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首页> 外文期刊>Journal of caves and karst studies: the National Speleological Society bulletin >VARIABLE CALCITE DEPOSITION RATES AS PROXY FORPALEO-PRECIPITATION DETERMINATION AS DERIVEDFROM SPELEOTHEMS IN CENTRAL FLORIDA, U.S.A.
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VARIABLE CALCITE DEPOSITION RATES AS PROXY FORPALEO-PRECIPITATION DETERMINATION AS DERIVEDFROM SPELEOTHEMS IN CENTRAL FLORIDA, U.S.A.

机译：在美国佛罗里达州中部，变化的方解石沉积速率与近岸古沉积定额的确定方法一样

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Deposition rates derived from speleothems have been shown to be a useful paleoclimatic proxy. Past studies have shown that the most common climatic parameter measured by variable deposition rates is precipitation, where increased precipitation leads to increased calcite deposition. This was the premise of our study, where three Floridian stalagmites' deposition rates were measured and compared to paleohydrologic indicators taken from the sample or from other regional records. Deposition rates were measured by determining the volume of calcite precipitated between TIMS U-series dates (mm3 yr-1), thereby accounting for morphological changes on the stalagmite over its depositional history. Most prior research relied on a simple linear interpolation between known ages to calculate rate (mm yr-1). Results show three distinct periods of increased deposition for our stalagmites centered on 2.0, 1.25 and 0.5 ka BP. A comparison with Mg/Ca and Sr/Ca ratios and calcite deposition tentatively shows elevated elemental ratios during the three aforementioned periods. Elevated trace element ratios have been shown to be correlated with increased residence time of percolation waters in the overlying bedrock above caves and consequently decreased rainfall. To corroborate this finding, paleo-precipitation records from Little Salt Spring, Florida and Lake Miragoane, Haiti, were examined for coeval arid periods with our stalagmites. Both records do possess similar dry periods and provide added support that the region experienced periods of abrupt aridity over the last two millennia. The combined effect of a change in the mean position of the Intertropical Convergence Zone and the easterly winds associated with the North Atlantic High appear to be the major causes for these times of aridity.
机译：已经显示了源自脾针类的沉积速率是有用的古气候代用物。过去的研究表明，通过变化的沉积速率测得的最常见的气候参数是降水，降水增加导致方解石沉积增加。这是我们研究的前提，在这里测量了三个佛罗里达石笋的沉积速率，并将其与从样本或其他区域记录中获取的古水文指标进行了比较。通过确定在TIMS U系列日期之间沉淀的方解石的体积（mm3 yr-1）来测量沉积速率，从而解释了整个沉积历史上石笋的形态变化。大多数先前的研究都依赖于已知年龄之间的简单线性插值来计算比率（mm yr-1）。结果显示，以2.0、1.25和0.5 ka BP为中心，石笋的沉积增加了三个不同的时期。与Mg / Ca和Sr / Ca之比和方解石沉积的比较初步显示，在上述三个时期中元素比有所提高。痕量元素比率的增加与渗透水在洞穴上方的基岩中停留时间的增加和降雨的减少相关。为了证实这一发现，我们与石笋一起研究了佛罗里达州Little Salt Spring和海地Miragoane湖的古降水记录，记录了该时期的干旱时期。两种记录的确具有相似的干旱时期，并提供了额外的支持，表明该地区在过去的两千年中经历了干旱的突然时期。热带辐合带平均位置的变化和与北大西洋高压有关的东风的综合作用似乎是造成这些干旱时期的主要原因。

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