Ocean current observations from Nares Strait to the west of Greenland: Interannual to tidal variability and forcing

Andreas Münchow1 and Humfrey Melling2 During 2003–06, as part of the Arctic Sub-Arctic Ocean Flux (ASOF) experiment, an array of ocean-sensing instruments was deployed at 80.5N latitude to investigate the flux of seawater from the Arctic Ocean via Nares Strait, the pathway to the west of Greenland. Three-year measurements of current from this experiment provide, for the first time at periods longer than a single season, the seawater flux and its variability via this important pathway. Below 30-m depth the average flux of volume 2003–06 was 0.57±0.09 Sv (1 Sv=106 m3 s−1) southward over a 38-km wide section reaching 360 m in depth. A linear trend, statistically significant at the 95 % confidence level, indicates an increase in the section-ally averaged flow below 30-m depth of 20 ± 10 % between 2003 and 2006. The flow is dominated by mixed diurnal and semi-diurnal tidal currents with kinetic energy an order of magnitude larger than that of the subtidal flow. The range of seasonal variation is 30–50 % of the long-term mean flow. Variations in flow of daily to monthly period are comparable in magnitude to the average flow. The flow through the cross-section is the net result of a larger southward flux in the deep western two thirds of the strait and a small northward flux within about 5 km of Greenland. The latter is about 5 % of the former. Spec-tral analyses indicates that the cross-channel pressure gradient is highly correlated with the sectionally averaged flow consistent with geostrophy. Along-channel pressure gradient explains 70 % of the vari-ance at a 33-day period with a phase lag consistent with a frictional response; at 3–7 day period the response is weaker (30%) with a phase relation suggestive of contributions by both friction and local acceleration. 1.