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

摘要

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 = 10(6) m(3) 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 sectionally 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. Spectral 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 variance 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.