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The Carbon Cycle - a geologists view

Euan Mearns
An Ice-Age glacier carried boulder deposited at the top of a cliff on the Cornwall Coast in Britain. Earth's climate is the best thing in the solar system for life. Our natural climate and climate changes are amazing.

IPCC AR5 carbon cycle model sees 8.9±1.4GtC emitted in a non-specified year. 2.6±1.2GtC was sequestered in land biomass, 2.3±0.7GtC sequestered in the oceans mainly by plankton and 4GtC remained in the atmosphere. These numbers are estimates but seem to be a reasonable rendering of current understanding.

Since the beginning of the industrial revolution a total of 240GtC from human emissions have accumulated in the atmosphere while a similar amount has been sequestered by the non-permanent reservoirs of the deep ocean and terrestrial biomass, soils and biodetritus. What will be the fate of the emissions C in these non-permanent reservoirs and of that which remains in the atmosphere?

It appears that virtually all of the manmade emissions that are sequestered are removed by photosynthesis, trees on land and phytoplankton in the oceans. Land based sequestration is in live and dead biomass, biodetritus and soils. In the oceans, dead plankton sink quickly by gravity taking organic material and carbonate into the deep ocean where it is stored. It is relevant to ask for how long these sinks can go on absorbing ever larger quantities of CO2.