8 resultados para C-12

em Publishing Network for Geoscientific


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The diabases cut across the ophiolites as parallel and variably thick dyke-swarms. Geochemistry of the diabases reveals three distinct groups, including a) supra-subduction zone (SSZ) type, which is characterized by marked Nb-anomaly and normal mid-ocean ridge basalt (N-MORB) like HFSE distribution, b) enriched MORB (E-MORB) type, showing some degree of enrichment relative to N-MORB, c) oceanic-island basalt (OIB) type with characteristic hump-backed trace element patterns, coupled with fractionated REE distribution.

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In the current context of environmental change, ocean acidification is predicted to affect the cellular processes, physiology and behaviour of all marine organisms, impacting survival, growth and reproduction. In relation to thermal tolerance limits, the effects of elevated pCO2 could be expected to be more pronounced at the upper limits of the thermal tolerance window. Our study focused on Crepidula fornicata, an invasive gastropod which colonized shallow waters around European coasts during the 20th century. We investigated the effects of 10 weeks' exposure to current (380 µatm) and elevated (550, 750, 1,000 µatm) pCO2 on this engineer species using an acute temperature increase (1 °C/12 h) as the test. Respiration rates were measured on both males (small individuals) and females (large individuals). Mortality increased suddenly from 34 °C, particularly in females. Respiration rate in C. fornicata increased linearly with temperature between 18 and 34 °C, but no differences were detected between the different pCO2 conditions either in the regressions between respiration rate and temperature or in Q10 values. In the same way, condition indices were similar in all the pCO2 treatments at the end of the experiment, but decreased from the beginning of the experiment. This species was highly resistant to acute exposure to high temperature regardless of pCO2 levels, even though food was limited during the experiment. Crepidula fornicata appears to have either developed resistance mechanisms or a strong phenotypic plasticity to deal with fluctuations of physicochemical parameters in its habitat. This suggests that invasive species may be more resistant to future environmental changes than its native competitors.

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The Climatological Database for the World's Oceans: 1750-1854 (CLIWOC) project, which concluded in 2004, abstracted more than 280,000 daily weather observations from ships' logbooks from British, Dutch, French, and Spanish naval vessels engaged in imperial business in the eighteenth and nineteenth centuries. These data, now compiled into a database, provide valuable information for the reconstruction of oceanic wind field patterns for this key period that precedes the time in which anthropogenic influences on climate became evident. These reconstructions, in turn, provide evidence for such phenomena as the El Niño-Southern Oscillation and the North Atlantic Oscillation. Of equal importance is the finding that the CLIWOC database the first coordinated attempt to harness the scientific potential of this resource represents less than 10 percent of the volume of data currently known to reside in this important but hitherto neglected source.

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A 100 cm long sediment sequence was recovered from Beaver Lake in Amery Oasis, East Antarctica, using gravity and piston corers. Sedimentological and mineralogical analyses and the absence of micro and macrofossils indicate that the sediments at the base of the sequence formed under glacial conditions, probably prior to c. 12 500 cal. yr BP. The sediments between c. 81 and 31 cm depth probably formed under subaerial conditions, indicating that isostatic uplift since deglaciation has been substantially less than eustatic sea-level rise and that large areas of the present-day floor of Beaver Lake must have been subaerially exposed following deglaciation. The upper 31 cm of the sediment sequence were deposited under glaciomarine conditions similar to those of today, supporting geomorphic observations that the Holocene was a period of relative sea-level highstand in Amery Oasis.