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.

In 2017 and 2018, we sampled about 20 locations across Frobisher Bay, mostly in the deeper portions of outer Frobisher Bay that are only accessible for sampling from large ships. Sample stations were chosen to span the range of depth and slope values in the multibeam sonar dataset, and in 2018 sampling, also included gross bottom morphology, such as ridges and troughs. We also targeted some particular geomorphic features, such as suspected submarine extensions of moraines. In 2017, bottom samples were acquired using box-cores, and small scientific trawl (Agassiz trawl). In 2018, bottom samples were acquired using box-cores, combined with a drop-video camera. Agassiz trawls were collected at two stations in 2018. Sediment samples were described visually and subsamples frozen for grain size and organic content analysis. Where informative, subsamples of lithic fragments within the sediments were kept for mapping. Bottom faunal samples were enumerated and preserved in 2% formalin in seawater, except for larger faunal samples such as soft corals, which were frozen.

A video-survey using a Super Mohawk remotely operated vehicle (ROV) was conducted in October 2015 in a site near Cape Dyer, Nunavut. The benthic environment was video-recorded and opportunistically photographed using a high-definition camera (1Cam Alpha, Sub C Imaging, 24.1 megapixels), at a depth of ~750 m along a transect line 935 m long.

A video-survey using a Super Mohawk remotely operated vehicle (ROV) was conducted in August 2013 in the Disko Fan area, SE Baffin Bay. A multibeam survey was conducted in the area before the ROV dive. The benthic environment was video-recorded using a standard-definition color camera, at depths of ~900-950 m.

In July 2014 and October 2015 a Super Mohawk (SuMo) remotely operated vehicle (ROV) aboard the CCGS Amundsen was used to video-survey a deep-water environment at Scott Inlet. In 2014, a video-transect ~2.7 km long was followed across depths of 475-650 m. Videos and photographs were obtained using a high-definition camera, and specimens of invertebrates (sponges) were collected using the ROV. In 2015, no transect was followed and the main objective was to sample carnivorous sponges using a sampling platform.

A benthic survey using a Super Mohawk remotely operated vehicle (ROV) was conducted in July 2017 at Disko Fan, SE Baffin Bay. The benthic environment was video-recorded and opportunistically photographed using a high-definition camera (1Cam Alpha, Sub C Imaging, 24.1 megapixels), at a water depth of ~930 m. An experimental frame deployed in 2016 was recovered during this ROV dive, but no other collections took place at this site during this dive.

Video surveys were conducted in July 2016 aboard CCGS Amundsen, using a Super Mohawk remotely operated vehicle (ROV) at Hatton Basin, Labrador (Canada). ROV dives occurred at two nearby sites (~28 km apart) in the Hatton Basin area (Dives 50 and 51). The benthic environment was video-recorded and photographed using a high-definition camera (1Cam Alpha, Sub C Imaging, 24.1 megapixels) mounted on the ROV, at depths ranging between 556-633 m. ROV transects were conducted to collect video data, and samples of corals and sponges were also collected during dive 51. Box-cores were deployed at the two sites. Sea water was collected at several depth intervals from surface to near-bottom to characterize particulate organic matter and to determine calcium carbonate saturation.

Multibeam echosounder data near Qikiqtarjuaq were collected by the CCGS Amundsen in 2007 and by the RV Nuliajuk from 2012-2015. Data collected between 2007 and 2014 were processed by the Ocean Mapping Group at the University of New Brunswick (http://www.omg.unb.ca/) and were retrieved from their data sharing interface (http://www.omg.unb.ca/Projects/Arctic/SE_Baffin/). Data collected in 2015 were processed by the Fisheries and Marine Institute at Memorial University of Newfoundland (https://www.mi.mun.ca/) and were obtained directly from them. These datasets were clipped to only include the area near Qikiqtarjuaq relevant to the benthic habitat mapping project lead by the Memorial University Marine Habitat Mapping Group. Individual datasets were mosaicked to create single continuous bathymetry (m) and backscatter (dB) raster layers at 5 m resolution. Mapping activities were funded by ArcticNet and the Government of Nunavut, Department of Environment, Fisheries and Sealing Division to support benthic habitat mapping for marine ecosystem management in this area.

A video-survey using a Super Mohawk remotely operated vehicle (ROV) was conducted in October 2015 near Qikiqtarjuaq, Nunavut. The benthic environment was video-recorded and opportunistically photographed using a high-definition camera (1Cam Alpha, Sub C Imaging, 24.1 megapixels), at a depth of ~620-680 m along a transect line 954m long.

A video-survey using a Super Mohawk remotely operated vehicle (ROV) was conducted in October 2015 at Inner Frobisher Bay, Nunavut. The benthic environment was video-recorded and opportunistically photographed using a high-definition camera (1Cam Alpha, Sub C Imaging, 24.1 megapixels), at a depth of ~59-139 m along a transect line 1.2 km long.