Question

Explain why the CaCO₃ tests (shells) from planktonic (floating) marine organisms dissolve when they sink into the ocean.

Answer 1

Planktonic marine organisms carry their shells to the ocen floor when they die and sink. These shells are deposited as rocks for a long time. Deep down in the ocean many organisms live. They respire and produce carbon dioxide as a result. It gets accumulated in the bottom as it cannot find an escape like it does on the surface (to the atmosphere).

Calcium carbonate shells get dissolved in this carbon dioxide. This has further increased, due to ocean acidification taking place. Ocean acidification is leading to increasing CO₂ levels and low pH as carbon dioxide is acidic in nature.

As enough carbon dioxide is present in the ocean water in the deep, leading to the formation of soluble calcium bicarbonate, shells dissolve when they sink.