Quantifying marine reservoir effect variability along the Northwest Coast of North America

Recognition of marine reservoir effect (MRE) spatial and temporal variability must be accounted for in any radiocarbon-based paleoclimate, geomorphological, or archaeological reconstruction in a coastal setting. Delta R values from 37 shell-wood pairs across southern Southeast Alaska provide a robust local evaluation of the MRE, reporting a local Early Holocene weighted Delta R average of 265 +/- 205, with a significantly higher Delta R average of 410 +/- 60 for samples near limestone karst. Integration with our synthesis of extant MRE calibrations for the Northwest Coast of North America suggests that despite local variability, regional Delta R averages echo proxies for coastal upwelling: regional weighted averages were at their highest in the Bolling-Allerod interstade (575 +/- 165) and their lowest in the Younger Dryas stade (-55 +/- 110). Weighted Delta R averages across the Northwest Coast rose to a Holocene high during the Early Holocene warm period (245 +/- 200) before settling into a stable Holocene average Delta R of 145 +/- 165, which persisted until the late Holocene. Our quantification of local and regional shifts in the MRE shines a light on present methodological issues involved in MRE corrections in mixed-feeder, diet-based calibrations of archaeological and paleontological specimens.

Automated summary

This study emphasizes the significance of recognizing the marine reservoir effect in radiocarbon analysis and provides a local evaluation of MRE, showing both local variability and regional correlation with coastal upwelling. Regional Delta R averages fluctuate during specific time periods, affecting calibrations of archaeological and paleontological specimens.