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  • American Geophysical Union  (54)
  • American Association for the Advancement of Science (AAAS)
  • 2020-2023  (54)
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  • 1
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Reviews of Geophysics 58(3), (2020): e2019RG000672, doi:10.1029/2019RG000672.
    Description: Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea‐level observing system, the knowledge of regional sea‐level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea‐level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea‐level change. Here we review the individual processes which lead to sea‐level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea‐level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea‐level observation network—particularly as related to satellite observations—in the improved scientific understanding of the contributors to regional sea‐level change.
    Description: The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The authors acknowledge support from the National Aeronautics and Space Administration under Grants 80NSSC17K0565, 80NSSC170567, 80NSSC17K0566, 80NSSC17K0564, and NNX17AB27G. A. A. acknowledges support under GRACE/GRACEFO Science Team Grant (NNH15ZDA001N‐GRACE). T. W. acknowledges support by the National Aeronautics and Space Administration (NASA) under the New (Early Career) Investigator Program in Earth Science (Grant: 80NSSC18K0743). C. G. P was supported by the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists at the Woods Hole Oceanographic Institution.
    Keywords: Sea level ; Satellite observations ; Remote sensing
    Repository Name: Woods Hole Open Access Server
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  • 2
    Publication Date: 2022-05-27
    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: Oceans 126(8), (2021): e2021JC017510, https://doi.org/10.1029/2021JC017510.
    Description: The air-sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O2 has been shown to be closely related to the air-sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air-sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon-to-nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–70°). The amplitude ratio, A APO/A ArN2, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. A APO/A ArN2 is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of δAPO is compensated by similar variations in δ(Ar/N2). From the relationship between O2/heat and A APO/A ArN2 in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct O2/heat flux ratios of 3.3 ± 0.3 and 4.7 ± 0.8 nmol J-1 between 40 and 70° in the Northern and Southern Hemispheres respectively, providing a useful constraint for O2 and heat air-sea fluxes in earth system models and observation-based data products.
    Description: The recent atmospheric measurements of the Scripps program have been supported via funding from the NSF and the National Oceanographic and Atmospheric Administration (NOAA) under grants 1304270 and OAR-CIPO-2015-2004269. M. Manizza and R. F. Keeling thank NSF for financial support via the OCE-1130976 grant. M. Manizza thanks additional financial support from NSF via the ARRA OCE-0850350 grant. S. C. Doney acknowledges support from NSF PLR-1440435. Keith Rodgers acknowledges support from IBS-R028-D1. Gael Forget and the ECCO group kindly provided the ECCOv4 heat fluxes.
    Description: 2022-01-22
    Repository Name: Woods Hole Open Access Server
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  • 3
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wallace, E. J., Donnelly, J. P., van Hengstum, P. J., Winkler, T. S., McKeon, K., MacDonald, D., d'Entremont, N. E., Sullivan, R. M., Woodruff, J. D., Hawkes, A. D., & Maio, C. 1,050 years of hurricane strikes on long island in the Bahamas. Paleoceanography and Paleoclimatology, 36(3), (2021): e2020PA004156, https://doi.org/10.1029/2020PA004156.
    Description: Sedimentary records of past hurricane activity indicate centennial-scale periods over the past millennium with elevated hurricane activity. The search for the underlying mechanism behind these active hurricane periods is confounded by regional variations in their timing. Here, we present a new high resolution paleohurricane record from The Bahamas with a synthesis of published North Atlantic records over the past millennium. We reconstruct hurricane strikes over the past 1,050 years in sediment cores from a blue hole on Long Island in The Bahamas. Coarse-grained deposits in these cores date to the close passage of seven hurricanes over the historical interval. We find that the intensity and angle of approach of these historical storms plays an important role in inducing storm surge near the site. Our new record indicates four active hurricane periods on Long Island that conflict with published records on neighboring islands (Andros and Abaco Island). We demonstrate these three islands do not sample the same storms despite their proximity, and we compile these reconstructions together to create the first regional compilation of annually resolved paleohurricane records in The Bahamas. Integrating our Bahamian compilation with compiled records from the U.S. coastline indicates basin-wide increased storminess during the Medieval Warm Period. Afterward, the hurricane patterns in our Bahamian compilation match those reconstructed along the U.S. East Coast but not in the northeastern Gulf of Mexico. This disconnect may result from shifts in local environmental conditions in the North Atlantic or shifts in hurricane populations from straight-moving to recurving storms over the past millennium.
    Description: This work was funded by the National Science Foundation Graduate Research Fellowship (to E. J. W.), the Dalio Explore Foundation, and National Science Foundation grant OCE-1356708 (to J. P. D. and P. J. vH.).
    Keywords: Bahamas ; Blue holes ; Carbonates ; Paleohurricanes ; Sediment cores
    Repository Name: Woods Hole Open Access Server
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  • 4
    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
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC015989, doi:10.1029/2019JC015989.
    Description: Relatively minor amounts of methane, a potent greenhouse gas, are currently emitted from the oceans to the atmosphere, but such methane emissions have been hypothesized to increase as oceans warm. Here, we investigate the source, distribution, and fate of methane released from the upper continental slope of the U.S. Mid‐Atlantic Bight, where hundreds of gas seeps have been discovered between the shelf break and ~1,600 m water depth. Using physical, chemical, and isotopic analyses, we identify two main sources of methane in the water column: seafloor gas seeps and in situ aerobic methanogenesis which primarily occurs at 100–200 m depth in the water column. Stable isotopic analyses reveal that water samples collected at all depths were significantly impacted by aerobic methane oxidation, the dominant methane sink in this region, with the average fraction of methane oxidized being 50%. Due to methane oxidation in the deeper water column, below 200 m depth, surface concentrations of methane are influenced more by methane sources found near the surface (0–10 m depth) and in the subsurface (10–200 m depth), rather than seafloor emissions at greater depths.
    Description: This research was supported by DOE Grant (DE‐FE0028980) to J. K. and by DOE‐USGS Interagency Agreement DE‐FE0026195.
    Description: 2020-10-04
    Keywords: Methane ; Ocean ; Isotopes ; Gas seeps ; Mid Atlantic bight ; Oxidation
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Riedel, M., Rohr, K. M. M., Spence, G. D., Kelley, D., Delaney, J., Lapham, L., Pohlman, J. W., Hyndman, R. D., & Willoughby, E. C. Focused fluid flow along the Nootka fault zone and continental slope, explorer-Juan de Fuca Plate Boundary. Geochemistry Geophysics Geosystems, 21(8), (2020): e2020GC009095, doi:10.1029/2020GC009095.
    Description: Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from 〉20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios 〈500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate‐related bottom‐simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.
    Description: This study represents data from numerous cruises acquired over more than two decades. We would like to thank all the scientific personnel and technical staff involved in data acquisition, processing of samples, and making observations during the ROV dives, as well as the crews and captains of the various research vessels involved. This is contribution #5877 from the University of Maryland Center for Environmental Science. This is NRCan contribution number / Numéro de contribution de RNCan: 20200324.
    Keywords: Fluid flow ; Nootka transform fault ; Gas hydrate ; Intrusion ; Heat flow
    Repository Name: Woods Hole Open Access Server
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  • 7
    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(1), (2021): e2019JG005621, https://doi.org/10.1029/2019JG005621.
    Description: Ongoing ocean warming can release methane (CH4) currently stored in ocean sediments as free gas and gas hydrates. Once dissolved in ocean waters, this CH4 can be oxidized to carbon dioxide (CO2). While it has been hypothesized that the CO2 produced from aerobic CH4 oxidation could enhance ocean acidification, a previous study conducted in Hudson Canyon shows that CH4 oxidation has a small short‐term influence on ocean pH and dissolved inorganic radiocarbon. Here we expand upon that investigation to assess the impact of widespread CH4 seepage on CO2 chemistry and possible accumulation of this carbon injection along 234 km of the U.S. Mid‐Atlantic Bight. Consistent with the estimates from Hudson Canyon, we demonstrate that a small fraction of ancient CH4‐derived carbon is being assimilated into the dissolved inorganic radiocarbon (mean fraction of 0.5 ± 0.4%). The areas with the highest fractions of ancient carbon coincide with elevated CH4 concentration and active gas seepage. This suggests that aerobic CH4 oxidation has a greater influence on the dissolved inorganic pool in areas where CH4 concentrations are locally elevated, instead of displaying a cumulative effect downcurrent from widespread groupings of CH4 seeps. A first‐order approximation of the input rate of ancient‐derived dissolved inorganic carbon (DIC) into the waters overlying the northern U.S. Mid‐Atlantic Bight further suggests that oxidation of ancient CH4‐derived carbon is not negligible on the global scale and could contribute to deepwater acidification over longer time scales.
    Description: This study was sponsored by U.S. Department of Energy (DE‐FE0028980, awarded to J. D. K; DE‐FE0026195 interagency agreement with C. D. R.). We thank the crew of the R/V Hugh R. Sharp for their support, G. Hatcher, J. Borden, and M. Martini of the USGS for assistance with the LADCP, and Zach Bunnell, Lillian Henderson, and Allison Laubach for additional support at sea.
    Description: 2021-06-23
    Keywords: Radiocarbon ; Methane ; DIC ; Ocean acidification ; Climate change ; U.S Mid-Atlantic Bight
    Repository Name: Woods Hole Open Access Server
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  • 8
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Little, C. M., Hu, A., Hughes, C. W., McCarthy, G. D., Piecuch, C. G., Ponte, R. M., & Thomas, M. D. The relationship between U.S. East Coast sea level and the Atlantic Meridional Overturning Circulation: a review. Journal of Geophysical Research-Oceans, 124(9), (2019): 6435-6458, doi:10.1029/2019JC015152.
    Description: Scientific and societal interest in the relationship between the Atlantic Meridional Overturning Circulation (AMOC) and U.S. East Coast sea level has intensified over the past decade, largely due to (1) projected, and potentially ongoing, enhancement of sea level rise associated with AMOC weakening and (2) the potential for observations of U.S. East Coast sea level to inform reconstructions of North Atlantic circulation and climate. These implications have inspired a wealth of model‐ and observation‐based analyses. Here, we review this research, finding consistent support in numerical models for an antiphase relationship between AMOC strength and dynamic sea level. However, simulations exhibit substantial along‐coast and intermodel differences in the amplitude of AMOC‐associated dynamic sea level variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of ageostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections.
    Description: The authors acknowledge funding support from NSF Grant OCE‐1805029 (C. M. L.) and NASA Contract NNH16CT01C (C. M. L. and R. M. P.), the Regional and Global Model Analysis (RGMA) component of the Earth and Environmental System Modeling Program of the U.S. Department of Energy's Office of Biological & Environmental Research Cooperative Agreement DE‐FC02‐97ER62402 (A. H.), Natural Environment Research Council NE/K012789/1 (C. W. H.), Irish Marine Institute Project A4 PBA/CC/18/01 (G. D. M.), and NSF Awards OCE‐1558966 and OCE‐1834739 (C. G. P.). The National Center for Atmospheric Research is sponsored by National Science Foundation. The authors thank the two reviewers for their comments, and CLIVAR and the U.S. AMOC Science Team for inspiration and patience. All CMIP5 data used in Figures 4-6 are available at http://pcmdi9.llnl.gov/ website; the AMOC strength fields were digitized from Chen et al. (2018, supporting information Figure S3).
    Keywords: Sea level ; AMOC ; United States ; Coastal ; Climate model ; Review
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  • 9
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 125 (2020): e2019JF005446, doi: 10.1029/2019JF005446.
    Description: Atoll reef islands primarily consist of unconsolidated sediment, and their ocean‐facing shorelines are maintained by sediment produced and transported across their reefs. Changes in incident waves can alter cross‐shore sediment exchange and, thus, affect the sediment budget and morphology of atoll reef islands. Here we investigate the influence of sea level rise and projected wave climate change on wave characteristics and cross‐shore sediment transport across an atoll reef at Kwajalein Island, Republic of the Marshall Islands. Using a phase‐resolving model, we quantify the influence on sediment transport of quantities not well captured by wave‐averaged models, namely, wave asymmetry and skewness and flow acceleration. Model results suggest that for current reef geometry, sea level, and wave climate, potential bedload transport is directed onshore, decreases from the fore reef to the beach, and is sensitive to the influence of flow acceleration. We find that a projected 12% decrease in annual wave energy by 2100 CE has negligible influence on reef flat hydrodynamics. However, 0.5–2.0 m of sea level rise increases wave heights, skewness, and shear stress on the reef flat and decreases wave skewness and shear stress on the fore reef. These hydrodynamic changes decrease potential sediment inputs onshore from the fore reef where coral production is greatest but increase potential cross‐reef sediment transport from the outer reef flat to the beach. Assuming sediment production on the fore reef remains constant or decreases due to increasing ocean temperatures and acidification, these processes have the potential to decrease net sediment delivery to atoll islands, causing erosion.
    Description: This study was supported by the Strategic Environmental Research and Development Program through awards SERDP: RC‐2334, and RC‐2336. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    Description: 2021-03-25
    Keywords: Coral atolls ; Fringing reefs ; Sediment transport ; Wave model ; Wave climate ; Sea level rise
    Repository Name: Woods Hole Open Access Server
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  • 10
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(12), (2020): e2020GC008914, https://doi.org/10.1029/2020GC008914.
    Description: Rarely have small seamounts on the flanks of hotspot derived ocean‐island volcanoes been the targets of sampling, due to sparse high‐resolution mapping near ocean islands. In the Galápagos Archipelago, for instance, sampling has primarily targeted the subaerial volcanic edifices, with only a few studies focusing on large‐volume submarine features. Sampling restricted to these large volcanic features may present a selection bias, potentially resulting in a skewed view of magmatic and source processes because mature magmatic systems support mixing and volcanic accretion that overprints early magmatic stages. We demonstrate how finer‐scale sampling of satellite seamounts surrounding the volcanic islands in the Galápagos can be used to lessen this bias and thus, better constrain the evolution of these volcanoes. Seamounts were targeted in the vicinity of Floreana and Fernandina Islands, and between Santiago and Santa Cruz. In all regions, individual seamounts are typically monogenetic, but each seamount field requires multigenerational magmatic episodes to account for their geochemical variability. This study demonstrates that in the southern and eastern regions the seamounts are characterized by greater geochemical variability than the islands they surround but all three regions have (Sr‐Nd‐He) isotopic signatures that resemble neighboring islands. Variations in seamount chemistry from alkalic to tholeiitic near Fernandina support the concept that islands along the center of the hotspot track undergo greater mean depths of melting, as predicted by plume theory. Patterns of geochemical and isotopic enrichment of seamounts within each region support fine‐scale mantle heterogeneities in the mantle plume sourcing the Galápagos hotspot.
    Description: This work was carried out with funding from National Science Foundation Division of Ocean Sciences (OCE‐1634952 to V. D. Wanless, OCE‐1634685 to S. A. Soule). The authors have no competing interests to declare. We thank Sally Gibson and three anonymous reviewers for providing detailed and critical feedback on this manuscript.
    Description: 2021-05-06
    Keywords: Basalt ; Hotspot ; Mantle ; Ocean island ; Radiogenic isotope ; Trace element
    Repository Name: Woods Hole Open Access Server
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