Ostracod shell chemistry as proxy for paleoenvironmental change

摘要

The application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades. Most studies have investigated Mg and Sr in ostracod shells as proxies for temperature and salinity, and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems. Only a few preliminary studies have used trace metals in paleolimnological studies such as Cd, Ba and Zn as paleonutrient indicators, or Mn, Fe and U as redox and oxygenation indicators. This paper reviews the state of the art of geochemical analyses in microfossils such as ostracods, foraminifera, and corals, and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies. In paleoceanography, foraminifera and corals are most prominently used to reconstruct past climate conditions. Well-established proxies such as δ~(18)O, Mg/Ca and Sr/Ca provide information about changes in sea surface temperatures. In addition, a great number of new proxies have been developed recently, such as radiogenic isotopes and redox sensitive trace elements. In paleolimnology, ostracod shell chemistry is widely used to assess paleohydrological changes. Reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as Mg/Ca and Sr/Ca ratios, but depending on the hydrological and geological settings of the lake system, local calibrations are needed to assess which proxy is suited to reflect which processes. New proxies need to be tested by novel techniques that recently have become available. Compared to conventional instrumentation used in ostracod shell chemistry, methods such as Laser Ablation ICP-MS and NanoSIMS allow single shell analysis and provide high-resolution data. The potential of ostracods in paleolimnology is not yet fully assessed, but can be developed by learning from paleoceanographic studies.