The North-Atlantic Current (NAC) is the main northward branch of the Gulf Stream (Krauss 1986, Rossby 1996), transporting warm water towards higher latitudes. After splitting from the Gulf Stream near the Tail of the Grand Banks of Newfoundland and extending north into the Labrador Sea, the NAC turns east at the so-called Northwest Corner and flows eastward. The front associated with the NAC is called the Subpolar (or Subarctic) Front (Belkin & Levitus 1996). The Subpolar Front is a relatively wide region that separates the subtropical gyre from the subpolar gyre and where the main thermocline shoals to the surface (Rossby 1996). The NAC is different from surrounding areas and can be visualised through satellite altimetry and NEMO (Nucleus for European Modelling of the Ocean) ocean models (e.g., Miller et al. 2013; Marzocchi et al. 2015) and oceanographic sections (Belkin & Levitus 1996) (see also Figures 1-2). The NAC pathways are not randomly located but remain between a number of preferred latitudes, with surface thermal fronts appearing in a banded structure, aligned west to east in the area south of the Charlie-Gibbs Fracture Zone (CGFZ), and aligned roughly SW to NE in the north; this alignment follows the direction of the NAC (Miller et al. 2013). The NAC is a transition zone and has a wide banded structure with distinct water types that get progressively cooler and fresher from south to north separated by the three branches and their density fronts. The fronts are associated with vigorous vertical velocities (bringing nutrients to the surface) and some horizontal exchange, especially southward from the subpolar region (Dutkiewicz et al. 2001; Figures 1-2). Density contrasts across the fronts lead to instability and the development of eddies (Volkov 2005). These eddies enhance and concentrate primary production and represent an important habitat for oceanic higher predators, including seabirds, as evident from studies on seabirds, turtles, whales, sharks and tunas (e.g., Hays et al. 2004, Walli et al. 2009, Egevang et al. 2010, Dias et al. 2011, 2012, Gilg et al. 2013; Queiroz et al. 2016), which frequently target areas of higher prey availability. A large quantity of seabird tracking data confirms this is an area of high productivity, with a high intensity of foraging activity in the area (BirdLife International 2019a, Figure 3a). Seabird tracking data shows 21 species of seabird foraging in the area including endangered Zino's petrel (Pterodroma madeira), endangered Bermuda petrel (Pterodroma cahow), vulnerable Atlantic puffin (Fratercula arctica), and vulnerable black-legged kittiwake (Rissa tridactyla).

This site is identified from in situ and remote sensing (or satellite) data and validated with biological data (tracking data collected for seabirds and other marine megafauna).

This area has a well-defined western boundary (front), defined by the maritime boundary of the OSPAR Commission. It extends north along the east flank of the Grand Banks, where it forms a loop called the Northwest Corner and continues to the east. The northern boundary is defined by the northern extent of the Subpolar Front at 54°N. The North Subarctic Front is topographically fixed at the Charlie-Gibbs Fracture Zone (Belkin & Levitus 1996), at 30°W. It is known that the North Atlantic Current and frontal branches vary strongly, with latitudinal shifts up to 250-300 km (Belkin & Levitus 1996). Thus, maps of annual means have been used to ensure the full temporal variability has been captured (Marzocchi et al. 2015; Figure 2).

The area includes the water column and surface used by seabirds and other marine top predators as foraging areas throughout the year, as revealed by recent telemetry studies (see Figures 3-5; e.g., Dias et al. 2011, 2012; Egevang et al. 2010; Frederiksen et al. 2016; Frederiksen et al. 2012; Gilg et al. 2013; Hedd et al. 2012; Kopp et al. 2011; Queiroz et al. 2016;). Some seabird species travel to this area during the breeding season, mostly from colonies located in the Azores (e.g., Magalhães et al. 2008) and Madeira (Silva et al. 2019, Figure 3). The area is also very important as a stopover site during the migration of Arctic species such as the Arctic tern (Sterna paradisea) and the long-tailed jaeger (Stercorarius longicaudus) (Egevang et al. 2010, Gilg et al. 2013), and as a wintering ground for species both from the North and the South Atlantic (e.g., Atlantic Puffin–Fratercula arctica, black-legged kittiwake–Rissa tridactyla, Cory’s shearwater–Calonectris diomedea, great shearwater–Ardenna gravis, sooty shearwater– Ardenna grisea and South Polar skua–Catharacta maccormicki; Dias et al. 2011, 2012, Kopp et al. 2011, Hedd et al. 2012; Figure 3). Twenty-one species of seabirds are known to use the area on a regular basis, including the OSPAR-listed Audubon’s shearwater (Puffinus lherminieri baroli) and thick-billed murre (Uria lomvia) and several globally threatened species as Atlantic puffin (Fratercula arctica), black-legged kittiwake (Rissa tridactyla), Desertas petrel (Pterodroma deserta), Zino’s petrel (Pterodroma madeira) and Bermuda petrel (Pterodroma cahow). A scientific expedition to the area carried out in 2018 confirmed the enhanced abundance and diversity of seabird species in the area in comparison with adjacent waters (Wakefield 2018), and provided further evidence of the use of the area by other seabird species for which tracking data are not available, such as Leach’s storm petrel (Hydrobates leucorhous), Wilson’s storm petrel (Oceanites oceanicus), great black-backed gull (Larus marinus), Arctic jaegar (Stercorarius parasiticus), pomarine jaegar (Stercorarius pomarinus) and northern gannet (Morus bassanus) (Wakefield 2018).

Other marine megafauna occur in the area, such as marine mammals, sea turtles and sharks (Hays et al. 2004, Olsen et al. 2009, Walli et al. 2009, Silva et al. 2013, Prieto et al. 2014, Queiroz et al. 2016). A number of tracking and telemetry studies on marine mammals, particularly for baleen whale species, have indicated the presence of known migratory pathways transiting through the region. Such cetaceans include the endangered sei whale (Balaenoptera borealis), which migrate through the area from the Azores, likely longitudinally from waters on the Eastern Atlantic, to highly productive foraging areas in the Labrador Sea (Figure 4) as well as Greenlandic and Icelandic waters (Olsen et al. 2009, Prieto et al. 2014). Other tracking studies of endangered fin whales (Balaenoptera physalus) and blue whales (Balaenoptera musculus) have described long migratory movements between the area of the Azores northward towards key foraging areas in the region of eastern Greenland and western Iceland (Figure 4; Silva et al. 2013). Furthermore, fin and blue whales remained at middle latitudes along their migration in the area for prolonged periods, exhibiting area-restricted search (ARS) behaviour, indicative of foraging activity. Satellite tracking studies of humpback whales (Megaptera novaeangliae) tagged in Norwegian waters as part of the Arctic University of Norway’s Whaletrack project has further recorded the use of the area by migrating animals (Whaletrack 2019; Figure 4). Observations carried out during scientific expeditions (e.g., 2004 Mid-Atlantic Ridge (MAR)-ECO expedition on the R.V. G.O. Sars; Skov et al. 2008) also provided evidence of the use of the area by sei whale, blue whale, fin whale  and sperm whale, as well as long and Short-finned pilot whales (Globicephala melas, G. macrorhynchus), humpback whale (Megaptera novaeangliae), killer whale (Orcinus orca), beaked whales (Mesoplodon sp.) and  Atlantic white-sided dolphin (Lagenorhynchus acutus) (Waring et al. 2009; Figure 4). Analysis of the data collected from the same expedition revealed that modelled aggregations of sperm whales and sei whales along the MAR are primarily associated with fine-scale frontal processes interacting with the topography in the upper 100 m of the water column just north of the Sub-Polar Front (SPF) and the CGFZ, as well as moderate and high habitat suitability estimated only for areas downstream from the SPF (Skov et al. 2008; Figure 4).

Tracking studies on the leatherback turtle (Dermochelys coriacea) have indicated that the area is also used by this species during the summer and autumn for months at a time (Hays et al. 2004). The Atlantic bluefin tuna, listed by OSPAR as a Threatened and Declining Species, is known to use the area during all seasons (Walli et al. 2009).  Tracking studies have indicated that the area is also used by basking sharks (Cetorhinus maximus) (Gore et al. 2008) (Figure 5).

The high abundance and diversity of megafaunais likely linked to the presence of multiple frontal zones and persistent eddies, which are known to aggregate primary productivity and zooplankton, providing a temporally and spatially reliable foraging zone for higher trophic level predators (Scales et al. 2014). Prey availability can be further enhanced when these features occur over seamounts, as zooplankton can become entrained over the abrupt topography (the topographic blockage), and are then further restricted in their vertical migrations, thereby rendering them more accessible for mesopelagic fish and other top predators (Dias et al. 2016; Morato et al. 2016; Sweetman et al. 2013). Broad-scale and remotely sensed studies of the region have demonstrated that the frontal zone is subject to large-scale phytoplankton blooms during spring and summer (Taylor and Ferrari 2011) with much higher chlorophyll concentrations than the adjacent waters (Gaard et al. 2008; Pelegrí et al. 2006; Vecchione et al. 2015).

In relation to zooplankton communities, the available evidence suggests a high abundance of copepods, gelatinous zooplankton and euphausiids (Gaard et al. 2008; Letessier et al. 2011; Vecchione et al. 2015). Copepods are important prey for gelatinous zooplankton, mesopelagic fish, and some seabird species and are often associated with high seabird numbers in the North Atlantic as indicators of abundant food (Frederiksen et al. 2013; Karnovsky et al. 2008). Euphausiids are also abundant across the region and are important prey for mesopelagic fish, cetaceans and seabirds, including thick-billed murre, little auk and black-legged kittiwake (Mehlum and Gabrielsen 1993).

Mesopelagic fish are a major source of biomass in the oceans and important prey for higher trophic predators, including seabirds (Gjøsaeter and Kawaguchi 1980; Harris et al. 2015; Paredes et al. 2014; Waap et al. 2017). Mesopelagic fish prey on gelatinous zooplankton, and they in turn are preyed on by larger fish, cetaceans and seabirds (Granadeiro et al. 1998; Granadeiro et al. 2002; Waap et al. 2017). These small fish are particularly associated with fronts and eddies, such as those occurring within the area (Paredes et al. 2014). Within the areas investigated by MARECO/ECOMAR (Vecchione et al. 2015, mesopelagic species such as the goiter blacksmelt (Bathylagus euryops) and lanternfish (Myctophids) were found in the highest abundance at the Subpolar Front and the CGFZ and with a tendency to be distributed in the upper surface layers (Sweetman et al. 2013).

Cephalopods are also potentially concentrated within the boundary and broader region of the area, with studies from the MARECO/ECOMAR programme indicating the highest diversity and abundance occurring south of the CGFZ (Vecchione et al. 2015). The importance of cephalopods in the diet of some Atlantic seabirds is well documented, for example in Audubon’s shearwater (Puffinus lherminieri), Cory’s shearwater (Calonectris borealis), Manx shearwater (Puffinus puffinus) and Bulwer’s petrel (Bulweria bulwerii) (Den Hartog & Clarke 1996; Neves et al. 2012; Petry et al. 2008; Waap et al. 2017); other species such as Desertas petrel (Pterodroma deserta) and Atlantic puffin (Fratercula arctica) are also known to prey on squid (Harris et al. 2015; Ramos et al. 2016).

Due to the remoteness of the area and lack of long-term studies, there is no information to determine the trends of the conditions. Satellite information and other databases suggest that the area is less commercially important for fishing than adjacent areas, and that no other major activities occur in the area, apart from shipping (major shipping lines between Canada, USA and Europe pass through the area; GFW 2019, PASTA MARE 2019). There is an ongoing project, led by University of Glasgow, to study the community of seabirds, cetaceans and turtles in the area (Wakefield et al. 2018). There is also a proposal to designate part of the area as a marine protected area under the OSPAR Convention.

The site is known or thought to hold regularly significant numbers of a globally threatened species (Donald et al. 2018)

The site is known or thought to hold congregations of ≥1 per cent of the global population of one or more species on a regular or predictable basis (Donald et al. 2018)
The area meets the criteria to be classified as an Important Bird and Biodiversity Area (IBA) by BirdLife International (Donald et al. 2018, BirdLife International 2019c), which are very closely aligned with the EBSA criteria (Waliczky et al. 2018).