Complex controls on the trace-element chemistry of non-marine ostracods: an example from Lake Patzcuaro, central Mexico

The calcitic shells of non-marine ostracods are sources of geochemical info rmation that have the potential to record changes in the water chemistry of closed-basin lakes resulting from variations in the hydrological budget wi thin the catchment. In particular the uptake of Sr and Mg into the shell ha s been shown to be a function of salinity, and salinity and temperature, re spectively. This paper assesses the trace-element chemistry records from 4 short (1.5-2.8 m) cores from Lake Patzcuaro, central Mexico, in the light o f a detailed limnological study of the lake. The following three environmen tal factors are believed to have influenced the interpretation of the trace -element chemistry record: (i) salinity: the salinity of Lake Patzcuaro lie s close to the calcite branchpoint, below which the linear relationship bet ween Mg/Ca or Sr/Ca and salinity has been lost in the fossil record; (ii) e nvironmental stresses: e.g. low HCO3- concentrations, produced poor ly calc ified valves. This study found this had no significant effect on the trace- element chemistry results; and (iii) solute composition of the host water: changes in the solute concentration of inwash waters played a primary role in determining major water chemistry changes within the lake. (C) 1999 Else vier Science B.V. All rights reserved.