Water Sources for Georges Bank

Bob Houghton and Rick Fairbanks

Oxygen isotope analysis is used to identify water sources on George's Bank (GB). In the Gulf of St. Lawrence and on the Scotian Shelf, St. Lawrence River water (SLRW) and Labrador Shelf water (LShW) mix with Labrador Slope water (LSW) to produce the water entering the Gulf of Maine via the Northeast Channel. The oxygen-salinity properties of this water are distributed along a mixing curve between LSW and a freshwater end-member (NEC) consisting of 5% SLRW and 95% LShW. The SLRW provides 45% of the freshwater content (relative to 34.8 psu) of this water. Water on George's Bank (GBW) is derived primarily from the Northeast Channel inflow either mixing with Maine Coastal water (MCW) within the Gulf or from flow shunted directly onto the Bank. There has been significant variations over the past decade. In 1996 and 1997, when George's Bank salinities have been low, there was no MCW component so presumably the shunt circulation predominated. In 1995 GBW appears to be distributed along a mixing line with end-members consisting of LSW and a mixture of 43% MCW and 58% NEC. Along this curve Maine River water contributes 19% of the freshwater on GB (relative to 34.8 psu). In 1994 the coastal influence was even greater with contributions of 55% and 26% respectively. In June 1994 the coastal influence was greatest in the Great South Channel and on the northwest flank of the Bank. In 1996 the influence of MCW was observed only in June on the northwest flank.