Coastal Waters a. Salinity is often reduced in coastal waters by river runoff, especially in surface waters if there is little mixing. The runoff from rain peaks during the same season that the salinity is a minimum. The runoff from snow melt peaks in the summer. The temperature in shallow coastal waters can have large ranges during the year. The degree of mixing affects the depth and strength of the thermocline.
Tidal currents can influence vertical mixing.
The prevailing winds blowing from the continent can warm surface waters in summer and cool them in winter. Coastal geostrophic currents are produced by wind and runoff. Wind blowing parallel to the coast may pile up water against the shore. This water is pulled back down by gravity, and as it moves offshore it veers to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, as you know. A high volume of freshwater runoff can also produce a slope of water away from the shore.