Надзор органов прокуратуры за коррупционной сферой бизнеса в России и Беларуси в современных условиях

Материалы IX Междунар. науч. конф., 21–22 мая 2015 г

Microfossil evidence for trophic changes during the Eocene-Oligocene transition in the South Atlantic (ODP Site 1263, Walvis Ridge)

The biotic response of calcareous nannoplankton to environmental and climatic changes during the Eocene-Oligocene transition was investigated at a high resolution at Ocean Drilling Program (ODP) Site 1263 (Walvis Ridge, southeast Atlantic Ocean) and compared with a lower-resolution benthic foraminiferal record. During this time interval, global climate, which had been warm under high levels of atmospheric CO2 (pCO(2)) during the Eocene, transitioned into the cooler climate of the Oligocene, at overall lower pCO(2). At Site 1263, the absolute nannofossil abundance (coccoliths per gram of sediment; N g(-1)) and the mean coccolith size decreased distinctly after the E-O boundary (EOB; 33.89 Ma), mainly due to a sharp decline in abundance of large-sized Reticulofenestra and Dictyococcites, occurring within a time span of similar to 47 kyr. Carbonate dissolution did not vary much across the EOB; thus, the decrease in abundance and size of nannofossils may reflect an overall decrease in their export production, which could have led to variations in the food availability for benthic foraminifers. The benthic foraminiferal assemblage data are consistent with a global decline in abundance of rectilinear species with complex apertures in the latest Eocene (similar to 34.5 Ma), potentially reflecting changes in the food source, i.e., phytoplankton. This was followed by a transient increased abundance of species indicative of seasonal delivery of food to the sea floor (Epistominella spp.; similar to 33.9-33.4 Ma), with a short peak in overall food delivery at the EOB (buliminid taxa; similar to 33.8 Ma). Increased abundance of Nuttallides umbonifera (at similar to 33.3 Ma) indicates the presence of more corrosive bottom waters and possibly the combined arrival of less food at the sea floor after the second step of cooling (Step 2). The most important changes in the calcareous nannofossil and benthic communities occurred similar to 120 kyr after the EOB. There was no major change in nannofossil abundance or assemblage composition at Site 1263 after Step 2 although benthic foraminifera indicate more corrosive bottom waters during this time. During the onset of latest-Eocene-earliest-Oligocene climate change, marine phytoplankton thus showed high sensitivity to fast-changing conditions as well as to a possibly enhanced, pulsed nutrient supply and to the crossing of a climatic threshold (e.g., pCO(2) decline, high-latitude cooling and changes in ocean circulation)

Disentangling Eocene/Oligocene ocean changes on the Western North Atlantic margin using three different micropaleontological groups and foraminiferal stable isotopes (DSDP site 612)

The Eocene-Oligocene climate transition (EOT) is associated with pronounced ocean cooling and changes in ocean circulation that culminated in the onset of glaciation on Antarctica. Much of the cooling and ocean restructuring has been linked to southern high latitude processes while details of North Atlantic (NA) circulation remain uncertain. This study contributes new insights into the ocean environment on the western NA margin during the EOT using 3 micropaleontological groups (calcareous nannofossils, planktonic and benthic foraminifera) and foraminiferal stable isotopes from DSDP Site 612. Located on the New Jersey Continental Slope (1404 m), this site today has potential to feel oceanic changes from high (Labrador Current) and low latitudes (Gulf Stream). Isotopic and biostratigraphic data imply that the first phase of the EOT (EOT-1 and the Eocene/Oligocene boundary, EOB) is captured and that the rest is truncated by a hiatus. Based on microfossil assemblages we identify three paleoenvironmental phases: pre -EOT (~34.7-34.46 Ma), high primary productivity/high organic matter flux to the sea floor, evidenced by abundant ‘euthrophic’ planktonic taxa and deep-infaunal benthic taxa indicative of high food supply; Latest Eocene to EOT-1 event (~34.46-33.9 Ma), oxygen minimum zone expanding to the sea floor, evidenced by hypoxic benthic indices; and EOB (~33.9-33.85 Ma), lower productivity and increased seasonality, inferred by abundant opportunistic benthic taxa suggestive of seasonally fluctuating organic input. These observations imply changes in nutrient supply and mixing in the NA prior to the EOT

Export of nutrient rich northern component water preceded early Oligocene Antarctic glaciation

The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland–Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO₂ to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica