ALBERT

Description: Duvalo “volcano” is a site of anomalous geogenic degassing close to Ohrid (North Macedonia) not related to volcanic activity, despite its name. CO2 flux measurements made with the accumulation chamber (321 sites over ∼50,000 m2) showed fluxes up to nearly 60,000 g m−2 d−1, sustaining a total output of ∼67 t d−1. Soil gas samples were taken at 50 cm depth from sites with high CO2 fluxes and analyzed for their chemical and isotope composition. The gas is mainly composed by CO2 (〉90%) with significant concentrations of H2S (up to 0.55%) and CH4 (up to 0.32%). The isotope compositions of He (R/RA 0.10) and of CO2 (δ13C ∼ 0‰) exclude significant mantle contribution, while δ13C-CH4 (∼−35‰) and δ2H-CH4 (∼−170‰) suggest a thermogenic origin for CH4. The area is characterized by intense seismic activity and Duvalo corresponds to an active tectonic structure bordering the Ohrid graben. The production of H2S within the stratigraphic sequence may be explained by thermochemical reduction of sulfate. The uprising H2S is partially oxidized to sulfuric acid that, reacting with carbonate rocks, releases CO2. The tectonic structure of the area favors fluid circulation, sustaining H2S production and oxidation, CO2 production and allowing the escape of the gases to the atmosphere. In the end, Duvalo represents a tectonic-related CO2 degassing area whose gases originate mostly, if not exclusively, in the shallowest part of the crust (〈10 km). This finding highlights that even systems with trivial mantle contribution may sustain intense CO2 degassing (〉1,000 t km−2 d−1).

Description: Published

Description: e2021GC010198

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal

Description: Three devastating earthquakes of MW ≥ 5.9 activated a complex system of high-angle normal, antithetic, and sub-horizontal detachment faults during the 2016–2017 central Italy seismic sequence. Waveform cross-correlation based double-difference location of nearly 400,000 aftershocks illuminate complex, fine-scale structures of interacting fault zones. The Mt. Vettore–Mt. Bove (VB) normal fault exhibits wide and complex damage zones, including a system of bookshelf faults that intersects the detachment zone. In the Laga domain, a comparatively narrow, shallow dipping segment of the deep Mt. Gorzano fault progressively ruptures through the detachment zone in four subsequent MW ∼ 5.4 events. Reconstructed fault planes show that the detachment zone is fragmented in four sub-horizontal, partly overlaying shear planes that correlated with the extent of the mainshock ruptures. We find a new, deep reaching seismic barrier that coincides with a bend in the VB fault and may play a role in controlling rupture evolution.

Description: Published

Description: e2021GL092918

Description: 4T. Sismicità dell'Italia

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Moulin and Benedetti (2018), https://doi.org/10.1029/2018tc00495810.1029/2018tc004958 present a new interpretation of the Neogene-Quaternary tectonic evolution of the Eastern Southern Alps (ESA) in Friuli. After the reinterpretation of literature field data by means of remote sensing analysis (Digital Elevation Model interpretation), they calculated deformation rates of the tectonic structures through age interpretation of geomorphological surfaces of the Veneto-Friuli piedmont plain. The authors linked the result of surface analysis to the thrust and fold architecture of the ESA basing on the Castellarin et al. (2006), https://doi.org/10.1016/j.tecto.2005.10.013 interpretation of TRANSALP project and the Friuli geological map at the scale 1:150,000 (Carulli, 2006). Discussing their new architecture of the ESA, the Authors finally yielded rates of Europe-Adria plates convergence and suggest fragmentation of Adria over the last 1–2 Ma. The present comment is aimed at discussing several critical points concerning: the use of the geomorphological and chronological data; the misinterpretation of the Digital Terrain Model; the reconstruction of the balanced geological cross section. Moreover, the application of a structural model defined in a certain area to another without considering peculiar structural complexities available in the literature results is geologically and methodologically questionable.

Description: Published

Description: e2019TC005696

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: Tephra fallout hazard assessment is undertaken with probabilistic maps that rely on numerical models. Regarding maps production, the input parameters of the model (including atmospheric conditions), the physical approximations of the numerical simulations, and the probabilities of occurrence of different eruption types in specific time frames are among the most critical sources of uncertainty. We therefore present a tephra fallout hazard assessment study for two active volcanoes (Cotopaxi and Guagua Pichincha) in Ecuador. We utilize PLUME-MoM/HYSPLIT models, and a procedure for uncertainty quantification where: (a) the uncertainty on eruptive source parameters and eruption type occurrence is quantified through expert elicitation; (b) we implement a new procedure for correlations between the different parameters, and (c) we use correction coefficients to take into account the uncertainty of the numerical model. Maps of exceedance probability given a deposit thickness threshold, and thickness maps given a probability of exceedance, are produced (a) for two eruptive scenarios (sub-Plinian and Plinian) and (b) as a combination of these scenarios in case the next eruption will be sub-Plinian or Plinian. These maps are described according to the uncertainty distribution of eruption type occurrence probabilities, considering their 5th percentile, mean, and 95th percentile values. We finally present hazard curves describing exceeding probabilities in 10 sensitive sites within the city of Quito. Additional information includes the areal extent and the population potentially affected by different isolines of tephra accumulation. This work indicates that full uncertainty quantification helps in providing more robust scientific information, improving the hazard assessment reliability.

Description: Published

Description: e2021JB022780

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: The Campi Flegrei caldera is considered the most dangerous volcano in Europe and is currently in a new phase of unrest (started in 2000 and still ongoing) that has persisted intermittently for several decades (main crisis occurred from 1950-52, 70-72 and 82-84). Here, by combining the petrological and geochemical data collected in recent decades with numerical simulations, we place new constraints on the source(s) of the current dynamics of the volcano. In particular, we show that the measured (N2-He-CO2) geochemical changes at the fumaroles of Solfatara hydrothermal site are the result of massive (about 3 km3) magma degassing in the deep portion (≥ 200 MPa, 8 km of depth) of the plumbing system. This degassing mechanism would be able to flood the overlying hydrothermal system with hot gas, thus heating and fracturing the upper crust inducing shallow seismicity and deformation. This implies that the deep magma transfer process (≥8 km) has been decoupled from the source of deformation and seismicity, localized in the first kilometers (0-4 km) of caldera-filling rocks. This information on magma transfer depth can have important implications for defining the best monitoring strategies and for forecasting a future eruption. Finally, this study highlights how petrological and geochemical data allow us to explore the dynamics of the deep portion of the plumbing system and thus trace the occurrence of recharge episodes, in a portion of the ductile lower crust where magma transfer occurs in the absence of earthquakes. Plain Language Summary Calderas are volcanic depressions formed as the ground collapses during huge volcanic eruptions. They often exhibit pronounced unrest, with frequent earthquakes, ground uplift, and considerable heat and mass flux that are monitored by volcanologists for eruption forecasting. However, as this activity is due to the complex interactions among magma and hydrothermal system stored beneath the volcano, it is always difficult to predict the evolution of the unrest towards critical conditions until to eruption. The Campi Flegrei caldera is among the most dangerous volcanos in Europe and is currently in a new phase of unrest that has lasted for several decades, whose nature (magmatic or not magmatic) has remained unclear. Here, we combine petrological and geochemical observations collected in recent decades with numerical simulations to place new constraints on the source of the recent dynamics of the volcano. In particular, we show that new deep magma has recharged the shallow reservoir beneath the volcano and flooded the overlying hydrothermal system with hot gas; thereby weakening the upper rocks allowing deformation (ground uplift) and fracturing (seismicity). This information is particularly important in the case of high-risk Campi Flegrei caldera, because it can help to improve defense strategies in case of future eruption.

Description: Published

Description: e2021JB023773

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: Natural gas microseepage in petroleum-bearing sedimentary basins is an important complement to geophysical methods in oil-gas exploration and a natural source of methane (CH4) for the atmosphere. Microseepage, typically occurring in correspondence with petroleum fields throughout the world, is generally lower in summer, due to temperature-driven methanotrophic consumption, and higher in winter. The global estimates of microseepage methane emission have, however, relatively high uncertainties because of limited amounts of flux data, leading to poor knowledge of the spatial distribution and temporal variability of the gas emission factors. We studied the seasonal variation of microseepage flux to the atmosphere from a petroleum field in China (the Dawanqi oilfield), through methane flux measurements performed in summer 2014, winter 2015, and summer 2019. Winter data refer to frozen soil conditions, with snow cover and ice thickness in the soil exceeding 60 cm. Gas concentration (CH4, CO2, C2+ alkanes) and stable C isotopic composition of CH4 and CO2 in shallow (4 m deep) boreholes confirmed the existence of thermogenic gas seepage. Methane microseepage is higher in summer and lower or nil in winter. This seasonal trend is opposite to what was observed in areas where winter soil is not or poorly frozen. Our data suggest that seasonal microseepage variation may not be univocal worldwide, being strongly dependent on the presence of ice and snow cover in winter. The regional increase of temperature due to climate change, already demonstrated for the Tarim Basin over the last 50 years, could, in the future, reduce winter ice and enhance annual methane emission to the atmosphere.

Description: Published

Description: e2021JD034637

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal

Description: The Val d'Agri basin hosts an oil-field, the largest in onshore Europe, and it is one of the areas of highest seismic hazard in Italy. In an unproductive marginal portion of the reservoir, wastewater is re-injected by a high-rate well. Since the beginning of re-injection in June 2006, a spatio-temporal correlation between microseismicity (ML ≤ 2.0) and wastewater injection has been observed (suggesting induced seismicity). In this study, we perform a slip-tendency analysis on the fault system involved in the induced seismicity through a coupled fluid-flow and geomechanical numerical model simulating the stress partitioning due to the tectonic forces and to the fluid injection. The model results show that the fluid diffusion is strongly dependent on the active stress field and the geological structure in which fluids are injected, which conditioned the occurrence of seismicity that aligned on a small portion of a NE-dipping fault. However, another fault located closer to the injection well and where no seismicity was detected, is the better well-oriented fault with the active stress field and, also, the one more susceptible to the pore pressure increase. These results suggest different types of fault deformation acting in the Val d'Agri oilfield as response to the fluid injection (i.e., a mixed-mode fault slip behavior). Understanding the stress partitioning in tectonically active regions where underground activities such as fluid injection are ongoing is fundamental to give strong constraints for the discrimination between natural and induced seismicity, and finally for a more reliable and robust definition of seismic hazard.

Description: Published

Description: 2019JB019185

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: 7T. Variazioni delle caratteristiche crostali e "precursori"

Description: JCR Journal

Description: Identifying deformation and pre-failure mechanisms preceding faulting is key for fault mechanics and for interpreting precursors to fault rupture. This study presents the results of a new and robust derivation of first motion polarity focal mechanism solutions (FMS) applied to acoustic emission (AE). FMS are solved using a least squares minimization of the fit between projected polarity measurements and the deviatoric stress field induced by dilatational (T-type), shearing (S-type), and compressional (C-type) sources. 4 × 10 cm cylindrical samples of Alzo Granite (AG, porosity 〈1%) and Darley Dale Sandstone (DDS, porosity ≈14%) underwent conventional triaxial tests in order to investigate the relationships between increasing confining pressure (5, 10, 20, and 40 MPa), deformation and failure mode, and role of microstructural features. Results highlight that S-type events occur in very low numbers with poor spatial correlation to fault structure. Instead, deformation is driven by a complex interplay between compactant (C-type) and dilatant (T-type) regions of deformation. C-type events are the earliest precursor related to crack nucleation and T-type events mark new cracks opening, with the onset of fracture growth characterized by periodic cycles of coalescence. For AG a single sequence is able to lead to dynamic failure, while for DDS several cycles are needed for coalescence to take place due to the competition between dilatant and compactant deforming regions induced by multiple fracture nucleation sites. The occurrence of C- and S-type events is also consistent with a quasi-static premonitory phase, or foreshock, before a critical nucleation length allows the development of a planar localization.Identifying deformation and pre-failure mechanisms preceding faulting is key for fault mechanics and for interpreting precursors to fault rupture. This study presents the results of a new and robust derivation of first motion polarity focal mechanism solutions (FMS) applied to acoustic emission (AE). FMS are solved using a least squares minimization of the fit between projected polarity measurements and the deviatoric stress field induced by dilatational (T-type), shearing (S-type), and compressional (C-type) sources. 4 × 10 cm cylindrical samples of Alzo Granite (AG, porosity 〈1%) and Darley Dale Sandstone (DDS, porosity ≈14%) underwent conventional triaxial tests in order to investigate the relationships between increasing confining pressure (5, 10, 20, and 40 MPa), deformation and failure mode, and role of microstructural features. Results highlight that S-type events occur in very low numbers with poor spatial correlation to fault structure. Instead, deformation is driven by a complex interplay between compactant (C-type) and dilatant (T-type) regions of deformation. C-type events are the earliest precursor related to crack nucleation and T-type events mark new cracks opening, with the onset of fracture growth characterized by periodic cycles of coalescence. For AG a single sequence is able to lead to dynamic failure, while for DDS several cycles are needed for coalescence to take place due to the competition between dilatant and compactant deforming regions induced by multiple fracture nucleation sites. The occurrence of C- and S-type events is also consistent with a quasi-static premonitory phase, or foreshock, before a critical nucleation length allows the development of a planar localization.

Description: Published

Description: e2020JB021059

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: How major crustal-scale seismogenic faults nucleate and evolve in crystalline basements represents a long-standing, but poorly understood, issue in structural geology and fault mechanics. Here, we address the spatio-temporal evolution of the Bolfin Fault Zone (BFZ), a 〉40-km-long exhumed seismogenic splay fault of the 1000-km-long strike-slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile) and formed during the oblique subduction of the Aluk plate beneath the South American plate. Seismic faulting occurred at 5-7 km depth and ≤ 300°C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite veining. Ancient (125-118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes. Field geologic surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Seismic faulting exploited the segments of precursory anisotropies that were optimal to favorably oriented with respect to the long-term far-stress field associated with the oblique ancient subduction. The large-scale sinuous geometry of the BFZ resulted from the hard linkage of these anisotropy-pinned segments during fault growth.

Description: European Research Council Project (NOFEAR) 614705

Description: Published

Description: e2021TC006818

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: Seismological constraints obtained from receiver function (RF) analysis provide important information about the crust and mantle structure. Here, we explore the utility of the free-surface multiple of the P-wave (PP) and the corresponding conversions in RF analysis. Using earthquake records, we demonstrate the efficacy of PPs-RFs before illustrating how they become especially useful when limited data is available in typical planetary missions. Using a transdimensional hierarchical Bayesian deconvolution approach, we compute robust P-to-S (Ps)- and PPs-RFs with InSight recordings of five marsquakes. Our Ps-RF results verify the direct Ps converted phases reported by previous RF analyses with increased coherence and reveal other phases including the primary multiple reverberating within the uppermost layer of the Martian crust. Unlike the Ps-RFs, our PPs-RFs lack an arrival at 7.2 s lag time. Whereas Ps-RFs on Mars could be equally well fit by a two- or three-layer crust, synthetic modeling shows that the disappearance of the 7.2 s phase requires a three-layer crust, and is highly sensitive to velocity and thickness of intra-crustal layers. We show that a three-layer crust is also preferred by S-to-P (Sp)-RFs. While the deepest interface of the three-layer crust represents the crust-mantle interface beneath the InSight landing site, the other two interfaces at shallower depths could represent a sharp transition between either fractured and unfractured materials or thick basaltic flows and pre-existing crustal materials. PPs-RFs can provide complementary constraints and maximize the extraction of information about crustal structure in data-constrained circumstances such as planetary missions.

Description: Published

Description: e2021JE006983

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Focal mechanisms of selected earthquakes, recorded in the Mount Pollino region (southern Italy) from 2010 through 2014, are used to infer the pore fluid pressure at hypocenter depths. The 3-D excess pore pressure field provides evidence that the sequence occurs in a fluid-filled volume with values reaching 35 MPa. The mechanisms underlying this swarm-like sequence and the triggering of earthquakes are investigated by computing the cumulative static Coulomb stress change at hypocenter depths and analyzing the pore-pressure diffusion mechanism. The results indicate that static Coulomb stress change was lower than 0.01 MPa, which is the value generally assumed as threshold for the triggering, and seismicity distribution was actually driven by pore-pressure diffusion with relatively low diffusivity value. This latter mechanism could also explain the delayed triggering of the two larger events ML 4.3 and ML 5.0, respectively, that occurred about 150 days apart.

Description: Published

Description: e2021GL094552

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: A gas blowout during an unauthorised well drilling occurred on 9 June 2020 at the Rome-Ciampino boundary at the periphery of Colli Albani quiescent volcano. This zone hosts a shallow confined gas-pressured aquifer, which recently produced further three gas blowouts. Dangerous atmospheric CO2 and H2S concentrations killed some birds and 12 families were evacuated. The helium isotopic composition indicates that the gas has a magmatic origin. It rises toward the surface along leaky faults, pressurizing the shallow confined aquifer and creating a permanent gas blowout hazard. Colli Albani volcano is characterized by anomalous uplift, release of magmatic gas and episodic seismic crises. Should a volcanic unrest occur, gas hazard would increase in this densely inhabited zone of Rome city, as the input of magmatic gas into the confined aquifer might create overpressure conditions leading to a harmful phreatic explosion, or increase the emission of hazardous gas through newly created fractures.

Description: Published

Description: e2020GL089797

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Most basaltic explosive eruptions intensify abruptly, allowing little time to document processes at the start of eruption. One opportunity came with the initiation of activity from fissure 8 (F8) during the 2018 eruption on the lower East Rift Zone of Kīlauea, Hawaii. F8 erupted in four episodes. We recorded 28 min of high-definition video during a 51-min period, capturing the onset of the second episode on 5 May. From the videos, we were able to analyze the following in-flight parameters: frequency and duration of explosions; ejecta heights; pyroclast exit velocities; in-flight total mass and estimated mass eruption rates; and the in-flight total grain size distributions. The videos record a transition from initial pulsating outgassing, via spaced, but increasingly rapid, discrete explosions, to quasisustained, unsteady fountaining. This transition accompanied waxing intensity (mass flux) of the F8 eruption. We infer that all activity was driven by a combination of the ascent of a coupled mixture of small bubbles and melt, and the buoyant rise of decoupled gas slugs and/or pockets. The balance between these two types of concurrent flow determined the exact form of the eruptive activity at any point in time, and changes to their relative contributions drove the transition we observed at early F8. Qualitative observations of other Hawaiian fountains at Kīlauea suggest that this physical model may apply more generally. This study demonstrates the value of in-flight parameters derived from high-resolution videos, which offer a rapid and highly timesensitive alternative to measurements based on sampling of deposits posteruption.

Description: Published

Description: e2020JB020903

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Seismic event detection and phase picking are the base of many seismological workflows. In recent years, several publications demonstrated that deep learning approaches significantly outperform classical approaches, achieving human-like performance under certain circumstances. However, as studies differ in the datasets and evaluation tasks, it is unclear how the different approaches compare to each other. Furthermore, there are no systematic studies about model performance in cross-domain scenarios, that is, when applied to data with different characteristics. Here, we address these questions by conducting a large-scale benchmark. We compare six previously published deep learning models on eight data sets covering local to teleseismic distances and on three tasks: event detection, phase identification and onset time picking. Furthermore, we compare the results to a classical Baer-Kradolfer picker. Overall, we observe the best performance for EQTransformer, GPD and PhaseNet, with a small advantage for EQTransformer on teleseismic data. Furthermore, we conduct a cross-domain study, analyzing model performance on data sets they were not trained on. We show that trained models can be transferred between regions with only mild performance degradation, but models trained on regional data do not transfer well to teleseismic data. As deep learning for detection and picking is a rapidly evolving field, we ensured extensibility of our benchmark by building our code on standardized frameworks and making it openly accessible. This allows model developers to easily evaluate new models or performance on new data sets. Furthermore, we make all trained models available through the SeisBench framework, giving end-users an easy way to apply these models.

Description: This work was supported by the Helmholtz Association Initiative and Networking Fund on the HAICORE@KIT partition. J. Münchmeyer acknowledges the support of the Helmholtz Einstein International Berlin Research School in Data Science (HEIBRiDS). The authors thank the Impuls-und Vernetzungsfonds of the HGF to support the REPORT-DL project under the grant agreement ZT-I-PF-5-53. This work was also partially supported by the project INGV Pianeta Dinamico 2021 Tema 8 SOME (CUP D53J1900017001) funded by Italian Ministry of University and Research “Fondo finalizzato al rilancio degli investimenti delle amministrazioni centrali dello Stato e allo sviluppo del Paese, legge 145/2018.” Open access funding enabled and organized by Projekt DEAL.

Description: Published

Description: e2021JB023499

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: We study the drivers behind the global atmospheric methane (CH4) increase observed after 2006. Candidate emission and sink scenarios are constructed based on proposed hypotheses in the literature. These scenarios are simulated in the TM5 tracer transport model for 1984-2016 to produce three-dimensional fields of CH4 and δ 13C-CH4, which are compared with observations to test the competing hypotheses in the literature in one common model framework. We find that the fossil fuel (FF) CH4 emission trend from the Emissions Database for Global Atmospheric Research 4.3.2 inventory does not agree with observed δ 13C-CH4. Increased FF CH4 emissions are unlikely to be the dominant driver for the post-2006 global CH4 increase despite the possibility for a small FF emission increase. We also find that a significant decrease in the abundance of hydroxyl radicals (OH) cannot explain the post-2006 global CH4 increase since it does not track the observed decrease in global mean δ 13C-CH4. Different CH4 sinks have different fractionation factors for δ 13C-CH4, thus we can investigate the uncertainty introduced by the reaction of CH4 with tropospheric chlorine (Cl), a CH4 sink whose abundance, spatial distribution, and temporal changes remain uncertain. Our results show that including or excluding tropospheric Cl as a 13 Tg/year CH4 sink in our model changes the magnitude of estimated fossil emissions by ∼20%. We also found that by using different wetland emissions based on a static versus a dynamic wetland area map, the partitioning between FF and microbial sources differs by 20 Tg/year, ∼12% of estimated fossil emissions.

Description: Published

Description: e2021GB007000

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal

Description: Muography represents a recent and innovative tool for investigating the interior of active volcanoes. However, when dealing with frequently erupting open-vent volcanoes such as Stromboli, any result should take into con- sideration the structural and morphology changes caused by the eruptive activity. This may cause either summit collapses by magma withdrawal, or morphology growth by the accumulations of a fallout from the explosive activity, or more often a combination of both. In this chapter, we present an integration of various techniques, comprising muography and digital elevation model reconstruction, together with GBInSAR ground deformation and volcano seismicity, to reconstruct the geometry of the shallow magma supply system of the volcano and its changes in time. We show how muography can display the interior of the volcano as well as its outer growth, being sensitive to all volume changes that occurred between the framed surface and the detector. This was discovered in Stromboli by comparing digital topography in the interval between 2010 and 2012, when the rapid growth of the volcano summit by the accumulation of ballistic products in the area between the crater zone and the muon detec- tor occurred. This deposit, together with the filling in of the graben-like depression, formed during the 2007 eruption, by fallout during the persistent explosive activity, contributed to generating a remarkable anomaly in the summit area of the volcano visualized by muography. In addition, the shallow feeding system of the volcano was surveyed by GBInSAR and seismicity, which allowed us to reconstruct its path up to a depth of a few hundred meters.

Description: Published

Description: 75-91

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: Active faulting and deep-seated gravitational slope deformation (DGSD) are common geological hazards in mountain belts worldwide. In the Italian central Apennines, kilometer-thick carbonate sedimentary sequences are cut by major active normal faults that shape the landscape, generating intermontane basins. Geomorphological observations suggest that the DGSDs are commonly located in fault footwalls. We selected five mountain slopes affected by DGSD and exposing the footwall of active seismogenic normal faults exhumed from 2 to 0.5 km depth. Field structural analysis of the slopes shows that DGSDs exploit preexisting surfaces formed both at depth and near the ground surface by tectonic faulting and, locally, by gravitational collapse. Furthermore, the exposure of sharp scarps along mountain slopes in the central Apennines can be enhanced either by surface seismic rupturing or gravitational movements (e.g., DGSD) or by a combination of the two. At the microscale, DGSDs accommodate deformation mechanisms similar to those associated with tectonic faulting. The widespread compaction of micro-grains (e.g., clast indentation), observed in the matrix of both normal faults and DGSD slip zones, is consistent with clast fragmentation, fluid-infiltration, and congruent pressuresolution active at low ambient temperatures (〈60°C) and lithostatic pressures (〈80 MPa). Although clast comminution is more intense in the slip zones of normal faults because of the larger displacement accommodated, we are not able to find microstructural markers that allow us to uniquely distinguish faults from DGSDs.

Description: Published

Description: e2021TC006698

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: The increase of available seismic data prompts the need for automatic processing procedures to fully exploit them. A good example is aftershock sequences recorded by temporary seismic networks, whose thorough analysis is challenging because of the high seismicity rate and station density. Here, we test the performance of two recent Deep Learning algorithms, the Generalized Phase Detection and Earthquake Transformer, for automatic seismic phases identification. We use data from the December 2019 Mugello basin (Northern Apennines, Italy) swarm, recorded on 13 permanent and nine temporary stations, applying these automatic procedures under different network configurations. As a benchmark, we use a catalog of 279 manually repicked earthquakes reported by the Italian National Seismic Network. Due to the ability of deep learning techniques to identify earthquakes under poor signal-to-noise-ratio (SNR) conditions, we obtain: (a) a factor 3 increase in the number of locations with respect to INGV bulletin and (b) a factor 4 increase when stations from the temporary network are added. Comparison between deep learning and manually picked arrival times shows a mean difference of 0.02–0.04 s and a variance in the range 0.02–0.07 s. The improvement in magnitude completeness is ∼0.5 units. The deep learning algorithms were originally trained using data sets from different regions of the world: our results indicate that these can be successfully applied in our case, without any significant modification. Deep learning algorithms are efficient and accurate tools for data reprocessing in order to better understand the space-time evolution of earthquake sequences.

Description: Published

Description: e2021JB023405

Description: 4T. Sismicità dell'Italia

Description: JCR Journal

Description: Volcanism has played a major role in modifying the Martian surface. The Tharsis volcanic province dominates the western hemisphere of the planet with numerous effusive volcanic constructs and deposits. Here, we present the results of an in-depth study aimed at characterizing and modeling the emplacement conditions of 40 lava flows in the Tharsis volcanic province. These lava flows display a range of lengths (∼15–310 km), widths (∼0.5–29 km), and thicknesses (∼11–91 m). The volumes and flow masses range from ∼1 to 440 km3 and ∼1011 to 1014 kg, respectively. Using three different models, we calculated a range of eruption rates (0.3–3.5 × 104 m3/s), viscosities (104–107 Pa s), yield strengths (800–104 Pa), and emplacement times (8 h–11 years). While the flow lengths and volumes are typically larger than terrestrial lava flows by an order of magnitude, rheologies and eruption rates are similar based on our findings. Emplacement times suggest that eruptions were active for long periods of time, which implies the presence and persistence of open subsurface pathways. Differences in flow morphology and emplacement conditions across localities within Tharsis highlight different pathways and volumes of available material between the central volcanoes and the plains. The scale of the eruptions suggests there could have been eruption-driven local, regional, and perhaps, global impacts on the Martian climate. The relatively recent age of the eruptions implies that Mars has retained the capability of producing significant localized volcanism.

Description: Published

Description: e2020JE006791

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Knowledge of the global distribution of Earth volcanism is critical in many fields of the Geosciences involving large-scale assessments, such as plate tectonics, global volcanic hazards, and climate change. Recent analysis has revealed that global eruption inter-event times are exponentially distributed, implying that on the global scale volcanic eruptions are Poisson distributed. Here, we employ those findings to calibrate a continuous frequency-volume distribution for subaerial eruptions of any size on Earth from small lava flows to super-eruptions. Obtaining such a continuous global distribution implies considering the existing data and the way they are collected and categorized into databases, as well as extending the available eruption volume data to eruption VEI classes less than 4. The continuous global distribution shows an initial log-normal section up to volumes of about 170 Mm3, followed by a power-law section, tapered on its extreme right-end side, encompassing about five orders of magnitude of eruption volumes. The potential implications are discussed in terms of short-term eruption forecasts of the size of an impending eruption, critical for volcanic emergency management.

Description: Published

Description: e2021JB021763

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Cenozoic climate changes have been linked to tectonic activity and variations in atmospheric CO2 concentrations. Here we present Miocene and Pliocene sensitivity experiments performed with the climate model COSMOS. The experiments contain changes with respect to paleogeography, ocean gateway configuration, and atmospheric CO2 concentrations, as well as a range of vertical mixing coefficients in the ocean. For the Mid-Miocene, we show that the impact of ocean mixing on surface temperature is comparable to the effect of the possible range in reconstructed CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2-concentrations of 450 ppmv enable global mean surface, deep-water and meridional temperature characteristics representative of Mid-Miocene Climatic Optimum (MMCO) reconstructions. The Miocene climate shows a reduced meridional temperature gradient and reduced seasonality. In the case of enhanced mixing, surface and deep ocean temperatures show significant warming of up to 5-10°C and an Arctic temperature anomaly of more than 12°C. In the Pliocene simulations, the impact of vertical mixing and CO2 is less important for the deep ocean, which we interpret as a different sensitivity dependence on the background state and mixed layer dynamics. We find a significant reduction in surface albedo and effective emissivity for either a high level of atmospheric CO2 or increased vertical mixing. Our mixing sensitivity experiments provide a warm deep ocean via ocean heat uptake. We propose that the mixing hypothesis can be tested by reconstructions of the thermocline and seasonal paleoclimate data indicating a lower seasonality relative to today.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dzwonkowski, B., Fournier, S., Lockridge, G., Coogan, J., Liu, Z., & Park, K. Cascading weather events amplify the coastal thermal conditions prior to the shelf transit of Hurricane Sally (2020). Journal of Geophysical Research: Oceans, 126(12), (2021): e2021JC017957, https://doi.org/10.1029/2021JC017957.

Description: Changes in tropical cyclone intensity prior to landfall represent a significant risk to human life and coastal infrastructure. Such changes can be influenced by shelf water temperatures through their role in mediating heat exchange between the ocean and atmosphere. However, the evolution of shelf sea surface temperature during a storm is dependent on the initial thermal conditions of the water column, information that is often unavailable. Here, observational data from multiple monitoring stations and satellite sensors were used to identify the sequence of events that led to the development of storm-favorable thermal conditions in the Mississippi Bight prior to the transit of Hurricane Sally (2020), a storm that rapidly intensified over the shelf. The annual peak in depth-average temperature of 〉29°C that occurred prior to the arrival of Hurricane Sally was the result of two distinct warming periods caused by a cascade of weather events. The event sequence transitioned the system from below average to above average thermal conditions over a 25-day period. The transition was initiated with the passage of Hurricane Marco (2020), which mixed the upper water column, transferring heat downward and minimizing the cold bottom water reserved over the shelf. The subsequent reheating of the upper ocean by surface heat flux from the atmosphere, followed by downwelling winds, effectively elevated shelf-wide thermal conditions for the subsequent storm, Hurricane Sally. The coupling of climatological downwelling winds and warm sea surface temperature suggest regions with such characteristics are at an elevated risk for storm intensification over the shelf.

Description: his paper is a result of research funded by the National Oceanic and Atmospheric Administration's RESTORE Science Program under awards NA17NOS4510101 and NA19NOS4510194 to the University of South Alabama and Dauphin Island Sea Lab and by the NASA Physical Oceanography program under award 80NSSC21K0553 and WBS 281945.02.25.04.67 to the University of South Alabama and the Jet Propulsion Laboratory. A portion of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We thank the NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group for the Moderate-resolution Imaging Spectroradiometer (MODIS) Terra ocean color data; 2014 Reprocessing. NASA OB.DAAC, Greenbelt, MD, USA. 10.5067/AQUA/MODIS/MODIS_OC.2014.0.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49, (2022): e2021GL096180, https://doi.org/10.1029/2021gl096180.

Description: In the subtropical gyres, phytoplankton rely on eddies for transporting nutrients from depth to the euphotic zone. But, what controls the rate of nutrient supply for new production? We show that vertical nutrient flux both depends on the vertical motion within the eddying flow and varies nonlinearly with the phytoplankton growth rate. Flux is maximized when the growth rate matches the inverse of the decorrelation timescale for vertical motion. Using a three-dimensional ocean model and a linear nutrient uptake model, we find that phytoplankton productivity is maximized for a growth rate of 1/3 day−1, which corresponds to the timescale of submesoscale dynamics. Variability in the frequency of vertical motion across different physical features of the flow favors phytoplankton production with different growth rates. Such a growth-transport feedback can generate diversity in the phytoplankton community structure at submesoscales and higher net productivity in the presence of community diversity.

Description: MAF and AM were funded by N00014-16-1-3130 (ONR) and MAF was also supported by the Martin Fellowship, MIT.

Description: 2022-07-20

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Goodkin, N. F., Samanta, D., Bolton, A., Ong, M. R., Hoang, P. K., Vo, S. T., Karnauskas, K. B., & Hughen, K. A. Natural and anthropogenic forcing of multi-decadal to centennial scale variability of sea surface temperature in the South China Sea. Paleoceanography and Paleoclimatology, 36(10), (2021): e2021PA004233, https://doi.org/10.1029/2021PA004233.

Description: Four hundred years of reconstructed sea surface temperatures (SSTs) from a coral located off the coast of Vietnam show significant multi-decadal to centennial-scale variability in wet and dry seasons. Wet and dry season SST co-vary significantly at multi-decadal timescales, and the Interdecadal Pacific Oscillation (IPO) explains the majority of variability in both seasons. A newly reconstructed wet season IPO index was compared to other IPO reconstructions, showing significant long-term agreement with varying amplitude of negative IPO signals based on geographic location. Dry season SST also correlates to sea level pressure anomalies and the East Asian Winter Monsoon, although with an inverse relationship from established interannual behavior, as previously seen with an ocean circulation proxy from the same coral. Centennial-scale variability in wet and dry season SST shows 300 years of near simultaneous changes, with an abrupt decoupling of the records around 1900, after which the dry season continues a long-term cooling trend while the wet season remains almost constant. Climate model simulations indicate greenhouse gases as the largest contributor to the decoupling of the wet and dry season SSTs and demonstrate increased heat advection to the western South China Sea in the wet season, potentially disrupting the covariance in seasonal SST.

Description: This research was supported by a Singapore National Research Fellowship to N.F. Goodkin (NRFF-2012-03) as administered by the Earth Observatory of Singapore and by a Singapore Ministry of Education Academic Research Fund Tier 2 award to N.F. Goodkin, K.A. Hughen, and K.B. Karnauskas (MOE-2016-T2-1-016). D. Samanta was partially supported by a Singapore Ministry of Education Tier 3 award (MOE2019-T3-1-004).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gawarkiewicz, G., Fratantoni, P., Bahr, F., & Ellertson, A. Increasing frequency of mid‐depth salinity maximum intrusions in the Middle Atlantic Bight. Journal of Geophysical Research: Oceans, 127(7), (2022): e2021JC018233, https://doi.org/10.1029./2021jc018233.

Description: Shelfbreak exchange processes have been studied extensively in the Middle Atlantic Bight. An important process occurring during stratified conditions is the Salinity Maximum Intrusion. These features are commonly observed at the depth of the seasonal pycnocline, and less frequently at the surface and bottom. Data collected from NOAA's National Marine Fisheries Service Ecosystem Monitoring program as well as data collected from the fishing industry in Rhode Island show that the middepth intrusions are now occurring much more frequently than was reported in a previous climatology of the intrusions (Lentz, 2003, https://doi.org/10.1029/2003JC001859). The intrusions have a greater salinity difference from ambient water and penetrate large distances shoreward of the shelf break relative to the earlier climatology. The longer term data from the Ecosystem Monitoring program indicates that the increase in frequency occurred in 2000, and thus may be linked to a recent regime shift in the annual formation rate of Warm Core Rings by the Gulf Stream. Given the increased frequency of these salty intrusions, it will be necessary to properly resolve this process in numerical simulations in order to account for salt budgets for the continental shelf and slope.

Description: Data collection for the Shelf Research Fleet and salary for G. Gawarkiewicz, F. Bahr, and A. Ellertson were provided by the van Beuren Charitable Foundation of Newport, RI. G. Gawarkiewicz, F. Bahr, and A. Ellertson were also supported in analysis of this data by NSF grant OCE-1851261.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, O., Lee, T., Piecuch, C., Fukumori, I., Fenty, I., Frederikse, T., Menemenlis, D., Ponte, R., & Zhang, H. Local and remote forcing of interannual sea‐level variability at Nantucket Island. Journal of Geophysical Research: Oceans, 127(6), (2022): e2021JC018275, https://doi.org/10.1029/2021jc018275.

Description: The relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual variations in Nantucket dynamic sea level. Wind forcing explains 67% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies indicating that sea-level variations in the subpolar gyre and along the United States northeast coast can both be influenced by subpolar buoyancy forcing. Forward perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although coastally trapped waves can cause rapid Nantucket sea level response within a few weeks.

Description: This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). CGP was supported by NASA Sea Level Change Team awards 80NSSC20K1241 and 80NM0018D0004.

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(10), (2021): e2021GB007058, https://doi.org/10.1029/2021GB007058.

Description: Continental shelves are important sources of iron (Fe) in the land-dominated Arctic Ocean. To understand the export of Fe from the Arctic to Baffin Bay (BB) and the North Atlantic, we studied the alteration of the Fe signature in waters transiting the Canadian Arctic Archipelago (CAA). During its transit through the CAA, inflowing Arctic Waters from the Canada Basin become enriched in Fe as result of strong sediment resuspension and enhanced sediment-water interactions (non-reductive dissolution). These high Fe waters are exported to BB, where approximately 10.7 kt of Fe are delivered yearly from Lancaster Sound. Furthermore, if the two remaining main CAA pathways (Jones Sound and Nares Strait) are included, this shelf environment would be a dominant source term of Fe (dFe + pFe: 26–90 kt y−1) to Baffin Bay. The conservative Fe flux estimate (26 kt y−1) is 1.7–38 times greater than atmospheric inputs, and may be crucial in supporting primary production and nitrogen fixation in BB and beyond.

Description: This work was supported by the Natural Sciences and Engineering Research Council of Canada (Grant NSERC-CCAR), the Northern Scientific Training Program, and by the University of British Columbia through a Four Year Fellowship to B. Rogalla.

Description: 2022-03-20

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Durkin, C. A., Buesseler, K. O., Cetinic, I., Estapa, M. L., Kelly, R. P., & Omand, M. A visual tour of carbon export by sinking particles. Global Biogeochemical Cycles, 35(10), (2021): e2021GB006985, https://doi.org/10.1029/2021GB006985.

Description: To better quantify the ocean's biological carbon pump, we resolved the diversity of sinking particles that transport carbon into the ocean's interior, their contribution to carbon export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity of particles was used to model their contribution to particulate organic carbon (POC) flux. Measured POC fluxes were reasonably predicted by particle images. Nine particle types were identified, and most of the compositional variability was driven by the relative contribution of aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition varied across locations and seasons, the entire range of compositions was measured at a single well-observed location in the subarctic North Pacific over one month, across 500 m of depth. The magnitude of POC flux was not consistently associated with a dominant particle class, but particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with depth whereas certain other classes attenuated little or not at all with depth. Small particles (〈100 μm) consistently contributed ∼5% to total POC flux in samples with higher magnitude fluxes. The relative importance of these small particle classes (spherical mini pellets, short oval fecal pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux). Imaging approaches that resolve large variations in particle composition across ocean basins, depth, and time will help to better parameterize biological carbon pump models.

Description: This work was supported by an NSF EAGER award to C. A. Durkin (OCE-1703664), M. L. Estapa (OCE-1703422), and M. Omand (OCE-1703336), and also by the NASA EXPORTS program (80NSSC17K0662), a NASA New Investigator award to M. L. Estapa (NNX14AM01G), the Rhode Island Endeavor Program (RIEP), NASA's PACE mission, and the Schmidt Ocean Institute.

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(11), (2021): e2021JC017526, https://doi.org/10.1029/2021JC017526.

Description: The traditional understanding of the regional circulation in the Northwest Pacific marginal seas is that the Korean Coastal Current flows southward, following the isobaths of 20–50 m. However, an unusual tongue-shaped structure of cold water is observed in satellite SST data in January 2017, indicating a possible offshore spread of cold coastal water into the middle Southern Yellow Sea (SYS). Additional observations, including in situ hydrographic data as well as direct current measurement, also suggest this cross-shelf transport of the Korean Coastal Water in January 2017. Our analysis shows that this flow breaks through the isobaths at ∼37°N, moves southward between 50–75 m, and eventually veers anti-cyclonically at ∼35°N to join the western slope of the SYS. This circulation pattern is further supported by heat budget analysis. Diagnosis of potential vorticity (PV) reveals that the elevated negative PV anomaly imposed by surface wind stress favors this unusual cross-shelf transport. The change of wind pattern, although under a deceasing wind speed condition, plays an important role. This work provides an alternative view of the wintertime circulation pattern and motivates future studies of the variability of the coastal currents over interannual and longer time scales in the SYS.

Description: his study was supported by the Shandong Provincial Key Research and Development Program (2019JZZY020713, 2019GHY112057), the National Key Research and Development Program (2016YFC1401406, 2016YFA0600900), the National Natural Science Foundation of China (42076010, 42130403), National Fund Committee-Shandong joint fund (U1706215), the Fundamental Research Funds for the Central Universities (2020042010), and Ocean University of China-Woods Hole Oceanographic Institution Cooperative Research Initiative (24887).

Description: 2022-05-01

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Horner, T. J., Little, S. H., Conway, T. M., Farmer, J. R., Hertzberg, J. E., Janssen, D. J., Lough, A. J. M., McKay, J. L., Tessin, A., Galer, S. J. G., Jaccard, S. L., Lacan, F., Paytan, A., Wuttig, K., & GEOTRACES–PAGES Biological Productivity Working Group Members (2021). Bioactive trace metals and their isotopes as paleoproductivity proxies: an assessment using GEOTRACES-era data. Global Biogeochemical Cycles, 35(11), e2020GB006814. https://doi.org/10.1029/2020GB006814.

Description: Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history.

Description: T. J. Horner acknowledges support from NSF; S. H. Little from the UK Natural Environment Research Council (NE/P018181/1); T. M. Conway from the University of South Florida; and, J. R. Farmer from the Max Planck Society, the Tuttle Fund of the Department of Geosciences of Princeton University, the Grand Challenges Program of the Princeton Environmental Institute, and the Andlinger Center for Energy and the Environment of Princeton University.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Brinkmann, I., Ni, S., Schweizer, M., Oldham, V. E., Quintana Krupinski, N. B., Medjoubi, K., Somogyi, A., Whitehouse, M. J., Hansel, C. M., Barras, C., Bernhard, J. M., & Filipsson, H. L. Foraminiferal Mn/Ca as bottom-water hypoxia proxy: an assessment of Nonionella stella in the Santa Barbara Basin, USA. Paleoceanography and Paleoclimatology, 36(11), (2021): e2020PA004167, https://doi.org/10.1029/2020PA004167.

Description: Hypoxia is of increasing concern in marine areas, calling for a better understanding of mechanisms leading to decreasing dissolved oxygen concentrations ([O2]). Much can be learned about the processes and implications of deoxygenation for marine ecosystems using proxy records from low-oxygen sites, provided proxies, such as the manganese (Mn) to calcium (Ca) ratio in benthic foraminiferal calcite, are available and well calibrated. Here we report a modern geochemical data set from three hypoxic sites within the Santa Barbara Basin (SBB), USA, where we study the response of Mn/Caforam in the benthic foraminifer Nonionella stella to variations in sedimentary redox conditions (Mn, Fe) and bottom-water dissolved [O2]. We combine molecular species identification by small subunit rDNA sequencing with morphological characterization and assign the SBB N. stella used here to a new phylotype (T6). Synchrotron-based scanning X-ray fluorescence (XRF) imaging and Secondary Ion Mass Spectrometry (SIMS) show low Mn incorporation (partition coefficient DMn 〈 0.05) and limited proxy sensitivity of N. stella, at least within the range of dissolved [O2] (2.7–9.6 μmol/l) and Mnpore-water gradients (2.12–21.59 μmol/l). Notably, even though intra- and interspecimen Mn/Ca variability (33% and 58%, respectively) was only partially controlled by the environment, Mn/Caforam significantly correlated with both pore-water Mn and bottom-water [O2]. However, the prevalent suboxic bottom-water conditions and limited dissolved [O2] range complicate the interpretation of trace-elemental trends. Additional work involving other oxygenation proxies and samples from a wider oxygen gradient should be pursued to further develop foraminiferal Mn/Ca as an indicator for hypoxic conditions.

Description: We acknowledge funding from the Swedish Research Council VR (grant numbers 2017-04190 and 2017-00671), the Crafoord Foundation, and the Royal Physiographic Society in Lund, Sweden. Shiptime provided by US NSF IOS 1557430. We acknowledge SOLEIL for provision of synchrotron radiation facilities and the beamline NANOSCOPIUM (proposal number 20181115). The synchrotron-based experiments were supported by CALIPSOplus under the EU Framework Programme for Research and Innovation HORIZON 2020 (grant agreement 730872). The SIMS analyses were jointly supported by the Swedish Museum of Natural History and Swedish Research Council. This is NordSIMS contribution No. 694. J. M. Bernhard and C. M. Hansel also acknowledge funding from the US National Science Foundation (IOS 1557430).

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hawco, N. J., Barone, B., Church, M. J., Babcock-Adams, L., Repeta, D. J., Wear, E. K., Foreman, R. K., Bjorkman, K. M., Bent, S., Van Mooy, B. A. S., Sheyn, U., DeLong, E. F., Acker, M., Kelly, R. L., Nelson, A., Ranieri, J., Clemente, T. M., Karl, D. M., & John, S. G. Iron depletion in the deep chlorophyll maximum: mesoscale eddies as natural iron fertilization experiments. Global Biogeochemical Cycles, 35(12), (2021): e2021GB007112, https://doi.org/10.1029/2021GB007112.

Description: In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum (DCM) are isolated from atmospheric iron sources above and remineralized iron sources below. Reduced supply leads to a minimum in dissolved iron (dFe) near 100 m, but it is unclear if iron limits growth at the DCM. Here, we propose that natural iron addition events occur regularly with the passage of mesoscale eddies, which alter the supply of dFe and other nutrients relative to the availability of light, and can be used to test for iron limitation at the DCM. This framework is applied to two eddies sampled in the North Pacific Subtropical Gyre. Observations in an anticyclonic eddy center indicated downwelling of iron-rich surface waters, leading to increased dFe at the DCM but no increase in productivity. In contrast, uplift of isopycnals within a cyclonic eddy center increased supply of both nitrate and dFe to the DCM, and led to dominance of picoeukaryotic phytoplankton. Iron addition experiments did not increase productivity in either eddy, but significant enhancement of leucine incorporation in the light was observed in the cyclonic eddy, a potential indicator of iron stress among Prochlorococcus. Rapid cycling of siderophores and low dFe:nitrate uptake ratios also indicate that a portion of the microbial community was stressed by low iron. However, near-complete nitrate drawdown in this eddy, which represents an extreme case in nutrient supply compared to nearby Hawaii Ocean Time-series observations, suggests that recycling of dFe in oligotrophic ecosystems is sufficient to avoid iron limitation in the DCM under typical conditions.

Description: The expedition and analyses were supported by the Simons Foundation SCOPE Grant 329108 to S. G. John, M. J. Church, D. J. Repeta, B. Van Mooy, E. F. DeLong, and D. M. Karl. N. J. Hawco was supported by a Simons Foundation Marine Microbial Ecology and Evolution postdoctoral fellowship (602538) and Simons Foundation grant 823167.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hudak, M. R., Bindeman, I. N., Loewen, M. W., & Giachetti, T. Syn-eruptive hydration of volcanic ash records pyroclast-water interaction in explosive eruptions. Geophysical Research Letters, 48(23), (2021): e2021GL094141, https://doi.org/10.1029/2021GL094141.

Description: Magma-water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn- and post-eruptive diffusion of external (non-magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn-eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas 〈50 km from the vent. Diffusion models show that the high temperatures of pyroclast-water interactions (〉400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn-eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration.

Description: This work was supported by a Geological Society of America Bruce L. "Biff" Reed Scholarship Award and NSF Grant EAR 1822977.

Description: 2022-05-15

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12), (2021): e2021JC017860, https://doi.org/10.1029/2021JC017860.

Description: An appropriate proxy could help to better understand dissolved oxygen variations in the past, helping to predict potential outcomes of future environmental changes. In the Changjiang Estuary (China), the foraminifer Cribrononion subincertum (C. subincertum) shows a distinct population maximum in the topmost sediment, an indication of an epifaunal species. Therefore, the geochemical composition of C. subincertum tests could record changes in the region’s bottom water chemistry. Our results showed that Mn/Ca ratios in tests of living (Rose-Bengal stained) C. subincertum analyzed by LA-ICP-MS were responsive to variations of bottom water dissolved oxygen concentrations, with average foraminiferal Mn/Ca ratios three times higher during low-oxygen period than in winter. In the uppermost centimeters of sediment, wider ranges of foraminiferal Mn/Ca occurred in summer compared to winter ranges. Our results imply that this epifaunal benthic foraminiferal species could serve as a useful benthic monitor with the Mn/Ca ratios representing a reliable proxy of hypoxia in the past.

Description: This study was financially supported by the Natural Science Foundation of China (NSFC Grants 41876075, 42130410, and 41620104001), and Fundamental Research Funds for the Central Universities (201841007, 201962003, and 201961012). JMB acknowledges the Investment in Science Fund at WHOI, which supported her participation in this project.

Description: 2022-06-17

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(1), (2022): e2021GB007113, https://doi.org/10.1029/2021GB007113.

Description: Stordalen Mire is a peatland in the discontinuous permafrost zone in arctic Sweden that exhibits a habitat gradient from permafrost palsa, to Sphagnum bog underlain by permafrost, to Eriophorum-dominated fully thawed fen. We used three independent approaches to evaluate the annual, multi-decadal, and millennial apparent carbon accumulation rates (aCAR) across this gradient: seven years of direct semi-continuous measurement of CO2 and CH4 exchange, and 21 core profiles for 210Pb and 14C peat dating. Year-round chamber measurements indicated net carbon balance of −13 ± 8, −49 ± 15, and −91 ± 43 g C m−2 y−1 for the years 2012–2018 in palsa, bog, and fen, respectively. Methane emission offset 2%, 7%, and 17% of the CO2 uptake rate across this gradient. Recent aCAR indicates higher C accumulation rates in surface peats in the palsa and bog compared to current CO2 fluxes, but these assessments are more similar in the fen. aCAR increased from low millennial-scale levels (17–29 g C m−2 y−1) to moderate aCAR of the past century (72–81 g C m−2 y−1) to higher recent aCAR of 90–147 g C m−2 y−1. Recent permafrost collapse, greater inundation and vegetation response has made the landscape a stronger CO2 sink, but this CO2 sink is increasingly offset by rising CH4 emissions, dominated by modern carbon as determined by 14C. The higher CH4 emissions result in higher net CO2-equivalent emissions, indicating that radiative forcing of this mire and similar permafrost ecosystems will exert a warming influence on future climate.

Description: We would like to acknowledge the following funding in support of this project: Swedish Research Council (Vetenskapsrådet, VR) grants (NT 2007-4547 and NT 2013-5562 to P. Crill), U.S. Department of Energy grants (DE-SC0004632 and DE-SC0010580 to V. Rich and S. Saleska), and U.S. National Science Foundation MacroSystems Biology grant (NSF EF #1241037, PI Varner). This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under the Genomic Science program. We also acknowledge funding from the National Science Foundation for the EMERGE Biology Integration Institute, NSF Award #2022070.

Description: 2022-07-03

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(1), (2022): e2021JC017424, https://doi.org/10.1029/2021JC017424.

Description: By compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind-driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind-driven upwelling of CO2-rich bottom water can cause episodic outgassing. Seasonal surface ΔfCO2 (oceanic fCO2 – air fCO2) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer ΔfCO2 during the periods of 1989–2013 and 2014–2019, we suggest that temperature does drive long-term, multi-decadal patterns in ΔfCO2. In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea-ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high-resolution time series of inorganic carbonate parameters lengthen and short-term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long-term changes in the source/sink status of regional sub-Arctic seas.

Description: We gratefully acknowledge the support of the funding agencies that supported this analysis, including the New Sustained Observations for Arctic Research project and the DBO-NCIS project (NA14OAR4320158, NA19OAR4320074) from the NOAA Arctic Research Program.

Description: 2022-06-17

Description: © The Author(s), [year]. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Barreyre, T., Parnell‐Turner, R., Wu, J., & Fornari, D. Tracking crustal permeability and hydrothermal response during seafloor eruptions at the East Pacific Rise, 9°50’N. Geophysical Research Letters, 49(3), (2022): e2021GL095459, https://doi.org/10.1029/2021gl095459.

Description: Permeability controls energy and matter fluxes in deep-sea hydrothermal systems fueling a 'deep biosphere' of microorganisms. Here, we indirectly measure changes in sub-seafloor crustal permeability, based on the tidal response of high-temperature hydrothermal vents at the East Pacific Rise 9°50’N preceding the last phase of volcanic eruptions during 2005–2006. Ten months before the last phase of the eruptions, permeability decreased, first rapidly, and then steadily as the stress built up, until hydrothermal flow stopped altogether ∼2 weeks prior to the January 2006 eruption phase. This trend was interrupted by abrupt permeability increases, attributable to dike injection during last phase of the eruptions, which released crustal stress, allowing hydrothermal flow to resume. These observations and models suggest that abrupt changes in crustal permeability caused by magmatic intrusion and volcanic eruption can control first-order hydrothermal circulation processes. This methodology has the potential to aid eruption forecasting along the global mid-ocean ridge network.

Description: This research is funded by National Science Foundation (NSF) grants to D. J. Fornari and T. Barreyre (OCE-1949485), and to R. Parnell-Turner (OCE-1948936). T. Barreyre was supported by the University of Bergen, Norway.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fan, S., Cross, A. J., Prior, D. J., Goldsby, D. L., Hager, T. F., Negrini, M., & Qi, C. Crystallographic preferred orientation (CPO) development governs strain weakening in ice: insights from high-temperature deformation experiments. Journal of Geophysical Research: Solid Earth, 126(12), (2021): e2021JB023173, https://doi.org/10.1029/2021JB023173.

Description: Strain weakening leads to the formation of high-strain shear zones and strongly influences terrestrial ice discharge. In glacial flow models, strain weakening is assumed to arise from the alignment of weak basal planes—the development of a crystallographic preferred orientation, CPO—during flow. However, in experiments, ice strain weakening also coincides with grain size reduction, which has been invoked as a weakening mechanism in other minerals. To interrogate the relative contributions of CPO development and grain size reduction toward ice strain weakening, we deformed initially isotropic polycrystalline ice samples to progressively higher strains between −4 and −30°C. Microstructural measurements were subsequently combined with flow laws to separately model the mechanical response expected to arise from CPO development and grain size reduction. Magnitudes of strain weakening predicted by the constitutive flow laws were then compared with the experimental measurements. Flow laws that only consider grain size do not predict weakening with strain despite grain size reduction. In contrast, flow laws solely considering CPO effects can reproduce the measured strain weakening. Thus, it is reasonable to assume that strain weakening in ice is dominated by CPO development, at least under high temperature (Th ≥ 0.9) and high stress (〉1 MPa), like those in our experiments. We speculate that at high homologous temperatures (Th ≥ 0.9), CPO development will also govern the strain weakening behavior of other viscously anisotropic minerals, like olivine and quartz. Overall, we emphasize that geodynamic and glaciological models should incorporate CPOs to account for strain weakening, especially at high homologous temperatures.

Description: This work was supported by a NASA fund (grant no. NNX15AM69G) to David L. Goldsby and two Marsden Funds of the Royal Society of New Zealand (grant nos. UOO1116, UOO052) to David J. Prior. Sheng Fan was supported by the University of Otago doctoral scholarship, the Antarctica New Zealand doctoral scholarship, a research grant from New Zealand Ministry of Business, Innovation and Employment through the Antarctic Science Platform (ANTA1801) (grant no. ASP-023-03), and a New Zealand Antarctic Research Institute (NZARI) Early Career Researcher Seed Grant (grant no. NZARI 2020-1-5).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Slater, D., Carroll, D., Oliver, H., Hopwood, M., Straneo, F., Wood, M., Willis, J., & Morlighem, M. Characteristic depths, fluxes and timescales for Greenland’s tidewater glacier fjords from subglacial discharge‐driven upwelling during summer. Geophysical Research Letters, 49(10),(2022): e2021GL097081, https://doi.org/10.1029/2021gl097081.

Description: Greenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two-thirds of the glaciers. Our study provides a first pan-Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet-wide upwelling fluxes. This analysis provides important context for site-specific studies and is a step toward implementing fjord-scale heat, freshwater and nutrient fluxes in large-scale ice sheet and climate models.

Description: DAS acknowledges support from NERC Independent Research Fellowship NE/T011920/1. DAS and FS acknowledge support from NSF award 2020547. HO acknowledges support from a WHOI Postdoctoral Scholar award. MW and JKW performed this work at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Description: This paper is a review of the International Reference Ionosphere (IRI) project and model. IRI is recognized as the official standard for the Earth's ionosphere by the International Standardization Organization, the International Union of Radio Science, the Committee on Space Research, and the European Cooperation for Space Standardization. As requested by these organizations, IRI is an empirical (data-based) model representing the primary ionospheric parameters based on the long data record that exists from ground and space observations of the ionosphere. The core model describes monthly averages of the electron density, electron temperature, ion temperature, and ion composition globally in the altitude range from 60 to 2,000 km. Over time additional parameters were added in response to requests from the user community, this includes the equatorial ion drift, the occurrence probability of spread-F and of an F1 layer, auroral boundaries and the electron content from the bottom of the ionosphere to user-specified altitude. IRI has undergone extensive validations and is used for a wide range of applications in science, engineering, and education. This review is the result of many requests we have received for a comprehensive description of the model. It is also meant as a guide for users who are interested in a deeper understanding of the model architecture and its mathematical formalism.

Description: Published

Description: e2022RG000792

Description: 2A. Fisica dell'alta atmosfera

Description: JCR Journal

Description: At Mt. Etna volcano, flank eruptions are often accompanied by seismic swarms with damaging earthquakes; the most recent case-history is the 2018 flank eruption, associated with a destructive earthquake (Mw 5.0). In this paper, we analyze the earthquake and eruptive catalogs from 1800 to 2018, to produce quantitative estimates of the earthquake rate under the influence of flank eruptions. We quantify that 30% of the flank eruption onsets precede a major (i.e., damaging, Ix ≥ V–VI EMS) earthquake by 30 days or less; 18% of the major earthquakes follow a flank eruption onset in 30 days or less. Thus, we show that the probability of major earthquakes increases 5–10 times after the onset of flank eruptions and this effect lasts for 30–45 days. This is also observed after the end of the eruptions. Results indicate different relationships depending on the location of the volcano-tectonic systems considered individually (eruptive fissures, seismogenic faults). For instance, we describe a 10–20 times increased probability of earthquakes for 65–70 days after eruptions on the northeastern flank, and of new flank eruptions for 45–70 days after earthquakes of the Pernicana fault.

Description: Published

Description: e2022JB024145

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Post-orogenic back-arc magmatism is accompanied by hydrothermal ore deposits and mineralizations derived from mantle and crustal sources. We investigate Zannone Island (ZI), back-arc Tyrrhenian basin, Italy, to define the source(s) of mineralizing hydrothermal fluids and their relationships with the regional petrological-tectonic setting. On ZI, early Miocene thrusting was overprinted by late Miocene post-orogenic extension and related hydrothermal alteration. Since active submarine hydrothermal outflow is reported close to the island, Zannone provides an ideal site to determine the P-T-X evolution of the long-lived hydrothermal system. We combined field work with microstructural analyses on syn-tectonic quartz veins and carbonate mineralizations, X-ray diffraction analysis, microthermometry and element mapping of fluid inclusions (FIs), C, O, and clumped isotopes, and analyses of noble gases (He-Ne-Ar) and CO2 content in FIs. Our results document the evolution of a fluid system of magmatic origin with increasing mixing of meteoric fluids. Magmatic fluids were responsible for quartz veins precipitation at ∼125 to 150 MPa and ∼300°C–350°C. With the onset of extensional faulting, magmatic fluids progressively interacted with carbonate rocks and mixed with meteoric fluids, leading to (a) host rock alteration with associated carbonate and minor ore mineral precipitation, (b) progressive fluid neutralization, (c) cooling of the hydrothermal system (from ∼320°C to ∼86°C), and (d) embrittlement and fracturing of the host rocks. Both quartz and carbonate mineralizations show noble gases values lower than those from the adjacent active volcanic areas and submarine hydrothermal systems, indicating that the fossil-to-active hydrothermal history is associated with the emplacement of multiple magmatic intrusions.

Description: Published

Description: e2022GC010474

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: 7T. Variazioni delle caratteristiche crostali e "precursori"

Description: 9T. Geochimica dei fluidi applicata allo studio e al monitoraggio di aree sismiche

Description: 2TR. Ricostruzione e modellazione della struttura crostale

Description: JCR Journal

Description: We introduce a back-projection method to locate tremor sources using products of cross-correlation envelopes of time series between seismic stations. For a given subset of n stations, we calculate the (n − 1)th-order product of cross-correlation envelopes and we stack the back-projected products over combinations of station subsets.We show that compared to existing correlation methods and for realistic signal and noise characteristics, this way of combining information can significantly reduce the effects of correlated (spurious or irrelevant signals) and uncorrelated noise. Each back-projected product constitutes an individual localized estimate of the source locations, as opposed to a hyperbola for the existing correlation techniques, assuming a uniform velocity in two dimensions. We demonstrate the method with synthetic examples and a real-data example from tremor at Katla Volcano, Iceland, in July 2011. Despite very complex near-surface structure, including strong topography and thick ice cover, the method appears to produce robust estimates of tremor location.

Description: Published

Description: 3156–3164

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: 4V. Processi pre-eruttivi

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(12), (2022): e2022GL097779, https://doi.org/10.1029/2022GL097779.

Description: Outer-rise faults are predominantly concentrated near ocean trenches due to subducted plate bending. These faults play crucial roles in the hydration of subducted plates and the consequent subducting processes. However, it has not yet been possible to develop high-resolution structures of outer-rise faults due to the lack of near-field observations. In this study we deployed an ocean bottom seismometer (OBS) network near the Challenger Deep in the Southernmost Mariana Trench, between December 2016 and June 2017, covering both the overriding and subducting plates. We applied a machine-learning phase detector (EQTransformer) to the OBS data and found more than 1,975 earthquakes. An identified outer-rise event cluster revealed an outer-rise fault penetrating to depths of 50 km, which was inferred as a normal fault based on the extensional depth from tomographic images in the region, shedding new lights on water input at the southmost Mariana subduction zone.

Description: This study is supported by National Natural Science Foundation of China (Nos. 91858207, 92158205, 41890813), Hong Kong Research Grant Council Grants (No. 14304820), Award from CORE (a joint research center for ocean research between QNLM and HKUST), Chinese Academy of Sciences (Nos. Y4SL021001, QYZDY-SSW-DQC005), and Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (No. GML2019ZD0205), Faculty of Science at CUHK.

Description: 2022-12-06

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(17), (2021): e2021GL094128, https://doi.org/10.1029/2021GL094128.

Description: Ocean warming is causing declines of coral reefs globally, raising critical questions about the potential for corals to adapt. In the central equatorial Pacific, reefs persisting through recurrent El Niño heatwaves hold important clues. Using an 18-year record of coral cover spanning three major bleaching events, we show that the impact of thermal stress on coral mortality within the Phoenix Islands Protected Area (PIPA) has lessened over time. Disproportionate survival of extreme thermal stress during the 2009–2010 and 2015–2016 heatwaves, relative to that in 2002–2003, suggests that selective mortality through successive heatwaves may help shape coral community responses to future warming. Identifying and facilitating the conditions under which coral survival and recovery can keep pace with rates of warming are essential first steps toward successful stewardship of coral reefs under 21st century climate change.

Description: Support was provided by the US National Science Foundation (NSF) 1737311 to A. L. Cohen; The Atlantic Donor Advised Fund to A. L. Cohen; a Woods Hole Oceanographic Institution post-doctoral scholarship to M. D. Fox; the Robertson Foundation, The Prince Albert Foundation, the New England Aquarium, and the Akiko Shiraki Dynner Fund.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(11), (2022): e2021GL097618, https://doi.org/10.1029/2021GL097618.

Description: Krypton-81 dating provides new insights into the timing, mechanisms, and extent of meteoric flushing versus retention of saline fluids in the subsurface in response to changes in geologic and/or climatic forcings over 50 ka to 1.2 Ma year timescales. Remnant Paleozoic seawater-derived brines associated with evaporites in the Paradox Basin, Colorado Plateau, are beyond the 81Kr dating range (〉1.2 Ma) and have likely been preserved due to negative fluid buoyancy and low permeability. 81Kr dating of formation waters above the evaporites indicates topographically-driven meteoric recharge and salt dissolution since the Late Pleistocene (0.03–0.8 Ma). Formation waters below the evaporites (up to 3 km depth), in basal aquifers, contain relatively young meteoric water components (0.4–1.1 Ma based on 81Kr) that partially flushed remnant brines and dissolved evaporites. We demonstrate that recent, rapid denudation of the Colorado Plateau (〈4–10 Ma) activated deep, basinal-scale flow systems as recorded in 81Kr groundwater age distributions.

Description: Funding for this research was provided by the W.M. Keck Foundation, CIFAR Earth 4D Subsurface Science and Exploration program, NSF EAR (#2120733), National Key Research and Development Program of China (Grant No. 2016YFA0302200), and National Natural Science Foundation of China (Grants No. 41727901). McIntosh and Ballentine are fellows of the CIFAR Earth4D Subsurface Science and Exploration program.

Description: Rupture directivity and its potential frequency dependence is an open issue within the seismological community, especially for small‐to‐moderate events. Here, we provide a statistical overview based on empirical evidence of seismological observations, thanks to the large amount of high‐quality seismic recordings (more than 30,000 waveforms) from Central Italy, which represents an excellent and almost unique natural laboratory of normal faulting earthquakes in the magnitude range between 3.4 and 6.5 within the time frame 2008–2018. In order to detect an anisotropic distribution of ground motion amplitudes due to the rupture directivity, we fit the smoothed Fourier Amplitude Spectra (FAS) cleared of source‐, site‐ and path‐effects. According to our criteria, about 36% of the analyzed events (162 out of 456) are directive and the distribution of rupture direction is aligned with the strikes of the major faults of the Central Apennines. We find that the directivity is a band‐limited phenomenon whose width may extend up to five times the corner frequency. The results of this research provide useful insights to parameterize directivity, to be explicitly implemented in future ground motion modeling and scenario predictions.

Description: Published

Description: e2021JB023498

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(7), (2022): e2021JC018333, https://doi.org/10.1029/2021JC018333.

Description: As part of a project focused on the coastal fisheries of Isla Natividad, an island on the Pacific coast of Baja California, Mexico, we conducted a 2-1/2 year study of flows at two sites within the island's kelp forests. At one site (Punta Prieta), currents are tidal, whereas at the other site (Morro Prieto), currents are weaker and may be more strongly influenced by wind forcing. Satellite estimates of the biomass of the giant kelp (Macrocystis pyrifera) for this period varied between 0 (no kelp) and 3 kg/m2 (dense kelp forest), including a period in which kelp entirely was absent as a result of the 2014–2015 “Warm Blob” in the Eastern Pacific. During this natural “deforestation experiment”, alongshore velocities at both sites when kelp was present were substantially weaker than when kelp was absent, with low-frequency alongshore currents attenuated more than higher frequency ones, behavior that was the same at both sites despite differences in forcing. The attenuation of cross-shore flows by kelp was less than alongshore flows; thus, residence times for water inside the kelp forest, which are primarily determined by cross-shore velocities, were only weakly affected by the presence or absence of kelp. The flow changes we observed in response to changes in kelp density are important to the biogeochemical functioning of the kelp forest in that slower flows imply longer residence times, and, are also ecologically relevant in that reduced tidal excursions may lead to more localized recruitment of planktonic larvae.

Description: The work we describe here was supported by NSF grants DEB 1212124, OCE 1416934, OCE 1736830, and OCE 2022927, by an equipment grant from the Kuwait Foundation for the Advancement of Sciences, and through grants from the Marisla Foundation, Packard Foundation, and Walton Family Foundation.

Description: 2022-12-24

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(12), (2022): e2021GL097598, https://doi.org/10.1029/2021GL097598.

Description: The ocean is inhomogeneous in hydrographic properties with diverse water masses. Yet, how this inhomogeneity has evolved in a rapidly changing climate has not been investigated. Using multiple observational and reanalysis datasets, we show that the spatial standard deviation (SSD) of the global ocean has increased by 1.4 ± 0.1% in temperature and 1.5 ± 0.1% in salinity since 1960. A newly defined thermohaline inhomogeneity index, a holistic measure of both temperature and salinity changes, has increased by 2.4 ± 0.1%. Climate model simulations suggest that the observed ocean inhomogeneity increase is dominated by anthropogenic forcing and projected to accelerate by 200%–300% during 2015–2100. Geographically, the rapid upper-ocean warming at mid-to-low latitudes dominates the temperature inhomogeneity increase, while the increasing salinity inhomogeneity is mainly due to the amplified salinity contrast between the subtropical and subpolar latitudes.

Description: This work is supported by the Strategic Priority Research Program of Chinese Academy of Sciences (grant XDB42000000 and XDB40000000), the National Key R&D Program of China (2017YFA0603200), and the Shandong Provincial Natural Science Foundation (ZR2020JQ17), and the U.S. National Science Foundation Physical Oceanography Program (OCE- 2048336).

Description: 2022-12-23

Description: The impact of hazardous pyroclastic density currents (PDCs) increases with runout distance, which is strongly influenced by the mass flux. This article shows that the mass flux of a PDC may derive not only from vent discharge during the eruption, but also from partly hot, temporary stores (accumulations) of aerated pyroclastic material perched high on the volcano. The unforeseen PDC at Fuego volcano (Guatemala) on 3 June 2018 happened c.1.5 hr after the eruption climax. It overran the village of San Miguel Los Lotes causing an estimated 400+ fatalities. Analysis of the facies architecture of the deposit combined with video footage shows that a pulsatory block-and-ash flow flowed down the Las Lajas valley and rapidly waxed, the runout briefly increasing to 12.2 km as it filled and then spilled out of river channels, entered a second valley where it devastated the village and became increasingly erosive, prior to waning. Paleomagnetic analysis shows that the PDC contained only 6% very hot (〉590°C) clasts, 39% moderately hot (∼200°C–500°C) clasts, and 51% cool (〈200°C) clasts. This reveals that the block-and-ash flow mostly derived from collapse of loose and partly hot pyroclastic deposits, stored high on the volcano, gradually accumulated during the last 2–3 years. Progressive collapse of unstable deposits supplied the block-and-ash flow, causing a bulk-up process, waxing flow, channel overspill and unexpected runout. The study demonstrates that deposit-derived pyroclastic currents from perched temporary tephra stores pose a particular hazard that is easy to overlook and requires a new, different approach to hazard assessment and monitoring.

Description: Published

Description: e2021JB023699

Description: 1A. Geomagnetismo e Paleomagnetismo

Description: JCR Journal

Description: This paper is not subject to U.S. copyright. The definitive version was published in ten Brink, U. S., Vanacore, E. A., Fielding, E. J., Chaytor, J. D., Lopez-Venegas, A. M., Baldwin, W. E., Foster, D. S., & Andrews, B. D. Mature diffuse tectonic block boundary revealed by the 2020 southwestern Puerto Rico seismic sequence. Tectonics, 41(3), (2022): e2021TC006896, https://doi.org/10.1029/2021TC006896.

Description: Distributed faulting typically tends to coalesce into one or a few faults with repeated deformation. The progression of clustered medium-sized (≥Mw4.5) earthquakes during the 2020 seismic sequence in southwestern Puerto Rico (SWPR), modeling shoreline subsidence from InSAR, and sub-seafloor mapping by high-resolution seismic reflection profiles, suggest that the 2020 SWPR seismic sequence was distributed across several short intersecting strike-slip and normal faults beneath the insular shelf and upper slope of Guayanilla submarine canyon. Multibeam bathymetry map of the seafloor shows significant erosion and retreat of the shelf edge in the area of seismic activity as well as slope-parallel lineaments and submarine canyon meanders that typically develop over geological time. The T-axis of the moderate earthquakes further matches the extension direction previously measured on post early Pliocene (∼〉3 Ma) faults. We conclude that although similar deformation has likely taken place in this area during recent geologic time, it does not appear to have coalesced during this time. The deformation may represent the southernmost part of a diffuse boundary, the Western Puerto Rico Deformation Boundary, which accommodates differential movement between the Puerto Rico and Hispaniola arc blocks. This differential movement is possibly driven by the differential seismic coupling along the Puerto Rico—Hispaniola subduction zone. We propose that the compositional heterogeneity across the island arc retards the process of focusing the deformation into a single fault. Given the evidence presented here, we should not expect a single large event in this area but similar diffuse sequences in the future.

Description: 2022-08-08

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(6), (2022): e2021GL095559, https://doi.org/10.1029/2021GL095559.

Description: The valuable ecosystem services of salt marshes are spurring marsh restoration projects around the world. However, it is difficult to determine the final vegetated area based on physical drivers. Herein, we use a 3D fully coupled vegetation-hydrodynamic-morphological modeling system to simulate the final vegetation cover and the timescale to reach it under various forcing conditions. Marsh development in our simulations can be divided in three distinctive phases: A preparation phase characterized by sediment accumulation in the absence of vegetation, an encroachment phase in which the vegetated area grows, and an adjustment phase in which the vegetated area remains relatively constant while marsh accretes vertically to compensate for sea level rise. Sediment concentration, settling velocity, sea level rise, and tidal range each comparably affect equilibrium coverage and timescale in different ways. Our simulations show that the Unvegetated-Vegetated Ratio also relates to sediment budget in marsh development under most conditions.

Description: This study was supported by the Department of the Interior Hurricane Sandy Recovery program (ID G16AC00455), NSF awards 1637630 (PIE LTER) and 1832221 (VCR LTER), and China Scholarship Council.

Description: 2022-09-16

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(10),(2021): e2021JB022050, https://doi.org/10.1029/2021JB022050.

Description: On-fault earthquake magnitude distributions are calculated for northern Caribbean faults using estimates of fault slip and regional seismicity parameters. Integer programming, a combinatorial optimization method, is used to determine the optimal spatial arrangement of earthquakes sampled from a truncated Gutenberg-Richter distribution that minimizes the global misfit in slip rates on a complex fault system. Slip rates and their uncertainty on major faults are derived from a previously published GPS block model for the region, with fault traces determined from offshore geophysical mapping and previously published onshore studies. The optimal spatial arrangement of the sampled earthquakes is compared with the 500-year history of earthquake observations. Rupture segmentation of the subduction interface along the Hispaniola-Puerto Rico Trench (PRT) fault and seismic coupling on the PRT fault appear to exert the primary control over this spatial arrangement. Introducing a rupture barrier for the Hispaniola-PRT fault northwest of Mona Passage, based on geophysical and seismicity observations, and assigning a low slip rate of 2 mm/yr on the PRT fault are most consistent with historical earthquakes in the region. The addition of low slip-rate secondary faults as well as segmentation of the Hispaniola and Septentrional strike-slip fault improves the consistency with historical seismicity. An important observation from the modeling is that varying the slip rate on the PRT fault and different segmentation scenarios result in significant changes to the optimal magnitude distribution on faults farther away. In general, optimal on-fault magnitude distributions are more complex and inter-dependent than is typically assumed in probabilistic seismic hazard analysis and probabilistic tsunami hazard analysis.

Description: Funding for this study is from the U.S. Geological Survey Coastal and Marine Hazards and Resources Program.

Description: 2022-04-11

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Loescher, H., Vargas, R., Mirtl, M., Morris, B., Pauw, J., Yu, X., Kutsch, W., Mabee, P., Tang, J., Ruddell, B., Pulsifer, P., Bäck, J., Zacharias, S., Grant, M., Feig, G., Zheng, L., Waldmann, C., & Genazzio, M. Building a global ecosystem research infrastructure to address global grand challenges for macrosystem ecology. Earth’s Future, 10(5), (2022): e2020EF001696, https://doi.org/10.1029/2020ef001696.

Description: The development of several large-, “continental”-scale ecosystem research infrastructures over recent decades has provided a unique opportunity in the history of ecological science. The Global Ecosystem Research Infrastructure (GERI) is an integrated network of analogous, but independent, site-based ecosystem research infrastructures (ERI) dedicated to better understand the function and change of indicator ecosystems across global biomes. Bringing together these ERIs, harmonizing their respective data and reducing uncertainties enables broader cross-continental ecological research. It will also enhance the research community capabilities to address current and anticipate future global scale ecological challenges. Moreover, increasing the international capabilities of these ERIs goes beyond their original design intent, and is an unexpected added value of these large national investments. Here, we identify specific global grand challenge areas and research trends to advance the ecological frontiers across continents that can be addressed through the federation of these cross-continental-scale ERIs.

Description: This manuscript is in part the product of several workshops and ongoing GERI development. The first workshop was the Terrestrial Ecosystem Research Network (TERN) sponsored and entitled: “Towards a Global Ecosystem Observatory”, 5–7 March 2017, University of Queensland, Brisbane Australia. Another workshop was sponsored by Chinese Academy of Sciences (CAS) and entitled: “Global Integrated Research Infrastructure component in Next Generation ILTER”, 17–20 April, 2018, South China Botanical Garden, Zhaoqing, Guangdong Province, China. The National Science Foundation (NSF) supported two workshops. The first was entitled: ‘Building a Global Ecological Understanding’ held at the University of Delaware, Newark Delaware, 3–6 June, 2016 (NSF 1347883) and the second entitled: “Global Environmental Research Infrastructure (GERI) Planning Workshop”, held at NEON HQ, Boulder Colorado, 25–27 June 2019 (NSF 1917180). The authors wish to thank the workshop attendees for their thoughtful contributions. NEON is a project sponsored by the NSF and managed under cooperative support agreement (DBI-1029808) to Battelle.

Description: This paper is not subject to U.S. copyright. The definitive version was published in Hegermiller, C. A., Warner, J. C., Olabarrieta, M., Sherwood, C. R., & Kalra, T. S. Modeling of barrier breaching during hurricanes Sandy and Matthew. Journal of Geophysical Research: Earth Surface, 127(3), (2022): e2021JF006307, https://doi.org/10.1029/2021JF006307.

Description: Physical processes driving barrier island change during storms are important to understand to mitigate coastal hazards and to evaluate conceptual models for barrier evolution. Spatial variations in barrier island topography, landcover characteristics, and nearshore and back-barrier hydrodynamics can yield complex morphological change that requires models of increasing resolution and physical complexity to predict. Using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system, we investigated two barrier island breaches that occurred on Fire Island, NY during Hurricane Sandy (2012) and at Matanzas, FL during Hurricane Matthew (2016). The model employed a recently implemented infragravity (IG) wave driver to represent the important effects of IG waves on nearshore water levels and sediment transport. The model simulated breaching and other changes with good skill at both locations, resolving differences in the processes and evolution. The breach simulated at Fire Island was 250 m west of the observed breach, whereas the breach simulated at Matanzas was within 100 m of the observed breach. Implementation of the vegetation module of COAWST to allow three-dimensional drag over dune vegetation at Fire Island improved model skill by decreasing flows across the back-barrier, as opposed to varying bottom roughness that did not positively alter model response. Analysis of breach processes at Matanzas indicated that both far-field and local hydrodynamics influenced breach creation and evolution, including remotely generated waves and surge, but also surge propagation through back-barrier waterways. This work underscores the importance of resolving the complexity of nearshore and back-barrier systems when predicting barrier island change during extreme events.

Description: C. A. Hegermiller is grateful to the U.S. Geological Survey (USGS) Mendenhall Research Fellowship Program for support. This project was supported by the USGS Coastal and Marine Geology Program and the Office of Naval Research, Increasing the Fidelity of Morphological Storm Impact Predictions Project. M. Olabarrieta acknowledges support from the NSF project OCE-1554892.

Description: 2022-07-26

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zeigler, S. L., Gutierrez, B. T., Lentz, E. E., Plant, N. G., Sturdivant, E. J., & Doran, K. S. Predicted sea-level rise-driven biogeomorphological changes on Fire Island, New York: implications for people and plovers. Earth’s Future, 10(4), (2022): e2021EF002436, https://doi.org/10.1029/2021EF002436.

Description: Forecasting biogeomorphological conditions for barrier islands is critical for informing sea-level rise (SLR) planning, including management of coastal development and ecosystems. We combined five probabilistic models to predict SLR-driven changes and their implications on Fire Island, New York, by 2050. We predicted barrier island biogeomorphological conditions, dynamic landcover response, piping plover (Charadrius melodus) habitat availability, and probability of storm overwash under three scenarios of shoreline change (SLC) and compared results to observed 2014/2015 conditions. Scenarios assumed increasing rates of mean SLC from 0 to 4.71 m erosion per year. We observed uncertainty in several morphological predictions (e.g., beach width, dune height), suggesting decreasing confidence that Fire Island will evolve in response to SLR as it has in the past. Where most likely conditions could be determined, models predicted that Fire Island would become flatter, narrower, and more overwash-prone with increasing rates of SLC. Beach ecosystems were predicted to respond dynamically to SLR and migrate with the shoreline, while marshes lost the most area of any landcover type compared to 2014/2015 conditions. Such morphological changes may lead to increased flooding or breaching with coastal storms. However—although modest declines in piping plover habitat were observed with SLC—the dynamic response of beaches, flatter topography, and increased likelihood of overwash suggest storms could promote suitable conditions for nesting piping plovers above what our geomorphology models predict. Therefore, Fire Island may offer a conservation opportunity for coastal species that rely on early successional beach environments if natural overwash processes are encouraged.

Description: Funding for this work was provided by the U.S. Geological Survey's Coastal and Marine Hazards and Resources Program, with supplemental funding through the Disaster Relief Act.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chandanpurkar, H. A., Lee, T., Wang, X., Zhang, H., Fournier, S., Fenty, I., Fukumori, I., Menemenlis, D., Piecuch, C. G., Reager, J. T., Wang, O., & Worden, J. Influence of nonseasonal river discharge on sea surface salinity and height. Journal of Advances in Modeling Earth Systems, 14(2), (2022): e2021MS002715, https://doi.org/10.1029/2021MS002715.

Description: River discharge influences ocean dynamics and biogeochemistry. Due to the lack of a systematic, up-to-date global measurement network for river discharge, global ocean models typically use seasonal discharge climatology as forcing. This compromises the simulated nonseasonal variation (the deviation from seasonal climatology) of the ocean near river plumes and undermines their usefulness for interdisciplinary research. Recently, a reanalysis-based daily varying global discharge data set was developed, providing the first opportunity to quantify nonseasonal discharge effects on global ocean models. Here we use this data set to force a global ocean model for the 1992–2017 period. We contrast this experiment with another experiment (with identical atmospheric forcings) forced by seasonal climatology from the same discharge data set to isolate nonseasonal discharge effects, focusing on sea surface salinity (SSS) and sea surface height (SSH). Near major river mouths, nonseasonal discharge causes standard deviations in SSS (SSH) of 1.3–3 practical salinity unit (1–2.7 cm). The inclusion of nonseasonal discharge results in notable improvement of model SSS against satellite SSS near most of the tropical-to-midlatitude river mouths and minor improvement of model SSH against satellite or in-situ SSH near some of the river mouths. SSH changes associated with nonseasonal discharge can be explained by salinity effects on halosteric height and estimated accurately through the associated SSS changes. A recent theory predicting river discharge impact on SSH is found to perform reasonably well overall but underestimates the impact on SSH around the global ocean and has limited skill when applied to rivers near the equator and in the Arctic Ocean.

Description: This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004) with support from the Physical Oceanography (PO) and Modeling, Analysis, and Prediction (MAP) Programs. High-end computing resources for the numerical simulation were provided by the NASA Advanced Supercomputing Division at the Ames Research Center.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in German, C., Baumberger, T., Lilley, M., Lupton, J., Noble, A., Saito, M., Thurber, A., & Blackman, D. Hydrothermal exploration of the southern Chile Rise: sediment‐hosted venting at the Chile Triple Junction. Geochemistry Geophysics Geosystems, 23(3), (2022): e2021GC010317, https://doi.org/10.1029/2021gc010317.

Description: We report results from a hydrothermal plume survey along the southernmost Chile Rise from the Guamblin Fracture Zone to the Chile Triple Junction (CTJ) encompassing two segments (93 km cumulative length) of intermediate spreading-rate mid-ocean ridge axis. Our approach used in situ water column sensing (CTD, optical clarity, redox disequilibrium) coupled with sampling for shipboard and shore based geochemical analyses (δ3He, CH4, total dissolvable iron (TDFe) and manganese, (TDMn)) to explore for evidence of seafloor hydrothermal venting. Across the entire survey, the only location at which evidence for submarine venting was detected was at the southernmost limit to the survey. There, the source of a dispersing hydrothermal plume was located at 46°16.5’S, 75°47.9’W, coincident with the CTJ itself. The plume exhibits anomalies in both δ3He and dissolved CH4 but no enrichments in TDFe or TDMn beyond what can be attributed to resuspension of sediments covering the seafloor where the ridge intersects the Chile margin. These results are indicative of sediment-hosted venting at the CTJ.

Description: We acknowledge University of California Ship Funds for their support of that shiptime and the NOAA Ocean Exploration and Research Grant NA08OAR4600757 which supported the research presented here. Finally, we thank two anonymous reviewers whose important contributions helped to improve the final version of this paper. This is PMEL contribution number 5341.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(1), (2022): e2021JC017927, https://doi.org/10.1029/2021JC017927.

Description: Observations and high-resolution numerical modeling are used to investigate the dynamical processes related to the initiation of an advective Marine Heatwave in the Middle Atlantic Bight of the Northwest Atlantic continental shelf. Both the observations and the model identify two significant cross-shelf intrusions in November 2016 and January 2017, with the latter inducing large-magnitude water mass anomalies across the shelf. Model prognostic fields reveal the importance of the combination of cyclonic eddies or ringlets and upwelling-favorable winds in producing the large-distance cross-shelf penetration and temperature/salinity anomalies. The cyclonic eddies in close proximity to the shelfbreak set up local along-isobath pressure gradients and provide favorable conditions for the intensification of the shelfbreak front, both processes driving cross-isobath intrusions of warm, salty offshore water onto the outer continental shelf. Subsequently, strong and persistent upwelling-favorable winds drive a rapid, bottom intensified cross-shelf penetration in January 2017 composed of the anomalous water mass off the shelfbreak. The along-shelf settings including realistic representation of bathymetric features are essential in the characteristics of the cross-shelf penetration. The results highlight the importance of smaller scale cyclonic eddies and the intricacy of the interplay between multiple processes to drive significant cross-shelf events.

Description: This work was supported by Woods Hole Oceanographic Institution (WHOI) Independent Research and Development (IR&D) award and National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) Climate Variability and Predictability (CVP) program under grant NA20OAR4310398. Numerical modeling work was conducted at WHOI High-Performance Computing cluster Poseidon with startup support to Ke Chen.

Description: 2022-06-08

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49, (2022): e2021GL096530, https://doi.org/10.1029/2021gl096530.

Description: Water-mass transports in the vast and seemingly quiescent abyssal ocean, basically along topographically-guided pathways, play a pivotal role in the Earth's climate. The pulse of abyssal circulations can be taken with observations at topographic choke points. The Yap-Mariana Junction (YMJ) is the exclusive choke point through which the Lower Circumpolar Deep Water (LCDW) enters the Philippine Sea. Here, we quantify the LCDW transport and its variability based on mooring observations at the YMJ and the Mariana Trench (MT). The LCDW flows northward toward the Philippine Sea as an intensified current on the western side of the YMJ, with maximum mean velocity reaching 7.6 cm/s. The mean LCDW transports through the MT and the YMJ are 2.2 ± 1.0 Sv and 2.1 ± 0.4 Sv, respectively. Reversal flow at autumn in both the YMJ and MT is captured, indicating seasonal variability of the abyssal flow.

Description: This work was supported by the National Natural Science Foundation of China (Grant no. 91858203, 91958205, 42076027, 41676011), the National Key R&D Program of China (Grant no. 2018YFC0309800), the Global Change and Air–Sea Interaction Project (Grant no. GASI-IPOVAI-01-03, GASI-IPOVAI-01-02).

Description: 2022-07-28

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wu, J., Parnell‐Turner, R., Fornari, D., Kurras, G., Berrios‐Rivera, N., Barreyre, T., & McDermott, J. Extent and volume of lava flows erupted at 9°50’N, East Pacific Rise in 2005–2006 from autonomous underwater vehicle surveys. Geochemistry Geophysics Geosystems, 23, (2022): e2021GC010213, https://doi.org/10.1029/2021gc010213.

Description: Seafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid-ocean ridges. Volcanic eruptions in 2005–2006 at 9°50′N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near-bottom bathymetric data. We present near-bottom data collected during 19 autonomous underwater vehicle (AUV) Sentry dives at 9°50′N in 2018, 2019, and 2021. The resulting 1 m-resolution bathymetric grid and 20 cm-resolution sidescan sonar images cover 115 km2, and span the entire area of the 2005–2006 eruptions, including an 8 km2 pre-eruption survey collected with AUV ABE in 2001. Pre- and post-eruption surveys, combined with sidescan sonar images and seismo-acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005–2006 eruptions, lava flowed up to ∼3 km away from the axial summit trough, covering an area of ∼20.8 km2; ∼50% larger than previously thought. Where pre- and post-eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from ∼1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that ∼57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9°50′N area.

Description: This project is supported by National Science Foundation grants OCE-1834797, OCE-1949485, OCE-194893, OCE-1949938, and by Scripps Institution of Oceanography's David DeLaCour Endowment Fund.

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(12), (2021): e2021JB022201, https://doi.org/10.1029/2021JB022201.

Description: Sparse wide-angle seismic profiling supported by coincident reflection imaging has been instrumental for advancing our knowledge about rifted margins. Nevertheless, features of critical importance for understanding rifting processes have been poorly resolved. We derive a high-resolution velocity model by applying full waveform inversion to the dense OETR-2009 wide-angle seismic profile crossing the northeastern Nova Scotian margin. We then create a coincident reflection image by prestack depth migrating the multichannel seismic data. This allows for the first detailed interpretation of the structures related to the final stages of continental breakup and incipient oceanic accretion at the Eastern North America Margin. Our interpretation includes a hyperextended continental domain overlying partially serpentinized mantle, followed by a 10-km-wide domain consisting of a continental block surrounded by layered and bright reflectors indicative of magmatic extrusions. A major fault, representing the continent-ocean boundary, marks a sharp seaward transition to a 16-km-wide domain characterized by smoother basement with chaotic reflectors, where no continental materials are present and a 3-km-thick embryonic oceanic crust overlying partially serpentinized mantle is created by the breakup magmatism. Further seaward, thin oceanic crust overlies the serpentinized mantle suggesting magma-poor oceanic spreading with variable magma supply as determined from variable basement topography, 2–4 km thick volcanic layer, and magnetic anomalies. Our results demonstrate that magmatism played an important role in the lithospheric breakup of the area crossed by the OETR-2009 profile. Considering that the northeastern Nova Scotian margin has been classified as amagmatic, large margin-parallel variations in magma supply likely characterize a single rift segment.

Description: H. Jian was supported by the Ocean Frontier Institute International Postdoctoral Fellowship at Dalhousie University and NSF grant OCE-2001012.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Rovira‐Navarro, M., Katz, R., Liao, Y., Wal, W., & Nimmo, F. The tides of Enceladus’ porous core. Journal of Geophysical Research: Planets, 127, (2022): e2021JE007117, https://doi.org/10.1029/2021je007117.

Description: The inferred density of Enceladus' core, together with evidence of hydrothermal activity within the moon, suggests that the core is porous. Tidal dissipation in an unconsolidated core has been proposed as the main source of Enceladus' geological activity. However, the tidal response of its core has generally been modeled assuming it behaves viscoelastically rather than poroviscoelastically. In this work, we analyze the poroviscoelastic response to better constrain the distribution of tidal dissipation within Enceladus. A poroviscoelastic body has a different tidal response than a viscoelastic one; pressure within the pores alters the stress field and induces a Darcian porous flow. This flow represents an additional pathway for energy dissipation. Using Biot's theory of poroviscoelasticity, we develop a new framework to obtain the tidal response of a spherically symmetric, self-gravitating moon with porous layers and apply it to Enceladus. We show that the boundary conditions at the interface of the core and overlying ocean play a key role in the tidal response. The ocean hinders the development of a large-amplitude Darcian flow, making negligible the Darcian contribution to the dissipation budget. We therefore infer that Enceladus' core can be the source of its geological activity only if it has a low rigidity and a very low viscosity. A future mission to Enceladus could test this hypothesis by measuring the phase lags of tidally induced changes of gravitational potential and surface displacements.

Description: M. Rovira-Navarro has been financially supported by the Space Research User Support program of the Netherlands Organization for Scientific Research (NWO) under contract number ALW-GO/16–19. F. Nimmo and Y. Liao have been supported by the National Aeronautics and Space Administration (NASA) Solar System Workings (SSW) Program, Grant No. 80NSSC21K0158. R. Katz acknowledges funding from the Leverhulme Trust through a Research Project Grant.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(5), (2022): e2021JC018359, https://doi.org/10.1029/2021JC018359.

Description: Climate change is transforming the Arctic Ocean in unprecedented ways which can be most directly observed in the systematic decline in seasonal ice coverage. From the collection and analysis of particulate and dissolved activities of 210Po and 210Pb from four deepwater superstations, as a part of the US Arctic GEOTRACES cruise during 2015, and in conjunction with previously published data, the temporal and spatial variations in their activities, inventories and residence times are evaluated. The results show that the partitioning of particulate and dissolved phases has changed significantly in the 8 years between 2007 and 2015, while the total 210Po and 210Pb activities have remained relatively unchanged. Observed total 210Po/210Pb activity ratio was less than unity in all deepwater stations, implying disequilibria in the entire water column. From the distribution of total 210Po and 210Pb in the upper 500 m of all major Arctic Basins, the derived scavenging efficiencies decrease as per the following sequence: Makarov Basin 〉 Gakkel Bridge 〉 Canada Basin Nansen Basin ∼ Amundsen Basin 〉 Alpha Ridge, which is the reverse order of the calculated residence times of 210PoT. The scavenging intensities differ between the fully ice-covered, partially ice-covered, and no ice-covered stations, as observed from the differences in the average activities of 210Po and 210Pb. The average settling velocity of particulate matter based on the 210Pb activity is similar to the published values based on 230Th, indicating removal mechanism(s) of Th and Pb is (are) similar.

Description: This work was supported by National Science Foundation grants (NSF-PLR-1434578, MB; and NSF-OPP-1435376 KM). Mark Baskaran (PI) and Kanchan Maiti were independently funded by NSF.

Description: 2022-10-06

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(6), (2022): e2022GB007330, https://doi.org/10.1029/2022gb007330.

Description: Processes controlling dissolved barium (dBa) were investigated along the GEOTRACES GA03 North Atlantic and GP16 Eastern Tropical Pacific transects, which traversed similar physical and biogeochemical provinces. Dissolved Ba concentrations are lowest in surface waters (∼35–50 nmol kg−1) and increase to 70–80 and 140–150 nmol kg−1 in deep waters of the Atlantic and Pacific transects, respectively. Using water mass mixing models, we estimate conservative mixing that accounts for most of dBa variability in both transects. To examine nonconservative processes, particulate excess Ba (pBaxs) formation and dissolution rates were tracked by normalizing particulate excess 230Th activities. Th-normalized pBaxs fluxes, with barite as the likely phase, have subsurface maxima in the top 1,000 m (∼100–200 μmol m−2 year−1 average) in both basins. Barite precipitation depletes dBa within oxygen minimum zones from concentrations predicted by water mass mixing, whereas inputs from continental margins, particle dissolution in the water column, and benthic diffusive flux raise dBa above predications. Average pBaxs burial efficiencies along GA03 and GP16 are ∼37% and 17%–100%, respectively, and do not seem to be predicated on barite saturation indices in the overlying water column. Using published values, we reevaluate the global freshwater dBa river input as 6.6 ± 3.9 Gmol year−1. Estuarine mixing processes may add another 3–13 Gmol year−1. Dissolved Ba inputs from broad shallow continental margins, previously unaccounted for in global marine summaries, are substantial (∼17 Gmol year−1), exceeding terrestrial freshwater inputs. Revising river and shelf dBa inputs may help bring the marine Ba isotope budget more into balance.

Description: The International GEOTRACES Programme is possible in part thanks to the support from the U.S. National Science Foundation (Grant OCE-1840868) to the Scientific Committee on Oceanic Research (SCOR). This research was supported by the National Science Foundation under Grant No. NSF OCE-0927951, NSF OCE-1137851, NSF OCE-1261214, and NSF OCE-1925503 to A. M. Shiller; NSF OCE-1829563 to R. F. Anderson; NSF OCE-0927064 and NSF OCE-1233688 to R. F. Anderson and M. Q. Fleisher; NSF OCE-0927754 to R. Lawrence Edwards; NSF OCE-1233903 to R. Lawrence Edwards and H. Cheng; NSF OCE-0926860 to L. F. Robinson; NSF OCE-0963026 and NSF OCE-1518110 to P. J. Lam; and NSF OCE-1232814 to B. S. Twining.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Reyes-Macaya, D., Hoogakker, B., Martinez-Mendez, G., Llanillo, P. J., Grasse, P., Mohtadi, M., Mix, A., Leng, M. J., Struck, U., McCorkle, D. C., Troncoso, M., Gayo, E. M., Lange, C. B., Farias, L., Carhuapoma, W., Graco, M., Cornejo-D’Ottone, M., De Pol Holz, R., Fernandez, C., Narvaez, D., Vargas, C. A., García-Araya, F., Hebbeln, D. Isotopic characterization of water masses in the Southeast Pacific Region: paleoceanographic implications. Journal of Geophysical Research: Oceans, 127(1), (2022): e2021JC017525, https://doi.org/10.1029/2021JC017525.

Description: In this study, we used stable isotopes of oxygen (δ18O), deuterium (δD), and dissolved inorganic carbon (δ13CDIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ18O and δD can be used to differentiate between SAAW-STW, SAAW-ESSW, and ESSW-AAIW. δ13CDIC signatures can be used to differentiate between STW-ESSW (oceanic section), SAAW-ESSW, ESSW-AAIW, and AAIW-PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present-day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.

Description: R/V Sonne cruises (SO102, SO211 ad SO245) were financed by the German Federal Ministry of Education and Research projects #03G0102A, #03G0211A and #03G0245A. SO261 cruise was funded by the HADES-ERC Advanced Grant (“Benthic diagenesis and microbiology of hadal trenches” Grant agreement No. 669947) awarded to R. N. Glud (SDU, Denmark). SO245 cruise recived contributions from the Max Planck Society (Germany), the German State of Lower Saxony, the National Environmental Research Council of Great Britain and the Science Foundation of Ireland. R/V Meteor cruise M93 was financed by the Sonderforschungsbereich 754 “Climate-Biogeochemistry Interactions in the Tropical Ocean” (www.sfb754.de), which is supported by the Deutsche Forschungsgemeinschaft. “Expedición TAITAO” was financed by the grant “Concurso Nacional de Asignación de Tiempo de Buque ASG-61 Cabo de Hornos” AUB180003, FONDECyT grants 11161091 (DN), 1180954 (CF), and the COPAS Sur-Austral Center (CONICYT PIA APOYO CCTE AFB170006). Sampling at Time-Series station 18 off Concepción during 2015 was funded by several FONDECYT/ANID grants from researchers at the Department of Oceanography and Research Line 5 of COPAS Sur-Austral (UdeC). ANID—Chile National Competition for ship time (AUB 150006/12806) financed the expedition LowpHOX organized by the Millennium Institute of Oceanography (IMO). The expedition Crio1218 was financed by the PPR 137 titled “Proyecto de Estudio Integrado del Afloramiento Costero Frente a Perú" and sponsored by IMARPE-Perú. Additional funding was provided by the ANID—Millennium Science Initiative Program—NCN19_153 (Millennium Nucleus UPWELL), ANID/FONDAP (CR)2 15110009 (LF and EMG), FONDECYT Grant 1210171 (CAV), ANID/FONDAP IDEAL 15150003 (CBL), and the Millennium Institute of Oceanography (IMO, ICN12_019). Dharma A. Reyes-Macaya was supported by Becas Chile (17342817-0), DAAD (57144001) and FARGO project (FAte of ocean oxygenation in a waRminG wOrld, UKRI).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Liao, F., Liang, X., Li, Y., & Spall, M. Hidden upwelling systems associated with major western boundary currents. Journal of Geophysical Research: Oceans. 127, (2022): e2021JC017649, https://doi.org/10.1029/2021jc017649.

Description: Western boundary currents (WBCs) play an essential role in regulating global climate. In contrast to their widely examined horizontal motions, less attention has been paid to vertical motions associated with WBCs. Here, we examine vertical motions associated with the major WBCs by analyzing vertical velocity from five ocean synthesis products and one eddy-resolving ocean simulation. These data reveal robust and intense subsurface upwelling systems, which are primarily along isopycnal surfaces, in five major subtropical WBC systems. These upwelling systems are part of basin-scale overturning circulations and are likely driven by meridional pressure gradients along the western boundary. Globally, the WBC upwelling contributes significantly to the vertical transport of water mass and ocean properties and is an essential yet overlooked branch of the global ocean circulation. In addition, the WBC upwelling intersects the oceanic euphotic and mixed layers, and thus likely plays an important role in ocean biological and chemical processes by transporting nutrients, carbon and other tracers vertically inside the ocean. This study calls for more research into the dynamics of the WBC upwelling and their role in the ocean and climate systems.

Description: X. Liang is supported by the National Science Foundation through Grants OCE-2021274, OCE-2122507, and the Alfred P. Sloan Foundation through Grant FG-2019-12536. M. Spall is supported through the National Science Foundation Grants OCE-1947290 and OCE-2122633.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 37(1), (2022): e020PA004137, https://doi.org/10.1029/2020PA004137.

Description: Reconstructions of aeolian dust flux to West African margin sediments can be used to explore changing atmospheric circulation and hydroclimate over North Africa on millennial to orbital timescales. Here, we extend West African margin dust flux records back to 37 ka in a transect of sites from 19° to 27°N, and back to 67 ka at Ocean Drilling Program (ODP) Hole 658C, in order to explore the interplay of orbital and high-latitude forcings on North African climate and make quantitative estimates of dust flux during the core of the Last Glacial Maximum (LGM). The ODP 658C record shows a Green Sahara interval from 60 to 50 ka during a time of high Northern Hemisphere summer insolation, with dust fluxes similar to levels during the early Holocene African Humid Period, and an abrupt peak in flux during Heinrich event 5a (H5a). Dust fluxes increase from 50 to 35 ka while the high-latitude Northern Hemisphere cools, with peaks in dust flux associated with North Atlantic cool events. From 35 ka through the LGM dust deposition decreases in all cores, and little response is observed to low-latitude insolation changes. Dust fluxes at sites from 21° to 27°N were near late Holocene levels during the LGM time slice, suggesting a more muted LGM response than observed from mid-latitude dust sources. Records along the northwest African margin suggest important differences in wind responses during different stadials, with maximum dust flux anomalies centered south of 20°N during H1 and north of 20°N during the Younger Dryas.

Description: This research was supported by NSF #OCE-1103262 to L. Bradtmiller, NSF #OCE-1030784 to D. McGee, P. deMenocal, and G. Winckler, and by internal grants from Macalester College and MIT.

Description: 2022-06-07

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhou, P., Stockli, D. F., Ireland, T., Murray, R. W., & Clift, P. D. Zircon U-Pb age constraints on NW Himalayan exhumation from the Laxmi Basin, Arabian Sea. Geochemistry Geophysics Geosystems, 23(1), (2022): e2021GC010158, https://doi.org/10.1029/2021GC010158.

Description: The Indus Fan, located in the Arabian Sea, contains the bulk of the sediment eroded from the Western Himalaya and Karakoram. Scientific drilling in the Laxmi Basin by the International Ocean Discovery Program recovered a discontinuous erosional record for the Indus River drainage dating back to at least 9.8 Ma, and with a single sample from 15.6 Ma. We dated detrital zircon grains by U-Pb geochronology to reconstruct how erosion patterns changed through time. Long-term increases in detrital zircon U-Pb components of 750–1,200 and 1,500–2,300 Ma record increasing preferential erosion of the Himalaya relative to the Karakoram between 8.3–7.0 and 5.9–5.7 Ma. The average contribution of Karakoram-derived sediment to the Indus Fan fell from 70% of the total at 8.3–7.0 Ma to 35% between 5.9 and 5.7 Ma. An increase in the contribution of 1,500–2,300 Ma zircons starting between 2.5 and 1.6 Ma indicates significant unroofing of the Inner Lesser Himalaya (ILH) by that time. The trend in zircon age spectra is consistent with bulk sediment Nd isotope data. The initial change in spatial erosion patterns at 7.0–5.9 Ma occurred during a time of drying climate in the foreland. The increase in ILH erosion postdated the onset of dry-wet glacial-interglacial cycles suggesting some role for climate control. However, erosion driven by rising topography in response to formation of the ILH thrust duplex, especially during the Pliocene, also played an important role, while the influence of the Nanga Parbat Massif to the total sediment flux was modest.

Description: This work was partially funded by a grant from the USSSP, as well as additional funding from the Charles T. McCord Chair in petroleum geology at LSU, and the Chevron (Gulf) Centennial professorship and the UTChron Laboratory at the University of Texas.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chase, A. P., Boss, E. S., Haentjens, N., Culhane, E., Roesler, C., & Karp-Boss, L. Plankton imagery data inform satellite-based estimates of diatom carbon. Geophysical Research Letters, 49(13), (2022): e2022GL098076, https://doi.org/10.1029/2022GL098076.

Description: Estimating the biomass of phytoplankton communities via remote sensing is a key requirement for understanding global ocean ecosystems. Of particular interest is the carbon associated with diatoms given their unequivocal ecological and biogeochemical roles. Satellite-based algorithms often rely on accessory pigment proxies to define diatom biomass, despite a lack of validation against independent diatom biomass measurements. We used imaging-in-flow cytometry to quantify diatom carbon in the western North Atlantic, and compared results to those obtained from accessory pigment-based approximations. Based on this analysis, we offer a new empirical formula to estimate diatom carbon concentrations from chlorophyll a. Additionally, we developed a neural network model in which we integrated chlorophyll a and environmental information to estimate diatom carbon distributions in the western North Atlantic. The potential for improving satellite-based diatom carbon estimates by integrating environmental information into a model, compared to models that are based solely on chlorophyll a, is discussed.

Description: Funding for this work was provided by NASA grants #NNX15AE67G and #80NSSC20M0202. A. Chase is supported by a Washington Research Foundation Postdoctoral Fellowship.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(4), (2022): e2021JC018246, https://doi.org/10.1029/2021jc018246.

Description: Storm surge barriers are increasingly being considered as risk mitigation measures for coastal population centers. During non-storm periods, permanent barrier infrastructure reduces the flow cross-sectional area and affects tidal exchange. Effects of barrier structures on estuarine tidal and salinity dynamics have not been extensively examined, particularly for partially mixed estuaries. A nested, high-resolution model is used to characterize impacts of a potential storm surge barrier near the mouth of the Hudson River estuary. Maximum tidal velocities through barrier openings are more than double those in the base case. Landward of the barrier, tidal amplitude decreases on average by about 6% due to increased drag. The drag coefficient with the barrier is about 5 times greater than the base case due primarily to form drag from flow separation at barrier structures rather than increased bottom friction. The form drag scales with barrier geometry similar to previous studies of flow around headlands. Tidal water levels are reduced particularly during spring tides, such that marsh inundation frequency is reduced up to 25%. Strong tidal velocities through barrier openings enhance salinity mixing locally, but overall mixing in the estuary decreases due to reduced tidal velocities. Correspondingly, stratification decreases near the barrier and increases landward in the estuary. The salinity intrusion length increases by 5%–15% depending on discharge due to the decreased mixing and increased exchange flow. Exchange flow increases near the barrier due reflux into the lower layer with the increased mixing, which has the potential to increase estuarine residence times.

Description: Funding from Hudson Research Foundation (Award #003/19A).

Description: 2022-10-11

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(10), (2021): e2021JC017537, https://doi.org/10.1029/2021JC017537.

Description: Mixed-layer dynamics exert a first order control on nutrient and light availability for phytoplankton. In this study, we examine the influence of mixed-layer dynamics on net community production (NCP) in the Southern Ocean on intra-seasonal, seasonal, interannual, and decadal timescales, using biogeochemical Argo floats and satellite-derived NCP estimates during the period from 1997 to 2020. On intraseasonal timescales, the shoaling of the mixed layer is more likely to enhance NCP in austral spring and winter, suggesting an alleviation of light limitation. As expected, NCP generally increases with light availability on seasonal timescales. On interannual timescales, NCP is correlated with mixed layer depth (MLD) and mixed-layer-averaged photosynthetically active radiation (PAR) in austral spring and winter, especially in regions with deeper mixed layers. Though recent studies have argued that winter MLD controls the subsequent growing season's iron and light availability, the limited number of Argo float observations contemporaneous with our satellite observations do not show a significant correlation between NCP and the previous-winter's MLD on interannual timescales. Over the 1997–2020 period, we observe regional trends in NCP (e.g., increasing around S. America), but no trend for the entire Southern Ocean. Overall, our results show that the dependence of NCP on MLD is a complex function of timescales.

Description: Work was supported by NSF OPP-1043339 to N.Cassar and NASA NNX13AC94G to M. S. Lozier. Z. Li was supported by a NASA Earth and Space Science Fellowship (Grant No. NNX13AN85H) and the Postdoctoral Scholarship Program at Woods Hole Oceanographic Institution.

Description: 2022-03-21

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12), (2021): e2021JC017989, https://doi.org/10.1029/2021JC017989.

Description: Gulf Stream warm-core rings (WCRs) impinging onto the Mid-Atlantic Bight (MAB) shelf edge can induce substantial water exchange between the shelf and slope seas. Combining satellite imagery and idealized ocean models, this study investigates the long-neglected influence of submarine canyons on the WCR impingement process. Satellite images show onshore intrusion of the WCR water concentrated near the MAB shelf-break canyons, indicating canyon-induced enhancement of cross-shelf exchange. Model simulations of the ring-canyon interaction qualitatively reproduce the observed pattern and show greatly enhanced vertical motions and cross-shelf transport in a canyon. The ring-induced transient flow in a canyon resolved by the model is consistent with the three-dimensional canyon circulation driven by ambient along-slope steady flows as depicted in the literature. Cross-isobath flows occur over both canyon slopes with a strong upwelling onshore flow over the slope upstream to the coastal-trapped wave propagation (the upwave slope) and a weak downwelling offshore flow over the downwave slope. To conserve potential vorticity, a subsurface-intensified cyclonic eddy is formed inside the canyon, which interacts with the sloping bottom and enhances the upwelling onshore flow over the upwave slope. The upwelled deep ring water is transported either back offshore by the ring-edge current on the upwave side of the canyon or across the canyon onto the downwave shelf forming a localized bulge pattern. While the former is an ephemeral onshore transport process, the latter represents a more sustained onshore transport of the ring water, both of which have major implication for ecosystem dynamics at the shelf edge.

Description: XL was supported by the China Scholarship Council; ZR was supported by the National Key Research and Development Program of China (2016YFC1402000). This work was also support by the WHOI-OUC Collaborative Initiative Program.

Description: 2022-06-13

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zippel, S. F., Farrar, J. T., Zappa, C. J., & Plueddemann, A. J. Parsing the kinetic energy budget of the ocean surface mixed layer. Geophysical Research Letters, 49(2), (2022): 2021GL095920, https://doi.org/10.1029/2021GL095920.

Description: The total rate of work done on the ocean by the wind is of considerable interest for understanding global energy balances, as the energy from the wind drives ocean currents, grows surface waves, and forces vertical mixing. A large but unknown fraction of this atmospheric energy is dissipated by turbulence in the upper ocean. The focus of this work is twofold. First, we describe a framework for evaluating the vertically integrated turbulent kinetic energy (TKE) equation using measurable quantities from a surface mooring, showing the connection to the atmospheric, mean oceanic, and wave energy. Second, we use this framework to evaluate turbulent energetics in the mixed layer using 10 months of mooring data. This evaluation is made possible by recent advances in estimating TKE dissipation rates from long-enduring moorings. We find that surface fluxes are balanced by TKE dissipation rates in the mixed layer to within a factor of two.

Description: This work was funded by NSF Award No. 2023 020, and by NASA as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS), supporting field work for SPURS-1 (NASA Grant No. NNX11AE84G), and for analysis (NASA Grant No. 80NSSC18K1494), and as part of SASSIE (NASA Grant No. 80NSSC21K0832). This work was also funded by NSF through Grant Award Nos. 1756 839, 2049546, and by ONR through Grant N000141712880 (MISO-BoB).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Baranes, H., Woodruff, J., Geyer, W., Yellen, B., Richardson, J. & Griswold, F. Sources, mechanisms, and timescales of sediment delivery to a New England salt marsh. Journal of Geophysical Research: Earth Surface, 127, (2022): e2021JF006478, https://doi.org/10.1029/2021jf006478.

Description: he availability and delivery of an external clastic sediment source is a key factor in determining salt marsh resilience to future sea level rise. However, information on sources, mechanisms, and timescales of sediment delivery are lacking, particularly for wave-protected mesotidal estuaries. Here we show that marine sediment mobilized and delivered during coastal storms is a primary source to the North and South Rivers, a mesotidal bar-built estuary in a small river system impacted by frequent, moderate-intensity storms that is typical to New England (United States). On the marsh platform, deposition rates, clastic content, and dilution of fluvially-sourced contaminated sediment by marine material all increase down-estuary toward the inlet, consistent with a predominantly marine-derived sediment source. Marsh clastic deposition rates are also highest in the storm season. We observe that periods of elevated turbidity in channels and over the marsh are concurrent with storm surge and high wave activity offshore, rather than with high river discharge. Flood tide turbidity also exceeds ebb tide turbidity during storm events. Timescales of storm-driven marine sediment delivery range from 2.5 days to 2 weeks, depending on location within the estuary; therefore the phasing of storm surge and waves with the spring-neap cycle determines how effectively post-event suspended sediment is delivered to the marsh platform. This study reveals that sediment supply and the associated resilience of New England mesotidal salt marshes involves the interplay of coastal and estuarine processes, underscoring the importance of looking both up- and downstream to identify key drivers of environmental change.

Description: The project described in this publication was in part supported by Grant or Cooperative Agreement No. G20AC00071 from the U.S. Geological Survey and a Department of Interior Northeast Climate Adaptation Science Center graduate fellowship awarded to H.E.B (G12AC00001).

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(5), (2022): e2021JC018222, https://doi.org/10.1029/2021jc018222.

Description: Mixing processes in the upper ocean play a key role in transferring heat, momentum, and matter in the ocean. These mixing processes are significantly enhanced by wave-driven Langmuir turbulence (LT). Based on a paired analysis of observations and simulations, this study investigates wind fetch and direction effects on LT at a coastal site south of the island Martha’s Vineyard (MA, USA). Our results demonstrate that LT is strongly influenced by wind fetch and direction in coastal oceans, both of which contribute to controlling turbulent coastal transport processes. For northerly offshore winds, land limits the wind fetch and wave development, whereas southerly winds are associated with practically infinite fetch. Observed and simulated two-dimensional wave height spectra reveal persistent southerly swell and substantially more developed wind-driven waves from the south. For oblique offshore winds, waves develop more strongly in the alongshore direction with less limited fetch, resulting in significant wind and wave misalignments. Observations of coherent near-surface crosswind velocities indicate that LT is only present for sufficiently developed waves. The fetch-limited northerly winds inhibit wave developments and the formation of LT. In addition to limited fetch, strong wind–wave misalignments prevent LT development. Although energetic and persistent, swell waves do not substantially influence LT activity during the observation period because these relatively long swell waves are associated with small Stokes drift shear. These observational results agree well with turbulence-resolving large eddy simulations (LESs) based on the wave-averaged Navier–Stokes equation, validating the LES approach to coastal LT in the complex wind and wave conditions.

Description: We acknowledge the support of National Science Foundation grant OCE-1634578 for funding this work. The Office of Naval Research funded the CBLAST-low experiment. This research was supported in part through the use of Information Technologies (IT) resources at the University of Delaware, specifically the high-performance computing resources.

Description: 2022-10-20

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Opher, J., Brearley, J., Dye, S., Pickart, R., Renfrew, I., Harden, B., & Meredith, M. The annual salinity cycle of the Denmark Strait Overflow. Journal of Geophysical Research: Oceans, 127(4), (2022): e2021JC018139, https://doi.org/10.1029/2021jc018139.

Description: The Denmark Strait Overflow (DSO) is an important source of dense water input to the deep limb of the Atlantic Meridional Overturning Circulation (AMOC). It is fed by separate currents from the north that advect dense water masses formed in the Nordic Seas and Arctic Ocean which then converge at Denmark Strait. Here we identify an annual salinity cycle of the DSO, characterized by freshening in winter and spring. The freshening is linked to freshening of the Shelfbreak East Greenland Current in the Blosseville Basin north of the Denmark Strait. We demonstrate that the East Greenland Current advects fresh pycnocline water above the recirculating Atlantic Water, which forms a low salinity lid for the overflow in Denmark Strait and in the Irminger Basin. This concept is supported by intensified freshening of the DSO in lighter density classes on the Greenland side of the overflow. The salinity of the DSO in the Irminger Basin is significantly correlated with northerly/northeasterly winds in the Blosseville Basin at a lag of 3–4 months, consistent with estimated transit times. This suggests that wind driven variability of DSO source water exerts an important influence on the salinity variability of the downstream DSO, and hence the composition of the deep limb of the AMOC.

Description: This research was funded by: NERC EnvEast DTP studentship NE/L002582 (JO) and Cefas Seedcorn DP371 (JO, SRD); as well as by NERC, by AFIS (NE/N009754/1) (IR), JAB is funded by NE/L011166/1, ORCHESTRA (NE/N018095/1) and ENCORE (NE/V013254/1) and RP is funded by the US National Science Foundation grants OCE-1756361 and OCE-1558742. Cefas work on the Angmagssallik array was supported by multiple international partners including NSF, NOAA-CORC-ARCHES, WHOI-OCCI, European Community's fifth & seventh framework programme under grants ASOF-W (contract EVK2-CT-2002-00,149) & No. GA212643 (THOR: “Thermohaline Overturning—at Risk”, 2008–2012) and from UK Department for Environment, Food and Rural Affairs (DEFRA) including A1222, SD0440 & ME5102.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Whitmore, L., Shiller, A., Horner, T., Xiang, Y., Auro, M., Bauch, D., Dehairs, F., Lam, P., Li, J., Maldonado, M., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., & Thomas, H. Strong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis. Journal of Geophysical Research: Oceans, 127(4), (2022): e2021JC017417, https://doi.org/10.1029/2021jc017417.

Description: Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.

Description: This research was supported by the National Science Foundation [OCE-1434312 (AMS), OCE-1436666 (RN), OCE-1535854 (PL), OCE-1736949, OCE-2023456 (TJH), and OCE-1829563 (R. Anderson for open access support)], Natural Sciences and Engineering Research Council of Canada (NSERC)-Climate Change and Atmospheric Research (CCAR) Program (MTM), and LEFE-CYBER EXPATE (HP). HT acknowledges support by the Canadian GEOTRACES via NSERC-CCAR and the German Academic Exchange Service (DAAD): MOPGA-GRI (Make Our Planet Great Again—Research Initiative) sponsored by BMBF (Federal German Ministry of Education and Research; Grant No. 57429828).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Peña‐Molino, B., Sloyan, B., Nikurashin, M., Richet, O., & Wijffels, S. Revisiting the seasonal cycle of the Timor throughflow: impacts of winds, waves and eddies. Journal of Geophysical Research: Oceans, 127, (2022): e2021JC018133, https://doi.org/10.1029/2021jc018133.

Description: The tropical Pacific and Indian Oceans are connected via a complex system of currents known as the Indonesian Throughflow (ITF). More than 30% of the variability in the ITF is linked to the seasonal cycle, influenced by the Monsoon winds. Despite previous efforts, a detailed knowledge of the ITF response to the components of the seasonal forcing is still lacking. Here, we describe the seasonal cycle of the ITF based on new observations of velocity and properties in Timor Passage, satellite altimetry and a high-resolution regional model. These new observations reveal a complex mean and seasonally varying flow field. The amplitude of the seasonal cycle in volume transport is approximately 6 Sv. The timing of the seasonal cycle, with semi-annual maxima (minima) in May and December (February and September), is controlled by the flow below 600 m associated with semi-annual Kelvin waves. The transport of thermocline waters (〈300 m) is less variable than the deep flow but larger in magnitude. This top layer is modulated remotely by cycles of divergence in the Banda Sea, and locally through Ekman transport, coastal upwelling, and non-linearities of the flow. The latter manifests through the formation of eddies that reduce the throughflow during the Southeast Monsoon, when is expected to be maximum. While the reduction in transport associated with the eddies is small, its impact on heat transport is large. These non-linear dynamics develop over small scales (〈10 km), and without high enough resolution, both observations and models will fail to capture them adequately.

Description: B. Peña-Molino, B. M. Sloyan, M. Nikurashin, and O. Richet were supported by the Centre for Southern Hemisphere Oceans Research (CSHOR). CSHOR is a joint research Centre for Southern Hemisphere Ocean Research between QNLM and CSIRO. S. E. Wijffels was supported by the US National Science Foundation Grant No. OCE-1851333.

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(5), (2022): e2021JC018056, https://doi.org/10.1029/2021jc018056.

Description: As Arctic sea ice declines, wind energy has increasing access to the upper ocean, with potential consequences for ocean mixing, stratification, and turbulent heat fluxes. Here, we investigate the relationships between internal wave energy, turbulent dissipation, and ice concentration and draft using mooring data collected in the Beaufort Sea during 2003–2018. We focus on the 50–300 m depth range, using velocity and CTD records to estimate near-inertial shear and energy, a finescale parameterization to infer turbulent dissipation rates, and ice draft observations to characterize the ice cover. All quantities varied widely on monthly and interannual timescales. Seasonally, near-inertial energy increased when ice concentration and ice draft were low, but shear and dissipation did not. We show that this apparent contradiction occurred due to the vertical scales of internal wave energy, with open water associated with larger vertical scales. These larger vertical scale motions are associated with less shear, and tend to result in less dissipation. This relationship led to a seasonality in the correlation between shear and energy. This correlation was largest in the spring beneath full ice cover and smallest in the summer and fall when the ice had deteriorated. When considering interannually averaged properties, the year-to-year variability and the short ice-free season currently obscure any potential trend. Implications for the future seasonal and interannual evolution of the Arctic Ocean and sea ice cover are discussed.

Description: This work was supported by the Postdoctoral Scholar Program at Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship. S. T. Cole was supported by Office of Naval Research grant N00014-16-1-2381.

Description: 2022-10-14

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fendrock, M., Condron, A., & McGee, D. Modeling iceberg longevity and distribution during Heinrich Events. Paleoceanography and Paleoclimatology, 37(6), (2022): e2021PA004347, https://doi.org/10.1029/2021pa004347.

Description: During the last glacial period (120–12 ka), the Laurentide ice sheet discharged large numbers of icebergs into the North Atlantic. These icebergs carried sediments that were dropped as the icebergs melted, leaving a record of past iceberg activity on the floor of the subpolar North Atlantic. Periods of significant iceberg discharge and increased ice-rafted debris (IRD) deposition, are known as Heinrich Events. These events coincide with global climate change, and the melt from the icebergs involved is frequently hypothesized to have contributed to these changes in climate by adding a significant volume of cold, fresh water to the North Atlantic. Using an iceberg model coupled with the Massachusetts Institute of Technology Global Circulation Model numerical circulation model, we explore the various factors controlling iceberg drift and rates of melt that influence the spatial patterns of IRD deposition during Heinrich Events. In addition to clarifying the influence of sea surface temperature and wind on the path of an armada of icebergs, we demonstrate that the same volume of ice can produce very different patterns of iceberg drift simply by altering the size of icebergs involved. We note also a significant difference in the seasonal locations of icebergs, influenced primarily by the changing winds, and show that the spatial patterns of IRD for Heinrich Event 1 most closely corresponds to where icebergs are located during the summer months. Consistent with proxy evidence, the ocean must be several degrees colder than temperatures estimated for the Last Glacial Maximum in order for icebergs to travel the distance implied by Heinrich Layers.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Davila, X., Gebbie, G., Brakstad, A., Lauvset, S. K., McDonagh, E. L., Schwinger, J., & Olsen, A. How Is the ocean anthropogenic carbon reservoir filled? Global Biogeochemical Cycles, 36(5), (2022): e2021GB007055, https://doi.org/10.1029/2021GB007055.

Description: About a quarter of the total anthropogenic CO2 emissions during the industrial era has been absorbed by the ocean. The rate limiting step for this uptake is the transport of the anthropogenic carbon (Cant) from the ocean mixed layer where it is absorbed to the interior ocean where it is stored. While it is generally known that deep water formation sites are important for vertical carbon transport, the exact magnitude of the fluxes across the base of the mixed layer in different regions is uncertain. Here, we determine where, when, and how much Cant has been injected across the mixed-layer base and into the interior ocean since the start of the industrialized era. We do this by combining a transport matrix derived from observations with a time-evolving boundary condition obtained from already published estimates of ocean Cant. Our results show that most of the Cant stored below the mixed layer are injected in the subtropics (40.1%) and the Southern Ocean (36.0%), while the Subpolar North Atlantic has the largest fluxes. The Subpolar North Atlantic is also the most important region for injecting Cant into the deep ocean with 81.6% of the Cant reaching depths greater than 1,000 m. The subtropics, on the other hand, have been the most efficient in transporting Cant across the mixed-layer base per volume of water ventilated. This study shows how the oceanic Cant uptake relies on vertical transports in a few oceanic regions and sheds light on the pathways that fill the ocean Cant reservoir.

Description: X. Davila was supported by a PhD research fellowship from the University of Bergen. G. Gebbie was supported by U.S. NSF Grant 88075300. A. Brakstad was supported by the Trond Mohn Foundation under grant agreement BFS2016REK01. E. L. McDonagh was supported by UKRI grants Atlantic Biogeochemical fluxes (ref no. NE/M005046/2) and TICTOC:Transient tracer-based Investigation of Circulation and Thermal Ocean Change (ref no. NE/P019293/2). A. Olsen and S. K. Lauvset appreciate support from the Research Council of Norway (ICOS-Norway, project number 245972). J. Schwinger acknowledges support by the Research Council of Norway through project INES (project number 270061). Supercomputer time and storage resources were provided by the The Norwegian e-infrastructure for Research Education (UNINETT Sigma2, projects nn2980k and ns2980k).

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(6), (2022): e2021JC017307, https://doi.org/10.1029/2021jc017307.

Description: This study examines the spatial and temporal variability of eddy kinetic energy over the Northeast Shelf using observations of surface currents from a unique array of six high frequency radar systems. Collected during summer and winter conditions over three consecutive years, the horizontal scales present were examined in the context of local wind and hydrographic variability, which were sampled concurrently from moorings and autonomous surface vehicles. While area-averaged mean kinetic energy at the surface was tightly coupled to wind forcing, eddy kinetic energy was not, and was lower in magnitude in winter than summer in all areas. Kinetic energy wavenumber spectral slopes were generally near k−5/3, but varied seasonally, spatially, and between years. In contrast, wavenumber spectra of surface temperature and salinity along repeat transect lines had sharp k−3 spectral slopes with little seasonal or inter-annual variability. Radar-based estimates of spectral kinetic energy fluxes revealed a mean transition scale of energy near 18 km during stratified months, but suggested much longer scales during winter. Overall, eddy kinetic energy was unrelated to local winds, but the up- or down-scale flux of kinetic energy was tied to wind events and, more weakly, to local density gradients.

Description: This analysis was supported by NSF grants OCE-1657896 and OCE-1736930 to Kirincich, OCE-1736709 to Flament, and OCE-1736587 to Futch. Flament is also supported by NOAAs Integrated Ocean Observing System through award NA11NOS0120039.

Description: 2023-11-21

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hage, S., Galy, V., Cartigny, M., Heerema, C., Heijnen, M., Acikalin, S., Clare, M., Giesbrecht, I., Gröcke, D., Hendry, A., Hilton, R., Hubbard, S., Hunt, J., Lintern, D., McGhee, C., Parsons, D., Pope, E., Stacey, C., Sumner, E., Tank, S., & Talling, P. Turbidity currents can dictate organic carbon fluxes across river‐fed fjords: an example from Bute Inlet (BC, Canada). Journal of Geophysical Research: Biogeosciences, 127(6), (2022): e2022JG006824, https://doi.org/10.1029/2022jg006824.

Description: The delivery and burial of terrestrial particulate organic carbon (OC) in marine sediments is important to quantify, because this OC is a food resource for benthic communities, and if buried it may lower the concentrations of atmospheric CO2 over geologic timescales. Analysis of sediment cores has previously shown that fjords are hotspots for OC burial. Fjords can contain complex networks of submarine channels formed by seafloor sediment flows, called turbidity currents. However, the burial efficiency and distribution of OC by turbidity currents in river-fed fjords had not been investigated previously. Here, we determine OC distribution and burial efficiency across a turbidity current system within Bute Inlet, a fjord in western Canada. We show that 62% ± 10% of the OC supplied by the two river sources is buried across the fjord surficial (30–200 cm) sediment. The sandy subenvironments (channel and lobe) contain 63% ± 14% of the annual terrestrial OC burial in the fjord. In contrast, the muddy subenvironments (overbank and distal basin) contain the remaining 37% ± 14%. OC in the channel, lobe, and overbank exclusively comprises terrestrial OC sourced from rivers. When normalized by the fjord’s surface area, at least 3 times more terrestrial OC is buried in Bute Inlet, compared to the muddy parts of other fjords previously studied. Although the long-term (〉100 years) preservation of this OC is still to be fully understood, turbidity currents in fjords appear to be efficient at storing OC supplied by rivers in their near-surface deposits.

Description: S.H. acknowledges funding by the IAS postgraduate grant scheme, a Research Development funds offered by Durham University, and the NOCS/WHOI exchange program. S.H. has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 899546. The field campaign and geochemical analyses were supported by Natural Environment Research Council grants NE/M007138/1, NE/W30601/1, NE/N012798/1, NE/K011480/1 and NE/M017540/1. M.J.B.C. was funded by a Royal Society Research Fellowship (DHF\R1\180166). M.A.C. was supported by the U.K. National Capability NERC CLASS program (NE/R015953/1) and NERC grants (NE/P009190/1 and NE/P005780/1). C.J.H. and M.S.H. were funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 721403 - ITN SLATE. E.L.P. was supported by a Leverhulme Early Career Fellowship (ECF-2018-267).

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(10),(2021): e2021JC017375.,https://doi.org/10.1029/2021JC017375.

Description: The Deep Water Horizon oil spill dramatically impacted the Gulf of Mexico from the seafloor to the surface. While dispersion of contaminants at the surface has been extensively studied, little is known about deep water dispersion properties. This study describes the results of the Deep Water Dispersion Experiment (DWDE), which consisted of the release of surface drifters and acoustically tracked RAFOS floats drifting at 300 and 1,500 dbar in the Gulf of Mexico. We show that surface diffusivity is elevated and decreases with depth: on average, diffusivity at 1,500 dbar is 5 times smaller than at the surface, suggesting that the dispersion of contaminants at depth is a significantly slower process than at the surface. This study also examines the turbulent regimes driving the dispersion, although conflicting evidences and large uncertainties do not allow definitive conclusions. At all depths, while the growth of dispersion and kurtosis with time supports the possibility of an exponential regime at very short time scales, indicating that early dispersion is nonlocal, finite size Lyapunov exponents support the hypothesis of local dispersion, suggesting that eddies of size comparable to the initial separation (6 km), may dominate the early dispersion. At longer time scales, the quadratic growth of dispersion is indicative of a ballistic regime, where a mean shear flow would be the dominating process. Examination of the along- and across-bathymetry components of float velocities supports the idea that boundary currents could be the source for this shear dispersion.

Description: This research has been funded by the Mexican National Council for Science and Technology - Mexican Ministry of Energy - Hydrocarbon Fund, project 201441. This is a contribution of the Gulf of Mexico Research Consortium (CIGoM).

Description: 2022-03-18

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hines, S. K. V., Bolge, L., Goldstein, S. L., Charles, C. D., Hall, I. R., & Hemming, S. R. Little change in ice age water mass structure from Cape Basin benthic neodymium and carbon isotopes. Paleoceanography and Paleoclimatology, 36(11), (2021): e2021PA004281, https://doi.org/10.1029/2021PA004281.

Description: A common conception of the deep ocean during ice age episodes is that the upper circulation cell in the Atlantic was shoaled at the Last Glacial Maximum compared to today, and that this configuration facilitated enhanced carbon storage in the deep ocean, contributing to glacial CO2 draw-down. Here, we test this notion in the far South Atlantic, investigating changes in glacial circulation structure using paired neodymium and benthic carbon isotope measurements from International Ocean Discovery Program Site U1479, at 2,615 m water depth in the Cape Basin. We infer changes in circulation structure across the last glacial cycle by aligning our site with other existing carbon and neodymium isotope records from the Cape Basin, examining vertical isotope gradients, while determining the relative timing of inferred circulation changes at different depths. We find that Site U1479 had the most negative neodymium isotopic composition across the last glacial cycle among the analyzed sites, indicating that this depth was most strongly influenced by North Atlantic Deep Water (NADW) in both interglacial and glacial intervals. This observation precludes a hypothesized dramatic shoaling of NADW above ∼2,000 m. Our evidence, however, indicates greater stratification between mid-depth and abyssal sites throughout the last glacial cycle, conditions that developed in Marine Isotope Stage 5. These conditions still may have contributed to glacial carbon storage in the deep ocean, despite little change in the mid-depth ocean structure.

Description: This work was supported by NSF grant OCE-1831415 (S. K. V. Hines, S. L. Goldstein., S. R. Hemming.).

Description: 2022-04-25

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(22), (2021): e2021GL094396, https://doi.org/10.1029/2021GL094396.

Description: Newly available mooring observations from the Overturning in the Subpolar North Atlantic Program (OSNAP) show an abrupt decline in Iceland Scotland Overflow (ISOW) salinity from 2017 to 2018 summer. Previous declines in ISOW salinity of similar magnitude have largely been attributed to changes in convectively formed deep waters in the Nordic Seas on decadal time scales. We show that this rapid decline in salinity was driven by entrainment of a major upper ocean salinity anomaly in the Iceland Basin. This is shown by tracking the propagation of the upper ocean anomaly into ISOW using a combination of mooring and Argo observations, surface drifter trajectories, and numerical model results. A 2-year total transit time from the upper ocean into the ISOW layer was found. The results show that entrainment allows for rapid modification of ISOW, and consequently the lower limb of Atlantic Meridional Overturning Circulation, on subdecadal timescales.

Description: Financial support for this research was provided by the US National Science Foundation under grants OCE-1259398 and OCE-1756231. S. Zou is supported by the US National Science Foundation Grants OCE-1756361.

Description: 2022-05-15

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(20), (2021): e2021GL094693, https://doi.org/10.1029/2021GL094693.

Description: Pacific Summer Water (PSW) plays a critical role in the ecosystem of the western Arctic Ocean, impacting sea-ice melt and providing freshwater to the basin. Most of the water exits the Chukchi Sea shelf through Barrow Canyon, but the manner in which this occurs and the ultimate fate of the water remain uncertain. Using an extensive collection of historical hydrographic and velocity data, we demonstrate how the PSW outflow depends on different wind conditions, dictating whether the warm water progresses eastward or westward away from the canyon. The current carrying the water westward along the continental slope splits into different branches, influenced by the strength and extent of the Beaufort Gyre, while the eastward penetration of PSW along the shelfbreak is limited. Our results provide the first broad-scale view of how PSW is transferred from the shelf to the basin, highlighting the role of winds, boundary currents, and eddy exchange.

Description: Funding for the project was provided by National Science Foundation grant OPP-1733564 and National Oceanic and Atmospheric Administration grant NA14OAR4320158 (P. Lin, R. S. Pickart, J. Li), and Trond Mohn Foundation Grant BFS2016REK01 (K. Vage).

Description: 2022-04-01

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12),(2021): e2021JC017549, https://doi.org/10.1029/2021JC017549.

Description: Rivers deliver freshwater and entrained terrestrial materials into the coastal ocean from adjacent continental landmasses. In the coastal Arctic, a large fraction of terrestrially sourced dissolved and particulate organic carbon (DOC and POC) is delivered by snowpack meltwaters of the spring freshet, when many coastal ocean regions remain covered by landfast ice. Here we report on an array of moored sensors and telemetering ice buoys deployed in advance of the 2018 spring freshet in Stefansson Sound near Prudhoe Bay, Alaska. This instrumented array monitored temporal and spatial variations in hydrographic properties before and during the freshet, as well as optical properties that serve as proxies for DOC and POC contained in the freshet plumes. The temporal evolution of these optical signals occurred in five stages, each associated with characteristic water column structural and kinematic characteristics. Spatial differences among fluorescent dissolved organic matter (FDOM) and optical backscatter (OBS) signals across the ice buoy array, evident later during the freshet, allowed identification of plume waters sourced from the Kuparuk, Sagavanirktok, and Shaviovik drainage basins.

Description: This work was funded by the National Aeronautics and Space Administration's Carbon Cycle and Ecosystems program (NNX17AI72G). This is contribution #11 from the Scholarly Union of Bio-Physical Arctic Researchers.

Description: 2022-05-25

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(12),(2021): e2021JC017884, https://doi.org/10.1029/2021JC017884.

Description: The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air-sea carbon exchange remains unclear. Using a 1/20° physical-biogeochemical coupled ocean model, we examined the impact of the current-wind interaction on the surface carbon concentration and the air-sea carbon exchange in the Southern Ocean. The current-wind interaction decreased winter partial pressure of CO2 (pCO2) at the ocean surface mainly south of the northern subantarctic front. It also reduced pCO2 in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2 was found to be reduced by approximately 17% when including current-wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current-wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current-wind interactions in the Southern Ocean can overestimate winter CO2 outgassing.

Description: The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air-sea carbon exchange remains unclear. Using a 1/20° physical-biogeochemical coupled ocean model, we examined the impact of the current-wind interaction on the surface carbon concentration and the air-sea carbon exchange in the Southern Ocean. The current-wind interaction decreased winter partial pressure of CO2 (pCO2) at the ocean surface mainly south of the northern subantarctic front. It also reduced pCO2 in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2 was found to be reduced by approximately 17% when including current-wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current-wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current-wind interactions in the Southern Ocean can overestimate winter CO2 outgassing.

Description: 2022-05-15

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shinoda, T., Pei, S., Wang, W., Fu, J. X., Lien, R.-C., Seo, H., & Soloviev, A. Climate Process Team: improvement of ocean component of NOAA Climate Forecast System relevant to Madden-Julian Oscillation simulations. Journal of Advances in Modeling Earth Systems, 13(12), (2021): e2021MS002658, https://doi.org/10.1029/2021MS002658.

Description: Given the increasing attention in forecasting weather and climate on the subseasonal time scale in recent years, National Oceanic and Atmospheric Administration (NOAA) announced to support Climate Process Teams (CPTs) which aim to improve the Madden-Julian Oscillation (MJO) prediction by NOAA’s global forecasting models. Our team supported by this CPT program focuses primarily on the improvement of upper ocean mixing parameterization and air-sea fluxes in the NOAA Climate Forecast System (CFS). Major improvement includes the increase of the vertical resolution in the upper ocean and the implementation of General Ocean Turbulence Model (GOTM) in CFS. In addition to existing mixing schemes in GOTM, a newly developed scheme based on observations in the tropical ocean, with further modifications, has been included. A better performance of ocean component is demonstrated through one-dimensional ocean model and ocean general circulation model simulations validated by the comparison with in-situ observations. These include a large sea surface temperature (SST) diurnal cycle during the MJO suppressed phase, intraseasonal SST variations associated with the MJO, ocean response to atmospheric cold pools, and deep cycle turbulence. Impact of the high-vertical resolution of ocean component on CFS simulation of MJO-associated ocean temperature variations is evident. Also, the magnitude of SST changes caused by high-resolution ocean component is sufficient to influence the skill of MJO prediction by CFS.

Description: This research was supported by NOAA Grant NA15OAR431074. Computing resources were provided partly by the HPC systems at the Texas A&M University (College Station and Corpus Christi) and the Climate Simulation Laboratory at NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation. TS and SP are supported by DOD Grant W911NF-20-1-0309. TS is also supported by NSF Grant OCE-1658218 and NOAA Grant NA17OAR4310256.