Sampling the Deep Seafloor

One of the most exciting aspects of our work at sea is that when we bring up small sections of the seafloor onto the ship, we are able to see small areas of the planet that no one has ever seen before. Viewing tiny creatures and the tracks and trails that they make on micro-landscapes brings deep seafloor and its strange ecosystems into light.  Collecting and transporting these small, circular patches of seafloor up from thousands of feet to the surface takes specialized equipment.

The largest habitat

The deep sea, the largest habitat on the planet, is a mostly unexplored, perpetually dark environment, with crushing pressures and temperatures only a few degrees above freezing. As scientists, we seek to explore this remote, foreboding realm of our planet for many reasons.  One of the primary motivations for our quest for deep sea mud on this trip lies in the fact that deep sea sediments archive valuable clues to the history of changes in ocean conditions and climate. 
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The average depth of the ocean is about 3700 meters (over 12,000 feet), which is about 3670 meters deeper than most scuba divers can go.  Obtaining samples from this remote and extreme environment requires specially designed equipment.  There are several devices that can be used to collect seafloor sediments (including manned submersibles and remotely operated vehicles), but the most commonly used methods send sampling gear to the depths using a winch and a very long wire cable.  The primary device that we chose for sampling the top few inches of the seafloor on this expedition is the “multicorer”.

Ready for Launch. The mulitcorer with MISO camera system is ready for deployment into the deep sea. We work in shifts around the clock, so we launch and recover the multicorer day and night (and during spectacular sunsets).

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Just a little off the top

​The Ocean Instruments multicorer MC800 that we are using is designed to collect just the very surface of the seafloor, keeping intact the fluffy, dust-like materials that often lie on top of denser mud.  We are interested in the chemistry, sediment characteristics and microscopic life of these seafloor surface sediments.  An understanding of these surface muds will help us interpret clues about ancient oceans hidden in deeper muds.  Essentially, for this project we get to play with mud!

The multifaceted multicorer

​With a 12-foot-high metal teepee frame, and a 9-foot diameter base, the multicorer looks like a lunar lander.  A circular arrangement of eight (28-inch long, 4-inch diameter) clear tubes held in metal harnesses are visible in the center of the teepee.  These harnessed tubes are attached to a central metal “spider” that includes heavy lead bricks.  The multicorer is typically lowered through the ocean using a 9/16 inch diameter wire cable from a very large spool of cable attached to a winch housed within the ship.  We are using a different cable to accommodate the camera system on the multicorer.

The set up. Undergraduate students (L to R) Kira Sirois (University of Tasmania), Garrett Cooper and Trace Hicks (California State University, Bakersfield) set up the mulitcorer for deployment.

Three, two, one.. lift off! Josh Barnes, CSU Bakersfield (Left) is operating the A-frame that extends the multicorer over the water and into the fog. Ryan Tengelsen, CSU Bakersfield, and Kira Sirois, University of Tasmania (far left) hold tag lines to keep the multicorer steady during deployment. Andrew Naslund, Research Technician, Scripps Institution of Oceanography (center), directs the operation.

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Ocean views

​On this trip we have added a state-of-the-art camera system to the protected inner area of the teepee.  The Multidisciplinary Instrumentation in Support of Oceanography (MISO) camera system developed at Woods Hole Oceanographic Institution provides live views of the seafloor, and also enables us to watch part of the mud collection process.  Like the multicorer, this camera system is designed to function in the harsh conditions of the deep sea. With this unique camera system, we can view the seafloor several feet away before we decide to take a sample (sometimes there are just too many large rocks and not enough mud).  When we find a good spot, we send the multicorer down the rest of the way to the seafloor.

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Eight is enough

Once the “feet” of the metal teepee touches the seafloor, the cable begins to go slack, and the eight tubes are slowly pushed into the sediment by the lead weights.  A “slow-down” cylinder on the multicorer ensures that the tubes go into the seafloor slowly, keeping the sediment-water interface as intact as possible.  Under ideal conditions, the tubes are about half-filled with sediment and half filled with water when the process stops. At this point, the winch starts bringing the multicorer back.

Discovery

​The multicorer typically travels back to the surface at 130 feet/minute, and depending on the water depth, it can take a while to get the multicorer’s sediment cargo up to the ship.  Excitement builds as the multicorer reaches the surface.  We all can’t wait to see what the deep seafloor at this site looks like up close.  There is a strong sense of discovery and wonder when we look through the clear tubes to gaze at small patches of unexplored ocean bottom landscape.

Author

Anthony Rathburn