Phytoplankton in the surface desalted lens of the Kara Sea

Phytoplankton of a surface strongly desalinated water lens was investigated on the basis of materials collected during Cruise 57 of R/V Akademik Mstislav Keldysh in September 2007. The lens with salinity <18 psu had area of ca. 19000 sq. km and was located in the northwestern part of the Kara Sea near the eastern coast of Novaya Zemlya. It was a specific biotope that had been isolated from surrounding waters for more than three months. In the investigated area 66 algae species were identified. The maximal species diversity was found in the upper layers of the desalinated lens, where species number was 1.5 to 3 times higher than in other parts of the water column. Phytoplankton abundance in the upper layers of the lens was 1.5 to 4.5 times higher than in its lower part and generally higher than below the picnocline. Diatoms were the most abundant group in the upper layers of the lens, while flagellates dominated in the subpicnocline part of the water column. Maximal values of phytoplankton biomass were observed everywhere in the upper layers of the lens, where they were 1.2 to 3.7 times higher than in the lower part of the lens and 1.3 to 7.2 times higher than in the layer below the picnocline. Dinoflagellates generally gave the most contribution to total phytoplankton biomass. Phytoplankton of the desalinated surface lens in the northwestern part of the Kara Sea by its composition and quantitative parameters had the nearest resemblance to a phytocenosis that we observed two weeks later at a shallow desalinated shelf closely adjacent to the Ob estuary.

Chemistry of interstitial waters of samples from DSDP Leg 25

Interstitial water analyses from sediments collected during Leg 25 of the Deep Sea Drilling Project have revealed that in the southwest Indian Ocean, great chemical activity exists in sediments in various depositional environments. Variable sedimentation rates allow us to set some interesting boundary conditions on chemical and transport processes in these interstitial waters, particularly with regard to the distribution of dissolved sulfate. In terrigenous rapidly deposited sediments, large depletions are observed in magnesium and potassium, whereas relatively small decreases in dissolved calcium occur. In slowly deposited detrital sediments, also, large decreases in potassium and magnesium coincide with very large calcium increases. In truly pelagic sediments, a one to one replacement of magnesium by calcium is observed in the interstitial waters, presumably due to reactions in the basal sediment layers. Biogenous deposits have great influence on dissolved silica (sponge spicules and radiolarians) and on dissolved strontium (carbonate recrystallization). Otherwise, dissolved silica reflects the clay mineralogy and shows variations which seem particularly dependent on the presence or absence of kaolinite. Variable dissolved manganese values reflect reducing conditions and/or availability of manganese in the solid phases for mobilization in reducing sediments.

(Table 1) Composition of bottom sediments and pore waters from the West Africa shelf

Organic and mineral phosphorus (P_org and P_min) have been determined in pore waters of terrigenous, biogenous, as well as weakly phosphatic and phosphatic sediments from the shelf of the West Africa (in 30 samples). Concentrations of P_min in the pore waters have been examined in close relation to grain size and chemical composition (amounts of P and N_org) of solid phase of the sediments. It has been demonstrated that among sands and coarse silts, maximum concentrations of P_min (up to 1.7 mg/l) in the pore waters have been observed in weakly phosphatic and phosphatic sediments rich in organic matter of the highly productive shelf of the Southwest Africa. Concentrations of P_min in the pore waters are most clearly associated with contents of N_org in the solid phase of the sediments (correlation coefficient R = 0.71) and P_org in the pore waters (R = 0.78).