ChEss Home

Your dive today in the US submersible Alvin will take you to the 13ºN hydrothermal vent site (blue in the map), on the East Pacific Rise (EPR) (see Map). The northern section of the East Pacific Rise (red in the map) is a fast spreading ridge where the Pacific tectonic plate is being pulled apart from the North American and Cocos plates at rates between 6.5 and 10.5 cm per year. The ridge section between 11ºN and 13ºN on the EPR has active vents that have been well studied in the last two decades. Your dive is taking you to the vents at 13ºN. These vents are 2600 m deep, and it will take you around 3 hours to get down to the site.

Ready? Up the ladder then, and in the sub through the hatch on the top! Hope you're not claustrophobic - inside it's not big! The pilot will be lying down on the port side facing his little round window. You are lying down next to him, facing the starboard window.

© M.Baker, NOC, Southampton

Once in the sub, the pilot takes you through the safety briefing and performs the technical pre-dive checks. He then gives the OK to the bridge and you are ready to start the launch. The A-frame of the ship has put you overboard and the divers free the sub from the A-frame. You are floating on the surface of the ocean and ready to go!

You are now starting your journey to the deep sea....... As you start going down towards the bottom of the ocean, the environment around you changes: Light: The light slowly disappears until you are in complete darkness (apart from the sub lights!) below 500 m. However, if on the descent you ask the pilots to turn off the sub lights, you will experience the beauty of bioluminescence. Bioluminescence is light produced by some invertebrates when disturbed. They use the light for protection to startle potential predators or for communication such as attracting mates of the opposite sex.

© Photo couresy of HBOI/E.Widder

Temperature: The temperature is decreasing too, and will plumet to a chilly 2ºC at the bottom away from the vents. Pressure, on the other hand, increases by 1 atmosphere every 10 meters. The 13ºN site on the EPR where you are diving today is 2600 meters below the surface, so once you reach the bottom, the external pressure will be 260 atmospheres. It will take hours for the sub to reach the bottom. During this time, the sub is sinking freely towards the sea bed on the ridge valley. Time to relax, enjoy the ride, chat with the pilots and may be have some lunch...a nice sandwich, a drink and some chocolate. The dive will take around 6 to 7 hours in total, but don't worry, if you need the toilet, there is a special bottle that will do the job, both for ladies and gentlemen!

And finally the seafloor is in view! You are 2600 m deep, with an external pressure of 260 atmospheres, no natural light and a temperature of around 2ºC. Through your window you can only see a small area in front of you, where the submersible lights reach. First it's only sediments and basaltic rocks, but the pilots seem to know their way very well in this dark and cold environment. You start moving forward, slowly now that you are close to the oceanic crust.

And then you see them: chimneys with shimmering water, active black smokers and exuberant animal communities. What a contrast to the quiet, tranquil, dark background... The sight is so impressive!

© Photos courtesy of Lutz, Rutgers University

© Lutz, Rutgers University

As you were approaching the vents, a long, white zoarcid fish crossed in front of the sub. These fishes come around the vents looking for food.

Probably the most striking and beautiful sight you will see from your window are the communities of giant tubeworms Riftia pachyptila, with their white tubes and red plumes. These tubeworms can reach over 3m in height and form dense aggregations on rocks, in zones of diffuse venting. Riftia does not have a mouth or an anus, so it depends completely on the internal symbiotic chemoautotrophic bacteria for its feeding (see biology stuff). In many cases, the external surface of the tubes of Riftia are covered by tiny yellowish limpets called Lepetodrilus.

Living on the basalt rocks and other hard substrates you can see the yellow-brownish mussel Bathymodiolus thermophilus. This species forms mussel beds in areas of high levels of hydrogen sulfide. The gills of Bathymodiolus contain symbiotic chemoautotrophic bacteria. Also, in the mantle cavity of the mussel you can find the commensal polychaete Branchypolynoe symmytilida, which obtains protection and food from it's mussel host.

Another bivalve common at 13ºN and throughout the EPR and Galapagos Rift is the giant clam Calyptogena magnifica. This is a beautiful large white clam that lives in cracks and crevices of basaltic rocks where hydrothermal fluid emanates. Here again, the gills of Calyptogena contain symbiotic chemoautotrophic bacteria that are at the base of the nourishment of the clam.

The polychaetes are also a major element of the EPR vent fauna. A very interesting case of thermal tolerance occurs in Alvinella pompejana, commonly known as the Pompei worm. This worm lives in organic tubes in the walls of active chimneys, experiencing temperatures between 10º to 80ºC! The Pompei worm feeds on free bacteria. Another polychaete that lives in the hot waters of the vents is Alvinella caudata. This species also lives in organic tubes on the walls of active chimneys, experiencing temperatures between 10º and 50ºC. Other common polychaetes are Paralvinella grasslei and Paravinella pandorae. These two species are often associated with tubeworms in the warm part of active vent chimneys. They are deposit feeders that feed mainly on bacterial mats.

The scientists on board the ship eagerly await your return to hear stories from the dive and to get a first glimpse of any samples you may have obtained during the dive.

© M.Baker, NOC, Southampton

And so, after spending a total of 6-7 hours cramped into a very small space, you finally return to the surface. If this was your first dive in Alvin, you may be greeted by buckets of ice-cold water and hose pipes........ a typical initiation ceremony for the submersible first-timer......!

© M.Baker, NOC, Southampton

And then to work. The scientists work quickly to preserve their precious biological samples.

Well, hope you enjoyed your dive. You never know, maybe next time you dive it will be the real thing.....?

Follow this link to see video footage from an Alvin dive, courtesy of Cindy Van Dover, The college of William & Mary, Woods Hole Oceanographic Insititute:

http://www.coml.org/medres/img/van.htm