RRS Discovery DY087

Cruise summary report

Cruise Info. 
Ship name (ship code)RRS Discovery (74EQ)
Cruise identifierDY087
Cruise period2018-01-16 — 2018-03-02
Port of departurePunta Arenas, Chile
Port of returnPunta Arenas, Chile

1. Collect new seismic reflection profiles over the MEB, WGB, and NEGR, in order to understand the processes and patterns of sedimentation in these areas and identify expanded sedimentary successions.
2. Collect and analyse piston cores along newly collected seismic lines to identify locations with the most continuous geological successions, appropriate geological ages, and sediment lithologies suitable for multi-proxy palaeoceanographic investigations.
3. Assess potential IODP drill sites while underway and collect seismic reflection crossing lines at suitable localities, fulfilling IODP seismic data requirements for site selection and safety.
4. Collect short multicores, multibeam bathymetry, and acoustic sub-bottom profiler data at potential drillsites to characterise the surface sediments.
5. Correlate new seismic reflection and piston core age data to existing scientific drillcores to inform seismo-stratigraphic interpretations and refine drilling targets and science objectives for an IODP proposal.
6. Investigate physical properties and mixing in the modern ocean through collection of water-column temperature and salinity profiles and analysis of seismic data (seismic oceanography).

Cruise Achievements

The essential science objectives for DY087 as set out in the cruise proposal were achieved. Approximately 3270 line-km of multi-channel seismic reflection data were collected, including surveys of the Northeast Georgia Rise and the eastern area of the Maurice Ewing Bank and a long transect across the West Georgia Basin between the two main working areas. The targeted sedimentary strata were successfully cored at 19 sites. Recovery of short sediment cores was achieved at an additional 4 sites, but these cores likely did not penetrate into the older targeted strata.

Secondary objectives achieved on DY087 include: (1) nearly complete underway single-beam echosounder (EA640), multibeam echosounder (EM122), sub-bottom profiler (SBP120), and acoustic doppler current profiler (OS075 & OS150) datasets along the ship track, (2) magnetometer transects of the central Falkland Plateau and western West Georgia Basin, (3) SeaCAT CTD profiles at seven stations, and (4) 43 successful expendable bathythermograph (XBT) deployments and one expendable conductivity-temperature-depth (XCTD) probe deployment in the survey area. The SBP120 sub-bottom profiler data, in particular, were outstanding, which allowed imaging ~100-400m below the seafloor in most places in the survey area. The SBP120 data provide an excellent complement to the seismic reflection datasets and significantly enhance our ability to interpret the geology immediately below the seafloor.

Approximately one quarter of available science days (~8.5 out of 37 days) were lost due to rough seas and medical trips to the Falklands Islands. The loss of some working time due to weather was expected given nature of the seas at subantarctic latitudes, but planned science activities on a day-to-day basis were particularly disrupted during the first half of the cruise. The decision was taken very early to only concentrate on highest priority areas for multi-channel seismic data collection and coring. The original strategy of first collecting a few long seismic lines and then subsequently coring along those lines was also difficult to implement, and many of the core sites in our first round of deployments of the piston corer were selected along sub-bottom profiler survey lines. This proved to be possible since the sub-bottom profiler data were of such high quality, and we were subsequently able to collect multi-channel seismic data across several of the sites cored on the Maurice Ewing Bank in the early part of the cruise.

Although numerous challenges were faced during DY087, the cruise was successful in meeting the primary objectives set out for the cruise. A ~10 day spell of good weather at the end of the cruise resulted a very productive period of seismi
Chief scientistSteven Bohaty (University of Southampton School of Ocean and Earth Science)
Ocean/sea areas 
GeneralSouth West Atlantic Ocean (limit 20W)
Track chartsRRS Discovery DY087 cruise track — dy087trk.pdf (8.14 MB) 
Physical oceanography 
BathythermographQuantity: number of deployments = 48
Description: Expendable bathythermograph (XBT) probe
BathythermographQuantity: number of deployments = 1
Description: Expendable conductivity-temperature-depth (XCTD) probe
CTD stationsQuantity: number of profiles = 7
Description: SeaCAT CTD profiler
Current profiler (eg ADCP)Quantity: activity duration in days = 38
Description: Acoustic Doppler Current Profiler (ADCP) survey, 150 kHz, Ocean Surveyor Instruments OS150 (operated continuously while underway)
Current profiler (eg ADCP)Quantity: activity duration in days = 38
Description: Acoustic Doppler Current Profiler (ADCP) survey, 75 kHz, Ocean Surveyor Instruments OS075 (operated continuously while underway)
Geology and geophysics 
Core - soft bottomQuantity: number of cores = 4
Description: Gravity core using NIOZ coring system (4 deployments, 1 successful)
Core - soft bottomQuantity: number of cores = 26
Description: Piston core using NIOZ coring system (26 deployments, 23 successful)
Geophysical measurements made at depthQuantity: activity duration in days = 38
Description: Kongsberg SBP Sub-Bottom Profiler 120 (operated continuously while underway)
Multi-beam echosoundingQuantity: activity duration in days = 38
Description: Kongsberg EM122 deep-water multibeam echosounder (operated continuously while underway)
Multichannel seismic reflectionQuantity: track kilometres = 3272
Description: Multi-channel seismic reflection survey, 20 designated lines
Gravity measurementsQuantity: activity duration in days = 38
Description: Ship-fitted gravity meter, LaCoste & Romberg marine gravity meter S84 (operated continuously while underway)
Magnetic measurementsQuantity: track kilometres = 3445
Description: Marine Magnetics SeaSPY Overhauser towed magnetometer (6 deployments)
Other geological/geophysical measurementsQuantity: number of profiles = 3
Description: Sound velocity probe, Midas SVP system