Thermohaline stratification and double diffusion diapycnal fluxes in the hypersaline Dead Sea
Thermohaline stratification and double diffusion diapycnal fluxes in the hypersaline Dead Sea
复制标题
高盐死海的温盐层结和双扩散二重通量
DOI：
10.1002/lno.10285
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发表时间：
2016
影响因子：
4.5
通讯作者：
N. Lensky
中科院分区：
文献类型：
--
作者：
A. Arnon;J. Selker;N. Lensky
死海是一个高盐度的终端湖泊，经历了负水平衡，盐度上升和氯化钠(盐岩)结晶。与大多数湖泊相比，我们观察到了温盐层结的非典型演化，这是由于盐结晶和跨湖层的昼夜通量的作用。我们通过对温度剖面的高分辨率连续测量、新颖的水样方法和对盐结晶的垂直剖面的观察，表征了湖泊地层的温盐性质的动力学。通过金属离子的双扩散(DD)盐指进解释了跨金属的昼夜通量，这是由较暖的咸水高于较冷的较少咸水之间的不稳定所驱动的。DD通量与：(1)从初夏20m宽的过渡到阶梯，最终合并为一个尖锐的亚米级台阶；(2)从仲夏开始，盐度从表层开始下降，与次生离子的盐度和温度同步下降；(3)次生离子中的盐岩结晶活动。我们认为，饱和卤水中的盐指机制表现出一种独特的不对称性，即向下的冷却指变得过饱和并结晶盐岩，而向上的变暖的指变得不饱和。死海的DD通量是层结动力学的基础，为一般理解高盐度环境中的DD通量提供了一个框架。这一发现对于理解蒸散岩的沉积动力学具有广泛的意义。
The Dead Sea is a hypersaline terminal lake, experiencing negative water balance, increasing salinity, and NaCl (halite) crystallization. We observed atypical evolution of the thermohaline stratification in comparison to most lakes due to the role of salt crystallization and diapycnal fluxes across lake layers. We characterized the dynamics of the thermohaline properties of the lake strata through high‐resolution continuous measurements of temperature profiles, novel water sampling methods, and observation of vertical profiles of salt crystallization. The diapycnal fluxes across the metalimnion were explained by Double Diffusion (DD) salt fingering driven by instability between warmer saltier water above cooler less salty water. The DD flux is associated with: (1) sharpening of the metalimnion from a 20 m wide transition in early summer, to staircase, ultimately merging to a single sharp sub‐meter step, (2) salinity decline from the epilimnion starting from mid‐summer synchronous with increasing salinity and temperature of the hypolimnion, and (3) active halite crystallization in the hypolimnion. We hypnotize that the salt fingering mechanism in saturated brines reveals a unique asymmetry; i.e., the descending cooling fingers become supersaturated and crystallize halite, whereas the ascending warming fingers becomes undersaturated. The DD flux in the Dead Sea is shown to be fundamental in the dynamics of stratification, providing a framework for general understanding DD flux in hypersaline environments. The finding that the epilimnion experiences seasonal halite undersaturation whereas the hypolimnion continuously precipitates salt by DD flux, has wide implications on the understanding of the dynamics of deposition of evaporitic rocks.