Spivack Arthur J.

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Spivack
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Arthur J.
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  • Article
    Deep North Atlantic last glacial maximum salinity reconstruction
    (American Geophysical Union, 2021-04-24) Homola, Kira ; Spivack, Arthur J. ; Murray, Richard W. ; Pockalny, Robert ; D'Hondt, Steven ; Robinson, Rebecca
    We reconstruct deep water-mass salinities and spatial distributions in the western North Atlantic during the Last Glacial Maximum (LGM, 19–26 ka), a period when atmospheric CO2 was significantly lower than it is today. A reversal in the LGM Atlantic meridional bottom water salinity gradient has been hypothesized for several LGM water-mass reconstructions. Such a reversal has the potential to influence climate, ocean circulation, and atmospheric CO2 by increasing the thermal energy and carbon storage capacity of the deep ocean. To test this hypothesis, we reconstructed LGM bottom water salinity based on sedimentary porewater chloride profiles in a north-south transect of piston cores collected from the deep western North Atlantic. LGM bottom water salinity in the deep western North Atlantic determined by the density-based method is 3.41–3.99 ± 0.15% higher than modern values at these sites. This increase is consistent with: (a) the 3.6% global average salinity change expected from eustatic sea level rise, (b) a northward expansion of southern sourced deep water, (c) shoaling of northern sourced deep water, and (d) a reversal of the Atlantic's north-south deep water salinity gradient during the LGM.
  • Dataset
    Porewater measurements of nitrate and nitrite concentration and N and O isotopic ratios (d15N and d18O) collected from sites 3 and 10 on the North Atlantic Long Core Cruise R/V Knorr KN223 from October to December 2014
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-03-15) Buchwald, Carolyn ; Spivack, Arthur J. ; Wankel, Scott
    Porewater measurements of nitrate and nitrite concentration and N and O isotopic ratios (d15N and d18O) collected from sites 3 and 10 on the North Atlantic Long Core Cruise R/V Knorr KN223 from October to December 2014. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/748792
  • Article
    The contribution of water radiolysis to marine sedimentary life
    (Nature Research, 2021-02-26) Sauvage, Justine ; Flinders, Ashton F. ; Spivack, Arthur J. ; Pockalny, Robert ; Dunlea, Ann G. ; Anderson, Chloe H. ; Smith, David C. ; Murray, Richard W. ; D'Hondt, Steven
    Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock. Radiolytic H2 has been identified as the primary electron donor (food) for microorganisms in continental aquifers kilometers below Earth’s surface. Radiolytic products may also be significant for sustaining life in subseafloor sediment and subsurface environments of other planets. However, the extent to which most subsurface ecosystems rely on radiolytic products has been poorly constrained, due to incomplete understanding of radiolytic chemical yields in natural environments. Here we show that all common marine sediment types catalyse radiolytic H2 production, amplifying yields by up to 27X relative to pure water. In electron equivalents, the global rate of radiolytic H2 production in marine sediment appears to be 1-2% of the global organic flux to the seafloor. However, most organic matter is consumed at or near the seafloor, whereas radiolytic H2 is produced at all sediment depths. Comparison of radiolytic H2 consumption rates to organic oxidation rates suggests that water radiolysis is the principal source of biologically accessible energy for microbial communities in marine sediment older than a few million years. Where water permeates similarly catalytic material on other worlds, life may also be sustained by water radiolysis.
  • Article
    Relationship of bacterial richness to organic degradation rate and sediment age in subseafloor sediment
    (American Society for Microbiology, 2016-06-10) Walsh, Emily A. ; Kirkpatrick, John B. ; Pockalny, Robert ; Sauvage, Justine ; Spivack, Arthur J. ; Murray, Richard W. ; Sogin, Mitchell L. ; D'Hondt, Steven
    Subseafloor sediment hosts a large, taxonomically rich and metabolically diverse microbial ecosystem. However, the factors that control microbial diversity in subseafloor sediment have rarely been explored. Here we show that bacterial richness varies with organic degradation rate and sediment age. At three open-ocean sites (in the Bering Sea and equatorial Pacific) and one continental margin site (Indian Ocean), richness decreases exponentially with increasing sediment depth. The rate of decrease in richness with depth varies from site to site. The vertical succession of predominant terminal electron acceptors correlates to abundance-weighted community composition, but does not drive the vertical decrease in richness. Vertical patterns of richness at the open-ocean sites closely match organic degradation rates; both properties are highest near the seafloor and decline together as sediment depth increases. This relationship suggests that (i) total catabolic activity and/or electron donor diversity exerts a primary influence on bacterial richness in marine sediment, and (ii) many bacterial taxa that are poorly adapted for subseafloor sedimentary conditions are degraded in the geologically young sediment where respiration rates are high. Richness consistently takes a few hundred thousand years to decline from near-seafloor values to much lower values in deep anoxic subseafloor sediment, regardless of sedimentation rate, predominant terminal electron acceptor, or oceanographic context.
  • Article
    Isotopic constraints on nitrogen transformation rates in the deep sedimentary marine biosphere
    (American Geophysical Union, 2018-10-18) Buchwald, Carolyn ; Homola, Kira ; Spivack, Arthur J. ; Estes, Emily R. ; Wankel, Scott D.
    Little is known about the nature of microbial community activity contributing to the cycling of nitrogen in organic-poor sediments underlying the expansive oligotrophic ocean gyres. Here we use pore water concentrations and stable N and O isotope measurements of nitrate and nitrite to constrain rates of nitrogen cycling processes over a 34-m profile from the deep North Atlantic spanning fully oxic to anoxic conditions. Using a 1-D reaction-diffusion model to predict the distribution of nitrogen cycling rates, results converge on two distinct scenarios: (1) an exceptionally high degree of coupling between nitrite oxidation and nitrate reduction near the top of the anoxic zone or (2) an unusually large N isotope effect (~60‰) for nitrate reduction that is decoupled from the corresponding O isotope effect, which is possibly explained by enzyme-level interconversion between nitrite and nitrate.
  • Article
    Archaea dominate oxic subseafloor communities over multimillion-year time scales
    (American Association for the Advancement of Science, 2019-06-19) Vuillemin, Aurèle ; Wankel, Scott D. ; Coskun, Ömer K. ; Magritsch, Tobias ; Vargas, Sergio ; Estes, Emily R. ; Spivack, Arthur J. ; Smith, David C. ; Pockalny, Robert ; Murray, Richard W. ; D'Hondt, Steven ; Orsi, William D.
    Ammonia-oxidizing archaea (AOA) dominate microbial communities throughout oxic subseafloor sediment deposited over millions of years in the North Atlantic Ocean. Rates of nitrification correlated with the abundance of these dominant AOA populations, whose metabolism is characterized by ammonia oxidation, mixotrophic utilization of organic nitrogen, deamination, and the energetically efficient chemolithoautotrophic hydroxypropionate/hydroxybutyrate carbon fixation cycle. These AOA thus have the potential to couple mixotrophic and chemolithoautotrophic metabolism via mixotrophic deamination of organic nitrogen, followed by oxidation of the regenerated ammonia for additional energy to fuel carbon fixation. This metabolic feature likely reduces energy loss and improves AOA fitness under energy-starved, oxic conditions, thereby allowing them to outcompete other taxa for millions of years.