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On Board the OSV BOLD: Just Dropping a Line…Puerto Rico Highlights

2009 March 7

About the author: Mark Reiss is a marine environmental scientist with the dredging, sediments and oceans team in EPA Region 2, comprising New Jersey, New York, Puerto Rico and the U.S. Virgin Islands. He is one of the principal investigators on the OSV BOLD’s Puerto Rico voyage

image of two men standing on ship deck near columnar instrumentAnother component of the work we do on the OSV BOLD is lowering an instrument called a Conductivity, Temperature and Depth recorder—we just call it a CTD—through the water column down to 1,000 meters (3,280 feet) about every two hours. It takes about 40 minutes to get the CTD down to that depth and then back up on deck, but it’s important to use the CTD because it tells us about the structure of the ocean.

People tend to think of the ocean as all the same but there is actually a lot of structure in the ocean, and our CTD casts showed that structure. The structure of the water is based on density. Less dense water floats on top of denser water; warm water is less dense than cold water, and less salty water is less dense than saltier water. So, a river that runs into the sea does not mix with the seawater, but rather floats on top of it because it has less salt—it’s less dense. Our software calculates the density using the temperature and salt content measured by the CTD.

We completed all of the Conductivity, Temperature and Depth Recorder drops to 1,000 meters (3,280 feet), and on our last cast we sent the CTD down to 2,500 meters or 8,200 feet. That’s pretty deep—picture it as eight Empire State Buildings stacked on top of each other. As you can imagine, it took a long time to go all that distance and back up. You might think that after all the waiting, everybody onboard would have been pretty bored, but everyone was eagerly waiting for the CTD to come back onboard. We’d decided to have a little fun with the test by adding a simple experiment to demonstrate depth pressure. Make sure to check in tomorrow to see what kind of fun experiment we did with the CTD Recorder!

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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    May 17, 2010

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