Periglacial Lake Research Articles

The changes in the composition of Cladocera community in bottom sediments of Lake Maloye Shibrozero (Zaonezhsky Peninsula) as a consequence of shifts of environmental and climatic conditions

The study aims to explore the evolution of lakes of the boreal zone during the late- and postglacial time on the south-eastern periphery of the Fennoscandian crystalline shield since the last deglaciation. In order to reconstruct the past for virgin territories of the Zaonezhsky Peninsula current investigation on bottom sediments of Lake Maloye Shibrozero was conducted. Analyzes were performed using the new paleoindicator – subfossil remains of Cladocera (Cladocera, Branchiopoda). The 28 samples of bottom sediments were analyzed. It has been determined that discovered Cladocera remains belong to representatives of 6 families and 38 taxa. Species inhabiting Palaearctic zone are predominant in lake deposits; most of the identified subfossil remains are related to the pelagic species inhabiting the open part of the lake. According to the Lubarsky scale the dominant of Cladocera community is Bosmina (Eubosmina) cf. longispina. Secondary taxa are Chydorus sphaericus, Bosmina coregoni, Alonella nana, Alona guadrangularis, A. affinis, Chydorus gibbus. At a depth of 650-653 cm, a partial replacement of Bosmina (Eubosmina) cf. longispina by Bosmina coregoni takes place with a simultaneous increase in the significance of Chydorus sphaericus, which is used to be an indicator of eutrophication and increasing trophic status of the reservoir. Changes in Cladocera community could be attributed to decreasing the level of periglacial lake, as a result of which the Lake Maloye Shibrozero became a small isolated lake with the trend to trophic status increasing. Cold-water species were replaced by thermophilic ones with a further return to a cold-water fauna. In the upper layers of the column an increase of the number of phytophilous species is noted.

THE STUDY OF LAKE ONEGO AND ITS DRAINAGE BASIN PALEOGEOGRAPHY USING A SET OF METHODS

The authors own and literary data on long-term paleogeographical research of Lake Onego and its drainage basin carried out using a set of methods are summarized in the article. The deglaciation, transgressive-regressive activity of Lake Onego, time and features of the formation of small lakes, their water level regime and the transition of some of them to a telmatic development pathway are discussed. According to available data, deglaciation of the study area began at ~ 13000–14000 BP. The deglaciation of the lake was completed at 11600 BP and that of the modern catchment at the end of the Allerod. The water level of the newly formed periglacial Lake Onego was variable. As the level was decreasing starting from around 12300 BP, small and medium-sized paleolakes became separated and isolated in depressions. There also formed lakes produced by stagnant ice melting (from the Allerod to the end of the Boreal Period) and lakes in areas not flooded by periglacial waters. The formation of organic sediments in the lakes is shown to have commenced at ~ 10300 BP. Peat accumulation in shallow depressions also began in Preboreal time and that in the near-shore zone of the investigated paleolakes in Boreal time. Most of them were filled with peat by the end of the Sub-Boreal period. Vegetation dynamics was reconstructed from the Middle Dryas (DR 2 , ~12000 BP) to the present as related to changes in the environment, including the paleoclimate and hydrology of the territory, and taking into account the geomorphology of the territory and human impact. It was established that the composition and dynamics of vegetation in the Late Glacial and Holocene were controlled by climatic factors, while their distinctive characteristics by geologo-geomorphological factors. Plants were dispersing as the territory was liberated from ice and periglacial waters. The latter, as well as residual arrays of stagnant ice, delayed the formation of the plant cover.

A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl) in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (~4000 cal yr BP-present) are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid-elevation temperature reconstruction, which supported the strong influence of uphill pollen transport from montane forest vegetation and association between temperatures and montane vegetation dynamics. Pollen accumulation rates showed some variability related to minerogenic sediment input to the lake. The Oblong Tarn pollen record provides an indication of long term vegetation change atop Mount Kenya showing some decreases in local alpine and ericaceous taxa from 5300–3100 cal yr BP and minor centennial-scale variability of montane taxa from mid elevation forests. The record highlights potentials, challenges and opportunities for the use of proglacial lacustrine sediment to examine vegetation change on prominent mountain massifs.

Response of Sandy Lake in Schirmacher Oasis, East Antarctica to the glacial-interglacial climate shift

Freshwater lakes in Antarctica fluctuate from ice-free state (during austral summer) to ice-cover state (during austral winter). Hence the lakes respond instantly to the seasonal climate of the region. The Antarctic seasons respond sharply to the glacial and interglacial climates and these signatures are archived in the lake sediments. A sediment core from Sandy Lake, a periglacial lake located in Schirmacher Oasis of East Antarctica records distinct changes in grain-size, C, N, C/N ratios (atomic), δ13COM and δ15NOM contents during the last 36 ky. The contents of the sedimentary organic matter (OM) proxies (Corg ~ 0.3 ± 0.2%, C/N ratios ~9 ± 5 and δ13COM ~−18 ± 6‰) indicate that the OM in this lake sediment is a product of mixing of terrestrial and lacustrine biomass. Distinctly lower contents of Corg (~0.2%) and sand (~50%), low C/N ratios (~8) and depleted δ13COM (~−20‰) during the Last Glacial Maximum (LGM: 32–17 ky BP based on Vostok Temperatures) suggest greater internal (autochthonous) provenance of organic matter and limited terrestrial (allochthonous) inputs probably due to long and intense winters in the Antarctic. Such intense winters might have resulted the lake surface to be ice-covered for most part of the year when the temperatures remained consistently colder than the Holocene temperatures. The denitrification within the lake evident by enriched δ15NOM (>10‰) during Antarctic LGM might have resulted from oxygen-limitation within the lake environment caused by insulated lake surface. The gradual increases in δ13COM, C/N and sand content starting at ~11 ky BP and attaining high values (~−11‰, ~10 and ~80% respectively) at ~6 ky BP together suggest a subtle change in the balance of sources of organic matter between algal and macrophyte/bryophyte nearly 8–9 ky later to the beginning of the deglaciation. Thus the seasonal opening-up of the Sandy Lake similar to the modern pattern started with the establishment of the optimum temperature conditions (i.e., 0 °C anomaly) in the Antarctic, prior to which the lake environment might have remained mostly insulated or closed.

Effects of glaciological and hydro-meteorological conditions on the glacial danger in Zailiyskiy Alatau

A need to estimate a hazard of a mudflow stream appearance in the glacial-nival zone of the Northern slope of Zailiyskiy Alatau (Kasakhstan) is now one of the really urgent problems. The objective of this study was to inves‑ tigate influence of glacial and hydrometeorological factors on the condition of snow-glacial zone of Zailiyskiy Alatau and find out a mudflow-forming role of the mudflow centers arising due to climate warming and degra‑ dation of glaciation: periglacial lakes, intramoraine channels and reservoirs, and also talik massifs of morainic deposits. We analyzed glacial processes in the Zailiysky Alatau over a long period using meteorological data of the Almaty weather station and its close correlations with data from weather stations in the mountains. The area of glaciations was found out to be reduced after the maximum of the Little Ice Age. A combined diagram of occurrence of the mudflow manifestations and factors causing them had been constructed on the basis of sta‑ tistical data on the landslide phenomena. Glacial mudflows were the most frequent in 1960–1990, and later on activity of them became weaker. We believe, that in the next 10–20 years, the glacial mudflow hazard in Zailiys‑ kiy Alatau can sharply decrease, but at the same time, a probability of occurrence of the rainfall mudflows can increase in the mountainous zone of the ridge due the increase of areas with melted moraine and slope deposits.

Using ground-penetrating radar, topography and classification of vegetation to model the sediment and active layer thickness in a periglacial lake catchment, western Greenland

Abstract. The geometries of a catchment constitute the basis for distributed physically based numerical modeling of different geoscientific disciplines. In this paper results from ground-penetrating radar (GPR) measurements, in terms of a 3-D model of total sediment thickness and active layer thickness in a periglacial catchment in western Greenland, are presented. Using the topography, the thickness and distribution of sediments are calculated. Vegetation classification and GPR measurements are used to scale active layer thickness from local measurements to catchment-scale models. Annual maximum active layer thickness varies from 0.3 m in wetlands to 2.0 m in barren areas and areas of exposed bedrock. Maximum sediment thickness is estimated to be 12.3 m in the major valleys of the catchment. A method to correlate surface vegetation with active layer thickness is also presented. By using relatively simple methods, such as probing and vegetation classification, it is possible to upscale local point measurements to catchment-scale models, in areas where the upper subsurface is relatively homogeneous. The resulting spatial model of active layer thickness can be used in combination with the sediment model as a geometrical input to further studies of subsurface mass transport and hydrological flow paths in the periglacial catchment through numerical modeling. The data set is available for all users via the PANGAEA database, doi:10.1594/PANGAEA.845258.

DIATOMS IN THE BOTTOM SEDIMENTS OF ZAONEZHYE LAKES: ASSESSMENT OF THE PRESENT STATE OF THE LAKES AND RECONSTRUCTION OF LAKE ONEGO LEVEL VARIATIONS

New data, obtained by studying the composition of the diatom complexes in the top-core sediments from eight lakes in Zaonezhye located at different absolute altitudes above sea level, are reported. The evolutionary conditions for the diatom flora were assessed, and the water mineralization of the lakes, acidity of the medium and climatic variation trends in the modern era were reconstructed. The water mineralization of the lakes was found to be directly related to the type of the crystalline bedrock, the composition of Quaternary deposits, the size and depth of the lakes, and their position in fault zones. The diatom complexes evidence a directed climatic warming trend indicated by a decline or even vanishing of arctalpine forms and a greater variety of boreal forms and cospopolites. Dominant species were identified to reveal similarities and differences in the evolution of the lakes, preliminary conclusions regarding the timing of their detachment from the periglacial Lake Onega (PLO) were drawn, and variations in its water level in the Late Glacial and the Holocene are shown

Genetic differentiation of coregonid fishes in pechora river

A population–genetic study of five coregonid fish species has been carried out using 30 enzyme loci. The species under study included whitefish, a natural hybrid of vendace and least cisco, inconnu, peled, and Arctic cisco. The investigation revealed a low intraspecific genetic differentiation of the abovementioned species from Lower Pechora River and Usa River, which is the main tributary in the Pechora River basin, where coregonid fishes migrate to spawn. Presumably, whitefish, vendace, and inconnu inhabiting the main channels of Lower Pechora and Usa rivers are represented here by introgressive populations of species formed by a mix of discrete evolutionary lineages originating from geographically separated Late Quaternary refugia. Some lineages of whitefish, vendace, and inconnu from the West Siberian periglacial lake came to Eastern Europe together with the last migration wave of Siberian species to the west, including peled, broad whitefish, and Arctic cisco, during the Middle Weichselian glaciation (60000–50000 years ago), while in the Eastern European Periglacial refugium (Lake Komi), local lineages of these species had survived. The periglacial Lake Komi has probably been located on the Pechora Plain since early Weichselian glaciation (90000–80000 years ago), and the studied whitefish specimens from Upper Pechora River are probably the purest descendants of the periglacial race of whitefish from Lake Komi. This assumption is supported by the data on the high level of genetic differentiation between the whitefish of Upper Pechora and Lower Pechora (DN = 0.005), as well as by the pattern of allele distribution in some polymorphic loci. In our opinion, the ecologic and genetic differentiation of vendace in the Pechora River basin is also connected with the interaction between two evolutionary lineages that originated from independent periglacial refugia.

Oxygen isotope perspective on crustal evolution on early Earth: A record of Precambrian shales with emphasis on Paleoproterozoic glaciations and Great Oxygenation Event

We present stable isotope and chemical data for 206 Precambrian bulk shale and tillite samples that were collected mostly from drillholes on all continents and span the age range from 0.5 to 3.5 Ga with a dense coverage for 2.5–2.2 Ga time interval when Earth experienced four Snowball Earth glaciations and the irreversible rise in atmospheric O2. We observe significant, downward shift of several ‰ and a smaller range of δ18O values (7 to 9‰) in shales that are associated with the Paleoproterozoic and, potentially, Neoproterozoic glaciations. The Paleoproterozoic samples consist of more than 50% mica minerals and have equal or higher chemical index of alteration than overlying and underlying formations and thus underwent equal or greater degrees of chemical weathering. Their pervasively low δ18O and δD (down to −85‰) values provide strong evidence of alteration and diagenesis in contact with ultra-low δ18O glacial meltwaters in lacustrine, deltaic or periglacial lake (sikussak-type) environments associated with the Paleoproterozoic glaciations. The δDsilicate values for the rest of Precambrian shales range from −75 to −50‰ and are comparable to those for Phanerozoic and Archean shales. Likewise, these samples have similar ranges in δ13Corg values (−23 to −33‰ PDB) and Corg content (0.0 to 10 wt%) to Phanerozoic shales. Precambrian shales have a large range of δ18O values comparable to that of the Phanerozoic shales in each age group and formation, suggesting similar variability in the provenance and intensity of chemical weathering, except for the earliest 3.3–3.5 Ga Archean shales, which have consistently lower δ18O values. Moreover, Paleoproterozoic shales that bracket in age the Great Oxidation Event (GOE) overlap in δ18O values. Absence of a step-wise increase in δ18O and δD values suggests that despite the first-order change in the composition of the atmosphere, weathering cycle was not dramatically affected by the GOE at ∼2.4–2.3 Ga. Shales do not show comparable δ18O rise in the early Phanerozoic as is observed in the coeval δ18O trends for cherts and carbonates. There is however a sharp increase in the average δ18O value from the Early Archean to the Late Archean followed by a progressively decelerating increase into the Phanerozoic. This decelerating increase with time likely reflects declining contribution of mantle-extracted, normal-δ18O crust and lends support to crustal maturation and increasing 18O sequestration into the crust and recycling of high-δ18O (and 87Sr/86Sr) sedimentary rocks. This secular increase in the δ18O composition of the continental crust could have also had a mild effect on seawater δ18O composition.

Fate of Lamprodrilus isoporus (Oligochaeta: Lumbriculidae) in eutrophic lakes

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Response of Long Lake sediments to Antarctic climate: A perspective gained from sedimentary organic geochemistry and particle size analysis

Sediments from the pristine lakes of ice-free regions of Antarctica are a great source for proxies to reconstruct the effect of past-climate on the lake evolution and its response to Antarctic climate. A 50 cm long sediment core retrieved from Long Lake, a periglacial lake of Schirmacher Oasis in Dronning Maud Land was measured for elemental (C%, N% and C/N), isotopic (δ13C, δ15N) and particle size (sand-silt-clay percent) variation. The radiocarbon dated core spanning the last 48 cal ka BP has been deciphered for the lake's response to Antarctic climate. The C/N ratio (atomic ratio) predominantly indicates that the productivity has been autochthonous for majority of the down-core while the top 0–3 cm indicates that there has been addition of terrestrial organic matter into the lake system owing to longer ice-free conditions. The organic carbon shows significantly lower values (0.2%) throughout the glacial period and major part of the Holocene while the core-top values are consistent with the presence of a microbial mat which is reflected as higher organic carbon (12%). The δ13C and δ15N range from −33 to −9‰ and 2–18‰, respectively. The isotopic signals vary marginally for the entire glacial period (48–8 cal ka BP) suggesting an intense cold period. The gradual increase in C/N ratio, sand content and δ13C and decrease in δ15N beginning at about 6 cal ka BP suggest that the Long Lake experienced longer ice-free conditions owing to sustained warmer Holocene conditions suggesting that the ice-cover over the Long Lake persisted well through early-Holocene. The sand and silt percent shows inverse correlation likely reflecting the warmer and colder conditions. The Holocene is characterised by higher sand content owing to melting of ice due to warmer conditions. The Long Lake's response to Antarctic climate is reflected in its response to the ice-cover conditions which regulates the productivity and sedimentation in the lake system.

PLEISTOCENE GLACIATIONS IN THE EAST TRANSBAIKALIA AND THE SOUTHEAST OF MIDDLE SIBERIA

The maps of four Pleistocene glaciations were compiled: Samarovo (Q II sm), Taz (Q II tz), Muruktin (Q III mr), and Sartan (Q III sr). The maps show distribution of glaciers, ice sheets, and ice-dammed lakes, which occupied vast areas in the river basins of Lena, Vitim, and Olekma. The absolute heights of paleo lakes in the Lena basin are 400 m (tz), 560 m (sm); in the Vitim basin: 860 m (sr), 880 (mr) 900 m (tz); in the Olekma basin: 680 m (mr), 760 m (tz). Well drilling fulfilled to 1180 m depth revealed four glacial layers of Middle and Upper Pleistocene in the interval 0-450 m. Sand sediments were formed due to coastal accumulation of abraded granitic material in the Transbaikaline periglacial lake of the Samarovo age with short-term maximum level of 1020 m and stabile long-term one of 900 m.

A formal approach to the automated labeling of groups of features

A variety of recurring geographic entities form collections of point, line, or area features. Examples are groups of islands (Archipelago), relief features in deserts, periglacial lakes or geomorphological forms, such as drumlins and sinkholes. All these groups of features might be best identified with a single label. Surprisingly, the (automated) labeling of groups of features has received little attention so far. We propose a framework to determine formal measures that describe the geometric aspects of the cartographic design space for labeling feature groups. Our framework gives rise to a large variety of geometrically optimal labels. We list the optimal label positions and shapes for which labels can already be computed using existing algorithms. However, in many of the cases computing optimal label placements is still an open algorithmic question which can readily be investigated in future work. Once the necessary algorithms are developed, our framework provides an objective basis to investigate the geometric measures used by cartographers to label groups of features. We preliminarily explore the applicability of our framework using one of the geometric optimality choices.

Hydrological and meteorological investigations in a periglacial lake catchment near Kangerlussuaq, west Greenland – presentation of a new multi-parameter data set

Abstract. Few hydrological studies have been conducted in Greenland, other than on glacial hydrology associated with the ice sheet. Understanding permafrost hydrology and hydroclimatic change and variability, however, provides key information for understanding climate change effects and feedbacks in the Arctic landscape. This paper presents a new, extensive, and detailed hydrological and meteorological open access data set, with high temporal resolution from a 1.56 km2 permafrost catchment, with a lake underlain by a through-talik close to the ice sheet in the Kangerlussuaq region, western Greenland. The paper describes the hydrological site investigations and utilized equipment, as well as the data collection and processing. The investigations were performed between 2010 and 2013. The high spatial resolution, within the investigated area, of the data set makes it highly suitable for various detailed hydrological and ecological studies on catchment scale. The data set is available for all users via the PANGAEA database, http://doi.pangaea.de/10.1594/PANGAEA.836178.

CHANGES IN THE WORLD OCEAN AVERAGE DEPTH AS A POSSIBLE CAUSE OF THE COMPLETION OF THE WÜRM GLACIATION

The developed hypothesis suggests that the cause of the completion of the Wurm glaciation were the tectonic processes resulting in the decrease of the average depth of the World Ocean and the corresponding increase in its level. The latter turned the better part of the ice sheets in Europe and North America into the ice shelf, that caused their separation from the bed and the massive destruction by waves.A significant extension of the free water surface area led to the rise of the intensity of heat and mass transfer between the oceans and the atmosphere and the growth of its water vapor content. As a result, the greenhouse effect increased and the average temperatures in the troposphere rose as well.A substantial decrease of the cryosphere area in the Northern Hemisphere of the planet also led to the massive reduction of its mean albedo. All this resulted in the climate warming in the regions of our planet not only on the coasts of the oceans but also within the continents, melting glaciers located therein, overflow of the periglacial lakes with melt water and their breakthroughs into the oceans (“glacial flood” by Hancock).

Chronology of bathymetric variations of the Pueyrredón-Posadas-Salitroso lacustrine system during the Late Pleistocene to Early Holocene

The Pueyrredón-Posadas-Salitroso lacustrine system (PPS-LS) is located in the Andean Patagonia region of Argentina (47°22′28″S – 71°55′34″W) and represents a series of lakes formed as glaciers retreated during the late Pleistocene and early Holocene. These lakes began as proglacial lakes and later evolved into periglacial lakes. This research presents the chronological evolution of the PPS-LS bathymetric variations based on the analysis of stratigraphic profiles surveyed at different locations and the dates obtained from lake sediments. Four paleogeographic sketches representing the chronological evolution of the PPS-LS between 23,580BP and 5208BP have been developed based on the integration of these data.

LITHOLOGY AND PALEOMAGNETISM OF VARVED CLAYS

On an example of varved clays from two periglacial lakes on the territory of NW Russia the model of formation of glaciolacustrine sediments is reported. The geological-geomorphological background, lithology and genesis are interpreted in the framework of turbidity hypothesis. The textural and structural properties of the varved clays from the different zones and significant differences in magnetic parameters are established. In the framework of accepted model the paleomagnetic data have been analyzed. Taking into account the complex of investigation the paleomagnetic records have a different resolution for the ancient geomagnetic field research.

Terminal stages of the evolution of sheet and mountain glaciations in Khibiny

The purpose of this work is to reconstruct terminal stages of the evolution of sheet and mountain glaciations in the Khibiny mountainous massif. We investigated a vast area of nepheline syenites of the Khibiny pluton in the southern Khibiny Massif. This area is characterized by an abundance of glacial cirques and the existence of mountain glaciations [1, 2]. We revealed here typical structures of the marginal belt of the Scandinavian glacier as dump and push moraine ridges [3] (Fig. 1). The northern part of the area includes deposits of mountain glaciers with a specific composition of clastic material. Judging from the petrographic composition of the pebble fraction and the mineral composition of sand and silt, the clastic material is almost entirely represented by products of destruction of nepheline syenites of the Khibiny intrusive massif. Mountain glaciers and their meltwaters include the following structures: (i) end moraines damming valleys of the Poachvumjok and Vudjavrjok rivers; (ii) ridges resembling De Geer moraines; (iii) glaciofluvial deltas formed by meltwater running southward and located in valleys of the Poachvumjok and Vudjavrjok rivers behind end moraines; (iv) periglacial lake terraces developed at an altitude of about 500 m in the Poachvumjok river valley; and (v) a small sandur with an even surface complicated by “pocks” of the Malyi Vudjavr and Kupal’noe lakes obviously indicating the filling of lake depressions with dead ice during the sandur formation. The southern part of the study area includes sheet glaciation deposits that are developed represented by dump and push moraine ridges, as well as a thin cover

Aliens Associating with Caspian Sea Endemic Bivalves

Endemic species of the Caspian Sea fauna and flora are potentially and actually threatened by invasive species, particularly since the opening of the Volga-Don Shipping Canal in 1952. While the invaders are more or less known, their impact on the Caspian ecosystem is poorly understood, maybe with few exceptions such as the impact by the immigrated ctenophore Mnomiopsis leidyl. Here we describe the association of the invasive cirripedian crustacean Balanus improvisus and the cheilostomate bryozoan Conopeum seurati with the limnocardiid bivalve Didacna sp. endemic to the Caspian Sea. The description represents only the first step towards an understanding of the interactions between the invasive and endemic species. The Caspian Sea is the largest lake on our planet spanning an area of about 400,000 km 2 and with almost 79,000 km 3 water volume (Dumont, 1998). The extension of the Caspian Sea has varied quite significantly during the last several million years, due to tectonic events and climatically induced lake level changes, which have particularly strong impact on the shallow areas of the Caspian depression. In historical times lake level fluctuated in a range between )29 and )19 m below sea level. Since the last couple of years it varied around )27 m, having risen from )29 m since the late seventies of the 20th century (Kosarev and Yablonskaya, 1994; Dumont, 1998; De Mora and Turner, 2004). The Caspian Sea is the only extant lake which was formed from an ancient ocean. The Caspian depression with its two deep basins was once part of the Paratethys, a sea which disintegrated into several more or less isolated basins during the late Neogene and the Pleistocene (Nevesskaja et al. 2001). The Caspian Sea is considered to constitute a lake since the Messinian (late Miocene), but there were connections to the Black Sea basin several times during the Pliocene and the Quaternary (Grigorovich et al. 2003). During certain phases of Pleistocene glaciation cycles, the Caspian Sea probably had also temporal connections with northern periglacial lakes and with the Aral Sea. These connections facilitated the faunal exchange between the water basins with the consequence that the Caspian Sea fauna has different geographical origins. The Holocene has been a period of relative isolation until the beginning of the 20th century when man started to introduce alien species to the Caspian Sea deliberately, such as the bivalve Abra ovata, to serve as fish food (Grigorovich et al. 2002). With the opening of the Volga–Don Shipping Canal in 1952, a permanent connection between the Caspian Sea and the Black Sea was established. Since then quite many new invaders arrived or were accidentally

GIS-based modelling of glacial sediment balance

In view of ongoing atmospheric warming, there is concern as to whether retreating glaciers uncover a rocky or sedimentary bed. Sedimentary beds are abundant in high-mountain areas and represent, if exposed, a severe hazard potential for outbursts of periglacial lakes or debris flows. Furthermore, knowledge about glacier sediment balance is needed when dealing with climate sensitivity of recent and historical glaciers. The main factors influencing sediment balance of a glacierised mountain catchment have been organised into an index (Ies) of glacier erosion and sedimentation, which distinguishes between glaciers eroding into bedrock and those building up thick sedimentary beds. GIS-based methods were developed to extract the needed Ies-parameters from Digital Elevation Models (DEM), digitised glacier outlines and central flowlines. These methods were automated and tested on 84 Swiss Alpine glaciers. The results were validated through comparisons with forefield classifications and manually derived index results. The comparison with classified forefields confirms that the index allows for a rough assessment of the glacial sediment balance. In order to improve the predictability of glacier-bed characteristics, a better understanding of the periglacial debris production is necessary. However, the high overall accuracy of the comparison with the manual glacier-by-glacier investigation shows the potential of using GIS-based modelling with DEM in geomorphodynamics.