Explain what happens at the Calcium Carbonate Compensation Depth, and why only siliceous ooze is found on the bottom of the ocean below that depth.  

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Calcium carbonate is the main chemical in the mineral calcite.  This mineral is the main constituent in many ocean shells.  The carbonate compensation depth is the depth toward the bottom of the ocean where the rate of dissolving of calcium carbonate is equal to the rate of precipitation of calcium carbonate in ocean water.  Most chemicals increase their solubility in water at higher temperatures and pressures.  Calcium carbonate, however, actually is more soluble in water at lower temperatures.  And since water temperature decreases (and the water pressure increases) as you go to lower depths in the ocean, the calcium carbonate becomes more soluble as it sinks lower in the ocean.  Below the carbonate compensation depth, all calcium carbonate is dissolved in the ocean water.  That is why siliceous ooze is found exclusively below this level.  Siliceous ooze is a layer of silicate-based sediment produced by certain microorganisms.  All of the calcium carbonate is dissolved in the water so the silicates are the predominant species found on the deep ocean floor.

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