Where and how long ago was water in the western North Atlantic ventilated? Maximum entropy inversions of bottle data from WOCE line A20
Where and how long ago was water in the western North Atlantic ventilated? Maximum entropy inversions of bottle data from WOCE line A20
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DOI：
10.1029/2009jc005750
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发表时间：
2010-07-07
影响因子：
3.6
通讯作者：
Khatiwala, Samar
中科院分区：
文献类型：
--
作者：
Holzer, Mark;Primeau, Francois W.;Khatiwala, Samar
采用最大熵（ME）方法对示踪数据进行反卷积，得到自上次通风以来位置和时间的联合分布G。反褶解利用世界海洋环流实验线A20重复水文CFC-11、潜在温度、盐度、氧和磷酸盐，以及全球海洋数据分析项目（GLODAP）放射性碳数据，结合从CFC-11大气历史、2005年世界海洋地图集和GLODAP数据库获得的地表边界条件。由于可用示踪剂的数量有限，反卷积是高度不确定的，导致大的熵不确定性，这是使用相对于先验分布的G的信息熵来量化的。使用蒙特卡罗方法估计由数据稀疏性引起的附加不确定性，并发现它是次要的。ME反卷积客观地确定了关键水团形成区域，并量化了每个区域最后一次通气年龄在20岁或以上的水的局部比例。还估计了理想平均年龄和放射性碳年龄，但发现它们具有很大的熵不确定性，这可归因于根据最后一次通风的位置对给定水包进行分配的不确定性。Labrador/Irminger海水（L水）在A20北端的深西部边界流（DWBC）附近的年龄大多小于40岁，但在DWBC再次穿过更南边的部分时，年龄要大几十岁，这表明通过众多涡流扩散路径混合的重要性。溢流水主要分布在L水以下，A20北部中深度有年轻水（tau小于或接近40 a），在3500 m以下有接近600 a的水。
A maximum entropy (ME) method is used to deconvolve tracer data for the joint distribution G of locations and times since last ventilation. The deconvolutions utilize World Ocean Circulation Experiment line A20 repeat hydrography for CFC-11, potential temperature, salinity, oxygen, and phosphate, as well as Global Ocean Data Analysis Project (GLODAP) radiocarbon data, combined with surface boundary conditions derived from the atmospheric history of CFC-11 and the World Ocean Atlas 2005 and GLODAP databases. Because of the limited number of available tracers the deconvolutions are highly underdetermined, leading to large entropic uncertainties, which are quantified using the information entropy of G relative to a prior distribution. Additional uncertainties resulting from data sparsity are estimated using a Monte Carlo approach and found to be of secondary importance. The ME deconvolutions objectively identify key water mass formation regions and quantify the local fraction of water of age tau or older last ventilated in each region. Ideal mean age and radiocarbon age are also estimated but found to have large entropic uncertainties that can be attributed to uncertainties in the partitioning of a given water parcel according to where it was last ventilated. Labrador/Irminger seawater (L water) is determined to be mostly less than similar to 40 a old in the vicinity of the deep western boundary current (DWBC) at the northern end of A20 but several decades older where the DWBC recrosses the section further south, pointing to the importance of mixing via a multitude of eddy-diffusive paths. Overflow water lies primarily below L water with young waters (tau less than or similar to 40 a) at middepth in the northern part of A20 and waters as old as similar to 600 a below similar to 3500 m.