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Abstract

Stalagmite grey level provides limited information about palaeoclima as its interpretation depends on numerous factors. One of the best approaches entails calibrating grey level sequences with instrumental climate data. In this study, grey level variation covering a 105-year span was analysed in a lamina stalagmite, known as Namjang1 (NJ1), from Namjang cave (98°12 12 E, 19°40 30 N), in north-western Thailand. The grey level time series positively correlated with the five-year running average of rainfall in October (r = 0.22, p < 0.05), the five-year running average of ratio of August to October to May to July rainfall (r = 0.38, p < 0.01), and the five-year running average of ratio of August to October and May to October rainfall (r = 0.35, p < 0.01). This indicates that the calibrated grey level record can provide a high resolution proxy of rainfall in the late monsoon season. The observed correlation between grey level and rainfall in the late monsoon season is consistent with our previous study on the same stalagmite that used δ 18O and growth rate parameters (Cai B, Pumijumnong N, Tan M, Muangsong C, Kong X, Jiang X, Nan S, J Geophys Res, 115, D21104), which further demonstrates that this stalagmite is a robust proxy of rainfall in the late monsoon season in north-western Thailand.