Sources and sinks of water to Georges Bank during 1997

Richard Limeburner, Robert Beardsley, and Ken Brink

During January to June, 1997, approximately 69 satellite-tracked drifters with drogues centered at depths of 10 or 40 m were deployed monthly off the northern flank and over the central part of Georges Bank as part of the U.S. GLOBEC NW Atlantic/Georges Bank program. The primary objective of the 1997 drifter effort was to observe and characterize the Lagrangian flow over the Bank and identify both sources and sinks of water to the Bank.

The preliminary results of the drifter observations are shown in 2 animations of the subtidal drifter tracks available on the Woods Hole GLOBEC web site. The first animation shows variability in the near-surface Lagrangian flow field on scales of 100s of kilometers, the primary length scale of Gulf Stream meander/ring variability. Approximately 7 warm- and cold-core rings were observed near Georges Bank in the first half of 1997. Warm saline intrusions of Gulf Stream and Slope Water onto Georges Bank and detrainment of cold fresh Bank water to the offshore region (see Figure 1) were frequent in 1997. Thus Gulf Stream rings and meanders can provide important sources and sinks of water over Georges Bank.

The Gulf of Maine near-surface water was a source to Georges Bank during winter. During spring the development of a clockwise Bank circulation along the northern flank appeared to be a barrier to the Gulf of Maine as a source of Bank water. Direct crossover of cool low salinity water from Browns Bank to Georges Bank was observed during February-March, and crossover of cool low salinity coastal water near Nantucket Shoals to Georges Bank was observed in May, 1997. Finally, an intrusion of warm saline Gulf Stream water to Georges Bank was observed within the 60 m isobath in July, 1997.