RRS Discovery DY132 (BLT-Recipes)
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS Discovery (74EQ) |
| Cruise identifier | DY132 (BLT-Recipes) |
| Cruise period | 2021-06-19 — 2021-07-29 |
| Status | Completed |
| Port of departure | Southampton, United Kingdom |
| Port of return | Southampton, United Kingdom |
| Purpose | Research |
| Objectives | 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 -which the 40-day DY132 (or BLT1) research expedition initiates- 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. To enable such testing, in BLT1 a chemical tracer (SF5CF3) and a fluuorescein dye were injected and subsequently measured in a canyon on the eastern slope of the Rockall Trough, a representative ocean circulation microcosm with northern and southern deep-water sources, moderate tides and a comparatively weak mesoscale flow field. The tracer and dye are well suited to respectively assess the long term (up to O(1 year)) and short-term (up to O(1 day)) circulation, dispersion and mixing of deep waters in and beyond the canyon. The processes responsible for sustaining the circulation and mixing near and above the topographic boundary were investigated in two ways. First, through the deployment of three types of moorings (1 Moored Profiler mooring, 2 Modular Acoustic Velocity Sensor + fast thermistor moorings, 1 thermistor chain), which targeted the detailed observation of turbulent phenomena within a few hundreds of metres from the ocean
floor, along the canyon's axis. And second, through the frequent deployment of multiple fine- and microstructure profilers (the untethered HRP and VMP-6000 and untethered FastCTD, EpsiFish and VMP-2000) along, across and around the rim of the canyon. A Seaglider was also deployed in the region for the duration of the expedition, to provide contextual hydrographic information to interpret the specialised measurements from ship- and mooring-based instruments. Preliminary analyses of the data obtained in BLT1 provide evidence of strong diapycnal upwelling and mixing within the canyon, suggesting broad support for the project’s overarching hypothesis. |
| Chief scientist | Alberto C Naveira Garabato (University of Southampton School of Ocean and Earth Science) |
| Project | BLT-Recipes |
| Coordinating body | University of Southampton, School of Ocean and Earth Science |
| Cruise report |  (58.48 MB) |
| Ocean/sea areas | |
| General | North East Atlantic Ocean (limit 40W) |
| Specific | Rockall Trough |
| Measurements | |
| Physical oceanography | |
| CTD stations | Quantity: number of stations = 94 Description: Conductivity, Temperature, Lowered ADCP (LADCP), Chemical Tracer trifluoromethyl sulphur pentafluoride samples |
| Subsurface temperature and salinity measurements | Quantity: activity duration in hours = 136 Description: Towed Epsilometer Shear , Micro-structure Temperature |
| Subsurface temperature and salinity measurements | Quantity: activity duration in hours = 108 Description: Towed Fast-CTD measurements: Conductivity, Temperature, Fluorescence |
| Other physical oceanographic measurements | Quantity: number of profiles = 75 Description: VMP vertical turbulence profiles: Conductivity, Temperature, Shear , Micro-structure Temperature |
| Other physical oceanographic measurements | Quantity: number of profiles = 67 Description: HRP vertical turbulence profiles: Conductivity, Temperature, Shear , Micro-structure Temperature |
| Moorings, landers, buoys | |
| Physical oceanography | |
| Subsurface temperature measurements | 54° 11' 50" N 11° 51' 43" W — BLT MAVS1 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1612m depth on 6-7-2021 |
| Subsurface temperature measurements | 54° 11' 24" N 11° 51' 8" W — BLT TChain – thermistor chain over bottom 150m. 102 preattached thermistors. Deployed at 1525m depth on 6-7-2021. ADCP velocity and temperature |
| Subsurface temperature measurements | 54° 14' 18" N 11° 56' 55" W — BLT MP1 – Moored profiler deployed at 2028m depth on 28-6-2021 recovered 5-7-2021. Velocity, CTD, Temperature Variance, Fluorometer |
| Subsurface temperature measurements | 54° 12' 10" N 11° 52' 15" W — BLT MP2 – Moored profilier deployed at 1653m depth on 7-7-2021 redeployment of MP1 |
| Subsurface temperature measurements | 54° 10' 58" N 11° 50' 37" W — BLT MAVS2 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1466m depth on 7-7-2021 |
| Current meters | 54° 12' 10" N 11° 52' 15" W — BLT MP2 – Moored profilier deployed at 1653m depth on 7-7-2021 redeployment of MP1 |
| Current meters | 54° 14' 18" N 11° 56' 55" W — BLT MP1 – Moored profiler deployed at 2028m depth on 28-6-2021 recovered 5-7-2021. Velocity, CTD, Temperature Variance, Fluorometer |
| Current meters | 54° 10' 58" N 11° 50' 37" W — BLT MAVS2 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1466m depth on 7-7-2021 |
| Current meters | 54° 11' 50" N 11° 51' 43" W — BLT MAVS1 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1612m depth on 6-7-2021 |
| Current profiler (eg ADCP) | 54° 14' 18" N 11° 56' 55" W — BLT MP1 – Moored profiler deployed at 2028m depth on 28-6-2021 recovered 5-7-2021. Velocity, CTD, Temperature Variance, Fluorometer |
| Current profiler (eg ADCP) | 54° 11' 50" N 11° 51' 43" W — BLT MAVS1 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1612m depth on 6-7-2021 |
| Current profiler (eg ADCP) | 54° 12' 10" N 11° 52' 15" W — BLT MP2 – Moored profilier deployed at 1653m depth on 7-7-2021 redeployment of MP1 |
| Current profiler (eg ADCP) | 54° 10' 58" N 11° 50' 37" W — BLT MAVS2 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1466m depth on 7-7-2021 |
| Current profiler (eg ADCP) | 54° 11' 24" N 11° 51' 8" W — BLT TChain – thermistor chain over bottom 150m. 102 preattached thermistors. Deployed at 1525m depth on 6-7-2021. ADCP velocity and temperature |
| Other physical oceanographic measurements | 54° 12' 10" N 11° 52' 15" W — BLT MP2 – Moored profilier deployed at 1653m depth on 7-7-2021 redeployment of MP1 |
| Other physical oceanographic measurements | 54° 11' 50" N 11° 51' 43" W — BLT MAVS1 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1612m depth on 6-7-2021 |
| Other physical oceanographic measurements | 54° 10' 58" N 11° 50' 37" W — BLT MAVS2 – 8 MAVS high resolution velocity temperature sensors (4.7m, 12.1m, 26.5m, 50.3m, 76.1m, 125.8m, 199.5m, 276.3m height above bottom) and 80 thermistors. Deployed at 1466m depth on 7-7-2021 |
| Other physical oceanographic measurements | 54° 14' 18" N 11° 56' 55" W — BLT MP1 – Moored profiler deployed at 2028m depth on 28-6-2021 recovered 5-7-2021. Velocity, CTD, Temperature Variance, Fluorometer |
