Age characteristics of a shelf-break eddy in the western Arctic and implications for shelf-basin exchange

Abstract

Radioisotope evaluation of a cold-core, anticyclonic eddy surveyed in September 2004 on the Chukchi Sea continental slope was used to determine its age since formation over the shelf environment. Because the eddy can be shown to have been generated near the shelf break, initial conditions for several age-dependent tracers could be relatively well constrained. A combination of 228Ra/226Ra, excess 224Ra, and 228Th/228Ra suggested an age on the order of months. This age is consistent with the presence of elevated concentrations of nutrients, organic carbon, suspended particles, and shelf-derived neritic zooplankton within the eddy compared to ambient offshore water in the Canada Basin but comparable to values measured in the Chukchi shelf and shelf-break environment. Hence this feature, at the edge of the deep basin, was poised to deliver biogeochemically significant shelf material to the central Arctic Ocean.