Radiocarbon dating:
"The difference is the 14C reservoir age for coastal water at the west coast of Norway during the mid-Younger Dryas and equals 610 -655 yr. This is 230 yr older than the reservoir age for the Bolling/Allerod and for the present day in this area." [Bondevik, S et al.: The marine 14C age of the Vedde Ash Bed along the west coast of Norway. Journal of Quaternary Science (2001) 16 (1) 3-7]