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Seabirds represent a well documented biological transport pathway of nutrients from the ocean to the land by nesting in colonies and providing organic subsidies (feces, carcasses, dropped food) to these sites. We investigated whether seabirds that feed at different trophic levels vary in their potency as biovectors of metals, which can bioaccumulate through the marine foodweb. Our study site, located on a small island in Arctic Canada, contains the unique scenario of two nearby ponds, one of which receives inputs almost exclusively from upper trophic level piscivores (Arctic terns, Sterna paradisaea) and the other mainly from lower trophic level molluscivores (common eiders, Somateria mollissima). We used dated sediment cores to compare differences in diatoms, metal concentrations and also stable isotopes of nitrogen ([delta][sup.15]N), which reflect trophic position. We show that the seabirds carry species-specific mixtures of metals that are ultimately shunted to their nesting sites. For example, sediments from the tern-affected pond recorded the highest levels of [delta][sup.15]N and the greatest concentrations of metals that are known to bioaccumulate, including Hg and Cd. In contrast, the core from the eider-affected site registered lower [delta][sup.15]N values, but higher concentrations of Pb, AI, and Mn. These metals have been recorded at their greatest concentrations in eiders relative to other seabirds, including Arctic terns. These data indicate that metals may be used to track seabird population dynamics, and that some metal tracers may even be species-specific. The predominance of large seabird colonies on every continent suggests that similar processes are operating along coastlines worldwide. biological transport | paleolimnology | Arctic terns | common eiders | bioaccumulation doi/ 10.1073/pnas.1001333107

Organo-chlorine deposition in snow from mountain ranges in western Canada showing a 10- to 100-fold increase between altitudes of 770 and 3,100 m, have been reported. cold-condensation effects further enhance the concentrations of more-volatile organochlorines, with increasing altitude. This shows that temperate-zone mountain regions with high precipitation levels close to pollutant sources, are particularly vulnerable to semivolatile organochlorine compound accumulation.

IN THEIR BREVIA 'ARCTIC SEABIRDS TRANSport marine-derived contaminants' (15 July, p. 445), J. M. Blais et al. showed that contaminant concentrations increased exponentially with stable isotope ratio of nitrogen ([δ.sup.15]N) [...]

Transport of pollutants by migratory species, such as salmon, is known to affect contaminant distributions in Alaskan nursery lakes (1, 2). Arctic seabirds may also be transporting industrial and agricultural [...]