993 resultados para Yenisei expedition, 1875-1876.


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Resumen tomado de la revisa

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David Kaufmann

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Phytoplankton biomass distribution (chlorophyll a, chl. a) and species composition (cell numbers) were investigated during three expeditions to the Kara Sea with "Akademik Boris Petrov" (BP) in 1997, 1999, and 2000. The distribution of biomass in the estuaries of Ob and Yenisei showed a similar range in 1997 (0.2 to 3.2 µg/l) and 2000 (0.4 to 3.5 ug/l); higher chl. a concentrations during these two years were found in Yenisei than in Ob. In 1999, phytoplankton biomass in the Ob and Ob Estuary was much higher than in 1997 and 2000, with maximum values above 10.0 ug chl. a/l. In 1999, biomass in Yenisei was lower (1.5 to ~5 ug/l) than in Ob but slightly higher than in 1997 and in 2000. During the expedition in 2000, the research area extended farther to the north, here, lowest phytoplankton biomass during all three years was found. Typical summer values for integrated chl.a biomass (surface to bottom) ranged between 6 and 20 mg m**-2. Strong differences existed in species composition in both rivers, the estuaries, and the open Kara Sea. In general, three or four different populations could be distinguished in surface waters: (1) freshwater diatoms together with bluegreen algae in both rivers, (2) centric and small pennate diatoms mainly brackish species in the estuaries, (3) north of 74°N, brackish/marine species dominated, i.e. in 1999 Thalassiosira cfpunctigera and Chaetoceros spp prevailed in the phytoplankton bloom in Ob. (4) At the northernmost, almost marine stations, a region with a more heterogeneous composition of unicellular plankton was encountered. We assume, we found different seasonal signals of phytoplankton development during 1997/2000 and 1999, respectively. However, the yearly fluctuation of freshwater runoff of both rivers seems to have the strongest influence on the timing and duration of phytoplankton blooms, species compositions and biomass standing stocks during summer.

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Manganese nodules from Stations 252 and 281 of the Challenger Expedition, collected in 1875, have recently been discovered in the Redpath Museum. The nodules have been found to be quite typical specimens of two areas in the Central Pacific Ocean except for dehydration and other changes that have taken place during storage. The principal resolvable manganese mineral in nodules from Station 252 proved to be 10 A manganite; there was a very thin surface coating of birnessite. Delta manganite was the only manganese mineral found in nodules from Station 281. Through electron microprobe studies, findings from chemical, optical and x-ray crystallographic work were correlated with the detailed picture of the occurrence and quantities of the different elements within the nodules. In all cases it was found that the iron and manganese had an antithetical relationship, and that nickel and copper were associated with the manganese. Special study was given to a 300-micron-square area in a nodule from Station 252 which included a segregation of 49.39% Mn, 5.31 % Ni, and 1.64% Cu. Crystallization of the manganese phases is thought to have provided a mech¨anism for formation of segregations which were further enriched through chemical scavenger action as long as ocean floor conditions permitted.

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Microfilme. Valencia: BV, ca. 1990

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This layer is a georeferenced raster image of the historic paper map entitled: Pictorial map of the International Exhibition Grounds, presented by the Philadelphia, Wilmington and Baltimore Railroad. It was published by Van Ingen & Snyder & Gillett in 1876. Scale not given. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Pennsylvania South State Plane Coordinate System NAD83 (in Feet) (Fipszone 3702). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This image pictorially shows the grounds of the Philadelphia Centennial Exhibition, 1876. It includes features such as roads, railroads, drainage, buildings with uses, and more. Includes inset engraving: Birds-eye Centennial International Exhibition from Sawyer's Observatory. Copyright 1875 by Theo. Leonhardt & Son and lists of United States Centennial Commissions officers. This layer is part of a selection of digitally scanned and georeferenced historic maps from The Harvard Map Collection as part of the Imaging the Urban Environment project. Maps selected for this project represent major urban areas and cities of the world, at various time periods. These maps typically portray both natural and manmade features at a large scale. The selection represents a range of regions, originators, ground condition dates, scales, and purposes.

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Two main mechanisms are controlling the accumulation of organic matter in the sediments of the Kara Sea. The large rivers Ob and Yenisei supply significant quantities of freshwater onto the shelf (Lisitsyn and Vinogradov, 1995; Bobrovitskaya et al., 1996; Johnson et al., 1997) and deliver terrigenous organie matter and aquatic algae. Additionally, marine organic matter is produced in the water column. In order to distinguish between the different sources of the organic material maceral analysis, organic-geochemical bulk Parameters and biomarkers (short- and long-chain D-alkanes, fatty acids and pigments) were used to determine the quality (marine vs. terrigenous) and quantity of the organic carbon fraction in the surface sediments taken during the 28th cruise of RV Akademik Boris Petrov (Matthiessen and Stepanets, 1998) (Fig. 1). Previous organic-geochemical investigations (i.e., total organic-carbon content (TOC), hydrogen indices (Hl), CIN-ratios) indicate the importance of terrigenous input of organic matter (Galimov et al., 1996; Stein, 1996). Studies of lipid biomarkers in surface sediments in the Ob estuary show also a predominance of terrestrial constituents and an increase in planktonogenic and bacterial lipids further offshore (Belyaeva and Eglinton, 1997). In complex systems such as the Eurasian continental margin characterized by high input of terrestriallaquatic organic matter and strong seasonal variation in sea-ice Cover and primary productivity, the Interpretation of the organic geochemical data is much more complicated and restricted in comparison to similar data Sets from low-latitude open-ocean environments (Fahl and Stein, 1998). Microscopical studies (maceral analysisl palynology), however, allow a direct visual inspection of the particulate organic matter and allow to differentiate particles of different biological sources. Thus, a combination of both methods as shown in this study, yields a more precise identification of organic-carbon sources.