Passing Ships in the Night

by | 7.4.2012 at 11:04pm
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By Helene Carton

A rack of Ocean Bottom Seismometers on deck.

As part of our study of the Juan de Fuca plate from its birth at the mid-ocean ridge to its recycling at the Cascadia subduction zone, the R/V Oceanus has the task of conducting Ocean Bottom Seismometer (OBS) operations and oceanographic measurements: this is done in close coordination with the R/V Langseth, which tows the high-quality sound source used to generate the waves that the OBS listen to.

Chief Scientist Pablo Canales prior to departure from Newport.

The Chief Scientist Pablo Canales from Woods Hole Oceanographic Institution, three graduate and undergraduate students from Boston College, CSIC Barcelona in Spain, and Dalhousie University in Canada, and myself from LDEO boarded the ship at the Oregon State University Hatfield Marine Science Center on Yaquina Bay on sunny June 6. The two teams of OBS engineers from Woods Hole and Scripps Institution of Oceanography were onboard, and all the ocean bottom seismometers had been loaded, some neatly aligned on racks on the deck, others stored inside a dedicated container. The CTD (conductivity-temperature-depth) instrument stood firmly secure on deck, wrapped in its protective bag. Looking forward to our departure the next morning, we enjoyed some delicious seafood meals onshore.

Helene Carton and students in Newport. (Photo J.P Canales).

The course of operations has us visit a series of eighty-five “sites” carefully defined ahead of the cruise, typically located about ten miles away from one another, identified as red, blue and yellow dots on the colorful map of the seafloor topography on display in the ship’s main lab. In between sites the ship transits at a speed of about 11 mph. While at a site, we are either deploying an ocean bottom seismometer (dropping it off the side of the ship using a crane), interrogating it to get its precise coordinates on the ocean floor, picking it up using long poles equipped with a hook at the end, or sending the CTD instrument probe the water column all the way down to 20 meters above the sea bottom and then bringing it back up.

Deploying an OBS from the Scripps Institution of Oceanography from the Oceanus.

Our small science team has been keeping itself busy, with duties involving helping with deployment and recovery operations on deck (and occasionally getting our pants and hard-toed shoes soaked!), processing the CTD measurements to better understand the movements of water masses in this region of the NE Pacific, and taking a preliminary look at data downloaded from seismometers that, a few days ago, were still listening for sound waves at the sea bottom under 2000 meters of water.

Recovering one of the Woods Hole OBS (Photo J. Mojica).

Several times we have crossed paths with the R/V Langseth while she was towing equipment and recording data, and remained a precautionary distance of several miles away: in lieu of waving from the deck, watchstanders on one ship greeted watchstanders on the other ship through messages in our mutually-visible electronic logs!

In the course of our time at sea so far, we have seen whales, seals, dolphins, porpoises, and birds. Towards the end of our first suite of CTD casts, the sensors got intruded by jellyfish, which resulted in some unusually wiggly signals. We have also seen (and sometimes picked up!) a variety of floating debris, perhaps from the tsunami that struck the Japanese coast in March 2011. After traveling through the Pacific Ocean such debris have started washing ashore on the beaches of Oregon.

Our adventure at sea continues until July 14 (after a brief port stop in Newport conveniently timed to coincide with the July 4 holiday!), with the final recoveries of all the OBS.

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