Evaluating the use of 1‐D transit time distributions to infer the mean state and variability of oceanic ventilation

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• 作者：Andrew E. Shao ; Sabine Mecking ; LuAnne Thompson ; Rolf E. Sonnerup
• 刊名：Journal of Geophysical Research: Oceans
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：121
• 期：9
• 页码：6650-6670
• 全文大小：8.9MB
• ISSN：2169-9291

文摘

An offline tracer transport model transport is used to simulate chlorofluorocarbon (CFCs), sulfur hexafluoride (SF₆), oxygen, ideal age, and model transit time distributions (TTDs) to evaluate how well tracers can be used to constrain both the mean state and variability of oceanic ventilation. Using climatological transports, the two-parameter 1-D inverse Gaussian approximation of the model TTD is found to be an adequate representation of ventilation pathways within the parts of the subtropical gyres with simple ventilation dynamics, but a poor approximation for regions with large gradients in ideal age (i.e., near the base of the thermocline and the continental boundaries). TTDs inferred from CFC-12 and SF₆ using a Peclet number-based lookup table approach yield poor representations of the model TTD with a consistent bias toward ventilation being strongly dominated by along-isopycnal diffusion. In a run with variable circulation, ideal age is used to track changes in thermocline ventilation. Variability in both apparent oxygen utilization (AOU) and tracer-inferred TTD mean ages inferred using CFC-12 (assuming fixed Peclet number) and dual tracers (SF₆ and CFC-12) are well-correlated to ideal age variability in most of the thermocline. Changes in AOU are correlated with ideal age variability in even more regions compared to the TTD ages both horizontally and vertically down to intermediate depths. Generally, when changes in TTD mean age and AOU agreed in sign, correlations of both with ideal age changes were positive indicating the usefulness of tracers in diagnosing ventilation changes.