Non-Equilibrium Fractionation Factors for D/H and (18)O/(16)O During Oceanic Evaporation in the North-West Atlantic Region.
Non-Equilibrium Fractionation Factors for D/H and (18)O/(16)O During Oceanic Evaporation in the North-West Atlantic Region.
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DOI：
10.1029/2022jd037076
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发表时间：
2022-11-16
影响因子：
4.4
通讯作者：
Sveinbjornsdottir, A. E.
中科院分区：
文献类型：
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作者：
Zannoni, D.;Steen-Larsen, H. C.;Peters, A. J.;Wahl, S.;Sodemann, H.;Sveinbjornsdottir, A. E.
海洋同位素蒸发模型，如克雷格-戈登模型，依赖于非平衡分馏因子的描述，一般来说，约束不足。到目前为止，只有少数梯度扩散类型的测量已经在海洋环境中进行，以测试海洋蒸发过程中常用的非平衡同位素分馏参数化的有效性。在这项工作中，我们提出了6个月的水汽同位素观测收集的气象塔位于西北大西洋（百慕大）的目的是估计非平衡分馏因子（k，‰）的海洋蒸发和风速的依赖性。Keeling Plot方法和克雷格-戈登模型组合对计算蒸发过程中的非平衡分馏因子具有足够的灵敏度，得到平均值k18 = 5.2 ± 0.6‰和k2 = 4.3 ± 3.4‰。此外，我们还评估了k和海洋上10米风速之间的关系。从目前的蒸发理论和20世纪70年代的实验室实验中可以预期这种关系，但缺乏观测证据。我们发现：（a）在观测到的风速范围[0-10 m s−1]内，k对风速的敏感性很小，k 18的敏感性约为−0.2‰ m−1 s;（B）没有经验证据表明，在同位素分馏过程中，平滑和粗糙风速状态之间存在不连续性，如早期研究所提出的。在闭合假设下使用本研究中估计的k值预测的水汽d-过量变率与大西洋上空的观测结果一致。提出了海洋蒸发过程中水同位素的基于观测的非平衡分馏因子，在非平衡分馏因子和10米风速之间观察到显着相关性，没有证据表明海洋蒸发过程中同位素分馏的平滑和粗糙区域之间存在区别。
Ocean isotopic evaporation models, such as the Craig‐Gordon model, rely on the description of nonequilibrium fractionation factors that are, in general, poorly constrained. To date, only a few gradient‐diffusion type measurements have been performed in ocean settings to test the validity of the commonly used parametrization of nonequilibrium isotopic fractionation during ocean evaporation. In this work, we present 6 months of water vapor isotopic observations collected from a meteorological tower located in the northwest Atlantic Ocean (Bermuda) with the objective of estimating nonequilibrium fractionation factors (k, ‰) for ocean evaporation and their wind speed dependency. The Keeling Plot method and Craig‐Gordon model combination were sensitive enough to resolve nonequilibrium fractionation factors during evaporation resulting into mean values of k 18 = 5.2 ± 0.6‰ and k 2 = 4.3 ± 3.4‰. Furthermore, we evaluate the relationship between k and 10‐m wind speed over the ocean. Such a relationship is expected from current evaporation theory and from laboratory experiments made in the 1970s, but observational evidence is lacking. We show that (a) in the observed wind speed range [0–10 m s−1], the sensitivity of k to wind speed is small, in the order of −0.2‰ m−1 s for k 18, and (b) there is no empirical evidence for the presence of a discontinuity between smooth and rough wind speed regime during isotopic fractionation, as proposed in earlier studies. The water vapor d‐excess variability predicted under the closure assumption using the k values estimated in this study is in agreement with observations over the Atlantic Ocean. Observation‐based nonequilibrium fractionation factors for water isotopologues during ocean evaporation are proposed Significant correlation observed between nonequilibrium fractionation factors and 10‐m wind speed No evidence of distinction is found between smooth and rough regimes for isotopic fractionation during ocean evaporation