Horgan Martin J.

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Horgan
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Martin J.
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  • Preprint
    Increased accumulation of sulfur in lake sediments of the high Arctic
    ( 2010-08-31) Drevnick, Paul E. ; Muir, Derek C. G. ; Lamborg, Carl H. ; Horgan, Martin J. ; Canfield, Donald E. ; Boyle, John F. ; Rose, Neil L.
    We report a synchronous increase in accumulation of reduced inorganic sulfur since c. 1980 in sediment cores from eight of nine lakes studied in the Canadian Arctic and Svalbard (Norway). Sediment incubations and detailed analyses of sediment profiles from two of the lakes indicate that increases in sulfur accumulation may be due ultimately to a changing climate. Warming-induced lengthening of the ice-free season is resulting in well-documented increases in algal production and sedimentation of the resulting detrital matter. Algal detritus is a rich source of labile carbon, which in these sediments stimulates dissimilatory sulfate reduction. The sulfide produced is stored in sediment (as acid volatile sulfide), converted to other forms of sulfur, or reoxidized to sulfate and lost to the water column. An acceleration of the sulfur cycle in Arctic lakes could have profound effects on important biogeochemical processes, such as carbon burial and mercury methylation.
  • Preprint
    Increase in mercury in Pacific yellowfin tuna
    ( 2015-01) Drevnick, Paul E. ; Lamborg, Carl H. ; Horgan, Martin J.
    Mercury is a toxic trace metal that can accumulate to levels that threaten human and environmental health. Models and empirical data suggest that humans are responsible for a great deal of the mercury actively cycling in the environment at present. Thus, we would predict that the concentration of mercury in fish should have increased dramatically since the Industrial Revolution. Evidence in support of this hypothesis has been hard to find, however, and some studies have suggested that analyses of fish show no change in mercury concentration. By compiling and re-analyzing published reports on yellowfin tuna (Thunnus albacares) caught near Hawai’i over the past half century, we find that the concentration of mercury in these fish is currently increasing at a rate ≥ 3.8 % per year. This rate of increase is consistent with a model of anthropogenic forcing on the mercury cycle in the North Pacific, and suggests fish mercury concentrations are keeping pace with current loadings increases to the ocean. Future increases in mercury in yellowfin tuna and other fishes can be avoided by reductions in atmospheric mercury emissions from point sources.