Constraints of authigenic carbonates on trace elements (Sr, Mg) of lacustrine ostracod shells in paleoenvironment reconstruction and its mechanism

Abstract

Molar ratios of Mg/Ca and Sr/Ca were measured in two species of ostracod shells preserved in the upper core (15 55 m) of the Heqing Basin in Yunnan Province, southwest China. By correlating the molar ratios between Mg/Ca and Sr/Ca and comparing them with Sr concentrations of the sediments, we suggested that: (1) the molar Mg/Ca and Sr/Ca ratio variations in respective ostracod primo reflected the changes in its ambient water composition and ecology; (2) the molar Sr/Ca ratios responded better to the salinity change linearly than Mg/Ca without aragonite precipitation in the system, and otherwise there was no linear relation between them; and (3) the molar Sr/Ca ratios were mainly controlled by salinity and authigenic carbonate precipitation, whereas the molar Mg/Ca ratios were related to both salinity and temperature. In fact, the rate of ostracod growth owing to temperature controls the fluctuation of Mg/Ca in shells. Here, more attentions should be paid to the constraint of authigenic mineral precipitation processes on the trace elements in ostracod shells and to the correlation between these trace elements in biogenic carbonates and compositions of the sediments in systems and in future in vitro experiments. ostracod shell, molar Sr/Ca ratio, molar Mg/Ca ratio, environmental response, Heqing Basin

Ostracod Mg/Sr/Ca and 87Sr/86Sr geochemistry from Tibetan lake sediments: Implications for early to mid-Pleistocene Indian monsoon and catchment weathering

“…For example, when authigenic aragonite precipitates in a lake, aragonite has a high affinity for Sr, thus depleting Sr in water, resulting in a decreased Sr/Ca of ostracodes even in high salinity (e.g. Xia et al 1997; Hu et al 2008). Therefore, Sr/Ca in ostracod shells is sometimes an uncertain proxy for palaeosalinity, especially when authigenic aragonite precipitates in hydrologically closed and evaporative lakes.…”

[RECTRACTED: A 120,000 Year Record of Paleoenvironmental Variability in Lake George, Australia]

“…The interactions between climates and aquatic parameters in the lake is manifested through changes in ostracod ecology and productivity (De Deckker and Forester, 1988). This influence of environmental variability on ostracod ecology have enabled multiple studies to reconstruct past environmental variability in lakes from indicator species and transfer functions (Chivas et al, 1986a;De Deckker et al, 1999;Hu et al, 2008;Ruiz et al, 2013). In Lake George, De Deckker (1981a, 1982b provides a comprehensive review on the taxonomy of ostracods and their corresponding environmental tolerance in terms of temperature and salinity ranges.…”

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

“…can precipitate together with calcium carbonates or incorporate into biogenic carbonates (such as otoliths and ostracod shells etc.) in a way of isomorphism (replacement of calcium ions), so that the concentrations of those elements in the biogenic carbonates mainly depend on the concentrations of the corresponding ions in its host water, which usually has a positive correlation (Campana, 1999;Hu et al, 2008). To some degree, the vital effect may work when some of the trace elements are absorbed by the organisms.…”