Posted by: adorsk | June 21, 2008

Mud Slinging

Don’t worry, I’m not about to start a political blog. This post is about something far dirtier than politics: oceanic sediment. The ship recently returned from a sediment sampling cruise.

Dirty Work

The ship took chief scientist D and his group just off the continental shelf South East of WHOI. It was a fairly small group, 10 people total. About half of the science party was from WHOI. The other half consisted of guest students from universities in Indiana and Florida. Despite our small size we were still an international bunch. With the ship’s crew we represented Chile, Sri Lanka, Lithuania, and Honduras.

It took about a day to get to the first site. Then we started scooping up mud from the bottom 3300 m below. We were interested in the mud because it contains tiny tiny plankton called Foraminifera (forams). Forams are interesting because they build shells using chemicals from the seawater around them. This means that their shells serve as a kind of hydrological journal. “What was the water temperature like 20,000 years ago? Shucks, I don’t know. Oh, wait, just check how much Carbon-13 is concentrated in Ammonia tepida shells.”

Forams are often used to help paleo-oceanographers get dates for sediment samples. They are also useful as indicators for coastal reef health.

But in order to get more accurate and confident dating we need to learn more about the biology of forams. Right now not much is known.

D’s group hopes to incubate forams back at WHOI and observe them as they grow. They’ll find out how much they eat, how fast they grow. What kind of music they like (no, not really).

But before they can grow forams, you have to harvest them. This is why oceanographers make such lousy farmers…they’re always trying to harvest their crops before they plant them. Our harvesting tool was the Soutar Box Corer, a big metal scoop that gets lowered down to the seafloor.

E, the WHOI coring tech with the box corer.

Box Corer

When the corer touches down on the buttom it scoops up a chunk of mud. It’s kind of like those carnival games where you try to pick up a stuffed animal, or a squishy baseball, or the such. But instead you just get mud.

A typical box core deployment would go like this:

  • Put the box corer in the water with the ship’s crane.

    B, the ship’s Bosun, directs a deployment
    Box Corer Deployment

  • Lower it down with the ship’s trawl wire.

    J at the winch controls
    J at the Winch Controls

  • When the corer gets near the bottom watch for the wire tension to go slack. When it’s slack the corer is on the bottom and scooping mud.
  • Bring the corer back up to the surface

    The corer coming back on deck.
    Box Corer Recovery

  • Siphon off the top layer of mud

    Guest student Z got a real ‘taste’ for the work.
    Siphoning

  • Sieve the mud
    Cold bottom water in the white jugs washes the mud as it gets sievedSieving
  • Bottle it.
  • Cool it.

The last few steps have to be done in a hurry. Otherwise the forams dry up, heat up, and die.

When the depth is about 3300 m the whole process takes about an hour and half. Most of that time is spent just waiting for the corer to be raised and lowered.

Coring ops usually went from 6:00 to 6:00. At night we would usually steam to the next coring site, or do a CTD in the early morning to get cold bottom water for sieving the mud.  Only on our last night did we do a night core.

F, Z, D & N doing CTD Sampling

CTD Sampling

Mud at night:

Night Core

We did a couple days of coring near the shelf break, then worked our way back to WHOI.

Ship Life

We had incredible weather. Calm seas, cool, foggy mornings. Sunny, warm days. Just right for coring.

Some nights a bunch of us would sit out on the fantail. J, our steward, and E, our second mate would put out their fishing lines (to no avail) and I would bring out my guitar to play while the sun went down. Not bad at all.

E & J keeping it loose on the fantail

E & J on Fantail

Sunset from the bow

Sunset Mast

We saw a fair bit of wildlife. Birds, dolphins, a mola-mola, even a swordfish. The shelf break is a busy place for wildlife.

Dolphins off the bow:

Dolphins

Lay-up

Now the ship is lay-up until Mid-June. I’ll be home in Maine until August. Then it’s off to meet the ship in Barbados before heading over to the Red Sea. Check back in couple months to see how it goes.

Thanks for reading.

Pictures

L literally shows the science party the ropes.

L Teaching Knots

D & F sampling from the CTD

CTD Sampling

L in the crane

L in the Crane

A sieve, close-up

Sieve

A foggy morning on the bridge

Foggy Morning


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