You might have heard the saying that we still know less about the deep sea than about the surface of the moon. While I can neither confirm nor deny this, I am pretty sure that what we don’t know about the deep sea could fill a library or three. And isn’t that fascinating? A whole new world on our own planet yet to explore. So, being in a submarine at the bottom of the sea is probably the closest one can get to explore new planets without the need for very much in the realm of sci-fi technologies like faster-than-light travel or years of transiting – which does not lessen the experience in any way. On the contrary, the transit alone, a passing from clear blue surface water to darkness filled with fireworks of bioluminescence, is unforgettable.
A patch of Riftia tubeworms bathing in vent water at Crab Spa.
Being at the seafloor definitely feels surreal for me – it is hard to grasp that I actually am in this hidden world, which I knew till then only from videos and pictures and the Riftia tubeworms which were brought up and which are my focus of study. These organisms are indeed peculiar: Despite belonging to the kingdom of animals, they do not leave their tubes once they settled down as a larva. This means that they stay on the same spot during their entire life. And they do not possess a mouth or guts. Instead, they live in symbiosis with a species of bacteria in their body cavity that provides them with nutrients. These bacteria use a process very similar to photosynthesis in plants to make these nutrients – the main difference being that they of course cannot use light energy in the eternal darkness (or at least almost eternal, unless curious researchers deploy a submarine with floodlights) of the deep sea. Instead, their energy source is a chemical reaction, the oxidation of reduced sulfur compounds, like hydrogen sulfide, which many of us know from the smell of rotten eggs. These reduced sulfur compounds are brought up with warm vent water from below the seafloor. The tubeworm itself takes up the chemicals needed by the symbionts and for itself, like oxygen, via a special organ, the plume. This ‘breathing’ organ is the only part of the animal that is visible outside the tube. Its bright red and feathery softness pose a stark contrast against the parchment-like white of the plume and the black and grey of the surrounding basalt. And, if for example a hungry crab (or an Alvin manipulator) touches the plume, the worm retracts it with astonishing speed, so that nothing of the actual animal is sticking out of the tube anymore. But normally, the worms just sit peacefully in their tubes in assemblages of various sizes, taking up chemicals for their symbionts.
Measuring the temperature of warm vent fluids of about 24 °C amidst Riftia and mussels, and a curious fish
A lone octopus is casually passing by – there is an octopus during almost every dive, Stefan Sievert says, who is, together with the Pilot Jefferson Grau, in the sub on the seafloor with me. Of course, as in our own world, not all is harmony and peace in the deep sea. Directly in front of me, a crab is ripping out pieces of a cracked-open mussel. Bad for the mussel, good for the crab, I suppose.
Crablunch. Could also be dinner, I suppose. Or maybe it’s breakfast.
While munching on a peanut butter-jelly sandwich myself (all the needs of its human occupants are thought through and provided for in Alvin), I get to admire a huge black smoker through my starboard viewport. Extremely hot water of about 300 °C and higher comes out of several openings in huge grey to black fumes. These hot vents are, in contrast to the lukewarm ones were the Riftia worms settle, largely the realm of microbes, though even they can’t cope with the extremely hot black smoker fluids. But even at the warm vents, microbes, invisible to the naked eye, rule the world.
Sampling the hot fluids of a deep-sea hydrothermal vent black smoker at Bio9 vent with a titanium water sampler.
As our dive is dedicated to science, the pilot Jefferson is busy with steering the sub to different sampling sites and with the sampling itself, while Stefan is deciding where to take which samples and, together with me, recording the dive on video as well as a dive log. It is amazing to watch how delicately the quite large and powerful Alvin manipulators can be used to measure the temperature and take water samples, or to drape the long and somewhat unwieldy hose of a pump around a Riftia to make the pump nozzle stay in place, or to pick up colonizers which are used to grow and sample deep-sea bacteria.
Placing a round colonizer, marked with a red tag, to investigate microbial colonization at Bio9 vent.
We obtain samples and environmental parameters at several places of interest during the dive. These will be needed for the multitude of projects the researches onboard our research vessel Atlantis are involved, and which are all aimed to shed more light on this world, which is only separated by two and a half kilometers of water from our own. At the end of the day (a compressed travelling to a new world indeed!) we drop the weights on Alvin and move up again, with new data and samples and, of course, a multitude of impressions to process.
My gratitude and thanks goes to all the people who make these truly inestimable studies and gain of knowledge possible for us.
