摘要:
通过对江西万年县神农宫和陕西宁强县祥龙洞两个洞穴内、外温度连续19个月的同步监测以了解不同时间尺度下洞穴温度变化特征。结果显示神农宫及祥龙洞洞内温度存在明显的季节性变化:(1)神农宫夏秋季洞内温度在小时-日尺度上受到降水事件的影响显著,洞内夏秋季温度波动明显高于冬春季。祥龙洞监测点所处支洞环境相对封闭,温度波动在冬春季大于夏秋季,且全年洞温变幅小于神农宫。(2)旬—季节尺度的洞温数据显示,一个完整水文年内,神农宫两个监测点 SN1、SN2的温度变幅分别达到4.8℃和4.6℃,祥龙洞达到3.2℃。(3)两个洞穴洞内温度响应洞外气温的变化都存在滞后性,且冬春季滞后大于夏秋季,可能受深部围岩温度相对偏高、空气和围岩热导率的季节变化以及降水季节差异的影响。最后,针对洞温存在较大季节变化的洞穴讨论了不同沉积模式下洞穴温度变化对石笋氧同位素组成18 O 的可能影响。认为此类洞穴某一时期石笋δ18 O 出现较大幅度偏正或偏负不一定反映了外界气候的大幅变化,也可能仅仅是由于洞穴沉积条件发生改变而造成的。
Abstract:
Consecutive 1 9-month temperature measurements in Shennonggong and Xianglong caves were con-ducted synchronously.The results indicate that the temperature was not stable in both caves,but oscillated on both hourly and seasonal time scales.Temperature data from inside and outside the caves show that in Shennonggong cave the temperature fluctuated more significantly during the summer season than in winter, revealing the impact of the amount of precipitation on the cave temperature.On the other hand,in Xianglong cave the amplitude of temperature oscillations is smaller during summer than in winter,implying that the chamber structures limit ventilation during the summer as it is hard for cold cave air in to flow out the high opening of the cave.The temperature inside the cave corresponds well with temperature outside the cave, with summer-winter temperature differences of 4.8 ℃ (4.6 ℃ at second site)and 3.2 ℃ in Shennonggong and Xianglong caves,respectively.The cave temperature response time to outside temperature changes var-ied seasonally at both cave sites.The lags in the decrease of cave temperature at the end of autumn were lon-ger than those of the temperature increase at the end of spring in both caves.The different lags are likely due to the relatively high temperature in the deeper surrounding rock,the seasonal changes of the thermal con-ductivities of the air and the surrouding rock,as well as effects of seasonally changes in precipitation.It is noted that modern observations have shown the speleothem calcite may deposit only during the summer or winter (e.g.,summer deposition mode or winter deposition mode).Thus,it may be deduced that the shift in speleothem growth seasons (deposition mode)may induce significant calcite δ1 8 O changes in caves with large seasonal temperature changes.
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