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Logbook
September 16, 1998

Contents:

Daily Science Report - Sep 16 ship's location = 45 55.9N/130 00.8W

ROPOS is currently back at the ASHES vent field (map left) on dive 479. The first part of the dive consisted of fluid sampling of high-temperature vent fluids (up to 293 deg C) at black smoker chimneys with names like "Hell", "Inferno", and "Virgin Mound". This was followed by biological sampling with the slurp sampler. We will also be finishing our Imagenex sonar survey of the vent field on this dive.

On the next dive we plan to redeploy the acoustic extensometer instruments on the north rift zone with the elevator mooring, and then complete our Imagenex sonar survey there. If time and weather permit, we may then visit a high- temperature vent site on the north edge of Axial caldera called CASM. CASM was the first vent site discovered on the Juan de Fuca Ridge, back in 1983 (15 years ago!).

Listing of all Science News postings

Julia Getsiv
Graduate Student, Vanderbilt University

Two weeks into my budding career with NOAA, twenty-five scientists embarked upon the first event response voyage to a volcanic eruption detected just north of Axial Volcano on the Juan de Fuca ridge. Since that first cruise, one of my duties at sea has been to aid in the navigation of vehicles, like ROPOS, along the seafloor. You might be thinking to yourself, "Well that's easy, that's what satellites are for!" Yeah, I used to think so too. Unfortunately, the water acts as a barrier to such navigation, so we deploy instruments, called transponders (photo right shows Julia with a transponder), which are able to breach this barrier. Transponders are triggered by and talk back with sound, and each has a unique frequency which identifies it. Transponders look like bright yellow hard hats and are strung on a 200-meter-long tether anchored to the seafloor. Since we know the speed of sound through water, we use the length of time the sound takes to travel through the water and convert it into a distance, called a range.

Here's how the process of setting up navigation on the seafloor works: First, three or more transponders are deployed from the ship and drift down to the seafloor around the area we wish to explore, and we call this a transponder net. Then the ship drives around the area and ranges (sends and receives signals) to each of the transponders and these ranges (computed from the travel time of the speed of sound) are recorded in a special navigation program. Based on the various ranges and knowing where the ship was when each of those ranges were received, the program then determines where the transponders really landed on the seafloor. Next, ROPOS is equipped with a relay transponder which can also talk to the transponders as well as the ship. Again these travel times are converted into distance and the navigation software triangulates these ranges to determine the position of ROPOS within the net.

The ability to navigate instruments and find locations on the seafloor has numerous purposes. One purpose is to do time-series analysis. Time-series analysis in our case involves monitoring sites on the Juan de Fuca Ridge from year to year to see how things are changing, such as the water chemistry and temperature of hydrothermal vents, the arrival or disappearance of new animals to an area, and the discovery of fresh basalt. Therefore, excellent navigation helps us relocate these sites and is crucial to the long-term study of mid-ocean ridges. Axial Volcano has been one of those sites for many years and has proven to be a very exciting volcano to watch!

In just a few days I will go back to Vanderbilt and continue studying landslides on the Mid-Atlantic Ridge, but at night my dreams will most certainly drift back to the Pacific, where a reliable crew, fantastic group of scientists and the invincible ROPOS team once again made geologists, biologists, chemists and physical oceanographers dreams come true.

Listing of all Perspectives postings

September 16 - 0900 hours

And there, firmly banded to the right arm of ROPOS is a potato. A potato?? Yes, complete with a Mr. Potato-Head face painted on. And why, you ask, is there a potato strapped to ROPOS this morning. We are sampling high temperature vents this morning, and high temperature combined with high pressure equals quick cooking. This is the principal behind every pressure cooker. Under pressure the water reaches a higher temperature without boiling and so food cooks faster. Mr. Potato-Head is being sent to the cooking pot 1550 meters below the surface of the Pacific. I've got to say, scientists have just a bit of weird on them.

ROPOS has been on the bottom all night, and despite a couple of holes in the filter system, samples are being collected from a number of very hot vents. The chemists are concerned that the filter problems will invalidate their data for some of the samples, but some of the information will be useful, and their problem is now to determine which data are useful and which must be disregarded. It's the same problem you have faced in science class when the teacher says, "How confident are you about those results?" That's when you know you are going to have to do something over again!.

1400 hours

ROPOS has completed the work on the bottom and will be doing Imagenex lines for the next few hours before returning to the ship with the latest treasure trove of bottom samples. The scientists are beginning to talk about everyone having their work done. We have to replace the set of five extensometers along the northern rift zone. That will happen over night tonight. The refurbished extensometers will be loaded into the elevator and lowered to the ocean floor. Then ROPOS will take them one at a time and place them in positions where they have the necessary line-of-sight to their neighbors.

We caught some 20 knot winds in the last hour and were blown off station a couple of times. Once ROPOS had to make a quick ascent to the cage since we were drifting and within about 20 meters of the caldera wall. Caldera walls and ROV's don't get along real well unless the meeting is planned. It took about twenty minutes to put the ship back on station and then the last samples were grabbed.

Some of you have undoubtedly figured out the head mystery. Imagine that you had a cube of styrofoam exactly 1 inch on each side. If you were to step on that cube and put your full weight on it, what would happen? Obviously it would be crushed. If you weigh 140 pounds, you have just applied 140 pounds per square inch to the styrofoam and it has collapsed. Now imagine that the pressure is applied equally from all sides instead of just on the upper surface. Now the styrofoam collapses equally in all directions. Instead of just being flattened, it shrinks while maintaining roughly the shape of a cube. The ocean, at the depths we are working, applies over one ton of pressure to each square inch of the styrofoam head, and the head simply collapses. Since the air has been forced out of the styrofoam, the head does not expand again as it is returned to the surface. (photo above left)

One interesting thing that I did not notice when I photographed the heads was the calendar on the wall behind them. (photo right) Obviously the folks in the microbiology lab have some sort of countdown going on. It reminds me a lot of the calendar I kept at the end of last year when I knew that retirement was 10, 9, 8, 7. . .well, you get the idea. We are less than three days from firing up the engines and steaming for Victoria. There is plenty of work to do between now and then, but thoughts are definitely turning toward dry land.

We can't land until the cribbage tournament ends. Stay tuned to find out what member of our group wasted way too much of his or her youth playing cards.

Logbook of all Teacher At Sea postings