March 8, 2012
GEOLOGY: New Research Helps To Identify Ancient Droughts In China
Drought events are largely unknown in Earth's history, because reconstruction of ancient hydrological conditions remains difficult due to lack of proxy. New GEOLOGY research supported by China´s NNSF and MS&T uses a microbial lipid proxy of highly alkaline conditions to identify enhanced aridity in Miocene sediments on the Tibetan Plateau. This enhanced aridity is associated with significant uplift of the Tibetan Plateau nine million years ago.
According to the study's lead author, Xie Shucheng of the China University of Geosciences at Wuhan, the identification of ancient droughts and associated alkaline soils is particularly challenging at the regional or local level, and is beyond the predictive capabilities of available general circulation models (GCMs). GCMs, which are used to understand physical processes in the Earth surface system, are advanced tools for simulation of long-term temperature change.This new research proposes a microbial lipid proxy of highly alkaline conditions and enhanced aridity on the basis of investigation of modern Chinese soils. In modern Chinese soils, more abundant archaeal lipids known as iGDGTs (isoprenoid glycerol dialkyl glycerol tetraethers) relative to bacterial branched GDGTs were found to be associated with alkaline conditions and enhanced aridity. As a consequence, the ratio of archaeal GDGTs to bacterial GDGTs is indicative of the occurrence of ancient alkalinity and enhanced aridity.
Xie and colleagues also used the microbial lipid proxy to identify the enhanced aridity and alkalinity of Late Miocene sediments from the Zhada basin, which is located in the southwestern Tibetan Plateau, ~1000 km west of Lhasa. They find that the highly alkaline conditions and enhanced aridity identified in these sediments are associated with the most significant uplift of the Tibetan Plateau nine million years ago. The study's findings suggest that abrupt uplifts in the Tibetan Plateau can cause enhanced aridity in central Asia and a consequential development of alkaline soils.
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