mainly those of the oceans, provide long term sinks for carbon.
The remains of oceanic plants and animals sink to the sea bed as
'marine snow', with productive areas of the world's oceans producing
huge amounts of such particulate organic carbon.
In coastal areas, dissolved and particulate carbon
carried in rivers can also provide a significant source of carbon
to marine and estuarine sediments. Through the sedimentation of
dissolved and particulate organic carbon, sediments provide a global
carbon sink of about 10 million tonnes each year.
Additionally, the precipitation of calcium carbonate
and its deposition in sediments leads to a further 200 million tonnes
of carbon ending up in sediments annually. This deposition of carbon
is made even more important, global warming-wise, by the very long
periods (thousands of years) such carbon is generally taken out
of the atmosphere for.