Jason Takes a Bow on the Stern
|Jason returns for the last time.|
Jason has just surfaced from its last dive of the cruise to a warm welcome from a group of scientists hungry for their samples. The vehicle has completed ten nearly flawless dives, with one minor glitch during which its manipulator arms stopped responding mid-dive. Luckily, Jason has a hardworking crew available around the clock to make sure it functions properly. They fixed the arms and all is good, although many are tired.
The Plume Team launched one last, eight-hour CTD cast to get a background, or control, sample of ocean water far away from the mineral rich plumes. Using this, team members can study how different their plume samples are from the norm. Immediately after the CTD surfaced, the Plume Team removed their samples and sampling instruments and Atlantis began to head back to port. It will be a two-and-half-day journey, and everyone is in good spirits.
|Chris explains the dive plan to Matt.|
On Jason’s last dive, it investigated some unexplored mounds on its way to the Von Damm site. During this exploration dive, it picked up several rocks that looked interesting. This was an exciting time for the Geology Team, whose members are always thirsty for samples. In the ROV Van, the geologists noticed an outcrop of rock close to the Von Damm site they wanted to sample. After an hour trying, Jason’s incredibly strong robotic arms could not break off a piece of what we quickly dubbed ‘kryptonite’.
In addition to rock sampling, there were also important vent biology and fluid samples to be collected on our last dive, so around 10:00 p.m., Chris called off the attack on the rock and directed the Jason Team to make sure they completed everything else on their list. By 4:00 a.m., Frieder, Max, and Chris were back in the van, but there were still two vent-fluid samples to collect from the top of the Von Damm mound before the geologists could get back to it.
At 6:00 a.m. and with time running out, Jason moved off to the north of the Von Damm hydrothermal mound in the direction of the krypotinite outcrop to see if there might be more outcrops of the same material. Sure enough, a near-identical outcrop appeared, and Jason’s pilot tried valiantly once more to break off a sample, again without success.
|Happy geologist (Frieder) with basalt.|
Another 30 minutes had elapsed and we only had half an hour left. With not much time left on the clock, the geologists decided it was time to take a gamble and requested that Jason continue on further in the same direction. With fifteen minutes to go, the team found a third outcrop of similar rocks that had evidence of slightly more weathering than the previous ones and, at just three minutes after the hour when their time was up, they were finally able to collect a piece. In this case, the third time was indeed a charm. When the team got their sample back on deck, it turned out the rock wasn’t kryptonite at all, just a very (VERY) tough basalt.
Geology Takes Center Stage
The Geology Team is an international group composed of three members: Guy Evans and Frieder Klein from WHOI and Matt Hodgkinson from the University of Southampton in the U.K. They have the important job of analyzing rocks plucked from the seafloor, and their work will help tell the tale of the water-rock processes that go on beneath the seafloor at these vent sites. In addition expanding geologic knowledge , their research could have applications to both mining and the field of astrobiology.
|Beebe vents 1-4|
Let’s take a step back and recall how deep-sea hydrothermal vents are formed. Hydrothermal vents form when cold seawater seeps into the crust through cracks in the seafloor. In places where water meets very hot rocks, as happens in places like Yellowstone or along spreading centers like this one, the water becomes acidic, dissolves minerals from the rock, and is enriched in metals (iron, zinc, copper, etc.). Ultimately the hot, enriched water rises buoyantly through cracks, or faults, and meets the very cold ocean water. At the moment it does, the minerals in the fluid precipitate out as tiny, solid particulates. This is why the fluids coming out of the black smokers look, well, like black smoke. Over time, these sulfur-rich minerals accumulate to create the bizarre chimneys we see around vent sites.
As mentioned, the Geology Team’s research is potentially important in the mining world, as well. On land, copper, zinc, and other metals are readily available at what geologists call inactive volcanogenic sulfide-mineral deposits. The processes that form these land deposits are analogous to those that form deep-sea hydrothermal vents. At inactive sites on land, geologists can’t sample the mineral rich fluids responsible for creating the deposits, and this hinders their ability to answer some very fundamental questions.
|Geology Team (l-r): Frieder, Guy, and Matt|
“Since they are not active, it’s difficult to know how they were formed,” said Guy. “What we’re hoping to do is determine certain characteristics to make connections from active sites to inactive sites”. This information could help the mining industry determine locations to mine in the future.
Frieder is most interested in understanding what controls the fluid chemistry and the fluid-rock interactions in general, and is also working closely with the Fluids Team (who I’ll describe in a later post) on these and some much larger questions. “I’m trying to understand how fluids react with rocks and how this influences the chemistry of the oceans,” said Frieder.
From the information he gathers, the team can determine the temperature at which these reactions occurred and learn more about the environmental conditions beneath the seafloor when they were altered. This is important when considering the larger picture of life in the universe, as many astrobiologists believe hydrothermal systems possess the right conditions to have kick-started life on Earth. “There are some conditions you need to understand when thinking about the origin of life," said Freider. "The key components are pH, hydrogen concentration, methane, CO2, and temperature, which we try to constrain using the rock record.”
As mentioned in a previous post, this site is of particular interest because of the atypical spreading of the seafloor. New seafloor isn’t being freshly deposited by volcanic activity such as along the Mid-Atlantic Ridge, but rather the tectonic plate is actually being dragged up, stretching the seafloor and exposing old mantle rock. The Geology Team was hoping to collect samples of mantle rocks, proving this theory, but was stymied. “We haven’t found any rocks with mantle origin, and we’re not to sure why that is,” said Matt. “Probably it’s because they’re covered in sediment.”
Matt is also going to look at the radioactive isotope radium-226 and its decay product, barium, to pin down the ages of the chimneys at the two vent sites as well as the overall age of the system. In addition, he’ll be looking at a process known as secondary enrichment, which often results in an increase of concentrations of copper and zinc concentrations in the mound after it forms.
Thinking cosmically, studying the geology at hydrothermal sea vents may yield clues to hydrothermal interactions on other celestial bodies and may help us home in on interesting places to look for life. Hydrothermally altered mantle rocks, which we hoped to find at the Von Damm site, have been described on the dwarf planet Ceres and on Mars. By studying these rocks in situ on the seafloor scientists can learn more about possible fluid-rock interactions on extraterrestrial bodies, which are understandably difficult to examine. This opens doors to astrobiologists who are interested in studying extraterrestrial conditions similar to the ones present at the origin of life on Earth.