Search

The European Alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60-8 thousand years (ka) ago. We review quantitative and semi-quantitative approaches for reconstructing climatic variables in the Austrian and Swiss sector of the Alpine region within this time interval. Available quantitative to semi-quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids, cladocerans, co-leopterans, diatoms and pollen preserved in lake sediments and peat, the analysis of oxygen isotopes in speleothems and lake sediment records, the reconstruction of past variations in treeline altitude, the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence, and the interpretation of past soil formation processes, dust deposition and permafrost as apparent in loess-palaeosol sequences. Palaeoclimate reconstructions in the Alpine region are affected by dating uncertainties increasing with age, the fragmentary nature of most of the available records, which typically only incorporate a fraction of the time interval of interest, and the limited replication of records within and between regions. Furthermore, there have been few attempts to cross-validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence. Based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60-8 ka in the Alps and their forelands. These include (1) the compilation of individual, fragmentary records to longer and continuous reconstructions, (2) replication of climate records and the development of regional reconstructions for different parts of the Alps, (3) the cross-validation of different proxy-types and approaches, and (4) the reconstruction of past variations in climate, AuthorCount:19

The correlation of sedimentary and pedogenetic processes in Lower Austria is difficult due to significant discontinuities and local variability in soil formation. This hampers landscape reconstruction at a regional scale. However, at a local scale distinct landscape formation processes represented by a shift from fluvial to aeolian deposition can be observed in the brickyard of Langenlois, Lower Austria. Sedimentological and mineralogical analyses in combination with palaeontological finds suggest that the fluvial deposition took place during the Middle Pleistocene. This attribution is confirmed by infra-red stimulated luminescence (IRSL) dating, which gives a minimum age of 300 ka for the palaeosurface on which the fluvial sediments were deposited. This is consistent with a small faunal assemblage including Stephanorhinus sp., Dama sp. and an alcine cervid. Such a fauna is previously unknown in Austria; it indicates a Middle Pleistocene interglacial period. The low degree of weathering as well as Cryosols found in the loess sequence point to loess accumulation during the Last Glacial; the dating results (35–55 ka) indicate prolonged loess deposition. No signs of pedogenesis could be found; this is surprising because in other areas this period is known for weak soil development. The lack of soil formation seems to be specific to the western part of Lower Austria, as is the complete erosion of the last glacial maximum (LGM) loess, which can not be found at Langenlois.

Feldspar infrared stimulated luminescence (IRSL) signals saturate at 2000 Gy, i.e. 500–700 ka (assuming a dose rate of 3–4 Gy/ka, typical for loess) and it is therefore theoretically possible to date Middle Pleistocene loess. However, the accuracy of age estimates is hampered by anomalous fading, which leads to significant age underestimation. Fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses (as the growth curve approaches saturation). Recent studies have identified a post-IR IRSL signal that shows less fading and is thus less dependent on accurate fading corrections. This study builds upon these investigations and applies a post-IR IRSL SAR dating protocol to polymineral fine-grain samples of the loess/palaeosol sequence in Stratzing, Lower Austria. After a preheat at 320 °C (60 s) and an IR bleach at 50 °C (200 s) IRSL was measured at 290 °C for 200 s; the same set of conditions were used to measure the response to a test dose. Recycling ratios, recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation, although finite residual doses of up to 20 Gy are observed. For the oldest samples, the natural signal is in, or close to, saturation, indicating that fading is negligible in nature. This observation is inconsistent with the measured laboratory fading rates of 1–1.5%/decade and needs further investigation.

La secuencia de paleosuelo de loess del Pleistoceno superior de Val Sorda (Noreste de Italia) ha sido investigada utilizando métodos paleopedológicos, micromorfológicos y mineralógicos. Se ha puesto especial énfasis en parámetros magnéticos y análisis de minerales arcillosos. La base de la secuencia es un paleosuelo del Eemiano, que consiste en un horizonte Bt rubificado formado a partir de till. Este horizonte Bt está cubierto por loess, tres paleosuelos interestadiales y depósitos coluviales. Los tres paleosuelos interestadiales tienen una morfología de Chernozem y características que reflejan un paleoclima seco y de tipo continental. La cima de la secuencia está cubierta por till depositado durante el avance glacial de la etapa Solferino.

Se estudió una secuencia cuaternaria de loess-paleosuelos en Schattenhausen (SW de Alemania) por métodos isotópico). La composición de isótopos estables de carbón orgánico indican que vegetación de tipo C3 dominó el sitio durante la mayor parte del tiempo de formación de la secuencia. Sin embargo, se registró un periodo en el Pleniglacial Tardío con una oscilación pronunciada hacia C4 de los valores TM 13C (-16 to -19 ¿) de la materia orgánica. Las células de raíces calcificadas son isotópicamente diferentes de los carbonatos difundidos en la matriz del loess y del suelo. La composición de isótopos estables de carbono y oxígeno en las células de raíces calcificadas, en combinación con sus edades de 14C, sugieren que fueron formadas, al menos parcialmente, en el Holoceno.