Methodology:

The specimens in the dataset were collected in the following research cruises: JR17001, JR18003 and JR19002.

Sampling took place in 3 locations:

Marian Cove: -62.21637 -58.80814, depth (AVE = 107m ± 5 SE)

Borgen Bay: -64.77740 -63.46647, depth (AVE = 271 m ± 27 SE)

Sheldon Cove: -67.5700 -68.2253, depth (AVE = 261 m ± 96 SE)

Samples were taken using Agassiz Trawl (AGT), Hamon Grab.

Estimated sampling effort of the AGT: Marian Cove 964.5 m2, Borgen Bay 1157.4 m2 and Sheldon Cove 1157.4 m2.

Estimated sampling effort of the Hamon Grab: Marian Cove 1.3 m3, Borgen Bay 1.6 m3 and Sheldon Cove 1.1 m3.

Agassiz trawl samples: The mini AGT has a mesh size of 1 cm and a mouth width of 1.25 m. The trawl was modified for use on the RRS James Clark Ross by adding 160 kg (bolting 4 x 40 kg cylinders between the skid plates) to enable it to be deployed using the much larger A-frame and heavier winch wire.

The deployment protocol of the mini AGT deviated slightly from the standard AGT procedure. While the AGT was lowered, the ship had to compensate for the wire lowering speed of max of 50 m/min by steaming at 0.3 knots until the AGT reached the seabed and until the full trawling wire length was put out (standard BAS AGT increases speed to 0.5 knots once the trawl hits the sea floor). The full trawling cable length used was 2 times the water depth (standard BAS AGT uses a cable length of 1.5 times water depth). The net was then trawled at 0.3 knots for 5 minutes (standard BAS AGT protocol is a trawling speed of 1 knot). Afterwards, with the ship speed kept to 0.3 knots, the AGT was hauled at 30 m/min in order to avoid damaging the gear. When the AGT had left the seafloor, the hauling speed was increased to 45 m/min. The reduced size of the trawl and reduced trawling speed results in a slightly smaller catch, that damages substantially less seafloor, but the quality of the catch is much higher.

As the trawl was raised from the water, fire hoses were used to wash most of the mud out of the net - much more efficient that sieving on the deck (Fig. 6.9.1). Once the net was clean it was held over the 1mm mesh sieve and the cod end released so the catch was caught in its entirety into the sieves where the remaining mud was carefully washed off.

Samples were sorted to class and where possible to morphotype. Most specimens were preserved in pre-chilled 99.8 percent ethanol (total vial volume at least 80 percent ethanol) and stored in the -20 degrees Celsius freezer.

Hamon Grab samples: A Hamon grab with a 20 x 40 x 40 cm bucket was used to sample the infauna present in the muddy substrate of both glacial fjords. The grab was lowered at a maximum rate of 50 m/min which was reduced to 20 m/min roughly 50 m from the seabed. The multibeam maps and shelf underwater camera system (SUCS) images were used to ensure that the grab was deployed on to soft sediment and not bedrock, the Simrad echo sounder was also used to monitor bottom depth.

Once on deck, if the grab had fully deployed, two people steadied it back onto its stand. A large plastic box was placed underneath the stand to collect the sample and the grab arm was slowly lowered by releasing the tension on the cable and pulling down on the handles at the top of the arm. This generally resulted in the full grab contents falling into the plastic box beneath the stand. If the sample did not fall out easily, small shovels and pressured seawater were used to remove it from the grab bucket.

The sample collected was equally split between two 1 mm sieves. The rationale for splitting the sample was that both frozen and ethanol preserved samples were required for different team members. Deck hoses were then used to wash the sample with seawater through the sieve; the power of the hoses was carefully monitored to make sure the infaunal animals were not damaged by high water pressure. Once...(7)

Data collection:

Agassiz Trawl (AGT), Hamon Grab, 1 mm sieves, Microsoft Excel, shelf underwater camera system (SUCS; custom made by BAS)

Data quality:

Some factors affecting the data: the samples collected were distributed among several collaborating institutions in the project. This is reflected in the ''Final Destination'' column of the dataset. The most up-to-date location of the specimens is recorded in this column. The main specimen collection was moved from University of Exeter to University of Portsmouth in 2022, which is reflected in the dataset, at which point a tally of the collection was done. This tally identified that the samples from JR18003 were missing from the collection and they are not present either at University of Exeter or University or Portsmouth and therefore are presumed to be located at BAS. Some other samples are also unaccounted for. This is all reflected in the dataset.