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RRS Discovery DY090

Cruise summary report

Cruise Info. 
Ship name (ship code)RRS Discovery (74EQ)
Cruise identifierDY090
Cruise period2018-05-23 — 2018-06-28
StatusCompleted
Port of departureWalvis Bay, Namibia
Port of returnCape Town, South Africa
PurposeResearch
ObjectivesThis was the second of two cruises (first was DY086) aimed at evaluating the controls over mesopelagic remineralisation depth. This is the depth to which material sinks when it leaves the surface ocean, a factor we know to be a critical control over climate. There are three hypotheses explaining what controls this depth: plankton community structure, temperature and oxygen concentrations. The data collected during the COMICS cruises will test two of these: oxygen and community structure with DY090 examining the role of oxygen concentration, in particular how temporal variability in mesopelagic oxygen minima affects the remineralisation depth of sinking organic carbon.

In order to evaluate this 4 long stations of about 6 days duration each were worked over a 4 week period between May and June in the oxygen minimum zone in the Benguela upwelling region off the Namibian coast. Three of the stations were undertaken as a time series to investigate the evolution of the remineralisation depth in an oxygen minimum zone (~ 18S, 11E). The other station was in a relatively high oxygen region and served as a baseline to compare against (~ 21.5S, 9.5E). At each station surface and mesopelagic biomass and community structure, and a variety of metrics of downward particle flux were measured, together with estimates of the biomass and growth rates of the major taxonomic classes of organisms responsible for consuming sinking material.
Chief scientistStephanie Henson (National Oceanography Centre, Southampton)
ProjectControls over Ocean Mesopelagic Interior Carbon Storage: COMICS
Coordinating bodyNatural Environment Research Council (NERC)
Cruise reportRRS Discovery DY090 cruise report dy090.pdf (13.41 MB) 
Ocean/sea areas 
GeneralSouth East Atlantic Ocean (limit 20W)
SpecificBenguela Upwelling
Measurements 
Physical oceanography 
CTD stationsQuantity: number of profiles = 9
Description: Trace Metal CTD casts
CTD stationsQuantity: activity duration in days = 120
Description: Gliders
Transparency (eg transmissometer)Quantity: number of deployments = 35
Description: Red Camera Frame
Optics (eg underwater light levels)Quantity: number of deployments = 35
Description: Red Camera Frame
Chemical oceanography 
OxygenQuantity: number of profiles = 9
Description: Trace Metal CTD casts
Other dissolved gasesQuantity: number of profiles = 9
Description: Trace Metal CTD casts
PhosphateQuantity: number of profiles = 9
Description: Trace Metal CTD casts
NitrateQuantity: number of profiles = 9
Description: Trace Metal CTD casts
AmmoniaQuantity: number of deployments = 167
Description: Marine Snow Catchers
SilicateQuantity: number of profiles = 29
Description: Stainless Steel CTD Casts
AlkalinityQuantity: number of profiles = 29
Description: Stainless Steel CTD Casts
Other chemical oceanographic measurementsQuantity: number of profiles = 29
Description: Stainless Steel CTD Casts
Contamination 
Suspended matterQuantity: number of deployments = 167
Description: Marine Snow Catchers
Suspended matterQuantity: number of deployments = 8
Description: Stand Alone Pumping Systems
Biology and fisheries 
Primary productivityQuantity: number of profiles = 29
Description: Stainless Steel CTD Casts
Phytoplankton pigs (eg chlorophyll, fluorescence)Quantity: number of profiles = 29
Description: Stainless Steel CTD Casts
Particulate organic matter (inc POC, PON)Quantity: number of deployments = 167
Description: Marine Snow Catchers
Particulate organic matter (inc POC, PON)Quantity: activity duration in days = 120
Description: Gliders
Particulate organic matter (inc POC, PON)Quantity: number of profiles = 29
Description: Stainless Steel CTD Casts
Dissolved organic matter (inc DOC)Quantity: activity duration in days = 120
Description: Gliders
Dissolved organic matter (inc DOC)Quantity: number of profiles = 29
Description: Stainless Steel CTD Casts
ZooplanktonQuantity: number of profiles = 29
Description: Stainless Steel CTD Casts
ZooplanktonQuantity: number of hauls = 7
Description: Mango net
ZooplanktonQuantity: number of hauls = 29
Description: BONGO Net
ZooplanktonQuantity: number of hauls = 14
Description: MOCNESS Net
ZooplanktonQuantity: number of hauls = 7
Description: Mammoth net
NektonQuantity: number of hauls = 19
Description: RMT 25 NET
Moorings, landers, buoys 
Physical oceanography 
CTD stations18° 0' 0" S  11° 0' 0" E — 1 Slocum glider was deployed in February from the RV Mirabilis and recovered during this cruise.
Subsurface temperature and salinity measurements18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting neutrally bouyant sediment traps
Transparency (eg transmissometer)18° 0' 0" S  11° 0' 0" E — 1 Slocum glider was deployed in February from the RV Mirabilis and recovered during this cruise.
Surface drifters/drifting buoys18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting array of in situ respirometers
Neutrally buoyant floats18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting neutrally bouyant sediment traps
Chemical oceanography 
Oxygen18° 0' 0" S  11° 0' 0" E — 1 Slocum glider was deployed in February from the RV Mirabilis and recovered during this cruise.
Oxygen18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting array of in situ respirometers
Biology and fisheries 
Phytoplankton pigs (eg chlorophyll, fluorescence)18° 0' 0" S  11° 0' 0" E — 1 Slocum glider was deployed in February from the RV Mirabilis and recovered during this cruise.
Particulate organic matter (inc POC, PON)18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting neutrally bouyant sediment traps
Particulate organic matter (inc POC, PON)18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting array of in situ respirometers
Particulate organic matter (inc POC, PON)18° 0' 0" S  11° 0' 0" E — 1 Slocum glider was deployed in February from the RV Mirabilis and recovered during this cruise.
Biochemical measurements (eg lipids, amino acids)18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting neutrally bouyant sediment traps
Sediment traps18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting neutrally bouyant sediment traps
Sediment traps18° 0' 0" S  11° 0' 0" E — 7 Deployments of Drifting array of in situ respirometers
Data held at BODC Get data
Discrete samples 
29  CTD frame plus rosette sampler
41  Drifting rig with sediment traps
169  Marine snow catcher
35  Optical instruments
19  RMT multiple zooplankton net tow
8  Stand-alone pumps
29  Twin WP-2 net mounted on a frame
74  Unspecified zooplankton net or nets
10