Coral reefs growing in cold, deep ocean


London : In the icy, inky depths of the Atlantic ocean, 800 metres below the surface, lie a range of hills covered with large coral reefs.

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Royal Netherlands Institute for Sea Research (NIOZ) researcher Furu Mienis studied the formation of these unknown cold-water kins of the better-known tropical corals.

These reefs can be found along the eastern continental slope from Morocco to Norway, on the Mid-Atlantic Ridge and on the western continental slope along the east coast of Canada and the US. Mienis studied the area to the west of Ireland.

Mienis analysed environmental factors like temperature, current speed and flow direction of seawater as these determine the growth of cold-water corals and the carbonate mounds.

The measurements were made using bottom landers, observatories placed on the seabed from the NIOZ oceanographic research vessel ‘Pelagia’ and brought back to the surface a year later.

Cold-water corals are mainly found on the tops of carbonate mounds in areas where the current is high due to strong internal waves. These waves are caused by tidal currents and lead to an increase in local turbulence that results in the seawater being strongly mixed in a vertical direction.

The outcome is the creation of a kind of highway between the nutrient-rich, sunlit zone at the sea surface and the deep, dark strata where the 380 metre-high tops of the mounds are found, according to a Netherlands Organisation for Scientific Research (NWO) release.

This allows the cold-water corals to feed on algae and zooplankton that live in the upper layers of the sea. Lophelia pertusa and Madrepora oculata are the most important coral species found on the European continental slopes.