The significance of chemical, isotopic, and detrital components in three coeval stalagmites from the superhumid southernmost Andes (53°S) as high-resolution palaeo-climate proxies
The significance of chemical, isotopic, and detrital components in three coeval stalagmites from the superhumid southernmost Andes (53°S) as high-resolution palaeo-climate proxies
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DOI：
10.1016/j.quascirev.2010.12.006
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发表时间：
2011-02
影响因子：
4
通讯作者：
D. Schimpf;R. Kilian;A. Kronz;K. Simon;C. Spötl;G. Wörner;M. Deininger;A. Mangini
中科院分区：
文献类型：
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作者：
D. Schimpf;R. Kilian;A. Kronz;K. Simon;C. Spötl;G. Wörner;M. Deininger;A. Mangini
石笋是重要的古气候档案，因为它们的化学和同位素特征有可能记录数千年来温度和降水的高分辨率变化。本文报道了智利安第斯山脉南部（53°S）超湿润地区石笋（MA 1-MA 3）的铀钍年代记录。在过去的5000年（距今约1000万年），它们同时生长在一个发育于片岩和花岗闪长岩中的洞穴中。以高时空分辨率分析了石笋的常量和微量元素以及C和O同位素组成，作为古温度和古降水量的代用指标。校准是基于对洞穴内外气候和水文进行的五年监测数据以及区域气象站100年记录的数据。石笋中的Y、HREE等水不溶性元素反映了石笋中硅质碎屑的含量。监测表明，一旦超过阈值，碎屑的数量就受到滴水速度的控制。一般来说，石笋滴速的变化取决于降雨量。然而，不同的滴水路径以上的每个滴水位置引起了个人滴率水平。只有一个的三个石笋（MA 1）有足够高的滴率记录碎屑代理在其整个长度。碳酸盐兼容元素含量（如U，Sr，Mg），这是测量到次年度的分辨率，文件的变化，在大气降水和相关的滴水稀释。此外，这些可溶性元素在风化过程中的主机岩石和土壤取决于pH值的酸性孔隙沃茨的泥炭土壤的洞穴的集水区的沥滤控制。一般来说，降雨量越大，这些元素的浓度越低，反之亦然。用两个区域气象站近百年来的大气降水资料对石笋MA 1的Mg/Ca记录进行了校正。与碳酸盐相容的可溶性元素在三个石笋中表现出相似的模式，当滴水速率和碎屑示踪剂较低时，通常值较高，反之亦然。δ 13 C和δ 18 O值在每个石笋中高度相关，这表明蒸发和/或释气主要依赖于滴速的动力学控制。只有C和O同位素从石笋MA 1，收到最高滴率显示出良好的相关性之间的碎屑代用元素和碳酸盐兼容的元素。与温度相关的雨水同位素值的变化修改了小冰期（距今0.7-0.1 ka BP）期间的MA 1记录，比今天低1.5 °C。在较低的滴水速率下形成的石笋MA 2和MA 3的同位素组成与石笋MA 1和MA 1的所有其他化学指标的相关性较差。“亨迪试验”表明，MA 2和MA 3的脱气控制同位素分馏已经开始在洞顶，特别是当滴率低。改变的途径和停留时间的渗水造成了非气候控制的同位素分馏，这可能是普遍重要的通风洞穴在低滴率阶段。我们的代理人表明，新冰期冷阶段从1.3.5至2.5和从1.0.7至0.1 ka BP的特点是由30%的降水量减少相比，中世纪温暖期从1.2至0.8 ka BP，这是非常潮湿的在该地区。
Stalagmites are important palaeo-climatic archives since their chemical and isotopic signatures have the potential to record high-resolution changes in temperature and precipitation over thousands of years. We present three U/Th-dated records of stalagmites (MA1–MA3) in the superhumid southern Andes, Chile (53°S). They grew simultaneously during the last five thousand years (ka BP) in a cave that developed in schist and granodiorite. Major and trace elements as well as the C and O isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo-temperature and palaeo-precipitation. Calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records. Water-insoluble elements such as Y and HREE in the stalagmites indicate the amount of incorporated siliciclastic detritus. Monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded. In general, drip rate variations of the stalagmites depend on the amount of rainfall. However, different drip-water pathways above each drip location gave rise to individual drip rate levels. Only one of the three stalagmites (MA1) had sufficiently high drip rates to record detrital proxies over its complete length. Carbonate-compatible element contents (e.g. U, Sr, Mg), which were measured up to sub-annual resolution, document changes in meteoric precipitation and related drip-water dilution. In addition, these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the pH of acidic pore waters in the peaty soils of the cave’s catchment area. In general, higher rainfall resulted in a lower concentration of these elements and vice versa. The Mg/Ca record of stalagmite MA1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations. Carbonate-compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa. δ13C and δ18O values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and/or outgassing. Only C and O isotopes from stalagmite MA1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate-compatible elements. A temperature-related change in rainwater isotope values modified the MA1 record during the Little Ice Age (∼0.7–0.1 ka BP) that was ∼1.5 °C colder than today. The isotopic composition of the stalagmites MA2 and MA3 that formed at lower drip rates shows a poor correlation with stalagmite MA1 and all other chemical proxies of MA1. ‘Hendy tests’ indicate that the degassing-controlled isotope fractionation of MA2 and MA3 had already started at the cave roof, especially when drip rates were low. Changing pathways and residence times of the seepage water caused a non-climatically controlled isotope fractionation, which may be generally important in ventilated caves during phases of low drip rates. Our proxies indicate that the Neoglacial cold phases from ∼3.5 to 2.5 and from ∼0.7 to 0.1 ka BP were characterised by 30% lower precipitation compared with the Medieval Warm Period from 1.2 to 0.8 ka BP, which was extremely humid in this region.