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1.
Siberian river run-off and Late Quaternary glaciation in the southern Kara Sea, Arctic Ocean: preliminary results 总被引:3,自引:0,他引:3
Ruediger Stein Frank Niessen Klaus Dittmers Michael Levitan Frank Schoster Johannes Simstich Tatjana Steinke Oleg V. Stepanets 《Polar research》2002,21(2):315-322
The extent of the Barents-Kara Ice Sheet during the eastern Last Glacial Maximum (LGM) is not yet fully known. A detailed echo-sounding survey performed during the Boris Petrov Expedition 2001 permitted the detailed mapping of part of it. Based on the profiling results, a southern connection between the LGM Barents-Kara Ice Sheet and a local ice sheet on Taymyr Peninsula appears to be unlikely. Based on sediment core data and profiling results, most of the terrigenous river-derived material accumulated in the estuaries during late Holocene times, whereas during early Holocene times of lowered sea level major amounts were transported further offshore and accumulated on the shelf. During the post-glacial sea level rise, the main depocentre migrated southward, reaching its present position no earlier than about 6 cal. Ky BP (or 5.2 Kya). Future studies of accelerator mass spectrometry (AMS) 14 C-dated sediment cores will allow a detailed reconstruction of the variability of fluvial sediment discharge and the history of glaciation in the Kara Sea during late Quaternary times. 相似文献
2.
The response in floodplain respiration of an alpine river to experimental inundation under different temperature regimes
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Tatjana Simčič Nataša Mori Christian Hossli Christopher T. Robinson Michael Doering 《水文研究》2015,29(26):5438-5450
The respiratory potential [i.e. electron transport system activity (ETSA)] of soils and sediments from five floodplain habitats (channel, gravel, islands, riparian forest and grassland) of the Urbach River, Switzerland, and actual respiration rate (R) of the same samples exposed to experimental inundation were measured. Measurements were carried out at three incubation temperatures (4°C, 12°C and 20°C), and ETSA/R ratios (i.e. exploitation of the overall metabolic capacity) were investigated to better understand the effects of temperature and inundation on floodplain functional heterogeneity. Furthermore, ETSA/R ratios obtained during experimental inundation were compared with ETSA/R ratios from field measurements to investigate the exploitation in total metabolic potential at different conditions. Lowest ETSA and R were measured in samples from channel and gravel habitats, followed by those from islands. Substantially higher values were measured in soils from riparian forest and grassland. Both ETSA and R increased with increasing temperature in samples from all habitats, while the ETSA/R ratio decreased because of a rapid response in microbial community respiration to higher temperatures. The metabolic capacity exploitation (i.e. ETSA/R) during experimental inundation was lowest in predominantly terrestrial samples (riparian forest and grassland), indicating the weakest response to wetted conditions. Comparison of experimentally inundated and field conditions revealed that in rarely flooded soils, the metabolic capacity was less exploited during inundation than during non‐flooded conditions. The results suggest high sensitivity in floodplain respiration to changes in temperature and hydrological regime. ETSA/R ratios are considered good indicators of changes in metabolic activity of floodplain soils and sediments, and thus useful to estimate the impact of changes in hydrological regime or to evaluate success of floodplain restoration actions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
The purpose of this work was to study jointly the volcanic-hydrothermal system of the high-risk volcano La Soufrière, in
the southern part of Basse-Terre, and the geothermal area of Bouillante, on its western coast, to derive an all-embracing
and coherent conceptual geochemical model that provides the necessary basis for adequate volcanic surveillance and further
geothermal exploration. The active andesitic dome of La Soufrière has erupted eight times since 1660, most recently in 1976–1977.
All these historic eruptions have been phreatic. High-salinity, Na–Cl geothermal liquids circulate in the Bouillante geothermal
reservoir, at temperatures close to 250 °C. These Na–Cl solutions rise toward the surface, undergo boiling and mixing with
groundwater and/or seawater, and feed most Na–Cl thermal springs in the central Bouillante area. The Na–Cl thermal springs
are surrounded by Na–HCO3 thermal springs and by the Na–Cl thermal spring of Anse à la Barque (a groundwater slightly mixed with seawater), which are
all heated through conductive transfer. The two main fumarolic fields of La Soufrière area discharge vapors formed through
boiling of hydrothermal aqueous solutions at temperatures of 190–215 °C below the "Ty" fault area and close to 260 °C below
the dome summit. The boiling liquid producing the vapors of the Ty fault area has δD and δ18O values relatively similar to those of the Na–Cl liquids of the Bouillante geothermal reservoir, whereas the liquid originating
the vapors of the summit fumaroles is strongly enriched in 18O, due to input of magmatic fluids from below. This process is also responsible for the paucity of CH4 in the fumaroles. The thermal features around La Soufrière dome include: (a) Ca–SO4 springs, produced through absorption of hydrothermal vapors in shallow groundwaters; (b) conductively heated, Ca–Na–HCO3 springs; and (c) two Ca–Na–Cl springs produced through mixing of shallow Ca–SO4 waters and deep Na–Cl hydrothermal liquids. The geographical distribution of the different thermal features of La Soufrière
area indicates the presence of: (a) a central zone dominated by the ascent of steam, which either discharges at the surface
in the fumarolic fields or is absorbed in shallow groundwaters; and (b) an outer zone, where the shallow groundwaters are
heated through conduction or addition of Na–Cl liquids coming from hydrothermal aquifer(s).
Received: 9 November 1998 / Accepted: 15 July 1999 相似文献
4.
Application of SWACI products as ionospheric correction for single-point positioning: a comparative study 总被引:1,自引:0,他引:1
In Global Navigation Satellite Systems (GNSS) using L-band frequencies, the ionosphere causes signal delays that correspond with link related range errors of up to 100 m. In a first order approximation the range error is proportional to the total electron content (TEC) of the ionosphere. Whereas this first order range error can be corrected in dual-frequency measurements by a linear combination of carrier phase- or code-ranges of both frequencies, single-frequency users need additional information to mitigate the ionospheric error. This information can be provided by TEC maps deduced from corresponding GNSS measurements or by ionospheric models. In this paper we discuss and compare different ionospheric correction methods for single-frequency users. The focus is on the comparison of the positioning quality using dual-frequency measurements, the Klobuchar model, the NeQuick model, the IGS TEC maps, the Neustrelitz TEC Model (NTCM-GL) and the reconstructed NTCM-GL TEC maps both provided via the ionosphere data service SWACI (http://swaciweb.dlr.de) in near real-time. For that purpose, data from different locations covering several days in 2011 and 2012 are investigated, including periods of quiet and disturbed ionospheric conditions. In applying the NTCM-GL based corrections instead of the Klobuchar model, positioning accuracy improvements up to several meters have been found for the European region in dependence on the ionospheric conditions. Further in mid- and low-latitudes the NTCM-GL model provides results comparable to NeQuick during the considered time periods. Moreover, in regions with a dense GNSS ground station network the reconstructed NTCM-GL TEC maps are partly at the same level as the final IGS TEC maps. 相似文献
5.
In the western part of the city of Zagreb, Croatia, hydrogeochemical and isotopic investigations of the Samobor aquifer were
carried out with the aim of determining the differences in hydrogeochemical characteristics at increasing aquifer depths.
The aquifer comprises 40-m thick gravelly–sandy deposits, with lenses and interlayers of silt and clay. The analyses have
proven that with increasing aquifer depth, there are decreases in groundwater temperature and the values of electrical conductivity
and increases in the sodium, iron and manganese concentrations. The δ13C distribution shows an evident increase in biogenic carbon concentrations with increasing aquifer depth. The measured specific
14C activities showed that the deeper part of the aquifer is characterized by slow water exchange, while the shallower part
is influenced by current recharge, although the pumping wells located on the well-field downstream penetrate the aquifer fully.
A direct exchange of water from the Sava River and groundwater occurs in the near vicinity of the river. This exchange weakens
further away, while the difference in hydrogeochemical characteristics between the Sava River water and groundwater increases. 相似文献
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Clar Christoph Löschner Lukas Nordbeck Ralf Fischer Tatjana Thaler Thomas 《Natural Hazards》2021,105(2):1765-1796
Natural Hazards - This contribution explores the conceptual and empirical linkages between population dynamics and natural hazard risk management (NHRM). Following a review of the international... 相似文献
9.
Population structure and conservation status of the red gorgonian Paramuricea clavata (Risso, 1826) in the Eastern Adriatic Sea
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Silvija Kipson Cristina Linares Hrvoje Čižmek Emma Cebrián Enric Ballesteros Tatjana Bakran‐Petricioli Joaquim Garrabou 《Marine Ecology》2015,36(4):982-993
Gorgonians are important structuring species of the Mediterranean hard‐bottom communities that are threatened by disturbances such as increasing seawater temperature, mucilaginous events and destructive fishing, among others. In this study we assessed for the first time the population structure and conservation status of one of the most common gorgonians in the Eastern Adriatic Sea, the red gorgonian Paramuricea clavata. During late spring 2009, nine populations dwelling between 30 and 50 m depth were examined by SCUBA diving along 200 km of the Croatian coastline. The density ranged between 7 and 20 colonies·m?2. The mean and maximum colony heights were 31.2 ± 22.7 cm (±SD) and 138 cm, respectively. Two main patterns of P. clavata size frequency distributions were observed: the first one with a higher proportion of juveniles (~30%) observed mostly in the northernmost populations, and the second one with a higher proportion of larger colonies (>25% of colonies >40 cm in height). Regarding the disturbance impact level, the proportion of healthy colonies (with <10% of injured surface) was high in almost all of the studied populations (>60%) and the mean extent of injury (i.e. denuded axis or epibiosis) was 9.7 ± 4% (±SD), indicating low impacts. Contrasting population size structures with high recruitment in mature populations provides new insights into the demographic structure of the Mediterranean gorgonian forests dwelling in their upper bathymetric range (<50 m depth). Furthermore, these size structures and the low impact levels suggest a current favorable conservation status of the studied populations in the Eastern Adriatic Sea and provide a baseline for their monitoring in the future. 相似文献
10.
Tatjana?BrombachEmail author Stefano?Caliro Giovanni?Chiodini Jens?Fiebig Johannes?C.?Hunziker Brunella?Raco 《Bulletin of Volcanology》2003,65(7):505-516
The chemical and isotopic compositions (δDH2O, δ18OH2O, δ18OCO2, δ13CCO2, δ34S, and He/N2 and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ18O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H2–Ar, H2–N2, and H2–H2O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H2O–H2–CO2–CO–CH4 system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases. 相似文献