Stable H and O isotope-based investigation of moisture sources and their role in river and groundwater recharge in the NE Carpathian Mountains, East-Central Europe

ABSTRACT The region situated between the mountain area and the lowlands in NE Romania (East-Central Europe) is experiencing increased competition for water resources triggered by a growing population, intensification of agriculture, and industrial development. To better understand hydrological cycling processes in the region, a study was conducted using stable isotopes of water and atmospheric trajectory data to characterize regional precipitation and vapour sources derived from the Atlantic Ocean, Mediterranean and Black Seas, as well as recycled continental moisture, and to assess and partition these contributions to recharge of surface and groundwater. Atmospheric moisture in the lowlands is found to be predominantly delivered along easterly trajectories, while mountainous areas appear to be dominated by North Atlantic Ocean sources, with moisture transported along mid-latitude, westerly storm tracks. Large-scale circulation patterns affect moisture delivery, the North Atlantic Oscillation being particularly influential in winter and the East Atlantic pattern in summer. Winter precipitation is the main contributor to river discharge and aquifer recharge. As winter precipitation amounts are projected to decrease over the next decades, and water abstraction is expected to steadily increase, a general reduction in water availability is projected for the region

Atmospheric blocking induced by the strengthened Siberian High led to drying in west Asia during the 4.2\,ka\,BP event — a hypothesis

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

Stable oxygen isotopes in Romanian oak tree rings record summer droughts and associated large-scale circulation patterns over Europe

We present the first annual oxygen isotope record (1900 – 2016) from the latewood (LW) cellulose of oak trees (Quercus robur) from NW Romania. As expected, the results correlate negatively with summer relative humidity, sunshine duration and precipitation and positively with summer maximum temperature. Spatial correlation analysis reveals a clear signal reflecting drought conditions at a European scale. Interannual variability is influenced by large-scale atmospheric circulation and by surface temperatures in the North Atlantic Ocean and the Mediterranean Sea. There is considerable potential to produce long and well-replicated oak tree ring stable isotope chronologies in Romania which would allow reconstructions of both regional drought and large-scale circulation variability over southern and central Europe

Ice in Caves

Perennial ice in caves is a relatively uncommon occurrence in caves, resulting from the combination of peculiar cave morphology and local climatic conditions. It exists in various forms, ranging from delicate ice crystals, various types of stalagmites and stalactites, to underground glaciers, tens of meters thick and thousands of years old. The later are especially of great scientific importance, as they hold invaluable informations on past climatic and environmental changes. In this chapter, we briefly touch upon various aspects related to the presence of ice in caves, highlighting the recent advances in their scientific knowledge

Recognition and interpretation of paleosols sequences in a floodplain from the low tableland of Transylvania Depression, Romania

Palaeosols reflect quite accurately the paleogeographic conditions in which they formed and evolved. Many studies were focused on this target in different settings (lakes, loess plateaus and plains, floodplains and archaeological sites).Here we present the palaeosols sequences in the floodplain of Partoț River, situated in the low tableland of Transylvania Depression. The observations were performed on three cores, one located at ca. 1 km downstream  from theȘtiucilorLake(profile no. 3) and the other two at 1 km (profile no. 1), respectively 4 km (profile no. 2), upstream from the lake.The thickness of floodplain sediments is ca. 12 m upstream from Stiucilor Lake, and ca. 6 m downstream from this lake. In the bottom are present cobbles and pebbles, covered by 1-2 m thick sequence of fine and medium sands, followed by 5 to 10 m thick fine silty – clayey materials. The alluvial and lacustrine sediments suggest that the vertical aggradation was the main process on the surface of this floodplain.The maximum age of fine silty-clayie sediments, indicate that this sedimentary sequence starts in Bolling – Allerod interstadial. A very low sedimentation rate characterised the first part of the sequence, as only ca. 1 m of materials seams to be accumulated between Bolling – Allerod interstadial and Mid Holocene.After ca. 6000 yrs BP, when Stiucilor Lake has formed, the sedimentation rate increased dramatically, both  upstream and downstream from it. Upstream from the lake, the tickness of lacustrine/alluvial materials is ca. 9 to 10 m, while downstream, the sedimentation rate was slighlty reduced, and the thickness of fluvial/torrential sediments are of ca. 5 m.</p

Kinetic Processes and Stable Isotopes in Cave Dripwaters as Indicators of Winter Severity

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

Tectonic, climatic and autogenic controls on the Late Quaternary evolution of the Somes fluvial fan, North-East Pannonian Basin, Central Europe

The Somes fluvial fan is located in the NW extremity of the Great Hungarian Plain (Pannonian Basin). It was formed by the left-side tributaries of the Tisa River (a tributary of the Danube) as they developed westward, following the avulsion of the main Tisa channel. Drainage reorganisation after the avulsion has occurred via a complex interplay between tectonic, climatic and autogenic controls over the past similar to 50-30 ka. In this study, we discuss the role of these factors in the spatial and temporal dynamics of the fluvial system that constructed the Somes fluvial fan during the second half of the last glacial cycle, using a combination of cartographic, sedimentary, and chronological tools. Our data suggests that, within a general setting of subsidence, spatial and temporal variation in the rate of this subsidence between different tectonic blocks created four local base levels, while autogenic factors play only a secondary role. The modern drainage configuration results from spatial channel adjustments during the last ca. 3000 cal BP, related to the current subsidence centre located in the NW extremity of the Somes fluvial fan. Over the entire period analysed, the rivers draining across the fluvial fan predominantly meandered, except when the river switched to a braided pattern. This braided phase likely occurred before similar to 30-32 ka ago, apparently coeval with a similar short, braided phase that has been documented along the middle Tisa River. The braiding phase is coincident with intense deglaciation in the Somes catchment area and development of open forest vegetation at lower elevations. Climatic changes during and after the Last Glacial Maximum had a reduced impact on the style of fluvial flow, which returned to a meandering pattern. Ca. 5000 cal BP these changes impacted suspended sediment delivery to drainage networks resulting in the present-day channel dimensions, at least along their lower reaches (our study area). Our results highlight the lower sensitivity of rivers draining the Great Hungarian Plain to the Late Quaternary climate changes compared to the far more responsive rivers of Western European. This behaviour is, in our opinion, most likely due to the presence of glacial forest refugia in the catchment areas, which modulated the response of discharge and fluvial dynamics to climatic changes

The response of aquatic fauna to variable environmental conditions in Ghețarul de la Vârtop cave (Apuseni Natural Park, Romania)

Caves with permanent and temporary ice formations exists at mid-to-high northern latitudes, at elevations between 0 and >3000 meters above sea level. In such caves, rare and endemic species or glacial relicts strictly tied to cold microclimates habitat conditions have evolved and the negative temperatures have contributed significantly in shaping the structural pattern of both terrestrial and aquatic communities. Aquatic dwellers inhabiting ice caves are likely to show resistance and have special physiological adaptation to cope with constantly low air and water temperatures. Ghețarul de la Vârtop cave is a short (340 m) cave located in the Apuseni Natural Park (northwest Romania) that hosts temporary ice formations near its entrance. In 2021, we have initiated a study aiming to understand how low temperatures in the cave are shaping the structure of underground fauna, along a temperature gradient through the cave. The sampling design imply monthly monitoring of air temperature (hourly measurements using data loggers), water physical and chemical characteristics and the structure of aquatic fauna communities. In this paper we present preliminary data on the environmental conditions and aquatic invertebrate communities present in percolation water and associated gours from the cave. Aquatic fauna is represented by nematodes, oligochaetes and several crustacean species the majority stygobites, of which at least three are potentially new to science. The surprising presence of Acanthocyclops reductus, considered a Tertiary relict living in warm water raises discussions on its tolerance to highly variable temperatures but also on the colonisation history of the caves on a regional scale. Investigations of cave aquatic fauna in caves with permanent and temporary ice offer hints to understand the ecology of the fauna, and also to further assess the mechanisms involved in adaptations of species to cope with constantly low-water temperatures