Calculating uncertainty for the RICE ice core continuous flow analysis water isotope record

• Published in: Atmospheric Measurement Techniques
• Main Authors: E. D. Keller, W. T. Baisden, N. A. N. Bertler, B. D. Emanuelsson, S. Canessa, A. Phillips
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Antarctic; Roosevelt Island; Antarc*; ice core
• Online Access: https://doi.org/10.5194/amt-11-4725-2018; https://doaj.org/article/6ef681869c49417297c561cd3edca137

We describe a systematic approach to the calibration and uncertainty estimation of a high-resolution continuous flow analysis (CFA) water isotope ( δ 2 H, δ 18 O) record from the Roosevelt Island Climate Evolution (RICE) Antarctic ice core. Our method establishes robust uncertainty estimates for CFA δ 2 H and δ 18 O measurements, comparable to those reported for discrete sample δ 2 H and δ 18 O analysis. Data were calibrated using a time-weighted two-point linear calibration with two standards measured both before and after continuously melting 3 or 4 m of ice core. The error at each data point was calculated as the quadrature sum of three factors: Allan variance error, scatter over our averaging interval (error of the variance) and calibration error (error of the mean). Final mean total uncertainty for the entire record is δ 2 H = 0.74 ‰ and δ 18 O = 0.21 ‰. Uncertainties vary through the data set and were exacerbated by a range of factors, which typically could not be isolated due to the requirements of the multi-instrument CFA campaign. These factors likely occurred in combination and included ice quality, ice breaks, upstream equipment failure, contamination with drill fluid and leaks or valve degradation. We demonstrate that our methodology for documenting uncertainty was effective across periods of uneven system performance and delivered a significant achievement in the precision of high-resolution CFA water isotope measurements.