SATELLITE-OBSERVATIONS OF SEA-SURFACE TEMPERATURE VARIABILITY ON SOUTHERN GEORGES-BANK

Sea surface temperature (SST) residual time series, derived from declo uded Advanced Very High Resolution Radiometer (AVHRR) satellite imager y for southern Georges Bank, were examined for the period April-Octobe r 1987. Significant negative correlations were computed between the lo w-pass filtered SST residuals and daily-averaged tidal current magnitu de, suggesting that for periods of approximately 15 and approximately 28 days, SST variability was related to the spring-neap tidal cycle in both the stratified and unstratified portions of southern Georges Ban k during the stratified season. Maximum negative correlations occurred at a lag of approximately 3 days, indicating that negative (positive) SST residuals lagged the maximum spring (minimum neap) tidal current by this amount. This lag and the measured 3sigma SST residual of appro ximately 3.0-degrees-C are in agreement with the summer hydrography on southern Georges Bank and a one-dimensional model in which the depth- independent vertical eddy diffusivity varies with time. Because meteor ological forcing at the sea surface occurs on time scales of approxima tely 1-7 days, the data suggest that the observed, negative SST residu als are caused by periodic, enhanced vertical mixing of colder, sub-th ermocline water into surface waters as a result of spring tidal curren ts during the stratified season. Given the inverse temperature-nitrate correlation for the region during the stratified season, the data sug gest the occurrence of increased nitrate flux into the stratified and well-mixed regions of southern Georges Bank during spring tides. Perio ds of spring tides may result in the transport of a large fraction of the new nitrogen needed to sustain high primary production observed in the chlorophyll maximum within the stratified and well-mixed regions of southern Georges Bank during the stratified season.