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首页> 外文期刊>Journal of Physical Oceanography >Chlorofluorocarbon Constraints on North Atlantic Ventilation
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Chlorofluorocarbon Constraints on North Atlantic Ventilation

机译：氯氟烃对北大西洋通风的制约

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The North Atlantic Ocean vigorously ventilates the ocean interior. Thermocline and deep water masses are exposed to atmospheric contact there and are sequestered in two principal classes: Subtropical Mode Water (STMW: 26.5 ≤ σ_θ ≤ 26.8) and Subpolar Mode Water (SPMW: 26.9 ≤ σ_θ ≤ 27.8). These ventilation rates and pathways are uncertain, and a powerful way to estimate them is to monitor the penetration of Chlorofluorocarbon (CFC) tracers. Here, a CFC dataset of over 44 000 observations, taken between 1982 and 1998, is combined with a non-eddy-resolving ((4/3)° resolution) general circulation model of the North Atlantic Ocean. The CFC data are assimilated with the model by optimizing the uncertain air-sea CFC flux. The assimilated CFC fields are then systematically compared with the observations to identify the best fit and hence the most realistic ventilation. Three GCM experiments are performed this way to find the dependence on model thickness diffusivity. Each GCM solution is close to being statistically consistent with the CFC observations and likely sources of error. Lower diffusivity gives the best match to data although some systematic bias in sequestering tropospheric CFC remains. Lower diffusivity, around 150 m~2 s~(-1), permits a stronger circulation with a more realistic North Atlantic Current. For this experiment, the subduction rate is around 16 Sv (Sv ≡ 10~6 m~3 s~(-1)) in the subtropics and eastern subpolar Atlantic (26.35 ≤ σ_θ ≤ 27.13) averaged over 1975-95. Around 26 Sv is formed in the Labrador and Irminger Seas (27.58 ≤ σ_θ ≤ 27.8). Only about 40% of the CFC carried into the subpolar interior by this flux remained there in 1998, however. The rest was returned to the subpolar mixed layer after an average period of 6-8 yr. In contrast, 70% of the CFC subducted into the subtropical interior remained there in 1998.
机译：北大西洋极大地通风了海洋内部。温跃层和深水团块在那里暴露于大气，并被隔离在两个主要类别中：亚热带模式水（STMW：26.5≤σ_θ≤26.8）和亚极性模式水（SPMW：26.9≤σ_θ≤27.8）。这些通风速率和途径尚不确定，估计它们的有效方法是监视氯氟烃（CFC）示踪剂的渗透。在这里，将1982年至1998年之间的超过44000个观测值的CFC数据集与北大西洋的非涡旋解析（（4/3）°分辨率）一般环流模型相结合。通过优化不确定的海海CFC通量，将CFC数据与模型同化。然后将同化的CFC场与观测值进行系统比较，以确定最佳拟合，从而确定最真实的通风条件。以这种方式执行了三个GCM实验，以发现对模型厚度扩散率的依赖性。每个GCM解决方案在统计上都与CFC观察结果和可能的错误来源接近一致。较低的扩散率使数据最匹配，尽管在隔离对流层CFC时仍存在一些系统性偏差。较低的扩散率（大约150 m〜2 s〜（-1））可以实现更强的环流，并具有更逼真的北大西洋洋流。对于本实验，在1975-95年间，亚热带和东部亚极大西洋的俯冲速率约为16 Sv（Sv≡10〜6 m〜3 s〜（-1））（26.35≤σ_θ≤27.13）。拉布拉多和艾明格海形成约26 Sv（27.58≤σ_θ≤27.8）。但是，到1998年，由这种通量带入亚极内部的CFC大约只有40％。平均6-8年后，其余的物质返回到亚极混合层。相反，1998年俯冲到亚热带内部的氟氯化碳中有70％留在那里。

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