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Deep Atlantic Carbonate Ion and CaCO 3 Compensation During the Ice Ages

2018; Wiley; Volume: 33; Issue: 6 Linguagem: Inglês

10.1029/2017pa003312

2572-4525

Sindia Sosdian, Yair Rosenthal, J. R. Toggweiler,

Marine Biology and Ecology Research

Abstract Higher alkalinity compensates for reduced CaCO 3 burial in the deep ocean in response to increased carbon sequestration. This process could account for about half of the reduction in glacial atmospheric CO 2 . To date, our understanding of this process comes from benthic carbon isotope and CaCO 3 burial records. Here we present a 1.5 Myr orbitally resolved deep ocean calcite saturation record (ΔCO 3 2− ) derived from benthic foraminiferal B/Ca ratios in the North Atlantic. Glacial ΔCO 3 2− declines across the mid‐Pleistocene transition suggesting increased sequestration of carbon in the deep Atlantic. The magnitude, timing, and structure of deep Atlantic Ocean ΔCO 3 2− parallel changes in %CaCO 3 and contrasts with the small amplitude, anti phased swings in Indo‐Pacific ΔCO 3 2− and %CaCO 3 during the mid‐to‐late Pleistocene questioning the classic view of CaCO 3 compensatory mechanism. We propose that the increasing corrosivity of the deep Atlantic causes the locus of CaCO 3 burial to shift into the equatorial Pacific where the flux of CaCO 3 to the seafloor was sufficiently high to overcome low saturation and establish a new burial “hot spot.” Based on this mechanism, we propose that the persistently lowΔCO 3 2− levels at marine isotope stage 12 set the stage for the high p CO 2 levels at marine isotope stage 11 and subsequent interglacials via large swings in ocean alkalinity caused by shifts in CaCO 3 burial. Similarly, the development of classic (“anticorrelated”) CaCO 3 patterns was driven by enhanced ocean stratification and an increase in deep ocean corrosivity in response to mid‐Pleistocene transition cooling.