Low-Frequency Circulation at the Edge of the Scotian Shelf

Abstract

Abstract Records of current, temperature and salinity from a two-year mooring program at the shelf break off Nova Scotia are examined to determine the low-frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the Gulf Stream. The seasonal mean and subtidal variance (at periods of 2–10 days) of the cross-shelf currents reflect the strong annual cycle in the wind field measured at Sable Island. The mean vertical shear suggests a simple Ekman response to winter increases in the longshore wind component, but this model fails quantitatively because 1) the inferred surface-layer (20 m) transport is much too large and 2) the deep (150 m) “return” flow shows no annual signal. The excessive offshore near-surface transport in winter must be reconciled with the relatively stationary position of the shelf/slope-water boundary (SSB) by invoking intense cross-frontal mixing and/or a seasonal mean alongshore pressure gradient. The seasonal mean longshore currents...