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Identifying ancient droughts in China

Date:
March 8, 2012
Source:
The Geological Society of America
Summary:
Drought events are largely unknown in Earth's history, because reconstruction of ancient hydrological conditions remains difficult due to lack of proxy. New research 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.
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The Tibetan Plateau is home to more than 1,500 large and small lakes that cover 24,183 square kilometers (9,337 square miles). The area is also the source of many of Asia’s major rivers, including the Brahmaputra, Indus, Ganges, Salween (Nu Jiang), Mekong (Lancang Jiang), Yangtze (Chang Jiang), and Yellow (Huang He) Rivers. In this image, sapphire lakes dot the plateau’s rugged surface. Many of the larger lakes, including Siling Co (Siling Tso) and Nam Co (Namptso) are largely ice-free, evidenced by their uniform navy color. Some of the smaller lakes, however, appear in paler shades of blue due to ice cover. Image from 2008.
Credit: NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center

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 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.

Xie and colleagues acknowledge Hongfu Yin of the China University of Geosciences at Wuhan for advocacy of the development of molecular geobiology, which makes this type of research possible.


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The above post is reprinted from materials provided by The Geological Society of America. Note: Materials may be edited for content and length.


Journal Reference:

  1. S. Xie, R. D. Pancost, L. Chen, R. P. Evershed, H. Yang, K. Zhang, J. Huang, Y. Xu. Microbial lipid records of highly alkaline deposits and enhanced aridity associated with significant uplift of the Tibetan Plateau in the Late Miocene. Geology, 2012; DOI: 10.1130/G32570.1

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The Geological Society of America. "Identifying ancient droughts in China." ScienceDaily. ScienceDaily, 8 March 2012. <www.sciencedaily.com/releases/2012/03/120308062539.htm>.
The Geological Society of America. (2012, March 8). Identifying ancient droughts in China. ScienceDaily. Retrieved August 5, 2015 from www.sciencedaily.com/releases/2012/03/120308062539.htm
The Geological Society of America. "Identifying ancient droughts in China." ScienceDaily. www.sciencedaily.com/releases/2012/03/120308062539.htm (accessed August 5, 2015).

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