Investigating the Paleoceanographic Significance of Li/Ca in Foraminifera

Lithium exhibits conservative behavior in the ocean and has a constant concentration and isotopic composition throughout the world oceans. Given our current understanding of lithium and calcium systematics (i.e., residence time of Li/Ca over 1Ma), it is anticipated that seawater Li/Ca ratios, and subsequent lithium incorporation in foraminiferal tests would not change over glacial-interglacial timescales. However, recent results suggest that foraminiferal Li/Ca may be an expression of changes in the incorporation behavior of the foraminifera due to environmental changes associated with glaciation and can potentially be applied as a proxy for seawater carbonate ion concentration across glacial-interglacial time cycles. To further investigate this supposition, high precision Li/Ca ratios were measured in the planktonic foraminifer Globigerinoides sacculifer over a full glacial-interglacial cycle (100ka) from Pacific Ocean core RC17-177. Li/Ca varies with δ ¹⁸O showing an increase of 37 percent from the Holocene to the last glacial maximum. These results will be complemented with foraminiferal lithium isotopic data currently in progress. If foraminiferal Li/Ca proves to be dominantly controlled by calcification rate as a function of seawater carbonate ion concentration, then Li/Ca may act as a proxy of past atmospheric CO2.