Browsing by Author "Frenzel, P."
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Item Ostracod‐based reconstruction of Late Quaternary lake level changes within the Tangra Yumco lake system (southern Tibetan Plateau)(Journal of Quaternary Science, 2018-08) Alivernini, M.; Akita, L.G.; Ahlborn, M.; Börner, N.; Haberzettl, T.; Kasper, T.; Plessen, B.; Peng, P.; Schwalb, A.; Wang, J.; Frenzel, P.Tangra Yumco, a large saline lake located in the central–southern part of the Tibetan Plateau, liesin a hydrologically closed basin and is part of a cascade lake system including Tangqung Co, Tangra Yumco andXuru Co. The extension and position of this lake system makes it valuable for reconstructing palaeoclimaticvariations through the lake history and to compare both with the adjacent lake systems. We reconstructed LateQuaternary lake level changes based on data from two lacustrine sediment cores. A micropalaeontologicalanalysis focusing on Ostracoda was carried out combined with dating (14C,210Pb,137Cs), sedimentology andstable isotope data from bulk sediment. Ostracod analysis involves the quantitative documentation ofassociations. An ostracod-based transfer function for specific conductivity was applied to assess and refine lakelevel changes and to compare the results with other lake level reconstructions from the Tibetan Plateau forevaluating inter-regional climatic patterns. Seven ostracod species were detected, withLeucocytherella sinensisdominating the associations followed byLeucocythere?dorsotuberosa,Limnocythere inopinataandTonnacyprisgyirongensis.Fabaeformiscandona gyirongensis,Candona candidaandCandona xizangensiswere found in onlya few samples and at low percentages. The synthesis of ostracod-based environmental reconstruction andchronology for samples from Tangra Yumco reveals the evolution of the lake system during the past 17 ka. A lowlake level around 17 cal kaBPis followed by a recovering until the reaching of a high stand around 8–9 cal kaBP.Subsequently, between 7.7 and 2.5 cal kaBP, it remained relatively stable with a subsequent short-livinglowstand–highstand cycle at around 2 ka. Thereafter, the ostracod-based conductivity transfer function shows anincrease of conductivity corresponding to a lake level rising phase at around 0.4 ka. The recorded changes areindicators of past climatic conditions and refine the palaeoclimatic models in this area.Copyright#2018 John Wiley & Sons, Ltd.Item Quaternary Ostracoda as Palaeoenvironmental Proxies(2017-09-27) Frenzel, P.Ostracoda are minute crustaceans with a calcified, two-valved carapace. They are a classical group of micropalaeontology because of their long and rich record in earth history going back to Ordovician times. The presentation introduces into morphology, ecology and distribution of this group and demonstrates methods of its use in palaeoenvironmental analysis. Examples of application in coastal geology, palaeoclimatology, environmental micropalaeontology and geoarchaeology are givenItem Recent brackish water Foraminifera and Ostracoda from two estuaries in Ghana, and their potential as (palaeo)environmental indicators(Estuarine, Coastal and Shelf Science, 2021) Gildeeva, O.; Akita, L.G.; Biehler, J.; Frenzel, P.; Alivernini, M.To improve the indicator value of marginal marine Foraminifera and Ostracoda of Ghana, we analysed 22 surface sediment samples for microfauna. They were obtained from the Keta Lagoon and Densu Estuary covering a salinity range from marine waters to 17.5 and one sample within the hyperhaline range (70). Except one, all samples contain Ostracoda and Foraminifera. There are 34 ostracod species belonging to 24 genera. Dominating is Cyprideis remanei Klie, 1940, other abundant species are Pseudoconcha sp., Pseudoconcha hartmanni Omatsola, 1970, Loxoconcha lacunensis Omatsola, 1970 and Chrysocythere foveostriata Brady, 1870. We found 28 Foraminifera species belonging to 22 genera with the dominant taxa Ammonia sp. and Quinqueloculina spp. There are five associations, which are mainly driven by the hydrological regime and organic pollution. In contrast to a usual diversity trend reflecting high levels of pollution by lower diversity, our results show higher diversity associated with sites of higher pollution levels. The most tolerant (salinity and pollution) ostracod taxon is Cyprideis remanei, which is occurring over the whole salinity range documented as well as in contaminated areas with very high LOI and heavy metal concentrations. In the investigated samples we found many deformed Foraminifera with anomalies like multiple tests, changes in coiling and aberrant shapes of the chambers. Ongoing investigations in estuaries of Ghana are expanding our data set and will provide a better understanding of species-specific reactions of Ostracoda and Foraminifera to anthropogenic pressure.