Joint effects of boundary currents and thermohaline intrusions on the warming of Atlantic water in the Canada Basin, 1993-2007

The 1990-1991 influx of Atlantic water, both anomalously warm and in greater volume than in the past, enveloped the Chukchi Borderland in the western Canada Basin by 2002 and spread across the southeastern Canada Basin by 2007. Warmer, younger (more ventilated), and less dense Fram Strait Branch waters have replaced colder, older, and denser waters, increasing the temperature of the Fram Strait Branch core from a 50-year or more mean of similar to 0.45 degrees C to similar to 0.7 degrees C. Physical and geochemical data collected from 1993 to 2007 show that the two main transport mechanisms are the boundary current and thermohaline intrusions, established by large thermal gradients. The boundary current operates in a cyclonic direction whereas the thermohaline intrusions operate in an anticyclonic direction because of the influence of the Beaufort Gyre. This shows that the Beaufort Gyre's effect on ocean circulation extends into the Fram Strait Branch of the Atlantic layer. The boundary current, a fully pan-Arctic structure, is much slower in the Canada Basin than in basins upstream, with an effective speed of similar to 0.5 cm/s. The effective spreading rate of the thermohaline intrusions, relative to the core, is 0.2 cm/s. Thermohaline intrusions show signs of dissipation near the Northwind Ridge in 2007 suggesting that as temperature gradients between inflowing and resident waters decrease, they will disappear from the Canada Basin.