Can stable isotopes ride out the storms? The role of convection for water isotopes in models, records, and paleoaltimetry studies in the central Andes
Can stable isotopes ride out the storms? The role of convection for water isotopes in models, records, and paleoaltimetry studies in the central Andes
复制标题
稳定同位素能安然度过风暴吗？
DOI：
10.1016/j.epsl.2014.09.021
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发表时间：
2014
影响因子：
5.3
通讯作者：
Montero
中科院分区：
文献类型：
--
作者：
Rohrmann;Strecker;Bookhagen;Sachse;Pingel;Alonso;Schildgen;Montero
在全球范围内，大气水循环中氧和氢的稳定同位素比值（δ O 18和δ D）的变化是蒸馏和蒸发过程的结果。同位素分馏发生在空气质量上升的高度，冷却，并减少其水蒸气的容量与温度下降。因此，来自各种沉积档案的δ O 18和δ D值经常被用来重建大陆古水文学的变化以及山脉的古高度。基于234个河水样本，我们证明了在安第斯山脉东南部（22-28° S）经历深对流风暴的地区没有显示出通常观察到的δ O 18和δ D与海拔的关系。这些对流风暴来自山间盆地，在那里，昼夜加热迫使暖空气团上升，导致暴雨和雨滴蒸发。特别是在热带和热带外大气环流系统之间的边界，那里的深对流风暴非常常见（北纬26°至南纬32°），这种风暴的影响可能会产生非系统的稳定同位素高度关系，因为对流对空气质量的绝热提升起主导作用。由于对流风暴可以减少或掩盖降水中重同位素的消耗作为海拔的函数，将现代或过去的地形与稳定同位素代用记录的模式联系起来可能会在山区受到损害，试图预测稳定同位素模式的大气环流模型必须具有足够高的空间分辨率，以捕获对流单体的分馏动力学。
Globally, changes in stable isotope ratios of oxygen and hydrogen (δ O 18 and δ D) in the meteoric water cycle result from distillation and evaporation processes. Isotope fractionation occurs when air masses rise in elevation, cool, and reduce their water-vapor holding capacity with decreasing temperature. As such, δ O 18 and δ D values from a variety of sedimentary archives are often used to reconstruct changes in continental paleohydrology as well as paleoaltimetry of mountain ranges. Based on 234 stream-water samples, we demonstrate that areas experiencing deep convective storms in the eastern south–central Andes (22–28° S) do not show the commonly observed relationship between δ O 18 and δ D with elevation. These convective storms arise from intermontane basins, where diurnal heating forces warm air masses upward, resulting in cloudbursts and raindrop evaporation. Especially at the boundary between the tropical and extra-tropical atmospheric circulation regimes where deep-convective storms are very common (∼ 26° to 32° N and S), the impact of such storms may yield non-systematic stable isotope-elevation relationships as convection dominates over adiabatic lifting of air masses. Because convective storms can reduce or mask the depletion of heavy isotopes in precipitation as a function of elevation, linking modern or past topography to patterns of stable isotope proxy records can be compromised in mountainous regions, and atmospheric circulation models attempting to predict stable isotope patterns must have sufficiently high spatial resolution to capture the fractionation dynamics of convective cells.
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