Interpretation of orbital scale variability in mid-latitude speleothem δ18O: Significance of growth rate controlled kinetic fractionation effects
Interpretation of orbital scale variability in mid-latitude speleothem δ18O: Significance of growth rate controlled kinetic fractionation effects
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DOI：
10.1016/j.quascirev.2015.08.025
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发表时间：
2015-11
影响因子：
4
通讯作者：
H. Stoll;A. Méndez-Vicente;S. González-Lemos;A. Moreno;I. Cacho;Hai Cheng;R. Edwards
中科院分区：
文献类型：
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作者：
H. Stoll;A. Méndez-Vicente;S. González-Lemos;A. Moreno;I. Cacho;Hai Cheng;R. Edwards
氧同位素是石笋中使用最广泛的气候指标，用于重建过去降雨量 δ18O 和洞穴温度的变化。然而，洞穴中的 δ18O 信号也可能受到可变动力学分馏效应的影响，这里广义地认为分馏效应不是由温度变化引起的。洞穴δ18O信号的区域再现性已被提出作为区分直接由降雨δ18O和洞穴温度变化引起的δ18O变化与由于动力学效应而可能受到气候影响的变化的一种方法。在这里，我们比较了来自西班牙西北部两个邻近洞穴的 5 个同时代石笋的同位素记录，时间跨度为 140 至 70 ka，这些石笋在温度和降雨量 δ18O 方面经历了相同的主要变化，但在生长速率和生长速率的时间趋势方面表现出很大的变化范围。以接近 50 微米/年的较快生长速度的石笋，其氧同位素比比生长速度非常缓慢（5 微米/年）的同期石笋负超过 1‰。由于任何给定石笋内的生长速率也会随时间发生变化，因此给定石笋测量的氧同位素时间序列包括气候和动力学成分。基于动力学分量对生长速率的依赖性，去除每个石笋中变化的动力学分量对于提取多个石笋的氧同位素记录之间的共同时间演化是有效的。然而，这种方法受到年龄模型质量的限制。对于以生长非常缓慢和日期之间的持续时间长为特征的时间段，隐裂的存在可能会导致平均增长率低估瞬时洞穴沉积率，从而低估动力学效应的程度。叠加生长率校正的洞穴物 δ18O 受到洞穴温度和海洋水分源 δ18O 的轨道尺度变化的影响，而且还受到水文循环中随时间变化的分馏的影响。最显着的趋势是 GI-22 期间水文分馏增加，此时副热带大西洋湿气源区海面温度升高可能有利于降水量增加。
Oxygen isotopes have been the most widely used climate indicator in stalagmites, applied to reconstruct past changes in rainfall δ18O and cave temperature. However, the δ18O signal in speleothems may also be influenced by variable kinetic fractionation effects, here conceived broadly as fractionation effects not arising from temperature variation. The regional reproducibility of speleothem δ18O signals has been proposed as a way to distinguish the δ18O variations arising directly from changes rainfall δ18O and cave temperature, from variations due to kinetic effects which may nonetheless be influenced by climate. Here, we compare isotopic records from 5 coeval stalagmites from two proximal caves in NW Spain covering the interval 140 to 70 ka, which experienced the same primary variations in temperature and rainfall δ18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 μm/yr have oxygen isotopic ratios over 1‰ more negative than coeval stalagmites with very slow (5 μm/yr) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution of among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. The stacked growth rate-corrected speleothem δ18O is influenced by orbital scale variation in the cave temperature and the δ18O of the ocean moisture source, but also by temporally variable fractionation in the hydrological cycle. The most salient trend is increased hydrological fractionation during the GI-22 period, when warmer sea surface temperatures in the subtropical Atlantic moisture source region may have favored greater precipitation amounts.