Climate Change is Cause of Lower Oxygen Levels in the Sea

01-07-2012   Global warming is likely to cause lower oxygen levels in sea water. This is one of the conclusions German, Scandinavian and Dutch scientists present in an article published by the leading scientific journal Nature Climate Change. Jaap Sinninghe Damsté of the Royal Netherlands Institute for Sea Research (NIOZ) is one of the scientists involved in the research project, which was carried out in the Baltic Sea.

Continued warming of the earth will almost certainly have negative effects on marine life in the Baltic Sea. When the surface water gets warmer, the water mixes less easily so that the level of oxygen in the bottom water drops. In addition, blue-green algal blooms are likely to occur more often during summer, because these algae require water temperatures of 16o C or higher. So the primary production will increase considerably under these 'warm' circumstances. Unlike other species of algae, blue-green algae can fix nitrogen from the air. When the blue-green algae die en sink to the bottom, they are broken down by bacteria using oxygen from the water, which causes an even faster drop in oxygen levels in the water.

The scientists have based their conclusions on research of sediment cores from the Baltic Sea, containing sediment from the past millennium. A method for determining sea water temperatures on the basis of chemical fossils, which was developed by NIOZ, was used to show that the surface water temperature about a 1,000 years ago was equal to that in the past 100 years, but about 2o C lower during the Little Ice Age (c 1350-1850) .

The drop in temperatures during the Little Ice Age coincides with a period of higher oxygen levels in the bottom water, indicated by more benthic life. This shows that a relatively small change in water temperatures in the Baltic Sea has significant consequences for oxygen levels in the bottom water and thus on marine life.

The drop in oxygen levels in the ocean (known as hypoxia) has already been recognised as a possible harmful consequence of global warming, because it negatively affects most marine life in the oceans. This study has shown that this effect will likely have a large consequence for the Baltic area.

Jaap Sinninghe Damsté (1959) is the head of the Department of Marine Organic Biogeochemistry at the Royal Netherlands Institute for Sea Research (NIOZ) on the island of Texel. In addition, he is a professor of organic geochemistry at Utrecht University. In 2004, he was awarded the Spinoza Prize and he was appointed a member of the Royal Netherlands Academy of Arts and Sciences (KNAW). In addition, he has been granted the Treibs Medal and the Vernadsky Medal. He is the author of over 500 scientific publications and he is an authority on the use of chemical fossils for reconstructing climate change in the past.