The Bering Sea is a massive, subarctic marginal sea of the Pacific Ocean, bordered by Alaska to the east and Russia’s Siberia and Kamchatka Peninsula to the west. Spanning over 2 million square kilometers, it separates the North American and Asian continents. Its unique bathymetry is split between a deep southern basin and a broad, shallow northern continental shelf. This marine environment is known for its extreme cold and is one of the world’s most biologically productive oceans, supporting vast fisheries and marine mammal populations.
Seasonal Surface Temperatures
The surface temperature of the Bering Sea exhibits a profound seasonal and regional contrast. In winter, the northern and eastern regions overlying the shallow continental shelf frequently reach the freezing point of saltwater, typically hovering near -1.7 degrees Celsius (28.9 degrees Fahrenheit) before ice forms.
During summer, the surface layer warms considerably, generally ranging between 2 degrees Celsius and 10 degrees Celsius (36 degrees Fahrenheit to 50 degrees Fahrenheit) across the eastern shelf. However, this warming often fails to penetrate the entire water column in the shallows. A persistent feature known as the “Cold Pool” remains a sub-surface layer across the eastern shelf that stays below 2 degrees Celsius (36 degrees Fahrenheit) year-round.
The southern Bering Sea, dominated by a deep ocean basin, experiences less extreme seasonal temperature swings. The volume and depth of the basin prevent the widespread surface freezing seen further north, maintaining a more moderate subarctic temperature range.
Factors Driving the Cold Environment
The Bering Sea’s cold environment is maintained by its physical geography and regional oceanographic circulation. Its proximity to the Arctic Ocean is a primary driver, allowing frigid air masses from the north to sweep down during winter. This cold air dramatically chills the surface water, especially over the shallow continental shelf in the north.
The bathymetry of the northern shelf, averaging less than 150 meters in depth, allows for rapid cooling of the entire water column. This shallow nature accelerates the formation of the Cold Pool and facilitates the initiation of sea ice.
Ocean currents contribute to the export and recirculation of cold water. The Bering Slope Current flows northward along the continental slope, contributing water to the southward-flowing Kamchatka Current (KC) on the western side. The KC transports cold, low-salinity water from the Bering Sea shelf southward along the Russian coast, influencing the thermal regime of the North Pacific.
Formation and Extent of Sea Ice
The annual freezing of the Bering Sea is a direct result of its extreme cold, shaping the ecosystem. Ice formation typically begins in the northern reaches in late autumn, often starting in October or November, as surface temperatures hit the freezing point.
As winter progresses, the ice expands southward, driven by persistent north-northeasterly winds that push the ice across the shelf. The greatest extent of sea ice is usually observed in February or March, sometimes reaching as far south as the Aleutian Islands in cold years.
The ice cover is generally thin and highly mobile, making its extent sensitive to wind direction and atmospheric patterns. A shift in wind patterns, such as warm winds from the southwest, can quickly break up the ice and push the edge northward, leading to significant interannual variability. The ice begins its retreat and melt in the spring, typically vanishing completely from the Bering Sea by the end of June or early July.