Antler Gilad

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Antler
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Gilad
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  • Article
    Shallow calcium carbonate cycling in the North Pacific Ocean
    (American Geophysical Union, 2022-05-06) Subhas, Adam V. ; Dong, Sijia ; Naviaux, John D. ; Rollins, Nick E. ; Ziveri, Patrizia ; Gray, William R. ; Rae, James W. B. ; Liu, Xuewu ; Byrne, Robert H. ; Chen, Sang ; Moore, Christopher ; Martell-Bonet, Loraine ; Steiner, Zvi ; Antler, Gilad ; Hu, Huanting ; Lunstrum, Abby ; Hou, Yi ; Kemnitz, Nathaniel ; Stutsman, Johnny ; Pallacks, Sven ; Dugenne, Mathilde ; Quay, Paul D. ; Berelson, William M. ; Adkins, Jess F.
    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.
  • Article
    Trace element geochemistry in North Pacific red clay sediment porewaters and implications for water‐column studies
    (American Geophysical Union, 2023-11-14) Steiner, Zvi ; Antler, Gilad ; Berelson, William M. ; Crockford, Peter W. ; Dunlea, Ann G. ; Hou, Yi ; Adkins, Jess F. ; Turchyn, Alexandra V. ; Achterberg, Eric P.
    Geochemical analyses of trace elements in the ocean water column have suggested that pelagic clay-rich sediments are a major source of various elements to bottom-waters. However, corresponding high-quality measurements of trace element concentrations in porewaters of pelagic clay-rich sediments are scarce, making it difficult to evaluate the contributions from benthic processes to global oceanic cycles of trace elements. To bridge this gap, we analyzed porewater and bulk sediment concentrations of vanadium, chromium, cobalt, nickel, copper, arsenic, molybdenum, barium and uranium, as well as concentrations of the major oxidants nitrate, manganese, iron, and sulfate in the top 30 cm of cores collected along a transect from Hawaii to Alaska. The data show large increases in porewater concentrations of vanadium, manganese, cobalt, nickel, copper, and arsenic within the top cm of the sediment, consistent with the release of these elements from remineralized organic matter. The sediments are a sink for sulfate, uranium, and molybdenum, even though conditions within the sampled top 30 cm remain aerobic. Porewater chromium concentrations generally increase with depth due to release from sediment particles. Extrapolated to the global aerial extent of pelagic clay sediment, the benthic fluxes in mol yr−1 are Ba 3.9 ± 3.6 × 109, Mn 3.4 ± 3.5 × 108, Co 2.6 ± 1.3 × 107, Ni 9.6 ± 8.6 × 108, Cu 4.6 ± 2.4 × 109, Cr 1.7 ± 1.1 × 108, As 6.1 ± 7.0 × 108, V 6.0 ± 2.5 × 109. With the exception of vanadium, calculated fluxes across the sediment–water interface are consistent with the variability in bottom-water concentrations and ocean residence time of the studied elements.