Carbonate Saturation and Temperature Effects on Benthic Foraminiferal B/Ca, Sr/Ca, S/Ca, and Mg/Ca Inferred from Intermediate and Deep Pacific Ocean Records Spanning the Last 350 ky

The incorporation of trace elements into foraminiferal shells is not strictly controlled by thermodynamic effects but also influenced by biological or kinetic effects. While the exact mechanisms are hitherto unknown, empirical calibrations establish the use of trace element ratios as proxies for seawater properties such as temperature and the carbonate saturation state, CO3. Temperature and CO3 effects on the distribution coefficients are, however, intertwined for benthic foraminifera found in cold deep waters with minimally saturated to unsaturated carbonate ion conditions. B/Ca is an established proxy for CO3 calibrated for Cibicidoides wuellerstorfi using a global record. Sr/Ca has been suggested as a CO3 proxy and has been calibrated for the Atlantic and Pacific using core-top Sr/Ca measurements. However, evidence that the Sr/Ca calibration may change between ocean basins raises the possibility of secondary effects. More recently it has been argued that S/Ca may also reflect changes in the carbonate system (van Dijk et al., 2017), although a temperature effect cannot be ruled out. We present C. wuellerstorfi and Uvigerina B/Ca, Sr/Ca, S/Ca, and Mg/Ca records from Pacific sites north of Papua New Guinea, IODP sites U1486 (1332 m, upper deep water) and nearby U1487 (874 m, intermediate water) spanning the last three glacial-interglacial (G-IG) cycles. Here we compare CO3 reconstructions based on B/Ca, Sr/Ca, and S/Ca in the epifaunal C. wuellerstorfi. This comparison supports the argument that G-IG variability in benthic foraminiferal Sr/Ca are driven by changes in carbonate saturation. For S/Ca, we find that whereas its G-IG variability is likely dominated by CO3 variability in the deeper site where changes in bottom water temperature are minimal, the intermediate record suggests a more dominant effect of temperature, consistent with minimal G-IG changes in CO3. Further, comparison of the Mg/Ca-based temperature estimates derived from C. wuellerstorfi with records from infaunal Uvigerina at both sites suggest a strong influence of CO3 on the Mg/Ca record of C. wuellerstorfi. In this presentation we will discuss how using multi proxy, multi species records may allow us to reconstruct glacial-interglacial variability in both temperature and CO3 of the western Pacific intermediate and deep water.