Radiocarbon reservoir effects in human bone collagen from northern Iceland

Human bone collagen from a series of Icelandic human pagan graves was radiocarbon (C-14) dated to aid understanding of early settlement (landnam) chronologies in northern Iceland. These individuals potentially consumed marine protein. The C-14 age of samples containing marine carbon requires a correction for the marine C-14 reservoir effect. The proportion of non-terrestrial sample carbon was quantified via measurement of carbon stable isotopes (delta C-13) using a simple mixing model, based on delta C-13 measurements of archaeofaunal samples. Non-terrestrial carbon was also quantified in six pig bones from the archaeofaunal dataset. Assuming all non-terrestrial carbon in human and pig bone collagen was marine-derived, calibrated age ranges calculated using a mixed IntCal09/Marine09 calibration curve were consistent with an early settlement date close to landnam, but several samples returned pre-landnam age ranges. Measurements of nitrogen stable isotopes (delta N-13) strongly suggest that many of the human bone collagen samples contain freshwater diet-derived carbon. Icelandic freshwater systems frequently display large freshwater C-14 reservoir effects, of the order of 10,000 C-14 years, and we suggest that the presence of freshwater carbon is responsible for the anomalously early ages within our dataset. In pig samples, the majority of non-terrestrial carbon is freshwater in origin, but in human samples the proportion of freshwater carbon is within the error of the marine component (+/-10%). This presents a major obstacle to assessing temporal patterns in the ages of human remains from sampled graves, although the majority of grave ages are within the same, broad, calibrated range. (C) 2012 Elsevier Ltd. All rights reserved.