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Dr. Deborah Kelley: Lost City

The reason that we call Lost City, "Lost City," is that when we discovered the field in 2000 we were on the research ship Atlantis. And also the Lost City field is sitting on a very large mountain called the Atlantis Massif. And it's bounded to the south by a very large fracture zone kind of like the San Andreas Fault. It's also called the Atlantis fracture zone. So there was the Atlantis component and also when we first dove on the chimneys, they were very, kind of, reminiscent of Greek towers and so the whole thing just kind of fit in.

One of the reasons that I'm fascinated about hydrothermal fields in general and hydrothermal vent systems is that they can tell us a lot about how life evolved on the planet and also about the amazing environments that life can figure out how to make its way in. The hydrothermal vents that we're looked at range in temperatures from just a little bit above ambient temperature actually just a little bit above freezing sea water to temperatures of over 700 degrees Fahrenheit. In some causes, as it is with black smokers, the vent fluids are acidic, very, very hot, very rich in toxic metals that would kill most of us. In contrast to Lost City where the fluids are more temperate; about 200 degrees Fahrenheit and they have properties similar to liquid drain-o. So one of the amazing things for me is to try and figure out how the organisms live there and what the relationship of the geology is to the animal populations that live in these sites.

The best systems we look at the way that they form, either a Black Smoker system or in something like Lost City is it... Basically we have a heat source. imagine heating up a pan of water on your stove and what you see as you heat that up the fluids overturn and we call those convection cells. And the same thing happens in the oceanic crust where we have a heat source. Either a magma chamber or hot rock and as the crust ages in these environments and these spreading environments large fractures form in the sea floor and the sea water migrates down along the fracture and as it gets near the hot rock it heats up and as it does that it becomes buoyant, it rises to the surface, and it entrains cold seawater down on the down welling so it's very similar to a pot of boiling water.

One of the... in contrast to Black Smokers, one of the biggest differences about Lost City is that it's actually not driven by volcanic heat. The Atlantis Mountain is made by rocks that were formed very deep in the Earth and they're very unstable now, so just the interaction of seawater generates its own heat. Because volcanoes aren't involved the fluid chemistries are fundamentally different also than Black Smokers. They're not as warm. They're about 200 degrees Fahrenheit. That's the hottest that we see. About 90 degrees C. And they are... Instead of having a lot of Carbon Dioxide, they have a lot of methane and hydrogen associated with that. Because those gases are what the microbes live on, we also see very different kinds of microbial populations in Lost City than we do in Black Smoker.

I really like these two examples. In this hand I a sample of Black Smoker that had 300 degree Celsius fluid going through it, so about 700 degrees F. And these Black Smokers, this is a very characteristic sample. It's a piece of a big pipe, basically, it's all made out of metal sulfide. Things like calcium pyrite, it's a copper-iron sulfide. Fool's gold is another mineral called pyrite. And this is very characteristic of chimneys.

In contrast, one of the reasons we knew Lost City was so different, is that you can really just tell immediately just by looking at the chimneys. They're bright white in appearance. They're very porous and they're made out of a material called calcite or aragonite which is a calcium carbonate mineral similar to Limestone, similar to the same thing you'd find in a cave.

One of the big questions about Lost City is whether it's unique and how many more of them are out there. Black Smokers were first found in about 1977, 1979. Since then we've found over 200 fields and so there's no reason to believe that we were so lucky that we found the only Lost City. And one of the big challenges now for the next several years is to go in other places, other parts of the ocean, and look to see if we can find some more of these systems.

 

Related Links

Dr. Deborah Kelley Profile


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