Atlantis, the Floating Lab

At 6:00 a.m. on Saturday, January 28, Atlantis reached Port Everglades in Ft. Lauderdale, Florida. The science team is certainly ready and excited to be on land, and I don’t blame them. They have been working around the clock for the last three weeks with no breaks. And when I mean around the clock, I literally mean around the clock. When Jason or a CTD is in the water, two or three team members must be on watch, and many more must be up for the recovery of samples. Sometimes Jason is in the water for more than 24 hours, and watch shifts are partitioned in four-hour shifts among the science team.

Red rock from the seafloor

As mentioned in the last post, the Geology Team has the important job of categorizing the rocks found at both vent sites to understand how hydrothermal vents alter the seafloor landscape and how they chemically interact with the hot vent fluids. Although rocks may seem like solid, unchanging objects, they are still chemically active even if it isn’t in obvious ways. The easiest example to think of is iron. Ever see a red-colored rock? It probably had some iron in it that has reacted with oxygen to produce iron oxide—rust. The same has happened to a red rock taken from the seafloor; the iron in it has reacted with dissolved oxygen in the water.

In the Proterozoic Era (3.1 to2 billion years ago), before oxygen was abundant in Earth’s atmosphere, single-celled, ocean-dwelling cyanobacteria began releasing oxygen as a waste product. As this happened, it is thought the oxygen reacted with any iron that was around, and there was plenty in the oceans. It did this in cycles of high and low oxygen concentrations and iron-rich sediment was deposited on the seafloor over time. After millions of years, these sediments hardened into sedimentary, forming sedimentary rocks called banded iron formations, or BIFs. BIFs are  important economically speaking, as this is where most of our iron ore comes from.

Rocks react with seawater on the seafloor and they also react with the mineral-rich hydrothermal fluids. As hot water passes through seafloor rocks before exiting a vent, it will dissolve minerals in the rocks. The Fluids Team is measuring chemicals in the fluids coming out of the vents in order to piece together a bigger picture of the rocks below the vents based on the minerals and gases they will be measuring.  

The Fluids Team:  Getting into hot water

Jeff Seewald

Dr. Jeff Seewald, who has been working on vent fluids for over a decade, and his team from WHOI (Jill McDermott and Sean Sylva) are taking on the task of analyzing the chemicals in vent fluids. Eoghan Reeves from the University of Bremin and Freider Klien from WHOI are also associated with the Fluids Team.

In order to be effective chemical detectives the team uses specialized equipment able to sample vent fluids and, as they are brought to the surface, keep them at the very high pressures in which they were collected—over 240 times the atmospheric pressure at sea level. The gas-tight samplers are critical if they are to analyze dissolved gases in the fluids, which would escape from solution as the pressure dropped. Jill will be looking at the major gas chemistry of the fluids—CO2, methane, hydrogen sulfide, carbon monoxide, as well as others. They’ve already been measuring some of these on the ship.

As cold seawater sinks through cracks in the seafloor it dissolves minerals in the rock before emerging as enriched vent fluid. By looking at the chemistry of the fluids, the Fluids Team will be able to give a better idea of what kind of rocks the fluids interacted with. “Vent fluids are the window into the sub-surface processes that transform sea water because its hard to see what’s below the sea floor and technically very difficult to drill in ocean ridges,” said Jill.

Jill McDermott

Because these sites sit on old, mafic (silicate minerals with high magnesium and iron content) rocks, the resulting fluid chemistry is different than vents at other spreading centers and could be analogous to conditions present on early Earth.

The vent fluids are also what sustain these unique vent ecosystems, so it’s critical to understand what minerals, or nutrients, are available and to connect them with the life that is consuming them. So far the team has found unusually high concentrations of hydrogen, a great source of energy for microbes. “Ideally we like to link the chemistry with the biology conditions in what supports life—Julie [Huber] will be interested in the chemistry in the areas where she was collecting microbes, “said Jeff, which brings us to our next group the Microbiology Team.  

Microbiology Team: Looking out for the little guys

Microbial samples

Julie Huber, from WHOI’s Marine Biological Lab, and her research assistant Emily Reddington are studying seafloor microbiology. Hydrothermal vents make excellent homes for microbes as they exploit the complex chemistry of the fluids, consuming mainly methane, hydrogen, and sulfur compounds. The Microbiology Team collected samples of microbial mats near vent sites as well as microbes that live in the fluids themselves. The team brought special ovens on board so they could attempt to culture the microbes, as these critters like to live at high temperatures. In addition, some of their samples were frozen and shipped back to Julie’s lab for molecular analysis. “Once we get back to the lab, we can extract DNA and ask who is there and what genes are they carrying,” said Julie.  

Carbon Team: Heavy thoughts

Last, but certainly not least, are Max Coleman and Sarah Bennett, scientists from the NASA Jet Propulsion Lab that make up the Carbon Team. Max and Sarah are actually members of all the teams, and with good reason. They have been working with the Plume Team, the Biology Team, the Geology Team, the Fluids Team and the Microbiology Team to collect samples from every area on the vent systems here are the Mid-Cayman Rise. They are looking at the bigger picture to get a better sense of how the element carbon is altered as it passes through the vent system.

Max Coleman and Sarah Bennett

Taking a step back, carbon forms the backbone for ALL life on Earth and it comes in a few different forms or isotopes (number of neutrons in the atom). Roughly 99 percent of all carbon exists in its most stable (and lightest) form, carbon-12, which has six protons and six neutrons. Roughly 1 percent exists as the heavier carbon-13, which has seven neutrons, and a very small fraction is carbon-14, which is radioactive. When organisms consume carbon, it’s much easier for them to make use of the lighter isotope, carbon-12, than the heavier. Think of going backpacking—it’s much easier to carry around a lighter pack than a heavier one.

Even though carbon-12 is way more abundant than carbon-13, organisms will still take up a very small amount of carbon-13 and this can be detected through careful analysis. Larger animals that feed off of the microbes, will likewise be consuming the already carbon-light microbes, and so on up the food chain. Sarah and Max will be studying the ratios of carbon-12 to carbon-13 from the amount present in the rocks on the seafloor, to the amount in the vent chimney and the vent fluids, to the microbes and macrofauna, in the plume at various depths, and all the way up to the surface. They even collected a flying fish that found its way on deck!

Their work will also show how carbon is altered by life, which will be valuable when considering where and how to look for life on other planetary bodies. If we know how and how much the carbon signature is altered by living things, scientists will have a better grasp for discerning how the observed environment has been altered due to the presence of life.

Signing Off!

The OASES 2012: Return the Mid-Cayman Rise has come to a close and everyone is making their way back home. However, the science doesn’t stop here. The following weeks and months the teams will be analyzing their samples, some under microscopes, some in machines called gas-chromatographs, some even doused in x-rays at synchrotron radiation facilities. Eventually, these teams will write their results in papers and present them at conferences. So keep a look out for future news of the various results from this expedition.

It has been my pleasure communicating the very interesting science on board Atlantis. Not only did I learn a lot, I had an excellent experience during my first time at sea. I would like to thank everyone on the science team, the Jason team, and the crew for making this cruise such a memorable experience. This will be my last blog post and it has truly been an honor.

This is Julia DeMarines, signing off.