Abstract
A realistic estimation of uncertainty is an essential requirement for all analytical measurements. It is common practice, however, for the uncertainty estimate of a chemical measurement to be based on the instrumental precision associated with the analysis of a single or multiple samples, which can lead to underestimation. Within the context of chemical oceanography such an underestimation of uncertainty could lead to an over interpretation of the result(s) and hence impact on, e.g., studies of biogeochemical cycles, and the outputs from oceanographic models. Getting high quality observational data with a firm uncertainty assessment is therefore essential for proper model validation. This paper describes and compares two recommended approaches that can give a more holistic assessment of the uncertainty associated with such measurements, referred to here as the “bottom up” or modeling approach and the “top down” or empirical approach. “Best practice” recommendations for the implementation of these strategies are provided. The “bottom up” approach combines the standard uncertainties associated with each stage of the entire measurement procedure. The “top down” approach combines the uncertainties associated with day to day reproducibility and possible bias in the complete data set and is easy to use. For analytical methods that are routinely used, laboratories will have access to the information required to calculate the uncertainty from archived quality assurance data. The determination of trace elements in seawater is a significant analytical challenge and iron is used as an example for the implementation of both approaches using real oceanographic data. Relative expanded uncertainties of 10 – 20% were estimated for both approaches compared with a typical short term precision (rsd) of≤5%.
Highlights
THE OCEANOGRAPHIC CONTEXTThe 20th century was a productive period for development of analytical techniques for oceanographic chemical measurements and the motivation to increase the number of analytes determined in seawater via innovative analytical applications continues to this day
This paper describes and compares two recommended approaches that can give a more holistic assessment of the uncertainty associated with such measurements, referred to here as the “bottom up” or modeling approach and the “top down” or empirical approach
With an ever increasing suite of established methods adapted for global oceanographic studies, Trace Element Measurement Uncertainty Estimation more importance is placed on the determination and documentation of accuracy, repeatability and reproducibility and more rigorous uncertainty estimates to accompany reported data
Summary
THE OCEANOGRAPHIC CONTEXTThe 20th century was a productive period for development of analytical techniques for oceanographic chemical measurements and the motivation to increase the number of analytes determined in seawater via innovative analytical applications continues to this day. These intercalibration exercises have contributed to improving the accuracy of dissolved iron and other trace element measurements in seawater, thereby enhancing the ability of the oceanographic community to compare datasets that vary temporally and/or spatially or are obtained by different researchers using different analytical methods.
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