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.

Zooplankton samples were collected onboard the research Icebreaker CCGS Amundsen during Leg 1 in 2005 (4 stations) and Leg 1 in 2006 (8 stations) with a vertically towed net frame equipped with a set of 4 adjacent 1-m2 nets (mesh size 200 µm and 500 µm) from near the bottom to the surface and by trawling an oblique rectangular mid-water trawl (mesh size 1600 µm) or an oblique Tucker net (mesh size 2x500 µm) in the surface layer from 100 m depth to the surface. Samples were placed into 30 ml plastic vials and/or whirl-pak bags and were kept frozen at -20 degree Celsius. Representative sub-samples of individual zooplankton genera were placed in 4 ml glass vials for stable isotope analysis. Three keystone zooplankton genus were included in this study: Calanus spp. (mostly adult Calanus hyperboreus), Themisto spp. (mostly adult Themisto libellula) and Euchaeta spp. THg analysis was conducted at the Freshwater Institute with cold vapour atomic absorption spectroscopy (CVAAS). MMHg analysis was conducted at the University of Ottawa by Gas Chromatography Atomic Fluorescence Spectroscopy (GCAFS). Carbon and nitrogen isotopic analyses were performed at the University of Winnipeg Isotope Laboratory by continuous flow ion ratio mass spectrometry (CF-IRMS). Oceanographic data (Hg levels in water column, salinity, 18O) were collected by our team. Water samples were collected with 24 12-L Niskin bottles attached to a rosette sampler equipped with Seabird 911+ CTD (Sea-Bird Electronics, Inc.).

Samples collected by rosette or hand-deployed niskin, directly transferred into acid-washed and backed glass vials with teflon-lined silicone septa caps, and frozen at -20 or -80 C. Analyses conducted by high-temperature catalytic combustion and calibrated again standards provided by the University of Miami. In 2002, all samples were total organic carbon (TOC), and in 2003-04, all samples were dissolved organc carbon (DOC, filtered through combusted GFF), and TOC was also collected at full stations at in surface waters at the overwintering site.

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.

Zooplankton samples were collected onboard the research Icebreaker CCGS Amundsen during Leg 1 in 2005 (4 stations) and Leg 1 in 2006 (8 stations) with a vertically towed net frame equipped with a set of 4 adjacent 1-m2 nets (mesh size 200 µm and 500 µm) from near the bottom to the surface and by trawling an oblique rectangular mid-water trawl (mesh size 1600 µm) or an oblique Tucker net (mesh size 2x500 µm) in the surface layer from 100 m depth to the surface. Samples were placed into 30 ml plastic vials and/or whirl-pak bags and were kept frozen at -20 Degree Celcius. Representative sub-samples of individual zooplankton genera were placed in 4 ml glass vials for stable isotope analysis. Three keystone zooplankton genus were included in this study: Calanus spp. (mostly adult Calanus hyperboreus), Themisto spp. (mostly adult Themisto libellula) and Euchaeta spp. THg analysis was conducted at the Freshwater Institute with cold vapour atomic absorption spectroscopy (CVAAS). MMHg analysis was conducted at the University of Ottawa by Gas Chromatography Atomic Fluorescence Spectroscopy (GCAFS). Carbon and nitrogen isotopic analyses were performed at the University of Winnipeg Isotope Laboratory by continuous flow ion ratio mass spectrometry (CF-IRMS). Oceanographic data (Hg levels in water column, salinity, 18O) were collected by our team. Water samples were collected with 24 12-L Niskin bottles attached to a rosette sampler equipped with Seabird 911+ CTD (Sea-Bird)