The Magazine for Underwater Professionals
A fleet of robotic submarines, based in Southampton, UK, at the National Oceanography Centre (NOC), have been used to map vulnerable cold-water coral reefs in the deep ocean off southwest England. This data set is being used to inform the management of a new Marine Conservation Zone (MCZ) that protects the only area of deep-sea coral habitat in English waters.
Scientists at the NOC worked in partnership with the UK Department for Environment, Food and Rural Affairs (Defra) to collect data from The Canyons MCZ, which is more than 300 kilometres southwest of Cornwall, using an unprecedented variety of marine robotic vehicles deployed from the RRS James Cook. Collected data include 3D maps of the seafloor and high-quality video and photos, and show the location and extent of the corals. This data set is providing Defra with robust evidence that will guide decisions about how to implement management measures at the site.
Professor Russell Wynn of NOC, who led the project and is on part-secondment to Defra, said: “The vibrant cold-water coral reefs and associated fauna in The Canyons MCZ provide a rare example of relatively pristine seafloor habitat within English waters. They are the marine equivalent of our ancient oak woodlands, and just as that precious habitat is protected in sites such as the New Forest National Park, this MCZ will help to preserve this marine biodiversity hotspot and minimise the impacts of current and future human pressures.”
The Canyons MCZ is particularly challenging to survey as much of the site occurs within a deep-sea canyon more than a mile (1.6 kilometres) deep. By using the research ship and robotic vehicles together, the NOC team were able to create a series of detailed maps of the site at different scales from tens of kilometres down to a few millimetres. Ship-based seafloor mapping provided information on the overall shape of the canyon, and the Autosub6000 AUV was then ‘flown’ within the canyon to make more detailed maps of coral habitats. While Autosub6000 was undertaking its missions, the NOC’s Isis ROV was deployed to map steep canyon walls and collect images and samples that confirmed coral presence and species.
By using these robotic vehicles in combination, the team were able to collect a vast array of high-quality data in just three days, demonstrating how robotic vehicles can augment relatively expensive ship operations. In addition, by directly deploying the vehicles into the depths of the canyon, the team were able to map and image steep and overhanging rock walls that hosted extensive coral communities; these habitats were previously overlooked using conventional (downward-looking) ship-based instruments.
Dr Carole Kelly, a marine evidence manager at Defra, said: “The Canyons MCZ is a challenging site for us to survey, as it is in deep water far from land and has a complex and rugged landscape. The equipment and expertise provided by the NOC enabled us to gather high-quality data from this important site in a cost-effective way. These data are providing us with robust evidence about the location and extent of designated features such as cold-water coral habitats, which will enable us to make informed decisions about future site management.”
Oceanographers from Germany, using a number of ocean gliders, have for the first time managed to document the formation of a nearly 100-kilometre wide eddy off the coast of Peru.
Countless eddies constantly move through the seas. Having diameters of up to 300 kilometres, they can survive up to five years while wandering through the ocean basins. Similar to ocean currents, eddies play an important role for the transport of heat, nutrients and oxygen. Different mechanisms for the formation of these eddies are known, with long-lasting examples often forming on the eastern boundaries of the oceans before migrating west. As the formation process takes place within a few weeks they are difficult to predict, making a direct observation hard to conduct.
Scientists of the GEOMAR Helmholtz Centre for Ocean Research Kiel, the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research in Bremerhaven and the Max Planck Institute for Marine Microbiology in Bremen launched seven gliders from the German research vessel METEOR. Fortunately, the observed eddy formed exactly in the region where the team had launched the gliders.
They could examine the eddy’s impact on the salt, oxygen and nutrient distribution in greater detail than would be possible with a purely ship-based measurement campaign. Overall, more than 10,000 profiles of temperature, salinity, oxygen and chlorophyll were collected while the eddy was evolving.
“Via satellite communication, we were able to receive the data from the gliders directly on board RV METEOR in real-time and thus could adjust the cruise schedule to optimise the sampling strategy,” explained Dr Torsten Kanzow from the AWI.
“The data show, in a fascinating way, that the water inside the eddy’s core originates from the bottom layers of the continental slope,” added Sören Thomsen from GEOMAR.
The properties of this water differ greatly from those of waters in the open ocean.
“The coastal areas are biologically very productive. As a result, many plants and animals die there, too. They sink to the bottom and are decomposed by bacteria. Of course, these biogeochemical processes affect the characteristics of the bottom waters,” said Dr Marcus Dengler from GEOMAR.
The eddy transported the water that it had drawn in from the continental slope westward to the open Pacific. As almost no exchange occurs between the eddy and the surrounding waters, the differences in the properties persist. “With our study, we show that a large part of the eddy’s anomalous properties originate from the region where the eddy is formed,” said Dr Dengler.
Since these eddies transport water masses away from the Peruvian continental margin, they simultaneously create space for water richer in nutrients to ascend from the deep. Therefore, they also play a crucial role for the maintenance of high biological productivity off the coast of Peru. “This is highly relevant for the people. After all, fishing is an important economic factor in the region,” said Sören Thomsen. The results of the study have been published in the Journal of Geophysical Research – Oceans.