The frontal zone between the subtropical and subpolar gyres of the Northern Hemisphere.
In the Atlantic Ocean it is established by the meeting of the warm and saline Gulf Stream and the cold and fresh Labrador Current and extends as a temperature and salinity front, sometimes also known as the cold wall, from south of Newfoundland and the Grand Banks northeastward to the central North Atlantic. In the Pacific Ocean it consists of two parts, separated by the Japanese islands. The larger fresh is formed by the confluence of the warm and saline Kuroshio and the cold and fresh Oyashio and seen as a temperature and salinity front extending eastward from Japan near 35°N. The smaller fresh extends across the Sea of Japan in the west, where it separates the warm and saline Tsushima Current from the cold and fresh Mid-Japan Sea Cold Current.