High concentrations of amorphous,biogenic Si (BSi) in the sediment of a small high-latitude lake: implications for biogeochemical Si cycling and for the use of BSi as a paleoproxy     

Petra Tallberg  Sophie Opfergelt  Jean-Thomas Cornelis  Anne Liljendahl  Jan Weckström 《Aquatic Sciences - Research Across Boundaries》2015,77(2):293-305

  相似文献   

Importance of Spatial Resolution in Global Groundwater Modeling     

Robert Reinecke  Alexander Wachholz  Steffen Mehl  Laura Foglia  Christoph Niemann  Petra Döll 《Ground water》2020,58(3):363-376

Global-scale gradient-based groundwater models are a new endeavor for hydrologists who wish to improve global hydrological models (GHMs). In particular, the integration of such groundwater models into GHMs improves the simulation of water flows between surface water and groundwater and of capillary rise and thus evapotranspiration. Currently, these models are not able to simulate water table depth adequately over the entire globe. Unsatisfactory model performance compared to well observations suggests that a higher spatial resolution is required to better represent the high spatial variability of land surface and groundwater elevations. In this study, we use New Zealand as a testbed and analyze the impacts of spatial resolution on the results of global groundwater models. Steady-state hydraulic heads simulated by two versions of the global groundwater model G³M, at spatial resolutions of 5 arc-minutes (9 km) and 30 arc-seconds (900 m), are compared with observations from the Canterbury region. The output of three other groundwater models with different spatial resolutions is analyzed as well. Considering the spatial distribution of residuals, general patterns of unsatisfactory model performance remain at the higher resolutions, suggesting that an increase in model resolution alone does not fix problems such as the systematic overestimation of hydraulic head. We conclude that (1) a new understanding of how low-resolution global groundwater models can be evaluated is required, and (2) merely increasing the spatial resolution of global-scale groundwater models will not improve the simulation of the global freshwater system.  相似文献   

In memoriam for Prof. Tadepalli (Tad) Murty (1937–2018)     

Van Steenbergen  Petra 《Natural Hazards》2019,96(2):551-552

  相似文献   

Morphostratigraphy and provenance of Plio‐Pleistocene terraces in the south‐eastern Alpine foreland: the Mislinja and Upper Savinja valleys,northern Slovenia     

Eva Mencin Gale  Petra Jam&#x;ek Rupnik  Mirka Trajanova  Milo&#x; Bavec  Flavio S. Anselmetti  Andrej &#x;muc 《第四纪科学杂志》2019,34(8):633-649

This study focuses on the Plio‐Pleistocene fluvial deposits preserved in the terrace staircases in the south‐eastern Alpine foreland of the Mislinja (MV) and Upper Savinja valleys (USV) in northern Slovenia. The area is located at the north‐eastern margin of the Adria microplate, where neotectonic activity is the prevailing driving force for the terrace formation. The aim of this study is to determine the morphostratigraphy and provenance of the Pliocene to Early Pleistocene gravels using geomorphic and clast lithological analysis. The established morphostratigraphic framework encompasses three terraces in the MV and five terraces in the USV. Due to the lack of age‐relevant data, the morphostratigraphy of the MV and USV is based on the results of geomorphic analysis, clast petrography and data from the literature. Low‐level, middle‐level and high‐level terrace groups were tentatively attributed to the Late and Middle Pleistocene, Early Pleistocene–Pliocene and Pliocene, and compared with the traditional Quaternary stratigraphy of the Alpine foreland. The results of the clast lithological analysis revealed major provenance areas. Moreover, the evolution of long‐term drainage from the Miocene onward was inferred, which suggests that the system reached conformity with the present‐day drainage pattern at the Miocene to Plio‐Pleistocene transition. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

Palaeolimnology of Lake Sapanca and identification of historic earthquake signals,Northern Anatolian Fault Zone (Turkey)     

Markus J. Schwab  Petra Werner  Peter Dulski  Edward McGee  Norbert R. Nowaczyk  Sébastien Bertrand  Suzanne A.G. Leroy 《Quaternary Science Reviews》2009,28(11-12):991-1005

Lake Sapanca is located on a strand of the Northern Anatolian Fault Zone (NAFZ, Turkey), where a series of strong earthquakes (Ms >6.0) have occurred over the past hundred years. Identifying prehistoric earthquakes in and around Lake Sapanca is key to a better understanding of plate movements along the NAFZ. This study contributes to the development of palaeolimnological tools to identify past earthquakes in Lake Sapanca. To this end several promising proxies were investigated, specifically lithology, magnetic susceptibility, grain size (thin-section and laser analysis), geochemistry, pollen concentration, diatom assemblages, ¹³⁷Cs and ²¹⁰Pb. Sedimentological indicators provided evidence for reworked, turbidite-like or homogeneous facies (event layers) in several short cores (<45 cm). Other indicators of sediment input and the historical chronicles available for the area suggest that three of these event layers likely originated from the AD 1957, 1967 and 1999 earthquakes. Recent changes in sediment deposition and nutrient levels have also been identified, but are probably not related to earthquakes. This study demonstrates that a combination of indicators can be used to recognize earthquake-related event layers in cores that encompass a longer period of time.  相似文献   

A 40 ka record of temperature and permafrost conditions in northwestern Europe from noble gases in the Ledo‐Paniselian Aquifer (Belgium)     

Petra Corinne Blaser  Rolf Kipfer  Heinz Hugo Loosli  Kristine Walraevens  Marc van Camp  Werner Aeschbach‐Hertig 《第四纪科学杂志》2010,25(6):1038-1044

The Ledo‐Paniselian Aquifer in Belgium offers unique opportunities to study periglacial groundwater recharge during the Last Glacial Maximum (LGM), as it was located close to the southern boundary of the ice sheets at that time. Groundwater residence times determined by ¹⁴C and ⁴He reveal a sequence of Holocene and Pleistocene groundwaters and a gap between about 14 and 21 ka, indicating permafrost conditions which inhibited groundwater recharge. In this paper, a dataset of noble gas measurements is used to study the climatic evolution of the region. The derived recharge temperatures indicate that soil temperatures in the periods just before and after the recharge gap were only slightly above freezing, supporting the hypothesis that permafrost caused the recharge gap. The inferred glacial cooling of 9.5°C is the largest found so far by the noble gas method. Yet, compared to other palaeoclimate reconstructions for the region, recharge temperatures deduced from noble gases for the cold periods tend to be rather high. Most likely, this is due to soil temperatures being several degrees higher than air temperatures during periods with extended snow cover. Thus the noble‐gas‐derived glacial cooling of 9.5°C is only a lower limit of the maximum cooling during the LGM. Some samples younger than the recharge gap are affected by degassing, possibly related to gas production during recharge in part of the recharge area, especially during times of melting permafrost. The findings of this study, such as the occurrence of a recharge gap and degassing related to permafrost and its melting, are significant for groundwater dynamics and geochemistry in periglacial areas. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Inland-coastal demographic transformations in a karst area:a case study of the surroundings of Krka National Park (Croatia)     

TELBISZ Tamás  RADELJAK KAUFMANN Petra  BOI Neven 《山地科学学报》2022,(2):305-321

According to geographic possibilism,environment does not determine socio-economic development.However,the environment sets certain constraints and limitations f...  相似文献   

Diurnal precipitation cycle in Austria     

Asma Yaqub  Petra Seibert  Herbert Formayer 《Theoretical and Applied Climatology》2011,103(1-2):109-118

A back-trajectory clustering method was developed to identify synoptic patterns associated with heavy precipitation in Austria. Extending this work from daily precipitation sums to accumulation intervals from 12 to 48 hours, an unexpected problem was encountered related to the observation schedule of data. To modify available data to our specific needs, evening precipitation falling between 19 and 21 LT (Local Time) was studied. Hourly precipitation data for the period of 1950 to 2005 from 132 weather stations over Austria were used. It was found that the evening precipitation fraction has its maxima in the central Alps in all seasons, except in autumn when maxima shift more towards the south of the Alps. These results encouraged us to analyse the variation of diurnal precipitation for different seasons in Austria as well. A total of 119 stations with sixteen years (1990?C2005) of data were used for this purpose. Mean hourly precipitation values were calculated, which were then normalised, smoothed and were finally clustered to find regions with homogeneous diurnal cycles. The diurnal cycles of precipitation of the centres exhibit systematic patterns and seasonal cycles, reflecting intensity and timing of convective activity over these regions. The winter season is relatively dry and summer is associated with the highest precipitation. The areas inside the Alps receive higher amplitudes of precipitation in summer. Interesting features such as bimodal distributions, nocturnal maxima and early morning maxima were also observed in many regions.  相似文献   

How a Sphagnum fuscum‐dominated bog changed into a calcareous fen: the unique Holocene history of a Slovak spring‐fed mire     

Petra Hájková  Ab Grootjans  Mariusz Lamentowicz  Eliška Rybníčková  Mikuláš Madaras  Věra Opravilová  Dierk Michaelis  Michal Hájek  Hans Joosten  Lesław Wołejko 《第四纪科学杂志》2012,27(3):233-243

In general, mires develop by autogenic succession from more groundwater‐fed to more rainwater‐fed. This study from a calcareous mire in the West Carpathians (Slovakia) describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, macrofossil and testate amoeba analyses show that the site started as a minerotrophic open fen woodland. After 10 700 cal a BP autogenic succession led to the accumulation of at least 1 m of Sphagnum fuscum peat. Around 9000 cal a BP, as climate could no longer sustain a stable water regime, the bog desiccated and a fire broke out. The fire removed part of the peat layer and as a consequence relative water levels rose, leading to the establishment of a wet minerotrophic swamp carr with Thelypteris palustris, Equisetum sp. and Alnus sp. with extremely slow peat accumulation. After 600 cal a BP, rapid peat accumulation with calcareous tufa formation resumed as a result of anthropogenic deforestation and hydrological changes in the catchment and resulting increased groundwater discharge. At present the mire still hosts a wealth of relict and endangered plant and animal species typical of calcareous fens and fen meadows. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Imaging the Mariánské Lázně Fault (Czech Republic) by 3-D ground-penetrating radar and electric resistivity tomography     

Tomá? Fischer  Petra ?těpan?íková  Magda Karousová  Petr Tábo?ík  Christina Flechsig  Mahmoud Gaballah 《Studia Geophysica et Geodaetica》2012,56(4):1019-1036

Geodynamic activity in the area of West Bohemia is typified by the occurrence of earthquake swarms, Quaternary volcanism and high flux of mantle-derived CO₂. The highest swarm activity occurs beneath the eastern edge of the Cheb basin, which is delineated by the NW-SE trending morphologically pronounced Mariánské Lázn?? Fault (MLF) controlling the formation of the basin. The previous trenching survey across the MLF zone has identified several fault strands with possible Quaternary activity. In this paper we present the results of the geophysical survey focused to trace the faults signatures in geophysical sections and to build an image of near surface tectonics. The method of electric resistivity tomography (ERT) along two profiles parallel to the trench identified a strong resistivity contrast between the bodies of sandy gravels in the middle and conductive clayey sands to the west and weathered crystalline basement to the east. The 2-D ground penetration radar (GPR) sections show direct correlation of reflections with lithological boundaries identified in the trench. As expected, the GPR signal amplitudes increase with the resistivities found in the ERT sections. Two of the four faults identified in the trench are indicated in the resistivity and GPR sections. A 3-D GPR measurement has identified a spot of high amplitudes elongated parallel to the MLF trend, which coincides with the high resistivity body. To improve the signal-to-noise ratio of the time slices we stacked the GPR time slices within vertically homogeneous blocks. This provided a contrast image of the sand-gravel body including its boundaries in three dimensions. The detailed analysis of the 3-D GPR cube revealed additional fault that limits the highly reflective sands and appears to be offset by another younger fault. Our results suggest a complex fault pattern in the studied area, which deserves a further study.  相似文献