Atlantic water circulation over the Mendeleev Ridge and Chukchi Borderland from thermohaline intrusions and water mass properties

Abstract

Hydrographic and tracer data from 2002 illustrate Atlantic water pathways and variability in the Mendeleev Ridge and Chukchi Borderland (CBLMR) region of the Arctic Ocean. Thermohaline double diffusive intrusions (zigzags) dominate both the Fram Strait (FSBW) and Barents Sea Branch Waters (BSBW) in the region. We show that details of the zigzags' temperature‐salinity structure partially describe the water masses forming the intrusions. Furthermore, as confirmed by chemical tracers, the zigzags' peaks contain the least altered water, allowing assessment of the temporal history of the Atlantic waters. Whilst the FSBW shows the 1990s warming and then a slight cooling, the BSBW has continuously cooled and freshened over a similar time period. The newest boundary current waters are found west of the Mendeleev Ridge in 2002. Additionally, we show the zigzag structures can fingerprint various water masses, including the boundary current. Using this, tracer data and the advection of the 1990s warming, we conclude the strongly topographically steered boundary current, order 50 km wide and found between the 1500 m and 2500 m isobaths, crosses the Mendeleev Ridge north of 80°N, loops south around the Chukchi Abyssal Plain and north around the Chukchi Rise, with the 1990s warming having reached the northern (but not the southern) Northwind Ridge by 2002. Pacific waters influence the Atlantic layers near the shelf and over the Chukchi Rise. The Northwind Abyssal Plain is comparatively stagnant, being ventilated only slowly from the north. There is no evidence of significant boundary current flow through the Chukchi Gap.