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March 6, 2003: Leg 2, Day #5

Today was a very busy dive day that began at noon and lasted until long past dinnertime. We instrumented a high- and a low-temperature vent site, collected many samples, and made some new discoveries. Because we have placed acoustic marker beacons at most of our sites, we can now move rapidly between them. Our first day’s target was the 12 meter-high sulfide-carbonate spire at Rebecca’s Roost. The summit of this structure is a series of pagoda-like flanges that have successively broken away as the ROV attempted to park on them. All that was left of the summit was a tall chimney on one edge of the cliff with a connecting bridge to a “bush” of tubeworms.

 

We decided to place an OsmoSampler combined with a Hobo at this site to collect continuous fluid and temperature measurements over the next two months. The body of the OsmoSampler is a large cylinder filled with osmotic pumps and spools of Teflon tubing that connect to a small-bore titanium wand. The Hobo also has a long wand within which an RTD (temperature measuring device) resides. This thermocouple connects to a small datalogger that is well removed from the hot water. For this deployment, the two wands are connected together and fashioned into a “J” shape so that everything can be hung on the edge of the chimney, not unlike a garment bag hanging on a door.

 

Mar5_HobointoRR.jpg (63380 bytes)

 

Perching the ROV was precarious, but parking was out of the question. So the pilots flew up and dropped both parts of the system onto the bridge. Flying the ROV up to the other side of the chimney, they enlarged the orifice with a bar brought along for this task. Then, the pilots flew the vehicle to the bridge, grabbed the J-hook, and flew up to the vent to place the curved wands (see left). 

 

Mar5_RRosmo.jpg (57960 bytes)

 

 

 

When we left the site, the experiment could be seen draped around the rapidly growing summit chimney (see right). How will these instruments look after two months? Will we be able to pull it from the wall of the sulfide?

 

Mar5_themepark1.jpg (53561 bytes)The remainder of the day’s work was at the two new low temperature sites: Cathedral Hill found yesterday and a new vent we just stumbled across and named Theme Park (see left). We had hoped to place thermocouple arrays at both sites,Mar5_cathedralsample.jpg (95746 bytes) but one array malfunctioned and had to be returned to the ship. Hydrothermal fluid and chimney samples were collected at Cathedral Hill (see right) and at Theme Park (see below left). The high temperature probe was used to locate sediments over 60˚ C and a “hot push core” was taken from there (see below right). At the end of the day, a thermocouple array was left at Theme Park.

 

 

Mar5_themespire.jpg (80820 bytes)Mar5_hotpc.jpg (76150 bytes)

 

 

 

 

 

 

 

 

 

 

 

 

 

Mar5_oilycore.jpg (45859 bytes)

 

 

When the ROV returned, the smell of oil and rotten eggs filled the air. All of the fluid, mud, and chimney samples from the low temperature sites were drenched with hydrocarbons. We hurriedly moved all the chimneys outside and put the push cores under the hoods. The amount of hydrocarbons was amazing, bubbling to the top of the push cores (see left - the red drops in the image are hydrocarbons) and leaving oily spots on the mats. This was a slimy, gooey end to a successful day.

 

Debra Stakes

 

 

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