Global Change Abstracts The Swiss Contribution - SCNAT

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158 Global Change Abstracts – The Swiss Contribution | Past Global Changes cover) and pollen for the Juniperus site (eg, r(2) = 0.76 between crown cover and arboreal pollen, AP) and the Picea site (r(2) = 0.85), whereas the linkage is weaker at the Juglans site (r(2) = 0.35) and in mixed forests (r(2) = 0.32). The results of the surface samples of moss polsters are compared and discussed with surface samples of lake sediments that were taken at the same locations. We use vegetational maps from around the lakes to discuss the link between vegetation and pollen at extra-local scales (800 m around the sites). These comparisons show that AP underestimates the effective tree cover around all sites, with in extreme cases densely forested areas corresponding to AP values as low as < 60; 30%. We explain this finding by the prevalent background pollen load that derives from the dry lowland and slope steppes (Artemisia, Chenopodiaceae, Poaceae). Our investigation may improve the reconstruction of Quaternary vegetation and climate history of these forest belts in Kyrgyzstan (Central Asia) on the basis of fossil pollen assemblages from mire and lake sediments. It provides new insights into the pollen reflection of forest isles (eg, on humid slopes or mountain tops) that are surrounded by continental steppes; a vegetational situation that may be used as an analogue for the conditions during the full glacial in Eurasia and Northern America. Holocene, 2007, V17, N5, JUL, pp 599-611. 08.1-313 Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2cal ka, and Little Ice Age events Benson L, Madole R, Kubik P W, Mcdonald R USA, Switzerland Paleontology , Meteorology & Atmospheric Sciences , Geomorphology , Geology Surface-exposure (Be-10) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-mlong Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to similar to 3.0 Be-10 ka. (1) Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 Be-10 ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0-11.7 Be-10 ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation. Quaternary Science Reviews, 2007, V26, N11-12, JUN, pp 1638-1649. 08.1-314 Palaeoclimate-induced range shifts may explain current patterns of spatial genetic variation in renosterbos (Elytropappus rhinocerotis, Asteraceae) Bergh N G, Hedderson T A, Linder H P, Bond W J South Africa, Switzerland Paleontology , Microbiology , Plant Sciences , Meteorology & Atmospheric Sciences The impact of Pleistocene climatic fluctuations on the distributions of plant species in the Greater Cape Floristic Region is largely unknown. We used a molecular fingerprinting tool, inter-simple sequence repeat (ISSR) PCR to examine the spatial distribution of genetic variation in the common and widespread shrub Elytropoppus rhinocerotis. We wished to test the hypothesis that refugia for the species were located in areas which were buffered from marked variations in precipitation between glacial and interglacial periods. Populations from less protected areas, in contrast, should have suffered size reductions or extinctions during the dry Holocene optimum. We detected a large amount of genetic variation in the species, which was apportioned largely amongst individuals within populations rather than amongst populations or regions, as expected for an outcrossing and well-dispersed plant species. However, there was significant spatial structure and an uneven distribution of diversity across the range. Geo-
Global Change Abstracts – The Swiss Contribution | Past Global Changes graphic distance is a very poor predictor of genetic distance between localities, especially towards the cast of the range. This may be due to range alteration over the time-scale reflected by ISSR polymorphism. Inter-SSR variation declined from south to north in the western arm of the range, consistent with the prediction of Holocene aridification starting first and being most extreme in the north. Areas shown by the marker to harbour populations with high levels of variability include most parts of the eastern arm of the range, and the Kamiesberg highlands. Possible explanations for the observed patterns of ISSR variation are discussed. Taxon, 2007, V56, N2, MAY, pp 393-408. 08.1-315 Decadal-scale autumn temperature reconstruction back to AD 1580 inferred from the varved sediments of Lake Silvaplana (southeastern Swiss Alps) Blass A, Bigler C, Grosjean M, Sturm M Switzerland, Sweden Limnology , Geology , Geochemistry & Geophysics Paleontology 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 degrees 27’N, 9 degrees 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 degrees 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 degrees 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. Quaternary Research, 2007, V68, N2, SEP, pp 184-195. 159 08.1-316 Signature of explosive volcanic eruptions in the sediments of a high- altitude Swiss lake Blass A, Grosjean M, Livingstone D M, Sturm M Switzerland Paleontology , Limnology , Geology The analysis of 125 years of well-dated varved sediments in Lake Silvaplana, located at 1,791 m a.s.l. in the Upper Engadine region of south-eastern Switzerland, reveals that 7 out of the 8 climatically relevant explosive volcanic eruptions between A.D. 1880 and 2004 were followed by distinct peaks in median grain-size. Although the underlying mechanisms are yet unclear, an analysis of local meteorological data suggests that this phenomenon is unlikely to be related to any change in air temperature associated with the eruptions, but instead may be related to an increase in autumn precipitation subsequent to the eruptions that led to the erosion and fluvial transport of particles larger than normal. Journal of Paleolimnology, 2008, V39, N1, JAN, pp 35-42. 08.1-317 A European pattern climatology 1766-2000 Casty C, Raible C C, Stocker T F, Wanner H, Luterbacher J Switzerland Meteorology & Atmospheric Sciences , Modelling , Paleontology Using monthly independently reconstructed gridded European fields for the 500 hPa geopotential height, temperature, and precipitation covering the last 235 years we investigate the temporal and spatial evolution of these key climate variables and assess the leading combined patterns of climate variability. Seasonal European temperatures show a positive trend mainly over the last 40 years with absolute highest values since 1766. Precipitation indicates no clear trend. Spatial correlation technique reveals that winter, spring, and autumn covariability between European temperature and precipitation is mainly influenced by advective processes, whereas during summer convection plays the dominant role. Empirical Orthogonal Function analysis is applied to the combined fields of pressure, temperature, and precipitation. The dominant patterns of climate variability for winter, spring, and autumn resemble the North Atlantic Oscillation and show a distinct positive trend during the past 40 years for winter and spring. A positive trend is also detected for summer pattern 2, which reflects an increased influence of the Azores High towards central Europe and the Mediterranean coinciding with warm
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