Distribution of particulate matter and particulate organic carbon in waters of the Caspian Sea

Data on concentrations and distribution of particulate matter in the Caspian Sea obtained during surveys in 1981-1983 with use of modified filtering units have shown that over the major part of the sea concentration of particulate matter does dot exceed 1-2 mg/l. Only in the northern Caspian and in coastal regions concentrations correspond to values measured earlier. Total amount of particulate matter in the Caspian Sea is about of 90 million ton, 19.6% in the Northern Caspian, 28.1% in the Middle Caspian, and 52.3% in the Southern Caspian. Contents of carbon in particulate matter of the Central Caspian reach 30-40%, and over a significant part of the sea - 20%. A correlation has been found between areas of increased carbon contents in particulate matter and in bottom sediments. An important role of biofiltration in enrichment of particulates in organic matter has been noted. From data on carbon contents and an estimate of particulate matter input biogenic portion in particulate matter exceeds 50% for the whole sea.

Organic geochemistry of sediment cores from the Arbian Sea

Two deep-sea sediment cores from the northeastern and the southeastern Arabian Sea were studied in order to reconstruct the palaeoenvironments of the past glacial cycles. Core 136KL was recovered from the high-productivity area off Pakistan within the modern oxygen-minimum zone (OMZ). By contrast, modern primary productivity at the site of MD900963 close to Maldives is moderate and bottom waters are today well oxygenated. For both cores, we reconstructed the changes in palaeoproductivity using a set of biomarkers (alkenones, dinosterol and brassicasterol); the main result is that primary productivity is enhanced during glacial stages and lowered during interstadials. The proxies associated with productivity show a 23 kyr cyclicity corresponding to the precession-related insolation cycle. Palaeoredox conditions were studied in both cores using a new organic geochemical parameter (C35/C31-n-alkane ratio) developed by analysing surface sediments from a transect across the OMZ off Pakistan. The value of this ratio in core 136KL shows many variations during the last 65 kyr, indicating that the OMZ was not stable during this time: it disappeared completely during Heinrich- and the Younger Dryas events, pointing to a connection between global oceanic circulation and the stability of the OMZ. The C35/C31 ratio determined in sediments of core MD900963 shows that bottom waters remained rather well oxygenated over the last 330 kyr, which is confirmed by comparison with authigenic metal concentrations in the same sediments. A zonally averaged, circulation-biogeochemical ocean model was used to explore how the intermediate Indian Ocean responds to a freshwater flux anomaly at the surface of the North Atlantic. As suggested by the geochemical time series, both the abundance of Southern Ocean Water and the oxygen concentration are significantly increased in response to this freshwater perturbation.

Dissolved and particulate organic carbon in the Sea of Okhotsk

Data on distribution of dissolved and particulate organic matter obtained during Cruises 21 and 24 of R/V Akademik A. Nesmeyanov in June-August 1992 and 1993 are presented. In general a remarkable heterogeneity in distributions of both dissolved and particulate organic carbon is revealed. Concentrations of dissolved organic carbon vary from 98 to 700 µmol/l and those of particulate organic carbon vary from 3 to 50 µmol/l. Maximum concentrations are commonly observed in the shelf region while minimum concentrations - in the central basin. Run-off of the Amur River raises dissolved matter concentration in the Sakhalin Bay, while oil exploitation at the Sakhalin shelf maximizes particulate organic carbon concentration and minimizes dissolved one. Concentrations of dissolved and particulate organic carbon in the surface microlayer were estimated for the first time and are shown to be 1.5-2.0 times higher than in surface waters.