Circulation and Property Changes in the North Pacific Ocean for the Last Glacial Maximum

Abstract

The property and circulation changes in the North Pacific Ocean during the last glacial maximum (LGM) are investigated using a coupled ocean-atmosphere-sea ice climate model. In the LGM, an increase in potential density in upper layers of the northern North Pacific makes the water column highly unstable and eventually results in the enhancement of the North Pacific Intermediate Water (NPIW) production. The NPIW outflow reaches deeper layers than in present, but confined to the North Pacific, in consistent with proxy evidence. The increase in potential density is predominantly due to the increase in salinity and secondarily decreases in temperature. The increase in surface salinity is especially high in the Sea of Okhotsk and the western Bering Sea, which are the possible source areas of the glacial NPIW production. In these regions, an increase in brine release due to the markedincrease in sea ice, the excessive evaporation over precipitation, and the reduction in river discharge contribute to the increase in surface salinity. In short, reduction in freshwater input to the northern North Pacific is mainly responsible for the increase in the production and outflow of glacial NPIW.