Daily Update: Welcome to 24 South
April 2, 2001
By Amy Nevala

We celebrated tonight, for two reasons.

First, after two and a half days, most of us no longer fall when the ship rolls -- we now walk with that strong, wide-legged swagger of veteran sailors. Second, we arrived this evening just before a dinner at an important coordinate -- 24°00’S 69°40’E, our first research site on the Central Indian Ridge.

We picked this site because Japanese and German scientists, who were here on expeditions between 5 and 12 years ago, detected hydrothermal plumes in a small valley on the ridge.

But with no sign posted in the middle of these blue waves saying “Welcome to the Hydrothermal Plume Valley,” how did we know that we came to the right place? We made a map of the sea floor to locate the valley using Knorr’s multibeam sonar system.

The system works through sound-producing sources mounted across the ship’s hull. All 120 sources transmit a “beam” of sound energy that bounces off the ocean bottom and returns to the ship. Computers then convert the time it takes for sound to travel that distance to water depth. Finally, computers plot the data on a chart.

Spreading out the site map we brought next to the one we just made, we saw that the sea floor hills and valleys matched. That was our sign that we were in the correct location.

Now our research can begin. Tonight while others sleep, oceanographers Bob Collier and Marv Lilley will lower the CTD sensor (Conductivity-Temperature-Depth) to begin a technique called a tow-yo to search for hydrothermal plumes.

Tonight’s survey will help us to decide if this site is a good one to return to later in the expedition to search for seafloor vents.

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