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  • American Geophysical Union  (232,449)
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  • 1
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    Carbon Stocks and Potential Greenhouse Gas Production of Permafrost-Affected Active Floodplains in the Lena River Delta (2024)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research (JGR): Biogeosciences, American Geophysical Union, 129, ISSN: 2169-8953
    Details
    Publication Date: 2024-04-19
    Description: Arctic warming increases the degradation of permafrost soils but little is known about floodplain soils in the permafrost region. This study quantifies soil organic carbon (SOC) and soil nitrogen stocks, and the potential CH4 and CO2 production from seven cores in the active floodplains in the Lena River Delta, Russia. The soils were sandy but highly heterogeneous, containing deep, organic rich deposits with 〉60% SOC stored below 30 cm. The mean SOC stocks in the top 1 m were 12.9 ± 6.0 kg C m−2. Grain size analysis and radiocarbon ages indicated highly dynamic environments with sediment re-working. Potential CH4 and CO2 production from active floodplains was assessed using a 1-year incubation at 20°C under aerobic and anaerobic conditions. Cumulative aerobic CO2 production mineralized a mean 4.6 ± 2.8% of initial SOC. The mean cumulative aerobic:anaerobic C production ratio was 2.3 ± 0.9. Anaerobic CH4 production comprised 50 ± 9% of anaerobic C mineralization; rates were comparable or exceeded those for permafrost region organic soils. Potential C production from the incubations was correlated with total organic carbon and varied strongly over space (among cores) and depth (active layer vs. permafrost). This study provides valuable information on the carbon cycle dynamics from active floodplains in the Lena River Delta and highlights the key spatial variability, both among sites and with depth, and the need to include these dynamic permafrost environments in future estimates of the permafrost carbon-climate feedback.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Constraints on the Cryohydrological Warming of Firn and Ice in Greenland From Rayleigh Wave Ellipticity Data (2024)
    American Geophysical Union
    Details
    Publication Date: 2024-04-05
    Description: Rayleigh wave ellipticity measurements from seismic ambient noise recorded on the Greenland Ice Sheet (GrIS) show complex and anomalous behavior at wave periods sensitive to ice (T 〈 3–4 s). To understand these complex observations, we compare them with synthetic ellipticity measurements obtained from synthetic ambient noise computed for various seismic velocity and attenuation models, including surface wave overtone effects. We find that in dry snow conditions within the interior of the GrIS, to first order the anomalous ellipticity observations can be explained by ice models associated with the accumulation and densification of snow into firn. We also show that the distribution of ellipticity measurements is strongly sensitive to seismic attenuation and the thermal structure of the ice. Our results suggest that Rayleigh wave ellipticity is well suited for monitoring changes in firn properties and thermal composition of the Greenland and Antarctic ice sheets in a changing climate.
    Description: Published
    Description: e2023GL103673
    Description: OST1 Alla ricerca dei Motori Geodinamici
    Description: JCR Journal
    Keywords: 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    North Pacific Mid-Depth and Deep Water Ventilation During the Last Glacial Cycle: Ventilation Patterns and Source Variations (2019)
    American Geophysical Union
    In:  EPIC3AGU Centennial Fall Meeting, San Francisco, CA, USA, 2019-12-09-2019-12-13American Geophysical Union
    Details
    Publication Date: 2023-06-21
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Drifter observations reveal intense vertical velocity in a surface ocean front (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tarry, D., Ruiz, S., Johnston, T., Poulain, P., Özgökmen, T., Centurioni, L., Berta, M., Esposito, G., Farrar, J., Mahadevan, A., & Pascual, A. Drifter observations reveal intense vertical velocity in a surface ocean front. Geophysical Research Letters, 49(18), (2022): e2022GL098969, https://doi.org/10.1029/2022gl098969.
    Description: Measuring vertical motions represent a challenge as they are typically 3–4 orders of magnitude smaller than the horizontal velocities. Here, we show that surface vertical velocities are intensified at submesoscales and are dominated by high frequency variability. We use drifter observations to calculate divergence and vertical velocities in the upper 15 m of the water column at two different horizontal scales. The drifters, deployed at the edge of a mesoscale eddy in the Alboran Sea, show an area of strong convergence (urn:x-wiley:00948276:media:grl64766:grl64766-math-0001(f)) associated with vertical velocities of −100 m day−1. This study shows that a multilayered-drifter array can be an effective tool for estimating vertical velocity near the ocean surface.
    Description: This research was supported by the Office of Naval Research (ONR) Departmental Research Initiative CALYPSO under program officers Terri Paluszkiewicz and Scott Harper. The authors' ONR Grant No. are as follows: DT, SR, AM, and AP N000141613130, TMSJ N000146101612470, PP N000141812418, TO N000141812138, LRC N000141712517, and N00014191269, MB and GE N000141812782 and N000141812039, and JTF N000141812431.
    Keywords: Drifters ; Vertical velocity ; Submesoscale ; Kinematic properties ; Fronts ; Alboran Sea
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Volcano monitoring with magnetic measurements: a simulation of eruptions at axial seamount, Kilauea, Baroarbunga, and Mount Saint Helens (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Tivey, M., & Fluegel, B. Volcano monitoring with magnetic measurements: a simulation of eruptions at axial seamount, Kilauea, Baroarbunga, and Mount Saint Helens. Geophysical Research Letters, 49(17), (2022): e2022GL100006, https://doi.org/10.1029/2022GL100006.
    Description: Monitoring of active volcanic systems is a challenging task due in part to the trade-offs between collection of high-quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically “transparent,” but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk.
    Description: This work was supported by the NSF Grant No 2052963 to J. Biasi and an internal Woods Hole Oceanographic Institution grant to M. Tivey.
    Keywords: Magnetism ; Volcanic hazards ; Hawaii ; Iceland ; Volcanology ; Monitoring
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  • 6
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    Radium inputs into the Arctic Ocean from rivers a basin‐wide estimate (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bullock, E., Kipp, L., Moore, W., Brown, K., Mann, P., Vonk, J., Zimov, N., & Charette, M. Radium inputs into the Arctic Ocean from rivers a basin‐wide estimate. Journal of Geophysical Research: Oceans, 127(9), (2022): e2022JC018964, https://doi.org/10.1029/2022jc018964.
    Description: Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for 226Ra and to refine the estimates for 228Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual 226Ra and 228Ra fluxes to the Arctic Ocean are [7.0–9.4] × 1014 dpm y−1 and [15–18] × 1014 dpm y−1, respectively. Of these totals, 44% and 60% of the river 226Ra and 228Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual 226Ra and 228Ra fluxes of [7.4–17] × 1015 and [15–27] × 1015 dpm y−1, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone.
    Description: This study was a broad, collaborative effort that would not have been possible without contributions from numerous funding sources, including the National Science Foundation (NSF-0751525, NSF-1736277, NSF-1458305, NSF-1938873, NSF-2048067, NSF-2134865), the NERC-BMBF project CACOON [NE/R012806/1] (UKRI NERC) and BMBF-03F0806A, and an EU Starting Grant (THAWSOME-676982).
    Keywords: Radium isotopes ; Arctic Ocean ; River fluxes
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  • 7
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    Accuracy and reproducibility of coral Sr/Ca SIMS timeseries in modern and fossil corals (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-08
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sayani, H., Cobb, K., Monteleone, B., & Bridges, H. Accuracy and reproducibility of coral Sr/Ca SIMS timeseries in modern and fossil corals. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010068, https://doi.org/10.1029/2021gc010068.
    Description: Coral strontium-to-calcium ratios (Sr/Ca) provide quantitative estimates of past sea surface temperatures (SST) that allow for the reconstruction of changes in the mean state and climate variations, such as the El Nino-Southern Oscillation, through time. However, coral Sr/Ca ratios are highly susceptible to diagenesis, which can impart artifacts of 1–2°C that are typically on par with the tropical climate signals of interest. Microscale sampling via Secondary Ion Mass Spectrometry (SIMS) for the sampling of primary skeletal material in altered fossil corals, providing much-needed checks on fossil coral Sr/Ca-based paleotemperature estimates. In this study, we employ a set modern and fossil corals from Palmyra Atoll, in the central tropical Pacific, to quantify the accuracy and reproducibility of SIMS Sr/Ca analyses relative to bulk Sr/Ca analyses. In three overlapping modern coral samples, we reproduce bulk Sr/Ca estimates within ±0.3% (1σ). We demonstrate high fidelity between 3-month smoothed SIMS coral Sr/Ca timeseries and SST (R = −0.5 to −0.8; p 〈 0.5). For lightly-altered sections of a young fossil coral from the early-20th century, SIMS Sr/Ca timeseries reproduce bulk Sr/Ca timeseries, in line with our results from modern corals. Across a moderately-altered section of the same fossil coral, where diagenesis yields bulk Sr/Ca estimates that are 0.6 mmol too high (roughly equivalent to −6°C artifacts in SST), SIMS Sr/Ca timeseries track instrumental SST timeseries. We conclude that 3–4 SIMS analyses per month of coral growth can provide a much-needed quantitative check on the accuracy of fossil coral Sr/Ca-derived estimates of paleotemperature, even in moderately altered samples.
    Description: We'd also like to thank Yolande Berta and Georgia Tech's Center for Nanostructure Characterization for providing access to their SEM facilities, and the Khaled bin Sultan Living Ocean Foundation and The Nature Conservancy for financial and logistical support for field excursions to Palmyra. Funding for this work was provided by the National Science Foundation (Award Numbers 1502832 and 2002458 to K.M.C) and the National Oceanic and Atmospheric Administration (Award Number: NA11OAR4310165 to K.M.C).
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  • 8
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    Observational and modeling evidence of seasonal trends in sediment-derived material inputs to the Chukchi Sea (2020)
    American Geophysical Union
    Details
    Publication Date: 2023-03-08
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC016007, doi:10.1029/2019JC016007.
    Description: Benthic inputs of nutrients help support primary production in the Chukchi Sea and produce nutrient‐rich water masses that ventilate the halocline of the western Arctic Ocean. However, the complex biological and redox cycling of nutrients and trace metals make it difficult to directly monitor their benthic fluxes. In this study, we use radium‐228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sediment‐derived tracer to study variability in sediment inputs to the Chukchi Sea. The 228Ra observations and modeling results are in general agreement and provide evidence of strong benthic inputs to the southern Chukchi Sea during the winter, while the northern shelf receives higher concentrations of sediment‐sourced materials in the spring and summer due to continued sediment‐water exchange as the water mass traverses the shelf. The highest tracer concentrations are observed near the shelfbreak and southeast of Hanna Shoal, a region known for high biological productivity and enhanced benthic biomass.
    Description: This study presents data from multiple Arctic expeditions over the past two decades, and we are indebted to the captains, crews, and scientific parties that made this data collection possible. This work was funded by NSF awards OCE‐1458305 to M. Charette, OCE‐1458424 to W. Moore, OCE‐1434085 to D. Kadko, PLR‐1504333 to R. Pickart, and OPP‐1822334 to M. Spall. Funding was also provided by National Oceanic and Atmospheric Administration Grant NA14‐OAR4320158 to R. Pickart. L. Kipp was supported by an Ocean Frontier Institute Postdoctoral Fellowship. Radium data used in this manuscript are available in Table S1.
    Description: 2020-10-27
    Keywords: Chukchi Sea ; Benthic flux ; Radium‐228 ; GEOTRACES
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  • 9
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    Can we estimate air‐sea flux of biological O2 from total dissolved oxygen? (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-02
    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(9), (2022): e2021GB007145, https://doi.org/10.1029/2021gb007145.
    Description: In this study, we compare mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen (F[O2]bio-as) by parameterizing the physical oxygen saturation anomaly (ΔO2[phy]) in order to separate the biological contribution from total oxygen. The first approach matches ΔO2[phy] to the monthly climatology of the argon saturation anomaly from a global ocean circulation model's output. The second approach derives ΔO2[phy] from an iterative mass balance model forced by satellite-based physical drivers of ΔO2[phy] prior to the sampling day by assuming that air-sea interactions are the dominant factors driving the surface ΔO2[phy]. The final approach leverages the machine-learning technique of Genetic Programming (GP) to search for the functional relationship between ΔO2[phy] and biophysicochemical parameters. We compile simultaneous measurements of O2/Ar and O2 concentration from 14 cruises to train the GP algorithm and test the validity and applicability of our modeled ΔO2[phy] and F[O2]bio-as. Among the approaches, the GP approach, which incorporates ship-based measurements and historical records of physical parameters from the reanalysis products, provides the most robust predictions (R2 = 0.74 for ΔO2[phy] and 0.72 for F[O2]bio-as; RMSE = 1.4% for ΔO2[phy] and 7.1 mmol O2 m−2 d−1 for F[O2]bio-as). We use the empirical formulation derived from GP approach to reconstruct regional, inter-annual, and decadal variability of F[O2]bio-as based on historical oxygen records. Overall, our study represents a first attempt at deriving F[O2]bio-as from snapshot measurements of oxygen, thereby paving the way toward using historical O2 data and a rapidly growing number of O2 measurements on autonomous platforms for independent insight into the biological pump.
    Description: N. Cassar was supported by the “Laboratoire d'Excellence” LabexMER (ANR-10-LABX-19) and co-funded by a grant from the French government under the program “Investissements d'Avenir.” Y. Huang was supported by grants from the China NSF (Nos. 42130401 and 42141002). Y. Huang was also partly supported by Chinese State Scholarship Fund to study at Duke University as a joint PhD student (No. 201806310052). R. Eveleth was supported by the NSF GRFP under grant (No. 1106401). D. Nicholson was supported by the NSF OCE-1129973 and OCE-1923915.
    Keywords: Air-sea gas biological oxygen flux ; Physical oxygen saturation anomaly ; Total dissolved oxygen ; Mechanistic and empirical models
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  • 10
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    Retrieving a “Weather Balloon” from the last Ice Age (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Seltzer, A. M., & Tyne, R. L. Retrieving a “Weather Balloon” from the last Ice Age. AGU Advances, 3(4), (2022): e2022AV000747, https://doi.org/10.1029/2022AV000747.
    Description: “How cold was the last ice age?” is a question that paleoclimate scientists have been trying to answer for decades. Constraining the magnitude of climate change since the Last Glacial Maximum (∼20,000 years ago) can help improve our understanding of Earth's climate sensitivity and, therefore enhance our ability to predict future change (Tierney et al., 2020). Of course, there is no single answer to this question: there is spatial structure to LGM temperature change that is linked to fundamental climate system properties and processes. Consequently, paleoclimate scientists have focused on variations of this question, like “What was the latitudinal gradient of LGM temperature change?” (Chiang et al., 2003), “What was the land-sea contrast?” (Rind & Peteet, 1985) or “What was the change in ocean heat content?” (Bereiter et al., 2018). These questions inform large-scale atmospheric and oceanic circulation, the intensity of the water cycle, and planetary energy balance; the answers to these questions come from proxies like planktic and benthic foraminifera, speleothems, ice cores, pollen records, ancient groundwater, lake sediments, and glacial moraines, to name a few. In short, the paleoclimate community has developed a proxy “tool kit” equipped to map changes across the Earth's surface and into the ocean interior; but, until now, no “tool” existed for the upper atmosphere.
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  • 11
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    Sediments in sea ice drive the Canada Basin surface Mn maximum: insights from an Arctic Mn Ocean model (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    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(8), (2022): e2022GB007320, https://doi.org/10.1029/2022GB007320.
    Description: Biogeochemical cycles in the Arctic Ocean are sensitive to the transport of materials from continental shelves into central basins by sea ice. However, it is difficult to assess the net effect of this supply mechanism due to the spatial heterogeneity of sea ice content. Manganese (Mn) is a micronutrient and tracer which integrates source fluctuations in space and time while retaining seasonal variability. The Arctic Ocean surface Mn maximum is attributed to freshwater, but studies struggle to distinguish sea ice and river contributions. Informed by observations from 2009 IPY and 2015 Canadian GEOTRACES cruises, we developed a three-dimensional dissolved Mn model within a 1/12° coupled ocean-ice model centered on the Canada Basin and the Canadian Arctic Archipelago (CAA). Simulations from 2002 to 2019 indicate that annually, 87%–93% of Mn contributed to the Canada Basin upper ocean is released by sea ice, while rivers, although locally significant, contribute only 2.2%–8.5%. Downstream, sea ice provides 34% of Mn transported from Parry Channel into Baffin Bay. While rivers are often considered the main source of Mn, our findings suggest that in the Canada Basin they are less important than sea ice. However, within the shelf-dominated CAA, both rivers and sediment resuspension are important. Climate-induced disruption of the transpolar drift may reduce the Canada Basin Mn maximum and supply downstream. Other micronutrients found in sediments, such as Fe, may be similarly affected. These results highlight the vulnerability of the biogeochemical supply mechanisms in the Arctic Ocean and the subpolar seas to climatic changes.
    Description: This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Climate Change and Atmospheric Research Grant: GEOTRACES (RGPCC 433848-12) and VITALS (RGPCC 433898), an NSERC Discovery Grant (RGPIN-2016-03865) to SEA, and by the University of British Columbia through a four year fellowship to BR. Computing resources were provided by Compute Canada (RRG 2648 RAC 2019, RRG 2969 RAC 2020, and RRG 1541 RAC 2021).
    Keywords: GEOTRACES ; Arctic Ocean ; Trace elements ; Canadian Arctic Archipelago ; Ocean modeling ; Micronutrients
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  • 12
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    WISTFUL: whole‐rock interpretative seismic toolbox for ultramafic lithologies (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shinevar, W., Jagoutz, O., & Behn, M. WISTFUL: whole‐rock interpretative seismic toolbox for ultramafic lithologies. Geochemistry, Geophysics, Geosystems, 23(8), (2022): e2022GC010329, https://doi.org/10.1029/2022gc010329.
    Description: To quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole-rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole-rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best-fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well-studied ultramafic xenoliths with known whole-rock compositions, mineral modes, and estimated P-T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root-mean-square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.
    Description: Funding for this study was provided by NSF Grants EAR-17-22935 (OJ) and EAR-18-44340 (MB).
    Keywords: Seismic velocity ; Seismic wave speed ; Thermodynamic modeling ; Density ; Composition ; Elastic moduli
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  • 13
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    Seismic imaging of Dante’s Domes oceanic core complex from streamer waveform inversion and reverse time migration (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    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: Solid Earth 127(8), (2022): e2021JB023814, https://doi.org/10.1029/2021jb023814.
    Description: Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long-lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges.
    Description: This research was supported by the National Natural Science Foundation of China (91858207), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (GML2019ZD0205), and Guangdong Basic and Applied Basic Research Foundation (2021B1515020023). M. X. acknowledges support from Special Foundation for National Science and Technology Basic Research Program of China (2018FY100505), Guangdong NSF research team project (2017A030312002), K. C. Wong Education Foundation (GJTD-2018-13), and the Chinese Academy of Sciences (Y4SL021001, QYZDY-SSWDQC005, 133244KYSB20180029, 131551KYSB20200021, and ISEE2021PY03). J. P. C. acknowledges support from the Independent Research and Development Program at WHOI.
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  • 14
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    Spatial variability of movement, structure, and formation of Warm Core Rings in the Northwest Atlantic Slope Sea (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    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(8),(2022): e2022JC018737, https://doi.org/10.1029/2022jc018737.
    Description: Gulf Stream Warm Core Rings (WCRs) have important influences on the New England Shelf and marine ecosystems. A 10-year (2011–2020) WCR dataset that tracks weekly WCR locations and surface areas is used here to identify the rings' path and characterize their movement between 55 and 75°W. The WCR dataset reveals a very narrow band between 66 and 71°W along which rings travel almost due west along ∼39°N across isobaths – the “Ring Corridor.” Then, west of the corridor, the mean path turns southwestward, paralleling the shelfbreak. The average ring translation speed along the mean path is 5.9 cm s−1. Long-lived rings (lifespan 〉150 days) tend to occupy the region west of the New England Seamount Chain (NESC) whereas short-lived rings (lifespan 〈150 days) tend to be more broadly distributed. WCR vertical structures, analyzed using available Argo float profiles indicate that rings that are formed to the west of the NESC have shallower thermoclines than those formed to the east. This tendency may be due to different WCR formation processes that are observed to occur along different sections of the Gulf Stream. WCRs formed to the east of the NESC tend to form from a pinch-off mechanism incorporating cores of Sargasso Sea water and a perimeter of Gulf Stream water. WCRs that form to the west of the NESC, form from a process called an aneurysm. WCRs formed through aneurysms comprise water mostly from the northern half of the Gulf Stream and are smaller than the classic pinch-off rings.
    Description: AS and AG are grateful for financial support from NOAA (NA11NOS0120038), NSF (OCE-1851242 and OCE-2123283), SMAST, and UMass Dartmouth. GG was supported by NSF under grant OCE-1657853. MA was supported by NSF under grant OCE-2122726 and by ONR under grant N00014-22-1-2112.
    Keywords: Gulf Stream ; Warm core rings ; Trajectories ; Eddies ; Aneurysm ; Ring formation
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  • 15
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    Eruption rates, tempo, and stratigraphy of Paleocene flood basalts on Baffin Island, Canada (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Asimow, P., Horton, F., & Boyes, X. Eruption rates, tempo, and stratigraphy of Paleocene flood basalts on Baffin Island, Canada. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010172, https://doi.org/10.1029/2021gc010172.
    Description: High-temperature melting in mantle plumes produces voluminous eruptions that are often temporally coincident with mass extinctions. Paleocene Baffin Island lavas—products of early Iceland mantle plume activity—are exceptionally well characterized geochemically but have poorly constrained stratigraphy, geochronology, and eruptive tempos. To provide better geologic context, we measured seven stratigraphic sections of the volcanic deposits and collected paleomagnetic data from 38 sites in the lavas and underlying Cretaceous sediments (Quqaluit Fm.). The average paleomagnetic pole from this study does not overlap with the expected pole for a stable North American locality at 60 Ma, yet the data have sufficient dispersion to average out secular variation. After ruling out other possibilities, we find that the picrites were probably erupted during a polarity transition, over less than 5 kyr. If so, the average eruption interval was ∼67 years per flow for the thickest sequence of exposed lavas. We also calculate that the flood basalts had a minimum total volume of ∼176 km3 (excluding submerged lavas in Baffin Bay). This implies a minimum eruption rate of ∼0.035 km3 yr−1, which is similar to rates found in West Greenland lavas but less than rates found in larger flood basalts. Despite this, the Baffin and West Greenland lavas temporally correlate with the “End C27n event” (a period of ∼2°C global warming) and may be its underlying cause.
    Description: his work was supported by the National Science Foundation (award #1911699 to F. Horton and award #2052963 to J. Biasi), Woods Hole Oceanographic Institution (WHOI) Andrew W. Mellon Foundation Endowed Fund for Innovative Research, a National Geographic Society grant (#CP4-144R-18), and internal funding from the Caltech Geological and Planetary Sciences Division.
    Keywords: Baffin island ; North Atlantic ; Flood basalt ; Paleomagnetism ; Volcanology ; Secular variation
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  • 16
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    Carbonation of serpentinite in creeping faults of California (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    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(15), (2022): e2022GL099185, https://doi.org/10.1029/2022gl099185.
    Description: Several large strike slip faults in central and northern California accommodate plate motions through aseismic creep. Although there is no consensus regarding the underlying cause of aseismic creep, aqueous fluids and mechanically weak, velocity-strengthening minerals appear to play a central role. This study integrates field observations and thermodynamic modeling to examine possible relationships between the occurrence of serpentinite, silica-carbonate rock, and CO2-rich aqueous fluids in creeping faults of California. Our models predict that carbonation of serpentinite leads to the formation of talc and magnesite, followed by silica-carbonate rock. While abundant exposures of silica-carbonate rock indicate complete carbonation, serpentinite-hosted CO2-rich spring fluids are strongly supersaturated with talc at elevated temperatures. Hence, carbonation of serpentinite is likely ongoing in parts of the San Andres Fault system and operates in conjunction with other modes of talc formation that may further enhance the potential for aseismic creep, thereby limiting the potential for large earthquakes.
    Description: This work was supported by National Science Foundation (NSF) grants NSF-EAR-1220280 to F. K. and J. L., NSF-EAR-1219908 to D. G., and NSF-OCE-2001728 to J. L.
    Keywords: Mineral carbonation ; Serpentinite ; Talc ; CO2 ; Aseismic creep ; San Andreas Fault
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  • 17
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    Does sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15) (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marsay, C. M., Landing, W. M., Umstead, D., Till, C. P., Freiberger, R., Fitzsimmons, J. N., Lanning, N. T., Shiller, A. M., Hatta, M., Chmiel, R., Saito, M., & Buck, C. S. Does sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15). Global Biogeochemical Cycles, 36(8), (2022): e2022GB007416. https://doi.org/10.1029/2022GB007416.
    Description: Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of “new” TE inputs. Low-mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a “recycled” SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging 〉1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained 〈1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition.
    Description: This research was supported by the National Science Foundation (NSF) grants OCE-1756103 to C. S. Buck, OCE-1756104 to W. M. Landing, OCE-1737024 to A.M. Shiller, OCE-1736906 to M. Hatta, OCE-1736875 to C. P. Till, OCE-1737167 to J. N. Fitzsimmons, and OCE-1736599 to M. Saito. In addition, N. T. Lanning was supported by the NSF Graduate Research Fellowship Program award 1746932.
    Keywords: Aerosols ; Trace elements ; GEOTRACES ; Sea spray aerosol ; Pacific Ocean
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  • 18
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    Lagrangian views of the pathways of the Atlantic meridional overturning circulation (2019)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(8), (2019): 5313-5335, doi:10.1029/2019JC015014.
    Description: The Lagrangian method—where current location and intensity are determined by tracking the movement of flow along its path—is the oldest technique for measuring the ocean circulation. For centuries, mariners used compilations of ship drift data to map out the location and intensity of surface currents along major shipping routes of the global ocean. In the mid‐20th century, technological advances in electronic navigation allowed oceanographers to continuously track freely drifting surface buoys throughout the ice‐free oceans and begin to construct basin‐scale, and eventually global‐scale, maps of the surface circulation. At about the same time, development of acoustic methods to track neutrally buoyant floats below the surface led to important new discoveries regarding the deep circulation. Since then, Lagrangian observing and modeling techniques have been used to explore the structure of the general circulation and its variability throughout the global ocean, but especially in the Atlantic Ocean. In this review, Lagrangian studies that focus on pathways of the upper and lower limbs of the Atlantic Meridional Overturning Circulation (AMOC), both observational and numerical, have been gathered together to illustrate aspects of the AMOC that are uniquely captured by this technique. These include the importance of horizontal recirculation gyres and interior (as opposed to boundary) pathways, the connectivity (or lack thereof) of the AMOC across latitudes, and the role of mesoscale eddies in some regions as the primary AMOC transport mechanism. There remain vast areas of the deep ocean where there are no direct observations of the pathways of the AMOC.
    Description: The authors extend their thanks to Xiaobiao Xu for valuable comments on the first draft of this manuscript. A. B. (WHOI), H. F., M. S. L., N. F., and K. D. were supported by Overturning in the Subpolar North Atlantic Program grants OCE‐1259618, OCE‐1259013, and OCE‐1259102 from the U.S. National Science Foundation. S. Z. was supported by the Climate Program Office of the National Oceanic and Atmospheric Administration under award NA16OAR4310168. M. L. was supported through the MOVE project, funded by NOAA's Global Ocean Monitoring and Observing Program under award NA15OAR4320071. A. B. (GEOMAR) and S. R. received funding from the Cluster of Excellence 80 “The Future Ocean” within the framework of the Excellence Initiative by the Deutsche Forschungsgemeinschaft (DFG) on behalf of the German federal and state governments (grant CP1412) and by the German Federal Ministry of Education and Research (BMBF) for the SPACES projects AGULHAS (grant 03F0750A) and CASISAC (grant 03F0796A). No new data are reported in this project. The data mentioned in the text may be found in repositories cited in each previously published paper cited in this review manuscript.
    Keywords: Floats ; Drifters ; Lagrangian methods ; AMOC ; Atlantic Ocean ; Numerical models
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  • 19
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    Using misorientation and weighted burgers vector statistics to understand intragranular boundary development and grain boundary formation at high temperatures (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    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: Solid Earth 127(8), (2022): e2022JB024497, https://doi.org/10.1029/2022JB024497.
    Description: During plastic deformation, strain weakening can be achieved, in part, via strain energy reduction associated with intragranular boundary development and grain boundary formation. Grain boundaries (in 2D) are segments between triple junctions, that connect to encircle grains; every boundary segment in the encircling loop has a high (〉10°) misorientation angle. Intragranular boundaries terminate within grains or dissect grains, usually containing boundary segments with a low (〈10°) misorientation angle. We analyze electron backscatter diffraction (EBSD) data from ice deformed at −30°C (Th≈ 0.9). Misorientation and weighted Burgers vector (WBV) statistics are calculated along planar intragranular boundaries. Misorientation angles change markedly along each intragranular boundary, linking low- (〈10°) and high-angle (10–38°) segments that exhibit distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual intragranular boundary segments comprising dislocations with distinct slip systems. There is a fundamental difference between misorientation axis distributions of intragranular boundaries (misorientation axes mostly confined to ice basal plane) and grain boundaries (no preferred misorientation axis). These observations suggest during progressive subgrain rotation, intragranular boundaries remain crystallographically controlled up to large misorientation angles (〉〉10°). In contrast, the apparent lack of crystallographic control for grain boundaries suggests misorientation axes become randomized, likely due to the activation of additional mechanisms (such as grain boundary sliding) after grain boundary formation, linking boundary segments to encircle a grain. Our findings on ice intragranular boundary development and grain boundary formation may apply more broadly to other rock-forming minerals (e.g., olivine, quartz).
    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). Open access publishing facilitated by University of Otago, as part of the Wiley – University of Otago agreement via the Council of Australian University Librarians.
    Keywords: High temperature deformation ; Misorientation ; Weighted Burgers vector ; Intragranular boundary ; Grain boundary ; Boundary geometry
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  • 20
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    Size-differentiated export flux in different dynamical regimes in the ocean (2021)
    American Geophysical Union
    Details
    Publication Date: 2023-02-17
    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(3), (2021): e2020GB006764, https://doi.org/10.1029/2020GB006764
    Description: Export of Particulate Organic Carbon (POC) is mainly driven by gravitational sinking. Thus, traditionally, it is thought that larger, faster-sinking particles make up most of the POC export flux. However, this need not be the case for particles whose sinking speeds are comparable to the vertical velocities of a dynamic flow field that can influence the descent rate of particles. Particles with different settling speeds are released in two process-oriented model simulations of an upper ocean eddying flow in the Northeast Pacific to evaluate the impact of (1) ocean dynamics on the respective contribution of the different sinking-velocity classes to POC export, and (2) the particle number size-spectrum slope. The analysis reveals that the leading export mechanism changes from gravitationally driven to advectively driven as submesoscale dynamics become more active in the region. The vertical velocity associated with submesoscale dynamics enhances the contribution of slower-sinking particles to POC export flux by a factor ranging from 3 to 10, especially where the relative abundance of small particles is large (i.e., steep particle size-spectrum slope). Remineralization generally decreases the total amount of biomass exported, but its impact is weaker in dynamical regimes where submesoscale dynamics are present and export is advectively driven. In an advectively driven export regime, remineralization processes counter-intuitively enhance the role of slower-sinking particles to the point where these slower-sinking velocity classes dominate the export, therefore challenging the traditional paradigm for POC export. This study demonstrates that slow-sinking particles can be a significant contribution, and at times, even dominate the export flux.
    Description: The work was funded by NASA grant NNX16AR48 G, to complement the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) program.
    Description: 2021-08-17
    Keywords: Export ; Flux ; Particulate organic carbon ; Sinking rates ; Submeso-scales ; Vertical velocities
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  • 21
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    The influence of ocean topography on the upwelling of carbon in the Southern Ocean (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-17
    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(19), (2021): e2021GL095088, https://doi.org/10.1029/2021GL095088.
    Description: The physical circulation of the Southern Ocean sets the surface concentration and thus air-sea exchange of CO2. However, we have a limited understanding of the three-dimensional circulation that brings deep carbon-rich waters to the surface. Here, we introduce and analyze a novel high-resolution ocean model simulation with active biogeochemistry and online Lagrangian particle tracking. We focus our attention on a subset of particles with high dissolved inorganic carbon (DIC) that originate below 1,000 m and eventually upwell into the near-surface layer (upper 200 m). We find that 71% of the DIC-enriched water upwelling across 1,000 m is concentrated near topographic features, which occupy just 33% of the Antarctic Circumpolar Current. Once particles upwell to the near-surface layer, they exhibit relatively uniform pCO2 levels and DIC decorrelation timescales, regardless of their origin. Our results show that Southern Ocean bathymetry plays a key role in delivering carbon-rich waters to the surface.
    Description: Riley X. Brady was supported by the Department of Energy's Computational Science Graduate Fellowship (DE-FG02-97ER25308), and particularly benefited from the fellowship's summer practicum at Los Alamos National Lab. Nicole S. Lovenduski and Riley X. Brady were further supported by the U.S. Department of Energy Biological and Environmental Research program (DE-SC0022243) and by the National Science Foundation (NSF-PLR 1543457; NSF-OCE 1924636; NSF-OCE 1752724; NSF-OCE 1558225). Mathew E. Maltrud and Phillip J. Wolfram were supported as part of the Energy Exascale Earth System Model (E3SM) project, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. This research used resources provided by the Los Alamos National Laboratory Institutional Computing Program, which is supported by the U.S. Department of Energy National Nuclear Security Administration under Contract No. 89233218CNA000001.
    Keywords: Southern Ocean ; Carbon cycle ; Upwelling ; Lagrangian modeling ; Ocean biogeochemistry ; Climate modeling
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  • 22
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    Relative timing of off‐axis volcanism from sediment thickness estimates on the 8°20’N seamount chain, East Pacific Rise (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-16
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fabbrizzi, A., Parnell‐Turner, R., Gregg, P., Fornari, D., Perfit, M., Wanless, V., & Anderson, M. Relative timing of off‐axis volcanism from sediment thickness estimates on the 8°20’N seamount chain, East Pacific Rise. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2022GC010335, https://doi.org/10.1029/2022gc010335.
    Description: Volcanic seamount chains on the flanks of mid-ocean ridges record variability in magmatic processes associated with mantle melting over several millions of years. However, the relative timing of magmatism on individual seamounts along a chain can be difficult to estimate without in situ sampling and is further hampered by Ar40/Ar39 dating limitations. The 8°20’N seamount chain extends ∼170 km west from the fast-spreading East Pacific Rise (EPR), north of and parallel to the western Siqueiros fracture zone. Here, we use multibeam bathymetric data to investigate relationships between abyssal hill formation and seamount volcanism, transform fault slip, and tectonic rotation. Near-bottom compressed high-intensity radiated pulse, bathymetric, and sidescan sonar data collected with the autonomous underwater vehicle Sentry are used to test the hypothesis that seamount volcanism is age-progressive along the seamount chain. Although sediment on seamount flanks is likely to be reworked by gravitational mass-wasting and current activity, bathymetric relief and Sentry vehicle heading analysis suggest that sedimentary accumulations on seamount summits are likely to be relatively pristine. Sediment thickness on the seamounts' summits does not increase linearly with nominal crustal age, as would be predicted if seamounts were constructed proximal to the EPR axis and then aged as the lithosphere cooled and subsided away from the ridge. The thickest sediments are found at the center of the chain, implying the most ancient volcanism there, rather than on seamounts furthest from the EPR. The nonlinear sediment thickness along the 8°20’N seamounts suggests that volcanism can persist off-axis for several million years.
    Description: This work was supported by National Science Foundation awards OCE-1356610, OCE-1356822, OCE-1357150, OCE-1754419, OCE-1834797, OCE-2001314, and OCE-2001331.
    Keywords: Off-axis seamounts ; East Pacific Rise ; Sediment thickness ; Seafloor morphology ; Autonomous underwater vehicle ; Eruption history
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  • 23
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    Monitoring volcanic activity through combined measurements of CO2 efflux and (222Rn) and (220Rn) in soil gas: an application to Mt. Etna (Italy) (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-07
    Description: We present measurements of soil CO2 effluxes combined with soil (222Rn) and (220Rn) from two high-degassing areas on the lower flanks of Mt. Etna volcano (ZE-SV on the E flank and PAT on the SW flank). Measurements were conducted periodically from June 2006 to January 2009 in the ZE-SV area and January 2007 to January 2009 in the PAT area. The results showed significant variations in discharge activity and style. Log values of (220Rn)/(222Rn) and CO2 efflux generally follow a negative correlation, herein parameterized as the Soil Gas Disequilibrium Index (SGDI). Deviations of the SGDI from this negative correlation provide insight into variance of localized and shallow system conditions, namely rock fracturing, residual magma degassing, and near surface interactions between magmatic gases and groundwater. Statistical analysis highlighted signal anomalies, both negative and positive, that were modeled according to the physical properties and the modes of transport for each of the SGDI gas components. The revealed anomalies show correspondence with episodes of magma ascent and eruption, thereby demonstrating the potential of using the SGDI as another instrument for forecasting volcanic activity. An important strength of the SGDI, compared to other magma gas proxies like CO2 or SO2, is that the very short and very different half-lives of 222Rn (t1/2 = 3.85 days) and 220Rn (t1/2 = 55 seconds) provide unique information on the timescales of soil gas transport. Coupling the SGDI with other pre-eruptive proxies enhances the volcanological community’s response capabilities, which is critical for effective hazard mitigation.
    Description: Published
    Description: 167-202
    Description: 4V. Processi pre-eruttivi
    Keywords: Soil gases ; radon ; carbon dioxide ; volcano monitoring ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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    Submarine groundwater discharge in the northern Bohai Sea, China: Implications for coastal carbon budgets and buffering capacity (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-20
    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: Biogeosciences 127(8), (2022): e2022JG006810, https://doi.org/10.1029/2022jg006810.
    Description: Submarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (〈1) of SGD-derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD-derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration.
    Description: his research was supported by National Natural Science Foundation of China (Grant Nos. 42130703, 42007170) and the Science, Technology and Innovation Commission of Shenzhen (Grant No. 20200925174525002.
    Description: 2023-01-20
    Keywords: Submarine groundwater discharge ; Radium isotopes ; Dissolved inorganic carbon ; Total alkalinity ; Carbon budgets ; Buffering capacity
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  • 25
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    Active alkaline traps to determine acidic-gas ratios in volcanic plumes: Sampling techniques and analytical methods (2015)
    American Geophysical Union
    Details
    Publication Date: 2023-01-19
    Description: In situ measurements have been the basis for monitoring volcanic gas emissions for many years and—being complemented by remote sensing techniques—still play an important role to date. Concerning in situ techniques for sampling a dilute plume, an increase in accuracy and a reduction of detection limits are still necessary for most gases (e.g., CO2, SO2, HCl, HF, HBr, HI). In this work, the Raschig-Tube technique (RT) is modified and utilized for application on volcanic plumes. The theoretical and experimental absorption properties of the RT and the Drechsel bottle (DB) setups are characterized and both are applied simultaneously to the well-established Filter packs technique (FP) in the field (on Stromboli Island and Mount Etna). The comparison points out that FPs are the most practical to apply but the results are errorprone compared to RT and DB, whereas the RT results in up to 13 times higher analyte concentrations than the DB in the same sampling time. An optimization of the analytical procedure, including sample pretreatment and analysis by titration, Ion Chromatography, and Inductively Coupled Plasma Mass Spectrometry, led to a comprehensive data set covering a wide range of compounds. In particular, less abundant species were quantified more accurately and iodine was detected for the first time in Stromboli’s plume. Simultaneously applying Multiaxis Differential Optical Absorption Spectroscopy (MAX-DOAS) the chemical transformation of emitted bromide into bromine monoxide (BrO) from Stromboli and Etna was determined to 3–6% and 7%, respectively, within less than 5 min after the gas release from the active vents.
    Description: Published
    Description: 2797–2820
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: plume ; volcano ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 26
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    The paroxysmal event and its deposits (2008)
    American Geophysical Union
    Details
    Publication Date: 2023-01-16
    Description: The 5 April 2003 eruption of Stromboli volcano (Italy) was the most violent in the past 50 years. It was also the best documented due to the accurate geophysical monitoring of the ongoing effusive eruption. Detailed field studies carried out a few hours to a few months after the event provided further information that were coupled with visual documentation to reconstruct the explosive dynamics. The eruption consisted of an 8-min-long explosive event preceded by a short-lived precursory activity that evolved into the impulsive ejection of gas and pyroclasts. Meter-sized ballistic blocks were launched to altitudes of up to 1400 m above the craters falling on the volcano flanks and on the village of Ginostra, about 2 km far from the vent. The vertical jet of gas and pyroclasts above the craters fed a convective plume that reached a height of 4 km. The calculated erupted mass yielded values of 1.1–1.4 × 108 kg. Later explosions generated a scoria flow deposit, with an estimated mass of 1.0–1.3 × 107 kg. Final, waning ash explosions closet the event. The juvenile fraction consisted of an almost aphyric, highly vesicular pumice mingled with a shallow-derived, crystal-rich, moderately vesicular scoria. Resuming of the lava emission a few hours after the paroxysm indicate that the shallow magmatic system was not significantly modified during the explosions. Combination of volume data with duration of eruptive phases allowed us to estimate the eruptive intensity: during the climactic explosive event, the mass discharge rate was between 106 and 107 kg/s, whereas during the pyroclastic flow activity, it was 2.8–3.6 × 105 kg/s. Strong similarities with other historical paroxysms at Stromboli suggest similar explosion dynamics.
    Description: Unpublished
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: open
    Keywords: Stromboli ; paroxysm ; explosive dynamics ; pyroclastic deposits ; ballistic ejecta ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Tephra sedimentation during the 2010 Eyjafjallajökull eruption (Iceland) from deposit, radar, and satellite observations (2012)
    American Geophysical Union
    Details
    Publication Date: 2023-01-16
    Description: The April–May 2010 eruption of the Eyjafjallajökull volcano (Iceland) was characterized by a nearly continuous injection of tephra into the atmosphere that affected various economic sectors in Iceland and caused a global interruption of air traffic. Eruptive activity during 4–8 May 2010 was characterized based on short-duration physical parameters in order to capture transient eruptive behavior of a long-lasting eruption (i.e., total grain-size distribution, erupted mass, and mass eruption rate averaged over 30 min activity). The resulting 30 min total grain-size distribution based on both ground and Meteosat Second Generation-Spinning Enhanced Visible and Infrared Imager (MSG-SEVIRI) satellite measurements is characterized by Mdphi of about 2 and a fine-ash content of about 30 wt %. The accumulation rate varied by 2 orders of magnitude with an exponential decay away from the vent, whereas Mdphi shows a linear increase until about 18 km from the vent, reaching a plateau of about 4.5 between 20 and 56 km. The associated mass eruption rate is between 0.6 and 1.2 × 105 kg s−1. In situ sampling showed how fine ash mainly fell as aggregates of various typologies. About 5 to 9 wt % of the erupted mass remained in the cloud up to 1000 km from the vent, suggesting that nearly half of the ash 〉7 settled as aggregates within the first 60 km. Particle sphericity and shape factor varied between 0.4 and 1 with no clear correlation to the size and distance from vent. Our experiments also demonstrate how satellite retrievals and Doppler radar grain-size detection can provide a real-time description of the source term but for a limited particle-size range.
    Description: Published
    Description: B12202
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: MSG-SEVIRI, PLUDIX ; particle aggregation ; settling velocity ; tephra deposits ; weak plumes ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
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    Contributions of different sea-level processes to high-tide flooding along the US coastline (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-14
    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): e2021JC018276, https://doi.org/10.1029/2021JC018276.
    Description: Coastal communities across the United States (U.S.) are experiencing an increase in the frequency of high-tide flooding (HTF). This increase is mainly due to sea-level rise (SLR), but other factors such as intra- to inter-annual mean sea level variability, tidal anomalies, and non-tidal residuals also contribute to HTF events. Here we introduce a novel decomposition approach to develop and then analyze a new database of different sea-level components. Those components represent processes that act on various timescales to contribute to HTF along the U.S. coastline. We find that the relative importance of components to HTF events strongly varies in space and time. Tidal anomalies contribute the most along the west and northeast coasts, where HTF events mostly occur in winter. Non-tidal residuals are most important along the Gulf of Mexico and mid-Atlantic coasts, where HTF events mostly occur in fall. We also quantify the minimum number of components that were required to cause HTF events in the past and how this number changed over time. The results highlight that at present, due to SLR, fewer components are needed to combine to push water levels above HTF thresholds, but tidal anomalies alone are still not sufficient to reach HTF thresholds in most locations. Finally, we explore how co-variability between different components leads to compounding effects. In some places, positive correlation between sea-level components leads to significantly more HTF events than would be expected if sea-level components were uncorrelated, whereas in other places negative correlation leads to fewer HTF events.
    Description: his work was supported by NASA's Sea Level Change Team award number 80NSSC20K1241. S.L. also acknowledges support by the China Scholarship Council (no. 201904910413) and the Ministry of Science and Technology of the People's Republic of China (grant no. 2011YQ120045).
    Description: 2023-01-14
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    Skillful long-lead prediction of summertime heavy rainfall in the US Midwest from sea surface salinity (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-07
    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(13), (2022): e2022GL098554, https://doi.org/10.1029/2022GL098554.
    Description: Summertime heavy rainfall and its resultant floods are among the most harmful natural hazards in the US Midwest, one of the world's primary crop production areas. However, seasonal forecasts of heavy rain, currently based on preseason sea surface temperature anomalies (SSTAs), remain unsatisfactory. Here, we present evidence that sea surface salinity anomalies (SSSAs) over the tropical western Pacific and subtropical North Atlantic are skillful predictors of summer time heavy rainfall one season ahead. A one standard deviation change in tropical western Pacific SSSA is associated with a 1.8 mm day−1 increase in local precipitation, which excites a teleconnection pattern to extratropical North Pacific. Via extratropical air-sea interaction and long memory of midlatitude SSTA, a wave train favorable for US Midwest heavy rain is induced. Combined with soil moisture feedbacks bridging the springtime North Atlantic salinity, the SSSA-based statistical prediction model improves Midwest heavy rainfall forecasts by 92%, complementing existing SSTA-based frameworks.
    Description: This study is supported by the NSF PREEVENTS program under ICER-1663138 (LL) and ICER-1663704 (RWS and CCU).
    Description: 2023-01-07
    Keywords: Sea surface salinity ; Midwest precipitation ; Heavy rainfall ; Long-lead prediction
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    Influence of kelp forest biomass on nearshore currents (2022)
    American Geophysical Union
    Details
    Publication Date: 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 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
    Keywords: Kelp ; Tides ; Coastal circulation ; Mixing
    Repository Name: Woods Hole Open Access Server
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    Increasing inhomogeneity of the global ocean (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-12-23
    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
    Keywords: Global ocean ; Temperature ; Salinity ; Spatial inhomogeneity ; Climate change
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    The role of wind stress in driving the along-shelf flow in the Northwest Atlantic Ocean (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-12-16
    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: Oceans 126(4), (2021): e2020JC016757, https://doi.org/10.1029/2020JC016757.
    Description: The along-shelf circulation in the Northwest Atlantic (NWA) Ocean is characterized by an equatorward flow from Greenland's south coast to Cape Hatters. The mean flow is considered to be primarily forced by freshwater discharges from rivers and glaciers while its variability is driven by both freshwater fluxes and wind stress. In this study, we hypothesize and test that the wind stress is important for the mean along-shelf flow. A two-layer model with realistic topography when forced by wind stress alone simulates a circulation system on the NWA shelves that is broadly consistent with that derived from observations, including an equatorward flow from Greenland coast to the Mid-Atlantic Bight (MAB). The along-shelf sea-level gradient is close to a previous estimate based on observations. The along-shelf flows exhibit strong seasonal variations with along-shelf transports being strong in fall/winter and weak in spring/summer, consistent with available observations. It is found that the NWA shelf circulation is affected by both wind-driven gyres through their western boundary currents and wind-stress forcing on the shelf especially along the coasts of Newfoundland and Labrador. The local wind stress forcing has more direct impacts on flows in shallower waters along the coast while the open-ocean gyres tend to affect the circulations along the outer shelf. Our conclusion is that wind stress is an important forcing of the main along-shelf flows in the NWA. One objective of this study is to motivate further examination of whether wind stress is as important as freshwater forcing for the mean flow.
    Description: Both Yang and Chen are also supported by NOAA Climate Program Office's Climate Variability and Prediction Program under grant NA20OAR4310398. JY is supported by Woods Hole Oceanographic Institution (WHOI) W. V. A. Clark Chair for Excellence in Oceanography and NSF Ocean Science Division under grant OCE1634886. Chen is supported by WHOI Independent Research and Development award.
    Description: 2021-09-30
    Keywords: Cross-shelf interactions ; Northwest Atlantic Ocean ; Numerical models ; Ocean dynamics ; Shelf flows ; Wind stress forcing
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    Closing the global marine Ra-226 budget reveals the biological pump as a dominant removal flux in the upper ocean (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-12-10
    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): e2022GL098087, https://doi.org/10.1029/2022GL098087.
    Description: Radium isotopes are powerful proxies in oceanography and hydrology. Radium mass balance models, including assessments of submarine groundwater discharge (SGD), often overlook particle scavenging (PS) as a pathway for dissolved radium removal from the world ocean. Here, we build a global ocean 226Ra mass balance model and reevaluate the potential importance of PS. We find that PS is the major 226Ra sink for the upper ocean, removing about 96% of the total input from various sources. Aside from vertical exchange with the lower ocean, SGD is the largest 226Ra source into the upper ocean. The biological pump transfers particles to the deep ocean, resulting in a major but often overlooked impact on the global 226Ra marine budget. Our findings suggest that radium mass balance models should consider PS in systems with high siliceous algae production and export fluxes and long water residence times to prevent underestimation of large-scale SGD fluxes.
    Description: The authors are grateful to the many researchers and funding agencies responsible for the collection of data and quality control. The authors are very grateful to Jesus Gomez-Velez of Vanderbilt University for suggesting the statistical approach for distribution expansion and helping with the coding. The authors from Ocean University of China were funded by the Natural Science Foundation of China 41876075, 42130410, and 91958214, and Fundamental Research Funds for the Central Universities China 201962003 and 202072001. Funding for M.A.C. was provided by U.S. National Science Foundation OCE-1736277 and a WHOI-OUC Cooperative Research Initiative award. Valentí Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral programme of the Catalan Government (2019-BP-00241).
    Description: 2022-12-10
    Keywords: Particle scavenging ; Submarine groundwater discharge ; Siliceous algae ; Global ocean
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    Deep outer-rise faults in the Southern Mariana Subduction Zone indicated by a machine-learning-based high-resolution earthquake catalog (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-12-06
    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 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
    Keywords: Outer-rise fault ; Mariana Subduction Zone ; EQTransformer ; Ocean bottom seismometer
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    Increasing coral reef resilience through successive marine heatwaves (2022)
    American Geophysical Union
    Details
    Publication Date: 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.
    Keywords: Coral reefs ; Thermal stress ; ENSO ; Adaptation ; Oceanography ; Central Pacific
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    Krypton-81 dating constrains timing of deep groundwater flow activation (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-12-06
    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 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.
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    Formation of ionospheric irregularities over Southeast Asia during the 2015 St. Patrickˈs Day storm (2017)
    American Geophysical Union
    Details
    Publication Date: 2022-11-23
    Description: We investigate the geospace response to the 2015 St. Patrickˈs Day storm leveraging on instruments spread over Southeast Asia (SEA), covering a wide longitudinal sector of the low-latitude ionosphere. A regional characterization of the storm is provided, identifying the peculiarities of ionospheric irregularity formation. The novelties of this work are the characterization in a broad longitudinal range and the methodology relying on the integration of data acquired by Global Navigation Satellite System (GNSS) receivers, magnetometers, ionosondes, and Swarm satellites. This work is a legacy of the project EquatoRial Ionosphere Characterization in Asia (ERICA). ERICA aimed to capture the features of both crests of the equatorial ionospheric anomaly (EIA) and trough (EIT) by means of a dedicated measurement campaign. The campaign lasted from March to October 2015 and was able to observe the ionospheric variability causing effects on radio systems, GNSS in particular. The multiinstrumental and multiparametric observations of the region enabled an in-depth investigation of the response to the largest geomagnetic storm of the current solar cycle in a region scarcely reported in literature. Our work discusses the comparison between northern and southern crests of the EIA in the SEA region. The observations recorded positive and negative ionospheric storms, spread F conditions, scintillation enhancement and inhibition, and total electron content variability. The ancillary information on the local magnetic field highlights the variety of ionospheric perturbations during the different storm phases. The combined use of ionospheric bottomside, topside, and integrated information points out how the storm affects the F layer altitude and the consequent enhancement/suppression of scintillations.
    Description: Published
    Description: 12211–12233
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: 2A. Fisica dell'alta atmosfera
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: 5IT. Osservazioni satellitari
    Description: JCR Journal
    Description: open
    Keywords: Saint Patrickˈs Day storm ; scintillation enhancement/suppression ; equatorial ionospheric anomaly ; positive and negative ionospheric storms ; spread F ; total electron content variability ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.05. Wave propagation ; 01. Atmosphere::01.02. Ionosphere::01.02.06. Instruments and techniques ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 01. Atmosphere::01.03. Magnetosphere::01.03.99. General or miscellaneous ; 01. Atmosphere::01.03. Magnetosphere::01.03.02. Magnetic storms ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics
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    Shallow calcium carbonate cycling in the North Pacific Ocean (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-11-06
    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(5), (2022): e2022GB007388, https://doi.org/10.1029/2022gb007388.
    Description: The cycling of biologically produced calcium carbonate (CaCO3) in the ocean is a fundamental component of the global carbon cycle. Here, we present experimental determinations of in situ coccolith and foraminiferal calcite dissolution rates. We combine these rates with solid phase fluxes, dissolved tracers, and historical data to constrain the alkalinity cycle in the shallow North Pacific Ocean. The in situ dissolution rates of coccolithophores demonstrate a nonlinear dependence on saturation state. Dissolution rates of all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods) are too slow to explain the patterns of both CaCO3 sinking flux and alkalinity regeneration in the North Pacific. Using a combination of dissolved and solid-phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO3 dissolution with a combination of ambient saturation state and oxygen consumption simultaneously explains solid-phase CaCO3 flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. We do not need to invoke the presence of carbonate phases with higher solubilities. Instead, biomineralization and metabolic processes intimately associate the acid (CO2) and the base (CaCO3) in the same particles, driving the coupled shallow remineralization of organic carbon and CaCO3. The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration within degrading particle aggregates. The coupling of these cycles acts as a major filter on the export of both organic and inorganic carbon to the deep ocean.
    Description: This work was funded by NSF OCE-1220301 to W.B., NSF OCE-1220600 to J.F.A., and startup funding for A.V.S.
    Description: 2022-11-06
    Keywords: Calcium carbonate ; Dissolution ; Carbon cycle
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    Hydroacoustic monitoring of seafloor spreading and transform faulting in the equatorial Atlantic Ocean (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-11-04
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Parnell-Turner, R., Smith, D. K., & Dziak, R. P. Hydroacoustic monitoring of seafloor spreading and transform faulting in the equatorial Atlantic Ocean. Journal of Geophysical Research: Solid Earth, 127(7), (2022): e2022JB024008, https://doi.org/10.1029/2022JB024008.
    Description: Seismicity along mid-ocean ridges and oceanic transform faults provides insights into the processes of crustal accretion and strike-slip deformation. In the equatorial Atlantic ocean, the slow-spreading Mid-Atlantic Ridge is offset by some of the longest-offset transform faults on Earth, which remain relatively poorly understood due to its remote location far from land-based teleseismic receivers. A catalog of T-phase events detected by an array of 10 autonomous hydrophones deployed between 2011 and 2015, extending from 20°N to 10°S is presented. The final catalog of 6,843 events has a magnitude of completeness of 3.3, compared to 4.4 for the International Seismic Center teleseismic catalog covering the same region, and allows investigation of the dual processes of crustal accretion and transform fault slip. The seismicity rate observed at asymmetric spreading segments (those hosting detachment faults) is significantly higher than that of symmetric spreading centers, and 74% of known hydrothermal vents along the equatorial Mid-Atlantic Ridge occur on asymmetric spreading segments. Aseismic patches are present on nearly all equatorial Atlantic transform faults, including on the Romanche transform where regional rotation and transpression could explain both bathymetric uplift and reduction in seismic activity. The observed patterns in seismicity provide insight into the thermal and mechanical structure of the ridge axis and associated transform faults, and potentially provide a method for investigating the distribution of hydrothermal vent systems.
    Description: This research was supported by National Science Foundation Grants EAR-1062238, EAR-1062165, and OCE-1839727. This paper is NOAA Pacific Marine Environmental Laboratory contribution 5323.
    Keywords: Mid-ocean ridge ; Oceanic transform fault ; T-phase ; Earthquake ; Hydrothermal vent
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    A century of observed temperature change in the Indian Ocean (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-11-04
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wenegrat, J. O., Bonanno, E., Rack, U., & Gebbie, G. A century of observed temperature change in the Indian Ocean. Geophysical Research Letters, 49(13), (2022): e2022GL098217, https://doi.org/10.1029/2022GL098217.
    Description: The Indian Ocean is warming rapidly, with widespread effects on regional weather and global climate. Sea-surface temperature records indicate this warming trend extends back to the beginning of the 20th century, however the lack of a similarly long instrumental record of interior ocean temperatures leaves uncertainty around the subsurface trends. Here we utilize unique temperature observations from three historical German oceanographic expeditions of the late 19th and early 20th centuries: SMS Gazelle (1874–1876), Valdivia (1898–1899), and SMS Planet (1906–1907). These observations reveal a mean 20th century ocean warming that extends over the upper 750 m, and a spatial pattern of subsurface warming and cooling consistent with a 1°–2° southward shift of the southern subtropical gyre. These interior changes occurred largely over the last half of the 20th century, providing observational evidence for the acceleration of a multidecadal trend in subsurface Indian Ocean temperature.
    Description: GG is supported by U.S. NSF-OCE 82280500.
    Keywords: Historical temperature observations ; Indian Ocean ; Ocean warming ; Ocean heat content ; Antarctic circumpolar current
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    Fluid‐mediated mass transfer between mafic and ultramafic rocks in subduction zones (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-11-04
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Codillo, E., Klein, F., Dragovic, B., Marschall, H., Baxter, E., Scambelluri, M., & Schwarzenbach‬, E. Fluid‐mediated mass transfer between mafic and ultramafic rocks in subduction zones. Geochemistry Geophysics Geosystems, 23, (2022): e2021GC010206, https://doi.org/10.1029/2021gc010206.
    Description: Metasomatic reaction zones between mafic and ultramafic rocks exhumed from subduction zones provide a window into mass-transfer processes at high pressure. However, accurate interpretation of the rock record requires distinguishing high-pressure metasomatic processes from inherited oceanic signatures prior to subduction. We integrated constraints from bulk-rock geochemical compositions and petrophysical properties, mineral chemistry, and thermodynamic modeling to understand the formation of reaction zones between juxtaposed metagabbro and serpentinite as exemplified by the Voltri Massif (Ligurian Alps, Italy). Distinct zones of variably metasomatized metagabbro are dominated by chlorite, amphibole, clinopyroxene, epidote, rutile, ilmenite, and titanite between serpentinite and eclogitic metagabbro. Whereas the precursor serpentinite and oxide gabbro formed and were likely already in contact in an oceanic setting, the reaction zones formed by diffusional Mg-metasomatism between the two rocks from prograde to peak, to retrograde conditions in a subduction zone. Metasomatism of mafic rocks by Mg-rich fluids that previously equilibrated with serpentinite could be widespread along the subduction interface, within the subducted slab, and the mantle wedge. Furthermore, the models predict that talc formation by Si-metasomatism of serpentinite in subduction zones is limited by pressure-dependent increase in the silica activity buffered by the serpentine-talc equilibrium. Elevated activities of aqueous Ca and Al species would also favor the formation of chlorite and garnet. Accordingly, unusual conditions or processes would be required to stabilize abundant talc at high P-T conditions. Alternatively, a different set of mineral assemblages, such as serpentine- or chlorite-rich rocks, may be controlling the coupling-decoupling transition of the plate interface.
    Description: M. Scambelluri acknowledges the Italian Ministry of Research MUR for granting the PRIN project n. 2017ZE49E7. This research was funded by NSF-OISE (Office of International Science & Engineering, Petrology & Geochemistry) PIRE, Award #1545903, and the WHOI Ocean Ventures Fund.
    Keywords: Fluid-rock interactions ; Magnesium metasomatism ; Subduction zones ; Voltri Massif
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    The roles of heat and gas in a mushy magma chamber (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-11-03
    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: Solid Earth 127(7),(2022): e2022JB024357, https://doi.org/10.1029/2022jb024357.
    Description: Crustal magmatic systems likely consist of magmatic reservoirs dominated by crystal mush. Recent studies suggest that the physical processes occurring in crystal mush could alter the response of magmatic reservoirs during volcanic unrest. Here, we present a magma chamber deformation model that incorporates two new aspects in crystal mush: heat and exsolved gas. The model is based on earlier studies by Liao et al. (2021, https://doi.org/10.1029/2020JB019395) with additional processes including thermal-mechanical coupling, dependence of material properties on gas content, and temperature evolution following an injection of hotter magma. The post-injection time-dependent evolution of the system can be grouped into three periods, which are dominated by poroelastic diffusion (short term), viscoelastic relaxation (mid term), and thermal equilibration (long term). All three time-regimes are strongly affected by gas distribution, which alters the relative compressibility of the crystal-rich and crystal-poor regions in the chamber. The contribution of thermal evolution emerges during the mid-term evolution. The time-dependent evolution of the system highlights the intrinsic ability of a gas-bearing mushy magma chamber to generate non-monotonic time series of stresses, deformation, and magma transport.
    Keywords: Crystal mush ; Magma chamber ; Exsolved volatiles
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    Xenon hydrate as an analog of methane hydrate in geologic systems out of thermodynamic equilibrium (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(5), (2019):2462-2472, doi:10.1029/2019GC008250.
    Description: Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.
    Description: This work was funded in part by the U.S. Department of Energy, DOE [awards DE‐FE0013999 and DE‐SC0018357 (to R. J.) and DOE Interagency Agreement DE‐FE0023495 (to W. F. W.)]. X. F. acknowledges support by the Miller Research Fellowship at the University of California Berkeley. W. F. W. acknowledges support from the U.S. Geological Survey's Gas Hydrate Project and the Survey's Coastal, Marine Hazards and Resources Program. L. C. F. acknowledges funding from the Spanish Ministry of Economy and Competitiveness (grants RYC‐2012‐11704 and CTM2014‐54312‐P). L. C. F. and R. J. acknowledge funding from the MIT International Science and Technology Initiatives, through a Seed Fund grant. The simulation data are available on the UC Berkeley Dash repository at https://doi.org/10.6078/D1G67B.
    Description: 2019-11-06
    Keywords: Methane hydrates ; Xenon hydrates ; Phase behavior ; Growth kinetics ; Nonstoichiometry
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    Nitrogen cycle patterns during forest regrowth in an African Miombo woodland landscape (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Biogeosciences, 124(6), (2019): 1591-1603, doi:10.1029/2018JG004803.
    Description: Tropical dry forests in eastern and southern Africa cover 2.5 × 106 km2, support wildlife habitat and livelihoods of more than 150 million people, and face threats from land use and climate change. To inform conservation, we need better understanding of ecosystem processes like nutrient cycling that regulate forest productivity and biomass accumulation. Here we report on patterns in nitrogen (N) cycling across a 100‐year forest regrowth chronosequence in the Tanzanian Miombo woodlands. Soil and vegetation indicators showed that low ecosystem N availability for trees persisted across young to mature forests. Ammonium dominated soil mineral N pools from 0‐ to 15‐cm depth. Laboratory‐measured soil N mineralization rates across 3‐ to 40‐year regrowth sites showed no significant trends and were lower than mature forest rates. Aboveground tree N pools increased at 6 to 7 kg N·ha−1·yr−1, accounting for the majority of ecosystem N accumulation. Foliar δ15N 〈0‰ in an N‐fixing canopy tree across all sites suggested that N fixation may contribute to ecosystem N cycle recovery. These results contrast N cycling in wetter tropical and Neotropical dry forests, where indicators of N scarcity diminish after several decades of regrowth. Our findings suggest that minimizing woody biomass removal, litter layer, and topsoil disturbance may be important to promote N cycle recovery and natural regeneration in Miombo woodlands. Higher rates of N mineralization in the wet season indicated a potential that climate change‐altered rainfall leading to extended dry periods may lower N availability through soil moisture‐dependent N mineralization pathways, particularly for mature forests.
    Description: This study depended on the knowledge, insights, and cooperation of many people and institutions. We thank the Millennium Villages Project‐Mbola site for providing introductions to the landscape and village headmen in many regions. We thank the ARI‐Tumbi staff (now TARI‐Tumbi) in Tabora, Tanzania for providing invaluable logistical support in identifying forest regrowth sites and help with labwork in Tabora, Tanzania. We thank other key local organizations, including Tabora Development Foundation Trust (Dick Mlimuka, Oscar Kisanji) and Tanzania Forest Service (Bw. Relingo), for logistical support and transportation. We thank many village headmen and farmers for access to forest sites within their lands for sampling. Finally, we would like to thank the MBL Stable Isotope laboratory and Dr. Marshall Otter for his expertise with producing and interpreting soil and leaf C, N and stable isotope data. This study was funded in part by NSF PIRE Grant OISE 0968211, a Dissertation Support Grant to Marc Mayes from Brown University (2015–2016), and completed with permission and cooperation from the Tanzania Commission on Science and Technology (COSTECH permits 2013‐261‐NA‐2014‐199 and 2015‐183‐ER‐2014‐199). Data and code for analyses can be accessed at a Github repository: https://github.com/mtm17/MiomboN.git.
    Description: 2019-11-08
    Keywords: Nitrogen ; Africa ; Miombo ; Tropical dry forest ; Carbon ; Secondary forest regrowth
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    Mature diffuse tectonic block boundary revealed by the 2020 southwestern Puerto Rico seismic sequence (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    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
    Keywords: Rupture of multiple faults ; Intra-arc deformation ; Earthquake-generated submarine canyon ; Anisotropic arc composition ; Caribbean seismic hazard
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    Dynamics of marsh-derived sediments in lagoon-type estuaries (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Donatelli, C., Kalra, T. S., Fagherazzi, S., Zhang, X., & Leonardi, N. Dynamics of marsh-derived sediments in lagoon-type estuaries. Journal of Geophysical Research: Earth Surface, 125(12), (2020): e2020JF005751, doi:10.1029/2020JF005751.
    Description: Salt marshes are valuable ecosystems that must trap sediments and accrete in order to counteract the deleterious effect of sea level rise. Previous studies have shown that the capacity of marshes to build up vertically depends on both autogenous and exogenous processes including ecogeomorphic feedbacks and sediment supply from in‐land and coastal ocean. There have been numerous efforts to quantify the role played by the sediments coming from marsh edge erosion on the resistance of salt marshes to sea level rise. However, the majority of existing studies investigating the interplay between lateral and vertical dynamics use simplified modeling approaches, and they do not consider that marsh retreat can affect the regional‐scale hydrodynamics and sediment retention in back‐barrier basins. In this study, we evaluated the fate of the sediments originating from marsh lateral loss by using high‐resolution numerical model simulations of Jamaica Bay, a small lagoonal estuary located in New York City. Our findings show that up to 42% of the sediment released during marsh edge erosion deposits on the shallow areas of the basin and over the vegetated marsh platforms, contributing positively to the sediment budget of the remaining salt marshes. Furthermore, we demonstrate that with the present‐day sediment supply from the ocean, the system cannot keep pace with sea level rise even accounting for the sediment liberated in the bay through marsh degradation. Our study highlights the relevance of multiple sediment sources for the maintenance of the marsh complex.
    Description: This study was supported by the Department of the Interior Hurricane Sandy Recovery program (ID G16AC00455, subaward to University of Liverpool). S. F. was partly supported by NSF awards 1637630 (PIE LTER) and 1832221 (VCR LTER). We thank Robert Chant from Rutgers University for sharing the hydrodynamic measurements in Jamaica Bay.
    Keywords: Marsh erosion ; Sediment recycling ; Sea level rise ; Jamaica Bay
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    Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ruppel, C. D., & Waite, W. F. Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems. Journal of Geophysical Research: Solid Earth, 125(8), (2020): e2018JB016459, doi:10.1029/2018JB016459.
    Description: Gas hydrate is an ice‐like form of water and low molecular weight gas stable at temperatures of roughly −10°C to 25°C and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one sixth of Earth's methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean‐atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean‐atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth's near‐surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some field studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems.
    Description: Both authors have received nearly two decades of support from the U.S. Geological Survey's (USGS's) Energy Resources Program and the Coastal/Marine Hazards and Resources Program and from numerous DOE‐USGS Interagency Agreements, most recently DE‐FE0023495. C. R. acknowledges support from NOAA's Office of Ocean Exploration and Research (OER) under NOAA‐USGS Interagency Agreement 16‐01118.
    Keywords: Gas hydrate ; Hydrate breakdown ; Hydrate formation ; Permafrost hydrate ; Geologic systems ; Marine hydrate
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    Emerging wetlands from river diversions can sustain high denitrification rates in a Coastal Delta (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    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: Biogeosciences 126(5), (2021): e2020JG006217, https://doi.org/10.1029/2020JG006217.
    Description: It is assumed that to treat excess NO3− high soil organic matter content (%OM) is required to maintain high denitrification rates in natural or restored wetlands. However, this excess also represents a risk by increasing soil decomposition rates triggering peat collapse and wetland fragmentation. Here, we evaluated the role of %OM and temperature interactions controlling denitrification rates in eroding (Barataria Bay-BLC) and emerging (Wax Lake Delta-WLD) deltaic regions in coastal Louisiana using the isotope pairing (IPT) and N2:Ar techniques. We also assessed differences between total (direct denitrification + coupled nitrification-denitrification) and net (total denitrification minus nitrogen fixation) denitrification rates in benthic and wetland habitats with contrasting %OM and bulk density (BD). Sediment (benthic) and soil (wetland) cores were collected during summer, spring, and winter (2015–2016) and incubated at close to in-situ temperatures (30°C, 20°C, and 10°C, respectively). Denitrification rates were linearly correlated with temperature; maximum mean rates ranged from 40.1–124.1 μmol m−2 h−1 in the summer with lower rates (〈26.2 ± 5.3 μmol m−2 h−1) in the winter seasons. Direct denitrification was higher than coupled denitrification in all seasons. Denitrification rates were higher in WLD despite lower %OM, lower total N concentration, and higher BD in wetland soils. Therefore, in environments with low carbon availability, high denitrification rates can be sustained as long as NO3− concentrations are high (〉30 μM) and water temperature is 〉10°C. In coastal Louisiana, substrates under these regimes are represented by emergent supra-tidal flats or land created by sediment diversions under oligohaline conditions (〈1 ppt).
    Description: This study was supported by the NOAA-Sea Grant Program-Louisiana (Grant 2013R/E-24) to Victor H. Rivera-Monroy and Kanchan Maiti. Victor H. Rivera-Monroy was also supported by the Department of the Interior South-Central Climate Adaptation Science Center (Cooperative Agreement #G12AC00002).
    Keywords: Coastal Louisiana ; Deltaic system ; Denitrification ; Nitrate loading ; Organic matter ; Seasonal change ; Sediment and freshwater diversions
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    Modeling the dynamics of salt marsh development in coastal land reclamation (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    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
    Keywords: Marsh restoration ; Land reclamation ; COAWST ; Vegetation dynamics ; Phases of marsh development ; Expectance of marsh coverage
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    Introduction to special issue on gas hydrate in porous media: linking laboratory and field-scale phenomena (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(8), (2019): 7525-7537, doi: 10.1029/2019JB018186.
    Description: The proliferation of drilling expeditions focused on characterizing natural gas hydrate as a potential energy resource has spawned widespread interest in gas hydrate reservoir properties and associated porous media phenomena. Between 2017 and 2019, a Special Section of this journal compiled contributed papers elucidating interactions between gas hydrate and sediment based on laboratory, numerical modeling, and field studies. Motivated mostly by field observations in the northern Gulf of Mexico and offshore Japan, several papers focus on the mechanisms for gas hydrate formation and accumulation, particularly with vapor phase gas, not dissolved gas, as the precursor to hydrate. These studies rely on numerical modeling or laboratory experiments using sediment packs or benchtop micromodels. A second focus of the Special Section is the role of fines in inhibiting production of gas from methane hydrate, controlling the distribution of hydrate at a pore scale, and influencing the bulk behavior of seafloor sediments. Other papers fill knowledge gaps related to the physical properties of hydrate‐bearing sediments and advance new approaches in coupled thermal‐mechanical modeling of these sediments during hydrate dissociation. Finally, one study addresses the long‐standing question about the fate of methane hydrate at the molecular level when CO2 is injected into natural reservoirs under hydrate‐forming conditions.
    Description: C. R. was supported by the U.S. Geological Survey's Energy Resources Program and the Coastal/Marine Hazards and Resources Program, as well as by DOE Interagency Agreement DE‐FE0023495. C. R. thanks W. Waite and J. Jang for discussions and suggestions that improved this paper and L. Stern for a helpful review. J. Y. Lee was supported by the Ministry of Trade, Industry, and Energy (MOTIE) through the Project “Gas Hydrate Exploration and Production Study (19‐1143)” under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM). Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    Keywords: Gas hydrate ; Methane ; Reservoir properties ; Multiphase flow
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