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Thar She Blows!

posted Jul 5, 2012, 4:13 PM by Shannon Bresnahan
We have been hard at work the past several days surveying San Diego's coastline for seeps. The multibeam and CHIRP instruments that we have been using for this have also proved useful in finding sunken treasure -- in our case, a sixty-some foot long female fin whale.

Many studies have investigated the decomposition of sunken whales, since these creatures provide a unique deep-sea ecosystem. At least three distinct "successional stages" exist in a whale's decomposition. During the first stage, the whale attracts scavengers such as hagfish, sharks, crabs, and the like. The second involves organisms such as crustaceans taking advantage of the nutrients provided by the whale's skeleton.

Photo: Scripps graduate student Valerie Sahakian is
hard at work in the lab aboard R/V

Over time, the organisms deplete the oxygen transforming the whale into an anaerobic environment -- this marks the third successional stage. Under these conditions, which include high concentrations of sulfide, the community develops into one similar to that found in seep environments. Since we believe cold seeps occur near San Diego, we are interested in comparing the connectivity between these environments and the similarities in the communities.

On November 19, 2011, a fin whale was found washed up at Point Loma. Scripps Professor Greg Rouse, Virgin Oceanic's Eddie Kisfaludy, and others collected seven tons of iron to sink the whale off the coast of La Jolla, giving scientists the perfect opportunity to study these stages and communities. Although the whale was dropped at a particular location, ocean currents could have caused the whale to drift during its decent. In order to study this sunken scientific treasure, we first had to find its exact position on the seafloor bottom.

Photo: Researchers tow the remains of a 67-foot-long fin whale killed during a collision with a ship out to sea off the San Diego coast on Nov. 25, 2011. The remains were weighted and sunk. Scripps marine biologist Greg Rouse plans return visits to the submerged carcass so  scientists can observe how it could create its own miniature seafloor ecosystem as it decomposes. Photo credit: Eddie Kisfaludy.

Enter our geophysical instruments! Large floats were attached to the whale when it was sunk, which we should be able to observe in the water column with the multibeam, as Jillian described in her recent post. At 2 a.m. on July 1, squeals of excitement could be heard in the main lab on the ship as our screen displayed an object in the water column -- only about 20 meters (65 feet) away from the location where the whale was sunk! We crossed the location two more times at different angles to confirm the location of the float. With our new Remotely Operated Vehicle (ROV), we will now be able to return to this site over time to observe the successional stages and how the community changes. If time permits, we may even be able to revisit this site in the upcoming days for a first glance at the whale!

--Valerie Sahakian, Scripps Graduate Student