Regional differences in 14C reservoir ages must be known to accurately compare radiocarbon-dated marine and continental records. Reservoir ages also provide critical information about past ocean circulation changes and CO2 exchange between the surface ocean and the atmosphere. The late glacial period (11,000-14,000 years ago) which is known for large and abrupt climatic changes, including the Younger Dryas (YD) cold episode, is of particular interest in the North Atlantic. Here we present the first continuous, centennial-scale record of changes in the sea-surface 14C reservoir age through this period using unique marine deposits on Norway's west coast that contain both marine shells and terrestrial plant remains. The marine reservoir ages derived from the difference between the 14C ages of the shells and the plants shows considerable variation, increasing from 400 to 650 years in the early YD, forming a 700-year-long plateau, and dropping 300 years at the end of YD, thus eliminating the 10.0 14C kyr plateau evident from the tree ring record and marine varves at low latitudes. Observed changes in reservoir ages were closely related to circulation changes in the North Atlantic, with lower reservoir ages during the warmer periods (Preboreal and Bølling/Allerød), and higher reservoir ages during the colder periods (Younger Dryas and Older Dryas-Inter Allerød). The rapid changes raise the need for regional calibration curves for accurate conversion of marine 14C dates to calendar ages.
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