Evaluating the water balance of inland seas using isotopic tracers: the Caspian Sea experience

Natural variations of the stable isotopes oxygen-18 and deuterium in lakes and seas can be used in studies of their hydrological regime and hydroclima tic changes of their environment, as demonstrated by recent Caspian Sea iso topic investigations. Practical applications of this technique are often ha mpered by difficulties inherent in the determination of parameters defining the isotopic enrichment during the evaporation of the lake/sea surface wat er. Conventional evaporation pan experiments carried out to estimate these parameters often fail to arrive at sufficiently accurate values. A new appr oach in evaluating drying evaporation pan experiments is presented here bas ed on the determination of the initial slope of the curves describing the e nrichment of the heavy isotopes in the evaporation pan. This approach in co nnection with the use of 'in-lake' evaporation pans can lead to a substanti al reduction of uncertainties of isotope-based lake investigations. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.