ARCUS | Arctic Research Consortium of the United States

6th Annual ARCUS Award for Arctic Research Excellence


Submitted by   Julie Bacle
Authors   Julie Bacle, E.C. Carmack, and R.G. Ingram
Category   Physical Science
Title   Water column structure and circulation under the North Water Polynya during spring transition: April-July, 1998
Affiliation   School of Earth and Ocean Sciences, University of Victoria, Sidney, BC, Canada

Abstract

The North Water is a large recurring polynya in northern Baffin Bay. Over 400 hydrographic CTD stations taken from this region between April and July 1998 were examined to better understand the water column structures underlying the polynya during spring transition. These data portray the North Water to be an area where imported and dissimilar water masses converge over a complex bathymetry. Arctic-derived inflows (termed 'northern assembly' waters, NA) and Atlantic-derived inflow (termed 'southern assembly' waters, SA) interleave and mix along isopycnal surfaces. NA waters are derived from inflows through Nares Strait and Jones Sound; SA waters are derived from a northern-moving branch of the West Greenland Current (WGC). The most important mixing site under the polynya was found to lie above the north-south setting Smith Sound Canyon, between 76.5° and 77°N latitude. Here, NA and SA waters advance and mix to form a distinct relatively thick halocline layer termed 'North Water assembly' (NWA) characterised by density-compensating thermohaline intrusions. Further south, a sharp front separating NWA waters from SA waters nearly 2°C warmer at depths between 200 and 400 m roughly aligns with the 500m isobath. Flow patterns deduced from correlations of potential temperature (0) vs salinity (S), and from minima in stability frequency (N) profiles indicate that this front is manifest by convergence associated with a branch of the WGC that is cyclonically redirected as it approaches Smith Sound Canyon. As noted above, not all SA waters are immediately re-directed south towards the front, as a second branch follows the Greenland coast toward Smith Sound. While 0 and S distributions show some evidence of upwelling along the Greenland coast (eg. outcropping of isopycnal surfaces), no surfacing of warm Atlantic-derived water was observed during the sampling period (1998), suggesting that the North Water's opening is primarily a function of mechanical ice removal by winds and currents. Some sensible heat exchange associated with brine rejection and penetrative convection may occur, but only during periods of active ice formation.