Pallacks Sven

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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
    Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean
    (Nature Research, 2023-02-20) Ziveri, Patrizia ; Gray, William Robert ; Anglada-Ortiz, Griselda ; Manno, Clara ; Grelaud, Michael ; Incarbona, Alessandro ; Rae, James William Buchanan ; Subhas, Adam V. ; Pallacks, Sven ; White, Angelicque ; Adkins, Jess F. ; Berelson, William
    Planktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO. Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate production in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolithophores dominate the living calcium carbonate (CaCO) standing stock, with coccolithophore calcite comprising ~90% of total CaCO production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO production is higher than the sinking flux of CaCO at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO production derived from satellite observations/biogeochemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO cycle and its impact on atmospheric CO will largely depend on how the poorly-understood processes that determine whether CaCO is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification.