Intermediate water formation in the Bering Sea during glacial periods: Evidence from neodymium isotope ratios

Changes in the flux and location of overturning circulation may have large effects on marine ecosystems and CO2 exchange between the ocean and atmosphere. However, unlike the Atlantic, little is known about ocean circulation and ventilation under glacial boundary conditions in the North Pacific, especially in regard to intermediate water circulation. Here we present new records of neodymium (Nd) isotopes (epsilon(Nd)) in Fe-Mn oxyhydroxides of Bering Sea sediments (884 m water depth). We found a systematic variation between radiogenic values (up to +0.8 epsilon(Nd)) during cold periods and relatively less radiogenic values (<-1 epsilon(Nd)) during warm periods. There are no water masses with such radiogenic Nd isotope signatures in the intermediate or deep North Pacific. Potential sources of radiogenic values in the subarctic North Pacific are limited to surface waters adjacent to the Aleutian Arc and Kamchatka Peninsula. Therefore, the radiogenic epsilon(Nd) values of Fe-Mn oxyhydroxides observed at the intermediate depth during glacial periods are best explained by subduction of the surface water to the intermediate depth (at least similar to 800 m) due to brine rejection. Our data strongly indicate that the northwestern Bering Sea (off northeastern Kamchatka) was a possible source region of glacial intermediate water in the Bering Sea and the subarctic North Pacific.