AN UPDATE AND CONFIRMATION OF AN ADJUSTED MARINE RESERVOIR EFFECT FROM COEVAL MARINE AND TERRESTRIAL RADIOCARBON DATA FROM THE LATE-GLACIAL PERIOD IN PORTLAND, MAINE

In “Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages” by Woodrow B. Thompson et al. (2011; https://doi.org/10.1016/j.yqres.2011.02.002), we showed that marine coastal environments produce more variability in marine radiocarbon content than in the open ocean. Rather than the established ~410-year marine reservoir effect, the value was around 1000 years for off of Portland.

Since then, radiocarbon calibration data has been modified for the late glacial period, and one segment of the innermost tree-rings from one log found at the Mercy Hospital site was radiocarbon-dated. The results of the two revised data sets are a slight adjustment of the calibrated date to about 50 years older with reduced error. The marine reservoir effect for the Maine coastal region remains at around 1000 years.