Clumped Isotope Temperatures of Coccolithophores From Global Sediment Traps

Abstract

Temperature proxies such as clumped isotope (Δ 47 ) thermometry on biogenic carbonates are applied to the past with greatest confidence when the proxy‐temperature relationship is shown to be robust within natural temperature conditions of the ocean. Especially well‐suited for this purpose are biogenic carbonates sampled from well‐constrained production period and oceanographic conditions of sediment traps. Since coccolithophorids have a cosmopolitan distribution and are major biogenic carbonate producers in the surface ocean, their coccoliths usually dominate the inorganic carbon flux in sediment traps and are sufficiently abundant in most traps for clumped isotope analysis. Here, we measured Δ 47 in the coccolith size fraction of 18 sediment trap samples across a 75° latitudinal gradient and three ocean basins. To identify the upper ocean provenance region of the coccoliths in each trap, a simple model of coccolith transport by ocean currents was constructed. The coccolith Δ 47 strongly follows upper ocean temperatures, and there is no evidence for a coccolithophore species‐specific effect on the Δ 47 ‐temperature relationship. Applying the coccolith‐specific Δ 47 ‐temperature calibration (Clark, Torres‐Romero, et al., 2024, https://doi.org/10.5194/cp‐20‐2081‐2024 ) to estimate calcification temperatures shows that inferred calcification depths match the depth of maximum coccolithophore production, and shows a good agreement with the depth of maximum coccolithophore abundance and the expected depth of coccolith production. We also measured dual clumped isotopes (Δ 47 and Δ 48 ) on coccoliths cultured under controlled temperatures, and confirm that the coccolith clumped isotopes are affected by kinetic bias, independently verifying the need for a coccolith‐specific calibration for accurate paleotemperature reconstructions by means of Δ 47 .