Abstract: A simple dynamic model of halocline depth and deepwater flushing in the Baltic proper
Author: Anders Stigebrandt
Dept. of Earth Sciences/Oceanography
University of Gothenburg
The depth of the halocline in the Baltic proper has been recorded through salinity observations during more than 100 years. The top has been astonishingly stable with usually only small annual fluctuations around about 60 m depth. However, a large transient event, during which the top was depressed down to about 100 m depth, started in the 1980’ies and cumulated in the first part of the 1990’ies. The volume of deepwater, i.e. the water beneath the top of the halocline, decreased by about 65% during the event. This had dramatic effects on the content of oxygen as seen in minima of the areas of hypoxic and oxic bottoms in 1995. A simple dynamic model of the deepwater of the Baltic proper is presented. The model is used to compute long-term effects of increased mixing of the inflowing deepwater, caused by e.g. human constructions and/or climate change, on the depth of the halocline and on the residence time of the deepwater. It is found that increased mixing of the inflowing deepwater will not influence the depth of the halocline but it should shorten the residence time and thereby improve oxygen conditions in the deepwater which might lead to decreased phosphorus content and decreased eutrophication. Effects of large scale pumping of surface water into the deepwater (geo-engineering) are also discussed. Finally, the reasons for large transient events in halocline depth are identified and discussed using the model.