Caribbean beach rich in marine carbonate sediment Copyrighted imageCredit: photos.com

In shallow productive seas - like those in the Bahamas - the sediments are rich in calcium carbonate. The source of this form of carbon are the shells and skeletons of dead sea creatures.

When creatures die most of the organic matter is effectively recycled by consumers. But the shells of plankton, molluscs and corals containing calcium carbonate are indigestible - even to a snail. So the material builds up as sediments around the continental margins.

In the deeper seas the carbonate debris that rains down is nearly all from the skeletons and shells of plankton. Near the surface, the amount of organic carbon in debris exceeds carbonate carbon by 4 to 1. But at the ocean floor the proportions are reversed. Because other organisms can’t consume calcium carbonate, these sediments accumulate slowly but surely at the bottom of the sea.

Where do you find the carbon?

The calcium carbonate sediments of the world's oceans and shallow seas

What form of carbon?

Calcium carbonate

How long will the carbon remain?

About 9000 years on average

How much carbon is there?

About 1800 x 1012kg

What processes will free the carbon?

Dissolution, lithification