Primary production and chlorophyll a in waters of the Kara Sea in September 2007

These studies were performed from September 10 to 29, 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River estuary (Obskay Guba), and on the adjacent shelf. Concentration of chlorophyll a in the euphotic layer varied from 0.02 to 4.37 µg/l, aver. 0.76 µg/l. Primary production in the water column varied from 10.9 to 148.0 mg C/m**2/day (aver. 56.9 mg C/m**2/day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. Maximum levels of primary production were measured in the deep part of the Yamal transect (132.4 mg C/m**2/day) and the shallow Kara Sea shelf near the Ob River estuary (74.9 mg C/m**2/day). Characteristics of these regions were low salinity of the surface water layer (19-25 psu) and elevated silicon concentration (12.8-28.1 µg-atom/l). It is explainable by river runoff. Frontal zones of the Yamal current within the Yamal and Ob transects showed high assimilation numbers reached to 2.32 and 1.49 mg C/mg Chl/hr, respectively; they were maximal for studied areas.

Pigments, phytoplankton and its production parameters in the Obskaya Guba and adjacent Kara Sea in the latest September 2007

Material was collected in the Ob River estuary and the adjacent shallow Kara Sea shelf between 71°14.0'N and 75°33.0'N at the end of September 2007. Latitudinal zonation in phytoplankton distribution was demonstrated; this zonation was determined by changes in salinity and concentration of nutrients. Characteristic of the phytocenosis in the southern desalinated zone composed of freshwater diatom and green algae species were high population density (1500000 cells/l), biomass (210 ?g C/l), chlorophyll concentration (4.5 ?g/l), and uniform distribution in the water column. High primary production (~40 ?g C/l/day) was recorded in the upper 1.5 m layer. The estuarine frontal zone located to the north had a halocline at depth 3-5 m. Freshwater species with low abundance (250000 cells/l), biomass (24 ?g C/l), and chlorophyll concentration (1.5 ?g/l) dominated above the halocline. Marine diatom algae, dinoflagellates, and autotrophic flagellates formed a considerable part of the phytocenosis below the halocline; community characteristics were two-fold lower as compared with the upper layer. Maximal values of primary production (~10 ?g C/l/day) were recorded in the upper 1.5 m layer. The phytocenosis in the seaward zone was formed by marine alga species and was considerably poorer as compared with the frontal zone. Assimilation rates of carbon per chlorophyll a at the end of the vegetation season within the studied area were low, average 0.4-1.0 ?g C/?g Chl/hour in the upper layer and 0.03-0.1 ?g C/?g Chl/hour below the pycnocline.