Orbital Scale Kuroshio Current Variations of the Northwestern Pacific Ocean in the Early Pleistocene (Marine Isotope Stage 40–36) Based on Calcareous Nannofossil Records

Abstract The Quaternary period was marked by distinct glacial‐interglacial climate cycles driven by orbital forcing, which are closely linked to marine environmental change. In the northwestern Pacific Ocean, the subtropical Kuroshio Current and subarctic Oyashio Current play crucial roles in global climate modulation. Despite their significance, paleoceanographic studies with high temporal resolutions are scarce. Here, we investigated calcareous nannofossil assemblages of the Kazusa Group to reconstruct the sea‐surface conditions around the Japanese Archipelago during the marine isotope stage (MIS) 40–36, providing an important climatic record prior to the mid‐Pleistocene transition. A time‐series analysis of nannofossil floral changes revealed orbital scale Kuroshio Current variability as well as Kuroshio Front migrations, suggesting that the Kuroshio Current variations were linked to the variability of the North Pacific subtropical gyre. Moreover, orbital‐scale southward migrations of the Kuroshio Front during the glacial periods may be correlated with the displacement of the intertropical convergence zone caused by the northern hemisphere climate changes. Finally, spectral and wavelet analyses of calcareous nannofossil abundance showed a periodicity of ∼20 Kyr, indicating that these variabilities in the Kuroshio Current are predominantly controlled by high‐latitude climate forcings. Therefore, the results obtained in this study suggest that Kuroshio Current variations are related to climatic changes from low to high latitudes during the MIS 40–36.