HR: 11:20h
AN: PP42B-05    [Abstracts]
TI: Evidence from the NorthGRIP ice core for rapid development of playa areas from Western Chinese lakes reinforced by the 8.2 ka BP Holocene cold event
AU: Clausen, H B
PP42B-05 AF: Ice and Climate, Niels Bohr Institute, Juliane Mariesvej 30, Copenhagen, DK-2100 Denmark
AU: * Siggaard-Andersen, M
EM: mlsa@gfy.ku.dk
AF: Ice and Climate, Niels Bohr Institute, Juliane Mariesvej 30, Copenhagen, DK-2100 Denmark
AB: Analysis of soluble ions in the NorthGRIP ice core has revealed a lithium anomaly in the aerosol dust material around the 8.2 ka BP event. This anomaly is characterized by a sudden increase in soluble lithium concentrations, still increasing over at least one century, and reaching up to two orders of magnitude higher concentrations than prior to the event. Geochemical properties of lithium suggest that this lithium-anomaly is an effect of rock - water interactions in the dust source area. Mineral dust in Greenland ice cores has provenance distinctly in Western and North-Western Chinese desert areas. High abundances of lithium in this area are found in the Chaerhan lake playa located in the Qaidam basin north of the Tibetan plateau. During early Pleistocene the Qaidam basin was occupied by the mega Chaerhan Lake, which was steadily shallowing during Late Pleistocene. Lake records have previously shown that around 8 ka BP, the lake turned into a playa. The lithium anomaly in the NorthGRIP ice core around 8.2 ka BP is likely to be associated with the transformation of the Chaerhan salt lake into a playa, exposing large areas of clayish lake sediments to the atmosphere, and indicating that the transformation of the lake occurred very rapidly. A weakening of the Asian monsoons during the 8.2 ka BP indicated by monsoonal proxies, suggests that the 8.2 ka BP event effected a retreat of the range of monsoonal precipitation from inland Western China. Reduced precipitation combined with high evaporation during the Holocene optimum could have resulted in rapid changes in Western Chinese desert areas from relatively wet into very dry conditions.
DE: 3617 Alteration and weathering processes (1039)
DE: 4932 Ice cores (0724)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005