DIATOM-INFERRED SALINITY IN PALAEOLAKES - AN INDIRECT TRACER OF CLIMATE-CHANGE

Lakes in arid and semi-arid regions respond to climatic change through shifts in lake water volume and ionic concentration. Because diatom d istribution is highly correlated with lake hydrochemistry, diatoms can be used to infer changes in salinity and brine composition and thus t o infer past climates. Here we critically examine the use of diatom-in ferred salinity as a climate proxy, with examples taken from both mode rn waterbodies and sedimentary profiles. Sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in sa line systems. Dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages. Furthermore thre shold effects, salinity regulation via groundwater seepage, antecedent conditions, and other aspects of local hydrology may modify the relat ionship between salinity change and climatic forcing. These complexiti es necessitate critical examination of the ecology and taphonomy of se dimentary assemblages, as well as evaluation of potential non-linearit ies in the salinity/climate relationship through comparison of diatom- inferred salinity with other proxy records of hydrochemical change, hi storical documents where they exist, and with other regional lake syst ems. (C) 1997 Elsevier Science Ltd.