How Do We Map the Ocean Floor? – Day 13, 7/17/09

So something I never questioned before: How do we know what the ocean floor looks like?  I found out a bit of the history of how we know what we know.

After I toured the Underway Lab on the aft end of the JR yesterday, I was formally introduced to the Precision Depth Recorder. A nice sonar array lies on the bow end of the ship below and behind the forward underway thruster. As we travel the sonar emits a chirp of sound from 12 different sources towards the ocean floor. The receiver picks up the echo (and also secondary echoes as the sound bounces back up, down and back again) and plots it for us. Through this we can visualize signal strength and since we know the speed of sound we can measure distance. This helps us to determine the depth of the ocean at our given location. Sonar stands for “sound navigation and ranging”.
And now we get to the cool part. At some point the military began collecting all of this data for any ships it could get its hands on. Obviously their intent was not scientific, but they took enough lines of travel across the ocean and combined them to create a workable map of the ocean floor. Imagine doing a tombstone rubbing with a crayon, but instead of broad strokes covering the entire surface, you can only make single line marks. And those lines may not cover all of the information. Now you have to read what was on the tombstone. Sure, it isn’t a perfect method, but it got us started, and I think it is pretty cool.
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We retrieved four sections of core from hole U1339A today. After a problem with drilling equipment they decided it was best to pull out of the A hole and move on to a new one, the B hole. In a way this is good. It gives the scientists a relatively small amount of core to work with now, and get the sampling methods firmed up before the near constant flood of core starts arriving. But a delay is a delay, and no one wants to sacrifice a later part of our expedition for lost time now. Hopefully we’ll make up some of the time later if the weather is good for our next transit.
One of the sampling techniques that we used today was the removal of pore water from the cores. Using rhizons (a soil water extracting device), we drilled holes into the core casing and pulled water out with suction from syringes.  Pretty cool, right? This is water that was trapped in the mud on the bottom of the ocean, for a long time, maybe millions of years (to be fair, the mud we are currently exploring is not that old... forgive the embellishment - maybe thousands?).  What will we find?  Hard to say right now, as much of the testing will be done later.  But it all starts here.

Comments

I think that there are a few

I think that there are a few drills on board, but I don't think they'll let me take home any souvenirs!

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NJ Greene
Arizona hardwood flooring

Rambling

Hey Doug,

Greetings from the South Cobb group. You probably heard that we have a new principal, came from Kennesaw Mountain. Getting ready for classes--lucky you to be out exploring. Pictures of the journey are incredible plus all the info is fantastic. Will incorporate it into the Environmental Science and Biology classes. Have any more drills? Be sure to get a picture in your survival suit. Sure would hate to have to get into the water.

Take care,
Sue De Rosa

Drills?

There are a few drills on board, but I don't think they'll let me take home any souvenirs! I will post pictures of me in the Gumby suit later. Let's just say they aren't very flattering. ;)

wireless notepad

Hi, Doug.

I think that's a splendid idea... : )
Trying to follow along here - I've been traveling quite a bit. In fact, I just got back to NH from Canada last night. And I'll be gone again in a few hours. How have the seas been treating you? Please say hello to Kazo for me. I really enjoyed talking with her while I was on board.

Heather - SOR

Seas...

Things were very calm at first. I'll be posting more in part 2 of my blog for today. Kazo must not be on this leg. I don't recognize the name. Folks rotate every two months so it can be hard to keep track of which team you are dealing with.

Your Role

Okay Doug.

The samples are now on board and the testing has begun. As "teacher-at-sea" what is your role in this part of the mission?

--Wayne M.

My Role

Good question Wayne,
I feel a bit like a fly on the wall here. I get to go around to just about every area of the ship unimpeded, and talk to whomever I wish. During this first site's drilling I spent time each day observing, and occasionally helping the techs in cutting and venting the core before it was brought inside. The venting was required because the core was very gassy. Lot's of biological activity. And when you pull up the core it is suddenly in a much lower pressure environment, and you may know that gasses expand when they are removed from pressure. That can be an explosive process!

I also got to help in processing core, which involves running the core through several tracks that measure various physical properties all along its length (or depth if you prefer). Then the core is split into two halves from the original "whole round". One half is marked as the working half, and the other if the archive half. The working half is sampled in whatever way the various scientists have requested and the samples are distributed for immediate testing or sealed and stored for later use. The archive half is scraped clean to avoid and disturbances caused by the cutting, which might effect interpretation of its composition. It is then digitally imaged and a few more properties are tested. The archive half is then packed and stored for shipping.

I've also spent some time working with the paleontologists, helping them clean and sort samples for identification on board the ship and some for later study.

I've probably missed a few things, and I'll try to go into more depth on some of these later, but that's a quick overview. Did it seem quick?

rhizons

fascinating!