919 resultados para Coded aperture
Resumo:
Arctic sea ice is declining rapidly, making it vital to understand the importance of different types of sea ice for ice-dependent species such as polar bears Ursus maritimus. In this study we used GPS telemetry (25 polar bear tracks obtained in Svalbard, Norway, during spring) and high-resolution synthetic aperture radar (SAR) sea-ice data to investigate fine-scale space use by female polar bears. Space use patterns differed according to reproductive state; females with cubs of the year (COYs) had smaller home ranges and used fast-ice areas more frequently than lone females. First-passage time (FPT) analysis revealed that females with COYs displayed significantly longer FPTs near (<10 km) glacier fronts than in other fast-ice areas; lone females also increased their FPTs in such areas, but they also frequently used drifting pack ice. These results clearly demonstrate the importance of fast-ice areas, in particular close to glacier fronts, especially for females with COYs. Access to abundant and predictable prey (ringed seal pups), energy conservation and reluctance to cross large open water areas are possible reasons for the observed patterns. However, glacier fronts are retracting in Svalbard, and declines in land-fast ice have been notable over the past decade. The eventual disappearance of these important habitats might become critical for the survival of polar bear cubs in Svalbard and other regions with similar habitat characteristics. Given the relatively small size of many fast-ice areas in Svalbard, the results observed in this study would not have been revealed using less accurate location data or lower-resolution sea-ice data.
Resumo:
There are about 30 species of planktonic Foraminifera, as contrasted with the more than 4200 benthic species in the oceans of the world. Most of the planktonic species belong to the families Globigerinidae and Globorotaliidae. Of the 30 species, 9 occur in Antarctic and Subantarctic waters; however, none of these cold-water species are restricted to the Southern Ocean, except possibly the newly recognized Globorotalia cavernula (Be, 1967b). These species are distributed in broad zones of similar temperature in both the Northern and Southern Hemispheres. Hence, it is not possible to refer to these species as endemic to the Antarctic or Subantarctic, although some of them do appear in very high concentrations of 10 specimens/m**3 or more in the Antarctic regions. The plankton samples upon which the accompanying maps are based were collected between 1960 and 1965 on the research vessels Eltanin of the National Science Foundation (U.S. Antarctic Research Program), and Vema and Conrad of the Lamont Geological Observatory. All surface (0 m to 10 m) and vertical (0 m to 300 m) tows were obtained with plankton nets of uniform mesh size and material (NITEX202 = 202 µm mesh-aperture width) and were provided with flowmeters for quantitative readings of amounts of water filtered.
Resumo:
Multibeam data were measured during R/V SONNE cruise SO202 (INOPEX) along track lines of 6938 NM total length in the North Pacific and Bering Sea during transits and stationary work. Starting from Hokkaido (Japan) data were achieved east of the Kuril-Kamchatka Trench and south of the Aleutian Trench. The track crosses the Bowers Ridge, the continental margin of Alaska and the Umnak Plateau in the Bering Sea. Further data were gained in the North Pacific in the area of the Patton Seamounts, Gibson Seamount, Hess Rise and Shatsky Rise. The multibeam sonar system Simrad EM 120 from Kongsberg was operated using 191 beams and an aperture angle of 90° to 140° due to particular conditions. The refraction correction was achieved utilizing 6 CTD profiles measured during the cruise and one from cruise SO201. The quality of data might be reduced during bad weather periods. The dataset contains raw data that are not processed and thus may contain errors and blunders in depth and position.
Resumo:
The chemical composition of shells of the planktonic foraminifer Globigerinoides ruber (white) is frequently used to determine past sea surface conditions. Recently, it has been shown that arbitrarily defined morphotypes within this species exhibit different chemical and isotopic signatures. Here, we investigate the occurrence through time and in space of morphological types of G. ruber (white) in late Quaternary and Holocene sediments of the central and the eastern Mediterranean Sea. In 115 samples representing two distinct time intervals (MIS 1-2 and MIS 9-12) at ODP Site 964 and the piston core GeoTü-SL96, we have defined three morphological types within this species and determined their relative abundances and stable isotopic composition. A quantitative analysis of morphological variation within G. ruber (white) in four samples revealed that the subjectively defined morphotypes occupy separate segments of a continuous and homogenous morphospace. We further show that the abundance of the morphotypes changes significantly between glacials and interglacials and that the three morphotypes of G. ruber show significant offsets in their stable isotopic composition. These offsets are consistent within glacial and interglacial stages but their sign is systematically reversed between the two Sites. Since the isotopic shifts among the three G. ruber morphotypes are systematic and often exceed 1per mil, their understanding is essential for the interpretation of all G. ruber-based proxy records for the paleoceanographic development of the Mediterranean during the late Quaternary.
Resumo:
Within the last decade, the Greenland ice sheet (GrIS) and its surroundings have experienced record high surface temperatures (Mote, 2007, doi:10.1029/2007GL031976; Box et al., 2010), ice sheet melt extent (Fettweis et al., 2011, doi:10.5194/tc-5-359-2011) and record-low summer sea-ice extent (Nghiem et al., 2007, doi:10.1029/2007GL031138). Using three independent data sets, we derive, for the first time, consistent ice-mass trends and temporal variations within seven major drainage basins from gravity fields from the Gravity Recovery and Climate Experiment (GRACE; Tapley et al., 2004, doi:10.1029/2004GL019920), surface-ice velocities from Inteferometric Synthetic Aperture Radar (InSAR; Rignot and Kanagaratnam, 2006, doi:10.1126/science.1121381) together with output of the regional atmospheric climate modelling (RACMO2/ GR; Ettema et al., 2009, doi:10.1029/2009GL038110), and surface-elevation changes from the Ice, cloud and land elevation satellite (ICESat; Sorensen et al., 2011, doi:10.5194/tc-5-173-2011). We show that changing ice discharge (D), surface melting and subsequent run-off (M/R) and precipitation (P) all contribute, in a complex and regionally variable interplay, to the increasingly negative mass balance of the GrIS observed within the last decade. Interannual variability in P along the northwest and west coasts of the GrIS largely explains the apparent regional mass loss increase during 2002-2010, and obscures increasing M/R and D since the 1990s. In winter 2002/2003 and 2008/2009, accumulation anomalies in the east and southeast temporarily outweighed the losses by M/R and D that prevailed during 2003-2008, and after summer 2010. Overall, for all basins of the GrIS, the decadal variability of anomalies in P, M/R and D between 1958 and 2010 (w.r.t. 1961-1990) was significantly exceeded by the regional trends observed during the GRACE period (2002-2011).
Resumo:
The Denmark Strait Overflow (DSO) today compensates for the northward flowing Norwegian and Irminger branches of the North Atlantic Current that drive the Nordic heat pump. During the Last Glacial Maximum (LGM), ice sheets constricted the Denmark Strait aperture in addition to ice eustatic/isostatic effects which reduced its depth (today ~630 m) by ~130 m. These factors, combined with a reduced north-south density gradient of the water-masses, are expected to have restricted or even reversed the LGM DSO intensity. To better constrain these boundary conditions, we present a first reconstruction of the glacial DSO, using four new and four published epibenthic and planktic stable-isotope records from sites to the north and south of the Denmark Strait. The spatial and temporal distribution of epibenthic delta18O and delta13C maxima reveals a north-south density gradient at intermediate water depths from sigma0 ~28.7 to 28.4/28.1 and suggests that dense and highly ventilated water was convected in the Nordic Seas during the LGM. However, extremely high epibenthic delta13C values on top of the Mid-Atlantic Ridge document a further convection cell of Glacial North Atlantic Intermediate Water to the south of Iceland, which, however, was marked by much lower density (sigma0 ~28.1). The north-south gradient of water density possibly implied that the glacial DSO was directed to the south like today and fed Glacial North Atlantic Deep Water that has underthrusted the Glacial North Atlantic Intermediate Water in the Irminger Basin.
Resumo:
Multibeam data were measured as part of the project HERMES during R/V Polarstern cruise ARK-XXII/1 (2007-05-29 to 2007-07-25) along transits and survey profiles and partly during stationary work. Data were achieved mainly in the coastal areas of northern Norway, at the Hakon Mosby Mud Volcano at the continental margin approx. 200 nm off the norwegian coast and the AWI-Hausgarten area approx. 150 nm west of Svalbard. A number of surveys were carried out in the coastal areas of northern Norway (Sula Reef, Roest Reef, Traena area, Floholmen area, Sotbakken area) and around the area of the Hakon Mosby Mud Volcano. The multibeam sonar system Atlas Hydrosweep DS-2 (Atlas Hydrographic, http://www.atlashydro.com) was operated using 59 beams and 90° aperture angle. The refraction correction was achieved using CTD profiles measured during this cruise or, during transits, utilizing the system's own cross fan calibration. The quality of data might be reduced during bad weather periods or adverse sea ice conditions (only in the AWI-Hausgarten area). This dataset contains raw data that are not processed and thus may contain errors and blunders in depth and position.
Resumo:
The file here provided, is the list of all characters that have been used in cladistic analysis on ammonoids published so far. It constitutes the base of a study which investigates practices in characters establishment. Find here after the abstract of the article that is associated to this file. Cladistics appears as one of the most useful method to reconstruct phylogeny of fossil taxa. However, ammonoids workers tend to sulk this method. The capital step of cladistic analysis is the recognition of homology hypothesis as clue to reconstruct monophyletic clades based on the sharing of derived traits. Previous authors have suggested that coding schemes are usually direct transcription of original taxa description. However, establishing a list of characters (i.e. a matrix taxa /characters) is a very different work compared to a compilation of diagnoses. How morphology is coded in ammonoids? How coding schemes are influenced by traditional descriptions / characters? Here, we review all cladistic analyses of ammonoids published in the literature to compare characters and the way authors have dealt with the treatment of continuous characters, polymorphism and ontogeny. Several barriers are usually invoked to justify that cladistics cannot be applied to reconstruct ammonoids phylogenies. We show that an appropriate use of improvements both on ammonoids' knowledge and cladistics methodology may overcome limitations usually invoked to perform cladistic analysis on ammonoids.
Resumo:
Multibeam data were collected without operator supervision on R/V Polarstern cruise ANT-XVI/4 along track lines of 6385 NM total length. Data were achieved during transits and stationary work on the route from Cape Town to Bremerhaven via the Cape Verde Islands and the Canary Islands. The multibeam sonar system Hydrosweep DS-2 was operated using 59 beams and 90° aperture angle. The quality of data might be reduced during bad weather periods or adverse sea ice conditions. The dataset contains raw data that are not processed and thus may contain errors and blunders in depth and position.
Resumo:
Our understanding of the effects of ocean acidification on whole organism function is growing, but most current information is for adult stages of development. Here, we show the effects of reduced pH seawater (pH 7.6) on aspects of the development, physiology and behaviour of encapsulated embryos of the marine intertidal gastropod Littorina obtusata. We found reduced viability and increased development times under reduced pH conditions, and the embryos had significantly altered behaviours and physiologies. In acidified seawater, embryos spent more time stationary, had slower rotation rates, spent less time crawling, but increased their movement periodicity compared with those maintained under control conditions. Larval and adult heart rates were significantly lower in acidified seawater, and hatchling snails had an altered shell morphology (lateral length and spiral shell length) compared to control snails. Our findings show that ocean acidification may have multiple, subtle effects during the early development of marine animals that may have implications for their survival beyond those predicted using later life stages.
Resumo:
Multibeam data were collected without operator supervision on R/V Polarstern cruise ANT-XV/4 along track lines of about 7000 NM total length. Data were achieved during transits and stationary work in the western Weddell Sea, at the Weddell-Scotia Confluence, and on a transect along the Prime Meridian of about 1300 NM length, between 69°S and 47°S. The multibeam sonar system Hydrosweep DS-2 was operated using 59 beams and 90° aperture angle. The quality of data might be reduced during bad weather periods or adverse sea ice conditions. The dataset contains raw data that are not processed and thus may contain errors and blunders in depth and position.