Saturday 29th October, cruise JC142 left Santa Cruz, Tenerife, bound for Tropic Seamount, some 300 nautical miles SW of the Canary Islands. We spent the preceding day on a geology field trip on Mount Teide, the islands tallest volcano. Teide is the 3rd highest volcano on Earth, rising almost 8km from the deep seafloor. The evolution of Teide and Tenerife has echoes in the formation of Tropic Seamount. On Tenerife we walked into the huge caldera and looked at the more recent peak which forms the summit of Teide. We examined cinder cones, lava flows and crystals, and discussed the distinction between minerals and life; crystals reproduce their unit cell structure and grow from chemical and energy gradients; the basic building blocks of life do much the same.
The RRS James Cook preparing to sail for Tropic Seamount. Our banner says it all, “Securing critical marine minerals for a sustainable low-carbon future”. Ferromanganese crusts forming on some ancient seamounts are rich in rare metals that are essential to making ‘green’ technologies like solar panels and wind turbines.
Tropic Seamount is one of a small province of 100 million year old underwater volcanoes SW of the Canary Islands.
Tropic Seamount started life about 120 million years ago, just after the Atlantic Ocean was born. At that time, the Atlantic was only as wide as the Red Sea, and Tropic Seamount was a palm-fringed volcanic island surrounded by a coral reef. Over the millennia, Tropic Seamount slowly sank beneath the waves. As it did so, the sea eroded the peak, giving it a flat top. Earthquakes shook the volcano causing its sides to collapse. We see the result today, a star-shaped, flat-topped seamount of the type called a gyot. Although much diminished from its former grandeur, Tropic Seamount is still 3km high and covers twice the area of the Isle of Wight.
The aim of our mission here is to understand what controls the formation and precipitation of cobalt-rich crusts on seamounts like Tropic. These crusts are potentially rich resources for scarce elements that are critical to new technologies and especially those that are used in low-carbon energy production like solar panels and wind turbines. While some seamounts are rich in these crusts, extraction of the minerals is also harmful to the immediate environment and part of our work is to study the potential impact of deep-sea mining.
During our mission we will be deploying the latest technology. The ship will use its sonar systems to map the seamount at a resolution of 25m2. This provides a base map and shows us where the hard and soft rock and sediment is distributed. We use this information to map the seafloor with our robotic submarine, Autosub6000. This yellow submarine is torpedo-shaped and is sent off on its own for 24 hours at a time. The images it brings back reveal the seafloor in great detail – with a resolution of 1m2 for the bathymetry and 25 cm2 for the acoustic sidescan sonar pictures, showing minute details of the crusts and sediment pockets. Once these images are back on board, we chose sites to dive on with our remotely operated submarine, Isis. This vehicle hangs on a cable and we control it from a room in the ship.
The remotely operated vehicle ‘Isis’ is launched over the side of the RS James Cook. This robotic submarine is controlled from a room onboard. We use it to drill and collect samples of the crusts from the seafloor. We also use ‘Isis’ to conduct experiments to simulate the effects of seafloor mining and the potential impact such activity might have on the surrounding environment. Isis can dive to 6500m below the surface and operate for days without a break.
Inside the ROV 'shack' – operating the ROV is a complex task and requires the pilots and scientists to work closely together.
The lander is placed on the seafloor by the ROV and waits for the first of our experiments to generate a sediment plume.
The ROV holds a hose as it blows a sediment plume in the water up-stream from the lander. This is the first time every that an experiment has been done to simulate the potential effects of disturbance from seabed mining on the surrounding environment. It is widely thought that sediment plumes can spread far and damage vulnerable animals such as sponges and corals. We aim to explore this by conducting small-scale experiments 1000m below the surface on the seabed.
One of our aims is to explore the potential effects of deep-sea mining on the surrounding environment. For this we have built a seafloor observatory, called a seabed lander, to image and measure dust plumes as they drift across the top of the seamount. The lander is deployed by ‘Isis’ which generates sediment plumes in the water. Modelling and monitoring of the currents allows us to predict how fast and how far the plumes will drift. We position the ROV up-stream from the lander, at different distances, and generate the plumes over a period of several hours. We plan to use the Autosub6000 to swim though the plumes at a distance of 1km. This information will be combined with an ecological study of the distribution of the animals most vulnerable to sediment disturbance to assess the potential impact of seafloor mining.
While modern civilization needs rare elements found in these deep-sea mineral deposits to function and reduce our overall planetary environmental impact, we have a duty to assess the impact that extracting these minerals may have on the immediate and local environment. These data will help shape future regulations and laws around deep-sea mining.