Dissolution Effects on Clumped Isotope Signatures in Planktic Foraminifera

The carbonate clumped isotope paleothermometer is becoming more widely used in the geosciences because it is less sensitive to solution δ 18 O and Mg/Ca than other carbonate‐based temperature proxies. Here, we examine the impacts of dissolution on foraminiferal clumped isotope records (Δ 47 ). Dissolution is known to impact carbonate minerals in ocean sediments near and below the carbonate saturation horizon. The effects of dissolution on foraminiferal mass, δ 18 O, and Mg/Ca have been the subject of prior work but have not yet been reported for the carbonate clumped isotope paleothermometer. We examine six planktic foraminiferal species from core‐tops collected at different water depths on the Ontong Java Plateau. Below the carbonate saturation horizon, multiple species exhibit higher Δ 47 values, biasing Δ 47 to cooler temperatures, though all species remain within error of their assumed calcification depth ranges. These effects are observed in Globigerinella siphonifera , Pulleniatina obliquiloculata , and Globorotalia tumida with an ∼0.01‰ difference from above to below the saturation horizon; p < 0.01 corresponding to a temperature bias of ∼4°C at a measured temperature of 28°C and of ∼3°C at a measured temperature of 18°C. Normalizing data for different species yields a pooled slope of −0.0006‰/μmol/kg Δ[CO 3 2− ] ( p < 0.01). Dissolution experiments show that for two species, Trilobus sacculifer and G . tumida , Δ 47 increased with mass loss. We propose multiple mechanisms by which dissolution may impact Δ 47 including intra‐test heterogeneous dissolution, which provide context to enable corrections for the impacts of dissolution on clumped isotope‐based paleo‐records.