Passage VII

Tiny marine organisms build shells from calcite (CaCO3) dissolved in seawater. After the organisms’ death, the shells sink. Some shells dissolve before they reach the seafloor, but some form layers of calcareous ooze (CaCO3-rich sediment). Figure 1 shows how seawater’s degree of saturation with respect to CaCO3 and the rate at which CaCO3 dissolves change with depth. The CaCO3 compensation depth (CCD) represents the depth beneath which CaCO3 dissolves faster than it precipitates. Figure 2 shows typical depths at which various seafloor sediments are found. Figure 3 shows the percent coverage for 2 seafloor sediments in 3 oceans.

36. Assume that the Arctic Ocean seafloor has an average depth of 4.9 km. According to Figures 2 and 3, the Arctic Ocean seafloor is most likely covered with:

Answer and Explanation

Your Answer is

Correct Answer is J

Explanation

It can be seen from figure 2 that at a sea depth of 4.9 km, the covering is mainly red clay;

It can be seen from figure 3 that the deeper the depth, the more red clay and the less calcareous ooze. Since the content of red clay at 4.3 km has exceeded the content of calcareous ooze, it can be determined that the content of red clay at 4.9 km is also more than that of calcareous ooze