Expedition to the Mariana forearc

Mar. 23 - May 4, 2003

Day 37, April 28th

(click on any image for the larger version)

Day 37

Yesterday we sent the elevator to the summit of South Chamorro Seamount all by itself. It has a transponder on it so it is easy to locate. The elevator is a platform that can take equipment down to the seafloor and bring it back up when we have to move more than Jason can carry.

Elevator loaded with flow meters ready to surface Elevator loaded with flow meters ready to surface

The elevator has both weights and floats. It sinks to the bottom when deployed and later floats to the surface when the weights are released. We used the elevator to pick up flow meters that Alison placed on areas of active flow 6 weeks ago. This site was about 100 meters south of the drill pipe we visited yesterday. Alison was only onboard for the first week. She supervised the placing of the flow meters. The flow meters collect in much the same way as the Osmo Sampler, but they also introduce a dye as the water is collected. Back in the lab, Alison will be able to determine the rate of flow by the amount of dye in the water.

Throughout this expedition we have focused our exploration on areas of recent serpentine mud flow. We have not seen much in the way of animals in these areas. There is very little food on the seafloor that in serpentine mud areas and, except for an occasional sponge or sea fan, we don’t see much life on the bottom. We do see pelagic critters such as fish and shrimp and drifting jellies, but only the jellies are abundant. There may be more pelagic creatures that Jason’s lights scare away. The areas of active flow at South Chamorro however, have interesting biological communities.

Sea fan close up Sea fan close-up
On land and in most aquatic communities, plants are found at the bottom of the food chain. Plants make carbohydrates using energy from sunlight in a process called photosynthesis. There are no plants in the deep sea because there is no sunlight. Chemosynthetic microbes are at the bottom of the food chain in these communities. Chemosynthetic microbes make carbohydrates using chemicals as a source of energy. These chemicals, predominately methane, come from the fluids seeping upward from the subducted plate.
Chemosynthetic communities, based on chemosynthesis, were first discovered in an active spreading center near the Galapagos Islands off Ecuador in 1977. Since then they have been found in numerous active spreading centers. These communities center around vents of extremely hot water. The first cold water chemosynthetic communities were discovered in the 1980’s at sites of methane seeps on the sea floor. Since the first discoveries, cold methane seep communities have been found in many locations.
Charlie with Mahi Mahi Charlie with Mahi Mahi

The first, and only, cold water chemosynthetic communities seen in a subduction zone, mud volcano environment were discovered in 1996 on South Chamorro Seamount. Mike Mottl, a member of this expedition, was on that trip and was in the submersible that made the discovery. The most numerous animals of these communities are mussels, whelks, Galatheid crabs and tube worms. The tube worms are about 12 inches long. We know very little about these animals so we collected a few mussels and gastropods that we froze and will pass on to biologists for future study.

Halfway through my watch in the control van, I stepped outside and was shocked to see a military vessel off our port side as close as any traffic has passed on this trip. Logan and Tim were on the bridge at the time and talked to the vessel which was either a guided missile frigate or destroyer. The military exercise I mentioned yesterday is much larger than we realized. It is a multinational event called Tandem Thrust working out of Guam. When I visited the bridge at 1800 Jake showed me the radar—there were 10 ships within a 48 mile radius of us. Their activities include bombing, underwater detonations and gunnery exercise—all hot, meaning live ammunition. This exercise includes an aircraft carrier flotilla and a submarine. We know about the submarine because we got pinged—it bounced sound waves off of us. We were mystified by the strange, almost musical sound that passed through the ship. John used to work on submarines and he explained it to us.

Several small planes from the aircraft carrier passed over us today at close range and one buzzed us last night, without lights, as we did our last piston core of the mud volcanoes. While we were setting up for the piston core a school of Mahi Mahi appeared in the water off the stern. Fishing poles and lures are always ready so within minutes the poles were in the water and 3 large fish were on the deck. We will have fresh fish for dinner tomorrow.
Akel, Matt and John with Mahi Mahi Akel, Matt and John with Mahi Mahi

Science Summary - Day 37, April 28th

Science Objectives, Day 37:

The thirty-seventh day of the cruise, Apr. 28, we will finish the S. Chamorro dive with Jason and do a final piston core on the apparent flow emanating from the area of the borehole at ODP Site 1200C. We will also perform a search for our missing transponders.

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