a. surface water warms to 4 C and sinksb. water mixes, bringing oxygen to the bottom and nutrients to the surfacec. warm surface water is separated from cooler bottom water by thermoclined. surface water cools to 4 C and sinkse. water mixes, bringing oxygen to the bottom and nutrients to the surface*The following diagram illustrates seasonal turnover in a lake. Note that in winter and summer, the lake is thermally stratified, which means that there are different temperatures at different depths. Turnover in spring and fall eliminates the thermal stratification.*