Grain-size distribution, sedimentation rate and x-ray fluorescence data of four sediment cores off the Senegal River estuary

Fine-grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively. A north-south elongated mud depocenter extends along the Senegalese coast in mid-shelf position. Shallow-acoustic profiling was carried out to determine extent, geometry and internal structures of this sedimentary body. In addition, four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter. A general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive. Intervals characterized by high terrigenous input, high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland. From 2750 to 1900 and from 1000 to 700 cal a BP, wetter conditions are recorded off Senegal, an observation which is in accordance with other records from NW-Africa. Nevertheless, the three employed proxies (sedimentation rate, grain size and elemental distribution) do not always display consistent inter-core patterns. Major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system. The Senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface. Early Holocene deceleration in the rate of the sea-level rise could have enabled initial mud deposition on the shelf. These favorable conditions for mud deposition occur coevally with a humid period over NW-Africa, thus, high river discharge. Sedimentation started preferentially in the northern areas of the mud belt. During mid-Holocene, a marine incursion led to the formation of an embayment. Afterwards, sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates. These sub-recent shifts in depocenters location are caused by migrations of the Senegal River mouth. During late Holocene times, the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards.

Rates of sulfide formation and oxidation in the Black Sea waters in February-April 1991

Rate of hydrogen sulfide oxidation in the redox zone of the Black Sea and rate of hydrogen sulfide formation due to bacterial sulfate reduction in the upper layer of anaerobic waters were measured in February-April 1991. These measurements were made using sulfur radioisotope under conditions close to those in situ. It was established that hydrogen sulfide is oxidized in the layer of oxygen and hydrogen sulfide coexistence under the upper boundary of the hydrogen sulfide layer. Maximum rate of hydrogen sulfide oxidation was recorded within the limits of density values dT of 16.20-16.30, while varying in the layer from 2 to 4.5 µmol/day. The average rate of hydrogen sulfide oxidation was 1.5-3 times higher than that during the warm season. Sulfide formation was not observed at most of the stations in the examined lower portion of the pycnocline layer (140 to 400 m). Noticeable sulfate reduction was detected only at one station on the northwestern shelf. Intensified hydrodynamics in the upper layers of the water mass during the cold season can be a probable reason for such noticeable changes in sulfur dynamics in the water mass of the Black Sea. Data suggesting that hydrogen sulfide oxidation proceeds under the hydrogen sulfide boundary indicate absence of the so-called "suboxic zone" in this basin.

(Table 1) Dominant species and total biomass of macrozoobenthos communities in the southwestern Kara Sea

The structure and distribution of the macrobenthic communities were studied in the southwestern Kara Sea. The material was collected in Baidaratskaya Bay in July 2007 and in a section running westward of the Yamal Peninsula in September 2007. The depths of the sampling stations ranged from 5 to 25 m in the Baidaratskaya Bay area and between 16 and 46 m in the Yamal section. A total of 212 benthic invertebrate species were recorded. In both areas, Bivalvia was the group with the highest biomass (54.88 g/m**2 in the Yamal section and 59.71 g/m**2 in the Baidaratskaya Bay area), while polychaetes were the group with the highest number of species (45 in the Yamal section and 64 the Baidaratskaya Bay area). Three major macrozoobenthic communities were recognized: the Astarte borealis community (20-46 m, the deepest sampling stations in both areas); the 'medium-depth' community (10-20 m, extremely mosaic, usually dominated by Serripes groenlandicus); and the Nephtys longosetosa community (depth smaller than 10 m, characterized by low biomass and the absence of large bivalves and echinoderms). The western Yamal shallow-water communities were shown to be generally similar to those of Baidaratskaya Bay. The comparison of these results with those of the benthos censuses performed in 1927-1945, 1975, and 1993 showed that the benthic communities in the southwestern Kara Sea remained relatively stable during the second half of the 20th century and the early 21st century.

Contents of hydrocarbons in waters and bottom sediments of the southwestern Amur Bay (Sea of Japan) in April 2005

Abundances and compositions of aliphatic hydrocarbons (AHC) and polyaromatic hydrocarbons (PAH) were investigated in water and bottom sediments of the southwestern Amur Bay, Sea of Japan. Water contained 0-129 ?g/l AHC (average 42.2 ?g/l) and 5-85 ng/l PAH (average 18 ng/l). Bottom sediments contained 168-2098 ?g/g AHC and 7.2-1100 ng/g dry mass PAH. It was shown that input of anthropogenic hydrocarbons is better recorded by molecular markers than by distribution of AHC and PAH concentrations. Discovery of elevated hydrocarbon concentrations in the bottom water layer suggests that bottom sediments induced secondary contamination of the water body.