Abstract
Temperature proxies such as clumped isotope (Δ47) 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 Δ47 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 Δ47 strongly follows the upper ocean
temperatures, in particular the average temperatures from the maximum
production depths of living coccolithophores from their provenance
areas. There is no evidence for a coccolithophore species-specific
effect on the Δ47-temperature relationship. Applying the recent
coccolith-specific Δ47-temperature calibration (Clark et al., 2024a) to
estimate calcification temperatures shows that inferred calcification
depths match the depth of maximum coccolithophore production in the
provenance area. Compared to other calibrations for biogenic carbonates,
the coccolith-specific Δ47-temperature calibration yields the best
agreement with the depth of maximum coccolithophore abundance and the
expected depth of coccolith production.