Southeastern Swiss Alps Research Articles

Filling the gap: Recent Mesolithic discoveries in the central and south-eastern Swiss Alps

Until 2007 only a handful of surface finds dating to between the end of the LGM and the Middle Neolithic were known in the alpine regions of central and south-eastern Switzerland. A number of recent rescue excavations, research projects and single finds have now shown the presence of people at high altitude in these parts of the Alps from the 9th millennium cal BC onwards. Both open-air sites and rock shelters are represented. Many sites lie above the valley floor, in the upper subalpine or alpine zones, and on routes to minor as well as major passes. Together with new palaeoenvironmental data, these archaeological finds allow us first insights into the nature of interaction of Mesolithic people in the south-eastern Swiss Alps with their social and natural environment, as well as their relationship with regions further afield. Furthermore, the finds allow us to start thinking about future research into the early prehistory of the south-eastern Swiss Alps.

Quantitative summer temperature reconstruction derived from a combined biogenic Si and chironomid record from varved sediments of Lake Silvaplana (south-eastern Swiss Alps) back to AD 1177

High-resolution quantitative temperature records are needed for placing the recent warming into the context of long-term natural climate variability. In this study we present a quantitative high-resolution (9-year) summer (June–August) temperature reconstruction back to AD 1177 for the south-eastern Swiss Alps. This region is a good predictor for summer temperatures in large parts of western and central Europe. Our reconstruction is based on a combination of the high-frequency component of annually resolved biogenic silica (bSi flux) data and the low-frequency component of decadal chironomid-inferred temperatures from annually laminated well dated sediments (varves) from proglacial Lake Silvaplana, eastern Swiss Alps. For the calibration (period AD 1760–1949) we assess systematically the effects of six different regression methods (Type I regressions: Inverse Regression IR, Inverse Prediction IP, Generalised Least Squares GLS; Type II regressions: Major Axis MA, Ranged Major Axis RMA and Standard Major Axis SMA) with regard to the predicted amplitude and the calibration statistics such as root-mean-square error of prediction (RMSEP), reduction of error (RE) and coefficient of efficiency (CE). We found a trade-off in the regression model choice between a good representation of the amplitude and good calibration statistics. The band-pass filtered bSi flux record is in close agreement both in the structure and the amplitude with two fully independent reconstructions spanning back to AD 1500 and AD 1177, respectively. All known pulses of negative volcanic forcing are represented as cold anomalies in the bSi flux record. Volcanic pulses combined with low solar activity (Spörer and Maunder Minimum) are seen as particularly cold episodes around AD 1460 and AD 1690. The combined chironomid and bSi flux temperature record (RMSEP = 0.57 °C) is in good agreement with the glacier history of the Alps. The warmest (AD 1190) and coldest decades (17th century; 1680–1700) of our reconstruction coincide with the largest anomalies in the Alpine tree-ring based reconstruction; both records show in the decadal variability an amplitude of 2.8 °C between AD 1180 and 1950, which is substantially higher than the amplitude of hemispheric reconstructions. Our record suggests that the current decade is slightly warmer than the warmest decade in the pre-industrial time of the past 800 years.

Glacier mass balance in the south-eastern Swiss Alps since 1900 and perspectives for the future

In this study, we analyzed the 20(th) century ice volume changes for 20 glaciers in the south-eastern Swiss Alps. Our sample included different glacier geometries, sizes and exposures and allowed us to investigate glacier response to climate change. Using a distributed accumulation and temperature-index melt model, we derived mass balance time series in seasonal resolution from 1900. The model was calibrated using ice volume changes obtained from differentiating digital elevation models based on (i) terrestrial topographic surveys, (ii) the Shuttle Radar Topographic Mission (SRTM), and (iii) aerial photogrammetry. In-situ point measurements of annual mass balance and winter accumulation were available for some glaciers, and long-term discharge records were used for model validation. The rate of mass loss between 1900 to 2008 strongly differed between adjacent glaciers. Whereas large valley glaciers (e.g. Vadrec del Forno) showed average mass balances of up to -0.60m w.e. a(-1), smaller and steeper glaciers (e.g. Vadret da Palu) exhibited slower mass loss in the order of -0.20m we. a(-1). Over the last century, the regional ice volume decreased by 47%, with strong differences between individual glaciers (30-75%). Using a combined model for 3D glacier evolution and stream-flow runoff driven by regional climate scenarios, we generated perspectives for the 21(st) century. We determined a decrease in glacier area of 63% until 2050 and an increase in annual discharge over the next three decades for catchments with high glacierization. By 2100, the model results indicated a shift in the hydrological regime and a 23% decrease in annual runoff attributed to increased evapotranspiration and strongly reduced glacier melt contribution. In dieser Studie analysieren wir die Eisvolumenveranderungen im 20. Jahrhundert fur 20 Gletscher in den sudostlichen Schweizer Alpen. Unsere Auswahl enthalt Gletscher verschiedener Typen, Grosen und Expositionen. Dies ermoglicht eine Untersuchung der Reaktion der Gletscher auf die aktuelle Klimaerwarmung. Durch die Anwendung eines verteilten Akkumulations- und Temperatur-Index-Schmelzmodells werden Massenbilanz-Zeitreihen seit 1900 in saisonaler Auflosung berechnet. Die Kalibrierung des Modells erfolgt mittels Eisvolumenveranderungen. Diese wurden durch verschiedene digitale Hohenmodelle, basierend auf (i) topographischen Karten, (ii) der Shuttle Radar Topographic Mission (SRTM), und (iii) Luftbildauswertungen gewonnen. Fur die Modell-Validierung kommen sowohl in-situ Punkt-Messungen der jahrlichen Massenbilanz und der Winterakkumulation, die fur einige Gletscher zur Verfugung stehen, als auch Langzeit-Abflussmessungen zum Einsatz. Die Rate des Massenverlustes zwischen 1900 bis 2008 unterscheidet sich stark zwischen benachbarten Gletschern. Wahrend grose Talgletscher (z.B. Vadrec del Forno) eine durchschnittliche Massenbilanz von bis zu -0.60 m w.e. a-1 aufweisen, zeigen kleinere und steilere Gletscher (z.B. Vadret da Palu) einen geringeren Massenverlust in der Grosenordnung von -0.20 m w.e. a-1. Im Laufe des letzten Jahrhunderts ist das regionale Eisvolumen um 47% zuruckgegangen, mit grossen Unterschieden zwischen den einzelnen Gletschern (30–75%). Mittels eines kombinierten 3D-Gletscherentwicklungs- und Abflussmodells, angetrieben durch regionale Klimaszenarien, generieren wir Perspektiven fur das 21. Jahrhundert. Die Modellierung prognostiziert einen Ruckgang der Gletscherflache von 63% bis ins Jahr 2050. Wahrend den nachsten drei Jahrzehnten erkennen wir einen Anstieg des jahrlichen Abflusses fur stark vergletscherte Einzugsgebiete. Bis 2100 zeigen die Resultate eine Verschiebung des hydrologischen Regimes und einen Ruckgang des Jahresabflusses von 23%. Dieser ist auf eine erhohte Evapotranspiration und einen stark reduzierten Beitrag der schmelzenden Gletscher zuruckzufuhren.

Frost weathering and rockwall erosion in the southeastern Swiss Alps: Long-term (1994–2006) observations

Rates and processes of frost weathering in the Alps were investigated by visual observations of intensively shattered rocks, continuous monitoring of frost wedging and rock temperatures in bedrock and measurements of rockfall activity. Rapid frost weathering of hard-intact rocks occurs along lakes and streams where seasonal freezing promotes ice segregation in the rock. Otherwise, rocks require pre-existing weakness or a long exposure period for intensively shattered. Automated monitoring shows that crack opening occurs at three scales, including small opening accompanying short-term frost cycles, slightly larger movements during seasonal freezing and occasional large opening originating from refreezing of snow-melt water during seasonal thawing. The opening events require at least partial water saturation in the crack. The repetition of crack opening (frost wedging) results in permanent opening and finally debris dislocation. Debris collections below fractured rockwalls show that pebble falls occur at an average rate of about 0.1 mm a − 1 with significant spatial and inter-annual variations. Occasional large boulder falls significantly raise the rockwall erosion rates, controlled by such factors as the joint distribution in the bedrock, repetition of annual freeze–thaw cycles and extraordinary summer thaw.

Quantifying human-induced eutrophication in Swiss mountain lakes since AD 1800 using diatoms

Sedimentary diatom assemblages from three lakes in the southeastern Swiss Alps were analysed at high temporal resolution since AD 1800. Altered land-use patterns, increasing population and exploitation through tourism are clearly reflected in annually laminated sediments of Lej da San Murezzan (Lake St Moritz) and Lej da Silvaplauna (Lake Silvaplana). Diatom assemblages originally dominated by Cyclotella taxa are replaced by taxa indicating higher total phosphorus (TP) concentrations, such as Asterionella formosa, Fragilaria crotonensis and Stephanodiscus parvus. In Lej da la Tscheppa, located well above the treeline in a catchment that was hardly exposed to human impact, Cyclotella comensis prevails throughout the entire sediment sequence. Quantitative estimates of past TP concentrations were inferred using a newly developed regional diatom-TP inference model based on 119 modern samples. In Lej da la Tscheppa diatoms imply stable, low TP concentrations (~10 µg/l), which can be considered as natural background concentration. Elevated TP levels are inferred for Lej da San Murezzan (max. 60 µg/l) since AD 1910 and for Lej da Silvaplauna (max. 40 µg/l) since AD 1950, corroborated by changes in sedimentary biogenic silica concentration and organic carbon content. Since ~AD 1970 improved waste water management led to a considerable reduction in TP loading in Lej da Silvaplauna and Lej da San Murezzan.

Decadal-scale autumn temperature reconstruction back to AD 1580 inferred from the varved sediments of Lake Silvaplana (southeastern Swiss Alps)

A quantitative high-resolution autumn (September–November) temperature reconstruction for the southeastern Swiss Alps back to AD 1580 is presented here. We used the annually resolved biogenic silica (diatoms) flux derived from the accurately dated and annually sampled sediments of Lake Silvaplana (46°27′N, 9°48′E, 1800 m a.s.l.). The biogenic silica flux smoothed by means of a 9-yr running mean was calibrated ( r = 0.70, p < 0.01) against local instrumental temperature data (AD 1864–1949). The resulting reconstruction (± 2 standard errors = ± 0.7 °C) indicates that autumns during the late Little Ice Age were generally cooler than they were during the 20th century. During the cold anomaly around AD 1600 and during the Maunder Minimum, however, the reconstructed autumn temperatures did not experience strong negative departures from the 20th-century mean. The warmest autumns prior to 1900 occurred around AD 1770 and 1820 (0.75 °C above the 20th-century mean). Our data agree closely with two other autumn temperature reconstructions for the Alps and for Europe that are based on documentary evidence and are completely unrelated to our data, revealing a very consistent picture over the centuries.

The last 1300 years of environmental history recorded in the sediments of Lake Sils (Engadine, Switzerland)

Proglacial Lake Sils is located in the Upper Engadine (south-eastern Swiss Alps) at 1800 m a.s.l. and is the uppermost of four lakes in the valley. A highresolution seismic survey combined with geophysical and chemical data of 22 short sediment cores, and 137Cs, 210Pb, and 14C AMS dating provide insight into the sedimentological development of the lake during the last 1300 years. The deposits consist of diffusely laminated clayey silts. In contrast to nearby Lake Silvaplana, no varves could be detected. Sedimentation rates are on average 1.1 mm per year (40 mg cm−2a−1) which is much lower than in the adjacent Engadine lakes. The most prominent sediment feature is a turbidite that was deposited around cal AD 700, has a thickness of up to more than 6 metres and a total estimated volume of 6.5*106 m3, which is more than the total cumulated sediment mass deposited since that time (4.5 * 106 m3). The sediments deposited after around AD 1880 show higher contents of organic carbon (Corg) and biogenic silica (bSi), which suggests enhanced primary production due to increasing tourism in the area and subsequent higher nutrient supply to the lake. Sediments with distinctly lower Corg and bSi concentrations, but with larger grain-size medians and higher mica concentrations were accumulated between AD 1500 and 1880. These features are related to a late period of the ‘Little Ice Age’ when major regional glacier advances occurred.

Trends in the upward shift of alpine plants

Questions: The 1990s were the warmest decade since the beginning of climate measurements. Based on almost 100 years of monitoring in the Swiss Alps, we asked (1) whether the extraordinary warm climatic conditions of the 1990s are reflected in the floristic composition of Alpine summit vegetation and, if so, (2) what the magnitude and rate of species change has been over the last few decades compared to the documented increase in species richness within the first 80 years of the 20th century. Location: Ten high mountain summits of the Bernina area in the southeastern Swiss Alps. Methods: Resurvey of the floristic composition of the uppermost altitudinal 10 m of these summits, applying the same methodology of former two surveys (1905 and 1985) and recording the presence of all vascular plant species. Results: Whereas the continued increase in plant species richness of high alpine summit vegetation is confirmed, our results also suggest an acceleration of the trend in the upward shift of alpine plants. Conclusion: Vegetation change in the southeastern Swiss Alps has accelerated since 1985, consistent with a climate change explanation.

Surface geometry of the Last Glacial Maximum (LGM) in the southeastern Swiss Alps (Graubünden) and its paleoclimatological significance

Abstract. Using detailed field evidence provided by trimlines on former nunataks, erratic boulders and the orientations of glacial striae, the surface geometry in the accumulation area during the Last Glacial Maximum was reconstructed for the area of SE Switzerland and adjacent Italy. Collectively, the trends of trimline elevations, flowlines deduced from glacial striae and bedrock morphology along the longitudinal valleys and their tributaries indicate that the former accumulation area consisted of an ice dome with the ice divide located over the area enclosed by Schlarignia, Cinuos-chel, Livigno and Piz Bernina. It attained a minimum altitude of approximately 3000 m. Modelling the topography of the ice surface using a Geographical Information System (GIS) is consistent with these results. The paleoclimatological signal included in this surface geometry was used to draw conclusions about the main atmospheric paleocireulation patterns and to outline the principal precipitation areas for the Alps during the last glaciation. It followed from this that ice build-up was principally related to dominating precipitation by southerly circulation (foehn). The prevaleance of foehn circulation most likely reflects a southward shift of the North Atlantic polar atmospheric front and of the accompanied storm track due to the advancing margin of sea ice. There exists good agreement between these assumptions and (a) results of global circulation models for the time of the LGM; (b) estimations of basal shear stress values and flow velocities for Ice Age glaciers; and (c) interpretations of paleowind indicators.