RRS Discovery Cruise DY090, 23 May – 28 June 2018, Walvis Bay, Namibia – Cape Town, South Africa. NMF Sensors and Moorings CTD, LADCP & SAPs Cruise.

Abstract

The purpose of the COMICS programme (Controls over Oceanic Mesopelagic Interior Carbon Storage) is to investigate three leading hypotheses on controls over the remineralisation depth of organic carbon. The remineralisation depth is key to setting the air-sea balance of CO2 and thus in regulating Earth’s climate. Nevertheless, the dominant controls on spatial and temporal variability in remineralisation depth remain unclear. The three potential controls are: temperature, oxygen concentration and ecosystem structure.

The COMICS programme includes 2 cruises to contrasting oceanic regions: DY086 which sampled the high productivity region downstream of South Georgia in November/December 2017, and this cruise, DY090, which targeted the low oxygen region offshore of Namibia in May/June 2018. The sampling strategy for DY090 was to conduct long stations (~6 days) in contrasting mesopelagic oxygen conditions. The two main stations were BS (Benguela South) at 21.5S, 9.5E and BN (Benguela North) at 18S, 11E. The original plan was to shuttle between the 2 sites multiple times, but after completing one cycle of the station at each of the BS and BN sites we decided instead to remain at the BN site and undertake a sequence of the 6 day station cycle to capture the temporal evolution of the mesopelagic oxygen minimum and consequent influence on remineralisation depth.

DY090 completed 1 cycle of the super-station at BS, 3 cycles at BN, and additionally completed some other random bits and bobs at the end of the cruise. In total, 464 events were completed in 4 weeks of science time.

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