994 resultados para Appendix Adenocarcinoma


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Benthic foraminiferal data from Ocean Drilling Program Site 1098 indicate significant changes in deep-water conditions of the Palmer Deep, western Antarctic Peninsula margin, throughout the Holocene (13 ka to present). The earliest Holocene represents a period of transition from the Last Glacial Maximum (LGM). Cold bottom waters, similar to saline shelf water (SSW), dominated the middle Holocene. The late Holocene in the Palmer Deep has been characterized by alternating dominance of circumpolar deep water (CDW) and saline shelf water. These changes have global oceanographic and climatic implications. We suggest that the middle Holocene bottom-water record, in the absence of circumpolar deep water on the western Antarctic Peninsula shelf, indicates high saline shelf water production and/or weakened circumpolar deep water production during the middle Holocene climatic optimum. The late Holocene benthic foraminiferal record indicates rapidly fluctuating sea-ice conditions and may indicate a teleconnection between the South Pacific and Southern Ocean, thus having implications related to the Southern Oscillation Index.

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Understanding species distribution patterns and the corresponding environmental determinants is a crucial step in the development of effective strategies for the conservation and management of plant communities and ecosystems. Therefore, a central prerequisite is the biogeographical and macroecological analysis of factors and processes that determine contemporary, potential, as well as future geographic distribution of species. This thesis has been conducted in the framework of the BIOMAPS-BIOTA project at the Nees Institute of Biodiversity of Plants, which was funded by the German Federal Ministry of Education and Research (BMBF). The study investigated patterns of plants species richness and phytogeographic regions under contemporary environmental conditions and forecasted future climate change in the area of West Africa covering five countries: Benin, Burkina Faso, Côte d'Ivoire, Ghana and Togo. Firstly, geographic patterns of vascular plant species richness have been depicted at a relatively fine spatial resolution based on the potential distribution of 3,393 species. Species richness is closely related to the steep climatic gradient existing in the region with a high concentration of species in the most humid areas in the south and decreases towards the northern drier areas. The investigation of the effectiveness of the existing network of protected areas shows an overall good coverage of species in the study area. However, the proportion of covered species is considerably lower at national extent for some countries, thus calling for more protected areas in order to cover adequately a maximum number of plants species in these countries. Secondly, based on the potential distribution range of vascular plant species, seven phytogeographic regions have been delineated that broadly reflect the vegetation zones as defined by White (1983). However notable differences to the delineation of White (1983) occur at the margins of some regions. Corresponding to a general southward shifted of all regions. And expansion of the Sahel vegetation zone is observed in the north, while the rainforest zone is decreased in the very south.This is alarming since the rainforest shelters a high number of species and a high proportion of range-restricted or endemic species, despite their relatively small extent compared to the other regions. Finally, the evaluation of the potential impact of climate change on plant species richness in the study area, results in a severe loss of future suitable habitat for up to 50% of species per grid cell, particularly in the rainforest region. Moreover, the analysis of the possible shift of phytogeographic regions shows in general a strong deterioration of the West African rainforest. In contrast the drier areas are expanding continuously, although a slight gain in species number can be observed in some particular regions. The overall lesson to retain from the results of this study is that the West African rainforest should be fixed as a high priority area for the conservation of biodiversity of plants, since it is subject to severe contemporary and projected future threats.

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The international, interdisciplinary biodiversity research project BIOTA AFRICA initiated a standardized biodiversity monitoring network along climatic gradients across the African continent. Due to an identified lack of adequate monitoring designs, BIOTA AFRICA developed and implemented the standardized BIOTA Biodiversity Observatories, that meet the following criteria (a) enable long-term monitoring of biodiversity, potential driving factors, and relevant indicators with adequate spatial and temporal resolution, (b) facilitate comparability of data generated within different ecosystems, (c) allow integration of many disciplines, (d) allow spatial up-scaling, and (e) be applicable within a network approach. A BIOTA Observatory encompasses an area of 1 km2 and is subdivided into 100 1-ha plots. For meeting the needs of sampling of different organism groups, the hectare plot is again subdivided into standardized subplots, whose sizes follow a geometric series. To allow for different sampling intensities but at the same time to characterize the whole square kilometer, the number of hectare plots to be sampled depends on the requirements of the respective discipline. A hierarchical ranking of the hectare plots ensures that all disciplines monitor as many hectare plots jointly as possible. The BIOTA Observatory design assures repeated, multidisciplinary standardized inventories of biodiversity and its environmental drivers, including options for spatial up- and downscaling and different sampling intensities. BIOTA Observatories have been installed along climatic and landscape gradients in Morocco, West Africa, and southern Africa. In regions with varying land use, several BIOTA Observatories are situated close to each other to analyze management effects.

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This study tests the hypothesis that the late Miocene to early Pliocene constriction and closure of the Central American Seaway (CAS), connecting the tropical Atlantic and East quatorial Pacific (EEP), caused a decrease in productivity in the Caribbean, due to decreased coastal upwelling and an end to the connection with high-productivity tropical Pacific waters. The present study compared paleoceanographic proxies for the interval between 8.3 and 2.5 Ma in 47 samples from south Caribbean ODP Site 999 with published data on EEP DSDP Site 503. Proxies for Site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor, the ratio of infaunal/epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates (BFARs). In addition, we calculated % resistant planktic foraminifers species and used the previously published % sand fraction and benthic carbon isotope values from Site 999. During early shoaling of the Isthmus (8.3-7.9 Ma) the Caribbean was under mesotrophic conditions, with little ventilation of bottom waters and low current velocity. The pre-closure interval (7.6-4.2 Ma) saw enhanced seasonal input of phytodetritus with even more reduced ventilation, and enhanced dissolution between 6.8 and 4.8 Ma. During the post-closure interval (4.2-2.5 Ma) in the Caribbean, paleoproductivity decreased, current velocity was reduced, and ventilation improved, while the seasonality of phytodetrital input was reduced dramatically, coinciding with the establishment of the Atlantic-Pacific salinity contrast at 4.2 Ma. Our data support the hypothesis that late Miocene constriction of the CAS at 7.9 Ma and its closure at 4.2 Ma caused a gradual decrease in paleoproductivity in the Caribbean, consistent with decreased current velocity and seasonality of the phytodetrital input.