323 resultados para Chiloé Archipelago


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The scope of this research was to find out, how important is the presence of brackish water for the formation of the characteristical littoral subsoil fauna in the interstitial spaces of beaches. There is little precipitation in the Red Sea area and therefore little influence of freshwater on the beach. Moreover, the sandy beach of Sarso Island (Farasan Archipelago) is bordered landwards and underneath by solid limestone, preventing subsoil fresh water, if there is any, from penetrating into the beach region. The salinity of the interstitial water from Sarso beach lies a little above the salinity of the adjacent sea. The microfauna of Sarso beach is composed to a rather big proportion of such species that are known to be characteristical littoral subsoil water species, partially of world wide distribution. The ecological analysis of this fauna, i.e. the freeliving Nematodes, reveals the presence of two distinct associations: 1. the association of the low level subsoil region, close to the sea, with clear interstitial water, subject to regular exchange with the water of the adjcent sea. 2. the association of the high level subsoil region, 4-10 meter distant from the sea, with brownish water. Contrary to earlier results there is no distinction in salinity between the two associations, so it is not longer justified to apply the term brackish water fauna on the animals living in the association of the high level subsoil region.

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The Arctic Ocean System is a key player regarding the climatic changes of Earth. Its highly sensitive ice Cover, the exchange of surface and deep water masses with the global ocean and the coupling with the atmosphere interact directly with global climatic changes. The output of cold, polar water and sea ice influences the production of deep water in the North Atlantic and controls the global ocean circulation ("the conveyor belt"). The Arctic Ocean is surrounded by the large Northern Hemisphere ice sheets which not only affect the sedimentation in the Arctic Ocean but also are supposed to induce the Course of glacials and interglacials. Terrigenous sediment delivered from the ice sheets by icebergs and meltwater as well as through sea ice are major components of Arctic Ocean sediments. Hence, the terrigenous content of Arctic Ocean sediments is an outstanding archive to investigate changes in the paleoenvironment. Glazigenic sediments of the Canadian Arctic Archipelago and surface samples of the Arctic Ocean and the Siberian shelf regions were investigated by means of x-ray diffraction of the bulk fraction. The source regions of distinct mineral compositions were to be deciphered. Regarding the complex circumpolar geology stable christalline shield rocks, active and ancient fold belts including magmatic and metamorphic rocks, sedimentary rocks and wide periglacial lowlands with permafrost provide a complete range of possible mineral combinations. Non- glaciated shelf regions mix the local input from a possible point source of a particular mineral combination with the whole shelf material and function as a sampler of the entire region draining to the shelf. To take this into account, a literature research was performed. Descriptions of outcropping lithologies and Arctic Ocean sediments were scanned for their mineral association. The analyses of glazigenic and shelf sediments yielded a close relationship between their mineral composition and the adjacent source region. The most striking difference between the circumpolar source regions is the extensive outcrop of carbonate rocks in the vicinity of the Canadian Arctic Archipelago and in N Greenland while siliciclastic sediments dominate the Siberian shelves. In the Siberian shelf region the eastern Kara Sea and the western Laptev Sea form a destinct region defined by high smectite, (clino-) pyroxene and plagioclase input. The source of this signal are the extensive outcrops of the Siberian trap basalt in the Putorana Plateau which is drained by the tributaries of the Yenissei and Khatanga. The eastern Laptev Sea and the East Siberian Sea can also be treated as one source region containing a feldspar, quartz, illite, mica, and chlorite asscciation combined with the trace minerals hornblende and epidote. Franz Josef Land provides a mineral composition rich in quartz and kaolinite. The diverse rock suite of the Svalbard archipelago distributes specific mineral compositions of highly metamorphic christalline rocks, dolomite-rich carbonate rocks and sedimentary rocks with a higher diagenetic potential manifested in stable newly built diagenetic minerals and high organic maturity. To reconstruct the last 30,000 years as an example of the transition between glacial and interglacial conditions a profile of sediment cores, recovered during the RV Polarstern" expedition ARK-VIIIl3 (ARCTIC '91), and additional sediment cores around Svalbard were investigated. Besides the mineralogy of different grain size fractions several additional sedimentological and organo-geochemical Parameterswere used. A detailed stratigraphic framework was achieved. By exploiting this data set changes in the mineral composition of the Eurasian Basin sediments can be related to climatic changes. Certain mineral compositions can even be associated with particular transport processes, e.g. the smectitel pyroxene association with sea ice transport from the eastern Kara Sea and the western Laptev Sea. Hence, it is possible to decipher the complex interplay between the influx of warm Atlantic waters into the Southwest of the Eurasian Basin, the waxing and waning of the Svalbard1Barents- Sea- and Kara-Sea-Ice-Sheets, the flooding of the Siberian shelf regions and the surface and deep water circulation. Until now the Arctic Ocean was assumed to be a rather stable System during the last 30,000 years which only switched from a completely ice covered situation during the glacial to seasonally Open waters during the interglacial. But this work using mineral assemblages of sediment cores in the vicinity of Svalbard revealed fast changes in the inflow of warm Atlantic water with the Westspitsbergen Current (< 1000 years), short periods of advances and retreats of the marine based Eurasian ice sheets (1000-3000 years), and short melting phases (400 years?). Deglaciation of the marine-based Eurasian and the land-based north American and Greenland ice sheets are not simultaneous. This thesis postulates that the Kara Sea Ice Sheet released an early meltwater signal prior to 15,000 14C years leading the Barents Sea Ice Sheet while the western land-based ice sheets are following later than 13,500 14C years. The northern Eurasian Basin records the shift between iceberg and sea-ice material derived from the Canadian Arctic Archipelago and N-Greenland and material transported by sea-ice and surface currents from the Siberian shelf region. The phasing of the deglaciation becomes very obvious using the dolomite and quartd phyllosilicate record. It is also supposed that the flooding of the Laptev Sea during the Holocene is manifested in a stepwise increase of sediment input at the Lomonosov Ridge between the Eurasian and Amerasian Basin. Depending on the strength of meltwater pulses from the adjacent ice sheets the Transpolar Drift can probably be relocated. These movements are traceable by the distribution of indicator minerals. Based on the outcome of this work the feasibility of bulk mineral determination can be qualified as excellent tool for paleoenvironmental reconstructions in the Arctic Ocean. The easy preparation and objective determination of bulk mineralogy provided by the QUAX software bears the potential to use this analyses as basic measuring method preceding more time consuming and highly specialised mineralogical investigations (e.g. clay mineralogy, heavy mineral determination).

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Inventory of some important datasets related to the physical characteristics of the seafloor surrounding the Azores Archipelago. The objective is to ensure that our compilation is readily available for any researchers interested in this type information but also to support institutions responsible for the management and conservation of local resources.

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A compilation of basal dates of peatland initiation across the northern high latitudes, associated metadata including location, age, raw and calibrated radiocarbon ages, and associated references. Includes previously published datasets from sources below as well as 365 new data points.

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During the expeditions ARK-VII/1, ARK-VII/3 and ARK-Xl2 sediment cores were taken by "RV Polarstern" from the shelf and the fjords of East Greenland and the Greenland Sea. The magnetic susceptibility and heavy mineral were determined at 48 surface sediment samples from undisturbed box cores. The main objective of this study was the identification of source areas and transport processes of terrigenous sediments at the East Greenland continental margin. The results can be summarized as lollows: 1a) Magnetic susceptibility in the North Atlantic is useful to detect delivery regions of the material transported by currents. b) The magnetic susceptibility is controlled by the ferromagnetic particles of the silt fraction. c) There are four important source areas: . The ferromagnetic particles of the box core PS2644-2 are transported from the Iceland Archipelago. . The material from the Geiki-Plateau effects the magnetic susceptibility in the Scoresby Sund Basin. . The magnetic susceptibility in the shelf regions in the North are produced by material from the fjords. . The ferromagnetic particles in the Greenland Sea are derived from the Mid Atlantic Ridges in the east. d) It is possible to determine the rock type, which delivers the ferromagnetic material because of differences in magnetic susceptibility of different intensity. . The erosion of the basalts of the Geiki-Plateau and the basalts of the Mid Atlantic ridges produce the high magnetic susceptibility in the south. . The magnetic susceptibility on the shelf in the north are probably produced by erosionproducts of the gneises of East Greenland. (2a) Heavy mineral assemblages show a significant difference between material transported by the Transpolar Drift from the Eurasian shelf regions (amphiboles, clinopyroxene, orthopyroxene) and material derived from East Greenland (garnets and opaque minerals). Transport via ice is dominant. b) lt is also possible to show different petrographic provenances (volcanic and metamorphic provenances). These associations verify the source areas. c) The information of heavy mineral composition gives no more detailed hint on the rock type or rock formation in the source area, due to mixing processes, large area of investigation and the sample quantity.

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The presence of glacial sediments across the Rauer Group indicates that the East Antarctic ice sheet formerly covered the entire archipelago and has since retreated at least 15 km from its maximum extent. The degree of weathering of these glacial sediments suggests that ice retreat from this maximum position occurred sometime during the latter half of the last glacial cycle. Following this phase of retreat, the ice sheet margin has not expanded more than ~1 km seaward of its present position. This pattern of ice sheet change matches that recorded in Vestfold Hills, providing further evidence that the diminutive Marine Isotope Stage 2 ice sheet advance in the nearby Larsemann Hills may have been influenced by local factors rather than a regional ice-sheet response to climate and sea-level change.

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Precise relative sea level (RSL) data are important for inferring regional ice sheet histories, as well as helping to validate numerical models of ice sheet evolution and glacial isostatic adjustment. Here we develop a new RSL curve for Fildes Peninsula, South Shetland Islands (SSIs), a sub-Antarctic archipelago peripheral to the northern Antarctic Peninsula ice sheet, by integrating sedimentary evidence from isolation basins with geomorphological evidence from raised beaches. This combined approach yields not only a Holocene RSL curve, but also the spatial pattern of how RSL change varied across the archipelago. The curve shows a mid-Holocene RSL highstand on Fildes Peninsula at 15.5 m above mean sea level between 8000 and 7000 cal a BP. Subsequently RSL gradually fell as a consequence of isostatic uplift in response to regional deglaciation. We propose that isostatic uplift occurred at a non-steady rate, with a temporary pause in ice retreat ca. 7200 cal a BP, leading to a short-lived RSL rise of ~1 m and forming a second peak to the mid-Holocene highstand. Two independent approaches were taken to constrain the long-term tectonic uplift rate of the SSIs at 0.22-0.48 m/ka, placing the tectonic contribution to the reconstructed RSL highstand between 1.4 and 2.9 m. Finally, we make comparisons to predictions from three global sea level models.

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Wind- induced exposure is one of the major forces shaping the geomorphology and biota in coastal areas. The effect of wave exposure on littoral biota is well known in marine environments (Ekebon et al., 2003; Burrows et al., 2008). In the Cabrera Archipelago National Park wave exposure has demostrated to have an effect on the spatial distribution of different stages of E.marginatus (Alvarez et al., 2010). Standarized average wave exposures during 2008 along the Cabrera Archipelago National park coast line were calculated to be applied in studies of littoral species distribution within the archipelago. Average wave exposure (or apparent wave power) was calculated for points located 50 m equidistant on the coastline following the EXA methodology (EXposure estimates for fragmented Archipelagos) (Ekebon et al., 2003). The average wave exposures were standardized from 1 to 100 (minimum and maximum in the area), showing coastal areas with different levels of mea wave exposure during the year. Input wind data (direction and intensity) from 2008 was registered at the Cabrera mooring located north of Cabrera Archipelago. Data were provided by IMEDEA (CSIC-UIB, TMMOS http://www.imedea.uib-csic.es/tmoos/boyas/). This cartography has been developed under the framework of the project EPIMHAR, funded by the National Park's Network (Spanish Ministry of Environment, Maritime and Rural Affairs, reference: 012/2007 ). Part of this work has been developed under the research programs funded by "Fons de Garantia Agrària i Pesquera de les Illes Balears (FOGAIBA)".

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The Rauer Group is an archipelago in Prydz Bay, East Antarctica. The ice-free islands and the surrounding shallow marine areas provide valuable archives for the reconstruction of the late Pleistocene and Holocene environmental and climatic history of the region. Two sediment records from two marine inlets of Rauer Group have been studied for their sedimentological, geochemical, and biological characteristics. Radiocarbon ages from one of the inlets indicate ice-free conditions within the last glacial cycle, probably during the second half of Marine Isotope Stage 3. Subsequent ice sheet coverage of Rauer Group during the Last Glacial Maxiumum (LGM) can be inferred from a till layer recovered in one of the basins. The inlets became ice-free prior to 11,200 cal yr BP, when biogenic sedimentation started. Deglacial processes in the catchments, however, influenced the inlets until ~9200 cal. yr BP as evidenced by the input of minerogenic material. Marine productivity under relatively open water conditions indicates an early Holocene climate optimum until 8200 cal. yr BP, which is followed by a cooler period with increased sea ice. Warmer conditions are inferred for the mid Holocene, when both basins experienced an input of freshwater between ~5700-3500 cal. yr BP, probably due to ice-sheet melting and increased precipitation on the islands. Neoglacial cooling in the late Holocene since c. 3500 cal yr BP is reflected by an increase in sea ice in both inlets.

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Deep-sea sediment cores from Scripps Institution of Oceanography's ANTIPODE Expedition were described to identify visually distinct units based on color, texture, or other feature, sedimentary structures, lithology and abundance of component grains, and paleontology. Sixty-eight cores were examined, of which 34 are large diameter piston cores. Photographs and graphic lithology legs are included as PLATES 1-48. ANTIPODE Expedition recovered cores from: the Monterey-Ascension Fan, the Northeast Pacific, the Aleutians, the Northwest Pacific, the Philippine Sea, Indonesia, the Tonga Ridge, the Seychelles, Chagos Archipelago, the Mid-Indian Ridge, the Bay of Bengal, near Sumatra, and near the Cocos Island in the Indian Ocean. The purpose of this report is to present sufficient basic data on ANTIPODE cores for invesiigators to choose samples for their own research.

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Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79°N). Here we present the first central Arctic Ocean (79-90°N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81-85°N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150-200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production.

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List of non-indigenous species (NIS) established in the Great Lakes-St. Lawrence River region and the North and Baltic Seas region, their geographic origin, and taxonomic assignment. Asterisks mark the NIS that occur in both the North and Baltic Seas and the Great Lakes-St. Lawrence River regions. GL, SL, NW, NE, SW and SE denote the Great Lakes, St. Lawrence River, north-west, north-east, south-west, and south-east, respectively. Eurasia represents inland freshwaters except Yangtze River, Indo-Pacific represents Indian Ocean and the archipelago of Indonesia, Malaysia, and Pilipinas, North America (N America) represents inland freshwaters except the Laurentian Great Lakes, St. Lawrence and Mississippi Rivers, while Australia, New Zealand, Africa and South America (S America) cover all inland freshwaters in these areas.

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Coral palaeoclimatic studies are under way at many sites throughout the wet tropics. However, arid environments have received less attention. Here we report a high-resolution, 63 yr record of coral d18O and d13C extracted from a Porites colony from the Dahlak Archipelago, off the Eritrean coast, in the southern Red Sea. The annual cycles of the coral d18O and d13C are inversely related while their inter-annual variations show a strong positive correlation, with similar inter-decadal trends. Inter-annual variations in coral d18O show a relatively weak correlation with the southern Red Sea SST, but are strongly correlated with the Indian Ocean SST, especially on the decadal time-scale. The range of the inter-annual variations in the coral d18O is high compared to changes in local SST, due to the amplifying effect of simultaneous changes in water isotopic composition. Due to this amplification of the climate signal the coral provides a better indication of regional oceangraphic behaviour than the local SST record. The norrtheast monsoon signal in the coral d18O dominates the mean annual signal and shows the best correlation with the instrumental data sets. It appears that variations in the coral d18O are controlled mainly by variations in the intensity of surface water influx from the Indian Ocean to the Red Sea during the winter northeast monsoon. Of particular significance is that the decadal time-scale variations in the coral skeletal d18O are closely correlated with both the Indian Ocean SST and with variations in the Pacific-based Southern Oscillation index. That is, isotopically light coral skeleton, indicating strong NE monsoon Red Sea inflow, correlates with periods of high Indian Ocean SST and with predominantly negative (El Nino) phases of the Southern Oscillation. The simultaneous nature of inter-decadal changes in Asian monsoon and ENSO behaviour suggest pan-Indo-Pacific tropical climate reorganisation and evolution.

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A new genus Abyssogena is established for A. phaseoliformis (Métivier, Okutani & Ohta, 1986) and A. kaikoi (Okutani & Métivier, 1986), which were previously assigned to the genus Calyptogena Dall, 1891, and also for two new species, A. southwardae and A. novacula. The most characteristic features of Abyssogena are an elongate shell up to about 280 mm in length; a pallial line starting from the ventral margin of the anterior adductor scar; secondary pallial attachment scars developed dorsal to the pallial line; radially arranged hinge teeth with a reduced anterior cardinal tooth in the right valve; and presence of an inner ctenidial demibranch only. Abyssogena occurs in deep water from 2,985 to 6,400 m and is distributed in the Pacific and Atlantic Oceans at cold seeps along continental margins and hydrothermal vents at mid-oceanic ridges. Some species have a remarkably wide geographic distribution; A. southwardae is present throughout the Atlantic and A. phaseoliformis is present in Japan, Kuril-Kamchatka, as well as Aleutian Trenches. No fossils of Abyssogena are known.

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Foraminiferal analysis of Miocene to recent strata of the Northwest Shelf of Australia is used to chart West Pacific Warm Pool (WPWP) influence. The assemblage is typified by "larger" foraminifera with ingressions of the Indo-Pacific "smaller" taxa Asterorotalia and Pseudorotalia at around 4 Ma and from 1.6 to 0.8 Ma. A review of recent and fossil biogeography of these taxa suggests their stratigraphic distribution can be used to document WPWP evolution. From 10 to 4.4 Ma a lack of biogeographic connectivity between the Pacific and Indian Ocean suggests Indonesian Throughflow (ITF) restriction. During this period, the collision of Australia and Asia trapped warmer waters in the Pacific, creating a central WPWP biogeographic province from the equator to 26°N. By 3 Ma Indo-Pacific species migrated to Japan with the initiation of the "modern" Kuroshio Current coinciding with the intensification of the North Pacific Gyre and Northern Hemisphere ice sheet expansion. Indo-Pacific taxa migrated to the northwest Australia from 4.4 to 4 Ma possibly because of limited ITF. The absence of Indo-Pacific taxa in northwest Australia indicates possible ITF restriction from 4 to 1.6 Ma. Full northwest Australian biogeographic connectivity with the WPWP from 1.6 to 0.8 Ma suggests an unrestricted stronger ITF (compared to today) and the initiation of the modern Leeuwin Current. The extinction of some Indo-Pacific species in northwest Australia after 0.8 Ma may be related to the effects of large glacial/interglacial oscillations and uplift of the Indonesian Archipelago causing Indonesian seaway restriction.