LEAD VARIABILITY IN THE WESTERN NORTH-ATLANTIC OCEAN AND CENTRAL GREENLAND ICE - IMPLICATIONS FOR THE SEARCH FOR DECADAL TRENDS IN ANTHROPOGENIC EMISSIONS
Ea. Boyle et al., LEAD VARIABILITY IN THE WESTERN NORTH-ATLANTIC OCEAN AND CENTRAL GREENLAND ICE - IMPLICATIONS FOR THE SEARCH FOR DECADAL TRENDS IN ANTHROPOGENIC EMISSIONS, Geochimica et cosmochimica acta, 58(15), 1994, pp. 3227-3238
As Patterson and coworkers have shown, most of the lead in the modern
ocean and atmosphere is of anthropogenic origin. Reductions in the uti
lization of leaded gasoline over the past two decades should decrease
lead deposition from the atmosphere in remote locations. The search fo
r trends in Pb deposition within a single decade is bedeviled by large
-amplitude short-term variability due to the inherent noisiness of the
atmosphere/ocean system. We find that, over the course of a year, lea
d concentrations in the surface waters of the western North Atlantic O
cean are variable (factor of 2), and in the snow deposited in central
Greenland, highly variable (order of magnitude). In the western North
Atlantic, Pb-210 normalization minimizes this problem because Pb-210 a
nd Pb sources are spatially correlated and continental Pb-210 emission
s are constant. It is clear the Pb in surface waters of the western No
rth Atlantic has decreased by a factor of 4 during the 1980s. Pb-210 n
ormalization does not help in the Arctic because stable Pb and Pb-210
are not spatially correlated. Because of the order-of-magnitude variab
ility in Greenland snow Pb linked to annual cycles, any discontinuous
time series is likely to be affected by the phenomenon of aliasing. Al
iasing makes it difficult to determine if there is a trend in Pb depos
ition in central Greenland during the 1980s; present evidence suggests
that the reduction in Pb concentration in snow during the 1980s is le
ss than a factor of two; certainly quite a bit less than observed in t
he western North Atlantic and less than the factor of >7 reduction in
leaded gasoline utilization in the United States during the decade. Al
though we expect that decadal-scale trends in the 1970s and 1980s are
in fact occurring due to the phasing out of leaded gasoline, the repor
ted magnitude of decadal-scale trends should be regarded with some res
ervation until confirmed by independent samplings.