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Poster Kurzvorträge - Themenblock 3: Paläoklima, Sedimentologie, Boden
15:30 - 15:33
Ein ~15 ka δ2Hn-alkane-Record vom Bichlersee, Oberbayern
1Physical Geography, Institute of Geography, Friedrich Schiller University Jena, Jena, Germany; 2Heisenberg Chair of Physical Geography, Institute of Geography, Technische Universität Dresden, Dresden, Germany
Die Alpen sind eine Schlüsselregion, um vergangene Veränderungen des Klimas und der atmosphärischen Zirkulation in Europa zu rekonstruieren. Biomarker- und komponentenspezifische Stabilisotopenanalysen in Seesedimenten bieten dabei großes Potenzial, sind aber bisher im Alpenraum kaum angewendet worden. Wir präsentieren neueste Ergebnisse vom Bichlersee, Oberbayern, die vor allem das Spätglazial hochaufgelöst (50 Proben) abdecken. Die Blattwachsmuster (n-Alkane) zeigen durchweg einen dominanten Eintrag langkettiger Homologe (C27 bis C33), also ein terrestrisches Signal (im Vergleich zu kürzerkettigen, aquatischen Homologen von Algen und Makrophyten). Die markante Abnahme der mittleren Kettenlänge von >30 auf <30 am Ende der Jüngeren Dryas hängt vermutlich mit der Wiederbewaldung zu Beginn des Holozäns zusammen. Die 2H-Isotopie der dominanten C29- und C31-Kettenlängen ändert sich sehr konsistent und nahezu stetig im Verlauf des Spätglazials von –180 auf –210‰, um dann im Holozän wieder auf positivere Werte anzusteigen. Auch wenn wir dies im Moment insbesondere auf eine Änderung der Niederschlagsisotopie zurückführen, können wir den Einfluss sich verändernder Vegetation – z. B. durch mehr Gräser während des Spätglazials – und evapotranspirativer Anreicherung nicht quantifizieren. Dazu sind für die folgenden Arbeiten komponentenspezifische 18O-Analysen an Zuckern geplant.
15:33 - 15:36
Last millennium hydroclimate variability from Lake Höglwörth, Bavaria, Germany
1Physical Geography, Institute of Geography, Friedrich Schiller University, Jena, Germany; 2Heisenberg Chair of Physical Geography, Institute of Geography, Technische Universität Dresden, Dresden, Germany
During the past decades, unusual rapid warming and significant changes in the precipitation seasonality and pattern have been recorded in almost the entire European Alps. To put these recent changes and climate projections into an adequate context, reconstructions of paleoenvironmental and –climate dynamics on a regional and local scale are prerequisite. Moreover, paleoenvironmental studies help to identify drivers and forcings of past (hydro)climate variability. In this study we present a high resolution continuous environmental and hydroclimatic record from a small forealpine lake “Lake Höglwörth” (Bavaria, Germany), covering the past millennium based on n-alkanes and their compound-specific isotopic composition (δ2H). The relatively high abundance of C27 to C33 indicates input from higher terrestrial plants, but also abundance of C23 and C25 document the presence of aquatic plants, particularly from AD 1100 to 1300, between AD 1550 and 1750, as well as since 1850. C29 and C31 reveal very similar isotopic (δ2H) signal and down-core trends. They are relatively enriched (~ -202.1 ‰ for C31) between AD 1100 and 1450 with maximum enrichment (~ -180 ‰ for C31) between AD 1200 and 1300. Rather depleted values (~ -210 ‰ for C31) are found from AD 1450 to 1650, however, an enrichment is obvious after 1650. Due to the primarily origin of the C29 and C31 in terrestrial vegetation, we assume that δ2H of these n-alkanesmainly reflects past changes in the isotopic composition of precipitation. However, effects related to changing vegetation and evapotranspirative enrichment cannot be ruled out. However, C23 is variably enriched compared to C29 and C31, and we suggest that this reflects the evaporative enrichment of the lake water and might thus enable to calculate relative humidity. We are now aiming to (i) increase the temporal resolution (continuous ~ decadal), (ii) compare our results to other regional records, and (iii) establish high-resolution d18O records from sugar biomarkers in order to more robustly disentangle the various factors influencing the isotopic composition of the leaf waxes.
15:36 - 15:39
Ca isotope partitioning upon experimental precipitation of carbonated hydroxy-apatite (CHAP)
1Institut für Mineralogie, Westfälische Wilhelms Universität Münster; 2Leibniz Institute of Baltic Sea Research and University of Greifswald, Deutschland; 3Institute of Geosciences, Goethe-University of Frankfurt, Germany, and Senckenberg Biodiversity and Climate Research Center, Frankfurt (Main), Germany; 4Economic Geology, University of Greifswald, Germany; 5Department of Experimental and Applied Mineralogy, Georg-August-University of Göttingen, Germany
Carbonated hydroxy-apatite (CHAP) was experimentally synthesized in batch-type set-ups by mixing of calcium (Ca)- and phosphate-bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11° and 65°C (Gussone et al., 2020). Compositional changes of the experimental solution and solid phase products were followed by elemental analysis, Raman spectroscopy, scanning-electron microscopy, and powder XRD. In the mixing experiments, crystallization of CHAP took place following the precipitation of metastable brushite as precursor that was then transformed into CHAP. In the transformation experiments using synthetic calcite as a precursor phase it was found that the reaction at pH values between 7.5 and 7.9 occurs via the direct replacement of calcium carbonate by CHAP.
Calcium isotope fractionation led to an enrichment of the light isotope in the solid CHAP compared to the aqueous solution by about -0.5 to -1.1 ‰, independent from the experimental approach, and the magnitude was essentially independent of temperature. The metastable brushite formed prior to transformation to CHAP showed a reduced fractionation compared to the CHAP. The observed Ca isotope fractionation into the CHAP lattice resembles that of natural phosphorites and lies within the range of the view existing theoretical and experimental studies.
Reference: Gussone N., Böttcher M.E., Conrad A.C., Fiebig J., Pelz M., Grathoff G., Schmidt B.C. (2020) Calcium isotope fractionation upon experimental apatite formation. Chem. Geol., 551, 119737
The study was supported by German Science Foundation (DFG) to M.E.B and J.F. within the EXCALIBOR project (BO1548/8 and FI 948/7), and to N.G. (GU1035/10), and by Leibniz IOW.
15:39 - 15:42
Stable isotopic and trace elemental fingerprints in carbonate precipitated by modern hard-water creeks of the temperate climate zone
1Leibniz Institute of Baltic Sea Research, FRG; 2Marine Geochemistry, University of Greifswald, FRG; 3Present address: Hydroisotop, Schweitenkirchen, FRG; 4Naturhistorisches Museum, Berlin, FRG; 5Applied Geology, University of Greifswald, FRG; 6Ecoandmore, Freiburg, FRG
Processes in the dissolved carbonate system of surface waters may contribute and are sensitive to variations of boundary conditions associated with climate change. Carbon dioxide super- and calcium carbonate -saturated ground waters that emerge from springs lose dissolved carbon dioxide to the atmosphere; this process leads to the development of CaCO3 supersaturation of the aqueous solution. When exceeding a critical value, solid carbonates precipitate, thereby linking the past marine with the present terrestrial carbon cycles. The associated distribution of trace elements and stable isotopes leads to proxy formations. The magnitude of trace element and isotope fractionations is linked to non-equilibrium processes, impacted by the initial solution composition, hydrodynamics, and possible biological activity in the stream beds.
Two examples of recent sinter formation from streams in the temperate climate zone were investigated: Site R is positioned in a cliff zone of Rügen Island, southern Baltic Sea and Site W near Westerhof in the south-western Harz foreland. Two phases of surface water development can be differentiated: An induction period starting at the spring, where only degassing of carbon dioxide takes place, and a second stage where calcite formation from the highly supersaturated solution is continuously driven by further degassing. The liberation of CO2 is associated with an enrichment of the heavy carbon isotope in the remaining dissolved inorganic carbon. By following the isotope and trace element composition of aqueous solutions and recent calcite precipitates along the flow path, distribution coefficient (Li, Na, Mg, Sr, Ba, SO4, 13C, 18O) are derived. The empirical quantitative observations at Site W can be compared with observations dating back to the late 60s of the last century. Those at Site R are compared to results from laboratory experiments using the natural water as starting solution. Furthermore, the distribution coefficients are compared to calibrated experimental studies to estimate calcite precipitation rates. Trace-element based rate estimates for Site W are higher than published direct measurements, which is likely due to hydrodynamic boundary conditions impacting the in-situ growth experiments. Idiomorphic BaSO4 was observed in recent carbonate sinter at Site W for the first time, which is in agreement with slight supersaturations modeled for the stream water.
At the bottom of the cliff (Site R), the carbonate stream water is finally entering the Baltic Sea where mixing with brackish surface waters occur. The excess in dissolved CO2 compared to the atmosphere is enhancing the degassing capacity in the mixed coastal waters.
15:42 - 15:45
Identification of paleosols of a Namibian sediment core (WW203303) using pedogenic features, trace fossils and stable isotope compositions
1TU Darmstadt, Deutschland; 2Federal Institute for Geosciences and Natural Resources, Geozentrum Hannover
Stable carbon and oxygen isotopes of carbonates from paleosols can be used as proxies to reconstruct paleoclimate and paleoenvironment conditions (Cerling & Quade, 1993). Paleosols are identified from the Namibian sediment core WW203302 (Houben et al., 2020) using stable isotopes, pedogenic features and a conceptual model generated by Hasiotis et al. (2012). Pedogenic features such as nodules, mottling and peds are clear indexes for paleosol in sediment. However, these features appear only sporadically in this 400 m long sediment core, trace fossils are used as index to distinguish paleosols from sediment.
Bioturbation patterns generally created by trace fossils occur nearly in the entire sediment core. Density, abundance, and depth of bioturbation follow the degree of soil development (Hasiotis et al. 2012). Pedogenesis, bioturbation and sedimentology are criteria to classify paleosols in sediment sections, from which nodules were selected, into compound, composite, and cumulative fractions (Kraus, 1999). Stable carbon and oxygen isotopes of bulk samples from different types of paleosols are compared to that of nodules to examine whether bulk samples from this sediment core can be used for paleoclimate interpretations.
The δ13C values of all types of bulk samples show basically the same trend as nodule samples (r2=0.88), bulk samples from well-developed paleosols, compound and composite paleosols show a better correlation to corresponding nodule samples than cumulative paleosols and phreatic layers for δ18O values (r2=0.64). Covering sands of nodule samples are more negative than corresponding nodules for δ18O, but either more negative or positive than nodules for δ13C, regardless of soil types. Furthermore, dolomites as a component of nodule samples, are generally more enriched in δ18O and mostly depleted in δ13C, regardless of soil type.
Cerling, T. E., & Quade, J. (1993). Stable Carbon and Oxygen Isotopes in Soil Carbonates. 217–231.
Hasiotis, S. T., & Platt, B. F. (2012). Exploring the sedimentary, pedogenic, and hydrologic factors that control the occurrence and role of bioturbation in soil formation and horizonation in continental deposits: An integrative approach. The Sedimentary Record, 10(3), 4–9
Houben, G. J., Kaufhold, S., Miller, R. M. G., Lohe, C., Hinderer, M., Noll, M., Hornung, J., Joseph, R., Gerdes, A., Sitnikova, M., & Quinger, M. (2020). Stacked megafans of the kalahari basin as archives of paleogeography, river capture, and cenozoic paleoclimate of Southwestern Africa. In Journal of Sedimentary Research (Vol. 90, Issue 9)
Kraus, M. J. (1999). Paleosols in clastic sedimentary rocks: Their geologic applications. Earth Science Reviews, 47(1–2), 41–70.