Varve counting reveals high resolution radiocarbon reservoir age variations in palaeolake Lisan

The laminated lacustrine sediments deposited in the last glacial Lake Lisan represent annual deposits of primary aragonite and silty detritus that reflect the annual supply of bicarbonate-bearing freshwater to the lake. A varve-counting curve was constructed for the time interval of ca. 17.4-22 cal. ka BP based on aragonite U/Th, and atmospheric radiocarbon ages of organic debris recovered from the studied section. Radiocarbon in the primary (evaporitic) aragonite comprises both atmospheric and old carbon (reflecting the reservoir age). The aragonite reservoir ages were determined by comparing the aragonite radiocarbon dates to the varve counting curve, and are found to lie in the range 1900-600 a and display a continuous decline. This opens the possibility for high (annual) resolution monitoring of the reservoir age, similar in quality to tree ring counting, during the upper part of Marine Isotope Stage (MIS) 2. Our work also demonstrates that a 'uniform' reservoir age correction is inappropriate when determining the chronology of short-term climate events in lacustrine environments. Copyright (C) 2009 John Wiley & Sons, Ltd.