Can the Weddell Sea (Southern Ocean) be a sink for atmospheric carbon dioxide (CO2)?
The source water mass of the Weddell Sea is Circumpolar Deep Water (CDW), which is high in CO2. Subsurface CDW is upwelled into the surface layer which tends to cause some CO2 outgassing. CDW is also involved in bottom water formation together with a surface water component, which generates water with CO2 content smaller than that of CDW. Both processes would tend to turn the Weddell Sea into a CO2 source to the atmosphere.
A sink function can only exist if water that is enriched in CO2 in the Weddell Sea is transferred out of it. Surface water is exported but has less CO2 than CDW. Similar holds for exported deep water. Modified CDW of the central Weddell is CO2-enriched; remineralization of organic matter, sinking from the surface layer, causes this CO2-enrichment. This organic matter has been produced near the surface, causes CO2 under-saturation which leads to uptake of atmospheric CO2. Whether the Weddell Sea is a CO2 sink in the end depends on the export rate of organic matter from the surface layer in relation to the strength of CDW upwelling. The offshore Weddell Sea is pivotal, not the coastal regions as claimed for long times.
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