436 resultados para BIDENS PILOSA
Resumo:
At present time, there is a lack of knowledge on the interannual climate-related variability of zooplankton communities of the tropical Atlantic, central Mediterranean Sea, Caspian Sea, and Aral Sea, due to the absence of appropriate databases. In the mid latitudes, the North Atlantic Oscillation (NAO) is the dominant mode of atmospheric fluctuations over eastern North America, the northern Atlantic Ocean and Europe. Therefore, one of the issues that need to be addressed through data synthesis is the evaluation of interannual patterns in species abundance and species diversity over these regions in regard to the NAO. The database has been used to investigate the ecological role of the NAO in interannual variations of mesozooplankton abundance and biomass along the zonal array of the NAO influence. Basic approach to the proposed research involved: (1) development of co-operation between experts and data holders in Ukraine, Russia, Kazakhstan, Azerbaijan, UK, and USA to rescue and compile the oceanographic data sets and release them on CD-ROM, (2) organization and compilation of a database based on FSU cruises to the above regions, (3) analysis of the basin-scale interannual variability of the zooplankton species abundance, biomass, and species diversity.
Resumo:
In order to examine the long-term development of offshore macrozoobenthic soft-bottom communities of the German Bight, four representative permanent stations (MZB-SSd, -FSd, -Slt, -WB) have been sampled continuously since 1969. Inter-annual variability and possible long-term trends were analysed based on spring-time samples from 1969 until 2000. This is part of the ecological long-term series of the AWI and is supplemented by periodic large-scale mapping of the benthos. The main factors influencing the development of the benthic communities are biological interactions, climate, food supply (eutrophication) and the disturbance regime. The most frequent disturbances are sediment relocations during strong storms or by bottom trawling, while occasional oxygen deficiencies and extremely cold winters are important disturbance events working on a much larger scale. Benthic communities at the sampling stations show a large inter-annual variability combined with a variation on a roughly decadal scale. In accordance with large-scale system shifts reported for the North Sea, benthic community transitions occurred between roughly the 1970ies, 80ies and 90ies. The transitions between periods are not distinctly marked by strong changes but rather reflected in gradual changes of the species composition and dominance structure.
Resumo:
The distribution of pollen in marine sediments is used to record vegetation changes over the past 30,000 years on the adjacent continent. A transect of marine pollen sequences from the mouth of the river Congo (~5°S) to Walvis Bay and Lüderitz (~25°S) shows vegetation changes in Congo, Angola and Namibia from the last glacial period into the Holocene. The comparison of pollen records from different latitudes provides information about the latitudinal shift of open forest and savannahs (Poaceae pollen), the extension of lowland forest (rain forest pollen) and Afromontane forest (Podocarpus pollen), and the position of the desert fringe (pollen of Caryophyllaceae, Chenopodiaceae and Amaranthaceae). High Cyperaceae pollen percentages in sediments from the last glacial period off the mouth of the river Congo suggest the presence of open swamps rather than savannah vegetation in the Congo Basin. Pollen from Restionaceae in combination with Stoebe-type pollen (probably from Elytropappus) indicates a possible northwards extension of winter rain vegetation during the last glacial period. The record of Rhizophora (mangrove) pollen is linked to erosion of the continental shelf and sea-level rise. Pollen influx is highest off river mouths (10-2000 grains year**-1 cm**-2), close to the coast (300-6000 grains year**-1 cm**-2), but is an order of magnitude lower at sites situated far from the continent (<10 grains year**-1 cm**-2).
Resumo:
A high-resolution calcareous nannofossil analysis of the Danian/Selandian boundary was conducted at Site 1262 (Walvis Ridge, South Atlantic) to pinpoint the lowest occurrence of fasciculiths and to unravel the evolutionary trends throughout nannofossil Zone NP4. Using quantitative analyses, numerous primary and secondary bioevents were identified, improving the biostratigraphic resolution of this interval. The main events recorded at Site 1262 were also identified at the Zumaia section Global Stratotype Section and Point (GSSP) of the base of the Selandian and at the Qreiya section (Egypt). The lowest occurrence of fasciculiths (represented by the LO of Gomphiolithus magnicordis and Gomphiolithus magnus) was observed in the middle part of Chron C27r, above the LO of Toweius pertusus and prior to the LO of the genus Sphenolithus. The synchroneity of the LO of fasciculiths was also verified at various latitudes, such as DSDP Site 384 (NW Atlantic), ODP Site 761B (Indian Ocean) and DSDP Site 577A (Pacific Ocean). The first and second diversification events (Steurbaut and Sztrákos, 2008, doi:10.1016/j.marmicro.2007.08.004), or radiation events (Bernaola et al., 2009, doi:10.1344/105.000000272), of fasciculiths have been thoroughly discussed and well characterized by a succession of events. The occurrence of the Latest Danian Event (LDE) and several paleoenvironmental changes recognized during this time interval, coupled with an ecological competition with Sphenolithus, appear to be the probable causes of the First and Second Radiations and the fasciculith barren interval between them. The occurrence of new morphostructures and taxa suggests evolutionary trends and a strict link between morphological evolution and paleoclimate.
Resumo:
Three of the six DSDP Leg 77 sites drilled in the western approaches to the Straits of Florida yielded thick sequences of Cenozoic sediment rich in calcareous nannofossils. Hiatuses are prominent in each of these continuously cored intervals. A prominent upper Oligocene hiatus, observed at each of these three sites, can be correlated to a large-scale "global" regression event. Other disconformable horizons present in the study area cannot be positively related to sealevel fluctuations and may be caused by a number of factors including local tectonic activity. Paleogene sections are generally marked by thick accumulations within the upper Oligocene Sphenolithus ciperoensis Zone and by a pronounced braarudosphaerid-holococcolith bloom recorded in the lower Oligocene and upper Eocene. This bloom is particularly well developed at Site 540. All samples examined contain abundant nannofossils. Preservation fluctuates throughout the sections from good to poor.