RRS Challenger Cruise 142, 19 Apr-19 May 1999. Temporal and spatial variability of benthic communities on the Porcupine Abyssal Plain and in the Porcupine Seabight

RRS Challenger Cruise 142 aimed to study 1) long-term change in abyssal benthic communities (4850m, Porcupine Abyssal Plain) and 2) coral communities on carbonate mounds (c. 800m, Porcupine Seabight). Sampling on the first leg was focussed at a central locality 48°50’N, 16°30’W) on the Porcupine Abyssal Plain. This locality had been sampled on 9 separate cruises over a 9-year period (1989-1998). A radical change in the composition of the benthic fauna had occurred in recent years and this cruise aimed to follow further long-term change in the benthic fauna and sediment biogeochemistry. In addition, in order to set the results from this central locality in a basin-wide context, further sampling was undertaken across the Porcupine Abyssal Plain. Sampling on the second leg concentrated on the giant carbonate mounds discovered in recent years on the eastern and northern flanks of the Porcupine Seabight. The mounds had well-developed coral communities. Samples and video of the coral were collected. Other seabed features also noted in sidescan sonar records on previous cruises were imaged as well.