Expedition to the Mariana forearc

Mar. 23 - May 4, 2003

Day 7, March 29

(click on any image for the larger version)

DSL 120 Sonar DSL-120 being deployed.
 Day 7- It was after midnight when we completed the DSL-120 sonar survey of Celestial Seamount. The DSL fish was back onboard just before sunrise. The entire survey of the seamount, including deployment and recovery times, was about 34 hours. Even though we were able complete this survey of 7 transects with just one deployment, the collection of data was not without problems.
Throughout the survey there were navigation complications because the transponders were out of sight (remember, this is “sight” by sound) so the depth information being recorded was frequently without exact fixes on the location. Celestial Seamount has steep bathymetry. Placing the transponders on the steep sides of the summit knoll with long tethers still left them invisible to the fish, hence the navigator couldn’t always get location readings.
Akel, the sonar data specialist, is still trying to determine how to best plot the data. He will combine the length of the wire from the ship to the fish and the position of the boat with other factors, such as current, to make the best estimate of location. Once Akel has gotten the best possible data, Nathan, our map guru, will use it to make actual bathymetric maps of the seamount. He has already completed the maps of South Chamorro Seamount and they are spectacular.
Akel with sonar data Akel is our sonar data specialist.
Nathan and some 3D maps Nathan showing some 3D maps.
 He has maps from the top looking down, profile maps and even 3D maps for viewing with 3D glasses. The maps on this website were made by Nathan and are similar to what he is doing now, but the higher resolution maps from this trip show much greater detail. Since these new maps are being constructed with brand new data, they must be further analyzed before publication so you won’t see them on the internet during this trip.
Additional problems with the DSL-120 fish may postpone our next sonar survey intended for Big Blue Seamount to the north. When the DSL fish was recovered after the Celestial Seamount survey, its tether was wrapped and tangled with the cable from the ship. Remember, the cable has a weight and the fish flies from that weight. When the ship turns, it is hard to keep the fish behind the weight.
DSL 120 Deployment DSL-120 Deployment
Navigator and Pilot in the control van Navigotor and Pilot in the control van.
 Before leaving Celestial, the scientists took a core sample at a depth of 1845 meters. The tension as the core pipe was lifted from the sea floor indicated they would get a good core. When the core pipe was lifted, it had a thick layer of green mud on the outside. Inside—the surprises never stop—just 1.5 feet of loose mud. Patty, the Chief Scientist, hypothesizes that the core pipe might have hit a rock and drove it deep into the sediments acting like a plug on the core pipe. She further speculated that there may have been just too much friction inside the core liner to push more mud up into the core liner.

Patty never expresses disappointment. With an ever positive attitude she says, “Mother Nature holds tightly to her secrets.”

So we pick up the transponders and we’re off to Big Blue. As always, we will use the ship’s multi beam sonar to get additional data for mapping along the way.

Science Summary - Day 7, March 29

Science Objectives, Day 7:

The seventh day of the cruise, March 29, will be spent finishing the survey of the summit region of Celestial Seamount with DSL-120. We will recover the instrument and then we will do a navigated core in the summit region of the seamount. We hope that the hole produced by the core will act as a channeling outlet for pore fluids escaping from the seamount. Precisely navigating the core will permit us to return to within a few meters of the core location when we return with Jason2 later in the cruise. We will recover transponders and will then transit to the next site, Big Blue Seamount, for a DSL120 survey. On the transit we will collect EM300 bathymetry data around the south flank of Celestial Seamount and will collect hydrosweep between Celstial Seamount and Big Blue Seamount. About half way between the two we will deploy Medea in order to record attitude changes during deployment. This is to gain a better understanding of the cable behavior during DSL120 deployments.

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