ALBERT

Description: Scattered groups of these ancient fish may all stem from a single remote population. Coelacanths were discovered in the Comoros archipelago to the northwest of Madagascar in 1952. Since then, these rare, ancient fish have been found to the south off Mozambique, Madagascar and South Africa, and to the north off Kenya and Tanzania — but it was unclear whether these are separate populations or even subspecies. Here we show that the genetic variation between individuals from these different locations is unexpectedly low. Combined with earlier results from submersible and oceanographic observations1, 2, our findings indicate that a separate African metapopulation is unlikely to have existed and that locations distant from the Comoros were probably inhabited relatively recently by either dead-end drifters or founders that originated in the Comoros.

Description: The biogeochemistry of the river-sea interface was studied in the Kem' River (the largest river flowing to the White Sea from Karelian coast) estuary and adjacent area of the White Sea onboard the RV "Ekolog" in summer 2001, 2002 and 2003. The study area can be divided into 3 zones: I - the estuary itself, with water depth from 1 to 5m and low salinity in the surface layer (salinity is lower than 0.2psu in the Kem' River and varies from 15 to 20psu in outer part of this zone); II - the intermediate zone with depths from 5 to 10m and salinity at the surface from 16 to 22psu; III - the marine zone with depths from 10 to 29 m and salinity 21-24.5psu. Highest concentrations of the suspended particulate matter (SPM) were registered in the Kem' mouth (5-7mg/l). They sharply decreased to values 〈1mg/l towards the sea. At beginning of July 2001, particulate organic carbon (POC) concentration in the river mouth was 404µg/l and POC content in total SPM was 5.64%. In the marine part of the studied area the POC concentration varied from 132 to 274µg/l and the POC contents in suspended matter increased to 19-52.6%. These studies show, that the majority of riverborne suspended matter in the Kem' estuary deposits near the river mouth within the 20psu isohaline, where sedimentation of the suspended matter takes place. The role of fresh-water phytoplankton species decreases and the role of marine species increases from the river to sea and the percentage of green algae decreases and the role of diatoms increases. The organic carbon (Corg) to nitrogen (N) ratio (Corg/N) in both suspended matter and bottom sediments decreases from the river to the marine part of the mixing zone (from 8.5 to 6.1 in the suspended matter and from 14.6 to 7.5 in the bottom sediments), demonstrating that content of terrestrial-derived organic matter decreases and content of marine organic matter increases from the river mouth to the sea. The Kem' estuary exhibits a similar character of biogeochemial processes as in the large Arctic estuaries, but the scale of these processes (amount of river input of SPM, POC, area of estuaries) is different.

Description: By combining the lithologic, original palynologic and published micropaleonthological data we reconstructed paleogeographical events On the Pechora shelf during the Younger Dryas and Holocene time. Our paleoenvironmental reconstructions are based On the regularities in formation of pollen-and-spores assemblages in the surface sediments of the Pechora Sea. The main stages in paleogeography of the Pechora Sea during the Late Pleistocene were emphasized. The Late Valdai sediments in the Pechora Sea region were accumulated under the influence of fluvioglacial flows probably from the melting ice cap on Kolguev Island and, also, coastal glaciers. Climate deterioration considerably changed coastal vegetation as reflected in the depleted taxonomic and quantitative composition of palynospectra. The pollen data suggest that Open steppe-like plant communities with Artemisia, Poaceae, Asteraceae and Caryophyllaceae dominated dry ecotopes On watersheds, whereas tundra-like communities with Betula nana, arctic Salix, Dryas, Saxifraga, Carex and Brassicaceae were common in more humid coastal lowlands. The overlying silts and loamy sands are believed to have been accumulated during early deglaciation, i.e., Older Dryas and Alleröd. During this phase the glacial sedimentation was rather rapidly replaced by a glaciomarine deposition. Progressive climate warming caused prominent changes in coastal vegetation. Discontinuous treeless tundra-steppe associations were replaced by dwarf and shrub ernik tundra. A "complex vegetation cover" of forest-tundra apparently existed in the northern part of the Kola Peninsula and in the Northern Dvina Lowland. By the end of the Alleröd alder-bushes and horsetails occupied riverbanks, and spruce occurred in the forest-tundra communities on the adjacent hinterland.

Description: More reliable reconstructions of the Late Quaternary glacial history of the Pechora Sea have been carried out due to new radiocarbon datings. The bulk of evidence favors the view that complete deglaciation of the Pechora Sea occurred in the middle Valdai epoch, about 35-40 ka. After a short interstadial period with normal marine conditions, sea-level fall gave rise to establishment of continental environments. In the late Valdai, the Novaya Zemlya ice sheet occupied only the northernmost Pechora Sea and did not reach the Pechora Lowland. In the Course of the subsequent Holocene transgression, the shelf was abraded. Modern lithodynamic conditions in the Pechora Sea determine accumulation of sandy-silty deposits.

Description: The article discusses the main results of the complex investigations of barrier beaches in the Pechora Sea including coastal dynamics and accompanying exogenous processes (eolian transportation), lithological and micropaleontological studies of the sediment sequence and radiocarbon dating. We were the first to reconstruct sedimentation conditions and evolution of these big accumulative forms in the Pechora Sea. Stationary observations on coastal dynamics and the rate of eolian sedimentation allowed estimating the rate of barrier retreat. The mechanism of formation and evolution of dune belts on these barriers is described. Composition of diatom associations and lithological data provide evidence for facial-genetic conditions of sedimentation during accumulation of barriers. Radiocarbon datings corroborate the "young" age of the modern avandune ridges of the barrier beaches.

Description: Sinking particles, once caught in sediment trap jars, release dissolved elements into the surrounding medium through leaching from their pore fluids, chemical dissolution and the activity of free exoenzymes. This results in an increase in dissolved elements in the trap jar supernatant. Elemental fluxes as traditionally measured by sediment traps underestimate total export when this particle-associated dissolved flux is not considered. The errors introduced are variable and alter both the absolute levels of flux as well as the stoichiometry of export. These errors have been quantified and corrections applied for samples from sediment traps in the North Atlantic based on measurements of excess dissolved carbon, nitrogen, phosphorus, silica and calcium in the supernatant of the collection cups. At the base of the winter mixed layer, on average 90±6% of phosphorus fluxes are found as excess phosphate whereas for carbon and nitrogen dissolved concentrations account for 30 (±8)% and 47(±11)% of total fluxes respectively. Excess dissolved silica is on average 61 (±17)% of total biogenic silica flux. Little (〈10%) of calcium is solubilized. The proportion of dissolved to total flux decreases with trap deployment depth. Calculations of the C:N:P ratios for particles only are well above the Redfield ratios of 106:16:1 (Redfield et al., 1963), although the mid-water dissolved N:P and N:Si values as well as the C:N:P ratios of remineralisation along isopycnals conform to the Redfield ratios at this site. Accounting for dissolved fluxes of all these elements brings the stoichiometry of export in agreement with the Redfield Ratio and with other geochemical estimates of winter mixed layer export. A factor of 3 to 4 higher ratios of organic: inorganic carbon export also implies that the net atmospheric CO2 sequestration by the biological pump is about 50% higher at this site when the dissolved elemental fluxes are considered. Solubilization is thus a process that should be accounted for in protocols used to measure vertical fluxes with sediment traps.

Description: In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.