diminishes. Precipitation increases with warming are expected to be smaller over land than ocean due to limitations on moisture convergence, exacerbated by feedbacks and affected by rapid adjustments. Thermodynamic increases in atmospheric moisture fluxes amplify wet and dry events, driving an intensification of precipitation extremes. The rate of intensification can deviate from a simple thermodynamic response due to in-storm and larger-scale feedback processes, while changes in large-scale dynamics and catchment characteristics further modulate the frequency of flooding in response to precipitation increases. Changes in atmospheric circulation in response to radiative forcing and evolving surface temperature patterns are capable of dominating water cycle changes in some regions. Moreover, the direct impact of human activities on the water cycle through water abstraction, irrigation, and land use change is already a significant component of regional water cycle change and is expected to further increase in importance as water demand grows with global population.
    Description: Published
    Description: 49-75
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Keywords: climate change; land surface; precipitation; radiative forcing; water cycle
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2021-01-20
    Description: Multivariate analysis of the elemental composition of hemipelagic sedimentary successions has provided invaluable information about palaeoenvironmental evolution, including records of short-lived Eocene hyperthermal events. However, few studies have analyzed the sedimentary record of these climatic events in turbidite-rich continental margin successions. In order to test the usefulness of multivariate statistical techniques (factor and cluster analysis) in palaeonvironmental and palaeoclimatic research on turbiditic successions, the lowermost Eocene Solondota section, which accumulated on the North Iberian continental margin, was studied. A prominent negative carbon isotope excursion from Solondota was correlated with the Ypresian (early Eocene) hyperthermal event J, also known as C24n.2rH1. High-resolution sedimentological, geochemical (stable isotopes, major and trace elements) and mineralogical (bulk and clay mineralogy) data show that multivariate statistical analysis helps to manage large-sized quantitative datasets objectively, avoiding arbitrary choice of representative elements and identifying environmental factors (virtual variables) that may not be evident otherwise. Variations in major and minor elements from hemipelagic carbonates across the Solondota carbon isotope excursion suggest a temporarily more humid continental climate, which caused increased terrigenous material input into the marine environment. The finer grained fraction boosted hemipelagic carbonate dilution, whereas the coarser grained sediment was transported by temporarily more frequent and voluminous turbidity currents. Thus, the results from the Solondota carbon isotope excursion revealed similarities with deep marine records of other early Eocene minor hyperthermal events. This demonstrates the validity of deep-marine turbiditic successions for providing reliable sedimentological, mineralogical and geochemical records of global palaeoclimatic significance, complementing the information obtained from other sedimentary environments. Furthermore, the generally expanded nature of turbiditic successions can potentially provide palaeoclimatic information at very high resolution, enriching, and perhaps improving, the commonly condensed and sometimes discontinuous record of hemipelagic- only successions.
    Description: Published
    Description: 881-904
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
    Publication Date: 2021-05-12
    Description: We introduce a mathematical model for the composting process in biocells. The model includes several phenomena, like the aerobic biodegradation of the soluble substrate by means of a bacterial population, the hydrolysis of insoluble substrate, and the biomass decay. We investigate the best strategies to reduce substrate components in minimal time by controlling the effects of cell oxygen concentration on the degradation phenomenon. It is shown that singular controls are not optimal for this model and the optimal control time profiles are of bang or bang-bang type. The occurrence of switching curves is discussed. In the case of a bang-bang control we prove that optimal control profiles have a unique switching time and the corresponding switching curve is determined.
    Description: Published
    Description: 1251-1266
    Description: 7A. Geofisica per il monitoraggio ambientale
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
    Publication Date: 2021-06-14
    Description: Southwestern Sicily is an area of infrequent seismic activity; however, some studies carried out in the archaeological Selinunte site suggest that, between the fourth century BC and the early Middle Ages, probably at least two earthquakes strucked this area with enough energy to damage and cause the collapse and kinematics of much of the architecture of Selinunte. Take into account that, in 2008, a noninvasive archaeological prospection and traditional data gathering methods along the Acropolis north fortifications were carried out. Following these first studies, after about 10 years, a new geophysical campaign was carried out. This second campaign benefited from the application of modern technologies for the acquisition and processing of the point cloud data on the northern part of the Acropolis, like terrestrial laser scanning and unmanned aerial vehicle photogrammetry. In this paper, we present the application of these techniques and a strategy for their integration for the 3D modelling of buildings and cultural heritages. We show how the integration of data acquired independently by these two techniques is an added value able to overcome the intrinsic limits of the individual techniques. The application to Selinunte's Acropolis allowed it to highlight and measure with high accuracy fractures, dislocation, inclinations of walls, depressions of some areas and other interesting observations, which may be important starting points for future investigations.
    Description: Published
    Description: 153-165
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: 3D reconstruction ; archaeological survey ; digital elevation model ; Selinunte Archaeological Park ; terrestrial laser scanning ; unmanned aerial vehicle photogrammetry ; 05.04. Instrumentation and techniques of general interest ; 04.02. Exploration geophysics ; 05.02. Data dissemination ; 05.06. Methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
    Publication Date: 2021-01-18
    Description: This paper provides a new methodological framework to generate empirical ground shaking scenarios, designed for engineering applications and civil protection planning. The methodology is useful both to reconstruct the ground motion pattern of past events and to generate future shaking scenarios, in regions where strong-motion datasets from multiple events and multiple stations are available. The proposed methodology combines (1) an ad-hoc nonergodic ground motion model (GMM) with (2) a spatial correlation model for the source region-, site-, and path-systematic residual terms, and (3) a model of the remaining aleatory error to take into account for directivity effects. The associated variability is a function of the type of scenario generated (bedrock or site, past or future event) and it is minimal for source areas where several events have occurred and for sites where recordings are available. In order to develop the region-specific fully nonergodic GMM and to compute robust estimation of the residual terms, the approach is calibrated on a highly dense dataset compiled for the area of central Italy. Example tests demonstrate the validity of the approach, which allows to simulate acceleration response spectra at unsampled sites, as well as to capture peculiar physical features of ground motion patterns in the region. The proposed approach could be usefully adopted for data-driven simulations of ground shaking maps, as alternative or complementary tool to physic-based and stochastic-based approaches.
    Description: Published
    Description: 60-80
    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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  • 6
    Publication Date: 2021-03-03
    Description: The present work aims to study the main chemical and physical water parameters in the upper and middle Volturno river catchment (southern Italy), between the Capo Volturno springs and the confluence with the Calore river. This study makes use of morphology, geolithology, tectonic, land use, and physico‐chemical (pH, electrical conductivity, redox potential, temperature, major ions, and 222Rn) data for the identification of the main sources of surface and groundwaters in the Volturno catchment and of their evolution and mixing both in base flow and peak flow conditions. The study was also performed to assess whether the alteration due to potential anthropogenic contamination may hamper the identification of natural “primitive” sources of surface waters, especially in the populated and farmed plains far from the river headwaters. Our data suggest that water chemistry of this stretch of the Volturno river is dominated mainly by lithology and, only marginally, by the intense exogenous activities and that this trend is appreciable in both base flow and peak flow conditions. The proposed simple geochemical approach based on easy‐to‐sample matrices and on cost‐effective standard methods is a valuable tool to address catchment functionality especially in upland areas, where complex geologic and structural settings, heterogeneous groundwater flow, and logistical issues are the rule rather than the exception. Because the upper and middle Volturno catchment is comparable with numerous valleys of the Mediterranean area, this study could be a reference for analogous applications.
    Description: Published
    Description: 627–638
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
    Publication Date: 2021-03-02
    Description: El Chichon is an active volcano located in the north-western Chiapas, southern Mexico. The crater hosts a lake, a spring, named Soap Pool, emerging from the underlying volcanic aquifer and several mud pools/hot springs on the internal flanks of the crater which strongly interact with the current fumarolic system (steam-heated pools). Some of these pools, the crater lake and a cold spring emerging from the 1982 pumice deposits, have been sampled and analysed. Water–volcanic gas interactions determine the heating (43–99°C) and acidification (pH 2–4) of the springs, mainly by H2S oxidation. Significantly, in the study area, a significant NH3 partial pressure has been also detected. Such a geochemically aggressive environment enhances alteration of the rock in situ and strongly increases the mineralization of the waters (and therefore their electrical conductivity). Two different mineralization systems were detected for the crater waters: the soap pool-lake (Na+/Cl = 0.4, Na/Mg〉10) and the crater mud pools (Na+/Cl 〉 10, Na/Mg 〈 4). A deep boiling, Na+-K+-Cl -rich water reservoir generally influences the Soap Pool-lake, while the mud pool is mainly dominated by water-gas–rock interactions. In the latter case, conductivity of sampled water is directly proportional to the presence of reactive gases in solution. Therefore, chemical evolution proceeds through neutralization due to both rock alteration and bacterial oxidation of ammonium to nitrate. The chemical compositions show that El Chichon aqueous fluids, within the crater, interact with gases fed by a geothermal reservoir, without clear additions of deep magmatic fluids. This new geochemical dataset, together with previously published data, can be used as a base line with which to follow-up the activity of this deadly volcano.
    Description: Published
    Description: 331–343
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
    Publication Date: 2020-09-07
    Description: This study presents and discusses horizontal and vertical geodetic velocities for a low strain rate region of the south Alpine thrust front in northeastern Italy obtained by integrating GPS, interferometric synthetic aperture radar (InSAR) and leveling data. The area is characterized by the presence of subparallel, south-verging thrusts whose seismogenic potential is still poorly known. Horizontal GPS velocities show that this sector of the eastern Southern Alps is undergoing ∼1 mm a−1 of NW–SE shortening associated with the Adria–Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provides limited constraints on the geometry and slip rate of the several subparallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ∼ 1.5 mm a−1, across the mountain front, which can hardly be explained solely by isostatic processes. We developed an interseismic dislocation model whose geometry is constrained by available subsurface geological reconstructions and instrumental seismicity. While a fraction of the measured uplift can be attributed to glacial and erosional isostatic processes, our results suggest that interseismic strain accumulation at the Montello and the Bassano–Valdobbiadene thrusts it significantly contributing to the measured uplift. The seismogenic potential of the Montello thrust turns out to be smaller than that of the Bassano–Valdobbiadene fault, whose estimated parameters (locking depth equals 9.1 km and slip rate equals 2.1 mm a−1) indicate a structure capable of potentially generating a Mw〉6.5 earthquake. These results demonstrate the importance of precise vertical ground velocity data for modeling interseismic strain accumulation in slowly deforming regions where seismological and geomorphological evidence of active tectonics is often scarce or not conclusive.
    Description: Published
    Description: 1681–1698
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Southern Alps ; Vertical Velocities ; GPS and InSAR integration ; Interseismic Deformation ; Dislocation Model ; Seismic Potential ; 04.03. Geodesy ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
    Publication Date: 2021-02-03
    Description: Gases present in the Earth crust are important in various branches of human activities. Hydrocarbons are a significant energy resource, helium is applied in many high-tech instruments, and studies of crustal gas dynamics provide insight in the geodynamic processes and help monitor seismic and volcanic hazards. Quantitative analysis of methane and CO2 migration is important for climate change studies. Some of them are toxic (H2S, CO2, CO); radon is responsible for the major part of human radiation dose. The development of analytical techniques in gas geochemistry creates opportunities of applying this science in numerous fields. Noble gases, hydrocarbons, CO2, N2, H2, CO, and Hg vapor are measured by advanced methods in various environments and matrices including fluid inclusions. Following the “Geochemical Applications of Noble Gases”(2009), “Frontiers in Gas Geochemistry” (2013), and “Progress in the Application of Gas Geochemistry to Geothermal, Tectonic and Magmatic Studies” (2017) published as special issues of Chemical Geology and “Gas geochemistry: From conventional to unconventional domains” (2018) published as a special issue of Marine and Petroleum Geology, this volume continues the tradition of publishing papers reflecting the diversity in scope and application of gas geochemistry.
    Description: Published
    Description: 976190
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: geochemistry ; Atmosphere ; 03. Hydrosphere ; 04. Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
    Publication Date: 2021-06-07
    Description: The diagnosis of the conservation state of monumental structures from constraints to the spatial distribution of their physical properties on shallow and inner materials represents one of the key objectives in the application of non-invasive techniques. In situ, CRP and 3D ultrasonic tomography can provide an effective coverage of stone materials in space and time. The intrinsic characteristics of the materials that make up a monumental structure and affect the two properties (i.e., reflectivity, longitudinal velocity) through the above methods substantially differ. Consequently, the content of their information is mainly complementary rather than redundant. In this study we present the integrated application of different non-destructive techniques i.e., Close Range Photogrammetry (CRP), and low frequency (24 KHz) ultrasonic tomography complemented by petrographycal analysis based essentially on Optical Microscopy (OM). This integrated methodology has been applied to a Carrara marble column of the Basilica of San Saturnino, in Byzantine-Proto-Romanesque style, which is part of the Paleo Christian complex of the V-VI century. This complex also includes the adjacent Christian necropolis in the square of San Cosimo in the city of Cagliari, Sardinia, Italy. The column under study is made of bare material dating back probably to the first century A.D., it was subjected to various traumas due to disassembly and transport to the site, including damage caused by the close blast of a WWII fragmentation bomb. High resolution 3D modelling of the studied artifact was computed starting from the integration of proximal sensing techniques such as CRP based on Structure from Motion (SfM), with which information about the geometrical anomalies and reflectivity of the investigated marble column surface was obtained. On the other hand, the inner parts of the studied body were successfully inspected in a non-invasive way by computing the velocity pattern of the ultrasonic signal through the investigated materials using 3D ultrasonic tomography. This technique gives information on the elastic properties of the material related with mechanical properties and a number of factors, such as presence of fractures, voids, and flaws. Extracting information on such factors from the elastic wave velocity using 3D tomography provides a non-invasive approach to analyse the property changes of the inner material of the ancient column. The integrated application of in situ CRP and ultrasonic techniques provides a full 3D high resolution model of the investigated artifact. This model enhanced by the knowledge of the petrographic characteristics of the materials, improves the diagnostic process and affords reliable information on the state of conservation of the materials used in the construction processes of the studied monumental structure. The integrated use of the non-destructive techniques described above also provides suitable data for a possible restoration and future preservation.
    Description: Copernicus
    Description: Published
    Description: On line
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Cultural Heritage ; Monumental Structures ; Non-Destructive Testing ; Close Range Photogrammetry ; 3D Ultrasonic Tomography ; High resolution 3D modelling ; Restoration ; Conservation ; 05.04. Instrumentation and techniques of general interest
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Abstract
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  • 11
    Publication Date: 2020-05-04
    Description: We examine CMIP6 simulations of Arctic sea‐ice area and volume. We find that CMIP6 models produce a wide spread of mean Arctic sea‐ice area, capturing the observational estimate within the multi‐model ensemble spread. The CMIP6 multi‐model ensemble mean provides a more realistic estimate of the sensitivity of September Arctic sea‐ice area to a given amount of anthropogenic CO2 emissions and to a given amount of global warming, compared with earlier CMIP experiments. Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea‐ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area 〈 1 million km2) in September for the first time before the year 2050 in each of the four emission scenarios SSP1‐1.9, SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5 examined here.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 12
    Publication Date: 2020-07-07
    Description: We analyzed velocity and hydrographic data from 23 moorings in the northeast Chukchi Sea from 2011 to 2014. In most years the eastern side of Hanna Shoal was strongly stratified year-round, while weakly stratified regions prevailed on the shelf south and west of the Shoal. Stratification differences cause differential vertical mixing rates, which in conjunction with advection of different bottom water properties resulted in seasonally-varying along-isobath density gradients. In agreement with numerical models, we find that bottom waters flow anticyclonically around the Shoal. Whereas most of the shelf responded barotropically to wind-forcing, there was a strong baroclinic component to the flow field northeast of Hanna Shoal, resulting in no net vertically-integrated transport on average. In contrast there is a net eastward transport from west of the Shoal, which implies convergence north of the Shoal. Convergence and along-isobath density gradients may foster cross-shelf exchange north of Hanna Shoal. Modal analyses indicate that the shelf south of the Shoal and Barrow Canyon responded coherently to local and remote winds, whereas the wind-current response around Hanna Shoal was less coherent. Barotropic topographic waves, of ~3-day period, were generated episodically northeast of the Shoal and propagate clockwise around Hanna Shoal, but are blocked from entering Barrow Canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the Shoal. Analysis of water properties on the western side of Hanna Shoal suggests that these include contributions from the western and southern portions of the Chukchi Sea.
    Repository Name: EPIC Alfred Wegener Institut
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  • 13
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(13), ISSN: 0094-8276
    Publication Date: 2020-07-20
    Description: The response of the East Antarctic Ice Sheet to global warming represents a major source of uncertainty in sea level projections. Thinning of the East Antarctic George V and Sabrina Coast ice‐cover is currently taking place, and regional ice‐sheet instability episodes might have been triggered in past warm climates. However, the magnitude of ice retreat in the past can not yet be quantitatively derived from paleo‐proxy records alone. We propose that a runaway retreat of the George V coast grounding line and subsequent instability of the Wilkes Basin ice‐sheet would either leave a clear imprint on the water isotope composition in the Talos Dome region or prohibit a Talos Dome ice‐core record from the Last Interglacial altogether. Testing this hypothesis our ice sheet model simulations suggest, that Wilkes Basin ice‐sheet retreat remained relatively limited during the Last Interglacial and provide a constraint on Last Interglacial East Antarctic grounding line stability.
    Repository Name: EPIC Alfred Wegener Institut
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  • 14
    Publication Date: 2020-08-21
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
    Publication Date: 2020-08-10
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
    Publication Date: 2021-02-16
    Description: A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205±0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by ∼2.3°C for the combined proxy data (foraminifera Mg∕Ca and alkenones), or by ∼3.2–3.4°C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
    Publication Date: 2021-08-05
    Description: Paleoceanographic evidence commonly indicates that Last Glacial Maximum surface temperatures in the Japan Sea were comparable to modern conditions, in striking difference to colder neighboring regions. Here, based on a core from the central Japan Sea, our results show similar UK′37‐ and TEXL86‐derived temperatures between 24.7 and 16.3 ka BP, followed by an abrupt divergence at ~16.3 ka BP and a weakening of divergence after ~8.7 ka BP. We attribute this process to a highly stratified glacial upper ocean controlled by the East Asian Summer Monsoon, increasing thermal gradient between surface and subsurface layers during the deglaciation and the intrusion of Tsushima Warm Current since the mid‐Holocene, respectively. Therefore, we suggest that threshold‐like changes in upper‐ocean temperatures linked to sea level rise and monsoon dynamics, rather than just sea surface temperatures, play a critical role in shaping the thermal and ventilation history of this NW Pacific marginal sea.
    Repository Name: EPIC Alfred Wegener Institut
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  • 18
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(16), pp. e2019GL086810, ISSN: 0094-8276
    Publication Date: 2020-09-14
    Description: We simulate the two Coupled Model Intercomparison Project scenarios RCP4.5 and RCP8.5, to assess the effects of melt‐induced fresh water on the Atlantic meridional overturning circulation (AMOC). We use a newly developed climate model with high resolution at the coasts, resolving the complex ocean dynamics. Our results show an AMOC recovery in simulations run with and without an included ice sheet model. We find that the ice sheet adds a strong decadal variability on the freshwater release, resulting in intervals in which it reduces the surface runoff by high accumulation rates. This compensating effect is missing in climate models without dynamic ice sheets. Therefore, we argue to assess those freshwater hosing experiments critically, which aim to parameterize Greenland's freshwater release. We assume the increasing net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of the AMOC recovery.
    Repository Name: EPIC Alfred Wegener Institut
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  • 19
    Publication Date: 2020-09-28
    Description: Reconstructions of global hydroclimate during the Common Era (CE; the past ∼2000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ2H) isotopic compositions of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 759 isotope records from the terrestrial and marine realms, including glacier and ground ice (210); speleothems (68); corals, sclerosponges, and mollusks (143); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and nonexperts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate-model-simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model–data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at https://doi.org/10.25921/57j8-vs18 (Konecky and McKay, 2020) and is also accessible via the NOAA/WDS Paleo Data landing page: https://www.ncdc.noaa.gov/paleo/study/29593 (last access: 30 July 2020).
    Repository Name: EPIC Alfred Wegener Institut
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  • 20
    Publication Date: 2021-07-23
    Description: Originating from the boreal forest and often transported over large distances, driftwood characterises many Arctic coastlines. Here we present a combined assessment of radiocarbon (14C) and dendrochronological (ring width) age estimates of driftwood samples to constrain the progradation of two Holocene beach-ridge systems near the Lena Delta in the Siberian Arctic (Laptev Sea). Our data show that the 14C ages obtained on syndepositional driftwood from beach deposits yield surprisingly coherent chronologies for the coastal evolution of the field sites. The dendrochronological analysis of wood from modern driftlines revealed the origin and recent delivery of the wood from the Lena River catchments. This finding suggests that the duration transport lies within the uncertainty of state-of-the-art 14C dating and thus substantiates the validity of age indication obtained from driftwood. This observation will help to better understand changes in similar coastal environments, and to improve our knowledge about the response of coastal systems to past climate and sea-level changes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 21
    Publication Date: 2020-11-16
    Description: The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography of interior Greenland exist, but their accuracy is not well constrained by in situ observations. Here we present the results from a GPS mapping of surface velocity in an area located approximately 150 km from the ice divide near the East Greenland Ice-core Project (EastGRIP) deep-drilling site. A GPS strain net consisting of 63 poles was established and observed over the years 2015–2019. The strain net covers an area of 35 km by 40 km, including both shear margins. The ice flows with a uniform surface speed of approximately 55 m a^−1 within a central flow band with longitudinal and transverse strain rates on the order of 10−4 a^−1 and increasing by an order of magnitude in the shear margins. We compare the GPS results to the Arctic Digital Elevation Model and a list of satellite-derived surface velocity products in order to evaluate these products. For each velocity product, we determine the bias in and precision of the velocity compared to the GPS observations, as well as the smoothing of the velocity products needed to obtain optimal precision. The best products have a bias and a precision of ∼0.5 m a^−1. We combine the GPS results with satellite-derived products and show that organized patterns in flow and topography emerge in NEGIS when the surface velocity exceeds approximately 55 m a−1 and are related to bedrock topography.
    Repository Name: EPIC Alfred Wegener Institut
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  • 22
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    Copernicus
    In:  EPIC3Climate of the Past, Copernicus, 16(6), pp. 2275-2323, ISSN: 1814-9332
    Publication Date: 2021-07-01
    Description: We present the Alfred Wegener Institute's contribution to the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) wherein we employ the Community Earth System Models (COSMOS) that include a dynamic vegetation scheme. This work builds on our contribution to Phase 1 of the Pliocene Model Intercomparison Project (PlioMIP1) wherein we employed the same model without dynamic vegetation. Our input to the PlioMIP2 special issue of Climate of the Past is twofold. In an accompanying paper we compare results derived with COSMOS in the framework of PlioMIP2 and PlioMIP1. With this paper we present details of our contribution with COSMOS to PlioMIP2. We provide a description of the model and of methods employed to transfer reconstructed mid-Pliocene geography, as provided by the Pliocene Reconstruction and Synoptic Mapping Initiative Phase 4 (PRISM4), to model boundary conditions. We describe the spin-up procedure for creating the COSMOS PlioMIP2 simulation ensemble and present large-scale climate patterns of the COSMOS PlioMIP2 mid-Pliocene core simulation. Furthermore, we quantify the contribution of individual components of PRISM4 boundary conditions to characteristics of simulated mid-Pliocene climate and discuss implications for anthropogenic warming. When exposed to PRISM4 boundary conditions, COSMOS provides insight into a mid-Pliocene climate that is characterised by increased rainfall (+0.17 mm d−1) and elevated surface temperature (+3.37 ∘C) in comparison to the pre-industrial (PI). About two-thirds of the mid-Pliocene core temperature anomaly can be directly attributed to carbon dioxide that is elevated with respect to PI. The contribution of topography and ice sheets to mid-Pliocene warmth is much smaller in contrast – about one-quarter and one-eighth, respectively, and nonlinearities are negligible. The simulated mid-Pliocene climate comprises pronounced polar amplification, a reduced meridional temperature gradient, a northwards-shifted tropical rain belt, an Arctic Ocean that is nearly free of sea ice during boreal summer, and muted seasonality at Northern Hemisphere high latitudes. Simulated mid-Pliocene precipitation patterns are defined by both carbon dioxide and PRISM4 paleogeography. Our COSMOS simulations confirm long-standing characteristics of the mid-Pliocene Earth system, among these increased meridional volume transport in the Atlantic Ocean, an extended and intensified equatorial warm pool, and pronounced poleward expansion of vegetation cover. By means of a comparison of our results to a reconstruction of the sea surface temperature (SST) of the mid-Pliocene we find that COSMOS reproduces reconstructed SST best if exposed to a carbon dioxide concentration of 400 ppmv. In the Atlantic to Arctic Ocean the simulated mid-Pliocene core climate state is too cold in comparison to the SST reconstruction. The discord can be mitigated to some extent by increasing carbon dioxide that causes increased mismatch between the model and reconstruction in other regions.
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  • 23
    Publication Date: 2020-11-30
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  • 24
    Publication Date: 2021-05-10
    Description: In this work we describe the compilation and homogenization of an extensive dataset of aerosol iodine field observations in the period between 1963 and 2018 and we discuss the spatial and temporal dependences of total iodine in bulk aerosol by comparing the observations with CAM-Chem model imulations. Total iodine in aerosol shows a distinct latitudinal dependence, with an enhancement towards the northern hemisphere (NH) tropics and lower values towards the poles. This behavior, which has been predicted by atmospheric models to depend on the global distribution of the main ceanic iodine source (which in turn depends on the reaction of surface ozone with aqueous iodide on he sea water-air interface, generating gas-phase I2 and HOI), is confirmed here by field observations for the first time. Longitudinally, there is some indication of a wave-one profile in the Tropics, which peaks in the Atlantic and shows a minimum in the Pacific, following the wave-one longitudinal variation of tropical tropospheric ozone. New data from Antarctica show that the south polar seasonal variation of iodine in aerosol mirrors that observed previously in the Arctic, with two equinoctial maxima and the dominant maximum occurring in spring. While no clear seasonal variability is observed in NH middle latitudes, there is an indication of different seasonal cycles in the NH tropical Atlantic and Pacific. A weak positive long-term trend is observed in the tropical annual averages, which is consistent with an enhancement of the anthropogenic ozone-driven global oceanic source of iodine over the last 50 years.
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  • 25
    Publication Date: 2021-01-04
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  • 26
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48(10), pp. e2020GL090951, ISSN: 0094-8276
    Publication Date: 2021-07-01
    Description: Freshwater in the Arctic Ocean is one of the key climate components. It is not well understood how the capability of the Arctic Ocean to store freshwater will develop when freshwater supplies increase in a warming climate. By using numerical experiments, we find that this capability varies with the Arctic sea ice decline nonmonotonically, with the largest capability at intermediate strength of sea ice decline. Through enhancing the ocean surface stress, sea ice decline not only accumulates freshwater toward the Amerasian Basin but also tends to reduce the amount of freshwater in both the Eurasian and Amerasian basins by increasing the occupation of Atlantic-origin water in the upper ocean. An increase in river runoff modulates the counterbalance of the two competing effects, leading to the nonmonotonic changes of the Arctic freshwater storage capability in a warming climate.
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  • 27
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    Wiley
    In:  EPIC3Reviews of Geophysics, Wiley, 59(2), pp. e2020RG000727, ISSN: 8755-1209
    Publication Date: 2021-06-17
    Description: The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available.
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  • 28
    Publication Date: 2021-07-05
    Description: Earth system and climate modelling involves the simulation of processes on a wide range of scales and within and across various compartments of the Earth system. In practice, component models are often developed independently by different research groups, adapted by others to their special interests and then combined using a dedicated coupling software. This procedure not only leads to a strongly growing number of available versions of model components and coupled setups but also to model- and high-performance computing (HPC)-system-dependent ways of obtaining, configuring, building and operating them. Therefore, implementing these Earth system models (ESMs) can be challenging and extremely time consuming, especially for less experienced modellers or scientists aiming to use different ESMs as in the case of intercomparison projects. To assist researchers and modellers by reducing avoidable complexity, we developed the ESM-Tools software, which provides a standard way for downloading, configuring, compiling, running and monitoring different models on a variety of HPC systems. It should be noted that ESM-Tools is not a coupling software itself but a workflow and infrastructure management tool to provide access to increase usability of already existing components and coupled setups. As coupled ESMs are technically the more challenging tasks, we will focus on coupled setups, always implying that stand-alone models can benefit in the same way. With ESM-Tools, the user is only required to provide a short script consisting of only the experiment-specific definitions, while the software executes all the phases of a simulation in the correct order. The software, which is well documented and easy to install and use, currently supports four ocean models, three atmosphere models, two biogeochemistry models, an ice sheet model, an isostatic adjustment model, a hydrology model and a land-surface model. Compared to previous versions, ESM-Tools has lately been entirely recoded in a high-level programming language (Python) and provides researchers with an even more user-friendly interface for Earth system modelling. ESM-Tools was developed within the framework of the Advanced Earth System Model Capacity project, supported by the Helmholtz Association.
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  • 29
    Publication Date: 2021-07-26
    Description: Plate reconstruction studies show that the Neotethys Ocean was closing due to the convergence of Africa and Eurasia toward the end of the Cretaceous. The period around 75 Ma reflects the onset of continental collision between the two plates as convergence continued to be taken up mostly by subduction of the Neotethys slab beneath Eurasia. The Owen transform plate boundary in the northeast accommodated the fast northward motion of the Indian plate relative to the African plate. The rest of the plate was surrounded by mid-ocean ridges. Africa was experiencing continent-wide rifting related to northeast-southwest extension. We aim to quantify the forces and paleostresses that may have driven this continental extension. We use the latest plate kinematic reconstructions in a grid search to estimate horizontal gravitational stresses (HGSs), plate boundary forces, and the plate's interaction with the asthenosphere. The contribution of dynamic topography to HGSs is based on recent mantle convection studies. We model intraplate stresses and compare them with the strain observations. The fit to observations favors models where dynamic topography amplitudes are smaller than 300 m. The results also indicate that the net pull transmitted from slab to the surface African plate was low. To put this into context, we notice that available tectonic reconstructions show fragmented subduction zones and various colliding micro-continents along the northern margin of the African plate around this time. We therefore interpret a low net pull as resulting from either a small average slab length or from the micro-continents' resistance to subduction.
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  • 30
    Publication Date: 2020-09-18
    Description: We investigate hydrology during a past climate slightly warmer than the present: the Last Interglacial (LIG). With daily output of pre‐industrial and LIG simulations from eight new climate models we force hydrological model PCR‐GLOBWB, and in turn hydrodynamic model CaMa‐Flood. Compared to pre‐industrial, annual mean LIG runoff, discharge, and 100‐year flood volume are considerably larger in the Northern Hemisphere, by 14%, 25% and 82%, respectively. Anomalies are negative in the Southern Hemisphere. In some boreal regions, LIG runoff and discharge are lower despite higher precipitation, due the higher temperatures and evaporation. LIG discharge is much higher for the Niger, Congo, Nile, Ganges, Irrawaddy, Pearl, and lower for the Mississippi, Saint Lawrence, Amazon, Paraná, Orange, Zambesi, Danube, Ob. Discharge is seasonally postponed in tropical rivers affected by monsoon changes. Results agree with published proxies on the sign of discharge anomaly in 15 of 23 sites where comparison is possible.
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  • 31
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    Copernicus
    In:  EPIC3Climate of the Past, Copernicus, 16(4), pp. 1643-1665, ISSN: 1814-9332
    Publication Date: 2021-02-16
    Description: We compare results obtained from modeling the mid-Pliocene warm period using the Community Earth System Models (COSMOS, version: COSMOS-landveg r2413, 2009) with the two different modeling methodologies and sets of boundary conditions prescribed for the two phases of the Pliocene Model Intercomparison Project (PlioMIP), tagged PlioMIP1 and PlioMIP2. Here, we bridge the gap between our contributions to PlioMIP1 (Stepanek and Lohmann, 2012) and PlioMIP2 (Stepanek et al., 2020). We highlight some of the effects that differences in the chosen mid-Pliocene model setup (PlioMIP2 vs. PlioMIP1) have on the climate state as derived with COSMOS, as this information will be valuable in the framework of the model–model and model–data comparison within PlioMIP2. We evaluate the model sensitivity to improved mid-Pliocene boundary conditions using PlioMIP's core mid-Pliocene experiments for PlioMIP1 and PlioMIP2 and present further simulations in which we test model sensitivity to variations in paleogeography, orbit, and the concentration of CO2. Firstly, we highlight major changes in boundary conditions from PlioMIP1 to PlioMIP2 and also the challenges recorded from the initial effort. The results derived from our simulations show that COSMOS simulates a mid-Pliocene climate state that is 0.29°C colder in PlioMIP2 if compared to PlioMIP1 (17.82°C in PlioMIP1, 17.53°C in PlioMIP2; values based on simulated surface skin temperature). On the one hand, high-latitude warming, which is supported by proxy evidence of the mid-Pliocene, is underestimated in simulations of both PlioMIP1 and PlioMIP2. On the other hand, spatial variations in surface air temperature (SAT), sea surface temperature (SST), and the distribution of sea ice suggest improvement of simulated SAT and SST in PlioMIP2 if employing the updated paleogeography. Our PlioMIP2 mid-Pliocene simulation produces warmer SSTs in the Arctic and North Atlantic Ocean than those derived from the respective PlioMIP1 climate state. The difference in prescribed CO2 accounts for 0.5°C of temperature difference in the Arctic, leading to an ice-free summer in the PlioMIP1 simulation, and a quasi ice-free summer in PlioMIP2. Beyond the official set of PlioMIP2 simulations, we present further simulations and analyses that sample the phase space of potential alternative orbital forcings that have acted during the Pliocene and may have impacted geological records. Employing orbital forcing, which differs from that proposed for PlioMIP2 (i.e., corresponding to pre-industrial conditions) but falls into the mid-Pliocene time period targeted in PlioMIP, leads to pronounced annual and seasonal temperature variations. Our result identifies the changes in mid-Pliocene paleogeography from PRISM3 to PRISM4 as the major driver of the mid-Pliocene warmth within PlioMIP and not the minor differences in forcings.
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  • 32
    Publication Date: 2021-07-01
    Description: Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The PlioMIP2 ensemble simulates Arctic (60–90 °N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 °C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 °C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to −10.4×106 km2, with a MMM anomaly of −5.6×106 km2, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×106 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.
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  • 33
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    Copernicus
    In:  EPIC3The Cryosphere, Copernicus, 14(11), pp. 3843-3873, ISSN: 1994-0424
    Publication Date: 2020-11-11
    Description: Antarctic geothermal heat flow (GHF) affects the temperature of the ice sheet, determining its ability to slide and internally deform, as well as the behaviour of the continental crust. However, GHF remains poorly constrained, with few and sparse local, borehole-derived estimates and large discrepancies in the magnitude and distribution of existing continent-scale estimates from geophysical models. We review the methods to estimate GHF, discussing the strengths and limitations of each approach; compile borehole and probe-derived estimates from measured temperature profiles; and recommend the following future directions. (1) Obtain more borehole-derived estimates from the subglacial bedrock and englacial temperature profiles. (2) Estimate GHF from inverse glaciological modelling, constrained by evidence for basal melting and englacial temperatures (e.g. using microwave emissivity). (3) Revise geophysically derived GHF estimates using a combination of Curie depth, seismic, and thermal isostasy models. (4) Integrate in these geophysical approaches a more accurate model of the structure and distribution of heat production elements within the crust and considering heterogeneities in the underlying mantle. (5) Continue international interdisciplinary communication and data access.
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  • 34
    Publication Date: 2020-12-07
    Description: Northwestern Alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. In particular, the Baldwin and northern Seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage like many other regions at the southern margins of continuous permafrost. We used Sentinel-1 synthetic aperture radar (SAR) and Planet CubeSat optical remote sensing data to analyze recently observed widespread lake drainage. We then used synoptic weather data, climate model outputs and lake ice growth simulations to analyze potential drivers and future pathways of lake drainage in this region. Following the warmest and wettest winter on record in 2017/2018, 192 lakes were identified as having completely or partially drained by early summer 2018, which exceeded the average drainage rate by a factor of ∼ 10 and doubled the rates of the previous extreme lake drainage years of 2005 and 2006. The combination of abundant rain- and snowfall and extremely warm mean annual air temperatures (MAATs), close to 0 ∘C, may have led to the destabilization of permafrost around the lake margins. Rapid snow melt and high amounts of excess meltwater further promoted rapid lateral breaching at lake shores and consequently sudden drainage of some of the largest lakes of the study region that have likely persisted for millennia. We hypothesize that permafrost destabilization and lake drainage will accelerate and become the dominant drivers of landscape change in this region. Recent MAATs are already within the range of the predictions by the University of Alaska Fairbanks' Scenarios Network for Alaska and Arctic Planning (UAF SNAP) ensemble climate predictions in scenario RCP6.0 for 2100. With MAAT in 2019 just below 0 ∘C at the nearby Kotzebue, Alaska, climate station, permafrost aggradation in drained lake basins will become less likely after drainage, strongly decreasing the potential for freeze-locking carbon sequestered in lake sediments, signifying a prominent regime shift in ice-rich permafrost lowland regions.
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  • 35
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(22), pp. 1-11, ISSN: 0094-8276
    Publication Date: 2020-11-18
    Description: Understanding changes in Antarctic ice shelf basal melting is a major challenge for predicting future sea level. Currently, warm Circumpolar Deep Water surrounding Antarctica has limited access to the Weddell Sea continental shelf; consequently, melt rates at Filchner‐Ronne Ice Shelf are low. However, large‐scale model projections suggest that changes to the Antarctic Slope Front and the coastal circulation may enhance warm inflows within this century. We use a regional high‐resolution ice shelf cavity and ocean circulation model to explore forcing changes that may trigger this regime shift. Our results suggest two necessary conditions for supporting a sustained warm inflow into the Filchner Ice Shelf cavity: (i) an extreme relaxation of the Antarctic Slope Front density gradient and (ii) substantial freshening of the dense shelf water. We also find that the on‐shelf transport over the western Weddell Sea shelf is sensitive to the Filchner Trough overflow characteristics.
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  • 36
    Publication Date: 2021-03-11
    Description: 129I measurements on samples collected during GEOTRACES oceanographic missions in the Arctic Ocean in 2015 have provided the first detailed, synoptic 129I sections across the Eurasian, Canada and Makarov Basins. During the 1990s, increased discharges of 129I from European nuclear fuel reprocessing plants produced a large, tracer spike whose passage through the Arctic Ocean has been followed by 129I time series measurements over the past 25 years. Elevated 129I levels measured over the Lomonosov and Alpha-Mendeleyev Ridges in 2015 were associated with tracer labeled, Atlantic-origin water bathymetrically steered by the ridge systems through the central Arctic while lower 129I levels were evident in the more poorly ventilated basin interiors. 129I levels of 200-400 x 107 at/l measured in intermediate waters in 2015 had increased by a factor of 10 compared to results from the same locations in 1994-1996 owing to the circulation of the 1990s, 129I input spike mainly associated with enhanced discharges from the La Hague nuclear fuel reprocessing plant. Comparisons of the patterns of 129I distributions between the mid-1990s and 2015 delineate large scale circulation changes that occurred during the shift from a positive Arctic Oscillation and a cyclonic circulation regime in the mid-1990s to anticyclonic circulation in 2015. The latter is characterized by a broadened Beaufort Gyre in the upper ocean, a weakened boundary current and partial mid-depth, AW flow reversal in the southern Canada Basin. Tracer 129I simulations using the applied circulation model, NAOSIM agree with both historical 129I results and recent GEOTRACES data sets, thereby lending context and credibility to the interpretation of large scale changes in arctic circulation and their relationship to shifts in climate indices revealed by tracer 129I distributions. This paper reports measurements and simulation results for 129I for the 1990s and 2015, and interprets them in the context of ocean circulation responses to changing atmospheric forcing regimes.
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  • 37
    Publication Date: 2021-02-25
    Description: International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.
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  • 38
    Publication Date: 2021-04-01
    Description: Eolian mineral dust is an active agent in the global climate system. It affects planetary albedo and can influence marine biological productivity and ocean‐atmosphere carbon dynamics. This makes understanding of the global dust cycle crucial for constraining the dust/climate relationship, which requires long‐term dust emission records for all major dust sources. Despite their importance, the sources of atmospheric dust deposited in the Southern Ocean remain poorly constrained. Eolian dust in the Pacific sector of the Southern Ocean is generally assumed to originate from Australia, with minor contributions from New Zealand. Here we present a high‐resolution elemental record of terrestrial inputs for the past ∼410 kyr from marine sediment core PS75/100‐4 recovered from east of South Island, New Zealand. Sediment grain size is slightly finer than that of loess deposits from South Island, New Zealand, and is coarser than that of marine sediments in the Tasman Sea to the west of New Zealand, which indicates that the dust originated mainly from New Zealand and not only from Australia. Core PS75/100‐4 records lithogenic mass accumulation rates ranging from ∼0.01 to 0.69 g/cm2/kyr (∼0.20 g/cm2/kyr average), with variations over a factor of ∼3‐4 over glacial versus interglacial timescales for the past 410 kyr. Our geochemical data correlate well with Southern Ocean and Antarctic eolian dust records and suggest a westerly wind‐supplied dust signal from New Zealand. Our findings, therefore, suggest that New Zealand should be considered an important long‐term regional dust source in global dust cycle models.
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  • 39
    Publication Date: 2021-07-20
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  • 40
    Publication Date: 2020-07-08
    Description: The ESA Earth Explorer CryoSat-2 was launched on 8 April 2010 to monitor the precise changes in the thickness of terrestrial ice sheets and marine floating ice. To do that, CryoSat orbits the planet at an altitude of around 720 km with a retrograde orbit inclination of 92∘ and a quasi repeat cycle of 369 d (30 d subcycle). To reach the mission goals, the CryoSat products have to meet the highest quality standards to date, achieved through continual improvements of the operational processing chains. The new CryoSat Ice Baseline-D, in operation since 27 May 2019, represents a major processor upgrade with respect to the previous Ice Baseline-C. Over land ice the new Baseline-D provides better results with respect to the previous baseline when comparing the data to a reference elevation model over the Austfonna ice cap region, improving the ascending and descending crossover statistics from 1.9 to 0.1 m. The improved processing of the star tracker measurements implemented in Baseline-D has led to a reduction in the standard deviation of the point-to-point comparison with the previous star tracker processing method implemented in Baseline-C from 3.8 to 3.7 m. Over sea ice, Baseline-D improves the quality of the retrieved heights inside and at the boundaries of the synthetic aperture radar interferometric (SARIn or SIN) acquisition mask, removing the negative freeboard pattern which is beneficial not only for freeboard retrieval but also for any application that exploits the phase information from SARIn Level 1B (L1B) products. In addition, scatter comparisons with the Beaufort Gyre Exploration Project (BGEP; https://www.whoi.edu/beaufortgyre, last access: October 2019) and Operation IceBridge (OIB; Kurtz et al., 2013) in situ measurements confirm the improvements in the Baseline-D freeboard product quality. Relative to OIB, the Baseline-D freeboard mean bias is reduced by about 8 cm, which roughly corresponds to a 60 % decrease with respect to Baseline-C. The BGEP data indicate a similar tendency with a mean draft bias lowered from 0.85 to −0.14 m. For the two in situ datasets, the root mean square deviation (RMSD) is also well reduced from 14 to 11 cm for OIB and by a factor of 2 for the BGEP. Observations over inland waters show a slight increase in the percentage of good observations in Baseline-D, generally around 5 %–10 % for most lakes. This paper provides an overview of the new Level 1 and Level 2 (L2) CryoSat Ice Baseline-D evolutions and related data quality assessment, based on results obtained from analyzing the 6-month Baseline-D test dataset released to CryoSat expert users prior to the final transfer to operations.
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  • 41
    Publication Date: 2020-08-03
    Description: The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica.
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  • 42
    Publication Date: 2020-08-10
    Description: The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of water samples. GLODAPv2.2020 is an update of the previous version, GLODAPv2.2019. The major changes are: data from 106 more cruises added, extension of time coverage until 2019, and the inclusion of available discrete fugacity of CO2 (fCO2) values in the merged product files. GLODAPv2.2020 includes measurements from more than 1.2 million water samples from the global oceans collected on 946 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl4) have undergone extensive quality control, especially systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to WOCE exchange format and (ii) as a merged data product with adjustments applied to minimize bias. These adjustments were derived by comparing the data from the 106 new cruises with the data from the 840 quality-controlled cruises of the GLODAPv2.2019 data product. They correct for errors related to measurement, calibration, and data handling practices, while taking into account any known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 μmol kg−1 in dissolved inorganic carbon, 4 μmol kg−1 in total alkalinity, 0.01–0.02, depending on region, in pH, and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete fCO2 were not subjected to bias comparison or adjustments. The original data, their documentation and doi codes are available at the Ocean Carbon Data System of NOAA NCEI (https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2020/, last access: 22 June 2020). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/2c8h-sa89 (Olsen et al., 2020). The bias corrected product files also include significant ancillary and approximated data. These were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2020 methods and provides a broad overview of the secondary quality control procedures and results.
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  • 43
    Publication Date: 2020-09-14
    Description: Ice nucleating particles (INPs) affect the radiative properties of cold clouds. Knowledge concerning their concentration above ground level and their potential sources is scarce. Here we present the first highly temperature resolved ice nucleation spectra of airborne samples from an aircraft campaign during late winter in 2018. Most INP spectra featured low concentration levels (〈3 · 10−4 L−1 at −15°C). −2 −1 However, we also found INP concentrations of up to 1.8·10 L at −15°C and freezing onsets as high as −7.5°C for samples mainly from the marine boundary layer. Shape and onset temperature of the ice nucleation spectra of those samples as well as heat sensitivity hint at biogenic INP. Colocated measurements additionally indicate a local marine influence rather than long‐range transport. Our results suggest that even in late winter above 80°N a local marine source for biogenic INP, which can efficiently nucleate ice at high temperatures, is present. Clouds are a key factor in the energy budget of the Arctic atmosphere. Ice nucleating particles (INPs) can modify the radiation properties and lifetime of clouds by affecting the relative abundance of liquid and frozen droplets in a cloud. Despite this important ability, knowledge about the INP concentration above ground level is limited as airborne INP measurements are very scarce in the Arctic. Here we present results from an aircraft campaign, which took place during the late winter of 2018 in latitudes above 80°N. We found INP concentrations at above −15°C, which are similar to those found in midlatitudes. These INPs also initiate freezing already at high temperatures. We found indications that the INPs are biogenic and originate from a local, marine source, rather than being transported from midlatitudes into the Arctic. Due to the presence of numerous cracks, open leads and polynyas in the sea ice in the investigation area, the ocean may provide a source for these biogenic INP in an environment, where sources on land are still shrouded in snow and ice. However, in a warming Arctic contributions from different sources might change, making the characterization of the current state important.
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  • 44
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    Wiley
    In:  EPIC3Geochemistry, Geophysics, Geosystems, Wiley, 21, pp. #e2020GC009133
    Publication Date: 2020-11-01
    Description: A regional seismic survey on the southeastern Lomonosov Ridge and adjacent basins provides constraints on the coupled evolution of ocean circulations, depositional regime and tectonic processes. First, Mesozoic strata on the Lomonosov Ridge, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence (HARS) covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the Lomonosov Ridge and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences, and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene (20 Ma). At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Faulting on the ridge slope has led to a series of terraces where sediment drifts have accumulated since the early Miocene. It is suggested that ongoing sagging of the ridge and currents may have shaped the steep sediment free flanks of the terraces. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations.
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  • 45
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. e2020GL088795, ISSN: 0094-8276
    Publication Date: 2020-11-16
    Description: Optically active water constituents attenuate solar radiation and hence affect the vertical distribution of energy in the upper ocean. To understand their implications, we operate an ocean biogeochemical model coupled to a general circulation model with sea ice. Incorporating the effect of phytoplankton and colored dissolved organic matter (CDOM) on light attenuation in the model increases the sea surface temperature in summer and decreases sea ice concentration in the Arctic Ocean. Locally, the sea ice season is reduced by up to one month. CDOM drives a significant part of these changes, suggesting that an increase of this material will amplify the observed Arctic surface warming through its direct thermal effect. Indirectly, changing advective processes in the Nordic Seas may further intensify this effect. Our results emphasize the phytoplankton and CDOM feedbacks on the Arctic ocean and sea ice system and underline the need to consider these effects in future modeling studies to enhance their plausibility.
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  • 46
    Publication Date: 2021-03-04
    Description: Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (≈4 nmol/mol) below the 2000 to 2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry-climate model simulations, which assume emissions reductions similar to those caused by the COVID-19 crisis. COVID-19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020.
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  • 47
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    Copernicus
    In:  EPIC3Geochemical evidence of a floating Arctic ice sheet and underlying freshwater in the Arctic Mediterranean in glacial periods, EGU General Assembly 2021, Copernicus, pp. EGU21-12910
    Publication Date: 2021-05-01
    Description: Numerous studies have addressed the possible existence of large floating ice sheets in the glacial Arctic Ocean from theoretical, modelling, or seafloor morphology perspectives. Here, we add evidence from the sediment record that support the existence of such freshwater ice caps in certain intervals, and we discuss their implications for possible non-linear and rapid behaviour of such a system in the high latitudes. We present sedimentary activities of 230Th together with 234U/238U ratios, the concentrations of manganese, sulphur and calcium in the context of lithological information and records of microfossils and their isotope composition. New analyses (PS51/038, PS72/396) and a re-analysis of existing marine sediment records (PS1533, PS1235, PS2185, PS2200, amongst others) in view of the naturally occurring radionuclide 230Thex and, where available, 10Be from the Arctic Ocean and the Nordic Seas reveal the widespread occurrence of intervals with a specific geochemical signature. The pattern of these parameters in a pan-Arctic view can best be explained when assuming the repeated presence of freshwater in frozen and liquid form across large parts of the Arctic Ocean and the Nordic Seas. Based on the sedimentary evidence and known environmental constraints at the time, we develop a glacial scenario that explains how these ice sheets, together with eustatic sea-level changes, may have affected the past oceanography of the Arctic Ocean in a fundamental way that must have led to a drastic and non-linear response to external forcing. This concept offers a possibility to explain and to some extent reconcile contrasting age models for the Late Pleistocene in the Arctic Ocean. Our view, if adopted, offers a coherent dating approach across the Arctic Ocean and the Nordic Seas, linked to events outside the Arctic.
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  • 48
    Publication Date: 2021-06-30
    Description: Biogeochemical processes in subseafloor sediments are closely coupled to global element cycles. To improve the understanding of changes in biogeochemical conditions on geological timescales, we investigate sediment cores from a 1180 m deep hole in the Nankai Trough offshore Japan (Site C0023) drilled during International Ocean Discovery Program Expedition 370. During its tectonic migration from the Shikoku Basin to the Nankai Trough over the past 15 Ma, Site C0023 has experienced significant changes in depositional, thermal, and geochemical conditions. By combining pore-water, solid-phase, and rock magnetic data, we demonstrate that a transition from organic carbon-starved conditions with predominantly aerobic respiration to an elevated carbon burial environment with increased sedimentation occurred at ∼2.5 Ma. Higher rates of organic carbon burial in consequence of increased nutrient supply and productivity likely stimulated the onset of anaerobic electron-accepting processes during organic carbon degradation. A significant temperature increase by ∼50°C across the sediment column associated with trench-style sedimentation since ∼0.5 Ma could increase the bioavailability of organic matter and enhance biogenic methanogenesis. The resulting shifts in reaction fronts led to diagenetic transformation of iron (oxyhydr)oxides into pyrite in the organic carbon-starved sediments several millions of years after burial. We also show that high amounts of reducible iron(III) which can serve as electron acceptor for microbial iron(III) reduction are preserved and still available as phyllosilicate-bound Fe. This is the first study that shows the evolution of long-term variations of (bio-)geochemical processes along tectonic migration of ocean floor, thereby altering the primary sediment composition long after deposition.
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  • 49
    Publication Date: 2020-02-17
    Description: Glacial isostatic adjustment (GIA) is a major source of uncertainty for ice and ocean mass balance estimates derived from satellite gravimetry. In Antarctica the gravimetric effect of cryospheric mass change and GIA are of the same order of magnitude. Inverse estimates from geodetic observations hold some promise for mass signal separation. Here, we investigate the combination of satellite gravimetry and altimetry and demonstrate that the choice of input data sets and processing methods will influence the resultant GIA inverse estimate. This includes the combination that spans the full GRACE record (April 2002–August 2016). Additionally, we show the variations that arise from combining the actual time series of the differing data sets. Using the inferred trends, we assess the spread of GIA solutions owing to (1) the choice of different degree-1 and C20 products, (2) viable candidate surface-elevation-change products derived from different altimetry missions corresponding to different time intervals, and (3) the uncertainties associated with firn process models. Decomposing the total-mass signal into the ice mass and the GIA components is strongly dependent on properly correcting for an apparent bias in regions of small signal. Here our ab initio solutions force the mean GIA and GRACE trend over the low precipitation zone of East Antarctica to be zero. Without applying this bias correction, the overall spread of total-mass change and GIA-related mass change using differing degree-1 and C20 products is 68 and 72 Gt a−1, respectively, for the same time period (March 2003–October 2009). The bias correction method collapses this spread to 6 and 5 Gt a−1, respectively. We characterize the firn process model uncertainty empirically by analysing differences between two alternative surface mass balance products. The differences propagate to a 10 Gt a−1 spread in debiased GIA-related mass change estimates. The choice of the altimetry product poses the largest uncertainty on debiased mass change estimates. The spread of debiased GIA-related mass change amounts to 15 Gt a−1 for the period from March 2003 to October 2009. We found a spread of 49 Gt a−1 comparing results for the periods April 2002–August 2016 and July 2010–August 2016. Our findings point out limitations associated with data quality, data processing, and correction for apparent biases.
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  • 50
    Publication Date: 2020-09-06
    Description: Antarctica's ice shelves play a key role in stabilizing the ice streams that feed them. Since basal melting largely depends on ice‐ocean interactions, it is vital to attain consistent bathymetry models to estimate water and heat exchange beneath ice shelves. We have constructed bathymetry models beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data, and incorporating seismic, multibeam and radar depth references. Our models reveal deep glacial troughs beneath the ice shelves and terminal moraines close to the continental shelf breaks, which currently limit the entry of Warm Deep Water from the Southern Ocean. The ice shelves buttress a catchment that comprises an ice volume equivalent to nearly 1 meter of eustatic sea level rise, partly susceptible to ocean forcing. Changes in water temperature and thermocline depth may accelerate marine based ice sheet drainage and constitute an underestimated contribution to future global sea level rise.
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  • 51
    Publication Date: 2020-06-02
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  • 52
    Publication Date: 2020-07-06
    Description: Climate simulations for the North Atlantic and Europe for recent and future conditions simulated with the regionally coupled ROM model are analyzed and compared to the results from the MPI‐ESM. The ROM simulations also include a biogeochemistry and ocean tides. For recent climate conditions, ROM generally improves the simulations compared to the driving model MPI‐ESM. Reduced oceanic biases in the Northern Atlantic are found, as well as a better simulation of the atmospheric circulation, notably storm tracks and blocking. Regarding future climate projections for the 21st century following the RCP 4.5 and 8.5 scenarios, MPI‐ESM and ROM largely agree qualitatively on the climate change signal over Europe. However, many important differences are identified. For example, ROM shows an SST cooling in the Subpolar Gyre which is not present in MPI‐ESM. Under the RCP8.5 scenario, ROM Arctic sea ice cover is thinner and reaches the seasonally ice‐free state by 2055, well before MPI‐ESM. This shows the decisive importance of higher ocean resolution and regional coupling for determining the regional responses to global warming trends. Regarding biogeochemistry, both ROM and MPI‐ESM simulate a widespread decline in winter nutrient concentration in the North Atlantic of up to ~35%. On the other hand, the phytoplankton spring bloom in the Arctic and in the North‐Western Atlantic starts earlier and the yearly primary production is enhanced in the Arctic in the late 21st century. These results clearly demonstrate the added value of ROM to determine more detailed and more reliable climate projections at the regional scale.
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  • 53
    Publication Date: 2020-07-28
    Description: Simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size. This study employs an unstructured‐mesh ocean‐sea ice model to conduct a decadal‐scale global simulation with a 1‐km Arctic. It provides a basinwide overview of Arctic eddy energetics. Increasing model resolution from 4 to 1 km increases Arctic eddy kinetic energy (EKE) and total kinetic energy (TKE) by about 40% and 15%, respectively. EKE is the highest along main currents over topography slopes, where strong conversion from available potential energy to EKE takes place. It is high in halocline with a maximum typically centered in the depth range of 70–110 m, and in the Atlantic Water layer of the Eurasian Basin as well. The seasonal variability of EKE along the continental slopes of southern Canada and eastern Eurasian basins is similar, stronger in fall and weaker in spring.
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  • 54
    Publication Date: 2021-03-25
    Description: Landfast sea ice (fast ice) attached to Antarctic (near-)coastal elements is a critical component of the local physical and ecological systems. Through its direct coupling with the atmosphere and ocean, fast-ice properties are also a potential indicator of processes related to a changing climate. However, in situ fast-ice observations in Antarctica are extremely sparse because of logistical challenges and harsh environmental conditions. Since 2010, a monitoring program observing the seasonal evolution of fast ice in Atka Bay has been conducted as part of the Antarctic Fast Ice Network (AFIN). The bay is located on the northeastern edge of Ekström Ice Shelf in the eastern Weddell Sea, close to the German wintering station Neumayer III. A number of sampling sites have been regularly revisited each year between annual ice formation and breakup to obtain a continuous record of sea-ice and sub-ice platelet-layer thickness, as well as snow depth and freeboard across the bay. Here, we present the time series of these measurements over the last 9 years. Combining them with observations from the nearby Neumayer III meteorological observatory as well as auxiliary satellite images enables us to relate the seasonal and interannual fast-ice cycle to the factors that influence their evolution. On average, the annual consolidated fast-ice thickness at the end of the growth season is about 2 m, with a loose platelet layer of 4 m thickness beneath and 0.70 m thick snow on top. Results highlight the predominately seasonal character of the fast-ice regime in Atka Bay without a significant interannual trend in any of the observed variables over the 9-year observation period. Also, no changes are evident when comparing with sporadic measurements in the 1980s and 1990s. It is shown that strong easterly winds in the area govern the year-round snow distribution and also trigger the breakup of fast ice in the bay during summer months. Due to the substantial snow accumulation on the fast ice, a characteristic feature is frequent negative freeboard, associated flooding of the snow–ice interface, and a likely subsequent snow ice formation. The buoyant platelet layer beneath negates the snow weight to some extent, but snow thermodynamics is identified as the main driver of the energy and mass budgets for the fast-ice cover in Atka Bay. The new knowledge of the seasonal and interannual variability of fast-ice properties from the present study helps to improve our understanding of interactions between atmosphere, fast ice, ocean, and ice shelves in one of the key regions of Antarctica and calls for intensified multidisciplinary studies in this region.
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  • 55
    Publication Date: 2020-11-23
    Description: Responses of marine primary production to a changing climate are determined by a concert of multiple environmental changes, for example in temperature, light, pCO2, nutrients, and grazing. To make robust projections of future global marine primary production, it is crucial to understand multiple driver effects on phytoplankton. This meta-analysis quantifies individual and interactive effects of dual driver combinations on marine phytoplankton growth rates. Almost 50% of the single-species laboratory studies were excluded because central data and metadata (growth rates, carbonate system, experimental treatments) were insufficiently reported. The remaining data (42 studies) allowed for the analysis of interactions of pCO2 with temperature, light, and nutrients, respectively. Growth rates mostly respond non-additively, whereby the interaction with increased pCO2 profusely dampens growth-enhancing effects of high temperature and high light. Multiple and single driver effects on coccolithophores differ from other phytoplankton groups, especially in their high sensitivity to increasing pCO2. Polar species decrease their growth rate in response to high pCO2, while temperate and tropical species benefit under these conditions. Based on the observed interactions and projected changes, we anticipate primary productivity to: (a) first increase but eventually decrease in the Arctic Ocean once nutrient limitation outweighs the benefits of higher light availability; (b) decrease in the tropics and mid-latitudes due to intensifying nutrient limitation, possibly amplified by elevated pCO2; and (c) increase in the Southern Ocean in view of higher nutrient availability and synergistic interaction with increasing pCO2. Growth-enhancing effect of high light and warming to coccolithophores, mainly Emiliania huxleyi, might increase their relative abundance as long as not offset by acidification. Dinoflagellates are expected to increase their relative abundance due to their positive growth response to increasing pCO2 and light levels. Our analysis reveals gaps in the knowledge on multiple driver responses and provides recommendations for future work on phytoplankton.
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  • 56
    Publication Date: 2021-07-01
    Description: The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ∼400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.7 and 5.2 °C relative to the pre-industrial era with a multi-model mean value of 3.2 °C. Annual mean total precipitation rates increase by 7 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases by 4.3 °C over land and 2.8 °C over the oceans. There is a clear pattern of polar amplification with warming polewards of 60°N and 60°S exceeding the global mean warming by a factor of 2.3. In the Atlantic and Pacific oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. There is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO2 (including ice sheet feedbacks) is 67 % greater than ECS; this is larger than the increase of 47 % obtained from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea surface temperatures are used to assess model estimates of ECS and give an ECS range of 2.6–4.8°C. This result is in general accord with the ECS range presented by previous Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.
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  • 57
    Publication Date: 2021-01-28
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  • 58
    Publication Date: 2021-06-16
    Description: In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.
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  • 59
    Publication Date: 2021-07-01
    Description: The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to the Coupled Model Intercomparison Project (CMIP6) is the Tier 1 Last Interglacial experiment for 127 000 years ago (lig127k), designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models as for the future and following a common experimental protocol. Here we present a first analysis of a multi-model ensemble of 17 climate models, all of which have completed the CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. The equilibrium climate sensitivity (ECS) of these models varies from 1.8 to 5.6 ∘C. The seasonal character of the insolation anomalies results in strong summer warming over the Northern Hemisphere continents in the lig127k ensemble as compared to the CMIP6 piControl and much-reduced minimum sea ice in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than the CMIP6 midHolocene simulations as expected from the larger insolation anomalies at 127 than 6 ka. New synthesis for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and for precipitation over the Northern Hemisphere continents. The model–data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions. The CMIP6–Paleoclimate Modeling Intercomparison Project (PMIP4) lig127k simulations, in combination with the proxy record, improve our confidence in future projections of monsoons, surface temperature, and Arctic sea ice, thus providing a key target for model evaluation and optimization.
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  • 60
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48, pp. e2021GL092826, ISSN: 0094-8276
    Publication Date: 2021-06-14
    Description: Year-round records of the ionic composition of Antarctic aerosol were obtained at the inland Dome C (DC) and coastal Neumayer (NM) sites, with additional observations of black carbon at NM. Discussions focus on the origin of ammonium in Antarctica. This first Antarctic atmospheric study of several species emitted by biomass burning indicates that black carbon, oxalate, and fine potassium reach a maximum in October in relation to biomass burning activity in the southern hemisphere. Ammonium reaches a maximum two months later, suggesting that biomass burning remains a minor ammonium source there. The ammonium maximum in December coincides with the occurrence of diatom blooms in the austral ocean, suggesting that oceanic ammonia emissions are the main source of ammonium in Antarctica. The ammonium to sulfur-derived biogenic species molar ratio of 0.15 in summer suggests far lower ammonia emissions from the Antarctic oceans than mid-latitude southern oceans.
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  • 61
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 126, ISSN: 0148-0227
    Publication Date: 2021-06-25
    Description: Saharan dust is transported in great quantities from the North African continent every year, most of which is deposited across the North Atlantic Ocean. This dust impacts regional and global climate by affecting the atmospheric radiation balance and altering ocean carbon budgets. However, little research has been carried out on time series of Saharan dust collected in situ across the open Atlantic. Here, we present a unique three-year time series of Saharan dust along a trans-Atlantic transect, sampled by moored surface buoys and subsurface sediment traps. Results show a good correlation between the particle-size distributions of atmospheric dust and the lithogenic particles settling to the deep ocean floor, confirming the aeolian origin of the lithogenic particles intercepted by the subsurface sediment traps, even in the distal western part of the Atlantic Ocean. Dust from both dry and wet deposition as collected by the sediment traps, shows increased deposition fluxes and coarser grain size in summer and/or autumn that coincides with increased precipitation at the sampling sites as derived from satellite data. In contrast, both buoys that sampled dust during transport at sea level show little seasonal variation in both concentration and particle size, as the large amounts of dust transported in summer and early autumn at high altitudes are far above their sampling range. This implies that wet deposition in summer and autumn defines the typical seasonal trends of both the dust deposition flux and its particle-size distribution observed in the sediment traps.
    Repository Name: EPIC Alfred Wegener Institut
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  • 62
    Publication Date: 2020-03-06
    Description: PuffinPlot is a program for paleomagnetic data analysis and plotting, first released in 2012 and under continuous development since then. It is free, cross‐platform software and provides both a graphical desktop interface for interactive use and an application‐programmer interface for scripting. We present a major new release of the program, describe significant new features added since the first release, and demonstrate their application to real‐world data. New features include automatic magnetic declination realignment, relative paleointensity calculation, virtual geomagnetic pole determination, calculation of inclination‐only statistics, support for reproducible research via the export of self‐contained data bundles, and support for reading a number of popular paleomagnetic file formats. We also discuss the application of unit tests in ensuring PuffinPlot's long‐term reliability and outline directions for future development of the software.
    Description: Published
    Description: 5578-5587
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 63
    Publication Date: 2020-05-25
    Description: We explore the three‐dimensional structure of the 2016–2017 Central Italy sequence using ~34,000 ML ≥ 1.5 earthquakes that occurred between August 2016 and January 2018. We applied cross‐correlation and double‐difference location methods to waveform and parametric data routinely produced at the Italian National Institute of Geophysics and Volcanology. The sequence activated an 80 km long system of normal faults and near‐horizontal detachment faults through the MW 6.0 Amatrice, the MW 5.9 Visso, and the MW 6.5 Norcia mainshocks and aftershocks. The system has an average strike of N155°E and dips 38°–55° southwestward and is segmented into 15–30 km long faults individually activated by the cascade of MW ≥ 5.0 shocks. The two main normal fault segments, Mt. Vettore‐Mt. Bove to the North and Mt. della Laga to the South, are separated by an NNE‐SSW‐trending lateral ramp of the Sibillini thrust, a regional structure inherited from the previous compressional tectonic phase putting into contact diverse lithologies with different seismicity patterns. Space‐time reconstruction of the fault system supports a composite rupture scenario previously proposed for the MW 6.5 Norcia earthquake, where the rupture possibly propagated also along an oblique portion of the Sibillini thrust. This dissected set of normal fault segments is bounded at 8–10 km depth by a continuous 2 km thick seismicity layer of extensional nature slightly dipping eastward and interpreted as a shear zone. All three mainshocks in the sequence nucleated along the high‐angle planes at significant distance from the shear zone, thus complicating the interpretation of the mechanisms driving strain partitioning between these structures.
    Description: Published
    Description: e2019JB018440
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Keywords: normal fault ; shear zone ; fault segmentation ; apennines ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 64
    Publication Date: 2020-07-08
    Description: The response of continental forelands to subduction and collision is a widely investigated topic in geodynamics. The deformation occurring within a foreland shared by two opposite‐verging chains, however, is uncommon and poorly understood. The Apulia Swell in the southern end of the Adria microplate (Africa‐Europe plate boundary, central Mediterranean Sea) represents one of these cases, as it is the common foreland of the SW verging Albanides‐Hellenides and the NE verging Southern Apennines merging into the SSE verging Calabrian Arc. We investigated the internal deformation of the Apulia Swell using multiscale geophysical data: multichannel seismic profiles recording up to 12‐s two‐way time (TWT) for a consistent image of the upper crust; high‐resolution multichannel seismic profiles, high‐resolution multibeam bathymetry, and CHIRP profiles acquired by R/V OGS Explora to constrain the Quaternary geological record. The results of our analyses characterize the geometry of the South Apulia Fault System (SAFS), a 100‐km‐long and 12‐km‐wide structure attesting an extensional (and possibly transtensional) response of the foreland to the two contractional fronts. The SAFS consists of two NW‐SE right‐stepping master faults and several secondary structures. The SAFS activity spans from the Early Pleistocene through the Holocene, as testified by the bathymetric and high‐resolution seismic data, with long‐term slip rates in the range of 0.2–0.4 mm/yr. Considering the position within an area with few or none other active faults in the surroundings, the dimension, and the activity rates, the SAFS can be a candidate causative fault of the 20 February 1743, M 6.7, earthquake.
    Description: Italian Ministry for Education, University, and Research (MIUR), Premiale 2014 D. M. 291 03/05/2016.
    Description: Published
    Description: e2020TC006116
    Description: 2T. Deformazione crostale attiva
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: JCR Journal
    Keywords: active tectonics ; apulia ; south apulia fault system ; 1743 earthquake ; marine geology ; stable continental region ; ionian sea ; active faults ; subsurface geology ; seismic interpretation ; 04.04. Geology ; 04.07. Tectonophysics ; 04.02. Exploration geophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 65
    Publication Date: 2020-01-23
    Description: The Campi Flegrei caldera is a large volcanic complex lying in the Campanian Plain, Southern Italy. During its history the caldera experienced episodes of bradyseism and intense swarm seismicity. The mechanism leading to unrest episodes is still debated, and great efforts are ongoing to improve the knowledge of this structure and its evolution due to the high volcanic risk in such a densely populated area. Here we present a resistivity model from a two‐dimensional inversion of audiomagnetotelluric data acquired along an approximately 5.6‐km long profile crosscutting the Solfatara‐Pisciarelli district and the Agnano plain. The resistivity model shows (1) very low resistivity values confined in the first 500 m of depth both in correspondence of the Solfatara‐Pisciarelli districts and the Agnano depression; (2) a resistive plume that extends underneath the Solfatara crater down to 2,000‐ to 3,000‐m depth, and (3) an adjoining relative conductive unit eastward. We discuss the resistivity structures in a multidisciplinary framework integrating inedited geochemical and seismological observations with existing surface geology and subsurface information. The Solfatara‐Pisciarelli district and the Agnano plain, both being expression of intense hydrothermal activity, show different characteristics. Below the Solfatara‐Pisciarelli area, the shallow conductive zone is interpreted as a faulted clay cap that overlies a highly active vapor‐dominated reservoir characterized by a convective mechanism. Conversely, below the Agnano plain, a liquid phase seems to prevail in the reservoir. The spatiotemporal variations of seismicity imply a combined action of preexisting tectonic lineaments and fluid interaction between the gas/steam reservoir and the outflow zone.
    Description: Published
    Description: 5336-5356
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 66
    Publication Date: 2020-01-23
    Description: Within a general volcanic unrest in the densely urbanized area of Campi Flegrei caldera (Italy) an increase in the activity of Pisciarelli hydrothermal area is occurring. The seismic amplitude of Pisciarelli fumarolic tremor is a proxy for the fluid emission rate of the entire Solfatara‐Pisciarelli hydrothermal system. The long‐term analysis indicates a significant increase, by a factor of ~3 of the fumarolic tremor amplitude since May 2017. This increment matches with the trend of geochemical and seismic parameters observed in Campi Flegrei, therefore highlighting that Pisciarelli is a key site to monitor the volcanic unrest underway in this high‐risk caldera. The analysis of data from three closely spaced seismic stations provided new clues about the source mechanism of the tremor. Analyzing the fumarolic tremor amplitude we could also identify an episode of enlargement of the emission area close to the main fumarole of Pisciarelli. We propose a monitoring system based on the fumarolic tremor analysis, which provides real‐time information on the Pisciarelli hydrothermal activity and therefore on the current unrest in Campi Flegrei caldera.
    Description: Published
    Description: 5544-5555
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 67
    Publication Date: 2020-02-10
    Description: Smectite clays occur in subduction zone fault cores at shallow depth (approximately 1 km; e.g., Japan Trench) and landslide décollements (e.g., Vajont, Italy, 1963). The availability of pore fluids affects the likelihood that seismic slip propagates from deeper to shallow fault depths or that a landslide accelerates to its final collapse. To investigate the deformation processes active during seismic faulting we performed friction experiments with a rotary machine on 2‐mm‐thick smectite‐rich gouge layers (70/30 wt % Ca‐montmorillonite/opal) sheared at 5‐MPa normal stress, at slip rates of 0.001, 0.01, 0.1, and 1.3 m/s, and total displacement of 3 m. Experiments were performed on predried gouges under vacuum, under room humidity and under partly saturated conditions. The fault shear strength measured in the experiments was included in a one‐dimensional numerical model incorporating frictional heating, thermal, and thermochemical pressurization. Quantitative X‐ray powder diffraction and scanning electron microscopy investigations were performed on pristine and deformed smectite‐rich gouges. Under dry conditions, cataclasis and amorphization dominated at slip rates of 0.001–0.1 m/s, whereas grain size sensitive flow and, under vacuum, frictional melting occurred at fast slip rates (1.3 m/s). Under partly saturated conditions, frictional slip in a smectite foliation occurred in combination with pressurization of water by shear‐enhanced compaction and, for V = 0.01–1.3 m/s, with thermal pressurization. Pseudotachylytes, the only reliable microstructural markers for seismic slip, formed only with large frictional power (〉2 MW/m2), which could be achieved at shallow depth with high slip rates, or, at depth, with high shear stress in dehydrated smectites.
    Description: Published
    Description: 10855-10876
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 68
    Publication Date: 2021-07-19
    Description: The Southern Ocean is a key player in the climate, ocean and atmospheric system. As the only direct connection between all three major oceans since the opening of the Southern Ocean gateways, the development of the Southern Ocean and its relationship with the Antarctic cryosphere has influenced the climate of the entire planet. Although the depths of the ocean floor have been recognized as an important factor in climate and paleoclimate models, appropriate paleobathymetric models including a detailed analysis of the sediment cover are not available. Here, we utilize more than 40 years of seismic reflection data acquisition along the margins of Antarctica and its conjugate margins, along with multiple drilling campaigns by the International Ocean Discovery Program (IODP) and its predecessor programs. We combine and update the seismic stratigraphy across the regions of the Southern Ocean and calculate ocean-wide paleobathymetry grids via a backstripping method. We present a suite of high-resolution paleobathymetric grids from the Eocene-Oligocene Boundary to modern times. The grids reveal the development of the Southern Ocean from isolated basins to an interconnected ocean affected by the onset and vigor of an Antarctic Circumpolar Current, as well as the glacial sedimentation and erosion of the Antarctic continent. The ocean-wide comparison through time exposes patterns of ice sheet development such as switching of glacial outlets and the change from wet-based to dry-based ice sheets. Ocean currents and bottom-water production interact with the sedimentation along the continental shelf and slope and profit from the opening of the ocean gateways.
    Repository Name: EPIC Alfred Wegener Institut
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  • 69
    Publication Date: 2022-04-19
    Description: The late Pleistocene Yedoma Ice Complex is an ice-rich and organic-bearing type of permafrost deposit widely distributed across Beringia and is assumed to be especially prone to deep degradation with warming temperature, which is a potential tipping point of the climate system. To better understand Yedoma formation, its local characteristics, and its regional sedimentological composition, we compiled the grain-size distributions (GSDs) of 771 samples from 23 Yedoma locations across the Arctic; samples from sites located close together were pooled to form 17 study sites. In addition, we studied 160 samples from three non-Yedoma ice-wedge polygon and floodplain sites for the comparison of Yedoma samples with Holocene depositional environments. The multimodal GSDs indicate that a variety of sediment production, transport, and depositional processes were involved in Yedoma formation. To disentangle these processes, a robust endmember modeling analysis (rEMMA) was performed. Nine robust grain-size endmembers (rEMs) characterize Yedoma deposits across Beringia. The study sites of Yedoma deposits were finally classified using cluster analysis. The resulting four clusters consisted of two to five sites that are distributed randomly across northeastern Siberia and Alaska, suggesting that the differences are associated with rather local conditions. In contrast to prior studies suggesting a largely aeolian contribution to Yedoma sedimentation, the wide range of rEMs indicates that aeolian sedimentation processes cannot explain the entire variability found in GSDs of Yedoma deposits. Instead, Yedoma sedimentation is controlled by local conditions such as source rocks and weathering processes, nearby paleotopography, and diverse sediment transport processes. Our findings support the hypothesis of a polygenetic Yedoma origin involving alluvial, fluvial, and niveo-aeolian transport; accumulation in ponding waters; and in situ frost weathering as well as postdepositional processes of solifluction, cryoturbation, and pedogenesis. The characteristic rEM composition of the Yedoma clusters will help to improve how grain-size-dependent parameters in permafrost models and soil carbon budgets are considered. Our results show the characteristic properties of ice-rich Yedoma deposits in the terrestrial Arctic. Characterizing and quantifying site-specific past depositional processes is crucial for elucidating and understanding the trajectories of this unique kind of ice-rich permafrost in a warmer future.
    Repository Name: EPIC Alfred Wegener Institut
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  • 70
    Publication Date: 2022-03-11
    Description: As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons and, eventually, integrates them into subsea permafrost. Lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions. In this research, borehole data, electrical resistivity surveying, and modelling of heat and salt diffusion were carried out at Polar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated water body connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover. The boreholes in the centre of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik, a thin ice‐bearing permafrost layer, and unfrozen ground. The bathymetry showed that most of the lagoon was ice‐grounded in spring. In bedfast ice areas, the electrical resistivity profiles suggest that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modelling suggests thermokarst lake taliks refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0 °C. This occurs, because the top‐down chemical degradation of newly formed ice‐bearing permafrost is slower than the cooling of the talik. Hence, lagoons may pre‐condition taliks with a layer of ice‐bearing permafrost before encroachment by the sea and this frozen layer may act as a cap on gas migration out of the underlying talik.
    Repository Name: EPIC Alfred Wegener Institut
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  • 71
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 127(3), pp. 1-18, ISSN: 0148-0227
    Publication Date: 2022-02-28
    Description: Fram Strait in the northern North Atlantic is a key region for marine cold air outbreaks (MCAOs), southward discharges of polar air under northerly air flow, which have a strong impact on air-sea heat fluxes, boundary layer processes and severe weather. This study investigates climatologies and decadal trends of Fram Strait MCAOs of different intensity classes based on the ERA5 reanalysis product for 1979–2020. Among striking interannual variability, it is shown that the main MCAO season is December through March, when MCAOs occur around 2/3 of the time. We report on significant decadal MCAO decreases in December and January, and a significant increase in March. While the mid-winter decrease is mainly related to the different paces of warming between the surface and the lower atmosphere, the increase in March can be related to changes in synoptic circulation patterns. As an explanation for the latter, a possible feedback between retreating Barents Sea sea ice, enhanced cyclonic activity and Fram Strait MCAOs is postulated. Exemplifying the trend toward stronger MCAOs during March, the study details the recordbreaking MCAO season in early 2020, and an observational case study of an extreme MCAO event in March 2020 is conducted. Thereby, radiosonde observations are combined with kinematic air back-trajectories to provide rare observational evidence for the diabatic cooling and drying during the MCAO preconditioning phase.
    Repository Name: EPIC Alfred Wegener Institut
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  • 72
    Publication Date: 2022-03-07
    Description: Fjords are recognized as hotspots of organic carbon (OC) burial in the coastal ocean. In fjords with glaciated catchments, glacier discharge carries large amounts of suspended matter. This sedimentary load includes OC from bedrock and terrigenous sources (modern vegetation, peat, soil deposits), which is either buried in the fjord or remineralized during export, acting as a potential source of CO2 to the atmosphere. In sub-Antarctic South Georgia, fjord-terminating glaciers have been retreating during the past decades, likely as a response to changing climate conditions. We determine sources of OC in surface sediments of Cumberland Bay, South Georgia, using lipid biomarkers and the bulk 14C isotopic composition, and quantify OC burial at present and for the time period of documented glacier retreat (between 1958 and 2017). Petrogenic OC is the dominant type of OC in proximity to the present-day calving fronts (60.4 ± 1.4% to 73.8 ± 2.6%) and decreases to 14.0 ± 2.7% outside the fjord, indicating that petrogenic OC is effectively buried in the fjord. Beside of marine OC, terrigenous OC comprises 2.7 ± 0.5% to 7.9 ± 5.9% and is mostly derived from modern plants and Holocene peat and soil deposits that are eroded along the flanks of the fjord, rather than released by the retreating fjord glaciers. We estimate that the retreat of tidewater glaciers between 1958 and 2017 led to an increase in petrogenic carbon accumulation of 22% in Cumberland West Bay and 6.5% in Cumberland East Bay, suggesting that successive glacier retreat does not only release petrogenic OC into the fjord, but also increases the capacity of OC burial.
    Repository Name: EPIC Alfred Wegener Institut
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  • 73
    Publication Date: 2022-04-24
    Description: Hillaire‐Marcelet al. bring forward several physical and geochemical arguments against our finding of an Arctic glaciolacustrine system in the past. In brief, we find that a physical approach to further test our hypothesis should additionally consider the actual bathymetry of the Greenland–Scotland Ridge (GSR), the density maximum of freshwater at 3–4°C, the sensible heat flux from rivers, and the actual volumes that are being mixed and advected. Their geochemical considerations acknowledge our original argument, but they also add a number of assumptions that are neither required to explain the observations, nor do they correspond to the lithology of the sediments. Rather than being additive in nature, their arguments of high particle flux, low particle flux, export of 230Th and accumulation of 230Th, are mutually exclusive. We first address the arguments above, before commenting on some misunderstandings of our original claim in their contribution, especially regarding our dating approach.
    Repository Name: EPIC Alfred Wegener Institut
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  • 74
    Publication Date: 2022-04-22
    Description: Integrated electron microprobe analyses (EMPAs) on glass and Sr–Nd isotope analyses have been performed on 17 tephras from the Middle Pleistocene Mercure lacustrine succession, southern Apennines. Two 40Ar/39Ar ages and the recognition of four relevant tephras from Colli Albani, Sabatini and possibly Roccamonfina volcanoes allowed us to ascribe the investigated succession to the late Marine Isotope Stage (MIS) 15–12 interval (560–440 ka). The Sr–Nd isotopes and major element glass compositions allowed us to attribute 10 out of the other 13 tephras to a poorly known activity of the Roccamofina volcano, whereas two layers were tentatively attributed to previously unknown Middle Pleistocene activity of Ponza Island or Campanian volcanoes, and one to Salina Island. The tephrostratigraphic correlation of the Mercure tephras with the Acerno lacustrine pollen record (Campania) also allowed us to evaluate the climatostratigraphic position of the tephras within the framework of the MIS 15–12 climatic variability. These results were obtained by combining the Sr–Nd isotope ratio with EMPA and 40Ar/39Ar geochronological data. This confirms the notable consistency of this approach for studying the Mediterranean Middle Pleistocene tephrostratigraphy, which, despite its great potential for both volcanology and Quaternary studies, has been hitherto barely explored.
    Description: Published
    Description: 232–248
    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: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: 40Ar/39Ar dating; EMPA glass compositions ; Middle Pleistocene; ; peri-Tyrrhenian explosive volcanisms ; Sr isotopes.
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 75
    Publication Date: 2022-05-03
    Description: Shallow seabed depressions attributed to focused fluid seepage, known as pock- marks, have been documented in all continental margins. In this study, we dem- onstrate how pockmark formation can be the result of a combination of multiple factors— fluid type, overpressures, seafloor sediment type, stratigraphy and bot- tom currents. We integrate multibeam echosounder and seismic reflection data, sediment cores and pore water samples, with numerical models of groundwa- ter and gas hydrates, from the Canterbury Margin (off New Zealand). More than 6800 surface pockmarks, reaching densities of 100 per km2, and an undefined number of buried pockmarks, are identified in the middle to outer shelf and lower continental slope. Fluid conduits across the shelf and slope include shal- low to deep chimneys/pipes. Methane with a biogenic and/or thermogenic origin is the main fluid forming flow and escape features, although saline and fresh- ened groundwaters may also be seeping across the slope. The main drivers of fluid flow and seepage are overpressure across the slope generated by sediment loading and thin sediment overburden above the overpressured interval in the outer shelf. Other processes (e.g. methane generation and flow, a reduction in hydrostatic pressure due to sea- level lowering) may also account for fluid flow and seepage features, particularly across the shelf. Pockmark occurrence coin- cides with muddy sediments at the seafloor, whereas their planform is elongated by bottom currents.
    Repository Name: EPIC Alfred Wegener Institut
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  • 76
    Publication Date: 2022-05-25
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Romagnoni, G., Kvile, K. o., Dagestad, K., Eikeset, A. M., Kristiansen, T., Stenseth, N. C., & Langangen, O. Influence of larval transport and temperature on recruitment dynamics of North Sea cod (Gadus morhua) across spatial scales of observation. Fisheries Oceanography, (2020): 1-16, doi:10.1111/fog.12474.
    Description: The survival of fish eggs and larvae, and therefore recruitment success, can be critically affected by transport in ocean currents. Combining a model of early‐life stage dispersal with statistical stock–recruitment models, we investigated the role of larval transport for recruitment variability across spatial scales for the population complex of North Sea cod (Gadus morhua ). By using a coupled physical–biological model, we estimated the egg and larval transport over a 44‐year period. The oceanographic component of the model, capable of capturing the interannual variability of temperature and ocean current patterns, was coupled to the biological component, an individual‐based model (IBM) that simulated the cod eggs and larvae development and mortality. This study proposes a novel method to account for larval transport and success in stock–recruitment models: weighting the spawning stock biomass by retention rate and, in the case of multiple populations, their connectivity. Our method provides an estimate of the stock biomass contributing to recruitment and the effect of larval transport on recruitment variability. Our results indicate an effect, albeit small, in some populations at the local level. Including transport anomaly as an environmental covariate in traditional stock–recruitment models in turn captures recruitment variability at larger scales. Our study aims to quantify the role of larval transport for recruitment across spatial scales, and disentangle the roles of temperature and larval transport on effective connectivity between populations, thus informing about the potential impacts of climate change on the cod population structure in the North Sea.
    Description: G.R. was supported by the Norden Top‐level Research Initiative sub‐programme “Effect Studies and Adaptation to Climate Change” through the Nordic Centre for Research on Marine Ecosystems and Resources under Climate Change (NorMER). K.Ø.K. was supported by the WHOI John H. Steele Post‐doctoral Scholar award and VISTA – a basic research program in collaboration between The Norwegian Academy of Science and Letters, and Equinor. We thank an anonymous referee for valuable comments that substantially improved the article.
    Keywords: Atlantic cod ; biophysical model ; larval transport ; North Sea ; populations ; stock–recruitment ; temperature
    Repository Name: Woods Hole Open Access Server
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  • 77
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    Wiley
    In:  EPIC3Paleoceanography, Wiley, 35, pp. 1-7, ISSN: 0883-8305
    Publication Date: 2020-03-13
    Description: The transition from the Pliocene to the Pleistocene was accompanied by major tectonic reorganizations of key oceanic gateways. In particular, the gradual closure of the Panama Gateway and the constriction of the Indonesian Gateway significantly affected the structure of the Pacific thermocline. In the East Pacific, the thermocline shoaled from an early Pliocene El Niño‐like depth to its modern state, which had significant implications for global climate. Here we use Mg/Ca temperature estimates from subsurface and thermocline dwelling foraminifera to reconstruct the meridional Plio‐Pleistocene evolution of the Southeast Pacific thermocline, in relation to atmospheric circulation changes. In combination with similar reconstructions from the north‐equatorial Pacific, our data indicate a change in the thermocline, responding to the northward displacement of the Intertropical Convergence Zone/South Pacific High system between ~3.8 and 3.5 Ma. After 3.5 Ma, we record a second major phase of thermocline shoaling, which points to the Intertropical Convergence Zone/South Pacific High‐system movement toward its modern position along with the gradual cooling of the Northern Hemisphere and its associated glaciation. These findings highlight that a warming globe may affect equatorial regions more intensively due to the potential temperature‐driven movement of the Intertropical Convergence Zone/South Pacific High and their associated oceanic systems.
    Repository Name: EPIC Alfred Wegener Institut
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  • 78
    Publication Date: 2020-03-13
    Description: It is widely assumed that the ventilation of the Southern Ocean played a crucial role in driving glacial‐interglacial atmospheric CO2 levels. So far, however, ventilation records from the Indian sector of the Southern Ocean are widely missing. Here we present reconstructions of water residence times (depicted as ΔΔ14C and Δδ13C) for the last 32,000 years on sediment records from the Kerguelen Plateau and the Conrad Rise (~570‐ to 2,500‐m water depth), along with simulated changes in ocean stratification from a transient climate model experiment. Our data indicate that Circumpolar Deep Waters in the Indian Ocean were part of the glacial carbon pool. At our sites, close to or bathed by upwelling deep waters, we find two pulses of decreasing ΔΔ14C and δ13C values (~21–17 ka; ~15–12 ka). Both transient pulses precede a similar pattern in downstream intermediate waters in the tropical Indian Ocean as well as rising atmospheric CO2 values. These findings suggest that 14C‐depleted, CO2‐rich Circumpolar Deep Water from the Indian Ocean contributed to the rise in atmospheric CO2 during Heinrich Stadial 1 and also the Younger Dryas and that the southern Indian Ocean acted as a gateway for sequestered carbon to the atmosphere and tropical intermediate waters.
    Repository Name: EPIC Alfred Wegener Institut
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  • 79
    Publication Date: 2020-03-23
    Repository Name: EPIC Alfred Wegener Institut
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  • 80
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(9), pp. e2020GL087965, ISSN: 0094-8276
    Publication Date: 2020-05-04
    Description: Both the Arctic and Antarctic sea ice extents (SIE) from 44 coupled models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) are evaluated by comparing them with observations and CMIP5 results. The CMIP6 multi‐model mean can adequately reproduce the seasonal cycles of both the Arctic and Antarctic SIE. The observed Arctic September SIE declining trend (−0.82±0.18 million km2/decade) between 1979 and 2014 is slightly underestimated in CMIP6 models (−0.70±0.06 million km2/decade). The observed weak but significant upward trend of the Antarctic SIE is not captured, which was an issue already in the CMIP5 phase. Compared with CMIP5 models, CMIP6 models have lower inter‐model spreads in SIE mean values and trends, although their SIE biases are relatively larger. The CMIP6 models did not reproduce the new summer tendencies after 2000, including the faster decline of Arctic SIE and the larger interannual variability in Antarctic SIE.
    Repository Name: EPIC Alfred Wegener Institut
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  • 81
    Publication Date: 2020-04-22
    Description: Current analyses and predictions of spatially‐explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long‐term average thermal conditions at coarse spatial resolutions only. Hence, many climate‐forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing, or cold‐air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free‐air temperatures, microclimatic ground and near‐surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near‐surface temperature data from all over the world. Currently this database contains time series from 7538 temperature sensors from 51 countries across all key biomes. The database will pave the way towards an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 82
    Publication Date: 2020-06-05
    Repository Name: EPIC Alfred Wegener Institut
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  • 83
    Publication Date: 2021-11-02
    Description: The Bransfield Basin is a young (∼4 Ma) back-arc basin related to the remnant subduction of the Phoenix Plate that once existed along the entire Pacific margin of the Antarctic Peninsula. Based on a recently deployed amphibious seismic network, we use ambient noise tomography to obtain the S-wave velocity structure in the Central Bransfield Basin (CBB). Combining with the stress field inverted from focal mechanisms, our images reveal that the CBB suffers a significant extension in the northwest-southeast direction. The extension is strongest in the northeastern CBB with associated mantle exhumation and weakens to the southwest with decoupled deformations between the upper crust and lithospheric mantle. Such an along-strike variation of extension can be explained by slab window formation and forearc rotation, which are associated with the Phoenix Plate detachment during the ridge–trench collisions at the southwest of the Hero Fracture Zone.
    Repository Name: EPIC Alfred Wegener Institut
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  • 84
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    Copernicus
    In:  EPIC3A global monthly climatology of oceanic total dissolved inorganic carbon: a neural network approach, Earth System Science Data Discussions, Copernicus, pp. 1-30
    Publication Date: 2020-03-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 85
    Publication Date: 2020-03-27
    Description: Widespread global declines in shellfish reefs (ecosystem-forming bivalves such as oysters and mussels) have led to growing interest in their restoration and protection. With restoration projects now occurring on four continents and in at least seven countries, global restoration guidelines for these ecosystems have been developed based on experience over the past two decades. The following key elements of the guidelines are outlined: (a) the case for shellfish reef resto- ration and securing financial resources; (b) planning, feasibility, and goal set- ting; (c) biosecurity and permitting; (d) restoration in practice; (e) scaling up from pilot to larger scale restoration, (f) monitoring, (g) restoration beyond oyster reefs (specifically mussels), and (h) successful communication for shell- fish reef restoration projects.
    Repository Name: EPIC Alfred Wegener Institut
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  • 86
    Publication Date: 2020-09-17
    Description: Recent evidence shows that wind‐driven ocean currents, like the western boundary currents, are strongly affected by global warming. However, due to insufficient observations both on temporal and spatial scales, the impact of climate change on large‐scale ocean gyres is still not clear. Here, based on satellite observations of sea surface height and sea surface temperature, we find a consistent poleward shift of the major ocean gyres. Due to strong natural variability, most of the observed ocean gyre shifts are not statistically significant, implying that natural variations may contribute to the observed trends. However, climate model simulations forced with increasing greenhouse gases suggest that the observed shift is most likely to be a response of global warming. The displacement of ocean gyres, which is coupled with the poleward shift of extratropical atmospheric circulation, has broad impacts on ocean heat transport, regional sea level rise, and coastal ocean circulation.
    Repository Name: EPIC Alfred Wegener Institut
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  • 87
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48, pp. e2021GL092773, ISSN: 0094-8276
    Publication Date: 2021-08-23
    Description: A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a “data-forward” approach, that clearly decouples the presentation of proxy data from plausible environmental inferences.
    Repository Name: EPIC Alfred Wegener Institut
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  • 88
    Publication Date: 2021-09-20
    Description: In order to investigate the impact of spatial resolution on the discrepancy between simulated δ18O and observed δ18O in Greenland ice cores, regional climate simulations are performed with the isotope-enabled regional climate model (RCM) COSMO_iso. For this purpose, isotope-enabled general circulation model (GCM) simulations with the ECHAM5-wiso general circulation model (GCM) under present-day conditions and the MPI-ESM-wiso GCM under mid-Holocene conditions are dynamically downscaled with COSMO_iso for the Arctic region. The capability of COSMO_iso to reproduce observed isotopic ratios in Greenland ice cores for these two periods is investigated by comparing the simulation results to measured δ18O ratios from snow pit samples, Global Network of Isotopes in Precipitation (GNIP) stations and ice cores. To our knowledge, this is the first time that a mid-Holocene isotope-enabled RCM simulation is performed for the Arctic region. Under present-day conditions, a dynamical downscaling of ECHAM5-wiso (1.1◦ × 1.1◦) with COSMO_iso to a spatial resolution of 50km improves the agreement with the measured δ18O ratios for 14 of 19 observational data sets. A further increase in the spatial resolution to 7km does not yield substantial improvements except for the coastal areas with its complex terrain. For the mid-Holocene, a fully coupled MPI-ESM-wiso time slice simulation is downscaled with COSMO_iso to a spatial resolution of 50km. In the mid-Holocene, MPI-ESM-wiso already agrees well with observations in Greenland and a downscaling with COSMO_iso does not further improve the model–data agreement. Despite this lack of improvement in model biases, the study shows that in both periods, observed δ18O values at measurement sites constitute isotope ratios which are mainly within the subgrid-scale variability of the global ECHAM5-wiso and MPI-ESM-wiso simulation results. The correct δ18O ratios are consequently not resolved in the GCM simulation results and need to be extracted by a refinement with an RCM. In this context, the RCM simulations provide a spatial δ18O distribution by which the effects of local uncertainties can be taken into account in the comparison between point measurements and model outputs. Thus, an isotope-enabled GCM–RCM model chain with realistically implemented fractionating processes constitutes a useful supplement to reconstruct regional paleo-climate conditions during the mid-Holocene in Greenland. Such model chains might also be applied to reveal the full potential of GCMs in other regions and climate periods, in which large deviations relative to observed isotope ratios are simulated.
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  • 89
    Publication Date: 2021-09-20
    Description: Proxy climate records are an invaluable source of information about the earth’s climate prior to the instrumental record. The temporal- and spatial-coverage of records continues to increase, however, these records of past climate are associated with significant uncertainties due to non-climate processes that influence the recorded and measured proxy values. Generally, these uncertainties are timescale-dependent and correlated in time. Accounting for structure in the errors is essential to providing realistic error estimates for smoothed or stacked records, detection of anomalies and identifying trends, but this structure is seldom accounted for. In the first of these companion articles we outlined a theoretical framework for handling proxy uncertainties by deriving the power spectrum of proxy error components from which it is possible to obtain timescale-dependent error estimates. Here in part II, we demonstrate the practical application of this theoretical framework using the example of marine sediment cores. We consider how to obtain estimates for the required parameters and give examples of the application of this approach for typical marine sediment proxy records. Our new approach of estimating and providing timescale-dependent proxy errors overcomes the limitations of simplistic single value error estimates. We aim to provide the conceptual basis for a more quantitative use of paleo-records for applications such as model-data comparison, regional and global synthesis of past climate states and data assimilation.
    Repository Name: EPIC Alfred Wegener Institut
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  • 90
    Publication Date: 2021-09-06
    Description: The mid-Pliocene warm period (mPWP; ∼3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar to modern geography and ∼400 ppmv atmospheric CO2 concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble, we analyse changes of the WAM rainfall during the mPWP by comparing them with the control simulations for the pre-industrial period. The ensemble shows a robust increase in the summer rainfall over West Africa and the Sahara region, with an average increase of 2.5 mm/d, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara and deepening of the Saharan Heat Low, seen in 〉90 % of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Though previous studies of future projections indicate a west–east drying–wetting contrast over the Sahel, PlioMIP2 simulations indicate a uniform rainfall increase in that region in warm climates characterized by increasing greenhouse gas forcing. We note that this effect will further depend on the long-term response of the vegetation to the CO2 forcing.
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  • 91
    Publication Date: 2021-08-26
    Description: Traditional bulk isotopic analysis is a pivotal tool for mapping consumer–resource interactions in food webs but has largely failed to adequately describe parasite–host relationships. Thus, parasite–host interactions remain undescribed in food web frameworks despite these relationships increasing linkage density, connectance and ecosystem biomass. Compound-specific stable isotopes from amino acids provides a promising novel approach that may aid in mapping parasite–host relationships in food webs. Here we apply a combination of traditional bulk stable isotope analyses and compound-specific isotopic analysis of nitrogen in amino acids to examine resource use and trophic interactions of five parasites from three hosts from a marine coastal food web (Wadden Sea, European Atlantic). By comparing isotopic compositions of bulk and amino acid nitrogen, we aimed to characterize isotopic fractionation occurring between parasites and their hosts and to clarify parasite trophic positions. Our results indicate that parasitic trophic interactions were more accurately identified using compound-specific stable isotope analysis due to removal of underlying source isotopic variation for both parasites and hosts. The compound-specific method provided clearer trophic discrimination factors in comparison to bulk isotope methods. Amino acid compound specific isotope analysis has widely been applied to examine trophic position within food webs, but our analyses suggest that the method is particularly useful for clarifying the feeding strategies for parasitic species. Baseline isotopic information provided by source amino acids allows clear identification of the fractionation from parasite metabolism by integrating underlying isotopic variations from the host tissues. However, like for bulk isotope analysis, the application of a universal trophic discrimination factor to parasite–host relationships remains inappropriate for compound-specific stable isotope analysis. Despite this limitation, compound-specific stable isotope analysis is and will continue to be a valuable tool to increase our understanding of parasitic interactions in marine food webs.
    Repository Name: EPIC Alfred Wegener Institut
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  • 92
    Publication Date: 2022-03-16
    Description: Tectono-stratigraphic interpretation and sequential restoration modelling was performed over two high-resolution seismic profiles crossing the Western Ionian Basin of southern Italy. This analysis was undertaken in order to provide greater insights and a more reliable assessment of the deformation rate affecting the area. Offshore seismic profiling illuminates the sub-seafloor setting where a belt of active normal faults slice across the foot of the Malta Escarpment, a regional-scale structural boundary inherited from the Permo-Triassic palaeotectonic setting. A sequential restoration workflow was established to back-deform the entire investigated sector with the primary aim of analysing the deformation history of the three major normal faults affecting the area. Restoration of the tectono-stratigraphic model reveals how deformation rates evolved through time. In the early stage, the studied area experienced a significant deformation with the horizontal component prevailing over the vertical element. In this context, the three major faults contribute to only one third of the total deformation. The overall throw and extension then notably reduced through time towards the present day and, since the middle Pliocene, ongoing crustal deformation is accommodated almost entirely by the three major normal faults. Unloading and decompaction indicate that when compared to the unrestored seismic sections, a revision and a reduction of roughly one third of the vertical displacement of the faults offset is required. This analysis ultimately allows us to better understand the seismic potential of the region.
    Description: Published
    Description: 321-341
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 93
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    Wiley
    In:  EPIC3Limnology and Oceanography Letters, Wiley, 7(2), pp. 167-174, ISSN: 2378-2242
    Publication Date: 2022-03-25
    Description: The end of the polar night with the concurrent onset of photosynthetic biomass production ultimately leads to the spring bloom, which represents the most important event of primary production for the Arctic marine ecosystem. This dataset shows, for the first time, significant in situ biomass accumulation during the dark–light transition in the high Arctic, as well as the earliest recorded positive net primary production rates together with constant chlorophyll a-normalized potential for primary production through winter and spring. The results indicate a high physiological capacity to perform photosynthesis upon re-illumination, which is in the same range as that observed during the spring bloom. Put in context with other data, the results of this study indicate that also active cells originating from the low winter standing stock in the water column, rather than solely resting stages from the sediment, can seed early spring bloom assemblages.
    Repository Name: EPIC Alfred Wegener Institut
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  • 94
    Publication Date: 2022-02-17
    Description: Free access at https://onlinelibrary.wiley.com/doi/10.1111/1755-6724.14824
    Description: Earthquake is a sudden release of energy due to fault motions. The severity of the damages can be minimized by development of a culture of prevention which includes the Seismic Hazard Assessment, microzonation studies and appropriate building codes. Earthquake risk assessment methods require seismo tectonic information usually organized in earthquake catalogues utilized in Probabilistic Seismic Hazard Assessment (PSHA) based on initial work by Cornell (1968), where probability distributions for magnitudes and source site distances reported in earthquake catalogues were utilized for the first time. In following years the method furtherly improved reporting an upper bound on the earthquake magnitude in each region avoiding the inclusion of unrealistically big earthquakes. A different approach has been followed in Countries characterized by significant incompletenesses in available earthquake catalogues. In these places the Deterministic Seismic Hazard Assessment (DSHA) methods have been often utilized. In particular the DSHA takes into account the maximum possible earthquake to evaluate the intensity of seismic ground motion distribution at a site by taking account the seismotectonic setup of the area. A deepening in the knowledge of seismotectonics and of morphostructural features of the studied area has been carried out in pattern recognition studies (Gelfand et al., 1976 and references therein). More updated applications named Neo-Deterministic Seismic Hazard Assessment (NDSHA) proposed by Wang et al. (2021) also consider morphostructural zoning which, in turn, considers nodes (fractured areas), lineaments and topographical features like the maximal elevation and the minimal elevation of the studied area. The steepness of topographic surfaces and sharp variations in morphostructural parameters indicate high tectonic activity. Some geological features are also presently utilized in PSHA methods in some Countries and considers basic parameters like the top and the bottom of seismogenic layers deduced by faults geometry within the frame of the Earthquake Rupture Forecasting (Bird and Liu, 2007).
    Description: Published
    Description: 31-33
    Description: 9T. Geochimica dei fluidi applicata allo studio e al monitoraggio di aree sismiche
    Description: JCR Journal
    Keywords: probabilistic seismic hazard assessment, deterministic seismic hazard assessment, helium isotopes, geochemical prospection, earthquake precursors ; seismic hazard estimation by geochemical methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 95
    Publication Date: 2022-02-21
    Description: Relative sea‐level (RSL) evolution during Marine Isotopic Stage (MIS) 5 in the Mediterranean basin is still not fully understood despite a plethora of morphological, stratigraphic and geochronological studies carried out on highstand deposits of this area. In this review we assembled a database of 323 U/Th‐dated samples (e.g. corals, molluscs, speleothems) which were used to chronologically constrain RSL evolution within MIS 5. The application of strict geochemical criteria to the U/Th samples indicates that only ~33% of data available for the Mediterranean Sea can be considered ‘reliable’. Most of these data (~65%) refer to the MIS 5e highstand, while only ~17% could be related to the MIS 5a. No attribution to MIS 5c can be unequivocally supported. Nevertheless, the resulting framework does not allow us to define a satisfactory RSL trend during the MIS 5e highstand and subsequent MIS 5 substages. Overall, the proposed selection of reliable/unreliable data would be useful for detecting areas where MIS 5 substage attributions are not supported by confident U/Th chronological data and thus the related reconstructions need to be revised. In this regard, the resulting framework calls for a reappraisal and re‐examination of the Mediterranean records with advanced geochronological methodologies.
    Description: Published
    Description: 1174-1189
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
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  • 96
    Publication Date: 2022-02-25
    Description: The Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow-water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn-orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central-southern Apennine fold-thrust beltforeland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post-date the onset of foredeep depozone. In this work, we provide new high-resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn-orogenic deposits overlying the Eocene-Cretaceous pre-orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the foldthrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre-orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.
    Description: Published
    Description: 2817-2836
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: central-southern Apennines (Italy) ; fold-thrust belt ; forebulge ; foredeep
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  • 97
    Publication Date: 2022-01-10
    Description: The mid-Pliocene warm period (3.264–3.025 Ma) is the most recent geological period during which atmospheric CO2 levels were similar to recent historical values (∼400 ppm). Several proxy reconstructions for the mid-Pliocene show highly reduced zonal sea surface temperature (SST) gradients in the tropical Pacific Ocean, indicating an El Niño-like mean state. However, past modelling studies do not show these highly reduced gradients. Efforts to understand mid-Pliocene climate dynamics have led to the Pliocene Model Intercomparison Project (PlioMIP). Results from the first phase (PlioMIP1) showed clear El Niño variability (albeit significantly reduced) and did not show the greatly reduced time-mean zonal SST gradient suggested by some of the proxies. In this work, we study El Niño–Southern Oscillation (ENSO) variability in the PlioMIP2 ensemble, which consists of additional global coupled climate models and updated boundary conditions compared to PlioMIP1. We quantify ENSO amplitude, period, spatial structure and “flavour”, as well as the tropical Pacific annual mean state in mid-Pliocene and pre-industrial simulations. Results show a reduced ENSO amplitude in the model-ensemble mean (−24 %) with respect to the pre-industrial, with 15 out of 17 individual models showing such a reduction. Furthermore, the spectral power of this variability considerably decreases in the 3–4-year band. The spatial structure of the dominant empirical orthogonal function shows no particular change in the patterns of tropical Pacific variability in the model-ensemble mean, compared to the pre-industrial. Although the time-mean zonal SST gradient in the equatorial Pacific decreases for 14 out of 17 models (0.2 ∘C reduction in the ensemble mean), there does not seem to be a correlation with the decrease in ENSO amplitude. The models showing the most “El Niño-like” mean state changes show a similar ENSO amplitude to that in the pre-industrial reference, while models showing more “La Niña-like” mean state changes generally show a large reduction in ENSO variability. The PlioMIP2 results show a reasonable agreement with both time-mean proxies indicating a reduced zonal SST gradient and reconstructions indicating a reduced, or similar, ENSO variability.
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  • 98
    Publication Date: 2022-01-10
    Description: The mid-Pliocene (∼3 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1∘ northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.
    Repository Name: EPIC Alfred Wegener Institut
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  • 99
    Publication Date: 2022-01-04
    Description: We present a novel method to estimate dynamic ice loss of Greenland's three largest outlet glaciers: Jakobshavn Isbræ, Kangerlussuaq Glacier, and Helheim Glacier. We use Global Navigation Satellite System (GNSS) stations attached to bedrock to measure elastic displacements of the solid Earth caused by dynamic thinning near the glacier terminus. When we compare our results with discharge, we find a time lag between glacier speedup/slowdown and onset of dynamic thinning/thickening. Our results show that dynamic thinning/thickening on Jakobshavn Isbræ occurs 0.87 ± 0.07 years before speedup/slowdown. This implies that using GNSS time series we are able to predict speedup/slowdown of Jakobshavn Isbræ by up to 10.4 months. For Kangerlussuaq Glacier the lag between thinning/thickening and speedup/slowdown is 0.37 ± 0.17 years (4.4 months). Our methodology and results could be important for studies that attempt to model and understand mechanisms controlling short-term dynamic fluctuations of outlet glaciers in Greenland.
    Repository Name: EPIC Alfred Wegener Institut
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  • 100
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    Wiley
    In:  EPIC3Journal of Geophysical Research: Oceans, Wiley, 126(10), ISSN: 2169-9275
    Publication Date: 2021-12-08
    Description: Globally, mesoscale processes create a rich and filamented pattern in biological productivity. Despite of remoteness and a harsh environment, observations likewise show an impact of mesoscale processes on phytoplankton growth in the Arctic. Observations of sufficiently high resolution are, however, difficult to carry out. Large-scale models are another way to gain knowledge about the system. In the current study, we use a global sea ice-ocean biogeochemical model, which is eddy resolving in Fram Strait, to show that the mesoscale dynamics has a strong effect on shaping phytoplankton growth. For the year 2009, we demonstrate that the growth season in the West Spitzbergen Current can be divided into two regimes; during Regime I, which takes place in May and June before and during the spring bloom, high chlorophyll concentrations are associated with areas of positive vorticity and a shallow mixed layer, pointing toward light limitation controlling growth. During Regime II, which occurs after the bloom from mid-July to late August, the highest chlorophyll concentration is found in areas of negative vorticity. Here, upwelling of nutrient-rich water occurs, through doming isopycnals, acting to raise the nutricline, may also play a role in alleviating nutrient limitation in the surface water. The study suggests that the mesoscale eddy environment locally modulates the seasonal cycle of light and nutrient limitation. Knowledge of the eddy field should be taken into consideration for making conclusions from point-wise measurements in Fram Strait.
    Repository Name: EPIC Alfred Wegener Institut
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