Influence of Past Changes in Atmospheric CO2 on Boron/Calcium of Planktic Fossil Foraminifera

Monday, 15 December 2014
Robert Andrew Domeyko, George Mason University Fairfax, College of Sciences, Fairfax, VA, United States, Katherine A Allen, Rutgers University, New Brunswick, NJ, United States; Columbia University, Palisades, NY, United States and Peter B deMenocal, Lamont-Doherty Earth Obs, Palisades, NY, United States
Culture experiments have revealed that B/Ca of shells grown by the foraminiferal species Globigerinoides ruber increase with increasing seawater pH. Specifically, B/Ca responds to changes in the relative abundance of pH-sensitive dissolved carbon and boron species (Allen et al. 2011, 2012). Here, we present a high-resolution study on fossilized G. ruber from two sites in North Atlantic subtropical gyres (VM25-21 and ODP 1055B) through 20 ka BP to evaluate how B/Ca responds to past changes in atmospheric CO2. Forams were picked and crushed gently, then cleaned and dissolved using a variation of the Boyle and Keigwin (1985) and Barker et al. (2003) cleaning protocols prior to analysis. ODP 1055B (from Carolina Slope, West Atlantic) produced a high-resolution record with lower B/Ca values during the glacial period followed by a rapid shift to higher B/Ca values in the early deglaciation, with values remaining high through the Holocene. These results were not predicted by culture calibrations, but they are consistent with B/Ca records from the Caribbean (ODP 999, Foster et al. 2008), suggesting this pattern is characteristic of surface waters in the greater North Atlantic region.