An increase in whole ocean alkalinity during glacial periods could account, in part, for the drawdown of atmospheric CO2 into the ocean. Such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity. We present evidence, based on down-core measurements of benthic foraminiferal B/Ca and Mg/Ca from a core in the Weddell Sea, that the deep ocean carbonate ion concentration, [CO3 2-], was elevated by ~25 µmol/kg during each glacial period of the last 800 kyrs. The heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the Atlantic and Pacific by the changing ventilation and chemistry of Weddell Sea waters. These waters are more corrosive than interglacial northern sourced waters, but not as undersaturated as interglacial southern sourced waters. Our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget, if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification. The Weddell records display low [CO3 2-] during deglaciations and peak interglacial warmth, coincident with maxima in %CaCO3 in the Atlantic and Pacific Oceans. Should the burial rate of alkalinity in the more alkaline glacial deepwaters outstrip the rate of alkalinity supply, then pelagic carbonate production by the coccolithophores, at the end of the glacial maximum could drive a decrease in ocean [CO3 2-] and act to trigger the deglacial rise in pCO2.

The age model for the core was developed by tuning the planktonic d18O to Lisiecki and Raymo, 2005, doi:10.1029/2004PA001071, incorporating the palaeomagnetic constraint of the Brunhes-Matuyama boundary. Trace metal analyses focussed on Cibicidoides spp.. 10-15 tests were hand-picked from the 250-355 µm fraction and cleaned by reductive and oxidative procedures [Boyle et al., 1985, doi:10.1016/0012-821X(85)90154-2]. B/Ca, and Mg/Ca ratios were analyzed by inductively coupled plasma mass spectrometer (ICP-MS) according to the method described in Yu et al., 2005, doi:10.1016/j.epsl.2008.09.015. By ICP-MS, the B blank is <2% of the consistency standards (B/Ca = 150 µmol/mol). When possible, duplicate measurements on the same solution were made. Based on replicate analyses of standard and samples, the precisions are <2.3% (RSD) for B/Ca and <1.4% (RSD) for Mg/Ca. Stable isotope data from both benthic and planktonic foraminifera and CaCO3 content have already been published in Mackensen et al., 1994, see doi:10.1594/PANGAEA.50031 for data.

Supplement to: Rickaby, Rosalind E M; Elderfield, Henry; Roberts, Natalie L; Hillenbrand, Claus-Dieter; Mackensen, Andreas (2010): Evidence for elevated alkalinity in the glacial Southern Ocean. Paleoceanography, 25(1), PA1209