An Observational Estimate of Volume and Freshwater Flux Leaving the Arctic Ocean through Nares Strait

Abstract

The Arctic Ocean is an important link in the global hydrological cycle, storing freshwater and releasing it to the North Atlantic Ocean in a variable fashion as pack ice and freshened seawater. An unknown fraction of this return flow passes through Nares Strait between northern Canada and Greenland. Surveys of ocean current and salinity in Nares Strait were completed in the summer of 2003. High-resolution data acquired by ship-based acoustic Doppler current profiler and via hydrographic casts revealed subtidal volume and freshwater fluxes of 0.8 Ϯ 0.3 Sv and -25 Ϯ 12 mSv (Sv ϭ 10 3 mSv ϭ 10 6 m 3 s Ϫ1 ), respectively. The observations resolved the dominant spatial scale of variability, the internal Rossby radius of deformation (L D ϳ9 km), and revealed a complex, yet coherent along-channel flow with a Rossby number of about 0.13, close to geostrophic balance. Approximately one-third of the total volume flux was associated with across-channel slope of the sea surface and two-thirds (68%) with across-channel slope of isopycnal surfaces. During the period of observation, sustained wind from the southwest weakened the average downchannel flow at the surface. The speed of tidal currents exceeded subtidal components by a factor of 2. Tidal signals were resolved and removed from the observations here using two independent methods resolving horizontal and vertical variability of tidal properties, respectively. Tidal current predictions from a barotropic model agreed well with depth-averaged observations in both amplitude and phase. However, because estimates of freshwater flux require accurate surface currents (and salinity), a least squares fitting procedure using velocity data was judged more reliable, since it permits quantification of vertical tidal current variations.

Nares Strait hydrography and salinity field from a 3‐year moored array

“…Stratified flows scale with the internal Rossby radius of deformation. In Nares Strait this radius is about 10 km [Münchow et al, 2006] and sets the width of baroclinic flow in geostrophic balance [LeBlond, 1980;Gill, 1982]. With the ∼5 km spatial resolution of our moorings in Nares Strait the internal Rossby radius of deformation is resolved and we thus are confident to interpret the spatial structure of the flow.…”

“…This is the fundamental spatial scale of motion in the CAA [LeBlond, 1980] and is about 10 km for Nares Strait [Münchow et al, 2006], significantly less than the width of the strait.…”

“…Münchow et al [2006] used data from a synoptic 2-day Acoustic Doppler Current Profiler (ADCP) survey to evaluate fluxes. The first longer term measurements were conducted as part of the Canadian Archipelago Throughflow Study from 2003 to 2006.…”

The Arctic Ocean—a Canadian perspective from IPY

“…The section missed the northward current of Atlantic water near Greenland (Zweng and Münchow 2006), but did sample its re-circulating branch ( Fig. 2: 9000 km), beneath the cold Canadian Arctic through-flow (CAT) in western Baffin Bay (Melling et al 2001;Lobb et al 2003;Münchow et al 2006;Melling et al 2008). South of Davis Strait, the C3O section passed into the warmer, weakly stratified cyclonic gyre of the Labrador Sea ( Fig.…”

Solar Arctic-Mediated Climate Variation on Multidecadal to Centennial Timescales: Empirical Evidence, Mechanistic Explanation, and Testable Consequences

“…7 See also discussion and estimates in Wadley and Bigg (2002), Jones et al (2003), Cuny et al (2005), Prinsenberg and Hamilton (2005), Kwok (2006Kwok ( , 2007, Munchow et al (2006), Serreze et al (2006), Zweng and Munchow (2006), Greene et al (2008), and Condron et al (2009). 8 This dipole index was defined as the difference of the annual-mean SSTs from the 40-60°N, 60-10°W box and 40-60°S, 50°W-0° box in Latif et al (2006), and is slightly different from a previous definition of the difference between the 40-60°N, 50-10°W box and 10-40°S, 50°W-10° box by Latif et al (2004).…”