Sediment cores (MR01‐K03 PC4/PC5, 1366 m water depth) collected from off northern Japan were studied using coexisting planktonic and benthic foraminiferal radiocarbon measurements to reconstruct the history of mid‐depth circulation in the northwest Pacific. Reconstructed ventilation ages indicate that, consistent with data from a previous radiocarbon study at a shallower site, there was significant variation in mid‐depth circulation during the last deglaciation, especially in the Bølling‐Allerød (13–15 ka) and Younger Dryas (11.5–13 ka) intervals. Our record indicates that the ventilation changes in the North Pacific were antiphase to those of the North Atlantic, suggesting that atmospheric moisture transport associated with the Asian Monsoon might have played a great role in millennium‐scale ventilation changes in the North Pacific during the last deglaciation.

No abstract

No abstract

[1] The variation of sea surface temperature (SST) in the Kuroshio-Oyashio transition area and the Okhotsk Sea during the last 40 kyr was estimated using long-chain unsaturated alkyl ketones (alkenones). The temperature difference between the present and the last glacial period was about 5°-6°C in the KuroshioOyashio transition area, slightly larger than the 4°C previously reported. Moreover, alkenones were not detected before 18 kyr B.P. in or near the Okhotsk Sea, perhaps because of nearly year-round sea-ice expansion, which would have prevented the growth of alkenone producers, or because alkenones were less well preserved in surface sediments during the glacial period. The northward and southward migrations of frontal zones were evaluated using differences in alkenone temperatures between stations located in the vicinity of the Subarctic Front (SAF), Subarctic Boundary (SAB), and Kuroshio Bifurcation Front (KBF). All three frontal zones migrated southward during the glacial period, compared with their present positions, and their relative positions were different between the Holocene and glacial periods. In particular, the distance between the SAF and the SAB was reduced during the glacial period compared with at present. The northward and southward migration of the frontal zones may relate to both mid to low atmospheric circulation and polar atmospheric circulation.