FeMO3 Dive Cruise 2008
Report Day 18 -- Thursday 9 October 2008 -- Trekking 8,000 m with Jason Along the South Rift

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R/V Thompson in port

All day Jason has been exploring the volcanic terrain of the South Rift. This dive (J2-374) started at 4,000 meters depth near FeMO Deep and far south of the summit, while Jason has worked up the rift getting further and further up Lo’ihi. The pilots have stopped at intervals to break off pieces of lava rock for noble gas and microbial analysis. The science basket and swing-arm sample boxes have been slowly filling up all day so the elevator was deployed to relieve Jason of the load.

The elevator was picked off the deck with a crane and set in the water just before dinner. The crew went to eat as it sinks through the water column. After dinner we are treated to a spectacular sunset of orange and pink over dark clouds. In the dark ocean far below Jason transfers rock samples to the elevator. Jason releases the elevator just as I go on watch. It takes more than an hour for the elevator to ascend the 2,300 meters to the surface so Jason continues the routine of moving up the South Rift and pausing to sample rocks as the elevator slowly ascends through the water column.

An audience gathers for a sunset!

Jason must be pulled off the bottom once the elevator reaches the surface so the R/V Thompson can maneuver to catch it. As the ship chases the drifting elevator Jason and Medea hang on the winch wire a couple hundred meters above the bottom. An interesting aspect of using an ROV is that the (long) winch wire from the ship weighs much more and has more drag in the water than the ROV itself. An ROV exploring the seafloor cannot tow the wire and the ship behind it as it explores. The only way for Jason to move beyond the length of Medea’s tether is to have the ship move in the direction Jason needs to go, towing the winch wire and Medea ahead of Jason. When Jason needs to transit long distances the whole string goes into “tow mode” with the ship towing the wire and Medea ahead, dragging Jason by its tether behind. Jason needs to be well off the bottom during towing and it is in tow mode as the R/V Thompson chases down the drifting elevator.

Plenty of lobate-shaped lave flows

After the elevator is on deck Jason returns to the bottom for a final hour of exploration. Jason is moving over some very rough lava. The landscape is steeply sloping and broken by ragged gullies and lumpy pillars – all of black basaltic lava. Some of the lava looks particularly jagged and glassy in contrast to the smoother lumpy flows that were common in other places. Strangely this brutal landscape is populated by dozens of frilly pink coral-like animals that bend in the current. They look like decorative feathers.

Jason leaves the bottom at 10:30pm to reach the surface by midnight. The entire dive has explored over 8,000 meters of the South Rift. Though no hot vents or bacterial mats were found, microbiologists are still interested in the rock samples because they may harbor iron oxidizing microbes that are able to tunnel into the basalt seeking iron. If microbes such as these are found they can tell us much about how the ocean crust weathers.

Shawn Doan onboard the R/V Thomas G. Thompson
9 October, 2008

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