SEASONAL AND INTERANNUAL VARIABILITY IN THE PROPERTIES OF THE SURFACEWATERS OF THE GULF OF MAINE

The MARMAP hydrographic data set (1977-1987) is used to determine the mean annual cycle of temperature, salinity, and density structure of s urface waters throughout the Gulf of Maine. The temperatures follow th e expected seasonal warming and cooling pattern. In the eastern Gulf t he salinity cycle is dominated by influx of low salinity Scotian Shelf water which enters near Cape Sable in the winter, and in the western Gulf by the local spring runoff. Phasing of temperature and salinity c ycles in different parts of the Gulf results in the western Gulf of Ma ine being more strongly stratified in the summer and more vertically u niform in the winter than is the eastern Gulf. The interannual variabi lity, derived by subtracting the annual cycles from the original data, reveals relatively little temperature variability (1-2 degrees C) dur ing the period 1977-1987, compared to observed changes of 4-6 degrees C in previous decades. Large interannual changes in salinity (0.5 psu) , however, are evident in the data. The salinity variability is shown to be due primarily to changes in local fresh water sources-precipitat ion and runoff. Comparison of salinity changes in the Gulf of Maine wi th data from Georges Bank and the Middle Atlantic Bight shows that the salinity variability is coherent over the northeast continental shelf region from the western Gulf (Wilkinson Basin) to Cape Hatteras.