The concentration and isotopic composition of mercury (Hg) were determined in glacier core samples from Canadian Arctic ice caps dating from preindustrial to recent time (early 21st century). Mean Hg levels increased from <= 0.2 ng L-1 in preindustrial time to similar to 0.8-1.2 ng L-1 in the modern industrial era (last similar to 200 years). Hg accumulated on Arctic ice caps has Delta Hg-199 and Delta Hg-201 that are higher (similar to-1 to 2.9 parts per thousand) than previously reported for Arctic snow impacted by atmospheric Hg depletion events (mostly <-1 parts per thousand), suggesting that these events contribute little to Hg accumulation on ice caps. The range of delta Hg-202, Delta Hg-199, and Delta Hg-201 in glacier cores overlaps with that of Arctic Hg-(g)(0) and of seawater in Baffin Bay and also with that of midlatitude precipitation and industrial Hg sources, including coal and Hg ores. A core from Agassiz ice cap (80.7 degrees N) shows a similar to+1 parts per thousand shift in delta Hg-202 over the nineteenth to twentieth centuries that could reflect changes in the isotopic composition of the atmospheric Hg pool in the High Arctic in response to growing industrial emissions at lower latitudes. This study is the first ever to report on historical variations of Hg stable isotope ratios in Arctic ice cores. Results could help constrain future modeling efforts of the global Hg biogeochemical cycle and the atmosphere's response to changing Hg emissions, past and future.

Several recent studies have highlighted the importance of salmon as a means to deliver biomagnifying contaminants to nursery lakes. There is a lack of studies, however, which demonstrate empirically how this source has varied through time. This is of great significance because past salmon-derived contaminant loading was potentially greater than it is today. By analyzing radiometrically dated sediment cores collected from ten lakes in Alaska and British Columbia (B.C.), we relate historical numbers of sockeye salmon spawners to SigmaPCB concentrations and delta(15)N values (a paleolimnological proxy for past salmon-derived nitrogen) in the sediments. The results confirm that sockeye salmon have provided an important route for PCBs to enter the lakes in the past, a finding that is especially evident when the data of all lakes are pooled. Significant relationships between sockeye salmon numbers and delta(15)N, as well as SigmaPCB concentrations and delta(15)N in sediments, were also found. However, it is difficult to establish relationships between salmon numbers, SigmaPCBs and delta(15)N in individual lakes. This may be due to a number of factors which may influence contaminant loadings to the lakes. The factors include: a) changing salmon contaminant loads over time resulting from a lag in the upper ocean reservoir and/or changing salmon feeding locations; b) greater importance of atmospheric transport in lakes with relatively low salmon returns; and c) increased PCB scavenging due to higher algae productivity in the lakes in recent years.