Trace metal/phytoplankton interactions in the Skagerrak

Algal community species composition, as estimated by high performance liquid chromatography (HPLC) pigments and microscopy analysis, and trace metal speciation (Cu and Co) and distributions (Fe, Zn, Co and Cu) were measured along a summer transect across the Skagerrak. In waters of Baltic origin, with elevated trace metals levels, but very low macronutrients, a mix of dinoflagellates and haptophytes dominated the low biomass. In the Jutland current, which had high dissolved iron concentrations, a mixed bloom (4–6 μg/l chl a) of diatoms (major species—Leptocylindricus danica) and dinoflagellates (Ceratium sp.) was present. In the waters of the central Skagerrak derived from the North Sea, below the low salinity Baltic water, a large diatom (major species—L. danica) bloom (7.7 μg/l) was present at 35 m. This bloom formed below the pycnocline, and was located at the nutricline for silicate. The lowest concentrations of trace metals were found in the water of North Sea origin. Synechococcus-like cyanobacteria were observed in the upper waters across the survey area, as were strong binding ligands for Cu, but no clear numerical relationship existed between them, as had been observed by Moffett [Deep-Sea Res. 42 (1995) 1273]in the Sargasso Sea. The [Co]/[Zn] hypothesis of Sunda and Huntsman [Limnol. Oceanogr. 40 (1995) 1404] for coccolithophorids and diatoms was examined using the field data collected.