Do coccolith clumped isotopes record sea surface temperatures? A sediment trap perspective

Some species of coccolithophores produce skeletal carbonate or coccoliths, which sink to the bottom of the ocean and accumulate as sediment. These sediments are an interesting target for paleoclimate reconstructions using carbonate clumped isotopes, as they are widespread in the Cenozoic on a broad range of latitudes. Coccoliths from laboratory grown coccolithophores have shown a systematic and robust Δ₄₇-temperature relationship (Clark et al., 2023). In this study, we measured the calcification temperature of coccolith calcite from sediment traps to better understand how the primary clumped isotope signal of coccoliths is transferred to the sediments to improve the interpretation of the geological record. Sediment traps anchored to the ocean floor and stationed at different depths capture sinking debris from organisms living above such as coccolithophores and diatoms. Through selection of only those open periods of the sediment trap corresponding to blooming or the maximum growth periods of coccolithophores, only coccoliths from a known period are dominantly present. Further, care was taken to select sediment traps with known production locations, production and mixed layer depths, and temperatures. For a temperature range of ~20°C, we show that the relationship found for laboratory grown coccolith calcite between Δ₄₇-temperature holds true for ocean-derived coccoliths. We also find the captured coccoliths approximate the temperatures from the estimated production depth better as opposed to the mixed layer depth, complete photic zone, or the sea surface. However, in certain locations a cold bias is present, potentially due to the presence of deep-water coccoliths or lithogenic particles.

Reference:

Clark, A. J., Torres-Romero, I., Jaggi, M., Bernasconi, S. M., and Stoll, H. M.: Coccolithophorids precipitate carbonate in clumped isotope equilibrium with seawater, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2581, 2023.