Geol

Lab 3B

1. When ice forms on a freshwater lake, it can be assumed that the [(warmest)(coldest)] and densest water is at the bottom of the lake.

2. Figure 1 portrays an actual temperature profile based on data collected in Lake Michigan when the lake was at its coldest for the year with considerable broken ice floating on its surface. With a mix of ice and water present, the surface water must have had a temperature of [(0)(1)(2)(4)] °C, as was observed and is reported in the figure.

3. Below the shallow surface layer of coldest and [(lowest)(highest)] density water, the temperature was a constant 4 °C.

4. This 4 °C temperature is [(lower than)(equal to)(higher than)] freshwater’s temperature of maximum density. As described earlier, during cooling of freshwater bodies the water temperature drops until convection produces an isothermal (constant temperature) condition throughout the water column. With further cooling, the coldest water remains at the surface because it is also the least dense. This suppresses convection (the sinking of more dense fluid and the rising of less dense fluid under the influence of gravity) within the water body. Continued cooling reduces the surface water temperature until 0 °C is reached and ice begins forming.

5. The addition of dissolved materials (i.e., salt) lowers the temperature at which water is most dense. The curve in Figure 2 labeled “Temperature of maximum density” shows this change as salinity increases. Draw the 0 °C isotherm on the chart, and note where the “Temperature of maximum density” crosses it. This shows that water with a temperature of maximum density of 0 °C would have a salinity of about [(12)(16)(18)].

6. According to Figure 2, the temperature of maximum density and the initial freezing point coincide for water with a salinity of [(0.0)(24.7)(26.7)]. At salinities greater than this value, seawater begins to freeze before reaching its temperature of maximum density.

7. Figure 3 displays Coriolis Profiling...