Abstract 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 (δ 13 C org-pforam ) with δ 13 C org of POM (δ 13 C org-POM ). We compare δ 13 C org-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ 13 C org-POM on a N-S Atlantic Ocean transect. Our results indicate that δ 13 C org-pforam of planktonic foraminifera are remarkably similar to δ 13 C org-POM . Application of our method on a glacial sample furthermore provided a δ 13 C org-pforam value similar to glacial δ 13 C org-POM predictions. We thus show that δ 13 C org-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ 13 C org-POM and better understanding of the evolution of the carbon cycle over geological time-scales.