The dataset derives from marine sediment core KC-13, recovered from the central Aegean Sea, Greece (38°14.6012′ N, 25°06.2470′ E; 652 m water depth), during the OTE-2019 expedition (HCMR, R/V Aegaeo). It comprises stable oxygen and carbon isotope data. Each sample consisted of 10–15 individual specimens of the planktonic foraminifer Globigerina bulloides (88 samples), hand-picked from the > 250 μm sediment fraction. The samples were gently crushed, ultrasonicated in methanol for 10 s to remove adhering clay particles, and dried under a laminar flow hood. Oxygen and carbon isotope analyses were performed using a Finnigan MAT 252 mass spectrometer at the Centres Científics i Tecnològics of the University of Barcelona (CCiT-UB).