RRS Discovery Cruise DY031, 28 May - 18 Jun 2015, Southampton to Liverpool. The 40th Anniversary Extended Ellett Line

Cruise DY031 was the 2015 annual occupation of the Extended Ellett Line, taking place 40 years after the start of the time series. The Extended Ellett Line is a hydrographic section between Iceland and Scotland that is occupied annually by scientists from the National Oceanography Centre (NOC) and the Scottish Association for Marine Science (SAMS), UK. The measurement programme began as a seasonally-occupied hydrographic section in the Rockall Trough in 1975, building on early surface observations made underway from ocean weather ships. In 1996 the section was extended to Iceland, sampling three basins: the Rockall Trough, the Hatton-Rockall Basin and the Iceland Basin. These three basins form the main routes though which warm saline Atlantic water flows northwards into the Nordic Seas and Arctic Ocean. The section crosses the eastern North Atlantic subpolar gyre; as well as the net northward flow there is a large recirculation of the upper layers as part of the wind-driven gyre. During its passage through the region, the warm saline water is subjected to significant modification by exchange of heat and freshwater with the atmosphere. The two deep basins (Rockall Trough and Iceland Basin) contain southward flowing dense northern overflow waters, and Labrador Sea Water in the intermediate layers. The specific objectives of cruise DY031 were: To complete the annual Extended Ellett Line CTD section To collect water samples for measuring biogeochemical properties including dissolved oxygen, nutrients, carbon and trace metals. To collect underway measurements of surface currents, surface temperature and salinity, bathymetry, surface meteorology. To complete epibenthic sled tows at a deep location in the central Rockall Trough. To launch a seaglider for a related research programme (near Rockall) which will stay in UK or international waters. To launch a second seaglider for a related research programme (near Iceland) which will operate in Iceland and Greenland waters. To deploy 2 Met Office Argo floats along the CTD section We successfully completed all of these objectives

RRS Discovery Cruise DY054, 27 Jul - 17 Aug 2016, Reykjavik to Southampton. OSNAP 2016 mooring refurbishment cruise, Leg 2

Cruise DY054 was the second leg of the 2016 UK OSNAP mooring refurbishment programme on RRS Discovery. Following the first leg (DY053, Cunningham et al 2016) which serviced and re-deployed US and UK moorings in the Iceland Basin and Rockall Trough, the scientific objectives of DY054 were: To service (recover and re-deploy) the 5 UK OSNAP moorings in the western Irminger Sea (the Deep Western Boundary Array, M1-M5) To service the 5 Dutch OSNAP moorings in the eastern Irminger Sea (the Irminger Currrent Array, IC0-IC4) To service the Dutch LOCO mooring in the central Irminger Sea To complete a CTD/LADCP section across the Irminger Basin, from the Greenland coast to the mid-Atlantic Ridge To collect and freeze nutrient samples from CTD stations for later analysis by NIOZ To deploy an Argos float for the UK Met Office To deploy a series of OSNAP RAFOS floats in the overflow waters To deploy a new WHOI sound source in the Maury Channel of the Iceland Basin To collect material for outreach programes, including film footage, audio recordings and photography for a US OSNAP website, and material to be used in an art project All objectives were achieved. All OSNAP moorings were previously deployed in 2014, refurbished in 2015, and will be recovered in 2018. The moorings and the CTD profiles will be used to measure the mean and variability of the surface-to-seafloor currents, and to compute the volume, heat and freshwater transport within the currents. They are part of a large international programme, OSNAP (Overturning in the Subpolar North Atlantic Programme) which has other moorings in the Labrador Sea, Iceland Basin and Rockall Trough

RRS Discovery Cruise 245, 27 Jan-20 Feb 2000. A hydrographic section from Scotland to Iceland

The report describes the RRS Discovery Cruise 245, designed as a repeat of the hydrographic section that includes the Ellett line from Scotland to Rockall, and the SOC extension to Iceland.The section consisted of stations for CTD, LADCP, chemistry (nutrients, oxygen) and biology (chlorophyll). Continuous measurements of high precision position and heading navigation data were made, also of surface currents (VM-ADCP), depth, surface temperature and salinity, surface nutrients and high-quality meteorological measurements. The cruise objectives also included recovering two deep ocean and two shelf current meter moorings, and collecting shallow sediment cores in the Muck Deep, a shelf depression. The cruise was severely hit by bad weather and as a consequence not all the scientific objectives were achieved

RRS James Clark Ross Cruise 302, 06 Jun - 21 Jul 2014. The 2015 RAGNARRoC, OSNAP AND Extended Ellett Line cruise report

Cruise JR302 was an NERC-NC funded cruise aiming to complete a full CTD section across the subpolar gyre, from Canada to Greenland to Scotland. The CTD section was located along the OSNAP track (www.ukosnap.org), providing a high quality and high resolution synoptic survey for the start of that programme. The objectives included a full suite of biogeochemistry measurements under the RAGNARRoC programmes. Finally, the eastern part of the section included the 2014 occupation of the Extended Ellett Line (projects.noc.ac.uk/ExtendedEllettLine) between Scotland and Iceland. Additional sections were made around the Cape Farewell region with the objective of measuring transport and the movement of water away from the boundary currents. Additional objectives included deploying eight Met Office Argo floats, and recovering one SAMS glider. Two new instruments were trialled by deploying them on the CTD frame; the IMP and RBR. All objectives were successfully completed

RRS Discovery Cruise DY078/079, 06-28 May 2017, Southampton to Reykjavik. Extended Ellett Line 2017 occupation and OSNAP Rockall Trough mooring refurbishment cruise

Cruise DY078/079 (hereafter called DY078) was the 2017 occupation of the Extended Ellett Line (EEL) and the 2017 refurbishment cruise for the OSNAP Rockall Trough moorings (Overturning in the Subpolar North Atlantic Program). The core scientific objectives of DY078 were: To service (recover and re-deploy) the 3 UK OSNAP moorings and 1 ADCP lander in the Rockall Trough (RTWB1, RTWB2, RTEB2 and RTADCP1). To complete the Extended Ellett Line CTD/LADCP section across the eastern subpolar North Atlantic between Scotland and Iceland via the Rockall-Hatton Plateau. To collect and freeze nutrient samples from CTD stations for later analysis at SAMS To deploy four Argos floats for the UK Met Office. To recover one WHOI OSNAP glider and one SAMS EEL glider. To deploy one WHOI OSNAP glider and one SAMS OSNAP glider. To collect water samples for isotopic analysis at Edinburgh and Cardiff Universities To survey the seabed for sediments with the subbottom profiler. To collect underway water samples for microplastics analysis To survey for seabirds and marine mammals To communicate the cruise work through social media To collect underwater film footage for an artist The opportunistic objectives, to be completed if weather conditions allowed were: To collect megacores for palaeoceanographic and microplastics analysis To collect water column water samples for microplastics analysis To collect wind data for air-flow distortion analysis Almost all objectives were achieved, including the opportunistic ones, along with 7 extra CTD stations. The OSNAP ADCP lander was not recovered or re-deployed. All OSNAP moorings were previously deployed in 2014, refurbished in 2015 and 2016, and will be recovered in 2018. The moorings and the CTD profiles will be used to measure the mean and variability of the surface-to-seafloor currents, and to compute the volume, heat and freshwater transport within the currents. They are part of a large international programme, OSNAP (Overturning in the Subpolar North Atlantic Programme) which has other moorings in the Labrador Sea, Irminger Sea and Iceland Basin

Simulating pathways of subsurface oil in the Faroe–Shetland Channel using an ocean general circulation model

Little is known about the fate of subsurface hydrocarbon plumes from deep-sea oil well blowouts and their effects on processes and communities. As deepwater drilling expands in the Faroe–Shetland Channel (FSC), oil well blowouts are a possibility, and the unusual ocean circulation of this region presents challenges to understanding possible subsurface oil pathways in the event of a spill. Here, an ocean general circulation model was used with a particle tracking algorithm to assess temporal variability of the oil-plume distribution from a deep-sea oil well blowout in the FSC. The drift of particles was first tracked for one year following release. Then, ambient model temperatures were used to simulate temperature-mediated biodegradation, truncating the trajectories of particles accordingly. Release depth of the modeled subsurface plumes affected both their direction of transport and distance travelled from their release location, and there was considerable interannual variability in transport

Multidecadal variability of potential temperature, salinity, and transport in the eastern subpolar North Atlantic

The Extended Ellett Line (EEL) hydrographic section extends from Scotland to Iceland crossing the Rockall Trough, Hatton-Rockall Basin and Iceland Basin. With 61 full-depth stations at a horizontal resolution of 10 to 50 km, the EEL samples the upper limb of the Atlantic Meridional Overturning Circulation flowing across the Iceland-Scotland Ridge into the Nordic Seas. The Rockall Trough has been sampled nearly four times per year from 1975 to 1996, and the full section annually since 1996. The EEL is an exceptionally long timeseries of deep-ocean temperatures and salinities. This study extends prior work in the Rockall Trough, and examines for the first time 18 year records in the Iceland and Hatton-Rockall Basins. We quantify errors in the timeseries from two sources: observational errors and aliasing. The data quality and annual sampling are suitable for observing interannual to decadal variability because the variability exceeds our error estimates. The upper waters of all 3 basins are cooler/fresher from 1997 to 2001, warmer/more saline 2001 to 2006, and cooler/fresher from 2006 to 2014. A reference level for geostrophic shear is developed heuristically and by comparison with sea-surface altimetry. The mean northward transport in the upper waters is 6.7±3.7 Sv and there is a 6.1±2.5 Sv southward flow below the thermocline. Although the magnitude of the Iceland Basin overturning circulation (4.3±1.9 Sv) is greater than in the Rockall Trough (3.0±3.7 Sv), the variability is greater in the Rockall Trough. We discuss the results in the context of our understanding of drivers of variability

Sources and distribution of fresh water around Cape Farewell in 2014

We investigate the origin of freshwater on the shelves near Cape Farewell (south Greenland) using sections of three hydrographic cruises in May (HUD2014007) and June 2014 (JR302 and Geovide) 2014. We partition the freshwater between meteoric water sources and sea ice melt or brine formation using the δ18O of sea water. The sections illustrate the presence of the East Greenland Coastal Current (EGCC) close to shore east of Cape Farewell. West of Cape Farewell, it partially joins the shelf break, with a weaker near‐surface remnant of the EGCC observed on the shelf southwest and west of Cape Farewell. The EGCC traps the freshest waters close to Greenland, and carries a brine signature below 50m depth. The cruises illustrate a strong increase in meteoric water of the shelf upper layer (by more than a factor 2) between early May and late June, likely to result from East and South Greenland spring melt. There was also a contribution of sea ice melt near the surface but with large variability both spatially and also between the two June cruises. Furthermore, gradients in the freshwater distribution and its contributions are larger east of Cape Farewell than west of Cape Farewell, which is related to the East Greenland Coastal Current being more intense and closer to the coast east of Cape Farewell than west of it. Large temporal variability in the currents is found between different sections to the east and south‐east of Cape Farewell, likely related to changes in wind conditions

Climate change impacts on ocean circulation relevant to the UK and Ireland

What is happening • Observations of the Atlantic Meridional Overturning Circulation or Gulf Stream System since the 1980s have shown a strengthening in the 1990s and a weakening in the 2000s, with no clear overall trend. • Shifts in North-east Atlantic circulation, leading to a greater influence of warmer subtropical-origin waters which can impact marine ecosystems and economically important fish species such as mackerel. The changing subpolar ocean circulation is also having impacts on the food supply for deep-sea ecosystems. • The subpolar gyre recorded its freshest values on record in the 2010s. Ongoing freshwater build-up in the rapidly changing Arctic Ocean may exacerbate this freshening. What could happen • Projections from climate models consistently project a weakening of the Atlantic Meridional Overturning Circulation due to anthropogenic climate change. • Warming of Atlantic waters is expected to reduce the depth of mixed layers and limit nutrient supply to surface layers