The Baltic Sea is home to some of the world’s largest dead zones, areas of oxygen-starved waters where most marine animals can’t survive. But while parts of this sea have long suffered from low oxygen levels, a new study by a team in Finland and Germany shows that oxygen loss in coastal areas over the past century is unprecedented in the last 1500 years. The research is published today in the European Geosciences Union journal Biogeosciences.
The Baltic Sea is home to some of the world’s largest dead zones, areas of oxygen-starved waters where most marine animals can’t survive. But while parts of this sea have long suffered from low oxygen levels, a new study by a team in Finland and Germany shows that oxygen loss in coastal areas over the past century is unprecedented in the last 1500 years. The research is published today in the European Geosciences Union journal Biogeosciences.
According to the researchers, human-induced pollution, from fertilisers and sewage running off the countries surrounding the Baltic into the sea, is the main driver of recent oxygen loss in the region’s coastal waters. The spread of low-oxygen areas can have dire consequences for the environment and for local populations as it can reduce fish yields and even lead to massive mortality of marine animals.
“The Baltic was strongly impacted by human nutrient inputs in the 20th century and is still experiencing the legacy of those inputs today,” says Tom Jilbert, an assistant professor at the University of Helsinki, Finland, who took part in the research. But despite recent measures to reduce the release of polluting nutrients, the researchers write in the new study that they found “no evidence of recovery” from oxygen depletion in the Archipelago Sea, a coastal area between mainland Finland and Sweden that is part of the Baltic.
A reason, they say, may be climate change. Since warm waters are less effective at holding oxygen, “global warming is likely to exacerbate oxygen depletion,” says Sami Jokinen, a researcher at the University of Turku, Finland, and lead-author of the Biogeosciences study. Jilbert adds: “Climate change was not the main cause of the current dead zone, but it is an important factor delaying the recovery.”
Read more at European Geosciences Union
Image: This is an aerial view of the Archipelago Sea (to the west, study location in the background). This shallow coastal area in the northern Baltic Sea is characterised by a mosaic of thousands of islands, comprising a remarkably diverse environment both geologically and biologically. (Credit: Kari Mattila, The Archipelago Research Institute)
