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Trace-element Variations in an Annually Layered Stalagmite Reveal Climatic Changes and Anthropogenic Pollution in Central China
author: source: Time:2014-04-15 font< big medium small >

Cave speleothems are ideal for reconstructing past climatic and environmental changes because of their accurate dates, high temporal resolution, and continuous growth. Studies of stable isotopes preserved in speleothems from the Asian monsoon region have achieved great success in recent years. However, trace-element researches in speleothems have received less attention.

In a recent paper, Dr. Liangcheng Tan and his colleagues have analyzed the variations of Sr/Ca, Ba/Ca, REE/Ca (REE: rare earth element), Zn/Ca, and Pb/Ca ratios in an annually layered stalagmite from central China during the last hundred years. By comparing with the observed temperature and rainfall records, they suggested that the Sr/Ca and Ba/Ca ratios in the stalagmite were primarily controlled by growth-rate variations. Higher temperature in this humid area could increase vegetation cover, microbial activity, and organic decomposition in the soil, resulting in enhanced pCO2, organic matter concentration and reduced pH, and consequently increased REE mobilization from the overlying soil layer and host rock, causing enhanced REE concentrations in the stalagmite over decadal to annual timescales. An notable increasing trend was seen in the Pb/Ca ratiosin the stalagmite since 1985,which was consistent with increased lead production in this area, indicating an increase in mine-derived lead pollution in the local environment over the past 30 years. This study highlight that absolutely-dated speleothem has the potential to record heavy metal contamination during historical time.

                  

Comparisons of temporal variations in (A) ΣREE/Ca, with (B) stalagmite growth rate, (C) local temperature, and the (D) Zn/Ca, (E) Pb/Ca, and (F) Pb/Zn ratios from stalagmite XL21. The dark yellow bars mark periods showing good agreement among the different records. Red arrows indicate the continuous increasing trend of the Pb/Ca and Pb/Zn ratios since 1985, which suggests increasing mine-derived Pb pollution in the local environment over the past 30 yr (gray areas).

Tan L., et al. Trace element variations in an annually layered stalagmite as recorders of climatic changes and anthropogenic pollution in Central China. Quaternary Research, 2014, 81: 181-188.

The article online: http://www.sciencedirect.com/science/article/pii/S0033589413001488

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