Researchers of the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany have discovered unexpectedly low oxygen environments several hundred kilometres off the coast of West Africa.
The paper, published in Biogeosciences describes 100-mile-long eddies of swirling water spinning their way across the Atlantic for months at a time.
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The group of researchers led by Dr Johannes Karstensen have suggested that: ‘the eddies propagate westward, at about four to five kilometres day, from their generation region off the West African coast into the open ocean.’
Dead zones are usually found in shallow bodies of water, such as lakes and shallow coastlines.
However, the swirling movement of the eddies found in the Atlantic ensures that no water can escape, so the oxygen supply is quickly used up.
“The fast rotation of the eddies makes it very difficult to exchange oxygen across the boundary between the rotating current and the surrounding ocean.
“Moreover, the circulation creates a very shallow layer – of a few tens of meters – on top of the swirling water that supports intense plant growth,” according to Dr Karstensen.
This in turn leads to faster oxygen depletion in the eddy, as the algal bloom eats into supplies.
Damage to animal life aside, Karstensen anticipates that the dead zones could impact the people of Cape Verde.
“Given that the few dead zones we observed propagated less than 100 kilometers north of the Cape Verde archipelago, it is not unlikely that an open-ocean dead zone will hit the islands at some point," he said.
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