Evaluating the Temperature Dependence of Δ44/40ca along with Δ18o, Mg/Ca, and Sr/Ca in Calcite Tests of Multiple Foraminifera Species

Preserved biomineral chemical compositions serve as valuable tools in constructing proxies for reconstructing past climates. A persistent effort exists to enhance and innovate temperature proxies, ensuring a comprehensive understanding of historical temperature variability-a vital Earth System parameter. Calcium isotopes (delta Ca-44/40) in foraminifera have been debated to be sensitive to temperature and requires further refinement. In this study we present a comprehensive assessment of delta Ca-44/40 temperature sensitivity in foraminifera by utilizing con-current delta Ca-44/40, delta O-18, Mg/Ca, and Sr/Ca ratios data on same samples. These coupled isotopic and elemental ratios were determined across various foraminifera species, including benthic (C. wuellerstorfi), thermocline planktic (G. truncatulinoides, G. inflata), and mixed layer planktic (G. ruber, G. bulloides, O. universa, G. siphonifera) from core-top and sediment trap samples from the Atlantic Ocean. The delta Ca-44/40-T calibration included calci-fication temperatures derived from both delta O-18 and Mg/Ca, utilizing established delta O-18-T and Mg/Ca-T relation-ships. The temperature sensitivity of delta Ca-44/40 in foraminifera is 0.042-0.058 %o/degrees C using all species data from published work and this study (except data from <3 degrees C habitat temperature). We report foraminifera delta Ca-44/40 and temperature relationships: delta Ca-44/40 (%o) = 0.042 x T (degrees C) + 0.289 (r(2) = 0.80, p < 0.0001), using tem-peratures derived from delta O-18 and Mg/Ca, respectively. Furthermore, we introduce a novel paleotemperature equation for foraminifera, employing a multi-regression approach that combines two temperature proxies, delta Ca-44/ 40 and Mg/Ca: SST (degrees C) = (9 +/- 2.6) x delta Ca-44/40 + (3.28 +/- 0.63) x Mg/Ca -(2.89 +/- 1.09). This multi-proxy approach can mitigate the uncertainty associated with individual proxy measurements and allows cross-validation. Application of this multi-proxy relationship to an East Atlantic Site (GeoB1112) yields a glacial -interglacial temperature change of 4.2 +/- 0.93 degrees C between MIS 1 and MIS 3 which is in agreement with published work.