To obtain the data, water samples of vertical profiles were firstly collected from the Rosette onboard the CCGS Amundsen, and then analyzed with instruments both onboard and in the lab in University of Manitoba. The total mercury were measured on a Tekran 2600 Model with the method EPA 1631 in the Portable In-situ Laboratory for Mercury Species onboard, while the methylmercury data were analyzed with the method EPA 1630 in the Ultra-Clean Trace Element Laboratory, which is located at the University of Manitoba. The main data types are the contaminants (along with O18 isotopes and dissolved organic carbon) concentrations in vertical profiles at the study sites.

Unfiltered aqueous total and methyl mercury concentrations were measured from water collection on board the NGCC/CCGS Amundsen at stations within the Beaufort Sea, Amundsen Gulf, and the Canadian Arctic Archipelago. Profiles of 10-12 m depth resolution were collected from 15 stations using the ship rosette system. Total mercury samples were analyzed on board. Methylmercury samples were preserved and transported to Winnipeg for analysis. Interpretation of results will also rely on supporting data from ArcticNet collaborators to identify water masses and determine biological productivity that determine the relative importance of external sources and internal cycling.

Sampling took place on legs 6, 7, 8b, and 9 of the CFL project on the CCGS Amundsen (2008). Zooplankton were sampled with a 1x1m2 (200 µm mesh) net through the moon-pool and with a 1m diameter (200 µm mesh) ring net on the ice at ice covered stations. In open water, samples were collected with 2x1 sq.m (500 µm mesh), 4x1 sq.m (500 and 200 µm mesh), and rectangular mid-water trawl (1600 µm mesh). Samples were live sorted to species and frozen at -25C. Algae were collected from the bottom ice via ice cores and the dive program, from the ice interface/surface water with a Hg clean Niskin and a hose and pump on a 1m arm, and from the chlorophyll a maximum depth via the rosette. Samples in ice were frozen in the dark, while samples in water were filtered via dual filtration following Morrison and Watras (1999) and filters were frozen at -25C. Zooplankton species Calanus glacialis and Calanus hyperboreus were analyzed for total mercury using CVAAS; C. hyperboreus was also analyzed for methyl mercury via Gas Chromatography Atomic Fluorescence Spectrophotometry (GC AFS). The algae samples were analyzed for THg using cold vapour atomic absorption spectrometry (CVAAS) and MeHg using cold vapour atomic fluorescence spectroscopy (CVAFS).

Sample collection took place during both legs of the 2005 CCGS Amundsen cruise, during Leg 1 in 2006 and during Leg 3 in 2007. Water samples were collected using Teflon-lined Niskin bottles mounted on the ship¿s rosette system, at sites ranging from Hudson Bay, the North Open Water Polynya, the Northwest Passage and the Beaufort Sea. The water column was sampled at the surface, middle and bottom in 2005 and 2006 and at the surface and chlorophyll maximum in 2007. The resulting water chemistry dataset includes concentrations of total Hg, MMHg, DMHg and GEM in water. In addition, samples were also analyzed for sulfate and dissolved organic carbon in 2007 and for sulfate only in 2006. To quantify rates of biogeochemical Hg transformations in the water column, some water samples were amended with Hg stable-isotope tracers, namely 198Hg(II) and MM199Hg, and incubated on-board the ship for up to 25 hours before being preserved by acidification or freezing. Samples were then analyzed for MMHg, DMHg and GEM, using various mass-spectroscopy techniques at either the University of Alberta or Trent University. Thus, the rate of transformation of the 198Hg(II) tracer into MM198Hg, for example, could be quantified. This dataset includes rate constants for the following water column processes: the methylation of Hg(II) to MMHg, the methylation of MMHg to DMHg, the demethylation of MMHg, the reduction of MMHg to Hg(0) and the reduction of Hg(II) to Hg(0).

Zooplankton (Calanus sp., Limacina helacina, Euphasiacea, Clione limacina, Themisto sp., Paraeuchaeta sp, Hyperoche sp. and Sagitta sp.) were collected in net tows during 2003 & 2004 (onboard the CCGS Pierre Radisson and Des Groseillers) and 2005 & 2010 (onboard the CCGS Amundsen). After taxonomical sorting, samples were frozen for chemical analysis. Total mercury (THg) analysis was conducted at the Freshwater Institute, Winnipeg (DFO) using cold vapor atomic absorpotion spectrometry; monomethylmercury (MMHg) was analyzed at the University of Ottawa using gas chromatography atomic fluorescence spectroscopy; stable isotope ratios of nitrogen and carbon were run at the University of Winnipeg Isotope Laboratory using continuous flow ion ratio mass spectrometry.