Modelling the effect of a slope-water intrusion on advection of fish larvae in May 1995 on Georges Bank

Abstract

In the spring of 1995, an intrusion of warm/salty slope water occurred on the southern flank of Georges Bank. As observed on several cross-bank hydrographic and acoustic Doppler current profiler sections, this intrusion resulted in a narrow (10 km) but intense shelfbreak jet (30 cm s⁻¹ westward residual) in the near-surface waters. A satellite tracked drifter with a drogue located in the core of this jet (15 m) travelled 120 km to the west in 5.5 d. To examine this process and demonstrate the potential redistribution of fish larvae (collected with bongo net hauls) in the presence of a slope-water intrusion, a finite-element 3D circulation model has been initialized with the observed CTD density field. Moored velocity records are assimilated into the model to estimate the oceanic boundary elevations of a limited-area grid. The simulated particle tracks indicate enhanced along-bank flow relative to the long-term seasonal mean and a downwelling convergence zone in the vicinity of the shelf/slope front. The model resolves most of the subtidal flow and provides insight into the vertical advection of the animals and potential mechanisms of retention and loss.