| Summary: | International audience The element lead is introduced to the marine atmosphere from combustion sources, but has had very large scale reductions in the North Atlantic due to the phasing out of leaded gasoline first in North America followed by Europe. The regional sources and transient fate of lead in the surface Sargasso Sea can be traced using its isotopic signature. The stable lead isotopic record has been documented in the atmosphere and waters of Bermuda over the past decade. Here, lead isotopes can be used as a proxy to trace atmospheric sources and particle exchange processes of trace elements within the water column. The long term record has allowed us to document seasonal/decadinal trends in emission source intensity, as well as atmospheric scavenging processes during changes in regional emissions. Also documented is the close link between such transient changes in lead atmospheric deposition, and its cycling within the oligotrophic Sargasso Sea. The impact of this atmospheric transient has been recorded throughout the water column (down to 4200m) at the Bermuda Atlantic Time Series (BATS). While the lead isotopic profiles show significant seasonal shifts in the mixed layer, they appear quite homogeneous at depth. Thus, one can distinguish the specific isotopic imprint of distinct water masses including (1) Atlantic central waters, (2) North Atlantic deep waters and (3) recirculating deep boundary current water. Included is the downward ventilation of the transient tracer, plus the role of surface advection in its mass balance. The signature in the suspended particles document scavenging and repackaging processes at depth in these oligotrophic waters. Lead isotope ratios (206Pb/207Pb) in suspended particles are confirmed to be in complete equilibrium with the dissolved fraction suggesting a rapid exchange between these reservoirs.
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