Deep Atlantic carbonate ion and CaCO3 compensation during the Ice Ages

• Published in: Paleoceanography and Paleoclimatology
• Main Authors: Sosdian, S. M., Rosenthal, Y., Toggweiler, J. R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2018
• Subjects: Pacific; North Atlantic
• Online Access: https://orca.cardiff.ac.uk/id/eprint/111258/; https://doi.org/10.1029/2017PA003312; https://orca.cardiff.ac.uk/id/eprint/111258/1/Deep%20Atlantic%20carbonate%20ion%20and%20CaCO3%20Compensation%20during%20the%20Ice%20Ages.pdf

Abstract Higher alkalinity is compensation for reduced CaCO3 burial in the deep ocean in response to increased carbon sequestration in the deep ocean. This process accounts 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 My orbitally resolved deep ocean calcite saturation record (∆CO32‐) derived from benthic foraminiferal B/Ca ratios in the North Atlantic. Glacial ∆CO32‐ declines across the mid‐Pleistocene transition (MPT) suggesting increased sequestration of carbon in the deep Atlantic. The magnitude, timing, and structure of deep Atlantic Ocean ∆CO32‐ parallels changes in ÊCO3 and contrasts the small amplitude, anti‐phased swings in IndoPacific ∆CO32‐ and ÊCO3 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 low∆CO32‐ levels at Marine Isotope Stages (MIS) 12, set the stage for the high pCO2 levels at MIS 11 and subsequent interglacials via large swings in ocean alkalinity caused by shifts in CaCO3 burial. Similarly, the development of classic (‘anti‐correlated’) CaCO3 patterns was driven by enhanced ocean stratification and an increase in deep ocean corrosivity in response to MPT cooling.