ALKOR AL519

An important factor for the ecological status of the coastal Baltic Sea is the availability of oxygen that is often strongly reduced during extended stagnation periods. During the last decades, suboxic and anoxic zones expanded in the deep basins of the Baltic Sea as well as in shallower coastal areas. Time series data confirm this development at station Boknis Eck (Eckernförde Bight) that has been sampled on a monthly basis since 1957 by GEOMAR scientists. A new underwater observatory for continuous measurements of currents, salinity, temperature, oxygen, carbon dioxide and methane has been installed at Boknis some weeks ago. As part of a research project financed by the federal state of Schleswig-Holstein (project CoastSens) the new underwater observatory will be extended by a module equipped for the detection of organic compounds in seawater. Recently developed sensor technique allow for the detection of several organic compounds like proteins and humic substances based on their optical properties (Chromophoric dissolved organic matter - CDOM). The efficiency of bacterial degradation of organic compounds is decisive for the oxygen consumption in bottom waters of the coastal Baltic Sea. Ship time will be used to investigate how the punctually measured parameters at Boknis Eck spatially change in the Eckernförder Bight and adjacent areas of the Kiel Bight including the Kiel Fjord. Data will be used to test whether knowledge gained from time series data of station Boknis Eck is valid for extended areas in the Kiel Bight. The aim of the envisaged cruise is the investigation of the following aspects:

(1) The identification of CDOM components in surface waters, oxygen-poor deep waters and oxygen-rich deep waters
(2) The dependence of heterotrophic bacterial activity on oxygen concentration
(3) The relevance of different organic substances for bacterial activity

Results will help to better understand the importance of different organic compounds for the bacterial oxygen consumption in deep waters of the coastal Baltic Sea.