Summary
SMHI performed an oxygen and nutrient mapping survey within SLU Aqua’s cruise; the International Bottom Trawl Survey (IBTS Q3), that covers the Skagerrak, North Sea and Kattegat. SMHI joins the cruise to perform CTD measurements in connection to each trawl and to take water samples for nutrients, chlorophyll and oxygen. Two of SMHIs standard stations; Anholt E and Fladen were also visited during the cruise.
Most parts of Kattegat's bottom water suffered from hypoxia as oxygen levels below 4 ml/l were found in the bottom water. Below this oxygen level, the first signs of oxygen deficiency in marine organisms are normally detected. In the south-eastern parts, levels were even lower, very close to the limit for acute hypoxia of < 2 ml/l. In acute oxygen deficiency, most benthic animals are negatively affected. In Skagerrak the oxygen levels in open water was good while hypoxic conditions were found at the coastal station Släggö.