Scotian shelf crossovers during winter/spring 1999

A field program detected direct "crossover" of Scotian Shelf Water (SSC) from Browns to Georges Bank during winter/spring 1999 using (1) moored measurements, (2) drogued drifters, and (3) satellite imagery. Statistics of the 30-day trajectories indicate that (18, 55) ± 17% of the drifters crossed the (100, 200) m isobaths on Georges Bank. Transit times ranged from 2 to 26 days. Four of the drifters crossed onto the Northeast Peak (NEP) coinciding with the detection of Scotian Shelf Water at the central NEP mooring. These events are deemed "significant" because they serve to deliver particles from the Scotian Shelf directly to the gadoid spawning grounds on Georges Bank. Depths of the SSC layers lie between 15 and 50 m, and "residence times" for the Scotian Shelf Water on the NEP are estimated at 3 to 4 weeks. Canonical correlation analysis of the NEP temperature and salinity records suggest that 10% of the correlation structure among the variables is related to SSCs, while 70% is associated with the annual cycle. A search for SSC driving mechanisms reveals that (1) interannual variability of the annual freshwater discharge from the Gulf of St. Lawrence is not a factor, (2) Ekman-like response of near-surface currents to southeast wind stress plays a role but is not the dominant factor, and (3) mesoscale baroclinic features penetrating Northeast Channel from offshore are the most likely cause. Furthermore, the incidence of SSCs may be related to offshore fronts whose proximity is positively correlated with the North Atlantic Oscillation index.