Does the north Atlantic oscillation affect hydrographic properties on the Canadian Atlantic continental shelf?

Abstract

An analysis of hydrographic data from the eastern Canadian continental shelf indicates that large‐scale spatial patterns of bottom temperature and salinity respond to sustained periods of weak and strong meteorological forcing represented by the winter North Atlantic Oscillation (NAO) index. Warm, salty (cold, fresh) conditions prevail on the Newfoundland‐Labrador Shelf, the eastern Scotian Shelf and the Gulf of St. Lawrence during periods of negative (positive) NAO anomalies. The opposite response is seen on the central and western Scotian Shelf and in the Gulf of Maine. Comparison of years when the NAO anomaly was positive and had the same sign for at least the two preceding years with those years when the NAO anomaly was negative and had the same sign for at least the two preceding years, shows differences in bottom temperature and salinity, at the same location, of up to approximately 2°C and 0.4. A plausible explanation of the pattern lies in a combination of local forcing and the highly advective nature of the oceanography that responds to NAO forcing. Greater westward transport of Labrador Slope Water along the shelf edge and subsequent on‐shelf penetration of hydrographic anomalies during periods of negative NAO anomalies give rise to the dipole nature of the temperature and salinity patterns. The effects on hydrographic properties appear to be integrated over several years of meteorological forcing, again likely related to advection in the region.