Marine Chemistry 
Nordseezustand 2003 
17 
Marine Chemistry 
During 2003 the routine chemical monitoring program was continued. Water, sediment 
and suspended particulate matter samples were taken on board a research vessel, 
and were analyzed afterwards for several groups of chemical compounds. Overall, a 
dataset with sufficient spatial and temporal resolution was obtained. Coastal, open 
sea, estuary and channel water bodies were investigated during all seasons. The re 
sults of these comprehensive chemical investigations will be addressed in separate 
chapters for nutrients, organic trace substances, metals and radioactive substances. 
Nutrients 
Both in the winter and summer seasons of 2003, nutrient monitoring was carried out 
in different areas of the North Sea. 
Analyses of long-term trends were based exclusively on measurements made in the 
winter months because biological activity is at its minimum then. In order to achieve 
comparability of the nutrient samples taken in the different areas (river estuaries, 
coastal waters, open seas), the samples were normalized to the typical regional salin 
ity. Also in the winter of 2003, phosphate levels in the German Bight were almost at 
their 1936 reference level. They still exceeded that level in the coastal waters. The sit 
uation of nitrogen compounds, for which 1936 reference values are not available, is 
less favorable because nitrogen inputs to the North Sea have not decreased in the 
same measure as phosphate levels. 
In the summer of 2003, the central North Sea had a stable thermohaline stratification 
with a nutrient-poor surface layer extending to 20 m depth. The chlorophyll maximum 
was found at the level of the pycnocline, where sufficient light and nutrients for algal 
growth were still available. On the whole, nutrient levels were on the order of the long 
term means of the period 1986 - 2000. 
Also long time series from Helgoland Roads confirmed trends toward unchanged or 
decreasing nutrient concentrations. 
Because of the unusually strong temperature stratification in the summer of 2003, ox 
ygen saturation in the bottom water of the White Bank area had decreased to 46 - 
60 % by the beginning of August, and was as low as 38 % by early September. The 
first autumn storms quickly dissolved the stratification, causing the oxygen deficit to 
disappear. 
Organic Pollutants 
In the routine monitoring programme for the North Sea, concentrations of organic pol 
lutants are determined mainly in May and July/August. In 2003, up to 120 different 
compounds were determined in sea water, suspended particulate matter, and sedi 
ments. The levels of most contaminants monitored were on the order of the preceding 
years. 
In the substance class of hexachlorocyclohexane - whose gamma isomer is the in 
secticide >lindane<, which has been used for many years - the downward trend ob 
served in the preceding years continued, and concentrations were at their lowest lev