Some of the world’s most interesting rocks aren’t accessible by foot. That’s why geologist and chemist Susan Humphris regularly uses Alvin--Woods Hole Oceanographic Institution’s deep-ocean submarine--to get to them. Humphris has had more than 30 dives in the US’s only sea-floor-landing submersible and, in fact, she was part of the team that made the first discovery of hydrothermal vents in the Atlantic back in 1986. Humphris has been the principal investigator in the group tasked with upgrading Alvin and its science abilities, a two-year-long project that was just recently completed. We chatted with Humphris about what it’s like to sit in a submarine the bottom of the deep ocean and why Alvin is cooler then a US Navy submarine.
What type of science are you doing that requires a deep-ocean sub?
I’m interested in the processes going on at hydrothermal vents. I tend to work out on the mid-ocean ridge system looking at the seafloor submarine hot springs that are gushing 350 centigrade (660 F) hot waters. The way these systems work is: it’s seawater that has percolated down into the earth’s crust, where there’s a lot of heat. The seawater reacts with the rocks and changes its chemistry. Then it comes back out as a hot spring with a different chemistry than the water that went in.
How is the chemistry different?
If you look at seawater it contains a lot of oxygen, it’s slightly alkaline, and it’s cold. It’s very depleted in metals. When it comes back out as a hydrothermal fluid all the oxygen has been removed and in its place are hydrogen sulfide and sometimes methane. It’s acidic and there’s no oxygen. It’s also picked up a lot of metals out the rock--and the actual chimneys are made out of those metals which have precipitated out as metal sulfides.
So what do you learn about the earth from studying the vents?
Quite a lot about how seawater maintains its composition. It has been relatively constant in composition for hundreds of millions years. You’ve got rivers pouring into it and rain coming in. As you input a variety of elements you have to be removing them or else the ocean’s composition would change. The hydrothermal vent system has a role in helping regulate the chemistry of seawater. The other is these vents are associated with a lot of exotic biological communities. If it wasn’t for the changes in chemistry in seawater those organisms would not be able to live. They’re living off energy stored in chemicals (because there’s no photosynthesis at the bottom of the ocean) and those chemical reactions are really critical for the existence of those communities.
Are there other factors that maintain the ocean’s chemistry?
If it wasn’t for the changes in chemistry in seawater those exotic biological communities would not be able to live.
Rivers bring in a lot of different chemicals and you have other things like rain that bring chemicals in. The hydrothermal vents were unknown until 1977, but now we know something about the chemistry.
There’s a lot of things that remove the chemicals from seawater. Biological organisms that remove nutrients in order to exist. Minerals form to remove elements. There are lots of different ways. But the vents are a discovery that’s impacted those ideas because it’s a relatively newly known way of removing chemicals.
So you use Alvin to help you study these systems?
One of the techniques that we can use is to go down to the sea floor and make observations and collect samples. Alvin is a really good one because you can actually observe what’s going on. You can see the minerals coming out of the fluid, see the relationship of the animals and the rocks. It’s the best way in terms of trying to study all aspects of vents because you can go down and observe a vent in action.
How many dives have you dived inside Alvin?
It’s some number greater than 30. I stopped counting at 30. You don’t get 10 or 15 in a year, you typically get a few every few years because Alvin’s very much in demand.
With so few opportunities to dive every year, you must have to be really careful about picking a location to study. How do you choose what vents to travel to?
What happens is, the work that you do ends up pointing to other areas that you think it would be important to go and study in comparison. The first thing you have to do is write a proposal to get the funds to go and do it. That’s a long process. Typically it’s to the NSF, but we have written it to NASA astrobiology and other places. It’s very, very competitive. Once you’re funded you have to wait for the ship and the Alvin to be in the right geographic location. It can be 2 to 5 years depending on where you’re trying to go.
How does the ship decide where it will be?
It’s part of a nationwide ship system for oceanographic research. There’s a scheduling group that looks at who has what cruises funded where and what’s the most efficient way to travel. If they have four dives funded in the pacific and one in the Atlantic, it doesn’t make sense to go. The Atlantic crews might have to wait until there’s three or four. Other people have to be funded, at least in the same ocean.
Alvin lives on a ship?
It lives on the Atlantis. There are two crews on board. The ship’s crew and an Alvin operations group that has pilots and engineers that are there specifically to operate the Alvin. There’s five or six pilots so they take it in turns.
You meet the ship in whatever port it’s in and you have with you a scientific team. In the case of vent research we have geologists and chemists and biologists all along. Usually about 20 scientists. You head out to the site and design a dive program that meets the needs of everybody who needs samples.
Two scientists and one pilot go down on each dive. They have a list of tasks that have to be accomplished for themselves but for other people as well--not everybody gets to go on the dive.
Can you describe what a day diving is like?
Typically you get in the Alvin sometime between 7:30 and 8 in the morning. If you’re in a warm climate obviously it’s gonna be hot, but you know that when you get to the bottom it’s gonna be cold. You always take warm clothes, but you don’t wear shoes in the Alvin. It’s such close quarters you don’t want to kick a person or equipment
It leaves the deck around 8 am. It takes an hour and half to two hours to get to the bottom depending on the depth. It’s a long commute to work. On the way down you sleep, listen to music (chosen by the pilot), and check equipment.
As you go down it gets colder and colder. At the bottom you’ve got socks and sweater sometimes a hat because it’s very cold.
At the bottom you have to find the site you’re looking for, which sometimes is not easy because vents can be as small as 50 meters (160 feet) across. One that I work on a lot is 150 meters across.
So you turn on the lights and figure out where you are and start making observations continuously either on a recorder or by taking notes. As a geologist I start observing as soon as we touch the sea floor, because at the end of the dive I want to draw a section showing how we crossed different rocks--just like geologists on land. The difference is, on land you can see for a long distance. A seafloor geologist can probably see ten feet. It’s a very different perspective.
What kinds of things are you saying into your recorder?
On land you can see for a long distance. A seafloor geologist can probably see ten feet. It’s a very different perspective.
I record the time and the direction the Alvin is heading and then I observe something like: “We’re going over very fresh glassy-looking pillow lavas and I can see some organisms that look like they might be vent-related so it appears we’re going in the right direction.”
So we make observations and then when we get to the site we start going down the list of tasks, types of samples we want to collect, and types of instruments we want to put on the seafloor to leave there. I mostly collect samples, but I have had to leave instruments for other people.
What types of samples do you collect?
Usually what we’re trying to do is collect samples around the vents. When you collect rock samples you also want a sample of the fluid coming out of the vent because you’re trying to relate the two to each other. The key is picking a good site for the sampling.
How do you decide on a good site?
Let’s say what you want is a very high temperature site, you will look for a chimney that has black smoker fluids coming out the top. You might stick a temperature probe in, you might look for one that has a really nice orifice because if you’re going to take a water sample you have to stick a tube down inside it.
What kinds of equipment do you use?
The sub has two manipulator arms and we take down with us special bottles for the water samples that are designed to withstand high temperatures. We also bring push cores, which are essentially plastic tubes that are used for soft material. You pick it up and push it into the material. Then when we want to collect biology we have something called a slurp gun, which does exactly what it sound like. It’s a tube--like on a vacuum cleaner--you essentially suck the animals into a container.
Do you have to keep the animals pressurized to keep them alive on the surface?
In general it’s very difficult technology to maintain the pressure all the way up to the surface so generally that’s not done. The animals that live in the deep ocean don’t have air pockets like lungs that are going to collapse. Their soft parts are filled with fluids so they don’t experience the types of changes you and I would when we go down in the ocean
But you don’t have to worry about that in Alvin, though, right?
The personnel sphere is kept at atmospheric pressure. All the walls of the sphere are three inches thick to withstand the pressure of the outside water. We also bleed oxygen into the atmosphere of the sub from cylinders to maintain it at the 20% we’re all used to and we have a system to remove the C02 and keep the atmosphere at what you’d experience at the surface.
How long do you usually spend on the bottom?
The general rule is that you have to be back on board the ship by 5 o'clock. If you’re running out of battery power you obviously have to come back up whatever the time. Typically you’re on the seafloor until 3 and then it’s a couple of hours back to the surface. It’s a 9 to 5 dive.
I’m sure you get asked this question all the time…
About the bathroom?
Yes! What do you do if you have to go?!
They send lunch down with you, besides the food they tend to send a thermos of coffee, which is really not the thing if you can’t go to the bathroom.
There are bottles that are easier for the guys to use than women. I dehydrate from 9 o'clock the night before so it doesn’t become an issue. The worst part is they send lunch down with you, besides the food they tend to send a thermos of coffee, which is really not the thing if you can’t go to the bathroom.
Don’t you get a dizzy or get a headache being so dehydrated?
I have not had the problem of headache. People who do just take liquids have to use the bottles. But I only dehydrate when I’m going down in the Alvin. Dehydrating for 18 hours in one day doesn’t affect me that much.
Is it scary being down so deep?
You know, it’s funny, because I’m a scuba diver and I think I’m much more anxious when I’m diving than when I go down in Alvin. You’re in a little ball with two other people. The very first dive I remember getting out of my bunk and making it up and the thought went through my head: “I wonder if I’ll sleep in this bunk tonight.” Now I don’t really think about it. I think: “Well, I’m going down to the bottom of the ocean today.”
Is it fun to be in the club of people who have dived in Alvin?
There are actually more people that have been to the bottom of the ocean then to space, but it’s a relatively small community of people that have been down in the sub. I don’t think of myself as being in a club--it might be something like a thousand people
So where’s Alvin right now?
In early September, the Alvin will be out on trials necessary for certification by the Navy. The Alvin pilots, the senior pilots, will take the vehicle down on the dives and the Navy will send some of their people. Until it’s certified they’re not allowed to take anybody else.
How does the Navy test it for safety?
That’s hard for me to answer. I will tell you one difference is that most Navy submarines don’t go to the bottom of the ocean. They don’t go very deep at all. So the testing in terms of the depth capability has to be completely different. And Alvin is the only deep diving sub in the United States.
Are you planning any dives for when it’s ready to go?
In November we're planning to have a group of scientists that will take the sub out and do some science testing. We’ll test the science gear because that’s not part of the Navy certification.
We’ll be putting it through its paces. It’ll include mapping, imagery, sampling, the whole range of science that the Alvin’s used for: biology, geology, chemistry, etc.
Are you looking forward to seeing the new renovations from underwater?
I’m really excited. Particularly because we now have five windows instead of three so the visibility has to be a huge improvement and I’m really excited to see how different the capabilities will be compared to the last.
A number of us use the vehicle for observing so the better you can make observations the better your science is.
Speaking of the science, how did you get this gig? Have you always been interested in geology?
I did not study geology in school. I grew up in England and in my last school years I studied physics, chemistry, and mathematics. But I didn’t want to go into a job where I’d be in a lab all the time. I wanted to work outside. So I did an undergraduate degree in environmental sciences. In my last year at college I took a course in marine chemistry and in the textbook I saw pictures of ships and I thought: “Wow, that looks fun.” I ended up applying to grad school at MIT and WHOI. (As a student you can take courses at MIT or at WHOI or a mix and you can choose an advisor that’s at either.)
The seafloor interested me and at the time hydrothermal vents had not been found, but they’d been predicted to exist. So I ended up working on rocks collected on the seafloor. It wasn’t until about seven years after I graduated that I made my first dive.
It’s great that you were able to change gears and discover your passion even after getting an education in a different field...
When I was 13 we moved to live near the ocean. And I learned to sail when i was 13 so I liked the ocean, but I hadn’t really considered it as a career. Until I saw a ship in a book.
Photos courtesy Woods Hole Oceanographic Institution
Not all science is done in a lab by guys in white coats staring into microscopes. Lots of discoveries require brave men and women to put their boots on the ground and get down and dirty in dangerous environments. Every month we’ll profile one of these field scientists, tell you how they do their job, and explain the science behind what they do. If there’s a scientist or field of science you’re dying to hear more about shoot us an email or a tweet: erin at erinbiba dot com, @erinbiba