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

Abstract

<p><strong>Abstract.</strong> 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 (δ<sup>18</sup>O and δ<sup>13</sup>C) 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. <i>Limnocythere inopinata</i> is present throughout the studied interval, while <i>Limnocythere</i> 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 <i>Candona</i> is limited to periods of lower salinity. Valves of limnocytherinae species (incl. <i>L. inopinata</i>) 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 δ<sup>18</sup>O record, the δ<sup>18</sup>O values of ostracod valves do record relative changes of the lake volume, with lower values during high lake level periods. The δ<sup>13</sup>C 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 δ<sup>13</sup>C 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.</p>