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  • Carbon cycling  (3)
  • Bay of Bengal  (2)
  • Climate variability  (2)
  • Carbon budget
  • American Geophysical Union  (5)
  • National Academy of Sciences  (2)
  • American Institute of Physics (AIP)
  • Annual Reviews
  • 2015-2019  (7)
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  • 2019  (7)
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  • 2015-2019  (7)
  • 2005-2009
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  • 2019  (7)
  • 1982
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  • 1947
  • 1
    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 Proceedings of the National Academy of Sciences.of the United States of America 116(36), (2019): 17666-17672. doi:10.1073/pnas.1907871116.
    Description: The conditions of methane (CH4) formation in olivine-hosted secondary fluid inclusions and their prevalence in peridotite and gabbroic rocks from a wide range of geological settings were assessed using confocal Raman spectroscopy, optical and scanning electron microscopy, electron microprobe analysis, and thermodynamic modeling. Detailed examination of 160 samples from ultraslow- to fast-spreading midocean ridges, subduction zones, and ophiolites revealed that hydrogen (H2) and CH4 formation linked to serpentinization within olivine-hosted secondary fluid inclusions is a widespread process. Fluid inclusion contents are dominated by serpentine, brucite, and magnetite, as well as CH4(g) and H2(g) in varying proportions, consistent with serpentinization under strongly reducing, closed-system conditions. Thermodynamic constraints indicate that aqueous fluids entering the upper mantle or lower oceanic crust are trapped in olivine as secondary fluid inclusions at temperatures higher than ∼400 °C. When temperatures decrease below ∼340 °C, serpentinization of olivine lining the walls of the fluid inclusions leads to a near-quantitative consumption of trapped liquid H2O. The generation of molecular H2 through precipitation of Fe(III)-rich daughter minerals results in conditions that are conducive to the reduction of inorganic carbon and the formation of CH4. Once formed, CH4(g) and H2(g) can be stored over geological timescales until extracted by dissolution or fracturing of the olivine host. Fluid inclusions represent a widespread and significant source of abiotic CH4 and H2 in submarine and subaerial vent systems on Earth, and possibly elsewhere in the solar system.
    Description: We are indebted to J. Eckert for his support with FE-EMPA; to K. Aquinho and E. Codillo for providing samples from Zambales; to K. Aquinho for Raman analysis of some of the samples from Zambales and Mt. Dent; to H. Dick for providing access to his thin section collection; to the curators of the IODP core repositories for providing access to Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP) samples; and to the captains and crews of the many cruises without whom the collection of these samples would not have been possible. Reviews by Peter Kelemen and an anonymous referee greatly improved this manuscript. This study is supported with funds provided by the National Science Foundation (NSF-OCE Award 1634032 to F.K. and J.S.S.).
    Description: 2020-02-19
    Keywords: Abiotic methane ; Fluid inclusions ; Serpentinization ; Methane seeps ; Carbon cycling
    Repository Name: Woods Hole Open Access Server
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  • 2
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 32(12), (2019): 1759-1775, doi:10.1029/2018GB006026.
    Description: Karst subterranean estuaries (KSEs) extend into carbonate platforms along 12% of all coastlines. A recent study has shown that microbial methane (CH4) consumption is an important component of the carbon cycle and food web dynamics within flooded caves that permeate KSEs. In this study, we obtained high‐resolution (~2.5‐day) temporal records of dissolved methane concentrations and its stable isotopic content (δ13C) to evaluate how regional meteorology and hydrology control methane dynamics in KSEs. Our records show that less methane was present in the anoxic fresh water during the wet season (4,361 ± 89 nM) than during the dry season (5,949 ± 132 nM), suggesting that the wet season hydrologic regime enhances mixing of methane and other constituents into the underlying brackish water. The δ13C of the methane (−38.1 ± 1.7‰) in the brackish water was consistently more 13C‐enriched than fresh water methane (−65.4 ± 0.4‰), implying persistent methane oxidation in the cave. Using a hydrologically based mass balance model, we calculate that methane consumption in the KSE was 21–28 mg CH4·m−2·year−1 during the 6‐month dry period, which equates to ~1.4 t of methane consumed within the 102‐ to 138‐km2 catchment basin for the cave. Unless wet season methane consumption is much greater, the magnitude of methane oxidized within KSEs is not likely to affect the global methane budget. However, our estimates constrain the contribution of a critical resource for this widely distributed subterranean ecosystem.
    Description: Funding for T. M. I. and D. B. was provided by TAMU‐CONACYT (project 2015‐049). D. B. was supported by the Research‐in‐Residence program (NSF award 1137336, Inter‐university Training in Continental‐scale Ecology), the Boost Fellowship (Texas A&M University at Galveston), and the Postdoctoral Scholar Program by Woods Hole Oceanographic Institution and U.S. Geological Survey. We thank Jacob Pohlman and István Brankovits for assistance with field expeditions. Special thanks to the late Bil Phillips (Speleotech) for the support and expertise provided us during field operations. We also thank Pete van Hengstum for productive discussions and guidance during the development of the manuscript. Michael Casso and Adrian Green helped with laboratory analyses. The manuscript was greatly improved by helpful comments from an anonymus reviewer, Jeff Chanton, and Meagan Gonneea. This work is contribution number UMCES 5541. Any use of trade names is for descriptive purposes and does not imply endorsement by the U.S. Government. The authors declare no competing financial interests. Archival data are available through the USGS ScienceBase‐Catalog at https://doi.org/10.5066/P9U0KRVM.
    Keywords: Subterranean estuary ; Coastal aquifer ; Carbon cycling ; Methane ; Hydrobiogeochemistry ; Anchialine ecosystem
    Repository Name: Woods Hole Open Access Server
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  • 3
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(7) (2019): 3927-3935, doi: 10.1029/2018GL081593.
    Description: Climate model simulations of the summer South Asian monsoon predict increased rainfall in response to anthropogenic warming. However, instrumental data show a decline in Indian rainfall in recent decades, underscoring the critical need for additional, independent records of past monsoon variability. Here, we present new reconstructions of annual summer South Asian Monsoon circulation over the past 250 years, based on the geochemical barium‐calcium signature of dust present in Red Sea corals. These records reveal how monsoon circulation has evolved with warming climate and indicate a significant multi‐century long monsoon intensification, with decreased multidecadal variance. Stronger monsoon circulation would have increased the moisture transport from the Arabian Sea and Bay of Bengal over the Indian subcontinent. If these trends continue, the monsoon circulation and associated moisture transport and precipitation will remain strong and stable for several decades.
    Description: We thank Editor Valerie Trouet and two anonymous reviewers for their constructive comments. We gratefully acknowledge Justin Ossolinski for assistance during core drilling; Maureen Auro, Laura Robinson, and Tom Marchitto for use of lab space and for technical advice; Margaret Sulanowska for providing XRD analysis of dust samples; and Sujata Murty and Ryan Davis for assistance in the lab. We thank Falmouth Hospital for use of X‐ray equipment. We acknowledge the use of the NSF‐supported WHOI ICP‐MS facility and thank Scot Birdwhistell for his assistance. This research was supported by grants to K. A. H. from NSF award OCE‐1031288 and KAUST award USA00002, and by a WHOI Postdoctoral Fellowship awarded to S. P. B. All data presented in this manuscript will be made publicly available online through the NOAA NCDC Paleoclimatology data archive (https://www.ncdc.noaa.gov/data‐access/paleoclimatology‐data/).
    Description: 2019-09-28
    Keywords: Paleoclimatology ; Climate variability ; Aerosols and particles ; Major and trace element geochemistry
    Repository Name: Woods Hole Open Access Server
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  • 4
    Publication Date: 2022-10-26
    Description: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (24), (2019):11646-11651, doi:10.1073/pnas.1900371116.
    Description: Measurements show large decadal variability in the rate of CO2 accumulation in the atmosphere that is not driven by CO2 emissions. The decade of the 1990s experienced enhanced carbon accumulation in the atmosphere relative to emissions, while in the 2000s, the atmospheric growth rate slowed, even though emissions grew rapidly. These variations are driven by natural sources and sinks of CO2 due to the ocean and the terrestrial biosphere. In this study, we compare three independent methods for estimating oceanic CO2 uptake and find that the ocean carbon sink could be responsible for up to 40% of the observed decadal variability in atmospheric CO2 accumulation. Data-based estimates of the ocean carbon sink from pCO2 mapping methods and decadal ocean inverse models generally agree on the magnitude and sign of decadal variability in the ocean CO2 sink at both global and regional scales. Simulations with ocean biogeochemical models confirm that climate variability drove the observed decadal trends in ocean CO2 uptake, but also demonstrate that the sensitivity of ocean CO2 uptake to climate variability may be too weak in models. Furthermore, all estimates point toward coherent decadal variability in the oceanic and terrestrial CO2 sinks, and this variability is not well-matched by current global vegetation models. Reconciling these differences will help to constrain the sensitivity of oceanic and terrestrial CO2 uptake to climate variability and lead to improved climate projections and decadal climate predictions.
    Description: We thank Rebecca Wright and Erik Buitenhuis at University of East Anglia, Norwich, for providing updated runs from the NEMO-PlankTOM5 model. T.D. was supported by NSF Grant OCE-1658392. C.L.Q. thanks the UK Natural Environment Research Council for supporting the SONATA Project (Grant NE/P021417/1). P.L. was supported by the Max Planck Society for the Advancement of Science. J.H. was supported under Helmholtz Young Investigator Group Marine Carbon and Ecosystem Feedbacks in the Earth System (MarESys) Grant VH-NG-1301. S.B. and R.S. were supported by the H2020 project CRESCENDO “Coordinated Research in Earth Systems and Climate: Experiments, Knowledge, Dissemination and Outreach,” which received funding from the European Union’s Horizon 2020 research and innovation program under Grant No 641816. SOCAT is an international effort, endorsed by the International Ocean Carbon Coordination Project, the Surface Ocean-Lower Atmosphere Study, and the Integrated Marine Biosphere Research program, to deliver a uniformly quality-controlled surface ocean CO2 database. The many researchers and funding agencies responsible for the collection of data and quality control are thanked for their contributions to SOCAT.
    Description: 2019-11-28
    Keywords: Carbon dioxide ; Ocean carbon sink ; Terrestrial carbon sink ; Climate variability ; Carbon budget
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters, 46(8), (2019):4346-4355, doi:10.1029/2018GL081577.
    Description: A yearlong record from moored current, temperature, conductivity, and four mixing meters (χpods) in the northernmost international waters of the Bay of Bengal quantifies upper‐ocean turbulent diffusivity of heat (Kt) and its response to the Indian monsoon. Data indicate (1) pronounced intermittency in turbulence at semidiurnal, diurnal, and near‐inertial timescales, (2) strong turbulence above 25‐m depth during the SW (summer) and NE (winter) monsoon relative to the transition periods (compare Kt 〉 10−4 m2/s to Kt  ∼ 10−5 m2/s, and (3) persistent suppression of turbulence (Kt 〈 10−5 m2/s) for 3 to 5 months in the latter half of the SW monsoon coincident with enhanced near‐surface stratification postarrival of low‐salinity water from the Brahmaputra‐Ganga‐Meghna delta and monsoonal precipitation. This suppression promotes maintenance of the low‐salinity surface waters within the interior of the bay preconditioning the upper northern Indian Ocean for the next year's monsoon.
    Description: This work was supported by the U.S. Office of Naval Research (ONR) Grants N00014‐14‐1‐0236 and N00014‐17‐1‐2472, and the Ocean Mixing and Monsoon program of the Indian Ministry of Earth Sciences. The deployment of the Woods Hole Oceanographic Institution mooring and RW and JTF were supported by ONR Grant N00014‐13‐1‐0453. The deployment and recovery of the mooring were carried out by RV Sagar Nidhi and RV Sagar Kanya, respectively, with the help of the crew and science parties. Thanks to National Institute of Ocean Technology (India) for buoy support. The authors acknowledge invaluable discussions with Johannes Becherer, Deepak Cherian, and Sally Warner at CEOAS, OSU, and Dipanjan Chaudhuri, J Sree Lekha, and Debasis Sengupta at CAOS, IISc. The authors thank two anonymous reviewers for their detailed reviews, which have helped sharpen many aspects of this paper. Data can be accessed as described in section S2.
    Description: 2019-10-08
    Keywords: Ocean turbulence ; Turbulence suppression ; Indian Monsoon ; Bay of Bengal ; Turbulent Mixing ; Chipod
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  • 6
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology, 34(7), (2019): 1218-1233, doi:10.1029/2018PA003537.
    Description: The last deglaciation (~20–10 kyr BP) was characterized by a major shift in Earth's climate state, when the global mean surface temperature rose ~4 °C and the concentration of atmospheric CO2 increased ~80 ppmv. Model simulations suggest that the initial 30 ppmv rise in atmospheric CO2 may have been driven by reduced efficiency of the biological pump or enhanced upwelling of carbon‐rich waters from the abyssal ocean. Here we evaluate these hypotheses using benthic foraminiferal B/Ca (a proxy for deep water [CO32−]) from a core collected at 1,100‐m water depth in the Southwest Atlantic. Our results imply that [CO32−] increased by 22 ± 2 μmol/kg early in Heinrich Stadial 1, or a decrease in ΣCO2 of approximately 40 μmol/kg, assuming there were no significant changes in alkalinity. Our data imply that remineralized phosphate declined by approximately 0.3 μmol/kg during Heinrich Stadial 1, equivalent to 40% of the modern remineralized signal at this location. Because tracer inversion results indicate remineralized phosphate at the core site reflects the integrated effect of export production in the sub‐Antarctic, our results imply that biological productivity in the Atlantic sector of the Southern Ocean was reduced early in the deglaciation, contributing to the initial rise in atmospheric CO2.
    Description: We would like to thank Bärbel Hönisch at Lamont‐Doherty Earth Observatory of Columbia University for help with methods development and Sarah McCart for technical assistance with ICP‐MS analyses. We would also like to give special thanks to Anna lisa Mudahy, who was responsible for picking a substantial portion of the benthic foraminifera used in this study. We are grateful to the WHOI core lab for sample collection and archiving. This work was supported by NSF grant OCE‐1702231 to D. L.
    Description: 2020-01-24
    Keywords: B/Ca ; Last deglaciation ; Carbon cycling
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(10), (2019): 5369-5377, doi: 10.1029/2019GL082078.
    Description: Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Bengal and their role on the mixed layer temperature (MLT) is examined using observations from a single Argo during December 2013 to July 2017. During fall, low salinity at surface generates BL in this region. It thickens to almost 80 m in winter enhanced by deepening of isothermal layer depth due to remote forcing. During winter, surface cooling lowers near‐surface temperature, and thus, the subsurface BL experiences a significant temperature inversion (~2.5 °C). This temperature inversion diffuses to distribute heat within ML and surface heating begins deep penetration of shortwave radiation through ML during spring. Hence, the ML becomes thermally well stratified, resulting in the warmest MLT. The Monin‐Obukhov length attains its highest value during summer indicating wind dominance in the ML. During spring and fall, upper ocean gains heat allowing buoyancy to dominate over wind mixing.
    Description: A. S. and S. S. thank financial support from Space Application Centre (SAC), Indian Space Research Organization (ISRO), Government of India (Grant: SAC/EPSA/4.19/2016). This study was also supported by the first phase of Ministry of Earth Sciences (MoES), Government of India grant to establish a Bay of Bengal Coastal Observatory (BOBCO) at IITBBS (Grant: RP088). Authors acknowledged NCPOR Contribution number J ‐ 03/2019‐20 for this work. The authors are grateful to the reviewers and the Editor for constructive suggestions. The figures are generated using Matlab. The data source and availability are given in the Text S1.
    Description: 2019-10-24
    Keywords: Argo ; Bay of Bengal ; mixed layer ; temperature inversion ; barrier layer ; Monin‐Obukhov length
    Repository Name: Woods Hole Open Access Server
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