What can hydrography tell Us about the strength of the Nordic Seas MOC over the last 70 to 100 years?

The flow of warm water into the Nordic Seas plays an important role for the mild climate of central and northern Europe. Here we estimate the stability of this flow thanks to the extensive hydrographic record that dates back to the early 1900s. Using all casts in two areas with little mean flow just south and north of the Greenland‐Scotland Ridge that bracket the two main inflow branches, we find a well‐defined approximately ±0.5 Sv volume transport (and a corresponding ±30 TW heat flux) variation in synchrony with the Atlantic multidecadal variability that peaked most recently around 2010 and is now trending down. No evidence is found for a long‐term trend in transport over the last 70 to 100 years

Technical report on the intercalibration of the sensors on the LION mooring line

The mooring site was chosen in the center of the convection zone at 42° 02.4'N, 4° 41.0'E with a water depth of 2350m. There were seven deployments during which the line was gradually equipped between September 2007 and July 2013 with initially 8 (4 Microcat SBE37) and up to 26 (11 SBE37) instruments. In this report we will only discuss about the Conductivity­Depth­Temperature sensors (Seabird Microcat SBE37). They were located all along the line between 150m deep and 2300 m

A persistent deep anticyclonic vortex in the Rockall Trough sustained by Anticyclonic Vortices Shed From the slope current and wintertime convection

The presence of a persistent surface anticyclone centered at approximately 55°N, 12°W in the Rockall Trough, northeast North Atlantic, has been previously noted in satellite altimetry data. Here, we show that this surface anticyclone is the imprint of a deep, persistent, non‐stationary anticyclonic vortex. Using wintertime 2007 and 2011 ship‐board data, we describe the anticyclone's vertical structure for the first time and find that the anticyclone core is partly made of warm and salty Mediterranean Overflow Water. The anticyclone has a radius of ~40 km, it stretches down to 2,000 m, with a velocity maximum around 500 m. To analyze the anticyclone's generating mechanism, we use a mesoscale‐resolving (~2 km) simulation, which produces a realistic pattern of the Rockall Trough anticyclone. The simulation indicates that the anticyclone is locally formed and sustained by two types of processes: wintertime convection and merger with anticyclonic vortices shed from the slope current flowing poleward along the eastern Rockall Trough slope. Intense negative vorticity filaments are generated along the Rockall Trough south‐eastern slope, and they encapsulate Mediterranean Overflow Water as they detach and grow into anticyclonic vortices. These Mediterranean Overflow Water‐rich vortices are advected into the trough, consequently merging with the Rockall Trough anticyclone and sustaining it. We suggest that the Rockall Trough anticyclone impacts regional intermediate water masses modifications, heat and salt budgets locally, and further afield into the neighboring subpolar northeast North Atlantic

RV Knorr Cruise KN221-02, 9th July – 1st August 2014. OSNAP Mooring Cruise Report

This cruise report details the scientific programme for SAMS led by Professor Stuart Cunningham of the Scottish Association for Marine Science (SAMS) on R/V Knorr cruise 221-02. Cruise 221-02 is a contribution to the international Overturning in the Subpolar North Atlantic Programme (OSNAP). Three additional scientific teams (from Rosentield School of Marine and Atmospheric Sciences, Royal Netherlands Institute for Sea Research, and Woods Hole Oceanographic Institution) participated on this cruise. SAMS objectives were to deploy moorings in the Rockall Trough, measuring temperature, salinity, currents and bottom pressure and; deploy Seaglider SG604 “Jura” in the Hatton-Rockall Basin. The OSNAP array as deployed between June and August 2014 is purposefully designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic, on a section from Newfoundland to Greenland to Scotland

RSS Discovery DY053, 26th June to 23rd July 2016, King George V Dock, Glasgow to Reykjavick, Iceland. OSNAP Mooring Cruise Report

This cruise report details the scientific programme for the Scottish Association for Marine Science (SAMS) led by Professor Stuart Cunningham on RSS Discovery DY053. This cruise is a contribution to the international Overturning in the Subpolar North Atlantic Programme (OSNAP). Two additional scientific teams (from Rosenstiel School of Marine and Atmospheric Sciences, and Woods Hole Oceanographic Institution / Ocean University of China) participated in this cruise. SAMS objectives were to recover and redeploy moorings in the Rockall Trough, measuring temperature, salinity, currents and bottom pressure and; recover Seaglider SG605 ‘’Bowmore’’ in the Hatton-Rockall Basin. The OSNAP array deployed since July 2014 is purposefully designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic, on a section from Newfoundland to Greenland to Scotland

R/V Pelagia PE399, 16th June to 8th July 2015, Southampton, UK to Reykjavik, Iceland. OSNAP Mooring Cruise Report.

This cruise report details the scientific programme for the Scottish Association for Marine Science (SAMS) led by Professor Stuart Cunningham on R/V Pelagia cruise 339. This cruise is a contribution to the international Overturning in the Subpolar North Atlantic Programme (OSNAP). Two additional scientific teams (from Rosenstiel School of Marine and Atmospheric Sciences, and Woods Hole Oceanographic Institution / Ocean University of China) participated in this cruise. SAMS objectives were to recover and redeploy moorings in the Rockall Trough, measuring temperature, salinity, currents and bottom pressure and; recover Seaglider SG605 ‘’Bowmore’’ in the Hatton-Rockall Basin. The OSNAP array deployed since July 2014 is purposefully designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic, on a section from Newfoundland to Greenland to Scotland

Observed deep cyclonic eddies around Southern Greenland

Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(10), (2021): 3235–3252, https://doi.org/10.1175/JPO-D-20-0288.1.Recent mooring measurements from the Overturning in the Subpolar North Atlantic Program have revealed abundant cyclonic eddies at both sides of Cape Farewell, the southern tip of Greenland. In this study, we present further observational evidence, from both Eulerian and Lagrangian perspectives, of deep cyclonic eddies with intense rotation (ζ/f > 1) around southern Greenland and into the Labrador Sea. Most of the observed cyclones exhibit strongest rotation below the surface at 700–1000 dbar, where maximum azimuthal velocities are ~30 cm s−1 at radii of ~10 km, with rotational periods of 2–3 days. The cyclonic rotation can extend to the deep overflow water layer (below 1800 dbar), albeit with weaker azimuthal velocities (~10 cm s−1) and longer rotational periods of about one week. Within the middepth rotation cores, the cyclones are in near solid-body rotation and have the potential to trap and transport water. The first high-resolution hydrographic transect across such a cyclone indicates that it is characterized by a local (both vertically and horizontally) potential vorticity maximum in its middepth core and cold, fresh anomalies in the deep overflow water layer, suggesting its source as the Denmark Strait outflow. Additionally, the propagation and evolution of the cyclonic eddies are illustrated with deep Lagrangian floats, including their detachments from the boundary currents to the basin interior. Taken together, the combined Eulerian and Lagrangian observations have provided new insights on the boundary current variability and boundary–interior exchange over a geographically large scale near southern Greenland, calling for further investigations on the (sub)mesoscale dynamics in the region.OOI mooring data are based upon work supported by the National Science Foundation under Cooperative Agreement 1743430. S. Zou, A. Bower, and H. Furey gratefully acknowledge the support from the Physical Oceanography Program of the U.S. National Science Foundation Grant OCE-1756361. R.S. Pickart acknowledges support from National Science Foundation Grants OCE-1259618 and OCE-1756361. N. P. Holliday and L. Houpert were supported by NERC programs U.K. OSNAP (NE/K010875) and U.K. OSNAP-Decade (NE/T00858X/1)

Transports and pathways of overflow water in the Rockall Trough

Water mass analysis reveals a persistent core of deep overflow water within the Rockall Trough which hugs the northern and western boundaries of the basin. Mean speeds within this overflow are 10–15 cm s−1 giving a transport time from the Wyville Thomson Ridge to the central basin of < 50 days. Analysis of the 40-year Extended Ellett Line record shows proportions of Norwegian Sea Deep Water associated with the deep core exceed 15% around one quarter of the time. We present the first transport estimates for overflow water in the Rockall Trough. This flux is for overflow water modified by mixing with a density greater than 27.65 kg m−3. Mean values calculated both from a newly deployed mooring array (OSNAP project) and indirectly from the Extended Ellett Line time-series are −0.3 ± 0.04 Sv. Although the flux is highly variable there is no long term trend. As some overflow appears to exit into the Iceland Basin via channels between the northern banks, we suggest that the volume transport will likely increase as the flow pathway is traced back around the boundary of the Rockall Trough towards the Wyville Thomson Ridge

The Scottish Marine Robotics Facility: Use of unmanned vehicles for environmental measurement, monitoring and decision making

Advances in marine technology are essential to allow us to study the marine environment on which life on our planet depends. The Scottish Association for Marine Science is the world’s largest independent marine research organisation with a long history in marine technology development. In 2015, the institute announced the opening of its new marine robotics facility. The facility pools together a broad range of technology’s spanning deep sea, coastal, surface and aerial platforms. The facility specialises in the integration of new and novel technologies into fundamental marine research to improve measurement, monitoring and decision making. Each case study presented in this paper highlights the importance of autonomous systems within marine research the diversity of applications being developed within the robotics facility, and the significance of science communities working in conjunction with technology developers to test, evaluate and support autonomous system development

Observed deep cyclonic eddies around Southern Greenland

Recent mooring measurements from the Overturning in the Subpolar North Atlantic Program have revealed abundant cyclonic eddies at both sides of Cape Farewell, the southern tip of Greenland. In this study, we present further observational evidence, from both Eulerian and Lagrangian perspectives, of deep cyclonic eddies with intense rotation (ζ/f > 1) around southern Greenland and into the Labrador Sea. Most of the observed cyclones exhibit strongest rotation below the surface at 700–1000 dbar, where maximum azimuthal velocities are ~30 cm s−1 at radii of ~10 km, with rotational periods of 2–3 days. The cyclonic rotation can extend to the deep overflow water layer (below 1800 dbar), albeit with weaker azimuthal velocities (~10 cm s−1) and longer rotational periods of about one week. Within the middepth rotation cores, the cyclones are in near solid-body rotation and have the potential to trap and transport water. The first high-resolution hydrographic transect across such a cyclone indicates that it is characterized by a local (both vertically and horizontally) potential vorticity maximum in its middepth core and cold, fresh anomalies in the deep overflow water layer, suggesting its source as the Denmark Strait outflow. Additionally, the propagation and evolution of the cyclonic eddies are illustrated with deep Lagrangian floats, including their detachments from the boundary currents to the basin interior. Taken together, the combined Eulerian and Lagrangian observations have provided new insights on the boundary current variability and boundary–interior exchange over a geographically large scale near southern Greenland, calling for further investigations on the (sub)mesoscale dynamics in the region