Methodology:

The sediment trap (Mclane PARFLUX, 0.5 m2 capture area; McLane labs, Falmouth MA, USA) was located at the observation site P3 in Northeast Scotia Sea (52.80 degrees S, 40.14 degrees W). The sampling location is a productive area of the Southern Ocean associated with consistent and strong phytoplankton blooms. The sediment trap was deployed at 400 m and secured using a mooring line anchored to the seabed at 3748 m depth. The trap was deployed from 25/01/2018 until 01/12/2018 during research cruise JR17002, RSS James Clark Ross (recovered during research cruise DY098; RRS Discovery).

The trap was fitted with 500 ml bottles filled with a formosaline solution (filtered seawater containing 2 % v/v formalin, mixed with sodium tetraborate (BORAX; 0.025 % w/v), and 0. 5 % w/v sodium chloride) to preserve organic material and prevent mixing with the water column. The trap was fitted with a baffle to prevent larger organisms entering. The bottles are placed in a carousel pre-programmed to rotate under the funnel and collect material every month (28-31 days). Once recovered, samples were stored at 4 degrees C until analysis.

Bottles were analysed for swimmers (Zooplankton who have actively swum into the trap). Specimens were identified and counted under an Olympus SZX16 fitted with a canon EOS 60D DSLR camera. For small individuals (< 1 mm) samples were analysed in sub-aliquots, with totals estimated from the aliquots; otherwise, bottles were analysed in their entirety. We have classified swimmers as any intact animal. Animals with shells (e.g., pteropods) are prone to more damage during storage and handling, consequently they were still considered "intact" where there was minor (non-structural) damage to the shell and the somas was still present and whole. In this study we do not discriminate between swimmers and carcasses (i.e., zooplankton that have died shortly before sinking into the trap). However, Ivory et al., (2014) found the number of swimmers to be an order of magnitude higher than sinking carcasses, indicating they are a relatively minor component of the trap. Swimmer size was measured using callipers accurate to 0.5 mm, and a range for each taxa within each sampling window is given.

The Sea-Bird SBE37 CTD instrument mounted on the P3 observation site mooring was used to obtain temperature data at depth 200 m, which accompany the zooplankton data provided here.

Data collection:

Sediment trap (Mclane PARFLUX, 0.5 m2 capture area; McLane labs, Falmouth MA, USA)

Olympus SZX16 fitted with a canon EOS 60D DSLR camera

Sea-Bird SBE37 CTD

Data quality:

Calipers accurate to 0.5 mm.

NA indicates where no size measurements were taken.