Abrupt enhanced Pacific warm water intrusion into the Sea of Okhotsk since the early Holocene

As the main heat and water mass sources, the warm and saline Pacific waters have significant influence on sea ice and intermediate water circulation in the Sea of Okhotsk (SO). However, the long-term history of Pacific warm water intrusion into the SO remains unknown, impeding accurate predictions of its future changes. In this study, provenance proxies (clay mineral assemblages and trace element ratios (<2 μm)) from surface sediments and Site LV87-55-1 were used to investigate the history of Pacific water intrusion into the SO over the past 20 kyr. Provenance analysis indicates that sediments in the central SO primarily originated from the Amur River before 11.7 ka, with a significant rise in sediment input from the Kamchatka Peninsula since that time. By integrating published data on sediment grain size, sea surface temperature (SST), and sea-ice diatoms, we observed that the enhanced inflow of Pacific warm water into the SO led to intensified counterclockwise surface currents and the retreat of sea ice since the early Holocene, which subsequently resulted in a noticeable shift in sediment sources in the central SO. Furthermore, based on modern observation and TraCE-21 model simulations, we deduce that the intensified Aleutian Low (AL) since the early Holocene stimulated the East Kamchatka Current (EKC) through increased Sverdrup transport caused by cyclonic wind patterns. This, in turn, facilitated greater intrusion of Pacific warm water into the SO. Overall, our findings suggest an increase in Pacific warm water intrusion into the SO under future global warming scenarios, potentially posing a significant threat to the marine environment of both the SO and the subarctic Pacific.