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

caused by the introduction of gasoline leads of Australian origin with very low 206 Pb/ 207 Pb
values. The minimum 206 Pb/ 207 Pb value (in 1979) is consistent with production records which
indicated leaded gasoline consumption in Europe reached its zenith in 1980 (Hagner, 2000).
Moreover, direct air Pb measurements in Denmark document strong declines in Pb
concentrations since the late 1970`s (Jensen and Fenger, 1994). However, there appears to be no
published air Pb data older than ca. 1970. The Pb isotope results presented in Fig. 6c are
significant, as they show that the greatest percentage of anthropogenic Pb recorded by the peat
profile in DK was not caused primarily by leaded gasoline consumption, but rather from coal-
burning and other industrial sources. Moreover, these results show that anthropogenic Pb went
into decline well before either the introduction of maximum allowable Pb concentration in
gasoline (in 1978 in the EU according to Hagner, 2000), or the ban on leaded gasoline sales in
the EU in 1987 (Hagner, 2000). While leaded gasoline certainly contributed to a pronounced
shift in the isotopic composition of Pb-bearing aerosols, other sources of anthropogenic Pb were
quantitatively more important in DK during the first half of the 20 th century. Similar conclusions
were drawn from a recent study of duplicate peat cores from a Swiss bog which showed a
maximum in Pb EF pre-dating the minimum in 206 Pb/ 207 Pb (Shotyk et al., 2003).
DISCUSSION
Natural sources of Hg to the minerotrophic GL core
The elevated Hg concentrations in the uppermost layers of the GL core are effectively
contemporaneous with those of the DK core (Fig. 2) which has received Hg solely from
atmospheric deposition. Given the fundamental differences in the hydrology and geochemistry
of the two sites (ombrotrophic, acidic bog in DK, minerotrophic, alkaline fen in GL), and the
differences in peat accumulation rates (Fig. 3), it is unlikely that natural processes could have
caused such a similar chronology of atmospheric Hg. The most likely explanation for the
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