The Nordic Seas, the ocean area connecting the North Atlantic with the Arctic Ocean, is of great importance for the formation and transformation of water masses and the transport of carbon both to the interior of the Arctic Ocean and the North Atlantic.
In a recently published study in Global Biogeochemical Cycles - and quoted as a 'Research highlight' i the November issue of Nature Geoscience , Emil Jeansson and colleagues at the Bjerknes Centre for Climate Research, University of Bergen, present a carbon budget of the Nordic Seas.
Combining the most recent carbon data and the present knowledge about ocean exchange into and out of the Nordic Seas, the authors calculated the contemporary carbon budget of the region.
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| The figure shows the net horizontal transport of total carbon in the different gateways of the Nordic Seas. The ‘net’ term (in italic) shows the resulting transport, when adding all horizontal in and outflows, where the negative sign means that the budget gives a net transport out of the region. Thus, balancing the budget requires an uptake of CO2 the same amount from the atmosphere. Figure: Emil Jeansson |
Estimated carbon transports
The authors estimated that 12.3 Gt (Gt = billion tons) of carbon is transported, annually, into the Nordic Seas, and that 12.5 Gt carbon is exported from the region.
Balancing the budget requires an ocean uptake of atmospheric carbon dioxide (CO2) to the Nordic Seas of 0.2 Gt of carbon each year. This is almost two orders of magnitude smaller than the carbon transported with ocean currents in the region.
However, it also indicates that a larger amount of carbon dioxide is taken up by northward flowing water masses before they enter the Nordic Seas, and that this is one of the main sources of carbon to the Nordic Seas.
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| The figure shows the distribution of anthropogenic carbon (Cant) in the different openings from the Nordic Seas. The abbreviations denote water masses and geographical locations: AW-Atlantic Water; DS-Denmark Strait; DW-Deep Water; FSC-Faroe-Shetland Current; IFR-Iceland-Faroe Ridge; MAW-Modified Atlantic Water; NCC-Norwegian Coastal Water; OW-Overflow Water; PW-Polar Water |
Surface-to-deep water transport of carbon
The authors estimate an annual export of about 0.09 Gt anthropogenic carbon (excess carbon resulting from perturbations of the “natural” carbon cycle), from the Nordic Seas to the deep North Atlantic.
Now removed from the surface ocean, this anthropogenic carbon will be transported around the oceans for decades to centuries, with the global ocean circulation.
This is a crucially important pathway for removing the climatically important CO2 from the atmosphere to the interior ocean and thus moderating the potential global warming of global fossil fuel combustion and land-use change.
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| Frontpage photo: Emil Jeansson |