Tim Shank (Woods Hole Oceanographic Institution, USA)

Over the past 4 weeks, a team of scientists from the Southampton Oceanography Centre, UK – together with colleagues from the Woods Hole Oceanographic Institution in the USA - have been working about 200 miles off the coast of Ascension studying a section of the Mid-Atlantic Ridge – the volcanic chain responsible for the opening of the Atlantic Ocean basin.

Indeed, this volcanic chain, which runs the entire length of the Atlantic from Iceland in the North to Tristan da Cunha in the south, actually passes within no more than about 60 miles east of Ascension at its closest point.

In 2001, a smaller group of us conducted some preliminary mapping of the seafloor  and basic chemical sampling in the region aboard the RRS James Clark Ross (some older school children might even remember a Sunday morning visit when we were at anchor here that September).

This year, our mission has been to try and locate new submarine hot-springs (so called “hydrothermal vents”) on this previously unexplored section of seafloor and, hopefully, to learn about the specially adapted life that might live there.  The SOC team sailed from Mindelo, Cape Verdes on 17^th Feb aboard the British research ship RRS Charles Darwin and about two weeks later we made a brief stop-over at anchor in Ascension to collect our WHOI colleagues having already used sonar to map out about 200 miles of seafloor.  The instrument we used first was the UK’s Towed Ocean Bottom Instrument (TOBI) which collects the underwater equivalent of aerial photographs of the seafloor at a ripping pace of about 2.5 miles per hour!

Once we had the seafloor mapped out we swung by Ascension to pick up our US colleagues who included a specialist team running the pre-programmable robot submarine “ABE” (Autonomous Benthic Explorer) – a quick translation is that “Autonomous” means it does things on its own, rather than being tied to the ship, while “Benthic” is just a scientific word for things that happen near the seafloor.

But what are hot springs and why did we need to come to Ascension for our work?

In 1977, scientists diving on the Galápagos Rift in the submersible Alvin discovered the first deep-sea hydrothermal vents.  These are places where cold dense seawater percolates several kilometers down into the fresh, hot, volcanic rock of young ocean crust, undergoes a series of chemical reactions as it gets hotter and deeper until it is so hot that it is buoyant and comes shooting up out of the seafloor just like a geyser at Yellowstone or on Iceland, for example, on land.  Perhaps the weirdest thing about hot vents on the seafloor is that as well as being very hot, very acidic and full of all kinds of nasty chemicals (hydrogen sulfide, heavy metals) they are typically surrounded oases of animals, previously unknown to scientists, apparently thriving in the sunless depths. Instead of photosynthetic plants, these communities obtain their energy from the chemical-rich fluids emitted from the vent-sites as they react with ordinary deep-ocean seawater.  Since the discovery of vents, scientists have explored approximately one hundred volcanically active vents in the Pacific, North Atlantic, and Indian Oceans, but the entire South Atlantic Ocean has remained unexplored- until now!

As well as using sonar to map the seafloor we have also been using chemical sensors to “sniff” the deep-sea water for the signature of vent fluids.  Once these signatures were found, we programmed ABE up and released into the water to “fly” a series of bottom-hugging missions precise patterns at heights of from 150m to less than 5m over the seafloor.

Here, again, we used chemical sensors, temperature probes and, eventually, a high-quality black-and-white camera to photograph where we thought the most promising results would be.

What we have found is that on the seafloor, as on land, distinct animal populations have evolved in different regions.  In the eastern Pacific, giant tubeworms – up to 8 feet long - domi­nate vent sites, but they are notably absent at vents in the Atlantic.  Instead, billions of blind shrimp swarm at vents along the northern Mid-Atlantic Ridge.  But these are not the only vent-sites known and so far, scientists have found 6 different region where the vent-biology is quite different, 2 in the North Atlantic, one in the Indian Ocean and three more in the East and West Pacific.

A big question now is “How does the South Atlantic compare with the North Atlantic, Pacific and Indian Ocean sites – finding the first vent-sites in the South Atlantic will go a long way to helping solve the puzzle of how vent life has evolved all around the planet.  After a long weekend of rest and recuperation we are flying back to the UK and USA in the next day or so where we will begin work analyzing over 17,000 seafloor images taken by ABE during the past 2 weeks.  If all goes well, we will hope to be back in Ascension in 2007 with our new British Research Ship the RRS “James Cook” (due to be launched in summer 2006) equipped with our even bigger unmanned submarine “Isis” which dives to the bottom of the sea while connected to the ship via fibre-optic umbilical so that it can relay back to the surface, and ashore, live video footage of not only any vent sites we have found but also the animals that live there – all in glorious technicolour!

Rest assured that we have all thoroughly enjoyed our time on Ascension and will be doing our very level best to get back here as soon as we are able.