Monterey Bay Aquarium Research Institute

West Coast Expedition
July 20 - August 30, 2002
West Coast of North America
Logbook

August 20, 2002: Day #32


The tops of four large sulfide chimneys were recovered in 1998 during the "Edifice Rex Expedition". Halves of three of these samples are now on display in the Hall of the Planet Earth at the American Museum of Natural History in New York. The structure here, named Roane, had the top ~ 1.5 meters removed and the flat surface is clearly visible. However, a clump of new tubeworms indicates that hydrothermal fluid is still venting from the orifice and that perhaps with time the top of the structure will regrow.

Debra Stakes writes: Our dive plan for today was ambitious, requiring us to carry down the milk crate full of samplers and tools attached to the siderail of to the drillsled. We planned to core both sulfide and basalt and brought down plugs for both boreholes. We also wanted to collect sediment in a push core and glass in two wax cores. There were two fluid samplers and the temperature gauge. All of this had to be carried in the red plastic crate, which was also the only place to stow rock grab samples we happened to pick up.

The Mothra vent field is the southernmost hydrothermal site on the Endeavour Segment of the Juan de Fuca Ridge. In 1998, the top ~two meters of chimney tops were recovered as part of an expedition jointly sponsored by the American Museum of Natural History, and the University of Washington. The successful recovery of pristine, 4000 lb pieces of chimney is allowing detailed examination of these sulfide-microbial habitats, which support rich and diverse microbial communities that thrive within the warm, nutrient rich walls of the sulfides. Novel organisms and microbes that grow at temperatures greater than 90°C have been cultured from within the interiors of all four of the structures recovered.

After a bit of searching we located the vent field and a quick survey showed that several of the structures had changed since a magmatic-tectonic event in 1999. Even the flat top of the chimney Roane, left after the Edifice Rex expedition, sported a new top hat of tube worms (Figure 1).

One of the myriad goals was to core a large diameter borehole in an active black smoker, which was successfully completed on the structure called "Giraffe" (Fig. 2). The sulfide wall proved to be much easier to core into, with the effort completed in less than one hour! Much like tapping a maple tree for syrup, the new hole leaked high temperature hydrothermal fluids. The sulfide borehole was plugged with a hollow insert that we planned to recover in a couple of days (Fig. 3). We were pleased that the borehole in this actively-growing sulfide edifice stayed open long enough for us to put in the plug!


Using the multiple barrel rock coring system to create a borehole in the wall of the active black smoker named Giraffe. The drillsled holds four barrels that can each recover a 0.6 meter long core. Each barrel has a custom coring bit set with carborundum. Recovering a simple core of basalt takes about an hour, but reaming the corehole to 7.62 cm requires 3-4 hours.

After creating two boreholes and collecting hydrothermal fluids from a recently developed black smoker, and a smoker previously sampled in 1998, Tiburon set off across the floor of the axial valley to find another site for a seismometer. We were hoping to place this corehole into fresh basalt with easy access for the ROV, but dive time was becoming a premium. As we hurried along looking for a flat spot, spectacular exposures of different lava generations in large fissures on the valley floor were imaged (Fig. 4). They were so beautiful that I was compelled to stop and grab a couple of samples and into the crate they went. As the clock ticked onward we realized that we had abandoned our acoustic marker back near the sulfide. We would need this to mark any borehole site and so we turned around and flew back. By this time the only prospect for a corehole was to drill into a piece of inactive sulfide that looked much like an old growth log - the corehole was cut in an hour and marked with the beacon.

As we pulled away to mark the borehole we were horrified to discover that our milkccrate full of samplers and samples was no longer connected to the ROV! It was lying on its side in the dust at the base of the borehole (Fig 5). What to do? We discussed the possibility of sending down an elevator to lift the crate back to the ship. However, this would take time, first to put together the elevator and then wait for it to transit from the ship to the seafloor and back again. We decided to heave the crate onto the drillsled and hold it in place with the Schilling arm. This worked fine and everything returned safely (Fig. 6) The dive ended a bit earlier but we did not lose any equipment, so we were satisfied.



Figure 3. After the borehole was cored into the side of Giraffe, the ROV inserted a hollow plug to keep the hole open for a later instrument placement. The borehole (visible on the right) is about 36 cm deep. The plug includes a syntactic marker to assist the ROV in locating the site more easily.

Figure 4. Exposure of lava horizons on the wall of a large fissure east of Mothra. Note the rounded pillow flows on top of a massive flow unit on tope of several layers of sheet flows. This exposure suggests that the valley floor was constructed of multiple events, but this can only be confirmed by the analysis of recovered rock samples.


Figure 5. The ROV is sitting at the base of a toppled sulfide "log", perhaps toppled by earthquake activity. The insert needs to be placed into the borehole. Then we need to decide how to recover the red milkcrate with its precious load of water samplers, push cores and rocks.

Figure 6. We decide to end the dive and carry up the milkcrate on top of the ROV coring sled. The cargo is held intact by the Schilling manipulator arm.

 

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