ESTIMATING MARINE RESERVOIR EFFECTS IN ARCHAEOLOGICAL CHRONOLOGIES: COMPARING Delta R CALCULATIONS IN PRINCE RUPERT HARBOUR, BRITISH COLUMBIA, CANADA

The best method for quantifying the marine reservoir effect (MRE) using the global IntCal Marine13 calibration curve remains unresolved. Archaeologists frequently quantify uncertainty on MRE values as errors computed from single pairs of marine-terrestrial radiocarbon ages, which we argue significantly overstates their accuracy and precision. Here, we review the assumptions, methods, and applications of estimating MRE via an estimate of the additional regional offset between the marine and terrestrial calibration curves (Delta R) for the Prince Rupert Harbour (PRH) region of British Columbia, Canada. We acknowledge the influence on Delta R of MRE variation as (1) a dynamic oceanographic process, (2) its variable expression in biochemical and geochemical pathways, and (3) compounding errors in sample selection, measurement, and calculation. We examine a large set of marine-terrestrial pairs (n = 63) from PRH to compare a common archaeological practice of estimating uncertainty from means that generate an uncertainty value of +/- 49 years with a revised, more appropriate estimate of error of +/- 230 years. However, we argue that the use of multiple-pair samples estimates the PRH Delta R as 273 +/- 38 years for the last 5,000 years. Calculations of error that do not consider these issues may generate inaccurate age estimates with unjustifiable precision.