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1. Cold and relatively less salty water enters the Arctic Ocean through the narrow Bering Strait between Alaska and Siberia.

2. In winter, frigid winds from the icy Alaskan interior blast over the shallow Chukchi Sea. The cold air freezes seawater into sea ice and then pushes it out to sea, leaving new pockets of seawater available for freezing. This is “the ice factory” which manufactures ice. When seawater freezes, it releases salt into surface waters. These cold, salty waters become denser and sink, spilling over the continental shelf into the western Arctic Ocean. They create a layer known as a halocline (from the Greek words for “salt” and “slope”). Halocline waters lie atop a deeper layer of saltier, denser—and warmer—waters that flow into the Arctic from the Atlantic Ocean.

3. Once in the Arctic Ocean basin, the water is swept into a huge circular current—driven by strong winds—called the Beaufort Gyre. Mighty Siberian and Canadian rivers also drain into the circular current to create a great reservoir of relatively fresh water.

4. Periodically, the winds shift and the circular current weakens, allowing large volumes of fresh water to leak out and cross the Arctic in the Transpolar Current.

5. The water exits the Arctic Ocean via several “gateways.” It can flow through the Fram Strait, between northeast Greenland and Svalbard Island, and then branch around either side of Iceland. It can flow around the west side of Greenland through Baffin Bay and out Davis Strait. It may also flow through a maze of Canadian islands and out Hudson Strait.

6. Warmer, more salty surface waters from the Atlantic penetrate the Arctic Ocean and are cooled as they move through the Greenland Sea and the Norwegian Sea. As they get colder, they sink beneath the cold, less salty waters to depths reaching several hundred meters. Eventually, they exit through the Fram Strait, the only “gateway” that allows deeper water to flow through.