Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling

The carbon cycle is a key regulator of Earth's climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ¹³C_org-pforam) with δ¹³C_org of POM (δ¹³C_org-POM). We compare δ¹³C_org-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ¹³C_org-POM on a N-S Atlantic Ocean transect. Our results indicate that δ¹³C_org-pforam of planktonic foraminifera are remarkably similar to δ¹³C_org-POM. Application of our method on a glacial sample furthermore provided a δ¹³C_org-pforam value similar to glacial δ¹³C_org-POM predictions. We thus show that δ¹³C_org-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ¹³C_org-POM and better understanding of the evolution of the carbon cycle over geological time-scales.