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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Jan 2019

Research article | 02 Jan 2019

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

Ostracods as ecological and isotopic indicators of lake water salinity changes: The Lake Van example

Jeremy McCormack1, Finn Viehberg2,3, Derya Akdemir2, Adrian Immenhauser1, and Ola Kwiecien1 Jeremy McCormack et al.
  • 1Sediment and Isotope Geology, Ruhr-University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
  • 2Institute for Geology and Mineralogy, University of Cologne, Zülpicher Straße 49A, 50674 Köln, Germany
  • 3Institute for Geography und Geology, University of Greifswald, Friedrich-Ludwig-Jahn Str. 16, 17487 Greifswald, Germany

Abstract. Ostracods are common lacustrine calcitic microfossils. Their faunal assemblage and morphological characteristics are important ecological proxies, while their valves are archives of geochemical information related to palaeoclimatic and palaeohydrological changes. In an attempt to assess ostracod ecology (taxonomic diversity and valve morphology) combined with valve geochemistry (δ18O and δ13C) as palaeosalinity indicators, we analysed material from terminal and alkaline Lake Van (Turkey) covering the last 150 kyr. Despite a low species diversity, the ostracod faunal assemblage reacted sensitive to changes in the concentration of total dissolved salts in their aquatic environment. Limnocythere inopinata is present throughout the studied interval, while Limnocythere sp. A is restricted to the Last Glacial period and related to increased lake water salinity and alkalinity. The presence of species belonging to the genus Candona is limited to periods of lower salinity. Valves of limnocytherinae species (incl. L. inopinata) display nodes (hollow protrusions) during intervals of increased salinity. Both the amount of noded valves and the number of nodes per valve appear to increase with rising salinity, suggesting that node formation is related to hydrological changes (salinity and/or alkalinity). In contrast to Lake Van's inorganic δ18O record, the δ18O values of ostracod valves do record relative changes of the lake volume, with lower values during high lake level periods. The δ13C values of different species reflect ostracod habitat preferences (i.e., infaunal versus epifaunal) but are less sensitive to hydrological changes. However, combined with other proxies, decreasing Holocene δ13C values may indicate a freshening of the lake water compared to the low lake level during the Last Glacial period. The Lake Van example underscores the significance and value of coupling ostracod ecology and valve geochemistry in palaeoenvironmental studies of endorheic lakes basins.

Jeremy McCormack et al.
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Status: final response (author comments only)
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Jeremy McCormack et al.
Jeremy McCormack et al.
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Short summary
We juxtapose changes in ostracod taxonomy, morphology (noding) and oxygen (δ18O) and carbon (δ13C) isotopic composition for the last 150 kyr with independent low-resolution salinity proxies. We demonstrate that for Lake Van, salinity is the most important factor influencing the composition of the ostracod assemblage and the formation of nodes on the valves of limnocytherinae species. Ostracod δ18O shows a higher sensibility towards climatic and hydrological variations than the bulk isotopy.
We juxtapose changes in ostracod taxonomy, morphology (noding) and oxygen (δ18O) and carbon...