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Offshore wind farms with no relevant impact on the water exchange of the Baltic Sea

13.10.2009 - (idw) Leibniz-Institut für Ostseeforschung Warnemünde

The impact of offshore wind parks on the salinity of the Baltic Sea deep water will be negligible, even if all plants which have been planned or applied for permit in the Western Baltic Sea will be built. This is the conclusion which scientists of an international consortium coordinated by IOW draw after a four-year project period. In the framework of two complementary projects (QuantAS-Off funded by the German Federal Ministry of Environment, Nature Protection and Nuclear Safety, and QuantAS-Nat funded by the German Research Foundation) the impact of density and positioning of wind farms on currents and water mixing in the transition area between North Sea and Baltic Sea was investigated by means of a laboratory flume, intensive field work and computer simulations.

The investigations concentrated specifically on the near-bottom pathways of saline and oxygen-rich North Sea waters in the Western Baltic Sea (Arkona Sea). This inflowing North Sea water provides the only oxygen source for the deep water in the Central Baltic Sea. It was the major aim of the research to identify potential constrictions to this transport path and to suggest - if necessary - alternative positions for wind farms.

This week, during October 14 and 15, all project participants get together in Warnemünde for their final workshop. The major result is that the extra mixing between dense and saline bottom water with less dense and brackish surface water caused by wind farms is too small to significantly modify the bottom waters flowing towards the Central Baltic Sea. Computer simulations showed that the mixing in extreme cases may cause maximum salinity changes of just about 0.3 g/kg. This impact may be neglected with respect to natural salinity fluctuations of typically 10 g/kg.

According to Prof. Dr. Hans Burchard, coordinator of both projects, this finding is only one among many: "Our understanding of salt water pathways through the Western Baltic Sea, which are so essential for the Baltic Sea ecosystem, have been significantly improved during the projects." One example is the exploration of a previously unknown major salt water vain north of the shoal Kriegers Flak. His colleague Dr. Lars Umlauf, responsible for the analysis of field observations obtained in the QuantAS-Nat project, highlights the global relevance of the results: "So-called dense bottom currents are an ubiquitous phenomenon in the world ocean. They play a key role in the global overturning circulation - and thus also for the Earth climate system. The Baltic Sea is an ideal laboratory to intensively investigate these currents." The analysis of the Baltic Sea data clearly showed that the effect of Earth rotation for the mixing in such dense bottom currents is important and must not be neglected. These results may significantly improve the parameterisation of mixing processes in global climate models. Umlauf, together with his colleague Dr. Lars Arneborg from Gothenburg published these findings recently in the renowned "Journal of Physical Oceanography".

Prof. Dr. Hans Burchard, Leibniz Institute for Baltic Sea Research (IOW), Physical Oceanography and Instrumentation, phone: +49 381 5197 140, email:

Dr. Lars Umlauf, IOW, Physical Oceanography and Instrumentation, phone: +49 381 5197 223, email:

Dr. Barbara Hentzsch, IOW, Public Relation, phone: +49 381 5197 102, email:

The QuantAS-consortium:
oLeibniz Institute for Baltic Sea Research Warnemünde (IOW), Prof. Dr. Hans Burchard, Dr. Lars Umlauf
oUniversity of Hanover, Prof. Dr. Mark Markofsky
oUniversity of Rostock, Prof. Dr. Alfred Leder
oDanish Hydraulic Institute, Danmark, Dr. Ole Petersen
oBolding & Burchard ApS, Danmark, Dr. Karsten Bolding
oUniversity of Gothenburg, Sweden, Prof. Dr. Anders Stigebrandt, Dr. Lars Arneborg

oInstitute of Oceanology, Polish Academy of Sciences, Poland, Prof. Dr. Jan Piechura
oThe Federal Armed Forces Underwater Acoustic and Marine Geophysics Research Institute, Germany (FWG), Dr. Jürgen Sellschopp, Dr. Heinz-Volker Fiekas
oFederal Maritime and Hydrographic Agency of Germany (BSH), Dr. Frank Janssen
oDanish Marine Safety Administration, Dänemark, Dr. Johan Mattsson
oISW Wassermesstechnik, Fünfseen, Dr. Hartmut Prandke
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