PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
927 
summer (p. 588). The fact that the surface averages somewhat cooler along the coast 
at that season, from Cape Cod to Cape Elizabeth, than a few miles offshore probably 
reflects the cumulative effect of such upwellings following the prevailing southwesterly 
Fig. 186.— Difference fn density between the surface and the 40-meter level in July and August for the several years of 
record, combined. Corrected for compression 
winds. No doubt this happens still more frequently there in winter, when northwest 
gales are frequent, though it is not so easily recognizable then. In the opposite 
side of the gulf the tendency is the reverse — i. e., the surface water is driven 
in against the shore and sinks; and with vertical mixing by the tides so active that 
