This study is based on sampling conducted partially within the framework of the (1) Arctic Biological Station program-Biological Oceanography Section (ABS-BOS) from 1973 to 1975, (2) CCGS Sir Wilfrid Laurier program and CASES from 2002 to 2004, (3) IPY-CFL from 2007 to 2008, (4) through research collaborations among the CCGS Amundsen program, ArcticNet, BP Exploration Operating Company Limited, ExxonMobil and Imperial Oil from 2009 to 2011, and (5) BREA in 2012. Macrobenthos communities were sampled at 235 stations from 1973 to 2012 between April and November through different scientific programs and onboard different research vessels. Faunal samples were collected mostly with a USNEL box corer (0.25 m2), except from 1973 to 2002 where different grab models were used. Due to shared sediment requirements, on average 0.12 ± 0.05 m2 of sediment were sieved from each box core or grab sample. All box core and grab catches were washed under running seawater onboard over a 0.4 mm sieve during the CASES program and over a 0.5 mm sieve during all other programs, resulting in all macrobenthic invertebrates considered here being ≥ 0.5 mm size. Taxa were preserved in a 4 to 5 % seawater-formaldehyde solution buffered with sodium tetraethylborate for later identification in the lab and then transferred in 70 % ethanol for long-term storage.

Processed atmospheric ceiling heights were recorded from a CT25K ceilometer. The instrument was mounted on the CCGS Amundsen icebreaker on the port side directly behind the ship's wheelhouse. Data were collected during transit, set transects, 24-hour stations, and multi-day drift stations. The instrument was running continuously during the IPY-CFL project, with only minor interruptions for maintenance activities.

The CTD data was obtained during the 2007-2008 scientific cruise #0801 within the framework of the Circumpolar Flaw Lead Study (CFL). This program included a year round sampling expedition to study the air-sea interactions occurring in the ice-free sections of the southern Beaufort Sea and Amundsen Gulf. The data were collected from February 2 to March 13, 2008, aboard the CCGS Amundsen. There were 139 CTD casts, associated to 10 ice-drift stations, located in the Amundsen Gulf area. The following parameters were measured: temperature, conductivity and pressure (with a Sea-Bird SBE-9plus), dissolved oxygen (Sea-Bird SBE-43), pH (Sea-Bird SBE-18-I), fluorescence (Seapoint chlorophyll fluorometer), nitrate concentration (Satlantic MBARI-ISUS 5T), transmittance (Wetlabs C-Star transmissometer), light intensity (PAR; Biospherical Instruments QCP2300) and surface light intensity (sPAR; Biospherical Instruments QCP2200). Quality control procedures were applied to the data. Data are available on the Polar Data Catalogue and at the Marine Environmental Data Service (MEDS) of Fisheries and Oceans Canada.

The CTD data was obtained during the 2007-2008 scientific cruise #0802 within the framework of the Circumpolar Flaw Lead Study (CFL). This program included a year round sampling expedition to study the air-sea interactions occurring in the ice-free sections of the southern Beaufort Sea and Amundsen Gulf. The data were collected from March 15 to April 23, 2008, aboard the CCGS Amundsen. There were 132 CTD casts, associated to 10 ice-drift stations, located in the Amundsen Gulf area. The following parameters were measured: temperature, conductivity and pressure (with a Sea-Bird SBE-9plus), dissolved oxygen (Sea-Bird SBE-43), pH (Sea-Bird SBE-18-I), fluorescence (Seapoint chlorophyll fluorometer), nitrate concentration (Satlantic MBARI-ISUS 5T), transmittance (Wetlabs C-Star transmissometer), light intensity (PAR; Biospherical Instruments QCP2300) and surface light intensity (sPAR; Biospherical Instruments QCP2200). Quality control procedures were applied to the data. Data are available on the Polar Data Catalogue and at the Marine Environmental Data Service (MEDS) of Fisheries and Oceans Canada.

The CTD data was obtained during the 2007-2008 scientific cruise #0708 within the framework of the Circumpolar Flaw Lead Study (CFL). This program included a year round sampling expedition to study the air-sea interactions occurring in the ice-free sections of the southern Beaufort Sea and Amundsen Gulf. The data were collected from December 22, 2007, to January 30, 2008, aboard the CCGS Amundsen. There were 158 CTD casts, associated to 10 ice-drift stations, located in the Amundsen Gulf area. The following parameters were measured: temperature, conductivity and pressure (with a Sea-Bird SBE-9plus), dissolved oxygen (Sea-Bird SBE-43), pH (Sea-Bird SBE-18-I), fluorescence (Seapoint chlorophyll fluorometer), nitrate concentration (Satlantic MBARI-ISUS 5T), transmittance (Wetlabs C-Star transmissometer), light intensity (PAR; Biospherical Instruments QCP2300) and surface light intensity (sPAR; Biospherical Instruments QCP2200). Quality control procedures were applied to the data. Data are available on the Polar Data Catalogue and at the Marine Environmental Data Service (MEDS) of Fisheries and Oceans Canada.

Continuous measurements of emissivity at 89 and 37 GHz frequencies in vertical and horizontal polarizations at a fixed elevation angle of 55 degrees during transit and scanning elevation angles of 30-150 degrees at every station were acquired. The radiometers were installed at the 200 level on the CCGS Amundsen icebreaker on the port side. Generally the instruments acquired data at the fixed elevation angle during transit, and 3-5 scans were performed at every station along with auxiliary data collection (GPS data, geographic location of the station, photographs of the same field of view, air temperature, wind data, atmospheric conditions, surface characteristics, etc.). The acquired data are in binary format which is produced for every scan and fixed modes. The time in the data logger is generally set to UTC. An example filename would be 'RADDAT-2007-11-06-122647.DAT'.

During the ArcticNet annual cruises of the research icebreaker CCGS Amundsen, characteristics of the surface sea water (temperature, salinity, dissolved CO2 and O2) are monitored in conjunction with properties of the near-surface atmosphere (basic meteorological elements, incident radiation, CO2 concentration) to observe the relationship between the surface microclimate and the air-sea exchange, with particular interest in CO2. Central to this integrated dataset is an under-way sea water pCO2 system (General Oceanics 8050) attached to the ship's clean water intake. The following variables were measured continuously and logged at 1 minute intervals: -pCO2sw (LI7000 gas analyzer) -Equilibrator water temperature -conductivity -pH -dissolved O2

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.

The data set is composed of raw files recorded with a SIMRAD EK60 three-frequency split-beam echosounder that was operated continuously during the annual ArcticNet (2005-2010) and the 15 months IPY-CFL (2007-2008) sampling expeditions aboard the CCGS Amundsen. Three 7° transducers were hull-mounted, two in oil-filled arctic wells protected by a 2.5 cm thick acoustically transparent polycarbonate plate (38 and 120 kHz) and one in a Traveocean piston well in direct contact with water (200 kHz). The acoustic signal was recorded continuously on a PC using ER60 software version 2.0.0. Ping interval was set at 2 or 3 s and the pulse length was set at 1.024 ms.

Raw backscatter data were collected from a CT25K ceilometer. A ceilometer is a device that uses a laser or other light source to determine the height of a cloud base. Ceilometers can also be used to measure the aerosol concentration within the atmosphere. Sampling took place from July to November 2009 in the southern Beaufort Sea and the Amundsen Gulf (Canadian Arctic) during the CFL cruise onboard the CCGS Amundsen icebreaker. The Circumpolar Flaw Lead System Study (CFL) is an IPY-funded project. Data were collected (1) during the ship transit, (2) set transects, (3) at several stations where we stayed 24 hours, and (4) at multi-day drift stations. The instrument was running continuously during the CFL project, with only minor interruptions for maintenance activities.