Sensitivity of the last glacial inception to initial and surface conditions     

Claudia Kubatzki  Martin Claussen  Reinhard Calov  Andrey Ganopolski 《Climate Dynamics》2006,27(4):333-344

We investigate the sensitivity of simulations of the last glacial inception (LGI) with respect to initial (size of the Greenland ice sheet) and surface (state of ocean/vegetation) conditions and two different CO₂ reconstructions. Utilizing the CLIMBER-2 Earth system model, we obtain the following results: (a) ice-sheet expansion in North America at the end of the Eemian can be reduced or even completely suppressed when pre-industrial or Eemian ocean/vegetation is prescribed. (b) A warmer surrounding ocean and, in particular, a large Laurentide ice sheet reduce the size of the Greenland ice sheet before and during the LGI. (c) A changing ocean contributes much stronger to the expansion of the Laurentide ice sheet when we apply the CO₂ reconstruction according to Barnola et al. (Nature 329:408–414, 1987) instead of Petit et al. (Nature 399:429–436, 1999). (d) In the fully coupled model, the CO₂ reconstruction used has only a small impact on the simulated ice sheets but it does impact the course of the climatic variables. (e) For the Greenland ice sheet, two equilibrium states exist under the insolation and CO₂ forcing at 128,000 years before present (128 kyear BP); the one with an ice sheet reduced by about one quarter as compared to its simulated pre-industrial size and the other with nearly no inland ice in Greenland. (f) Even the extreme assumption of no ice sheet in Greenland at the beginning of our transient simulations does not alter the simulated expansion of northern hemispheric ice sheets at the LGI.  相似文献   

Estuaries of the past and present: A biofacies perspective     

Claudia Schrder-Adams 《Sedimentary Geology》2006,190(1-4):289-298

Estuaries are complex sedimentary and ecological systems, where controlling factors are variable largely depending on wave vs. tidal dominance and fluvial processes. Paleoenvironmental reconstruction of their ancient counterparts in the form of coastal valley deposits in the subsurface or outcrop requires a multidisciplinary approach. Microfossils can play an integral part in identifying estuarine subenvironments. Foraminifera can be abundant in modern estuaries and resemble characteristics of brackish ichnofaunal communities in featuring low species diversity, but high abundances of opportunistic species, different feeding strategies and common infaunal species. Whereas sediment distribution is highly controlled by energy regimes, foraminifera seem to respond to salinities and tidal exposure. Whereas individual taxa can widely range bathymetrically, the combination of certain taxa becomes diagnostic for estuarine environments. Fossil marginal marine assemblages are dominated by agglutinated species due to taphonomic loss of the calcareous component that is often dominant in modern estuaries. When comparisons between fossil and modern assemblages are undertaken it is advisable to compare with Recent subsurface or remnant assemblages for a more accurate basis of paleoenvironmental interpretation. More integrated research with detailed taphonomic observations is needed on ancient coastal valley deposits to find the paleoecological requirements of extinct taxa and their link to sedimentary facies and ichnofacies.  相似文献   

Reference conditions of German stream types analysed and revised with macroinvertebrate fauna   总被引：2，自引：0，他引：2  

Claudia Rawer-Jost  Armin Zenker  Jürgen Bhmer 《Limnologica》2004,34(4):390-397

This study investigates reference conditions of German stream types using the top-down stream typology developed by Pottgiesser & Sommerhäuser (2004) and 264 macrozoobenthos samples selected as representing reference status. With the aid of discriminant and correlation analyses, the use of typological parameters is investigated as regards their relevancy and the study aims to show whether the metrics used in the newly developed type-specific indices (Böhmer et al. 2004b) reflect the reference conditions. The data cover 15 of the 24 German stream types. The use of stream size, of ecoregions as an indirect parameter for geographical altitude, and of the bottom substrate for the lowland stream types as typological factors can be confirmed, as can six stream types as separate and independent. As bottom substrate is an essential factor for the lowland stream types, their independency is at least probable. For the stream types of the lower mountain regions, a separation of siliceous and calcareous types seems not to be crucial for the bioassessment on metric level, while a new approach for and a possible splitting of the small streams in floodplains is recommended.  相似文献   

Pelagic trophic transfer efficiency in an oligotrophic, dimictic deep lake (Lake Stechlin, Germany) and its relation to fisheries yield     

Michael Schulz  Rainer Koschel  Claudia Reese  Thomas Mehner 《Limnologica》2004,34(3):264-273

We investigated trophic transfer efficiency in the pelagic food chain of deep, oligotrophic Lake Stechlin (Germany) by analyses of the primary, secondary, and fish production. Primary production between April and November 2000 was estimated at 78 g C m⁻², pelagic secondary production at 14 g C m⁻², and production of the main planktivorous fish species [European cisco, Coregonus albula (L.)] at 0.77 g C m⁻². Thus, trophic transfer efficiency between primary and pelagic secondary production was around 18%, whereas between pelagic and fish production around 6%. The high efficiency at the first step of the chain is discussed to be due to the high food quality in oligotrophic lakes due to the dominance of Bacillariophyceae and Chlorophyceae rich in essential fatty acids. In turn, the relatively low trophic transfer efficiency between the secondary and the fish production is mainly explained by the avoidance of calanoid copepods as food source by the ciscoes. Concerning the trophic transfer efficiency, results from this study support the general assumption of a 10% transfer between neighbouring trophic levels within ecosystems.  相似文献   

Ages of Detrital Zircon from Siliciclastic Successions South of the São Francisco Craton, Brazil: Implications for the Evolution of Proterozoic Basins     

Claudia Sayo Valladares  Nuno Machado  Monica Heilbron  Gilles Gauthier 《Gondwana Research》2004,7(4):913-921

In this work we report ²⁰⁷Pb/²⁰⁶Pb LA-ICPMS ages of 152 detrital zircons from lower greenschist facies quartzites from Proterozoic basin successions of the southern border of the São Francisco Craton, southern Minas Gerais State, Brazil. These are the intracratonic São João del Rei basin, the intraplate continental margin Andrelândia basin, and the Serra do Ouro Grosso sequence, developed on a crystalline basement older than 1.8 Ga, and deformed and metamorphosed during the Brasiliano Orogeny, ca. 0.59–0.50 Ga. The data constrain both the ages of the sources and the interval of sedimentation. The detrital zircons of the Serra do Ouro Grosso sequence were derived predominantly from the erosion of a Neoarchean crust, 2.5–2.8 Ga old, with only one grain showing a Paleoproterozoic age (2, 245±83 Ma) older than the Transamazonian event. Zircons extracted from a shelf quartzite of the lowermost sequence of the São João del Rei basin indicate derivation from the 1.8–2.2 Ga Transamazonian crust, with subordinate contribution from the 2.5–2.9 Ga Archean crust. The 1, 809±41 Ma age is interpreted as the maximum limit for sedimentation in this basin. The results confirm the regional correlation with the Espinhaço Rift successions. The zircons extracted from an autochthonous quartzite of the Andrelândia sequence yielded ages in the 1.0–2.2 Ga range, with a modal class at 1.2–1.3 Ga. Only two of the forty analyzed zircons yield Archean ages. The youngest zircon yields 1, 086±85 Ma. The zircons from the allochthonous quartzite yield ages between 1.0–2.7 Ga, with a modal class at 2.1–2.2 Ga. Only five of 45 analyzed grains yield Archean ages. The youngest zircon has an age of 1, 047±77 Ma. The results indicate that the detrital sediments deposited during the second marine flooding event of the Andrelândia sedimentation were mainly derived from the erosion of Mesoproterozoic and Paleoproterozic rocks. The 1, 047±77 Ma age is interpreted as the maximum depositional age for the described association.  相似文献   

Romanian industry in transition     

Claudia Popescu 《GeoJournal》1993,29(1):41-48

Restructuring of industry in Romania today is part of the transition from a centrally-planned to a free market economy. The paper deals with salient features of socialist industry and the trends which have occurred since 1989 in the context of greatly reduced state intervention. Current trends are identified as a key to further evolution in the future and some international comparisons are attempted now that industrial enterprises in all parts of Europe are developing new relationships with capital, labour and the state.  相似文献   

The response of drainage basins to the late Quaternary tectonics in the Sicilian side of the Messina Strait (NE Sicily)     

Pierpaolo Guarnieri  Claudia Pirrotta 《Geomorphology》2008,95(3-4):260-273

Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (k_d) and critical shear stress (τ_c) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in k_d and τ_c from soil desiccation and freeze–thaw cycling. Soil erodibility and τ_c were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted k_d was 2.9 and 2.1 times higher (p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in k_d was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions (r² = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.  相似文献   

Morphologic resilience and depositional processes due to the rapid evolution of the submerged Sciara del Fuoco (Stromboli Island) after the December 2002 submarine slide and tsunami   总被引：1，自引：0，他引：1  

Francesco L. Chiocci  Claudia Romagnoli  Alessandro Bosman   《Geomorphology》2008,100(3-4):356-365

In order to monitor the Stromboli submarine slope after the 30 December 2002 landslide and tsunami, repeated marine surveys were carried out offshore of Sciara del Fuoco. The morphological changes and depositional processes that brought to the gradual filling of the slide scar have been studied in detail. Thirteen surveys in a period of little more than 4 years provided a unique opportunity to reconstruct the morpho-sedimentary evolution of the submarine slope and its recovery after the mass-wasting event. The scar has been progressively filled with lava and volcanoclastic debris; in the first month and a half, the filling rate was very high due to the entrance of lava flows into the sea and to the morphological readjustment of the slope; in the following months/years the rate dramatically decreased when the eruptive vents moved upwards and the eruption finally stopped. After 4 years (February 2007) more than 40% of the scar was already filled. In early 2007, a new eruption occurred and a lava delta was constructed in the 2002 scar, influencing the natural readjustment of the slope; therefore, our reconstruction only encompasses the period between the 2002 and 2007 eruptions.The swath bathymetry reconstruction of geometry and volume of scar filling during the period 2002–2007 evidenced a punctuated and fast shift of depocenters and debris emplacement through avalanching processes. This process quickly obliterated the features produced by the 2002 tsunamigenic landslide so that a major question about the preservation potential of mass-wasting features on active volcanic flanks emerges.  相似文献   

Hydrocarbons in sediments of a chronically contaminated bay: the challenge of source assignment   总被引：2，自引：0，他引：2  

Wagener Ade L  Meniconi Mde F  Hamacher C  Farias CO  da Silva GC  Gabardo IT  Scofield Ade L 《Marine pollution bulletin》2012,64(2):284-294

Aliphatic hydrocarbons and 39 PAH (parental and alkylated homologs) determined in ca. 100 sediment samples from the Guanabara Bay, Rio de Janeiro, were evaluated for source discrimination using new approaches. Concentrations of total PAH were in the range of 96-135,000 μg kg(-1) similar to other coastal urbanized embayment. Traditional diagnostic ratios were not as efficient PAH source indicators, e.g. biomass combustion was assigned as the major source of the pyrolytic PAH although the hydrographic basin is highly industrialized and urbanized. It is proved petrogenic imprint cannot be detected if only the 16 USEPA PAH are determined. The high production in the eutrophic system is not apparent in the aliphatic fraction dominated by land derived n-alkanes due to the effectiveness of microbial degradation. The present work demonstrates the complexity of hydrocarbon forensics when applied to chronically contaminated environments.  相似文献   

The effect of differences between rainfall measurement techniques on groundwater and discharge simulations in a lowland catchment          下载免费PDF全文

Claudia C. Brauer  Aart Overeem  Hidde Leijnse  Remko Uijlenhoet 《水文研究》2016,30(21):3885-3900

Several rainfall measurement techniques are available for hydrological applications, each with its own spatial and temporal resolution and errors. When using these rainfall datasets as input for hydrological models, their errors and uncertainties propagate through the hydrological system. The aim of this study is to investigate the effect of differences between rainfall measurement techniques on groundwater and discharge simulations in a lowland catchment, the 6.5‐km² Hupsel Brook experimental catchment. We used five distinct rainfall data sources: two automatic raingauges (one in the catchment and another one 30 km away), operational (real‐time and unadjusted) and gauge‐adjusted ground‐based C‐band weather radar datasets and finally a novel source of rainfall information for hydrological purposes, namely, microwave link data from a cellular telecommunication network. We used these data as input for the, a recently developed rainfall‐runoff model for lowland catchments, and intercompared the five simulated discharges time series and groundwater time series for a heavy rainfall event and a full year. Three types of rainfall errors were found to play an important role in the hydrological simulations, namely: (1) Biases, found in the unadjusted radar dataset, are amplified when propagated through the hydrological system; (2) Timing errors, found in the nearest automatic raingauge outside the catchment, are attenuated when propagated through the hydrological system; (3) Seasonally varying errors, found in the microwave link data, affect the dynamics of the simulated catchment water balance. We conclude that the hydrological potential of novel rainfall observation techniques should be assessed over a long period, preferably a full year or longer, rather than on an event basis, as is often done. Copyright © 2016 The Authors. Hydrological Processes. Published by John Wiley & Sons Ltd.  相似文献