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

unpublished data for these parameters from the Store Vildmose bog.
Comparison of Pb and As concentrations and enrichments, GL versus DK
Lead and As concentrations are much higher in the DK core compared with GL (Fig.
5a). However, the maximum Pb concentrations in the DK core are very similar to the maximum
values found in the Draved Mose peat profile described by Aaby and Jacobsen (1978). To
emphasize the difference in Pb and As between the GL and DK profiles, and to take into account
the differences in abundance of mineral material, Enrichment Factors (EF) were calculated as
EF = ([M]/[Ti]) peat / ([M]/[Ti]) Earth`s crust
where [M] refers to the total concentration of Pb or As measured in the peat sample (µg/g) and
[Ti] to the total concentration of Ti. Although Sc is the preferred reference element for these
calculations (Shotyk et al., 2001), Sc concentration data is not yet available for these two peat
cores. The EF indicates the extent of elemental enrichment in the peats, relative to the abundance
of that metal in the Earth`s Upper Crust (Wedepohl, 1995) where Pb = 14.8, As = 1.7 and Ti =
4010 µg/g. The calculated Enrichment Factors (Fig. 5a) show that these elements are enriched
in the DK core up to 65x (Pb) and 85x (As). In contrast, the GL core reveals no significant
enrichment of Pb, and only very slight enrichments of As. Given that the As concentrations in
the GL profile are generally at or below the lower limit of detection by XRF (3 µg/g), any record
of anthropogenic As in the GL profile cannot be discerned using the total concentrations of As
as measured by XRF, and its ratio to Ti. Similarly, in the GL core the Pb concentrations are
comparatively low and concentrations of lithogenic trace elements such as Ti and Zr are
comparatively high; thus, using total metal concentrations it is not possible to discern any
significant impact of anthropogenic Pb. In the DK core, just the opposite is true: concentrations
of Pb and As are high but the concentrations of lithogenic elements (Ti, Zr) are comparatively
low. Thus, in the DK core, enrichments of Pb and As, relative to their crustal abundance, are
(i)
18