Trace element variability in single ostracod valves as a proxy for hydrochemical change in Nam Co, central Tibet, during the Holocene

Ostracod shells, belonging to three taxa (Leucocytherella sinensis Huang, 1982, ?Leucocythere dorsotuberosa Huang, 1982 and ?L. dorsotuberosa f. postilirata sensu Pang, 1985), were collected from two sediment cores from Lake Nam Co, on the central Tibetan Plateau. Two variants of LA–ICP–MS (laser ablation–inductively coupled plasma–mass spectrometry), spot and line-scan analyses, were used to investigate trace element concentrations (Mg, Sr, Ba, U and rare earth elements [REEs]) in single ostracod shells. The results suggest that the line-scan method can provide better precision than the spot analysis and is therefore preferred. No significant difference in trace element composition between taxa was detected in our study. Fluctuations of Mg/Ca and Sr/Ca in the shells show good agreement with the reported lake level changes during the Holocene, indicating that ostracod Mg and Sr can be related to palaeohydrochemical processes in this area. A high correlation between Ba/Ca and Sr/Ca was detected in our study, perhaps implying that both metals were controlled by the same mechanisms. A possible relationship between ostracod U/Ca and the past redox conditions on the lake bottom is discussed. Relatively low and constant La/Ca was observed, which could be due to the REE characteristics in the lake water, or ostracod biological processes, or even the associated Fe–Mn and/or organic contaminants. Future studies on more specimens from this area, especially shells from living ostracods, are essential to investigate the potential of ostracod Ba, U and REEs for use as palaeoenvironmental indicators.