1,721,113 research outputs found
Stable isotope composition of Littoridina australis from the coast of Buenos Aires Province, Argentina, during Holocene climatic fluctuations
No full textStable isotope (carbon and oxygen) analyses were performed on Littoridina australis shells collected from molluscan concentrations within Holocene littoral deposits along the Bonaerensian coastal area of Argentina (south-western Atlantic). Isotope data allow us to define two very different areas: the Samborombon Bay, where isotope composition of shells was mainly governed by mixing between marine and freshwater, and the Mar Chiquita lagoon, where the original brackish environment was dominated by evaporation of water that originated high isotope shell values. In both areas some isotope profiles show short and quite large oscillations in delta(18)O. Their origin may be tentatively explained as due to the changes in moisture regime that control freshwater supply. The results suggest that these deposits can represent natural archives potentially useful for palaeoclimate reconstruction
Stable isotopes of pedogenic carbonate from Somma-Vesuvius area, southern italy, over the last 18 ka: palaeoclimatic implications
No full textZanchetta G., Leone G., Fallick A.E., Oxygen isotope composition of living land snail shells: data from Italy
No full textMollusca stable isotope record of a core from Lake Frassino, northern Italy: hydrological and climatic changes during the last 14 ka
No full textA core retrieved from Lake Frassino (northern Italy) provided evidence of palaeohydrological change in this area during the last 14 ka. Lithological, malacological and, in particular, stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the Lateglacial and Holocene. Lateglacial conditions were drier than the Holocene, although a wetter period was inferred before c. 14 ka. According to the oxygen isotope composition of freshwater shells, the Holocene showed a clear bipartition. The first part, which lasted from _/9100 to 7000 yr BP, was drier and was followed by a rapid increase in humidity at _/7000_6800 yr BP. Between _/6800 and 5000 yr BP, there were wetter and more stable conditions, as indicated by smaller d18O oscillations of Pisidium and Valvata shells. From c. 5000 to 2600 yr BP the record is characterized by larger fluctuations, which may indicate that short-term and particularly pronounced alternation of wet and dry periods occurred
Oxygen isotope composition of living land snail shells: data from Italy
No full textSixty-seven shells of living land snails were selected from 31 different localities across Italy to investigate the relationships between their oxygen isotopic composition (δ18Os) and the mean value of local rainfall (δ18Op). Despite the difficulty for some localities to correctly estimate the oxygen isotopic composition of local rainfall, a good relationship was found. This indicates that the oxygen isotopic composition of environmental water used by the snails is, in Italy, strictly related to that of the local meteoric precipitation. However, the relationship found is substantially different from that previous established for central Europe, indicating that regional climatic conditions are important in defining the final isotopic composition of land snail shells. Moreover, these equations may not hold for different climatic conditions existing during, for instance, glacial and interglacial periods. The data also show that isotopic differences among species are relatively narrow and that they may depend on ecological factors (i.e., style of life) rather than any clearly identifiable different vital offset
Stable isotope composition of Late Glacial land snail shells from Grotto del Romito (Southern Italy): Palaeoclimatic implications
No full textStable isotope composition of living and fossil land snail shells was determined at Grotta del Romito (Southern Italy) with the aim to reconstruct environmental and climatic variation in the area during Late Upper Palaeolithic. The investigated succession comprised 15 different excavated layers spanning between ca 13,000 and 14,500 yr cal BP. The oxygen isotope composition of snail shells indicates a marked decrease at the layer D8 suggesting a climatic deterioration consistent with the GI 1d climatic event (Older Dryas). This climate deterioration may have been related to a substantial decrease of mean annual temperature with associated changes in the regional atmospheric circulation. However, the environmental conditions at the time of shell's growth in the other intervals sampled suggest condition comparable to the present day. The carbon isotope composition of fossil snail shells is in agreement with other records, which indicate a general increase of the δ13C values of organic matter during Pleniglacial to Late Glacial caused by substantially lower atmospheric CO2 concentration at that time
Intra-Tyrrhenian cooling event deduced by non-marine mollusc assemblage at Villa S. Giorgio (Livorno, Italy)
No full textThis paper deals with an interesting non-marine mollusc assemblage found in a sandy-mud deposit comprised between two calcarenitic layers linked to marine environment and correlated with oxygen isotope stage (OIS) 5e and 5c. The ecological and environmental characteristics of the recovered species suggest a woodland environment with abundant open areas and local marshy areas subject to frequent drying up. The presence of species quite characteristic of mountainous areas suggest conditions cooler than today. Stable isotope analyses performed on some well-preserved shells suggest a mean annual temperature of about 1°C lower than the present in the study area. According to these features, the non-marine mollusc assemblage is correlated with OIS 5d
Stable isotopes reveal Holocene changes in the diet of Adélie penguins in Northern Victoria Land (Ross Sea, Antarctica)
No full textAdélie penguin (Pygoscelis adeliae) modern and fossil eggshells and guano samples collected from ornithogenic soils in Terra Nova Bay (Victoria Land, Ross Sea) were processed for carbon and nitrogen isotopic ratios with the aim of detecting past penguin dietary changes. A detailed and greatly expanded Adélie penguin dietary record dated back to 7,200 years BP has been reconstructed for the investigated area. Our data indicate a signiWcant dietary shift between Wsh and krill, with a gradual decrease from past to present time in the proportion of Wsh compared to krill in Adélie penguin diet. From 7,200 to 2,000 years BP, delta13C and delta15N values indicate Wsh as the most eaten prey. The dietary contribution of lower-trophic prey in penguin diet started becoming evident not earlier than 2,000 years BP, when the 13C values reveal a change in the penguin feeding behavior. Modern eggshell and guano samples reveal a major dietary contribution of krill but not a krill-dominated diet, since 13C values remain much too high if krill prevail in the diet. According to the Holocene environmental background attested for Victoria Land, Adélie penguin dietary shifts between Wsh and krill seem to reflect penguin paleoecological responses to diVerent paleoenvironmental settings with diVerent conditions of sea-ice extension and persistence. Furthermore, Adélie penguin diet appears to be particularly aVected by environmental changes in a very specific period within the breeding season, namely the egg-laying period when penguin dietary and feeding habit shifts are clearly documented by the delta 13C of eggshell carbonate
Adelie Penguin dietary remains reveal Holocene environmental changes in the western Ross Sea (Antarctica)
No full textCarbon and nitrogen stable isotope analyses were performed on modern and Holocene Adélie penguin guano samples collected from ornithogenic soils along the Scott Coast (Southern Victoria Land, Antarctica), from Cape Irizar to Dunlop Island, and at Cape Bird (Ross Island). Guano samples also were sieved and sorted under stereomicroscope in order to select penguin dietary remains, such as fish bones and otoliths. Carbon and nitrogen stable
isotope composition, coupled with the taxonomic identification of fish otoliths from Scott Coast Holocene samples, indicated a mainly fish-based diet for this area, with Pleuragramma antarcticum as the most eaten prey throughout the investigated period (from 390 cal BP to ca 7300 cal BP). The isotopic values of Ross Island samples (from modern to 3850 cal BP) showed a krill consumption increase in the samples younger than 2000 cal BP, with the maximum in modern samples. Scott Coast and Ross Island Holocene samples showed δ 13 C and δ15N trends similar to those previously published from Terra Nova Bay(northern Victoria Land), whereas modern samples from Ross Island have similar δ15N composition but different δ13 C values. This δ 13C divergence started at ca 2000 BP and follows the abandonment of the Scott Coast colonies. The δ 13 C trend observed in Ross Island and Terra Nova Bay samples and the abandonment of the Scott Coast colonies could suggest the stability and the persistence of the previous oceanographic conditions (i.e. polynya) for the Terra Nova Bay area and the establishment of new conditions for water circulation in the Southern Ross Sea since ~2000 BP when persistent sea-ice sealed the Scott Coast
Stalagmite evidence for the precise timing of North Atlantic cold events during the early last glacial
No full textEvidence of millennial-scale cold events following the last interglacial
are well preserved in North Atlantic marine cores, Greenland
ice, and pollen records from Europe. However, their timing was previously
undetermined by radiometric dating. We report the fi rst precise
radiometric ages for two such events, C23 (105.1 ± 0.9 ka to 102.6 ±
0.8 ka) and C24 (112.0 ± 0.8 ka and 108.8 ± 1.0 ka), based on stable
carbon and oxygen isotope measurements on a stalagmite from Italy
(CC28). In addition to providing new information on the duration of
these events in southern Europe, the age data provide invaluable tuning
points for the Mélisey I (C24) and Montaigu (C23) pollen zones
identifi ed in western Europe. The former event is of particular signifi -
cance because it represents the end of the Eemian interglacial forest
phase in western Europe. The new age data will also allow fi ne tuning
of the timing and duration of Greenland stadial 24 (equivalent to
C23) in the North Greenland Ice Core Project ice core and, via a common
gas-age chronology, tuning of the Vostok and EPICA (European
Project for Ice Coring in Antarctica) ice cores
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