Salinity levels within the Chesapeake vary widely, both seasonally and from year to year, depending on the volume of freshwater flowing into the Bay. On a map, isohalines or salinity contours mark the salt content of surface waters. Because the greatest volume of freshwater enters the Bay from northern and western tributaries, isohalines tend to show a southwest to northeast tilt. The rotation of Earth also drives this salinity gradient. Known as the Coriolis Force, it deflects flowing water to the right in the Northern Hemisphere so that saltier water moving up the Bay is deflected toward the eastern shore.
Temperature dramatically changes the rate of chemical and biological reactions within the water.
Because the Bay is so shallow, its capacity to store heat over time is relatively small. As a result, water temperature fluctuates throughout the year, ranging from 34 to 84 degrees Fahrenheit. These changes in water temperature influence when plants and animals feed, reproduce, move locally or migrate. The temperature profile of the Bay is fairly predictable. During spring and summer, surface and shallow waters are warmer than deeper waters with the coldest water found at the bottom.