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Brine Rejection and the North Pacific Intermediate Water
Brine rejection plays a crucial role in ocean circulation. In coastal polynyas, it is the key to the ventilation of multiple water masses across both the Arctic and Antarctic. A coastal polynya is an area of open water surrounded by ice. The reason coastal polynyas are the most active areas of brine rejection is that these waters often see offshore winds which give the water direct contact with cold air. This leads to heat loss and ice production. One area that is commonly studied to look at these impacts is the coastal polynyas of the Okhotsk Sea. The Okhotsk Sea has wide, shallow shelves, severe wintertime conditions, high background salinity, and easy summertime access making it an ideal study location. There have been many studies done that look at the influence of brine rejection in the Okhotsk Sea.

In a paper done by Shcherbina et al. (2003), they analyze the influence of brine rejection well. Within the Okhotsk Sea, circulation is driven by the brine rejection that occurs in the winter months. As is typical for the rejection of brine, sea ice develops that is 70-90% fresher than seawater. The water underneath becomes saltier and colder, leading to an increase in density. This parcel of water in the Okhotsk Sea is referred to as dense shelf water (DSW). The saltier and colder a water parcel is, the denser it becomes, causing it to sink below other parcels of water. For this reason, the DSW will begin to sink within the water column. The parcel then moves southward along the coast of Sakhalin. From here, the water moves over into the Pacific and ventilates the North Pacific Intermediate Water (NPIW). The NPIW is known to be the densest water in the North Pacific, and it is a key water mass in ocean circulation.

Brine rejection has been shown to ventilate the North Pacific Ocean to a depth of 300-1,000 meters deep. Some studies have even shown it reaching mixing depths of 2,000 meters. The mixing and ventilation of the water column is key in helping to replenish the oxygen within intermediate waters. It can also lead to an upwelling of nutrients which can influence productivity. An increase in primary production can lead to an increase in other organisms such as krill to whales.