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181.
Maurice Tucker 《Geology Today》2020,36(4):156-160
Viruses are very much in the news these days, unfortunately, but what about their geological history? Are viruses preserved in the fossil record? If so, how does that happen, and how far back do they go? And what about the roles of viruses in the environment? Are they significant or were they just the nasty invisible parasites we regard them to be today, disrupting life as we know it and leading to the very sad and untimely death of 1000s of people? Or were they both—good and bad? This article explores some of these issues. 相似文献
182.
Crayfish produce small button‐like gastroliths in their stomachs. These curious calcitic objects are increasingly common in lakes and streams in the UK and Europe as the invasive American crayfish increase their domination of freshwater environments. These stomach stones are also present in the geological record. 相似文献
183.
Franck Lartaud Laurent Emmanuel Marc de Rafelis Stephane Pouvreau Maurice Renard 《Geo-Marine Letters》2010,30(1):23-34
Compared to oxygen isotopes, the carbon isotope composition of biogenic carbonates is less commonly used as proxy for palaeoenvironmental
reconstructions because shell δ13C is derived from both dissolved inorganic (seawater) and organic carbon sources (food), and interactions between these two
pools make it difficult to unambiguously identify any independent effect of either. The main purpose of this study was to
demonstrate any direct impact of variable food supply on bivalve shell δ13C signatures, using low/high rations of a 13C-light mixed algal diet fed to 14-month-old (adult) cultured Japanese Crassostrea gigas under otherwise essentially identical in vitro conditions during 3 summer months (May, June and July 2003, seawater temperature
means at 16, 18 and 20 °C respectively) in experimental tanks at the Argenton laboratory along the Brittany Atlantic coast
of France. At a daily ration of 12% (versus 4%) oyster dry weight, the newly grown part of the shells (hinge region) showed
significantly lower δ13C values, by 3.5‰ (high ration: mean of −5.8 ± 1.1‰, n = 10; low ration: mean of −2.3 ± 0.7‰, n = 6; ANOVA Scheffe’s test, p < 0.0001). This can be explained by an enhanced metabolic activity at higher food supply, raising 13C-depleted respiratory CO2 in the extrapallial cavity. Based on these δ13C values and data extracted from the literature, and assuming no carbon isotope fractionation between food and shell, the
proportion of shell metabolic carbon would be 26 ± 7 and 5 ± 5% for the high- and low-ration C. gigas shells respectively; with carbon isotope fractionation (arguably more realistic), the corresponding values would be 69 ± 14
and 24 ± 9%. Both groups of cultured shells exhibited lower δ13C values than did wild oysters from Marennes-Ol éron Bay in the study region, which is not inconsistent with an independent
influence of diet type. Although there was no significant difference between the two food regimes in terms of δ18O shell values (means of 0.1 ± 0.3 and 0.4 ± 0.2‰ at high and low rations respectively, non-significant Scheffe’s test),
a positive δ13C vs. δ18O relationship recorded at high rations supports the interpretation of a progressive temperature-mediated rise in metabolic
activity fuelled by higher food supply (in this case reflecting increased energy investment in reproduction), in terms not
only of δ13C (metabolic signal) but also of δ18O (seawater temperature signal). Overall, whole-shell δ18O trends faithfully recorded summer/winter variations in seawater temperature experienced by the 17-month-old cultured oysters. 相似文献
184.
Porter Hoagland Stace Beaulieu Maurice A. Tivey Roderick G. Eggert Christopher German Lyle Glowka Jian Lin 《Marine Policy》2010
The potential emergence of an ocean mining industry to exploit seafloor massive sulfides could present opportunities for oceanographic science to facilitate seafloor mineral development in ways that lessen environmental harms. 相似文献
185.
A new, inexpensive and easy-to-handle box corer (47 × 47 × 114 cm3) is described. It is found to be extremely handy when operated from ships equipped with piston coring devices. The box corer uses the same piston core-head (~1000 kg) and the same trigger mechanism as used in piston coring. The whole operation is similar to that of piston coring. At three sites in the nodule-rich abyssal-hill province in the northwest Atlantic, the vertical distributions of the manganese nodules were obtained from the box cores. More than 75% of the nodules by weight is present in the top 10 cm of the sediment; 16–24% is present in the 10–20 cm interval and about 1% in the 20–30 cm interval. Very few nodules are found below 30 cm. 相似文献
186.
187.
Typical abyssal tholeiites occur on both north and south walls of the Puerto Rico Trench. Probably they were erupted in the Mid-Atlantic Ridge in Cretaceous time and afterwards were moved to the present position. In addition, doleritic basalts containing phenocrysts of pigeonite rimmed by augite were found from the north wall, and these rocks presumably represent a new type of abyssal tholeiites characterized by ratios lower than those of ordinary abyssal tholeiites.A new analysis of serpentinite from the north wall is also recorded here. 相似文献
188.
Werner L Kutsch Lutz Merbold Waldemar Ziegler Mukufute M Mukelabai Maurice Muchinda Olaf Kolle Robert J Scholes 《Carbon balance and management》2011,6(1):5
Background
This study evaluates the carbon dioxide and other greenhouse gas fluxes to the atmosphere resulting from charcoal production in Zambia. It combines new biomass and flux data from a study, that was conducted in a miombo woodland within the Kataba Forest Reserve in the Western Province of Zambia, with data from other studies. 相似文献189.
Maurice PARDÉ 《水文科学杂志》2013,58(1):38-51
Abstract Hydrological modelling has faced the problem of ungauged basins for many years: how does one estimate hydrological characteristics for a river for which there are no data? Whatever the kind of model, it needs at least hydroclimatic input data and discharge data for calibration. However, the Yates model does not need any discharge data for calibration: it is a pre-calibrated model from a vegetation—climate classification map. In the specific context of West and Central Africa, where data are often of poor quality and very scarce, it is interesting to compare the performance of such a model with those of calibrated models, and with observed data. For this study, a platform including different semi-global rainfall—runoff models which allow the estimation of monthly runoff at a spatial resolution of 0.5° × 0.5° was used. The performance of the Yates model is very close to those of calibrated models, so that one can say that this simple model, based simply on a vegetation—climate classification, can be a very useful prediction tool in regions of scarce and unreliable data, such as those of interest to the International Association of Hydrological Sciences (IAHS) initiative on prediction in ungauged basins (PUB). Therefore, this model was applied to a period covering the last 30 years, and to a data set covering the first decades of the 21st century, from a climatic scenario of doubling the CO2 concentration in the atmosphere. The results show that, in West Africa, where drought conditions have now prevailed for 35 years, water resources should still be decreasing in the future, following the general decreasing trend of rainfall projected by the climatic scenarios. 相似文献
190.