Collaborative Research: New Diagnostics of Water-Mass Ventilation Estimated from Tracer Data

通风率量化了海洋如何在几个月到几千年的时间尺度上与气候系统的其他部分交流，并确定了海洋缓冲大气免受气候异常影响的能力，以及吸收大气痕量气体，包括人为二氧化碳的能力。根据最近的研究，必须根据水在海洋内部的停留时间来划分新通风的水的表面通量，以便正确描述瞬变示踪剂库存如何随时间演变，因此，通风率是一个分布，而不是像迄今认为的那样，足以代表一个整体通量的单一数字。这从根本上将估算问题转变为通风率分布的反褶积问题，通风率分布将已知的混合层浓度传播到测量的内部值。来自哥伦比亚大学和加州大学欧文分校的海洋学家建议使用氟氯化碳、氚和放射性碳的瞬变示踪剂数据，以及网格温度、盐度、营养物质和氧气数据，来估计海洋的通气率分布。将系统地估计一系列密度类别的通风率分布，这些密度类别的露头覆盖全球大部分海洋表面。这项拟议工作的主要部分将是严格量化由于数据误差和反卷积性质不足而造成的不确定性。将使用两种反卷积方法：经过测试的参数方法和最大熵方法的新应用。通风率分布的反卷积将在十年时间尺度上受到氟氯化碳、氚和炸弹放射性碳的限制，并受背景放射性碳在较长时间尺度上的限制。稳定的示踪剂将限制通风率分布的空间和季节相关性。最大熵反演将使用最先进的数据同化模型来产生通风率分布的预先猜测。该模型还将用于生成真实的合成示踪剂数据，以量化参数和最大熵反卷积的系统误差。这项研究将提供海洋与大气在几个月到几千年的时间尺度上如何沟通的一幅新颖的综合图景，并有助于协调先前基于不完整的整体通量图对通气量的不同估计。拟议的研究将首次提供对海洋当前状态的通气率分布的全球估计以及对其不确定性的基线估计，以便能够有意义地评估未来对通风的可变性和气候变化的估计。拟议的工作将与限制海洋对人为碳的吸收的气候研究协同进行。将向社区提供使用最大熵方法进行广义水团分析的MatLab工具箱。除了主要的科学贡献外，拟议的工作还将提供资金，支持博士后学者的职业发展，并在海洋运输诊断、数据分析技术、海洋建模以及分析海洋在气候系统中的作用方面为研究生提供教育和培训。

Ventilation rates quantify how the ocean communicates with the rest of the climate system on timescales ranging from month to millennia, and determine the ocean's ability to buffer the atmosphere from climate anomalies and to take up atmospheric trace gases, including anthropogenic carbon dioxide. Based on recent research that surface fluxes of newly-ventilated water must be partitioned according to the water's residence time in the ocean interior in order to describe correctly how inventories of transient tracers evolve with time, ventilation rate is therefore a distribution and not, as had been thought sufficient until now, a single number representing a bulk flux. This fundamentally changes the estimation problem to a deconvolution for a ventilation-rate distribution that propagates known mixed-layer concentrations to measured interior values.Oceanographers from Columbia University and University of California at Irvine propose to use CFC, tritium, and radiocarbon transient tracer data, together with gridded temperature, salinity, nutrient, and oxygen data, to estimate the ventilation-rate distributions of the ocean. The ventilation-rate distributions will systematically be estimated for a range of density classes whose outcrops cover most of the global ocean surface. A major part of the proposed work will be a rigorous quantification of the uncertainties due to errors in the data and due to the underdetermined nature of the deconvolutions.Two deconvolution methods will be employed: A tested parametric approach and a novel applicationof the maximum-entropy method. The deconvolution of the ventilation-rate distribution will be constrained on decadal timescales by CFCs, tritium and bomb radiocarbon and by the background radiocarbon on longer timescales. Steady tracers will constrain the ventilation-rate distribution's spatial and seasonal dependence. The maximum-entropy inversions will use a state-of-the-art data-assimilation model to produce a prior guess for the ventilation-rate distribution. This model will also be used to generate realistic synthetic tracer data to quantify the systematic errors of both the parametric and the maximum-entropy deconvolutions. The research will provide a novel comprehensive picture of how the ocean communicates with the atmosphere on timescales of months to millennia and help reconcile disparate previous estimates of ventilation based on the incomplete bulk-flux picture.The proposed research will provide the first global estimate of the ventilation-rate distribution for the current state of the ocean and a baseline estimate of its uncertainty so that future estimates of variability and climate change in ventilation can meaningfully be assessed. The proposed work will be synergistic with climate research on constraining the oceanic uptake of anthropogenic carbon. A MATLAB toolbox for performing generalized water-mass analysis using the maximum entropy method will be made available to the community. In addition to the primary scientific contributions, the proposed work will provide funding to support the career development of a postdoctoral scholar, and education and training for graduate students in ocean transport diagnostics, data analysis techniques, ocean modeling, and in analyzing the ocean's role in the climate system.