Volume and Freshwater Flux to the West of Greenland: Nares Strait from 2003 to 2009
Abstract:Nares Strait is a 30-40 km wide channel between northern Greenland and Canada where we collected time series observation of velocity, subsurface pressure, and salinity from 2003 to 2009 to quantify volume and freshwater flux. Direct sub-surface observations are augmented by ice velocity and dynamical constraints to interpolate observations to the surface. Measurements indicate a mean volume flux of 1.0 +/- 0.08 Sv (Sv=10^6 m^3/s) and a mean freshwater flux of 62 mSv from the Arctic Ocean through Nares Strait to the south. About 20% of the volume and 50% of the freshwater flux reside in the top 30-m of the water column.
Flux variability peaks at a 20-day time scale and correlates strongly with along-channel pressure gradients which explain more than 80% of the flux variance. Seasonal volume flux variations have an amplitude of about 0.1 Sv and a phase that result in maximal and minimal southward transports in March and November, respectively. Ice cover is usually land-fast in March and mobile in November suggesting that the frictional dynamics in a surface layer under the ice are secondary in importance to the along-channel pressure gradient that peaks in early spring with high sea level in the Arctic and low sea level in the more southerly Baffin Bay.
Observed changes in the duration of land-fast ice conditions impact ocean stratification and flux through Nares Strait. For example, volume and freshwater fluxes increased by 50% and 100% in years when the ice was mobile almost year-round from 2006 through 2010 as compared to the 2003 to 2006 period when the ice was not mobile for more than 6 month per year on average. Local winds explain almost 50% of the variance during the 2007 to 2009 period of year-round mobile ice when a southern ice arch did not form. This ice arch returned to southern Nares Strait in 2011 resulting in long periods of land-fast ice cover and, we hypothesize, reduced ocean flux.