北京石花洞石笋微层层面有机物质的形成时间及机理初探

TIMING AND POSSIBLE MECHANISM OF ORGANIC SUBSTANCES FORMATION IN STALAGMITES LAMINAE FROM BEIJING SHIHUA CAVE

通过对北京石花洞滴水水溶性有机碳(DOC)近一个水文年的观测,发现不同点滴水DOC浓度均表现出明显的季节性变化, 7月中旬均有一个大的主峰出现。初步说明中国北方石笋微层的层面物质沉积于 7月雨季,主要来源于大的雨量对土壤中有机质的淋溶;洞穴顶板较薄的滴水点在 5月和 8月有明显的DOC次峰,可能与石笋亚年层形成有关。

The discovery of annual bands in calcite speleothems and their ready detection by fluorescence has generated much interest in the potential palaeoclimatic information stored in them. The cause of fluorescence has been attributed to organic substances incorporated within calcite. Then organic substances can be transported by percolating waters from soil and reach the cave. Some speleothems possess annual laminae which, have been hypothesized to have generated by seasonal variation in the concentration of organic substances in cave drip water. To test this hypothesis, we preformed studies on dissolved organic carbon in cave drip waters in Beijing Shihua Cave. The paper focuses on the flux of dissolved organic carbon (DOC) in cave drip waters for an eastern monsoon zone. Five drip waters in the Beijing Shihua Cave were analyzed for DOC concentration for about a hydrological year. The results show that there are seasonal variations in the DOC concentration in all drip waters. High level of DOC concentration is introduced during rain period in July. This suggests that higher abundances of organic substances are flushed from the soil by rains in July, which results in the formation of organic substances laminae of stalagmite. In May and August, sub-high-level of DOC concentration of drip waters occurred in site PL, SH and JG, which may be due to thinner bedrock. Moreover, the sub-high-level of DOC concentration is possibly correlated with the forming of sub-layer in stalagmites.