A new look at ocean ventilation time scales and their uncertainties
A new look at ocean ventilation time scales and their uncertainties
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DOI：
10.1002/2016jc012529
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发表时间：
2017-05
影响因子：
--
通讯作者：
R. Fine;Synte Peacock;M. Maltrud;F. Bryan
中科院分区：
文献类型：
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作者：
R. Fine;Synte Peacock;M. Maltrud;F. Bryan
首先将一套涡旋分辨海洋瞬变示踪模型模拟与观测结果进行了比较。观测数据和pcfc-11模型的年龄吻合得很好，而涡旋分辨模型则增加了细节。氯氟化碳年龄表明，温跃层在45年的时间尺度上是海洋内部与大气交换的障碍，这是可测量的氯氟化碳瞬变，尽管也有例外。其次，模式模拟被用来量化内部海洋示踪剂可变性的空间相关性对示踪剂年龄的影响，这是由于涡旋的搅动和存在混合时大气瞬变的非平稳性造成的偏差。这些增加了示踪剂年龄的不确定性和偏差，在锋面边界地区很大，在副热带气旋内部很小。这些不确定性和偏差被用来重新解释从十多年前的观测中观察到的示踪剂得出的通风时间尺度的时间趋势，并评估对示踪剂年龄变化的解释是否站得住脚。对于南半球副热带涡旋，我们推断海洋通气率在20世纪90年代中期至21世纪初十年间增加了26-27.2σθ。然而，在20世纪90年代中期到2010年代的十年间，没有明显的趋势--也许除了南大西洋。观察到的年龄/AOU/通风变化与自然周期和气候变化相结合，并且存在区域差异。因此，对于未来来说，还不清楚海洋通风变化在空间和时间上的强度或稳定性。
A suite of eddy-resolving ocean transient tracer model simulations are first compared to observations. Observational and model pCFC-11 ages agree quite well, with the eddy-resolving model adding detail. The CFC ages show that the thermocline is a barrier to interior ocean exchange with the atmosphere on time scales of 45 years, the measureable CFC transient, although there are exceptions. Next, model simulations are used to quantify effects on tracer ages of the spatial dependence of internal ocean tracer variability due to stirring from eddies and biases from nonstationarity of the atmospheric transient when there is mixing. These add to tracer age uncertainties and biases, which are large in frontal boundary regions, and small in subtropical gyre interiors. These uncertainties and biases are used to reinterpret observed temporal trends in tracer-derived ventilation time scales taken from observations more than a decade apart, and to assess whether interpretations of changes in tracer ages being due to changes in ocean ventilation hold water. For the southern hemisphere subtropical gyres, we infer that the rate of ocean ventilation 26–27.2 σθ increased between the mid-1990s and the decade of the 2000s. However, between the mid-1990s and the decade of the 2010s, there is no significant trend—perhaps except for South Atlantic. Observed age/AOU/ventilation changes are linked to a combination of natural cycles and climate change, and there is regional variability. Thus, for the future it is not clear how strong or steady in space and time ocean ventilation changes will be.