Expedition to the Mariana forearc

Mar. 23 - May 4, 2003

Day 32, April 23

(click on any image for the larger version)

Day 32 LOST AND FOUND * PART II

Set transponders, retrieve transponders, set, retrieve—I mention transponders almost every day. At each seamount we set transponders and later, retrieve them. The transponders receive and send sound waves and make it possible for the ship and Jason to navigate and find specific locations on the sea floor. It takes a long time to set the transponders. Each is attached to an anchor weight by a line almost 1000 feet long. These are dropped from the stern of the ship at specific locations. When all three are in place the ship surveys the area to get exact locations of each.

Walk in science freezer

Tom C. with a transponder

Here at Blue Moon Seamount where the summit is in 3700 meters of water, the entire process was expected to take about 6 hours. Each transponder takes about 45 minutes to reach the sea floor. During the survey one transponder couldn’t be found. Tom C., our transponder expert, realized that the line had broken and the transponder was still at the surface. Since this is all being done at night, no one saw it once it was away from the lights of the ship. Finding, retrieving, re-deploying and surveying that single transponder added several more hours to the process. Tom was up all night.

At daybreak, we deployed a break-away core (BAC). This is only the second of this type of coring device ever used, but after our success at Big Blue Seamount, we are confident that this one will leave a core section in the seafloor. It was marked with one of the high tech plastic bucket lids that will float off the sea floor making it easier to spot when Jason visits.

Jason is launched by 0800. It takes about 2 hours to reach the summit of Blue Moon at a depth of almost 2.5 miles. Within minutes of reaching the sea floor, we find man-made objects. To me they look like snow skis, but the scientists recognize them as equipment lost during the 1997 expedition to this seamount. They are heat-flow outriggers that were attached to the core pipes and designed to take temperature readings at various depths. Each outrigger was attached to the core pipe with 4 steel bands but some still managed to break free when the core pipe penetrated the mud of the seafloor. These are expensive pieces of equipment so Jason picked them up. The scientist who headed that experiment in 1997 isn’t with us on this trip. He will be quite surprised when his equipment is returned 6 years later.

Terra in Antarctic attire

Tom and John deploying a transponder

Sam working in the nitrogen environment (bag)

Heat-flow outrigger lying on seafloor

Mike with the heat-flow outrigger recovered on this trip.

Jason spent 4.5 hours searching for the BAC and was still looking when most of the monitors in the control van blacked-out. There was an electrical short in the tether from Medea to Jason. Jason was brought up very slowly. The Jason technicians much prefer to do everything with the lights and cameras on so they know exactly where Jason and Medea are, relative to one another, at all times. Jason made it back safely. The Jason Team wasted no time and immediately started in on the repairs.

The Science Team took advantage of the time and immediately started rigging for a piston core. The core apparatus was on its way to the sea floor by 2130 with an anticipated midnight return. Doesn’t anybody sleep around here?

One more question about transponders: I asked Chris T. and John, “How do you get them back to the surface from 2.5 miles deep?” You send them a message. They are set to receive and send sound waves so you send them a message in a pattern of sounds called a “release code.” Each transponder in the network has its own unique code. The transponder is attached to its line by a lever arm that is secured by a burn wire. The burn wire is made of nichrome (nickel and chromium) and about the same diameter as a small paper clip. When the release message is received, a battery sends a current through the burn wire. It takes about 6 minutes for the wire to dissolve releasing the lever arm and thus, releasing the transponder. The dissolving of the wire, which will only occur in salt water, is called accelerated galvanic corrosion. The transponder floats to the surface at 60 meters per minute. The transponders at Blue Moon will take over an hour to reach the surface.

 

Science Summary - Day 32, April 23

Science Objectives, Day 32:

The thirty-second day of the cruise, Apr. 23, we will launch Jason and search for the break-away core barrel and explore the summit region of Blue Moon Seamount. The summit is split from NE-SW by a fault uplifted to the SE. At the SW end of the summit fault is a high-backscatter area that we will investigate in order to determine whether it is a site of recent serpentinite mud protrusion or fluid seepage.

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