The relationship between biophysical variables and halocarbon distributions in the waters of the Amundsen and Ross Seas, Antarctica

Abstract

Little is known regarding the distribution of volatile halogenated organic compounds (halocarbons) in Antarctic waters and their relation to biophysical variables. During the austral summer (December to January) in 2007–08 halocarbon and pigment concentrations were measured in the Amundsen (100–130°W) and Ross Sea (158°W–160°E). In addition, halocarbons were determined in air, snow and sea ice. The distribution of halocarbons was influenced to a large extent by sea ice, and to a much lesser extent by pelagic biota. Concentrations of naturally produced halocarbons were elevated in the surface mixed layer in ice covered areas compared to open waters in polynyas and in the bottom waters of the Ross Sea. Higher concentrations of halocarbons were also found in sea ice brine compared to the surface waters. Incubations of snow revealed an additional source of halocarbons. The distribution of halocarbons also varied considerably between the Amundsen and Ross Seas, mainly due to the different oceanographic settings. For iodinated compounds, weak correlations were found with the presence of pigments indicative of Phaeocystis, mainly in the Ross Sea. Surface waters of the Amundsen and Ross Seas are a sink for bromoform (saturation anomalies, SA, −83 to 11%), whereas sea ice was found to be both a source and sink (SA −61–97%). In contrast, both surface waters and sea ice were found to be a source of chloroiodomethane (SA −6–1 200% and 91–22 000 resp.). Consequently, polar waters can have a substantial impact on global halocarbon budgets and need to be included in large-scale assessments.