137 resultados para LAGOON-OF-VENICE


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Species distribution patterns in planktonic foraminiferal assemblages are fundamental to the understanding of the determinants of their ecology. Until now, data used to identify such distribution patterns was mainly acquired using the standard >150 µm sieve size. However, given that assemblage shell size-range in planktonic foraminifera is not constant, this data acquisition practice could introduce artefacts in the distributional data. Here, we investigated the link between assemblage shell size-range and diversity in Recent planktonic foraminifera by analysing multiple sieve-size fractions in 12 samples spanning all bioprovinces of the Atlantic Ocean. Using five diversity indices covering various aspects of community structure, we found that counts from the >63 µm fraction in polar oceans and the >125 µm elsewhere sufficiently approximate maximum diversity in all Recent assemblages. Diversity values based on counts from the >150 µm fraction significantly underestimate maximum diversity in the polar and surprisingly also in the tropical provinces. Although the new methodology changes the shape of the diversity/sea-surface temperature (SST) relationship, its strength appears unaffected. Our analysis reveals that increasing diversity in planktonic foraminiferal assemblages is coupled with a progressive addition of larger species that have distinct, offset shell-size distributions. Thus, the previously documented increase in overall assemblage shell size-range towards lower latitudes is linked to an expanding shell-size disparity between species from the same locality. This observation supports the idea that diversity and shell size-range disparity in foraminiferal assemblages are the result of niche separation. Increasing SST leads to enhanced surface water stratification and results in vertical niche separation, which permits ecological specialisation. Specific deviations from the overall diversity and shell-size disparity latitudinal pattern are seen in regions of surface-water instability, indicating that coupled shell-size and diversity measurements could be used to reconstruct water column structures of past oceans.

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Excavations were carried out in a Late Palaeolithic site in the community of Bad Buchau-Kappel between 2003 and 2007. Archaeological investigations covered a total of more than 200 m**2. This site is the product of what likely were multiple occupations that occurred during the Late Glacial on the Federsee shore in this location. The site is situated on a mineral ridge that projected into the former Late Glacial lake Federsee. This beach ridge consists of deposits of fine to coarse gravel and sand and was surrounded by open water, except for a connection to the solid shore on the south. A lagoon lay between the hook-shaped ridge and the shore of the Federsee. This exposed location provided optimal access to the water of the lake. In addition, the small lagoon may have served as a natural harbor for landing boats or canoes. Sedimentological and palynological investigations document the dynamic history of the location between 14,500 and 11,600 years before present (cal BP). Evidence of the deposition of sands, gravels and muds since the Bølling Interstadial is provided by stratigraphic and palynological analyses. The major occupation occurred in the second half of the Younger Dryas period. Most of the finds were located on or in the sediments of the ridge; fewer finds occurred in the surrounding mud, which was also deposited during the Younger Dryas. Direct dates on some bone fragments, however, demonstrate that intermittent sporadic occupations also took place during the two millennia of the Meiendorf, Bølling, and Allerød Interstadials. These bones were reworked during the Younger Dryas and redeposited in the mud. A 14C date from one bone of 11,600 years ago (cal BP) places the Late Palaeolithic occupation of the ridge at the very end of the Younger Dryas, which is in agreement with stratigraphic observations. Stone artifacts, numbering 3,281, comprise the majority of finds from the site. These include typical artifacts of the Late Palaeolithic, such as backed points, short scrapers, and small burins. There are no bipointes or Malaurie-Points, which is in accord with the absolute date of the occupation. A majority of the artifacts are made from a brown chert that is obtainable a few kilometers north of the site in sediments of the Graupensandrinne. Other raw materials include red and green radiolarite that occur in the fluvioglacial gravels of Oberschwaben, as well as quartzite and lydite. The only non-local material present is a few artifacts of tabular chert from the region near Kelheim in Bavaria. A unique find consists of two fragments of a double-barbed harpoon made of red deer antler, which was found in the Younger Dryas mud. It is likely, but not certain, that this find belongs to the same assemblage as the numerous stone artifacts. Although not numerous, animal bones were also found in the excavations. Most of them lay in sediments of the Younger Dryas, but several 14C dates place some of these bones in earlier periods, including the Meiendorf, Bølling, and Allerød Interstadials. These bones were reworked by water and redeposited in mud sediments during the Younger Dryas. As a result, it is difficult to attribute individual bones to particular chronological positions without exact dates. Species that could be identified include wild horse (Equus spec.), moose or elk (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus), aurochs or bison (Bos spec.), wild boar (Sus scrofa), as well as birds and fish, including pike (Esox Lucius).

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To assess the regional effects of glaciation on sedimentation in the Atlantic Ocean we compare sediment types, distributions, and rates between Recent (core top) and last glacial maximum (LGM: ~18,000 years B.P.) stratigraphic levels. Based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than Recent. During both the Recent and LGM, carbonate content shows an east/west asymmetry with western basins exhibiting lower carbonate values. Input of ice-rafted detritus into the North Atlantic during LGM time interrupts this topographic control on carbonate distribution considerably farther south than at present; in the South Atlantic this effect is minor. Comparison of LGM and Recent sediment distributions indicates that the LGM seafloor was dominated by biogenic oozes, calcareous clays, and clays, while the Recent is dominated by biogenic oozes and marls. Coarse-grained detritus is much more prevalent in LGM sediments, derived not only from glacial input but also from fluvial and aeolian sources. Sedimentation rates, calculated from LGM to Recent sediment thickness in cores, are <4 cm/1000 yr for most of the ocean. Higher rates are typical of the continental margin off the Amazon River, the North American Basin, and a small region off west equatorial Africa.

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Modeling studies predict that changes in radiocarbon (14C) reservoir ages of surface waters during the last deglacial episode will reflect changes in both atmospheric 14C concentration and ocean circulation including the Atlantic Meridional Overturning Circulation. Tests of these models require the availability of accurate 14C reservoir ages in well-dated late Quaternary time series. We here test two models using plateau-tuned 14C time series in multiple well-placed sediment core age-depth sequences throughout the lower latitudes of the Atlantic Ocean. 14C age plateau tuning in glacial and deglacial sequences provides accurate calendar year ages that differ by as much as 500-2500 years from those based on assumed global reservoir ages around 400 years. This study demonstrates increases in local Atlantic surface reservoir ages of up to 1000 years during the Last Glacial Maximum, ages that reflect stronger trades off Benguela and summer winds off southern Brazil. By contrast, surface water reservoir ages remained close to zero in the Cariaco Basin in the southern Caribbean due to lagoon-style isolation and persistently strong atmospheric CO2 exchange. Later, during the early deglacial (16 ka) reservoir ages decreased to a minimum of 170-420 14C years throughout the South Atlantic, likely in response to the rapid rise in atmospheric pCO2 and Antarctic temperatures occurring then. Changes in magnitude and geographic distribution of 14C reservoir ages of peak glacial and deglacial surface waters deviate from the results of Franke et al. (2008) but are generally consistent with those of the more advanced ocean circulation model of Butzin et al. (2012).

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We present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern North Atlantic and the South Atlantic between 87°N and 40°S, 35°E and 60°W including published Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) data. These species counts are linked to Levitus's [1982] modern water temperature data for the four caloric seasons, four depth ranges (0, 30, 50, and 75 m), and the combined means of those depth ranges. The relation between planktonic foraminiferal assemblages and sea surface temperature (SST) data is estimated using the newly developed SIMMAX technique, which is an acronym for a modern analog technique (MAT) with a similarity index, based on (1) the scalar product of the normalized faunal percentages and (2) a weighting procedure of the modern analog's SSTs according to the inverse geographical distances of the most similar samples. Compared to the classical CLIMAP transfer technique and conventional MAT techniques, SIMMAX provides a more confident reconstruction of paleo-SSTs (correlation coefficient is 0.994 for the caloric winter and 0.993 for caloric summer). The standard deviation of the residuals is 0.90°C for caloric winter and 0.96°C for caloric summer at 0-m water depth. The SST estimates reach optimum stability (standard deviation of the residuals is 0.88°C) at the average 0- to 75-m water depth. Our extensive database provides SST estimates over a range of -1.4 to 27.2°C for caloric winter and 0.4 to 28.6°C for caloric summer, allowing SST estimates which are especially valuable for the high-latitude Atlantic during glacial times.

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The exponential growth of studies on the biological response to ocean acidification over the last few decades has generated a large amount of data. To facilitate data comparison, a data compilation hosted at the data publisher PANGAEA was initiated in 2008 and is updated on a regular basis (doi:10.1594/PANGAEA.149999). By January 2015, a total of 581 data sets (over 4 000 000 data points) from 539 papers had been archived. Here we present the developments of this data compilation five years since its first description by Nisumaa et al. (2010). Most of study sites from which data archived are still in the Northern Hemisphere and the number of archived data from studies from the Southern Hemisphere and polar oceans are still relatively low. Data from 60 studies that investigated the response of a mix of organisms or natural communities were all added after 2010, indicating a welcomed shift from the study of individual organisms to communities and ecosystems. The initial imbalance of considerably more data archived on calcification and primary production than on other processes has improved. There is also a clear tendency towards more data archived from multifactorial studies after 2010. For easier and more effective access to ocean acidification data, the ocean acidification community is strongly encouraged to contribute to the data archiving effort, and help develop standard vocabularies describing the variables and define best practices for archiving ocean acidification data.

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This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

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The South America southern coast exhibits many outcrops with abundant shell beds, from the Pleistocene through the Recent. How much biological information is preserved within these shell beds? Or, what is the actual probability a living community has to leave a fossil record corresponding to these shell deposits? Although ecological and biogeographical aspects might had been pointed, considering these temporal scales, up to the moment there is no taphonomically-oriented studies available. Quantitative comparisons between living (LAs), death (DAs) and fossil assemblages (FAs) are important not only in strictly taphonomic studies, but have grown a leading tool for conservation paleobiology analysis. Comparing LAs, DAs and FAs from estuaries and lagoons in the Rio Grande do Sul Coastal Plain makes possible to quantitatively understand the nature and quantity of biological information preserved in fossil associations in Holocene lagoon facies. As already noted by several authors, spatial scale parts the analysis, but we detected that the FAs refl ects live ones, rather than dead ones, as previously not realized. The results herein obtained illustrates that species present in DA are not as good preserved in recent (Holocene) fossil record as originally thought. Strictly lagoon species are most prone to leave fossil record. The authors consider that the fi delity pattern here observed for estuarine mollusks to be driven by (i) high temporal and spatial variability in the LAs, (ii) spatial mixing in the DA and (iii) differential preservation of shells, due to long residence times in the taphonomically active zone.

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Seismic and multibeam data, as well as sediment samples were acquired in the South Malé Atoll in the Maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits. Multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15-20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea-level lowstand. Such depocenters are located in current-protected areas flanking the reef rim of the atoll or in infillings of karst dolinas. Much of the 50 m deep sea floor in the lagoon interior is current swept, and has no or very minor sediment cover. Erosive current moats line drowned patch reefs, whereas other areas are characterized by nondeposition. Karst sink holes, blue holes and karst valleys occur throughout the lagoon, from its rim to its center. Lagoonal sediments are mostly carbonate rubble and coarse-grained carbonate sands with frequent large benthic foraminifers, Halimeda flakes, red algal nodules, mollusks, bioclasts, and intraclasts, some of them glauconitic, as well as very minor ooids. Finer-grained deposits locally are deposited in current-protected areas behind elongated faros, i.e., small atolls which are part of the rim of South Malé Atoll. The South Malé Atoll is a current-flushed atoll, where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim. With an elevated reef rim and tower-like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record.

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A selective chemical photosynthesis inhibitor, DCMU (Dichorophenyl-dimethylurea), dissolved in DMSO (Dimethyl sulfoxide) was substituted for the dark incubation method commonly used to measure the oxygen consumption in metabolic and primary production studies. We compared oxygen fluxes during light incubations with DCMU and dark incubations procedure, on soft bottom benthos. For this purpose, we studied the effects of different DCMU concentrations. A concentration of 5 · 10-5 mol l-1 inside a clear incubation enclosure completely inhibits photosynthesis without affecting the metabolism of soft bottom benthos.