Due to the eastward-setting Arctic surface waters found along the southern shore of Lancaster Sound, the mean currents there are large (15.3 cm/s) as compared to smaller westward-setting mean currents of 2.2 cm/s along the northern shore. Standard deviations about the 8 year mean are 21.5 and 15.0 cm/s respectively for the southern and northern shore sites, while maximum values can reach up to 150 cm/s. Bi-monthly mean velocities reach up to 50 cm/s in summer months along the southern shore, while they only reach 10 cm/s along the northern shore.
Bi-monthly mean ice drifts are smaller because of the long period of land-fast ice conditions, but can similarly reach maximum speeds of 150 cm/s. Ice draft measurements were available for only 2 years and show that the mean, standard deviation and maximum keel depth depend on whether landfast ice occurs at the mooring site. Ice volume fluxes and derived freshwater fluxes in the form as ice are difficult to estimate but appear to be an order of magnitude less than the freshwater fluxes in the water column.
Volume, freshwater and heat transports estimated from the mooring data clearly show the strong seasonal as well as the interannual variability. Heat fluxes are predominantly negative indicating that the Arctic surface water is colder and will cool the Atlantic Ocean. Yearly means of the volume fluxes vary from 0.4 to 1.0 Sv, and have an 8-year mean of 0.7 Sv. In general, the freshwater flux is 1/15 of the volume flux and follows the volume seasonal variability. It has an 8-year mean of 0.048 Sv and varies interannually by ±0.015 Sv.
The 8-year mean monthly volume flux has a summer maximum (1.15 Sv) and a late-fall minimum (0.25 Sv). Seasonal mean values are as low as -0.01 Sv for fall and as high as 1.32 Sv for summer.
Volume transport in Lancaster Sound is significantly correlated with northeastward winds in the Beaufort Sea, parallel to the western side of the CAA, at monthly to interannual time scales. The optimum location and wind direction are consistent with the flow being driven by a sea level difference along the Northwest Passage, and the difference being determined by setup caused by alongshore winds in the Beaufort Sea.
Freshwater and heat transport are highly correlated with volume transport. The correlation coefficients between volume transport and freshwater and heat transport are greater than 0.96 for both total transport and transport anomalies. Thus based on the transport estimates, the results for volume transport generally apply for freshwater and heat transport as well. However, freshwater transport is likely underestimated since it is based on measurements from Conductivity-Temperature-Depth (CTD) sensors at depths greater than 25-30 m (Prinsenberg and Hamilton 2005).
Wind forcing is also important in determining transport in Bering Strait at both weekly to monthly time scales and interannual time scales (Woodgate et al. 2006). However, the transport is primarily affected by local winds parallel to the strait. The mean transport is northward, and is weakest in winter because of strong northerly winds, and strongest in summer.
In contrast, in Lancaster Sound, transport variability is largely determined by winds 1,000 km away at the western end of the Northwest Passage parallel to the adjoining coasts. The mean transport is eastward, and transport is lowest in the fall because of strong northeasterly winds. Transport increases in January-February because of a high pressure ridge over the area producing a weaker northeasterly wind component. Highest transport is observed in the summer because of moderate westerly winds. The correlation of alongshore wind at 75° N, 125° W with the AO index is 0.60 as the alongshore wind show similar trends and inter-decadal variability. However the annual AO index does not capture the interannual variability of the observed transport over the 8-year mooring deployment (r = 0.21).
The authors would like to thank Murray Scotney for managing the instrumentation for the collection of all the mooring data. Internal and external reviewers are thanked for their helpful comments on the various drafts of the manuscript. Personnel of Canadian Coast Guard icebreakers are thanked for their continued support during field operations. This work was supported by the Canadian Program of Energy Research Development (PERD) and the Department of Fisheries and Oceans' High Priority Program.
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