FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

512 M E Goodsite et al.
Figure 4 Hg concentration profiles for the Storelungmose (Denmark) and the Tasiusaq (Greenland) peat
cores. Hg concentrations are normalized to dry bulk density. Horizontal dashed lines indicate the depth where
the macrofossils used for 14 C dating were taken. The corresponding calibrated ages are given as numbers
close to the lines. Where two Hg concentration measurements were performed unweighted mean values and
error bars corresponding to the uncertainty of the mean are shown.
CONCLUSION
By comparing data sets from all over the extratropical northern hemisphere, the present paper shows
that 14 C dating of plants during the bomb-pulse period is generally possible at a precision of 1–2
years. For the first time, we were able to clearly reproduce the whole atmospheric 14 C bomb-pulse
curve in peat cores by measuring 14 C in macrofossils in peat from Greenland and Denmark, and we
could exclude any significant dampening effect for these cores. We compared the 14 C bomb-pulse
dating method, which allows precise dating of single points in the peat matrix, with the more familiar
techniques based on records of fallout radionuclides. 14 C is actively taken up into the living material
from the surrounding atmosphere and gets fixed via photosynthetic activity along with the stable
isotopes 12 C and 13 C, which provide normalization of the 14 C concentrations, allowing direct dating
of the material. In contrast, records of fallout 210 Pb, together with those of Pb and Hg, may be subject
to small displacements at the time of deposition on the bog surface. Comparisons between 14 C
and 210 Pb offer a means for determining a more precise interpretation of pollution records in bog
archives.
As an example of the usefulness of the 14 C bomb-pulse dating method combined with peat core analysis,
we applied the 14 C bomb-pulse dating method to two peat cores from Greenland and Denmark
to obtain high-resolution dates for Hg concentration profiles for the second half of the 20th century.