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331.
Kristiina Ehapalu Ilmar Tõnno Triin Reitalu Tiiu Alliksaar Merlin Liiv Rene Freiberg Peeter Nõges 《Journal of Paleolimnology》2017,57(1):81-93
Carbon storage in lakes can have huge implications for the global carbon cycle, as lakes annually accumulate up to one half the amount of organic carbon buried in marine sediments. Yet little is known of the effect of recent climate change on carbon storage in lakes. We analyzed century-scale time series of climate variables (precipitation, temperature, NAO winter index) and profiles of sediment characteristics in a dated sediment core from shallow, eutrophic Lake Võrtsjärv, south Estonia. We used path analysis to evaluate the effect of climate conditions on phytoplankton biomass in the lake and accumulation of organic and inorganic carbon in the sediment. Changes in winter and spring climate influenced the lake’s phytoplankton growth significantly. Carbon pathways in hard-water Lake Võrtsjärv were influenced by both hydrological (most significant in colder periods) and biogeochemical processes. Increased nutrient and water input to Lake Võrtsjärv, anticipated with projected climate warming, favours greater in-lake productivity, larger accumulation of inorganic carbon in sediments, and an increase in organic carbon mineralisation, which fuels atmospheric greenhouse gas emissions from the lake. 相似文献
332.
Bijeesh Kozhikkodan Veettil Ulisses Franz Bremer Sergio Florêncio de Souza Éder Leandro Bayer Maier Jefferson Cardia Simões 《国际地球制图》2016,31(5):544-556
This research focuses on the recent variations in the annual snowline and the total glaciated area of the Nevado Coropuna in the Cordillera Ampato, Peru. Maximum snowline altitude towards the end of dry season is taken as a representative of the equilibrium line altitude of the year, which is an indirect measurement of the annual mass balance. We used Landsat and IRS LISS3 images during the last 30 years due to its better temporal coverage of the study site. It is found that there was a decrease of 26.92% of the glaciated area during 1986–2014. We calculated the anomalies in precipitation and temperature in this region and also tried to correlate the changes in glacier parameters with the combined influence of El Niño – Southern Oscillation (ENSO) and pacific decadal oscillation (PDO). It is concluded that the snowline of Nevado Coropuna has been fluctuated during ENSO, and maximum fluctuations were observed when ENSO and PDO were in phase. 相似文献
333.
334.
de Jesus Eduardo Marcos da Rocha Rosmeri Porfírio Crespo Natália Machado Reboita Michelle Simões Gozzo Luiz Felippe 《Climate Dynamics》2021,56(1-2):537-557
Climate Dynamics - In this study, multi-model ensembles are used to understand regional features of future climate trends of cyclones and associated winds in eastern South America. For this, we... 相似文献
335.
Anna K. Sim Kristina J. Thomsen Andrew S. Murray Geraldine Jacobsen Russell Drysdale Wayne Erskine 《Boreas: An International Journal of Quaternary Research》2014,43(1):1-21
Two fluvial sediment cores taken from a floodplain of the Hawkesbury‐Nepean River system in the Sydney region, eastern Australia are dated using Optically Stimulated Luminescence (OSL) to provide a reliable chronology essential for the management and planning of water resources. Nine charcoal 14C (AMS) dates constrain these OSL ages. Quartz extracted from seven OSL samples from each of the cores was measured using both single‐grain and multi‐grain OSL techniques. Three of the single‐grain natural dose distributions appear to be well bleached, but the others appear to be incompletely bleached to various degrees. Three minimum‐age models (MAM, MAMUL and IEU) are applied to the single‐grain dose distributions. We conclude that these models give consistent age estimates. For one of the cores it appears to be necessary to use a minimum‐age model to obtain accurate ages, but in the other core incomplete bleaching is probably less important than postdepositional mixing and mixing during sampling. As a result, the burial age is probably best estimated using the weighted average of the individual single‐grain dose estimates. The application of multi‐grain OSL techniques to these samples results in an average apparent age overestimation of ~200 years, which is significant for these samples, but negligible for sediments older than a few thousand years. The intention is that the chronology obtained in this study will be used in conjunction with a proxy flood record, derived from floodplain sediments, to gain an understanding of the long‐term variability in periods of high and low rainfall in eastern Australia. 相似文献
336.
Intra- and inter-specific variability in total and methylmercury bioaccumulation by eight marine fish species from the Azores 总被引:1,自引:1,他引:0
Magalhães MC Costa V Menezes GM Pinho MR Santos RS Monteiro LR 《Marine pollution bulletin》2007,54(10):1654-1662
We relate fish biological and ecological characteristics to total and organic mercury concentrations to determine whether accumulation is influenced by trophic level, Hg concentration in the diet, and vertical distribution. Levels of total mercury and methylmercury were determined in the muscle tissue of eight species of fish: Pagellus acarne, Trachurus picturatus, Phycis phycis, P. blennoides, Polyprion americanus, Conger conger, Lepidopus caudatus and Mora moro, caught in the Azores. All such fishes are commercially valuable and were selected to include species from a wide range of vertical distributions from epipelagic (<200 m) to mesopelagic (>300 m) environments. Methylmercury was the major form accumulated in all species, comprising an average of 88.1% of total mercury. Concentrations of mercury (total and methylmercury) increased with age, length and weight. Based on data from other studies, mercury concentrations in fish diet were estimated. Mercury levels in food ranged from 0.08 to 0.32 ppm, dry weight. Hg concentrations in the food and in muscle tissue from different species were positively correlated. Total Hg levels in the muscles were approximately nine times those estimated in food. Total mercury concentrations in muscle were positively correlated with both trophic level and median depth. Such enhanced mercury bioaccumulation in relation to depth appears to be determined primarily by concentrations in food and ultimately by water chemistry, which controls mercury speciation and uptake at the base of the food chain. 相似文献
337.
The scheme of recent fault tectonics and neotectonic stresses of the area adjacent to the Strel’tsovka Caldera in the southeastern
Transbaikal region has been compiled for the first time on the basis of structural and geomorphic study. The faults were ranked
by criteria of slip direction stability along separate segments and their expression in topography. Neotectonic stresses of
corresponding ranks were ascertained as well. The heterogeneity of neotectonic stress field is related to the mosaic development
of compression, extension, and the three-axial stress state. Comparison of morphogenetic features of recent and older faults
shows the different character of the deformation mechanism and orientation of tectonic displacements. It has been established
that the Strel’tsovka Caldera and its northwestern segment, in particular, developed as an echeloned system of pull-apart
grabens, but the caldera itself is situated in a recent rise, whereas the northwestern segment is located in a neotectonic
depression corresponding to the Dry Urulyungui Basin filled with volcanic and sedimentary rocks. Such a structure markedly
expands the outlook for discovery of hidden uranium mineralization in the studied area. The elaborated scheme of neotectonic
faults and stresses reflects the postore geodynamic setting and completes the reconstruction of geodynamic conditions pertaining
to the periods of preore preparation and ore-forming tectonomagmatic reactivation. 相似文献
338.
Presence of fluoroquinolones and sulfonamides in urban sewage sludge and their degradation as a result of composting 总被引:4,自引:4,他引:0
M. Lillenberg M.Sc. S. Yurchenko Ph.D. K. Kipper M.Sc. K. Herodes Ph.D. V. Pihl Ph.D. R. Lõhmus Ph.D. M. Ivask A. Kuu Ph.D. S. Kutti M.Sc. S. V. Litvin B.Sc. L. Nei 《International Journal of Environmental Science and Technology》2010,7(2):307-312
The concentrations of some widely used pharmaceuticals, namely fluoroquinolones (ciprofloxacin C17 H18FN3O3, norfloxacin C17 H18FN3O3 and ofloxacin C18 H20FN3O4 and sulfonamides (sulfadimethoxine C12 H14N4O4s and sulfamethoxazole C10 H11N3O3S were determined in urban sewage sludge utilized for making compost. The levels of degradation of these pharmaceuticals resulting from sludge treatment were assessed. The concentrations of the studied pharmaceuticals sufficiently varied both in sewage sludge and in compost and due to this phenomenon the possible danger resulting from the presence of pharmaceuticals in sewage sludge, used for composting, can not be ignored. The concentrations of the studied pharmaceuticals were lower in compost, if compared to the relevant concentrations in sewage sludge. The highest pharmaceutical concentration in sewage sludge — 426 μg/kg — was detected in the case of ciprofloxacin. The highest concentrations present in compost were 22 μg/kg of norfloxacin and 20 μg/kg of ciprofloxacin. Results show that before using the sewage sludge for making compost or before using the compost a fertilizer for food plants, they should be carefully tested against the content of commonly used pharmaceuticals. 相似文献
339.
S. Taubenberger S. Valenti S. Benetti E. Cappellaro M. Della Valle N. Elias-Rosa S. Hachinger W. Hillebrandt K. Maeda P. A. Mazzali A. Pastorello F. Patat S. A. Sim M. Turatto 《Monthly notices of the Royal Astronomical Society》2009,397(2):677-694
In order to assess qualitatively the ejecta geometry of stripped-envelope core-collapse supernovae (SNe), we investigate 98 late-time spectra of 39 objects, many of them previously unpublished. We perform a Gauss-fitting of the [O i ] λλ6300, 6364 feature in all spectra, with the position, full width at half maximum and intensity of the λ6300 Gaussian as free parameters, and the λ6364 Gaussian added appropriately to account for the doublet nature of the [O i ] feature. On the basis of the best-fitting parameters, the objects are organized into morphological classes, and we conclude that at least half of all Type Ib/c SNe must be aspherical. Bipolar jet models do not seem to be universally applicable, as we find too few symmetric double-peaked [O i ] profiles. In some objects, the [O i ] line exhibits a variety of shifted secondary peaks or shoulders, interpreted as blobs of matter ejected at high velocity and possibly accompanied by neutron-star kicks to assure momentum conservation. At phases earlier than ∼200 d, a systematic blueshift of the [O i ] λλ6300, 6364 line centroids can be discerned. Residual opacity provides the most convincing explanation of this phenomenon, photons emitted on the rear side of the SN being scattered or absorbed on their way through the ejecta. Once modified to account for the doublet nature of the oxygen feature, the profile of Mg i ] λ4571 at sufficiently late phases generally resembles that of [O i ] λλ6300, 6364 , suggesting negligible contamination from other lines and confirming that O and Mg are similarly distributed within the ejecta. 相似文献
340.
Study of the transfer from the Earth to a halo orbit around the equilibrium pointL
1 总被引:2,自引:0,他引:2
G. Gómez A. Jorba J. Masdemont C. Simó 《Celestial Mechanics and Dynamical Astronomy》1993,56(4):541-562
The purpose of this paper is to study a transfer strategy from the vicinity of the Earth to a halo orbit around the equilibrium pointL
1 of the Earth-Sun system. The study is done in the real solar system (we use the DE-118 JPL ephemeris in the simulations of motion) although some simplified models, such as the restricted three body problem (RTBP) and the bicircular problem, have been also used in order to clarify the geometrical aspects of the problem. The approach used in the paper makes use of the hyperbolic character of the halo orbits under consideration. The invariant stable manifold of these orbits enables the transfer to be achieved with, theoretically, only one manoeuvre: the one of insertion into the stable manifold. For the total v required, the figures obtained are similar to the ones given by the standard procedures of optimization. 相似文献