RRS Discovery DY167 (GApr19, N-Arc)
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS Discovery (74EQ) |
| Cruise identifier | DY167 (GApr19, N-Arc) |
| Cruise period | 2023-07-09 — 2023-08-12 |
| Status | Completed |
| Port of departure | Southampton, United Kingdom |
| Port of return | Tromsø, Norway |
| Purpose | Research |
| Objectives | The Arctic Ocean is undergoing dramatic environmental change. It has warmed twice as fast as the rest of the planet, causing the areal extent of sea ice to decline by 9% since the 1970s. Expansion of summertime ice-free waters and removal of light limitation has enhanced primary production by 30% since 1998 and is predicted to increase primary production by 60% in an ice-free Arctic. Primary production ultimately drives production of higher trophic levels, including fished species, and impacts biogeochemical cycles in the oceans. How primary production will respond in a future Arctic Ocean depends on the evolution of other limiting factors such as nutrients. Primary productivity in the contemporary Arctic is already limited by nitrate availability and nitrate demand will increase as future productivity increases. Models predict the ultimate arrival of oligotrophy in the future Arctic Ocean – a condition of chronically low nutrients typically associated with the lower latitude warm subtropical waters. However, there is now sparse but accumulating evidence that nitrogen fixing organisms or ‘diazotrophs’ are present and active in the cold waters (< 5°C) of the Arctic Ocean. Nitrogen fixation fertilises the global ocean with nitrogen, relieves nitrogen limitation and thus supports primary production. The prevailing paradigm is that the thermal constraints of common diazotrophs, such as Crocosphaera and Trichodesmium (18 to 32 °C) effectively exclude all diazotrophs from the Arctic Ocean and instead restrict nitrogen fixation to the warm oligotrophic low latitude ocean. Indeed current ocean models that include nitrogen fixation ignore this process in the cold high latitude ocean. Thus, the occurrence of diazotrophs in the Arctic Ocean is unexpected. We hypothesise that nitrogen supply from diazotrophs is a fundamental yet understudied component of contemporary Arctic biogeochemistry, which will become critical as the Arctic Ocean rapidly moves towards a state of oligotrophy in the coming decades.
Data collected from this cruise will be used to challenge the prevailing paradigm that nitrogen fixation is restricted to the warm low latitude ocean and will enable quantification of the importance of nitrogen fixation as an essential nitrogen source to the Arctic Ocean. |
| Chief scientist | Claire Mahaffey (University of Liverpool Department of Earth, Ocean and Ecological Sciences), Jo Hopkins (National Oceanography Centre, Liverpool), Maeve Lohan (University of Southampton School of Ocean and Earth Science) |
| Project | GEOTRACES; Nitrogen Fixation in the Arctic (NArc) |
| Coordinating body | Natural Environment Research Council (NERC) |
| Cruise report |  (15.19 MB) |
| Ocean/sea areas | |
| General | Barents Sea North Sea Norwegian Sea |
| Track charts | (0.08 MB) |
| Measurements | |
| Physical oceanography | |
| Surface measurements underway (T,S) | Quantity: activity duration in days = 33 Description: Underway surface measurements of temperature, salinity, chlorophyll-a fluorescence, transmission |
| Water bottle stations | Quantity: number of samples = 192 Description: Water samples for salinity calibration of the stainless and titanium CTD |
| Water bottle stations | Quantity: number of samples = 144 Description: Water samples for underway salinity calibration |
| CTD stations | Quantity: number of profiles = 22 Description: Vertical profiles from Titanium CTD (temperature, salinity, oxygen, PAR, transmission, turbidity, chl-a fluorescence) |
| CTD stations | Quantity: number of profiles = 186 Description: Vertical profiles from Stainless CTD (temperature, salinity, oxygen, PAR, transmission, turbidity, chl-a fluorescence) |
| Current profiler (eg ADCP) | Quantity: number of profiles = 186 Description: Horizontal current velocities from LADCP (on stainless CTD frame) |
| Current profiler (eg ADCP) | Quantity: activity duration in days = 33 Description: Horizontal current velocities from the OS150 vessel mounted ADCP |
| Chemical oceanography | |
| Carbon dioxide | Quantity: activity duration in days = 33 Description: Continuous measurements of pCO2 from ships underway |
| Phosphate | Quantity: number of samples = 1732 Description: Phosphate from FISH, stainless steel CTD, Titanium CTD and nutrient limitation experiments |
| Nitrate | Quantity: number of samples = 1732 Description: Nitrate from FISH, stainless steel CTD, Titanium CTD and nutrient limitation experiments |
| Nitrite | Quantity: number of samples = 1732 Description: Nitrite from FISH, stainless steel CTD, Titanium CTD and nutrient limitation experiments |
| Silicate | Quantity: number of samples = 1732 Description: Silicate from FISH, stainless steel CTD, Titanium CTD and nutrient limitation experiments |
| Trace elements | Quantity: number of samples = 59 Description: Dissolved Iron Isotopes from FISH and Titanium CTD |
| Trace elements | Quantity: number of samples = 237 Description: Total dissolvable trace elements from FISH and Titanium CTD |
| Trace elements | Quantity: number of samples = 499 Description: Dissolved iron from FISH and Titanium CTD and experiments |
| Trace elements | Quantity: number of samples = 100 Description: Particulate trace elements from Titanium CTD |
| Trace elements | Quantity: number of samples = 506 Description: Dissolved Trace metals from FISH and Titanium CTD |
| Isotopes | Quantity: number of samples = 155 Description: Oxygen isotopes (d18O) from FISH and stainless CTD |
| Other chemical oceanographic measurements | Quantity: activity duration in days = 33 Description: FARACAS – continuous nitrogen fixation measurement |
| Other chemical oceanographic measurements | Quantity: number of samples = 175 Description: Dissolved humic substances |
| Biology and fisheries | |
| Phytoplankton pigs (eg chlorophyll, fluorescence) | Quantity: number of samples = 1304 Description: Chlorophyll concentration from FISH, stainless steel CTD, Titanium CTD and nutrient limitation experiments |
| Particulate organic matter (inc POC, PON) | Quantity: number of samples = 45 Description: Particulate matter samples for ultraplankton nitrogen fixation measurements (VivaFlow ultrafiltration) |
| Particulate organic matter (inc POC, PON) | Quantity: number of samples = 177 Description: Particulate matter samples for bulk nitrogen and carbon fixation rate measurements |
| Particulate organic matter (inc POC, PON) | Quantity: number of samples = 20 Description: Single-particle samples for nitrogen fixation rate measurements (Marine Snow Catcher) |
| Particulate organic matter (inc POC, PON) | Quantity: number of samples = 150 Description: Particulate matter samples for bulk particle-associated nitrogen fixation rate measurements (Marine Snow Catcher) |
| Dissolved organic matter (inc DOC) | Quantity: number of samples = 427 Description: DOC concentration: FISH, vertical profiles from titanium CTD and experiments |
| Phytoplankton | Quantity: number of samples = 216 Description: Phytoplankton (preserved samples) |
| Phytoplankton | Quantity: activity duration in days = 19 Description: Phytoplankton using the McLane IFCB |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 84 Description: RNA samples for community metabolic expression analyses (from stainless CTD casts) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 45 Description: Extracellular vesicle samples (VivaFlow ultrafiltration) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 45 Description: DNA samples for ultraplankton community characterization (VivaFlow ultrafiltration) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 280 Description: Single-particle samples for colonisation dynamics analyses (In Situ Colonisation Assay) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 20 Description: Single-particle samples for DNA analyses (Marine Snow Catcher) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 150 Description: Particulate matter samples for single-cell particle-associated nitrogen fixation rate measurements (Marine Snow Catcher) |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 412 Description: Samples for DNA/RNA analysis nifH gene and community metabolism from FISH, stainless steel CTD, diazotroph experiments and nutrient limitation experiments |
| Pelagic bacteria/micro-organisms | Quantity: number of samples = 350 Description: DNA samples for particle-associated diazotroph communities (Marine Snow Catcher) |
| Meteorology | |
| Other meteorological measurements | Quantity: activity duration in days = 33 Description: Wind speed/direction, air pressure, humidity, air temperature, PAR and TIR from sensors on ships mast |
| Data held at BODC | |
| Discrete samples | |
| 42 CTD frame plus rosette sampler | |
| 36 Marine snow catcher | |
| 320 SUDO Lightfish tow | |
| 22 |
