Deep Atlantic carbonate ion and CaCO3 compensation during the ice ages

Higher alkalinity compensates for reduced CaCO3 burial in the deep ocean in response to increased carbon sequestration. This process could account for about half of the reduction in glacial atmospheric CO2. To date, our understanding of this process comes from benthic carbon isotope and CaCO3 burial records. Here we present a 1.5 Myr orbitally resolved deep ocean calcite saturation record (ΔCO32−) derived from benthic foraminiferal B/Ca ratios in the North Atlantic. Glacial ΔCO32− declines across the mid‐Pleistocene transition suggesting increased sequestration of carbon in the deep Atlantic. The magnitude, timing, and structure of deep Atlantic Ocean ΔCO32− parallel changes in %CaCO3 and contrasts with the small amplitude, anti phased swings in Indo‐Pacific ΔCO32− and %CaCO3 during the mid‐to‐late Pleistocene questioning the classic view of CaCO3 compensatory mechanism. We propose that the increasing corrosivity of the deep Atlantic causes the locus of CaCO3 burial to shift into the equatorial Pacific where the flux of CaCO3 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 lowΔCO32− levels at marine isotope stage 12 set the stage for the high pCO2 levels at marine isotope stage 11 and subsequent interglacials via large swings in ocean alkalinity caused by shifts in CaCO3 burial. Similarly, the development of classic (“anticorrelated”) CaCO3 patterns was driven by enhanced ocean stratification and an increase in deep ocean corrosivity in response to mid‐Pleistocene transition cooling.

Sosdian S. M., Rosenthal Y. & Toggweiler J. R., 2018. Deep Atlantic carbonate ion and CaCO3 compensation during the ice ages. Paleoceanography and Paleoclimatology 33: 546-562. Article (subscription required).

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