Expedition to the Mariana forearc

Mar. 23 - May 4, 2003

Days 8 & 9, March 30 & 31

(click on any image for the larger version)

Days 8 and 9: BLUE MUD!!!

Day 8: Big Blue Seamount—we arrived early and set the transponders. The DSL-120 was deployed using Medea (from Jason 2) as the weight in hope of solving the problems of the cable twisting and tangling. Medea communicates with the control van and so does the DSL-120 so the system had to be electrically reconfigured before deployment. Once launched, there were unexpected electrical complications, so it was back onboard for Medea and the DSL-120. By 0930 we were preparing a gravity core of the summit of Big Blue. I asked Chris Moser, the coring specialist, why there was a plastic bucket lid tied near the end of the core pipe. He explained that this “high tech” device would, hopefully, break free when the core pipe penetrated the mud. Later, when we come back to this site with Jason 2, we will see the bucket lid marking the location of the core sample.
Blue Mud Blue Mud! One half of the core on the work table in the lab.
 This was the fastest core sample taken yet--perfect mechanical operations and a shallow summit at 1235 meters. (Shallow? That’s almost 4000 feet, but shallow compared to where we’ve been.) The gravity core plunged deeply into the mud but again came back with a short sample. It may have been short, at 24 inches, but it was BLUE MUD! There was no sediment on the surface at this location on the seamount. Four inches of green serpentine mud and the rest is layers in various shades of blue serpentine ranging from a lovely pale blue to a deep blue like the night sky. Blue mud, the consistency of clay--a pottery maker would love this stuff. I wanted a sample for myself but you can’t do mud pies around all these geologists and chemists.
The Mariana Forearc was first dredged in 1981 so the presence of serpentine mud has been known for over 20 years. It wasn’t until early 1990, when drilling was done at Conical Seamount, that the seamounts were discovered to be volcanic in nature. Patty discovered the blue serpentine in 1997, from this very ship, at Pacman Seamount. I wish I had been there. Patty still sparkles as she describes the moment the core pipe was opened and the bright blue mud was first seen.
sampling the core water Geoff is taking samples to study the chemistry of the core water.
taking samples to study microbes Jim and Andrea. Andrea is taking samples to study microbes.
 The serpentine, as it first forms from periodotite deep beneath the seafloor, is blue. It changes color to green as it seeps closer to the volcanic summit and interacts with sea water. The exact chemical processes involved here are not completely understood and are being studied during this expedition. Patty has found blue mud at South Chamorro, Blue Moon, Celestial, Big Blue, and Pacman Seamounts.

Back into the water with Medea and the DSL-120 at 1300, results in a perfect decent and a beautiful start to the 8 transects planned over Big Blue Seamount.

Day 9: The DSL-120 survey of Big Blue Seamount continues all day today and, probably, through the night. Medea is working beautifully as the weight for the DSL fish. Akel tells us the data is magnificent and will result in spectacular maps. Everything is going so well that the plan has expanded to include a deep water transect starting at the base of the seamount. We finished transect 8 just before sunset. The ship is now towing the DSL-120 south. Eight miles from the summit, at a depth of 3150 meters, we will start a single transect from the deep water up the south flank and over the summit of Big Blue.

In the control van when Jason II is working, it’s exciting watching the monitors—the sea floor, the navigation, and the placement and retrieval of the scientific equipment and samples. In the control van with the DSL-120 there is not the same thrill. During my last watch, Tito, the pilot, explained that watching the DSL-120 is as much fun as watching grass grow. Tom, the navigator, said it wasn’t that exciting, it was more like watching paint dry.

Science Summary - Day 8 & 9, March 30 & 31

Science Objectives, Days 8 and 9:

The eighth and ninth days of the cruise, March 30 -31, will be spent surveying Big Blue seamount. We will be finishing the transit to Big Blue seamount where we will drop transponders and navigate in the transponder net for our DSL-120 survey. A transect across the summit with EM300 will give us bathymetry to help plan the DSL-120 survey. We want to do a gravity core at the summit then will deploy DSL-120 and spend the rest of day eight and all of day nine finishing the survey of Big Blue Seamount. The survey will include a transect up the entire south flank of the seamount along a multi-channel seismic line collected in 2002 on the R/V Ewing. We will retrace the multi-channel seismic line to ground-truth features observed in the seismic profile.

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