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have been built independently but have been dendro matched to each other. Additional radiocarbon dated floating chronologies from Zurich, the floaters from Durance Valley and several single trees appear to bridge the ≈200 year gap between the absolute chronology (12,593 cal BP). The filling of this gap will result in nearly a two millennia extension of the absolute chronology. Lateglacial pines usually grew under geomorphic stress and were gradually buried by loamy alluvia until the aggrading sediment killed the trees. Crossdating is complicated by both growth disturbances during the first 100 years of a trees life and the poorer preservation of the outer sapwood cells. Crossdating is normally based on an overlap of 50 up to 100 rings. Numerous decadal high precision 14 C-age determinations assisted and verified the dendrochronological crossdating. While fluctuations in the chronology are driven in part by local geomorphic activities, fluctuations may also coincide with short stadials and interruptions such as Older Dryas [OD], volcanic events (e.g., Laacher See eruption) and the Gerzensee deviation. Splitting the spline-detrended dataset from Zurich into subgroups demonstrates the potential for detecting common environmental signals. Variations in age-related trends indicate changes in environmental conditions over the 2500 years of AL, YD and Preboreal. Comparisons of tree growth and life span of trees between AL and YD suggest the YD to be rather a period of reduced winter temperatures than of low temperatures during the growing season. The dendroclimatic-style analyses presented are the first performed on Lateglacial tree-ring chronologies. Future efforts should focus on robustly preserving lower-frequency environmental variations and comparisons with other high resolution archives to quantify and calendrically date the main climatic fluctuations during Lateglacial and early Holocene. .10 Oxygen isotopic composition of lacustrine cellulose and authigenic calcite – new insight into Late Glacial and Holocene temperature changes in central Poland Klisch* M.A., Rozanski* K., Edwards** T.W.D. * AGH-University of Science and Technology, Krakow, Poland (monikaklisch@gmail.com) ** University of Waterloo, Waterloo, Ontario, Canada The δ 18 O of lacustrine calcite potentially provides information about both temperature and δ 18 O of lake water. If the δ 18 O of lakewater is strongly controlled by the δ 18 O of local precipitation, such as in a groundwater-fed lake having rapid throughflow, and lakewater temperature covaries with climatic temperature, then δ 18 O calcite may serve as a direct palaeothermometer. The "calibration" of the thermometer will be determined by two opposing relationships: temperature-dependent changes in the δ 18 O precipitation (c. +0.64‰/K for Poland; Duliński et al., 2001) and changes in the temperature-dependent equilibrium fractionation between calcite and water (c. – 0.23‰/K; Craig, 1965): Δδ 18 O calcite /ΔT = 0.64‰/K – 0.23‰/K ≈ 0.4‰/K (1) Equations like (1) have been used in many situations to reconstruct palaeotemperatures, including, for example, the development of a Holocene palaeotemperature record from δ 18 O calcite in the sediments of Lake Gosciaz. A source of significant uncertainty in this approach, however, is the possibility that changes in the hydrologic balance of a lake may alter the relation between δ 18 O precipitation and δ 18 O lakewater , potentially adding spurious non-temperature-dependent signals. Here we report results from a pilot study to test the δ 18 O calcite thermometer in Lake Gosciaz sediments by using aquatic cellulose δ 18 O to directly estimate the δ 18 O of lakewater at times in the past. Since the isotopic fractionation between cellulose and lakewater is believed to be constant (Edwards and McAndrews, 1989; Wolfe et al., 2007), this allows us to isolate the effects of temperature-dependent calcite-water fractionation to obtain estimates of absolute temperature changes during and between selected intervals over the past 12,000 years, without interference from possible changes in the hydrologic balance of the lake. The calibration of the cellulose-calcite thermometer in this case is described by: ΔT = (Δδ 18 O calcite – Δδ 18 O cellulose )/(-0.23 ‰/K) (2) Our data from Lake Gosciaz yield some striking differences in estimated temperature changes. For example, for the Younger Dryas/Preboreal transition, equation (1) gives an increase in lakewater temperature of about +5K, meanwhile equation (2) suggests +20 K, because of the incorporation of a pronounced shift of +6.5 ‰ observed in δ 18 O cellulose . This shift in δ 18 O cellulose almost certainly reflects the influence of increased evaporative enrichment of the lakewater in response to drier conditions, which obviously cannot be accommodated by equation (1). 1 Symposium 5: Quaternary Research
1 6 Symposium 5: Quaternary Research REFERENCES Craig H., 1965: The measurement of oxygen isotopes paleotemperatures, In Tongiorgi, E. (ed.): Stable Isotopes in Oceanographic Studies and Paleotemperatures. Spoleto, Consiglio Nazionale delle Ricerche, Laboratorio di Geologia Nucleare, Pisa, Italy, 161-182 Duliński, M., Florkowski, T., Grabczak, J.& Różański, K. 2001: Twenty-five years of systematic measurements of isotopic composition of precipitation in Poland, Przegląd Geologiczny 49, 250-256 (in Polish) Edwards, T.W.D & McAndrews, J.H. 1989: Paleohydrology of a Canadian Shield lake inferred from 18 O in sediment cellulose, Can.J.Earth Sci.26, 1850-1859 Wolfe, B.B., Falcone, M.D., Clogg-Wright, K.P., Mongeon, C.L., Yi Yi, Brock, B.E., St Amour, N.A., Mark, W.A., Edwards, T. W.D. 2007: Progress in isotope paleohydrology using lake sediment cellulose, Journal of Paleolimnology, Vol 37, No 2, 221-231 .11 Variation of denudation rates in the partially fluvially and partially glacially scupltured Hörnli region, Switzerland Kober, F. *, Abbühl, L.**, Ivy-Ochs, S.***, Schlunegger, F.**, Kubik, P.W.****,Baur, H*****, Wieler, R. *****, *Geological Institute, ETH Zürich, CH-8092 Zürich (kober@erdw.ethz.ch) ** University of Bern, Baltzerstrasse 1+3, CH-3012 Bern ***Ion Beam Physics, Particle Physics, ETH Zürich, CH-8093 Zürich and Department of Geography, University of Zürich, CH-8057 Zürich ****Ion Beam Physics, Particle Physics, ETH Zürich, CH-8093 Züich *****Isotope Geology and Mineral Resources, ETH Zürich, CH-8092 Zürich The Hörnli region has long been recognized for its landscape with opposite appearance: the lower regions (mainly the western Hörnli/Glatt valley and eastern Hörnli/Thur valley) are glacially overprinted and have smooth surface expressions; whereas the inner part of the Hörnli region (the Töss valley and surrounding highs) is a fluvial overprinted landscape. This fact is a result of an ice free "Hörnli-nunataker", at least during the Würm glaciation (Hantke, 1980). Slopes, relief, river longitudinal and cross profiles complement this view, being U-shaped, subdued and partially filled with terraces or V-shaped and steep, in glacial or fluvial settings, respectively. Currently, U-shaped valleys are getting incised due to the lowering of the base-level further outward and transmission of this base-level change headward, producing step-morphologies. This is a common feature observed in the Alps. Such morphologies are characterized as being in a transient stage - in the transition from the glacial to a fluvial dominated system (Schlunegger et al., 2002). However, it is controversial to what extend and with what rates the inherited shape and form of a landscape (glacial vs. fluvial) or a transient stage of a valley form controls short and long-term denudation rates. The Hörnli region is an ideally suited field area to study those denudation processes because it is uniform in lithology (Upper Sweetwater Mollasse), tectonics (being very slow but uniform uplifted) and climate. As such, crucial parameters in controlling denudation rates can be ignored and focus can be given to isolate parameters such as inherited topography and relief (von Blanckenburg, 2006). In order to quantify denudation rates in such a two-process dominated landscape we have sampled various rivers around the Hörnli region for catchment-wide denudation rate estimations using cosmogenic nuclides ( 10 Be, 21 Ne; in a second step we aim to analyze 14 C to capture short-term variations in a steady or transient stages of erosion). The dataset comprises samples from rivers which show completely fluvial, glacial or a combination of both morphologies. Sample analysis however is ongoing. Preliminary results from samples of the Töss river and tributaries yield denudation rates that are on the order of rates previously acquired for Swiss Middleland rivers (Norton et al., 2008; Wittmann et al., 2007), though denudation rates tend to be higher in glacially compared to fluvial overprinted catchments. Additionally, local variations occur which are not directly linkable to a glacial or fluvial origin. So far 10 Be and 21 Ne concentrations and denudation rates correlate poorly, which is largely due to obtain precise low 21 Ne-concentration in our samples. REFERENCES Hantke, R., 1980. Eiszeitalter, 1-3. Ott Thun Verlag, Thun. Norton, K.P., von Blanckenburg, F., Schlunegger, F., Schwab, M. and Kubik, P.W., 2008. Cosmogenic nuclide-based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the Swiss Alps.
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