The North Atlantic Ocean
The Atlantic is the second largest of the ocean basins, as well as the most researched. It is bordered by five of the seven continents, with the Americas to the West, Antarctica to the South and Europe and Africa to the East.
With an area of 106,460,000 square kilometres, it is just over half the size of the Pacific Ocean. The average depth of the Atlantic is 3.3 km. The deepest point is located at the Milwaukee Deep, within the Puerto Rico, where it is submerged to 8.4 km. For reference – Mount Everest’s height is just short of 9km. The Atlantic Ocean is separated into North and South halves by the Equatorial Counter Current at latitude 8° N. The North Atlantic formed around 150 million years ago in the early Cenezoic era when the North American and Eurasian plate of Pangea separated due to secondary lithospheric extension from plate tectonics and primary processes of the Iceland plume.
The North Atlantic current/North Atlantic drift is a western warm boundary current originating at the Newfoundland rise where the Gulfstream turns north due to a submarine ridge projecting from the Grand Banks. The current transports a greater volume of tropical water towards northern currents than any other currents, meandering with topographic instability. The currents coupled with winds have a considerable substantial influence on European climate. The North Atlantic current beyond the Flemish Cap turns eastward as it reaches the Mid-Atlantic ridge. The current then widens and becomes less concentrated, before splitting into 2 branches: the eastern and the northwestern, with warmer water diverted southwards. The North Atlantic is mainly supplied by subpolar waters e.g. Labrador current. Remaining water divides into 2 branches with one running along the coast of North Africa and the other forming the Irminger and Norwegian Current.
The first crossing of the Atlantic is attributed to the Norse Vikings under Leif Erikson, with archaeological digs found on the coast of Newfoundland, Canada. Since then, famous expeditions of Christopher Columbus and Amerigo Vespucci have connected the two sides of the globe - a precursor to globalisation. Once a barrier to human movement, the Atlantic Ocean has developed into a hotspot for research. Even Benjamin Franklin, the then-to-be American President, made important contributions to our understanding of the Atlantic Ocean currents with focus on the Gulf Stream. He charted the route by recognising a time discrepancy between ships leaving America to the UK and vice versa. Today, much research is being done into cold water coral communities off the coast of Scotland.
The North Atlantic has a diverse array of deep-sea biota, interlinked in complex ecosystems crucial for the functioning and long-term prevalence of these communities. Until the 1960s, any endemism present in the North Atlantic was thought to be fully explained by the “nunatak hypothesis” whereby species survived and diversified during glacial periods. Postglacial immigration was thought to be just of historical interest, and the assumption was made that it could not explain the current diversity in the North Atlantic. Recent evidence now points towards this latest explanation, with species entering ice free regions of the ocean once the ice sheets had retreated.
Species historically introduced, which are now being regarded as native, are apparent in the North Atlantic. Far more species have been introduced than previously predicted, and these species may have shaped community ecology and evolution, acting as ecosystem engineers. Species of bivalve such as Neopycnodonte cochlear have been introduced to North American coastlines via European shipping vessels.
An often-overlooked component of the deep-sea biota are sponge communities. These sponges can reproduce rapidly, forming huge mixed species assemblages. Sponges vary in depth from the intertidal zone to abyssal zones, increasing the three-dimensional structure of the benthic habitat and are also crucial in nutrient recycling between the substrate and water column. One of the most abundant sponge species is Pheronema carpenteri, and their distribution is affected by silicate concentration, temperature and organic carbon.
Some of the most charismatic fish species breed in the North Atlantic, such as the Atlantic Bluefin tuna (Thunnus thynnus) which are of great economic importance and have experienced severe declines due to overfishing. One species often unheard of, but with an estimated biomass of 550-600 million tonnes, is the Lanternfish. It is thought that the lanternfish family accounts for 65% of deep-sea biomass across the major oceans. One species, Benthosema glaciale, is an inhabitant of the North Atlantic and occupies depths of 600-1000m.
Thanks to the numerous sampling expeditions that have taken place in the North Atlantic, especially in warm temperate regions, we now have extensive knowledge on the distribution of deep sea corals in this environment. They are mainly found near oceanic islands, on the steep slopes of seamounts and on continental slopes. Seamounts are known to harbour large reefs off the Norwegian coast, the coast of North and Central America, as well as Mauritania.
According to current research, scleractinian, antiptharian, and gorgonian corals appear to be the most commonly recorded throughout the North Atlantic, especially the North East. Even though a large number of species have been recorded over time in this area, the NE Atlantic still shows low levels of endemism. However, what was found is that coral communities on seamounts are still significantly different from those recorded on continental slopes. Despite their low levels of endemism in coral species, deep water corals are still fundamental for ocean life as they provide habitats for over 1000 species, which is comparable to what is seen on tropical reefs. However, few quantitative studies allowing regional comparisons have been made.
In general, the distribution of deep-water corals is mostly controlled by environmental factors. Physical factors such as a suitable seabed substrate, water temperature and salinity are requirements that must be met to enable the colonisation and growth of corals. You can discover more on cold water corals here.
Within the well studied North Atlantic Ocean, a group of research sites, from localised reefs, Island chains to marginal seas besides the Ocean basin, have been added as in depth case studies. Follow the links to find out more: