The Baltic Sea has been identified as home to the world's largest anthropogenic "dead zone", leading to death of organisms that live on the bottom.
Jacob Carstensen, together with Danish colleagues, now show that the dead zones have increased 10-fold over the last 115 years. They have grown from approximately 5,000 km² in 1900 to more than 60,000 km² in recent years.
This increase shows large decadal fluctuations over the last century, reducing the potential fish yield and favoring noxious algal blooms.
The extent of dead zones can be seen below, where areas in the Baltic Sea with low oxygen content are depicted in red color and no oxygen areas in black.
NEW METHOD TO ANALYZE HOW AND WHY DEAD ZONES DEVELOP
Scientists developed a new method to analyze how these large dead zones develop and what the underlying causes are.
By analyzing the different processes that affect oxygen concentration in bottom waters, they has reconstructed oxygen and stratification conditions, and separated the effects of climate, saltwater inflows and nutrients.
Nutrient inputs are the primary cause of severe hypoxia situation. In addition, there are indications that higher deep water temperatures in recent years may have had an addition effect.