ALBERT

Description: The quantification of sea-ice production in the Laptev Sea polynyas is important for the Arctic sea-ice budget and the heat loss to the atmosphere. We estimated the ice production for the winter season 2007/2008 (November–April) based on simulations with the regional climate model COSMO-CLM at a horizontal resolution of 5 km and compared it to remote sensing estimates. A reference and five sensitivity simulations were performed with different assumptions on grid-scale and subgrid-scale ice thickness considered within polynyas, using a tile approach for fractional sea ice. In addition, the impact of heat loss on the atmospheric boundary layer was investigated. About 29.1 km3 of total winter ice production was estimated for the reference simulation, which varies by up to +124 % depending on the thin-ice assumptions. For the most realistic assumptions based on remote sensing of ice thickness the ice production increases by +39 %. The use of the tile approach enlarges the area and enhances the magnitude of the heat loss from polynyas up to +110 % if subgrid-scale open water is assumed and by +20 % for realistic assumptions. This enhanced heat loss causes in turn higher ice production rates and stronger impact on the atmospheric boundary layer structure over the polynyas. The study shows that ice production is highly sensitive to the thin-ice parameterizations for fractional sea-ice cover. In summary, realistic ice production estimates could be retrieved from our simulations. Neglecting subgrid-scale energy fluxes might considerably underestimate the ice production in coastal polynyas, such as in the Laptev Sea, with possible consequences on the Arctic sea-ice budget.

Description: Spatial and temporal characteristics of the Storfjorden polynya, which forms regularly in the proximity of the islands Spitsbergen, Barentsøya and Edgeøya in the Svalbard archipelago under the influence of strong north-easterly winds, have been investigated for the period 2002/2003 to 2013/2014 using thermal infrared satellite imagery. Thin-ice thicknesses were calculated from MODIS ice-surface temperatures, combined with ECMWF ERA-Interim atmospheric reanalysis data in an energy-balance model. Based on calculated thin-ice thicknesses, associated quantities like polynya area and total ice production were derived and compared to previous remote sensing and modeling studies. A basic coverage-correction scheme was applied to account for cloud-gaps in the daily composites. The sea ice in the Storfjorden area experiences a late fall freeze-up in several years over the 12 winter-period, with an increasing frequency of large polynya events until the end of December. During the regarded period, the mean polynya area is 4555.7 ± 1542.9 km2. The average ice production in the fjord is estimated with 28.3 ± 8.5 km3 per winter and therefore lower than in previous studies. Despite this comparatively short record of 12 winter-seasons, a significant positive trend of 20.2 km3 per decade could be detected, which contrasts earlier reports of a slightly negative trend in accumulated ice production prior to 2002. Derived estimates underline the importance of this relatively small coastal polynya system considering its contribution to the cold halocline layer through salt release during ice formation processes.

Description: The River Rhine and its tributaries represent one of the largest drainage systems in Europe. Its prominence among other fluvial systems is due to the location of its headwaters within the central Swiss Alps, which were repeatedly glaciated during the Quaternary, and the concurrence of major parts of the River Rhine course with the European Cenozoic Rift System. Sediments of the Rhine have thus recorded both changes in climate and tectonic activity as well as sea level change in the lower part of the river course.The River Rhine is composed of different subdivisions characterised by distinct geographical and geological settings. Vorder-and Hinterrhein in the headwaters are inner-alpine rivers frequently influenced in their course by tectonic lines and the blockage of valley floors by the deposits of mass movements. The Alpenrhein is located in a main Alpine valley that drains into a large foreland basin, the Bodensee (Lake Constance). The Hochrhein flows out of the lake following the Jura Mountains in a western direction. All these areas display a series of geological features such as moraine ridges and outwash plains, which directly reflect Quaternary glaciations of the Alps. The Oberrhein (Upper Rhine) Valley, as a graben structure, is part of the rifting system that started to develop during the middle Tertiary. The northern end of the graben is represented by the triple junction of the Mainz Basin, which is mainly characterised by the remains of marine transgressions that occurred during the initial rifting phase. The Rhine continues following the western branch of the tectonic system by passing through the Rhenish Massif. Uplift in this so-called Mittelrhein (Middle Rhine) area is well documented by a flight of late Tertiary to Quaternary river terraces. This region is also characterised by young volcanic activity as found, for example, in the Eifel volcanic field. The Niederheinische Bucht (Lower Rhine Embayment), especially the Roer Valley Rift System, represents the northern continuation of the rifting system. This area is characterised by differential uplift in the southern and subsidence in the northern part of the basin, which continues into the Netherlands. Here, the main stream of the River Rhine is separated into different branches developing an active delta at the coast of the North Sea. When the North Sea Basin was covered by ice during the Elsterian, Saalian and probably also the Weichselian glaciation and global sea level was low, the Rhine continued its course through the English Channel and flowed into the North Atlantic off Brittany.

Description: Anhand von zwei Dünenprofilen wird die Art, Dauer und Intensität von spätglazialen und holozänen Flugsand- und Bodenbildungen innerhalb des Pommerschen Sandergebietes dargestellt. Hierfür wurde ein interdisziplinärer Ansatz aus Sedimentologie, Pedologie, Palynologie und Geochronologie verwendet. Während des Spätglazials kommen auf den Sanderhochflächen flache Flugsanddecken zur Ablagerung, unterbrochen durch die Bildung des Finowbodens. Durch die Ausbreitung einer geschlossenen Vegetationsdecke im Frühholozän, erfolgt eine Stabilisierung der Reliefoberfläche mit anschließender Bodenbildung. Nach intensiven mittelalterlichen Rodungen werden die Oberflächen erneut destabilisiert. Es kommt zur partiellen Aufarbeitung der Flugsande resultierend in Dünenbildungen und einem kuppigen Relief. Eine der untersuchten Dünen wurde dabei komplett im späten Subatlantikum gebildet. Diese Studie unterstreicht die zeitlich-räumliche Variabilität äolischer Aktivität, wobei Umlagerungen entsprechender Korngrößen während verschiedener Phasen nach der Deglaziation ermöglicht wurden.

Description: Eine revidierte Vergletscherungsgeschichte des nördlichen Vorlandes der Schweizer Alpen wird vorgestellt, basierend auf Feldbefunden und chronologischen Daten von verschiedenen Schlüssellokalitäten und Regionen. Die ältesten quartären Sedimente der Schweiz sind mehrphasige Kiese, in die Till und Hochflutsedimente eingeschaltet sind (’Deckenschotter’). Bedeutende Unterschiede im Basisniveau der Schotterablagerungen erlauben die Unterscheidung zweier komplex augebauter Einheiten (’Höhere Deckenschotter’, ’Tiefere Deckenschotter’), die durch eine Phase bedeutender Einschneidung getrennt sind. Säugetierreste stellen die ältere Einheit (‘Höhere Deckenschotter’) in die Zone MN 17 (2.6–1.8 Ma). Jeder der Komplexe enthält Belege für zumindest zwei, möglicherweise sogar bis zu vier eigenständige Eiszeiten, woraus sich in Summe bis zu acht frühpleistozäne Vergletscherungen des Schweizer Alpenvorlands ergeben. Die frühpleistozänen Deckenschotter sind von mittelpleistozänen Ablagerungen durch eine Zeit bedeutender Erosion getrennt, die wahrscheinlich durch tektonische Bewegungen und/oder eine Umleitung des Alpenrheins verursacht wurde (Mittelpleistozäne Reorganisation – MPR). Das Mittel-/Spätpleistozän beinhaltet vier oder fünf Eiszeiten, die nach ihren Schlüsselregionen als Möhlin-, Habsburg-, Hagenholz- (unsicher, unzureichend belegt), Beringen- und Birrfeld-Eiszeit benannt sind. Die Möhlin-Eiszeit repräsentiert die grösste Vergletscherung des Schweizer Alpenvorlandes, während die Beringen-Eiszeit von nur wenig geringerer Ausdehnung war. Der letzte Glazialzyklus (Birrfeld-Eiszeit) umfasst wahrscheinlich drei eigenständige Gletschervorstösse, die auf ca. 105 ka, 65 ka und 25 ka datiert wurden. Für den letzten Eisvorstoss wird eine detaillierte Radiokohlenstoffchronologie für den Eisaufbau und das Abschmelzen präsentiert.

Description: In den glazial übertieften Becken des würmzeitlichen Illergletschers wurden Untersuchungen zur Lagerung (Bohr- und Aufschlussdaten) und zur Chronologie (Lumineszenzdatierungen) limnischer Sedimente durchgeführt. Die Ergebnisse belegen drei getrennte Phasen mit einer Akkumulation von feinkörnigen lakustrinen Beckensedimenten im Bereich des Kemptener Beckens, die dem späten Hochglazial (Marines Isotopen-Stadium 2), dem Mittleren Würm (MIS 3) und dem Präwürm zugeordnet werden. Die Sedimentabfolgen dokumentieren mit ihrem typischen Profilaufbau (Tillkomplex an der Basis; Bänderschluffe mit dropstones; Bänderschluffe), dass im Bereich des Kemptener Beckens in den drei genannten Zeitbereichen jeweils eine Vergletscherung mit Eiszerfall und abschließender Seephase nachzuweisen ist. Die mittelwürmzeitlichen Sedimentabfolgen sind stratigraphisch von besonderer Bedeutung, da sie auf eine Vergletscherung des Kemptener Beckens hinweisen, die unter Berücksichtigung regionaler und überregionaler Klimaarchive dem MIS 4 zugeordnet wird. Entsprechende Eisrandlagen konnten bisher an der Reliefoberfläche nicht eindeutig nachgewiesen werden, da sie mit dem Eisvorstoß zum Würmhochstand (MIS 2) vermutlich überfahren und verschliffen wurden.

Description: Luminescence dating is a tool frequently used for age determination of Quaternary materials such as archaeological artefacts, volcanic deposits and a variety of sediments from different environmental settings. The present paper gives an overview of the physical basics of luminescence dating, the necessary procedures from sampling to age calculation, potential problems that may interfere with correct age calculation as well as procedures to identify and resolve those problems. Finally, a brief summary of the most common fields of application is given ranging from artefacts to the variety of different sediments suitable for luminescence dating.

Description: During the last glacial period, several large abrupt climate fluctuations took place on the Greenland ice cap and elsewhere. Often these Dansgaard/Oeschger events are assumed to have been synchronous, and then used as tie-points to link chronologies between the proxy archives. However, if temporally separate events are lumped into one illusionary event, climatic interpretations of the tuned events will obviously be flawed. Here, we compare Dansgaard/Oeschger-type events in a well-dated record from south-eastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, tuning of proxy archives should be avoided.

Description: Radiocarbon (14C) analysis is an important tool that can provide information on the dynamics of organic matter in soils. Radiocarbon concentrations of soil organic matter (SOM) however, reflect the heterogeneous mixture of various organic compounds and are affected by different chemical, biological, and physical soil parameters. These parameters can vary strongly in soil profiles and thus affect the spatial distribution of the apparent 14C age of SOM considerably. The heterogeneity of SOM and its 14C signature may be even larger in subsoil horizons, which are thought to receive organic carbon inputs following preferential pathways. This will bias conclusions drawn from 14C analyses of individual soil profiles considerably. We thus investigated important soil parameters, which may influence the 14C distribution of SOM as well as the spatial heterogeneity of 14C distributions in soil profiles. The suspected strong heterogeneity and spatial variability, respectively of bulk SOM is confirmed by the variable 14C distribution in three 185 cm deep profiles in a Dystric Cambisol. The 14C contents are most variable in the C horizons because of large differences in the abundance of roots there. The distribution of root biomass and necromass and its organic carbon input is the most important factor affecting the 14C distribution of bulk SOM. The distance of the soil profiles to a beech did not influence the horizontal and vertical distribution of roots and 14C concentrations. Other parameters were found to be of minor importance including microbial biomass-derived carbon and soil texture. The microbial biomass however, may promote a faster turnover of SOM at hot spots resulting in lower 14C concentration there. Soil texture had no statistically significant influence on the spatial 14C distribution of bulk SOM. However, SOM in fine silt and clay sized particles (〈 6.3 µm) yields slightly higher 14C concentrations than bulk SOM particularly at greater soil depth, which is in contrast to previous studies where silt and clay fractions contained older SOM stabilized by organo-mineral interaction. 14C contents of fine silt and clay correlate with the microbial biomass-derived carbon suggesting a considerable contribution of microbial-derived organic carbon. In conclusion, 14C analyses of bulk SOM mainly reflect the spatial distribution of roots, which is strongly variable even on a small spatial scale of few meters. This finding should be considered when using 14C analysis to determine SOM.