Resources

RRS Discovery DY132 (BLT-Recipes)

Cruise summary report

Cruise Info. 
Ship name (ship code)RRS Discovery (74EQ)
Cruise identifierDY132 (BLT-Recipes)
Cruise period2021-06-19 — 2021-07-29
StatusCompleted
Port of departureSouthampton, United Kingdom
Port of returnSouthampton, United Kingdom
PurposeResearch
ObjectivesA 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 scientistAlberto C Naveira Garabato (University of Southampton School of Ocean and Earth Science)
ProjectBLT-Recipes
Coordinating bodyUniversity of Southampton, School of Ocean and Earth Science
Cruise reportRRS Discovery DY132 (BLT-Recipes) cruise report dy132.pdf (58.48 MB) 
Ocean/sea areas 
GeneralNorth East Atlantic Ocean (limit 40W)
SpecificRockall Trough
Measurements 
Physical oceanography 
CTD stationsQuantity: number of stations = 94
Description: Conductivity, Temperature, Lowered ADCP (LADCP), Chemical Tracer trifluoromethyl sulphur pentafluoride samples
Subsurface temperature and salinity measurementsQuantity: activity duration in hours = 108
Description: Towed Fast-CTD measurements: Conductivity, Temperature, Fluorescence
Subsurface temperature and salinity measurementsQuantity: activity duration in hours = 136
Description: Towed Epsilometer Shear , Micro-structure Temperature
Other physical oceanographic measurementsQuantity: number of profiles = 75
Description: VMP vertical turbulence profiles: Conductivity, Temperature, Shear , Micro-structure Temperature
Other physical oceanographic measurementsQuantity: number of profiles = 67
Description: HRP vertical turbulence profiles: Conductivity, Temperature, Shear , Micro-structure Temperature
Moorings, landers, buoys 
Physical oceanography 
Subsurface temperature measurements54° 12' 10" N  11° 52' 15" W — BLT MP2 – Moored profilier deployed at 1653m depth on 7-7-2021 redeployment of MP1
Subsurface temperature measurements54° 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
Subsurface temperature measurements54° 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 measurements54° 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 measurements54° 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 meters54° 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 meters54° 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 meters54° 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 meters54° 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° 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° 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' 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
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
Other physical oceanographic measurements54° 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 measurements54° 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
Other physical oceanographic measurements54° 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 measurements54° 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