Monday, July 12th 2010, 2:44 AM EDT
On average, the world's oceans absorb 2% more carbon than they emit each year, forming an important sink in the overall carbon cycle. CO2 is absorbed by the ocean in a number of ways. Some dissolves into the water column, forming carbonic acid (H2CO3) while more enters the seas through the food chain. Green, photosynthesizing plankton converts as much as 60 gigatons of carbon per year into organic carbon—roughly the same amount fixed by land plants and almost 10 times the amount emitted by human activity. But this form of carbon is only stored for a short period of time.
According to a news focus article
in Science by Richard Stone: “Even more massive amounts of carbon are suspended in the water column as DOC. The oceans hold an estimated 700 billion tons of carbon as DOC—more than all land biomass put together (600 billion tons of carbon) and nearly as much as all the CO2 in the air (750 billion tons of carbon).” The carbon cycle with its various sinks and sources are shown in the IPCC diagram above.
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The ocean is Earth's largest single sink for CO2 outside of the planet's crust itself. Simple sea creatures depend on carbon dissolved in the ocean's water for their existence, and their actions create a biological carbon “pump” that removes vast quantities of CO2 from the atmosphere. Large amounts are suspended in the water column as dissolved organic carbon (DOC), and each year the ocean's biological pump deposits some 300 million tons of carbon in the deep ocean sink. New findings have revealed that massive amounts of carbon are converted into “inedible” forms of organic carbon that remain out of circulation for thousands of years, effectively sequestering the carbon by removing it from the ocean food chain. According to Jiao Nianzhi, a microbial ecologist here at Xiamen University, the amount stored is tremendous: “It's really huge. It's comparable to all the carbon dioxide in the air.”