Why is the surface water of the Bering Sea less salty than its deep water?

The surface water of the Bering Sea is less salty than its deep water primarily due to processes occurring at the Earth's surface that locally add fresh water, which dilutes the salinity of the upper layers.12

In the open ocean, salinity typically ranges from 33 to 37 parts per thousand. In the Bering Sea, surface salinity is relatively low, measuring between 31 and 33 parts per thousand, while the salinity of the deeper waters increases to approximately 35 parts per thousand near the bottom. This variation is consistent with broader oceanic patterns where regions experiencing high precipitation or the influx of fresh water—such as runoff from land—exhibit depressed surface salinities compared to deeper, more stable water masses.21