Low-frequency variability of sea level and currents off Newfoundland

Abstract

TOPEX/Poseidon (T/P) sea level data for the period from 1992 to 2002 are analysed to investigate sea level and current variability over the Newfoundland Slope. Sea level anomalies relative to local means for this period are derived and surface current anomalies normal to ground tracks are then calculated under the geostrophic approximation. Climatological mean surface currents normal to the ground tracks are also obtained from the solution of a regional circulation model. The sum of the model means and altimetric current anomalies is used to nominally represent absolute currents. Statistical analyses are carried out based on topographic regimes for along-slope and cross-slope current variability. The altimetric sea level and current variability increases offshore, toward the Gulf Stream or its extension the North Atlantic Current. Typical cross-track current variability is 10–20 cm/s over the southwestern (SW) and northeastern (NE) Slopes and 20–30 cm/s over the southeastern (SE) Slope. The total current variability may be estimated by a factor of 1.5 from the cross-track current variability of either the descending or ascending tracks. The sea level was higher in summer and lower in winter, with an increased range offshore. The shelf-edge current (water depth of 200–3000 m) was stronger in fall and weaker in spring. The seasonal range was up to 10–20 cm/s. Interannual sea level and current variations were also substantial. The sea level over the SW Newfoundland Slope had a fall from 1994 to 1996 and a rebound after 1997, more significant towards the deep sea, probably related to the north–south movement of the Gulf Stream. The NE Slope featured a sea level rise on the lower slope over the study period, associated with the freshening of the subpolar Northwest Atlantic. Patterns over the SE Slope appear to be in between those of the SW and NE Slopes. The Labrador Current over the slope (water depth of 200–3000 m) seemed to be strongest in 1996–1997, as a result of the equatorward traveling Labrador Current pulse.