RARE-EARTH PATTERNS WITH POSITIVE CERIUM ANOMALY IN ALKALINE WATERS FROM LAKE VAN, TURKEY

The distribution of rare-earth elements has been studied for aerobic, alkaline (pH 9.6), carbonate-rich waters from Lake Van, Turkey. Shale-normalized REE (REE(SN)) patterns display an almost linear increase from the light to the heavy REEs and strong positive Ce(SN) anomalies. There exist neither positive nor negative Gd(SN) anomalies. The REE(SN) patterns are consistent with domination of REE speciation in solution by (poly)carbonato-complexes, generating enrichment of the heavy REEs that is even more pronounced than that seen in seawater. This is the first report of positive Ce(SN) anomalies observed in REE(SN) patterns of aerobic natural waters. These anomalies apparently result from stabilization of (penta)carbonato-Ce(IV)-complexes in solution, leading to enhanced abundances of Ce in comparison with its trivalent REE neighbours. Thus, in remarkable contrast to seawater, positive Ce(SN) anomalies may be general features of alkaline, carbonate-rich and aerobic lake waters.