RRS Discovery DY138
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS Discovery (74EQ) |
| Cruise identifier | DY138 |
| Cruise period | 2021-09-17 — 2021-11-03 |
| Status | Completed |
| Port of departure | Southampton, United Kingdom |
| Port of return | Southampton, United Kingdom |
| Purpose | Research |
| Objectives | Bottom Boundary Layer Turbulence and Abyssal Recipes
A long-standing problem in Physical Oceanography has been balancing the sinking of cold, dense waters at high latitudes with deep-ocean upwelling across isopycnals at lower latitudes. The BLT Recipes project seeks to test an emergent new paradigm of ocean mixing, whereby deep-ocean upwelling is primarily driven by bottom boundary layer turbulence instead of by breaking internal waves in the ocean interior. The cruise DY138 follows the cruise DY132 (also known as BLT1, 19 June 2021 to 29 July 2021) during which two long-term observational schemes were launched in a canyon on the eastern slope of the Rockall Trough (RT). The RT is taken as a representative ocean circulation microcosm with northern and southern deep-water sources, moderate tides and a comparatively weak mesoscale flow field. First, tree type of moorings (1 Moored Profiler or MP mooring, 2 Modular Acoustic Velocity Sensor or MAVS with fast thermistor moorings, 1 thermistor chain) were deployed to investigate the processes responsible for sustaining the circulation and mixing near and above the topographic boundary. Those targeted the detailed observation of turbulent phenomena within a few hundreds of metres from the ocean floor, along the canyon’s axis. Second, the long-lived inert chemical tracer, SF5CF3, was released at the bottom of the canyon to assess the long-term circulation, dispersion and mixing of deep waters. The DY138 research expedition (or BLT2, 25/09/22 – 03/11/22) carried out the CTD, bottle water sampling and tracer measurements to documents the physical characteristics of the waters and the spreading of the tracer in and beyond the canyon 2 months after its release. Also, the MP mooring and the 2 MAVS mooring, were recovered, serviced and redeployed and informed on the turbulent phenomena in the canyon between BLT1 and BLT2. The thermistor-chain mooring remained in place and will be recovered during the cruise BLT3 planned July-August 2022. Three Argo floats were also released on behalf of the UK Met Office to increase the numbers floats in this region of interest. Preliminary analyses of the data obtained in BLT1 and BLT2 confirm evidence of strong diapycnal upwelling and mixing within the canyon, suggesting broad support for the project’s overarching hypothesis. |
| Chief scientist | Marie-Jose Messias (University of Exeter Department of Geography) |
| Project | Bottom Boundary Layer Turbulence and Abyssal Recipes (BLT Recipes) |
| Coordinating body | Natural Environment Research Council (NERC) |
| Cruise report |  (7.09 MB) |
| Ocean/sea areas | |
| General | North East Atlantic Ocean (limit 40W) |
| Specific | Rockall Trough |
| Track charts | (0.26 MB) |
| Measurements | |
| Physical oceanography | |
| Water bottle stations | Quantity: number of stations = 120 Description: Bottle water station taken concurrently with the CTD stations. 500ml water samples were taken on each of the 24 bottles per cast and stored in the cold room for GC analysis of Trifluoromethyl Sulphur Pentafluoride (CF3SF5) in the laboratory. |
| CTD stations | Quantity: number of stations = 120 Description: Vertical profiles CTD stations of varying depths. Parameters measured were Temperature, Salinity, Oxygen and LADCP. |
| Geochemical tracers (eg freons) | Quantity: number of stations = 120 Description: Bottle water station taken concurrently with the CTD stations. 500ml water samples were taken on each of the 24 bottles per cast and stored in the cold room for GC analysis of Trifluoromethyl Sulphur Pentafluoride (CF3SF5) in the laboratory. |
| Current profiler (eg ADCP) | Quantity: number of stations = 120 Description: Vertical profiles CTD stations of varying depths. Parameters measured were Temperature, Salinity, Oxygen and LADCP. |
| Chemical oceanography | |
| Oxygen | Quantity: number of stations = 120 Description: Vertical profiles CTD stations of varying depths. Parameters measured were Temperature, Salinity, Oxygen and LADCP. |
| Moorings, landers, buoys | |
| Physical oceanography | |
| Subsurface temperature and salinity measurements | 55° 21' 57" N 9° 3' 57" W — Standard Argo Float deployment (15/10/21) |
| Subsurface temperature and salinity measurements | 55° 3' 39" N 10° 15' 3" W — Standard Argo float deployment (10/10/21) |
| Subsurface temperature and salinity measurements | 54° 11' 13" N 10° 9' 25" W — MAVS4 current meter mooring deployment (22/10/21). Mooring depth – 1455m. |
| Subsurface temperature and salinity measurements | 54° 11' 49" N 10° 8' 13" W — MAVS1 current meter mooring recovery (05/10/21). Mooring depth – 1614m. |
| Subsurface temperature and salinity measurements | 54° 10' 58" N 10° 8' 56" W — MAVS3 current meter mooring deployment (22/10/21). Mooring depth – 1434m. |
| Subsurface temperature and salinity measurements | 54° 12' 14" N 10° 7' 37" W — MP2 McLane Moored Profiler recovery (05/10/21). Mooring depth – 1676m |
| Subsurface temperature and salinity measurements | 55° 48' 53" N 8° 9' 57" W — Standard Argo Float deployment (14/10/21) |
| Subsurface temperature and salinity measurements | 54° 11' 6" N 10° 9' 14" W — MP3 McLane Moored Profiler deployment (22/10/21). Mooring depth – 1491m. |
| Subsurface temperature and salinity measurements | 54° 10' 55" N 10° 9' 25" W — MAVS2 current meter mooring recovery (04/10/21). Mooring depth – 1465m. |
| Current meters | 54° 12' 14" N 10° 7' 37" W — MP2 McLane Moored Profiler recovery (05/10/21). Mooring depth – 1676m |
| Current meters | 54° 11' 49" N 10° 8' 13" W — MAVS1 current meter mooring recovery (05/10/21). Mooring depth – 1614m. |
| Current meters | 54° 10' 55" N 10° 9' 25" W — MAVS2 current meter mooring recovery (04/10/21). Mooring depth – 1465m. |
| Current meters | 54° 11' 13" N 10° 9' 25" W — MAVS4 current meter mooring deployment (22/10/21). Mooring depth – 1455m. |
| Current meters | 54° 10' 58" N 10° 8' 56" W — MAVS3 current meter mooring deployment (22/10/21). Mooring depth – 1434m. |
| Current meters | 54° 11' 6" N 10° 9' 14" W — MP3 McLane Moored Profiler deployment (22/10/21). Mooring depth – 1491m. |
| Current profiler (eg ADCP) | 54° 11' 13" N 10° 9' 25" W — MAVS4 current meter mooring deployment (22/10/21). Mooring depth – 1455m. |
| Current profiler (eg ADCP) | 54° 10' 58" N 10° 8' 56" W — MAVS3 current meter mooring deployment (22/10/21). Mooring depth – 1434m. |
| Current profiler (eg ADCP) | 54° 10' 55" N 10° 9' 25" W — MAVS2 current meter mooring recovery (04/10/21). Mooring depth – 1465m. |
| Current profiler (eg ADCP) | 54° 11' 49" N 10° 8' 13" W — MAVS1 current meter mooring recovery (05/10/21). Mooring depth – 1614m. |
| Current profiler (eg ADCP) | 54° 12' 14" N 10° 7' 37" W — MP2 McLane Moored Profiler recovery (05/10/21). Mooring depth – 1676m |
| Current profiler (eg ADCP) | 54° 11' 6" N 10° 9' 14" W — MP3 McLane Moored Profiler deployment (22/10/21). Mooring depth – 1491m. |
| Chemical oceanography | |
| Oxygen | 55° 48' 53" N 8° 9' 57" W — Standard Argo Float deployment (14/10/21) |
| Oxygen | 55° 3' 39" N 10° 15' 3" W — Standard Argo float deployment (10/10/21) |
| Oxygen | 55° 21' 57" N 9° 3' 57" W — Standard Argo Float deployment (15/10/21) |
