Wir untersuchen Klimawandel in der geologischen und historischen Vergangenheit und dessen Auswirkungen im unmittelbaren Lebensraum des Menschen sowie Änderungen des Erdmagnetfelds. Ein Schwerpunkt unserer Forschung sind schnelle Klimaänderungen, die sich in wenigen Jahren bis Jahrzehnten ereignet haben. Deshalb arbeiten wir mit zeitlich hochauflösenden terrestrischen Geoarchiven, wie jahresgeschichteten (warvierten) Ablagerungen in Seen und Baumringen. Ein zentraler Teil unserer Arbeit ist die Erstellung präziser Datierungen unserer Geoarchive als Grundvoraussetzung für verlässliche Rekonstruktionen von Änderungen in der Vergangenheit.
Schnelle Klimawechsel in der Vergangenheit sind natürliche Experimente, mit denen wir einen Einblick in die Ursachen und die Dynamik solcher Änderungen bekommen, um damit besser auf zukünftige Entwicklungen vorbereitet zu sein. Dazu nutzen wir Informationen aus der Struktur und chemischen Zusammensetzung von Jahresschichten (Proxidaten), die wir mit Beobachtungen heutiger Prozesse (Monitoring) abgleichen. Unsere Vision ist die Verknüpfung langer Zeitreihen aus unseren Geoarchiven mit instrumentellen Daten, um derzeitige Veränderungen in einen langfristigen Kontext stellen zu können.
Norbert R. Nowaczyk, Jiabo Liu, Birgit Plessen, Antje Wegwerth, Helge W. Arz: A High‐Resolution Paleosecular Variation Record for Marine Isotope Stage 6 From Southeastern Black Sea Sediments - JGR Solid Earth | doi:10.1029/2020JB021350
A full‐vector paleosecular variation (PSV) record (inclination, declination, and relative paleointensity) from the pen‐ultimate glacial (130–180 ka) could be constructed from a total of 12 sediment cores recovered from the Arkhangelsky Ridge in the SE Black Sea. Stacking of the individual partly fragmented records was achieved by a detailed correlation using high‐resolution data records from X‐ray fluorescence scanning, Ca/Ti and K/Ti log‐ratios, as well as magnetic susceptibility. Age constraints are provided by a detailed composite oxygen isotope stratigraphy from three of the cores, correlated to U‐Th‐dated speleothem oxygen isotope records from Hungary and Turkey. The temporal resolution of the stacked paleomagnetic data records is 200 years. Practically, this data set is the first high‐resolution PSV record for SE Europe/SW Asia from marine isotope stage 6, comprising inclination, declination and relative paleointensity. Besides an easterly swing in declination at ∼159 ka and a pronounced intensity low together with low inclinations at ∼148 ka, both not reaching an excursional PSV index of >0.5, the obtained directional variations reflect only normal PSVs, with a PSV index of <0.3.
Dräger, N., Plessen, B., Kienel, U., Słowiński, M., Ramisch, A., Tjallingii, R., Pinkerneil, S., Brauer, A. (2019 online first): Hypolimnetic oxygen conditions influence varve preservation and δ13C of sediment organic matter in Lake Tiefer See, NE Germany. - Journal of Paleolimnology. | doi:10.1007/s10933-019-00084-2
Stable carbon isotopes of sediment organic matter (δ13COM) are widely applied in paleoenvironmental studies. Interpretations of δ13COM, however, remain challenging and factors that influence δ13COM may not apply across all lakes. Common explanations for stratigraphic shifts in δ13COM include changes in lake productivity or changes in inputs of allochthonous OM. We investigated the influence of different oxygen conditions (oxic versus anoxic) on the δ13COM values in the sediments of Lake Tiefer See. We analysed (1) a long sediment core from the deepest part of the lake, (2) two short, sediment–water interface cores from shallower water depths, and (3) OM in the water column, i.e. from sediment traps. Fresh OM throughout the entire water column showed a relatively constant δ13COM value of approximately − 30.5‰. Similar values, about − 31‰, were obtained for well-varved sediments in both the long and short, sediment–water interface cores. In contrast, δ13COM values from non-varved sediments in all cores were significantly less negative (− 29‰). The δ13COM values in the sediment–water interface cores from different water depths differ for sediments of the same age, if oxygen conditions at the time of deposition were different at these sites, as suggested by the state of varve preservation. Sediments deposited from AD 1924 to 1980 at 62 m water depth are varved and exhibit δ13COM values around − 31‰, whereas sediments of the same age in the core from 35 m water depth are not varved and show less negative δ13COM values of about − 29‰. The relation between varve occurrence and δ13COM values suggests that δ13COM is associated with oxygen conditions because varve preservation depends on hypolimnetic anoxia. A mechanism that likely influences δ13COM is selective degradation of OM under oxic conditions, such that organic components with more negative δ13COM are preferably decomposed, leading to less negative δ13COM values in the remaining, undegraded OM pool. Greater decomposition of OM in non-varved sediments is supported by lower TOC concentrations in these deposits (~ 5%) compared to well-varved sediments (~ 15%). Even in lakes that display small variations in productivity and terrestrial OM input through time, large spatial and temporal differences in hypolimnetic oxygen concentrations may be an important factor controlling sediment δ13COM.
Ben Dor, Y., Neugebauer, I., Enzel, Y., Schwab, M. J., Tjallingii, R., Erel, Y., Brauer, A. (2019): Varves of the Dead Sea sedimentary record. - Quaternary Science Reviews, 215, pp. 173-184. | doi:10.1016/j.quascirev.2019.04.011
- The Dead Sea is the only deep hypersaline lake with varved sediments.
- The chronological and paleoclimatic value of Dead Sea varves is demonstrated.
- The interpretation of alternating aragonite-detritus laminae as varves is evaluated.
- Lake monitoring confirms the interpretation of laminated halite as varves.
- Distinguishing between annual and non-annual laminations requires micro-facies analyses.
The sedimentary record of the Dead Sea provides an exceptional high-resolution archive of past climate changes in the drought-sensitive eastern Mediterranean-Levant, a key region for the development of humankind at the boundary of global climate belts. Moreover, it is the only deep hypersaline lake known to have deposited long sequences of finely laminated, annually deposited sediments (i.e. varves) of varied compositions, including aragonite, gypsum, halite and clastic sediments. Vast efforts have been made over the years to decipher the environmental information stored in these evaporitic-clastic sequences spanning from the Pleistocene Lake Amora to the Holocene Dead Sea. A general characterisation of sediment facies has been derived from exposed sediment sections, as well as from shallow- and deep-water sediment cores. During high lake stands and episodes of positive water budget, mostly during glacial times, alternating aragonite and detritus laminae (‘aad’ facies) were accumulated, whereas during low lake stands and droughts, prevailing during interglacials, laminated detritus (‘ld’ facies) and laminated halite (‘lh’ facies) dominate the sequence. In this paper, we (i) review the three types of laminated sediments of the Dead Sea sedimentary record (‘aad’, ‘ld’ and ‘lh’ facies), (ii) discuss their modes of formation, deposition and accumulation, and their interpretation as varves, and (iii) illustrate how Dead Sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies.