An observational study of Davis Strait transports
Curry, Mary Beth
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Davis Strait is one of two main gateways where freshwater from the Arctic enters the North Atlantic. An observing system began operating in Davis Strait in September 2004 with the goal of providing sustained, long-term quantification of Arctic-subarctic exchange west of Greenland. The system, including moorings, Seaglider surveys and autumn hydrographic sections, was designed to quantify volume, freshwater and heat transports and associated uncertainties. The goal of this analysis is to quantify Davis Strait transport variability and identify atmospheric forcing mechanisms driving the variability to help aid in understanding how exchanges between the Arctic and North Atlantic are being modified due to recent changes observed in the Arctic. Data from six years (2004-10) of continuous measurements give annual volume, liquid freshwater and temperature transports through Davis Strait of -1.6 ± 0.5 Sv, -93 ± 6 mSv and 23 ± 2 TW, respectively (negative sign indicates southward transport). Sea ice export contributes additional 10 mSv of freshwater transport. The array provides the first year-round measurements in the upper 100 m and over the shelves, accounting for 38% (-0.6 Sv) of the net volume and 61% (-51 mSv) of the net freshwater transports. Davis Strait volume and freshwater fluxes are the same order of magnitude as those from Fram Strait, the other Arctic outflow gateway. Interannual and annual variability of the net transports are large, with average annual volume, freshwater and heat transport standard deviations of 0.7 Sv, 17 mSv and 12 TW and interannual standard deviations of 0.3 Sv, 15 mSv and 2 TW. Although there are no clear trends in the current transports, reanalysis of Davis Strait mooring data from 1987-90 reveals that less Arctic outflow and more warm, salty North Atlantic inflow occurred in 2004-10 as compared to the earlier period. A change in Arctic freshwater storage may have also caused a freshening event observed between September 2009 to August 2010. Lagged correlation analysis between Davis Strait transport and regional sea level pressure (SLP) and winds reveals that atmospheric variability within Baffin Bay significantly influences circulation and transport through Davis Strait. A seasonal SLP trough, related to high SLP over the Arctic and low SLP over the subpolar North Atlantic around Greenland and Iceland, establishes in Baffin Bay beginning around October and weakens rapidly around March and April. The SLP trough is an important mechanism driving Davis Strait transport and forms in response to seasonal temperature changes, seasonal ice variability, the rough ice covered topography of Greenland and the presence of strong low pressure systems that move across the subpolar seas.
- Oceanography