My Trip to the Bottom of the Sea
By Bridgit Boulahanis
The biggest question driving the OASIS mission is simple: How old are the lava flows along the 8°20’N seamount chain. Answering that question is far from simple, requiring a plethora of data, multitudinous methods of sample collection, and many experts in order to conduct the analysis.
We can get information about the magnetic polarity of the rocks below us from our magnetometer, allowing us to understand the relative age of the seafloor in relation to known magnetic pole reversals. We can use shipboard multibeam and autonomous underwater vehicle multibeam to gain an idea of the character of the seafloor we survey, generating maps of the major features and preliminary analysis of the sediment cover in the region. We can use dredges, large metal baskets lowered overboard with weights, to pick up rocks across a broad area in order to characterize the chemical composition of lavas in that region. Each of these forms of data collection adds an important piece to the puzzle we are trying to solve.
However, the most exciting form of data collection is the sampling we can do with Human Occupied Vehicle (HOV) Alvin. Alvin allows us to get precise samples of specific lava flows and morphological features, ensuring that we know exactly where the rocks we chemically analyze come from. Beyond its incredible sampling capabilities, it is the most exciting way to learn about the seafloor.
Last week, I had my first opportunity to dive in the submersible, and while the science is what drew me here, it was the thrill of seeing firsthand what was on the bottom of the ocean that had me wide awake many hours before launch, standing on deck as the sun came up, staring over the side into the depths that I would soon be exploring. In the morning air it was hard to imagine that soon I would be under thousands of meters of water, seeing with my own eyes what I have been studying for years.
After a small breakfast and what felt like years of excited pacing, we entered the submersible. I was diving with Alvin pilot Jefferson Grau and Mike Perfit, distinguished professor of geology at the University of Florida. The tight space that makes up the human occupied space of Alvin has just enough room for three, and so as the submersible was lowered into the sea off of the R/V Atlantis, we settled in for a cozy nine hours.
After bobbing with the waves on the surface for several minutes as the pilot and crew did their final safety checks, we began our descent. Almost immediately upon leaving the surface the motion of the waves faded away and the submarine felt still enough to almost trick me into believing we weren’t moving at all. However, soon the bright blue of the shallow ocean faded to the black of the deep, and bursts of bioluminescence surrounded the submersible. More seasoned colleagues had told me that I should keep an eye out for bioluminescence, but there was so much of it that it would have been hard to miss! It looked as if we were descending through a field full of fireflies, with occasional fireworks popping up as we passed larger organisms bursting out of the darkness.
It took us almost 90 minutes to reach the seafloor, and I spent the entire time looking out the two portholes I could reach from my side of the submersible. I was already enamored with the experience, and we hadn’t even gotten to the ocean bottom. During our final approach we turned on all of Alvin’s external lights, suddenly bringing daytime to a previously eternally dark part of the world. Grau and Perfit, both veterans of Alvin exploration, advised that I look out my side porthole to catch the soonest glimpse of the seafloor. For several minutes I waited, staring down to where light blue faded to darkness. Then, suddenly, it was there—sandy sediment extending in every direction with pillow basalts peaking out around.
Immediately we began collecting samples of the rocks around us using Alvin’s two manipulator arms, while writing descriptions of the area and recording audio descriptions of everything we saw. Following a dive track laid out before our descent, we traversed up the side of Avery Seamount while noting the characteristics of everything we passed. Perfit pointed out rocks for Grau to sample, while I operated cameras to ensure we attained high quality footage of each sampling location. Our conversations were filled with preliminary analysis, with Perfit guiding me in identifying the differences between the various rocks outside our window.
Midway through our dive we came to a steep wall approximately 30 meters high, a cliff face at a 90 degree angle to the seafloor. Even in the best multibeam maps of the ocean floor we cannot represent such rapid depth changes accurately—our sonar will smooth even the largest crags automatically, making knowing about these sorts of cliff faces elusive without underwater vehicles. Despite my years of looking at these maps, I never pictured vertical cliffs rising off of the seafloor. To say this realization rocked my world would not be hyperbole, but it would be a bad pun.
Our dive track took us past the steep wall, and so Alvin rose up, floating along the cliff face that seemed to climb endlessly from the sediment below. Soon the dark pillow basalts became speckled with sea life—corals and anemones, starfish and sponges. Everywhere we looked, life was not only present but appeared to be thriving. While as geologists and geophysicists we do not sample any of the living organisms we find, it was very exciting to see, and we noted their location to pass on to biologist colleagues who might return.
Alvin’s sample basket was almost full by the time we approached the summit of Avery Seamount, and we spent our last moments on the seafloor extracting one last rock for later analysis. Though the dive lasted its full nine hours, it passed far too quickly. Too soon we were rising to the surface, passing back up through the bioluminescence and the lightening shades of blue until we were again hoisted on board the ship.
Upon exiting Alvin we were met with a cheering science party, a tradition every time the submersible comes back on deck. After applause and hugs, we scientists did what we do best—got straight to work on the analysis. We classified the samples we had collected and began the description and photography process, logging each rock carefully so when they get back to a laboratory on land, the geochemists have all of the information they might need.
The descriptions and samples we collected while on the bottom will help us to characterize how old Avery Seamount might be, providing valuable insight into the processes that formed this expansive seamount chain. Having contributed to increasing scientific understanding in such a hands-on way is absolutely thrilling. Now when I look over the edge of the ship, it is impossible not to picture the varied terrain that must be slipping past me deep below, teeming with life and calling out for me to visit again soon.
Bridgit Boulahanis, a graduate student at Columbia University’s Lamont-Doherty Earth Observatory, is in the eastern Pacific Ocean aboard the R/V Atlantis on an expedition to investigate a chain of submarine volcanoes along the East Pacific Rise. Learn more about the expedition in her blog and on the OASIS Facebook page and YouTube channel.