ALBERT

Description: Recently, a series of studies have targeted the stable isotopic composition of cave ice as a possible source of paleoclimatic information, but none presented an explanation for the way in which the external climatic signal is transferred to cave ice. While the relation between the stable isotopic composition of precipitation and drip water can be relatively easily determined, a more complex problem arises, i.e., the possible alteration of the primary climatic signal recorded by the oxygen and hydrogen stable isotopes during the freezing of water to form cave ice. Here we report the results of the first detailed investigations of the oxygen and hydrogen stable isotope behavior during the formation of ice in Scărişoara Ice Cave. Samples of ice align on a straight line with a slope lower than 8 in a δ18O-δ2H plot, characteristic for ice formed by the freezing of water. A model is presented for the reconstruction of the initial isotopic composition of water, despite the complexity induced by kinetic effects during early stages of freezing. These results are consistent with ice that forms by the downward freezing of a stagnant pool of water, under kinetic conditions in the initial stages of the process, and isotopic equilibrium thereafter. As ice caves are described in many parts of the world, otherwise poorly represented in ice-based paleoclimatology, the results of this study could open a new direction in paleoclimatic research so that an array of significant paleoclimate data can be developed on the basis of their study.

Description: In this paper the spatial and temporal responses of Someşu Mic River (Romania) to natural and anthropogenic controls over the past 150 years, are analyzed, based on a series of morphometric parameters extracted from five successive sets of topographic maps and one set of orthophotos. Prior to the intensive hydrotechnical interventions of the last four decades, the river was characterised by a complex alternation of different channel types, resulting in a mixture of alluvial and mixed sinuous - meandering - sinuous anabranched - meandering anabranched reaches, each a few hundred meters to a few kilometres long. The main cause for this spatial behavior was the local geology. Its effects were intensified by a larger scale slope slightly higher than along a longitudinal profile with normal concavity, as a consequence of the presence of a 400 m elevation knick-point located in the catchment's area. Channel metamorphosis by canalisation, diminishing / elimination of overflows and medium scale avulsions by changes in flow regimes (dams) and the presence of dykes in the floodplain perimeter, channel narrowing (43%) and incision (at least after 1945) downstream from dams, along, and probably because of in-channel gravel mining, are the main anthropically induced changes along Someşu Mic River. Even if human impact is important, both at the drainage basin scale and along Someşu Mic River, it has only local impacts, subordinated to climate. The low level of human impact on this river could be the consequence of the higher general slope downstream from 400 m elevation knick-point, which probably forces the positioning of its effects under an important internal threshold of the fluvial system. This boundary condition defines Someşu Mic River as an atypical river. Also, the study supports the idea that climate has an important role in the post-LIA rivers' behavior. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We examine how the stable isotope composition of meteoric water is transmitted through soil and epikarst to dripwaters in a cave in western Romania. δ2H and δ18O in precipitation at this site are influenced by temperature and moisture sources (Atlantic and Mediterranean), with lower δ18O in winter and higher in summer. The stable isotope composition of cave dripwaters mimics this seasonal pattern of low and high δ18O, but the onset and end of freezing conditions in the winter season are marked by sharp transitions in the isotopic signature of cave dripwaters of approximately 1 ‰. We interpret these shifts as the result of kinetic isotopic fractionation during the transition phase from water to ice at the onset of freezing conditions and the input of meltwater to the cave at the beginning of the spring season. This process is captured in dripwaters and therefore speleothems from Urșilor Cave, which grew under such dripping points, may have the potential to record past changes in the severity of winters. Similar isotopic changes in dripwaters driven by freeze–thaw processes can affect other caves in areas with winter snow cover, and cave monitoring during such changes is essential in linking the isotopic variability in dripwaters and speleothems to surface climate. © 2018 The Authors Hydrological Processes Published by John Wiley & Sons Ltd

Description: Stable water isotopes were applied to trace hydrological processes in an undisturbed (mature spruce forest) and a nearby disturbed (deforested from a bark beetle outbreak) lake catchments in the Czech Republic. Both catchments are situated above 1,000 m a.s.l. within the Šumava National Park and have similar environmental conditions. The isotopic compositions of precipitation, creeks, springs, and lakes were sampled at 3-week intervals over one hydrological year. Water inputs to catchments were derived from isotopically similar local precipitation, whereas run-off was found to have different isotopic signatures. Creeks in the undisturbed catchment had ~1‰ and ~7‰ higher δ18O and δ2H with ~2‰ lower d-excess than in the disturbed catchment. The d-excess in creeks of the undisturbed catchment was more pronounced, particularly during snowmelt, and highly heterogeneous as compared with the disturbed catchment. Creeks in the undisturbed catchment were mainly fed by precipitation during the warm period (May–October), whereas creeks in the disturbed catchment were mostly fed by precipitation during the cold period (November–April). Estimated mean transit times of creeks and springs were ~6 months, except for two creeks in the undisturbed catchment, which had residence times of ~1 year. Although evaporation and transpiration fluxes were apparently reduced in the disturbed catchment, transpiration ratios were similar for both catchments. The difference in isotope signatures between catchments was attributed to the altered role of the forest canopy in temporal water distribution, which produced changes in the water cycle, potentially influencing important biogeochemical processes. © 2018 John Wiley & Sons, Ltd.

Description: The climate of east-central Europe (ECE) is the result of a combination of influences originating in the wider North Atlantic realm, the Mediterranean Sea, and the western Asian and Siberian regions. Previous studies have shown that the complex interplay between the large-scale atmospheric patterns across the region results in strongly dissimilar summer and winter conditions on timescales ranging from decades to millennia. To put these into a wider context, long-term climate reconstructions are required, but, largely due to historical reasons, these are lacking in ECE. We address these issues by presenting a high-resolution, radiocarbon-dated record of summer temperature variations during the last millennium in ECE, based on stable isotope analysis of a 4.84 m long ice core extracted from Focul Viu Ice Cave (Western Carpathians, Romania). Comparisons with both instrumental and proxy-based data indicate that the stable isotope composition of cave ice records the changes in summer air temperature and has a similar temporal evolution to that of the Atlantic Multidecadal Oscillation on decadal to multidecadal timescales, suggesting that changes in the North Atlantic are transferred, likely via atmospheric processes towards the wider Northern Hemisphere. On centennial timescales, the data show little summer temperature differences between the Medieval Warm Period (MWP) and the Little Ice Age (LIA) in eastern Europe. These findings are contrary to those that show a marked contrast between the two periods in terms of both winter and annual air temperatures, suggesting that cooling during the LIA was primarily the result of wintertime climatic changes.

Description: Glaciers worldwide are shrinking at an accelerated rate as the climate changes in response to anthropogenic influence. While increasing air temperature is the main factor behind glacier mass and volume loss, variable patterns of precipitation distribution also play a role, though these are not as well understood. Furthermore, while the response of surface glaciers (from large polar ice sheets to small alpine glaciers) to climatic changes is well documented and continuously monitored, little to nothing is known about how cave glaciers (perennial ice accumulations in rock-hosted caves) react to atmospheric warming. In this context, we present here the response of cave and surface glaciers in SE Europe to the extreme precipitation events occurring between May and July 2019 in SE Europe. Surface glaciers in the northern Balkan Peninsula lost between 17 % and 19 % of their total area, while cave glaciers in Croatia, Greece, Romania and Slovenia lost ice at levels higher than any recorded by instrumental observations during the past decades. The melting was likely the result of large amounts of warm water delivered directly to the surface of the glaciers, leading to rapid reduction in the area of surface glaciers and the thickness of cave glaciers. As climate models predict that such extreme precipitation events are set to increase in frequency and intensity, the presence of cave glaciers in SE Europe and the paleoclimatic information they host may be lost in the near future. Moreover, the same projected continuous warming and increase in precipitation extremes could pose an additional threat to the alpine glaciers in southern Europe, resulting in faster-than-predicted melting.

Description: Causal explanations for the 4.2 ka BP event are based on the amalgamation of seasonal and annual records of climate variability that was manifest across global regions dominated by different climatic regimes. However, instrumental and paleoclimate data indicate that seasonal climate variability is not always sequential in some regions. The present study investigates the spatial manifestation of the 4.2 ka BP event during the boreal winter season in Eurasia, where climate variability is a function of the spatiotemporal dynamics of the westerly winds. We present a multi-proxy reconstruction of winter climate conditions in Europe, west Asia, and northern Africa between 4.3 and 3.8 ka. Our results show that, while winter temperatures were cold throughout the region, precipitation amounts had a heterogeneous distribution, with regionally significant low values in W Asia, SE Europe, and N Europe and local high values in the N Balkan Peninsula, the Carpathian Mountains, and E and NE Europe. Further, strong northerly winds were dominating in the Middle East and E and NE Europe. Analyzing the relationships between these climatic conditions, we hypothesize that in the extratropical Northern Hemisphere, the 4.2 ka BP event was caused by the strengthening and expansion of the Siberian High, which effectively blocked the moisture-carrying westerlies from reaching W Asia and enhanced outbreaks of cold and dry winds in that region. The behavior of the winter and summer monsoons suggests that when parts of Asia and Europe were experiencing winter droughts, SE Asia was experiencing similar summer droughts, resulting from failed and/or reduced monsoons. Thus, while in the extratropical regions of Eurasia the 4.2 ka BP event was a century-scale winter phenomenon, in the monsoon-dominated regions it may have been a feature of summer climate conditions.