Higher temperatures cause rapid changes in arctic ecosystem

Science article reveals

14-02-2013  Because in the summer of 2012 Arctic sea ice has melted off much more than usual, algae living underneath the ice could grow faster than normally. In addition, the melting of the ice also caused these algae to sink to the sea floor in large numbers. This resulted in enormous spots without oxygen at large depths, which has considerable consequences for the ecosystem in the Arctic Ocean. These are some of the results published today in the journal Science by a team of scientists from a various countries. The Royal Netherlands Institute for Sea Research (NIOZ) also took part in this special expedition.

In the late summer of 2012, an international expedition with the research vessel Polarstern was organized with scientists and technicians from 12 countries. The scientists tried to find out if algae living on the underside of the sea ice grow faster if the sea ice is thinner. Three employees of NIOZ on Texel, including Karel Bakker, took part in this expedition led by Prof. Antje Boetius from the German research institute Helmholz.


The alga Melosira arctica grows on the underside of the sea ice and is responsible for almost half of the primary production in this region. When algae die, they normally whirl down very slowly to the sea floor. Most of them have been eaten well before they reach the bottom of the sea. Melosira, however, forms long chains, which makes it heavier than other algae. Its weight makes this alga sink to the sea floor much faster. This means that about 85% of the biomass is conveyed to the bottom of the sea and is no longer available as food in the upper water column.

In the late summer of 2012 the alga Melosira occurred in larger numbers than in previous years because the sea ice was much thinner as a consequence of higher temperatures. Moreover, on several spots on the bottom of the Arctic Ocean enormous lumps of dead algae were found. These lumps could be as big as 50 cm and cover up to 10% of the sea floor.

Large numbers of sea cucumbers and brittle stars were here to eat these dead algae. Bacteria then broke down the remains; as a consequence a large part of the oxygen on the sea floor was consumed. This resulted in large oxygenless areas on the sea floor.

'For the first time, we managed to demonstrate that global warming is the cause of reactions throughout the ecosystem and as deep down as the bottom of the deep sea', says the first author of the Science article, Prof. Antje Boetius. ‘Up to now, we thought that climate change only had a delayed effect on the sea floor’. The fact that this process causes spots without oxygen on the bottom of the deep sea worries the scientists. ‘We still do not know if this phenomenon is unique to 2012 or if this is going to happen more often in the coming years’. Current climate models predict that within several decades the entire Arctic Ocean will be completely free of ice in summer. There is still much to be found out about the functioning of the Arctic ecosystem, its biodiversity and productivity, to gain a good view of the consequences of the rapid loss of sea ice.

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