RRS Discovery Cruise 103, 21 June-10 July 2019. Water column and seafloor time-series studies at the Porcupine Abyssal Plain Sustained Observatory

Abstract

RRS Discovery cruise 103 departed Southampton late afternoon on the 21 June. DY103 operated in the Porcupine Abyssal Plain Sustained Observatory area (48°50´N 016°30´W) from the evening of 24th June – 6th July (with a 3 day loss to science due to a medivac into Cork from midnight 25th June to 9pm Friday 28th). DY103 then returned to Southampton 10th July 2019, a day later than scheduled. The overarching goal of the cruise was to continue various time-series observations of the surface ocean, water column, and seafloor at the site, as first studied by NOC (then the Institute of Oceanographic Sciences) in 1985. The specific objectives of the cruise were to recovery and redeploy, or service, three mooring systems (PAP1, PAP3, Bathysnap), and conduct a range of water column and seafloor observation and sampling operations. This cruise was a contribution to the Climate Linked Atlantic Section Science (CLASS) project supported by the UK Natural Environment Research Council (grant number NE/R015953/1).

The PAP 1 mooring, a Met Office (Balmoral ODAS) buoy and Autonomous Sensor Platform (ASP) suspended 30 m below the surface buoy, was successfully retrieved just prior to the medivac. It was fully serviced and redeployed on the 3rd July. The PAP 3 mooring, a sediment trap, microcat and current meter string, was successfully deployed and recovered, including colonisation substrata and larval traps for the on-going LO3CAted (Larval Occurrences in Open Ocean: Connectivity studies in NE Atlantic and Mediterranean Sea) project. The Bathysnap seafloor time-lapse camera mooring, and associated LO3CAted samplers from JC165, were also successfully recovered. However, this was only possible by a rescue mission with the HyBIS vehicle. The Bathysnap from DY077 was still not responding, despite an attempted HyBIS rescue mission, and this is now presumed lost. Two short-term (1-2 day) amphipod trap mooring deployments were also successfully carried out during the cruise.

A series of water column observation and sampling operations were successfully carried out with a CTD instrument package and water bottle rosette, and vertically hauled zooplankton nets. The former including pre- and post-deployment calibrations of PAP 1 sensors. Seafloor sampling operations were successfully carried out with a Megacorer and otter trawl, yielding samples for a broad range of subsequent analyses (eDNA; prokaryotic and viral dynamics; biogeochemistry; microplastics; metazoan meiobenthos; macrobenthos; megabenthos; biochemistry and microbiome studies of selected megabenthic taxa). A programme of seafloor survey photography was also undertaken using the HyBIS vehicle, assessing the seafloor environment and associated fauna of the abyssal plain. A further sediment trap mooring (with ADCPs and microcats) was deployed in the Whittard Canyon, as an additional component of the CLASS project, on the return passage to Southampton.

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