Adventures at Oil Mountain
posted by Mandy Joye, April 5, 2014
<note to readers: to see an image's caption, hover the mouse on the image>
One of the reasons I became an oceanographer is the thrill of discovery. Seeing something that no one else has ever seen generates an amazing rush of excitement. It's indescribable. I suspect that the word "WOW" comes out of my mouth about 30 times each dive. Since we know more about the surface of the Moon than we do about the seafloor on our own planet, there are numerous creatures and features on the seafloor, awaiting our discovery. This is why I believe I have the best job in the world.
Working in the deep sea is a challenge and making discoveries in the deep sea requires access to highly sophisticated technologies. First, you have to know where you are (on the bottom) and where you want to go (your sampling target). Navigation and site characterization are critically important. On land, if you are driving in your car and get lost, you can look at a map or stop at a gas station and ask directions. On the seafloor, it's not so simple. You have to be prepared and you have to know what is where and getting this information requires a lot of effort (see below). Second, you must have outstanding sampling capabilities (Alvin, its cameras and manipulators as nimble as the human hand) and tools (for example, custom-designed high-definition cameras and sophisticated chemical sensors). On this cruise, we have access to amazing instruments that have already enabled some surprising discoveries.
But, before getting into this, I want to give you all a feel for what a dive-day is like. For the Alvin crew, the day begins around 0600 with getting the sub prepped for launch. On dive days, I get up around 0500. For the science party, the day begins by checking the gear in the Alvin basket to make sure everything we need is there. Then, we prepare the styrofoam cups that will go down that day. Adults and kids alike love Alvin shrink cups. Styrofoam cups are comprised mostly of air. As you go deep beneath the sea surface towards the seafloor, the pressure increases, pressing the air out of the cups and shirinking them to about 1/3 to 1/4 of their original size. In the image gallery above, there is a picture of the cups prepared by my oldest daughter's class at school before the dive and after the dive to a site (images 2 & 3) about 900m water depth. You can see the difference!
At about 0740, the scientist board Alvin. In the "about to dive" photo, Ian MacDonald and Caroline Johansen from Florida State University board Alvin for a dive to GC600 (image 4). The day before I dove on the site with Kim Takagi, a post doc in my group at UGA. GC600 is the most prolific natural hydrocarbon seep in the Gulf of Mexico and is also a site where super-salty (brine), oil and gas saturated fluids seep from the seabed. A lot of what we know about GC600 is based on sampling from ships in the absence of remotely operated vehicles or HOVs, like Alvin. Having Alving at this site gives us eyes on the bottom, which give us a much greater chance of making surprising discoveries. Once Alvin is in the water (image 5), it takes about an hour to reach the bottom at this water depth (1225m).
People often ask me how we identify targets for sampling. One way to do this is to use a multibeam echosounder (MBES) (image 6). The MBES allows us to map the seafloor and, during the mapping, identify sites of oil/gas seepage from the seabed to the overlying water column. This MBES plot is a screenshot obtained during a survey we did last night in a 4 x 5 mile area around the main seepage field at GC600 [we have been here many times before so we have a good idea where the hot sopts are]. This lower triangular image shows a oil/gas plume jetting up into the water column. Many such features exist at GC600.
Upon arrival to the seafloor, we instantly saw evidence of active seepage (image 7). This area is noted for a high abundance of gas hydrate (the yellow colored featured protruding from the sediment) and authigenic carbonate (i.e. carbonate rocks that are formed in situ) and shells of active (and deceased) chemosynthetic organisms (i.e. clams and mussels). As we headed towards our first sampling target, we observed many areas of active seepage (image 8). Here, there were live clams and mussels, oil droplets on the sediment surface, suggesting oil saturated sediments, and white bacterial mats. These mats, usually Beggiatoa, which are sulfide-oxidizing bacteria. Sediments with active oil and gas seepage have high rates of microbial activity and this high activity leads to production of hydrogen sulfide, which feeds the Beggiatoa as well as chemosynthetic macrofauna (mussels, clams and tubeworms). The carbonate rock also serves as a shelter from predators for mobile fauna, like crabs. In image 9, there is a crab hidden beneath a carbonate chunk. Do you see it?
Once we arrived at the target, we were astonished to find a very large (3m wide x 2 m high) gas hydrate mound that was black; the hydrate was saturated with oil. We had seen these oil-saturated hydrates before but nothing prepares me for the site of black hydrate. Gas hydrate forms naturally at the seabed where the temperature is low enough, the pressure is high enough, and the methane flux is sustained and sufficient to promote hydrate formation. Gas hydrates are one of the largest reservoirs of organic carbon on Earth so developing a better understanding their dynamics is important in terms of the global carbon cycle. In the Gulf of Mexico, hydrates are abundant and can be found at most gas/oil seeps within the appropriate temperature and pressure window. In the Alvin's down-looking camera, we got this show of oil seeping up from the lower edge edge of the hydrate mound. We were a bit surprised to find a large fish hanging out immediately adjacent to the seeping oil (images 10 and 11). I wondered 'what is that fish doing there'?
The close up, "Beast Cam" helped answer that question.
Sophisticated technology drives advancement in deep sea science. The "Beast Cam", a high definition camera, which is held in position directly in front of a target by Alvin's manipulator arm, takes truly amazing pictures. In the words of its designer, Ian MacDonald, "Beast Cam is not just a camera, it's an in situ microscope". Indeed it is.
In image 12, we obtained for the first time, a close up view of the oil chimneys. We had assumed the chimneys were a homogenous feature but, far from it, there is incredible diversity in the chimney shape, color and structure. Some of the chimneys looks like handblown glass -- but it's obviously not. Other chimneys seem to be tarry and sealed. Others, clearly have oil seeping from them. Upon even closer inspection, chimneyland is home to numerous ice worms (image 13 & 14) -- which is probably what attracted that fish to this particular spot. Then, to our astonishment, we see (image 15) what looks like a cluster of small grapes except they appear to be cemented (or just stuck) together. And if we thought that was all we'd see, we were wrong, a little further down chimneyland alley, we observe oil actively, very actively, being released from a suite of chimneys.
Moving further up on the hydrate mound, we see hudreds of "ice worms" residing peacefully in their burrows along the face of the oil-saturated hydrate mound (image 17 & 18). The ice worms can also burrow and reside underneath the drape of sediment that lies atop the hydrate mound. At this particularly large mound, exposed ledges revealed extensive ice worm habitat.
Finally, I want to leave you with an image that speaks volumes to me (image 19). The surface of the ocean is blue and beautiful. Looking at the sea surface, it's easy to imagine the diversity of life within the water column beause most of us have heard about it, if not seen it in person: tuna, swordfish, jellyfish, phytoplankton, zooplankton, whales, sharks, sting rays, etc.
But, I imagine it is hard for you to imagine such spectacular diversity -- of both features and fauna -- along the seabed at a natural hydroabron seep. This rich diversity is clearly evident in this image. Oil-saturated hydrate. Something that one would not expect to find, but there it is. Oil and gas chimneys, as well as other features within chimneyland that we do not yet understand, underscore how much there is to learn about the processes and dynamics of these natural seeps. And those wiggly, hairy ice worms. They are not only present, but they are active and abundant in a harsh and extreme environment.
Today is dive #6 of this cruise. We have 16 dives remaining and many, many more discoveries to make!