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| Chloride as a Tracer and Climatic Change Record fr om Unsaturated Zone of Badain Jaran Desert |
| MA Jin-zhu1, LI Ding1, LI Xiang-hu1, EDMIMDS W M2 |
1. National Laboratory of Western China's Environment Systems, Center for Arid Environment and Paleoclimate Research, Lanzhou University, Lanzhou 730000, China;
2. British Geological Survey, Wallingford, Oxfordshire, UK |
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Abstract Chloride (Cl-) is ubiquitous in groundwater and soil water. One of the most useful properties of the Cl- ion is that highly soluble and therefore is a conservative tracer. The Cl- ion also has the advantage of simple analysis and of being conserved during the recharge process so that the Chloride Mass Balance (CMB) approach can be used to estimate the paleo-recharge and can provide a record of oscillating climate events at the decadal or longer scale. The 36Cl)/Cl can be well successfully used to estimate the pore water residence time over three different time scales, and well be used for validation of chloride cumulative age. The history of groundwater recharge and climatic changes during the last 800 years has been estimated and reconstructed using environmental chloride from unsaturated zone profile in the southeast Badain Jaran desert, NW China. By using a steady-state model for duplicate unsaturated zone chloride profiles, the long-term recharge at the site was estimated to be 1.3 mm·a-1. From one profile, which reached the water table, the climatic change events of 10~20 years duration were well preserved. There are 3 wet phases and 4 dry episodes during the recent 800 years according to the peaks and troughs of recharge rate calculated via chloride concentration and moisture content. It was a dry episode before 1290 AD. The time of 1500~1530 AD, which is an important period when climate occurred violent change from drought to wet. At the beginning of 1800s, the important turning events of the local climate from wet to dry occurred and then the climate deteriorated severely during the last 200 years. The unsaturated profile was compared with the Guliya ice core records. The agreement of wet and dry phases from 1200 to 1900 AD is quite good, whilst the conversely trends recorded during the last 100 years. It seems that the large-scale climate difference take place between mountain regions and the desert basin in the NW China during the 20th century, which are closely correspond to the water table reduction of some 1 m.
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Received: 06 May 2003
Published: 20 December 2004
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2004, Vol. 24 
