By Linda Tatreau

We arrived at South Chamorro Seamount at 0200 and deployed the DSL-120. The chief scientist, Patty Fryer, hoped to map a series of 9 parallel transects, going back and forth, over the seamount. This would result in an excellent bathymetric map. The fish (DSL-120) is deployed long before the start of the first transect because it takes a couple of hours for it to reach the bottom and then the navigator needs time to perfect the course.

The path of the fish is not always the same as the ship. Today there was a strong current running over the seamount and the fish was flying 400 meters north of the ship. When the navigator moves the ship to get the fish on the transect line, it takes up to an hour for the fish to respond because of the length of the tow line.

To completely stabilize the fish, towing at these depths, it would take 4 hours of tow time at 1.5 knots. Of course, there is not enough time to do this before each transect.

The fish was flying behind the ship from 3640 meters of cable to map a depth of from 2920 m to 3200 m. The cable is actually attached to a heavy weight. The fish comes off a line from the weight. There is also a cable behind the fish, like a tail, that helps stabilize the system. The pilot brings in cable and lets it out as the ship goes up and down over the seamount to keep the fish from getting too close to the bottom. The transects are about 1.5 miles in length.

The navigator keeps the ship on course, driving by computer, 4 decks below the bridge in the control van. He doesn’t even have a port hole but because he “sees” with sound, he doesn’t need a window. Windows don’t help anyway when you’re working in the deep sea. Turning requires more power so the navigator works with the mate on the bridge communicating via telephone. The turns are tricky and must be done with care to avoid tangling the towing cables.

From deployment to the start of the first transect line took 3.5 hours. The first transect line was completed in 70 minutes but the turn to the second line took 2.25 hours. The operation slowed after that. The second transect line took 90 minutes but the turn took almost 3 hours. During the third transect the DSL-120 quit transmitting information to the ship and the operation was discontinued. It was another 3 hours operation to get the DSL-120 back aboard the ship.

Everything about exploration and study of the deep sea takes a long time. Nothing happens fast here. It’s not easy, but when the DSL-120 works you get the greatest bathymetric maps.

The scientists have so much they want to accomplish on this trip-- they don’t want to waste a single second. Rather than wait for the DSL-120 to be repaired, they headed to Deep Blue Seamount in hopes of taking a gravity core at its summit.

Science Summary - Day 2, March 24

By Patricia Fryer

Science Objectives, Day 2:

The second day of the cruise, March 24, after arriving at the site for our first DSL120 side-scan sonar survey we deployed the system and began to map the seamount summit. After two survey lines with good data, however, we encountered difficulty with the instrument. It developed a problem after one of the turns and the DSL120 crew quickly determined that the instrument itself might be damaged and we would have to retrieve it to find what caused the problem. While the instrument was being examined we moved south to map and core a deeper seamount, one we hope to visit with Jason2 later in the cruise. This would be the first core of the cruise and we are doing the deepest core (6500m) that our coring technician Chris Moser has ever done. Patty Fryer had dredged the seamount in 1981 and recovered both serpentinite rocks (and a small amount of other interesting rock types). The seamount’s shape suggests it is a mud volcano like South Chamorro Seamount, but no muds were recovered in the dredges. The hydrosweep (one of the two hull-mounted multi-beam sonar systems on the ship) system works better in the deep water that we will be traversing and will provide us with a verification of the depth of the summit of the deep mud volcano.

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