Recent Reservoir Ages for Danish Fjords and Marine Waters

TLDR

The study measured AMS ¹⁴C dates on 28 mollusk shells from Danish fjords and marine waters (1885‑1945) and calculated reservoir ages using the tree‑ring calibration curve. Marine samples yielded a weighted‑average reservoir age of 377 ± 16 yr (ΔR = 13 ± 16 yr), supporting use of the marine calibration curve with ΔR = 0, while fjord samples showed highly variable ages (400–>900 yr) due to old soil carbonate, implying dating uncertainties of several hundred years.

Abstract

AMS 14 C dates were measured for 28 mollusk shells collected live in Danish waters over the period ad 1885 to 1945. Fourteen samples were from fjords and 14 were marine samples from the Danish Skagerrak-Kattegat coastal area and from the Belts. Reservoir ages were calculated for all samples on the basis of the tree-ring calibration curve. For the marine samples, which cover the period ad 1885–1916, we found a weighted-average reservoir age of 377 ± 16 yr. The marine ∆R values (the difference between the measured 14 C age and the age deduced from marine, mixed-layer model calculation of Stuiver, Pearson and Braziunas (1986)) were found to be uniform within the experimental uncertainty with a weighted average of ∆R = 13 ± 16 yr. Based on the observed scatter, the standard deviation is 21 yr. This result shows that it is justified to use the marine calibration curve with standard parameters (∆R = 0) when 14 C-dating marine samples from the Danish area. Our value is consistent with the result ∆R = −33 ± 27 yr previously found for the Norwegian and Swedish Skagerrak-Kattegat coasts. In contrast, reservoir ages for Danish fjords were found to vary from 400 to >900 yr, far beyond experimental uncertainty. We ascribe this to varying content of dissolved, old soil carbonate (hard-water effect). Therefore, dating of samples from such fjord environments is expected to be uncertain by several hundred years.