Using radium isotopes to characterize water ages and coastal mixing rates: A sensitivity analysis
Using radium isotopes to characterize water ages and coastal mixing rates: A sensitivity analysis
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DOI：
10.4319/lom.2011.9.380
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
K. Knee;E. Garcia-Solsona;J. García-Orellana;A. Boehm;A. Paytan
中科院分区：
文献类型：
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作者：
K. Knee;E. Garcia-Solsona;J. García-Orellana;A. Boehm;A. Paytan
许多研究使用天然存在的Ra同位素（223 Ra，224 Ra，226 Ra和228 Ra，半衰期分别为11.4 d，3.7 d，1600 y和5.8 y）来量化水团年龄，沿海海洋混合率和海底地下水排放（SGD）。使用蒙特卡罗模型，本研究调查了Ra同位素活动的不确定性以及由分析不确定性和自然变率引起的导出的活动比（AR）如何影响与Ra导出的水年龄和涡动扩散系数相关的不确定性，这两者都可用于计算SGD。在大多数已发表的研究中，与224 Ra、226 Ra和228 Ra活性相关的分析不确定度报告小于样品活性的10%; 223 Ra报告的分析不确定度范围为7%至40%。与自然变异性相关的相对不确定性-根据重复现场样品的223 Ra和224 Ra活性的变异性估计-范围为15%至50%，223 Ra活性，224 Ra活性和224 Ra/223 Ra AR相似。我们的分析表明，基于AR的水年龄短于3-5 d通常具有大于100%的相对不确定性，可能限制其实用性。当使用较少的点来确定线性趋势时，当决定系数（R2）较低时，以及当使用224 Ra而不是223 Ra时，基于短寿命Ra同位素活性的交叉海岸梯度估计的涡流扩散系数的不稳定性更大。通过探索与Ra导出的水年龄和涡动扩散系数相关的不确定性，这项研究将使研究人员能够更有效地应用这些方法并减少不确定性。
Numerous studies have used naturally occurring Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra, with half‐lives of 11.4 d, 3.7 d, 1600 y, and 5.8 y, respectively) to quantify water mass ages, coastal ocean mixing rates, and submarine groundwater discharge (SGD). Using Monte Carlo models, this study investigated how uncertainties in Ra isotope activities and the derived activity ratios (AR) arising from analytical uncertainty and natural variability affect the uncertainty associated with Ra‐derived water ages and eddy diffusion coefficients, both of which can be used to calculate SGD. Analytical uncertainties associated with 224Ra, 226Ra, and 228Ra activities were reported in most published studies to be less than 10% of sample activity; those reported for 223Ra ranged from 7% to 40%. Relative uncertainty related to natural variability — estimated from the variability in 223Ra and 224Ra activities of replicate field samples — ranged from 15% to 50% and was similar for 223Ra activity, 224Ra activity, and the 224Ra/223Ra AR. Our analysis revealed that AR‐based water ages shorter than 3–5 d often have relative uncertainties greater than 100%, potentially limiting their utility. Uncertainties in eddy diffusion coefficients estimated based on cross‐shore gradients in short‐lived Ra isotope activity were greater when fewer points were used to determine the linear trend, when the coefficient of determination (R2) was low, and when 224Ra, rather than 223Ra, was used. By exploring the uncertainties associated with Ra‐derived water ages and eddy diffusion coefficients, this study will enable researchers to apply these methods more effectively and to reduce uncertainty.