Marine Chemistry
Nordseezustand 2004
23
in the Fair Isle Current at the NW boundary to the North Atlantic undergoes quasi-cy-
clic variations at periods of 6 to 9 years, which stand out in the variance spectrum of
the NAO-index as well. This quasi-cycle was at maximum in 2004.
The runoff rates of Elbe River remained below climate normals almost throughout the
year. These low flow volumes, which persisted since April 2003, were continuing con
sequences of the extreme dry-year 2003. Precipitation, which was about normal for the
catchment area of the Elbe River, probably was used foremost in replenishing ground-
water reserves. The temporal course of salinity at Helgoland Roads was mostly anti
parallel to that of Elbe River runoff. Hence, monthly salinities exceeded climatological
means here most of the time.
Marine Chemistry
Within its chemical monitoring programme, BSH carried out five monitoring campaigns
in the German Exclusive Economic Zone (EEZ), largely corresponding to the German
Bight. Samples of sea water, suspended particulate matter, and sediment were either
analyzed on board the vessel or preserved for laboratory analyses at a later date for a
variety of substance groups. In 2004, monitoring activities outside the EEZ were only
possible during the North Sea overall survey in July/August and, for logistical rea
sons, were limited to nutrient sampling and associated variables such as chlorophyll-
a and oxygen.
Comprehensive monitoring of the chemical pollution of sea water with nutrients, trace
metals, artificial radionuclides, pesticides, and other organic pollutants was carried out
in the German Bight and provided a good spatial overview of the present situation. In
addition, concentrations of trace metals and organic pollutants were determined in
sediment samples.
The main source of most substances and compounds here is riverine inputs, especial
ly by the Elbe River. Since the general circulation in the German Bight is cyclonic, sub
stances tend to spread in northwesterly direction (Elbe River plume), while concentra
tions decrease through mixing with less polluted sea water. Spatial concentration
patterns thus are the more similar to the salinity distribution the more dominant this
mixing process is (e. g. nutrient distributions in times of low biological activity).
Deviations particularly show in stronger concentration gradients toward the open sea
than would be expected with conservative dispersion. They often result from a strong
tendency of some substances to attach to suspended particulate matter (SPM affinity).
This property brings about a relatively fast decrease in substance concentration in the
water column at the expense of substance enrichment in sediments through SPM pre
cipitation. Hence, pollutant levels in sediments often considerably exceed those in sea
water.
On the one hand, high sediment pollutant levels prove that the subsystem >seabed< is
a sink for many substances entering the subsystem >sea water< from external sources.
On the other hand, sediment also is an internal source of these same substances for
the total system because strong, storm and tide induced currents and turbulence are
causing continuous sediment transports and resuspension in the largely shallow and
sandy regions of the North Sea. For instance, only a fraction of the current volume ac
tivities of radioactive substances in the German Bight is due to recent, reduced dis-