14C-age tracers in global ocean circulation models
14C-age tracers in global ocean circulation models
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DOI：
10.5194/gmd-8-2079-2015
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发表时间：
2014-10
影响因子：
5.1
通讯作者：
W. Koeve;H. Wagner;P. Kähler;A. Oschlies
中科院分区：
文献类型：
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作者：
W. Koeve;H. Wagner;P. Kähler;A. Oschlies
海水中溶解的总 CO2 中 14C 的自然丰度是用于评估海洋和海洋模型中的水龄结构和环流的属性。在这项研究中，我们使用全球海洋环流的三种不同表示形式，并辅以一套理想化示踪剂来研究使用天然 14C 来确定水年龄（水体与大气接触以来经过的时间）的潜力和局限性。我们发现，在全球范围内，大量 14C 年龄由两个同样重要的组成部分主导，一个与老化相关，即循环的时间组成部分，另一个与“预先形成的 14C 年龄”相关。后一个量的存在是因为 14C 的大气/海洋平衡缓慢且不完全，特别是在形成许多水团的高纬度地区。预成型部件对大块 14C 时效的相对贡献在给定模型内因区域而异，而且在模型之间也存在差异。区域差异，例如大西洋中的 14C 年龄的最终成员与水的混合有关。在大西洋，预制成分随空间和时间的变化掩盖了环流成分，其模式仅从大量 14C 年龄中无法检测到。模型之间的年龄变化也可能相当大（系数为 2），与物理模型参数的组合有关，影响模型中的循环动力学和气体交换。发现预制部件对气体交换非常敏感，对冰盖中等敏感。在我们的模型评估工作中，在当前不确定性范围内选择气体交换常数对预成型和散装 14C 年龄有很大影响，如果模型评估基于散装 14C 年龄，则很容易损害全球和区域尺度上模型循环的评估和调整。根据这项研究的结果，我们建议考虑预先形成的 14C 年龄对于正确评估海洋模型中的环流至关重要。
The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering preformed 14C-age is critical for a correct assessment of circulation in ocean models.