A new approach to state the areas of oxygen deficits in the Baltic Sea

Typ: Rapport
Serie: Oceanografi 95
Författare: Ingemar Cato, Bertil Håkansson, Ola Hallberg, Bernt Kjellin, Pia Andersson, Cecilia Erlandsson, Johan Nyberg , Philip Axe


Sediment and near bottom water oxygen data was evaluated to look for correspondence in anoxic conditions. The SGU and SMHI monitoring data showed high correlation, although the actual data tested proved to be few, coincidence in space was promising. The conclusion drawn from the evaluation is that anoxic postglacial sediments were generally overlaid by near bottom anoxic waters. Hence, it is suggested that the spatial distribution of postglacial clays in the sea-bottom surface can be used, together with near bottom waters oxygen data, to improve spatial distribution in mapping oxygen deficits. Time series of oxygen deficit volume and area was calculated from near bottom data from several sub basins in the southern and central Baltic Proper. In general, hypoxic and anoxic water conditions increased over time but perturbations of improved oxygen conditions linked to major inflow events occurs especially in the Bornholm, Eastern and Western Gotland Basins. The high spatial variability of the postglacial sediments in the Western Gotland Basin compared to other basins indicates that it is indeed sensitive to the area coverage of anoxic waters. In addition, the relatively weak stratification and high variability over time of oxygen deficit make this basin favourable for oxygen improvement engineering methods. In coastal waters several bays along the Östergötland and Småland archipelagos should be further evaluated before selected for ecological engineering methods to improve oxygen conditions.