Wednesday, September 26, 2012

Deep-C Geomorphology/Benthic Studies Cruise - Fall 2012

Ship’s Blog:  Weatherbird II (WB1305)
26 September 2012
Map of Cruise Progress (as of 26 September)
 

Chrissy, Andrew, and Samantha wrangle
the CTD/Rosette on board. 
Each grey bottom holds a
10 liter water sample that has
to be passed through fine meshed filters.
The students working to process water and sediment samples sometime after breakfast this morning, having worked all night and a good piece of the previous day. The water samples take a long time to process because they have to be carefully pumped through a double filter system to get the very smallest particles. The sediments take a long time because the multicorer has to be lowered to the bottom and then hoisted up again, which is starting to take a longer time as our sampling sites move into deeper waters. Then each core is carefully sliced in sections so the scientists who are working on the samples can compare different depths into the seafloor.

Our solution to clips that pop loose
and drop core tubes: cable ties.
We suffered a slight mishap when one of the core tubes was lost because the clips that hold it onto the multicorer let go. This is the second time this has happened, so we have resorted to a time-honored solution of binding the clips with cable ties before we launch the corer.

Fortunately our schedule gave sediment and water folks a rest while we did photo surveys at AC2 and PCB06 and then one more in the early hours of Wednesday the 26th. The first two were challenging sites because the bottom slope was a complex mixture of valleys and ridges. When the MILET is near the bottom at a water depth of 1700 m, we frequently have over 2000 m of cable played out from the winch. We have to be careful to keep the ship moving ahead fast enough so that the water drags on the platform and all that cable and lifts it up. But we can’t lift it too much or we lose sight of the bottom. We are lucky to have two skillful boat drivers in Captain Matt White and Ryan the second captain. When the bottom is sloping up, we have to reel in constantly on the winch to keep the platform off the seafloor. Despite a few tense moments, we had no repeat of the first day’s dragging incident, where the cage got pulled across the bottom for a while before we could pull it up.
MILET goes over the stern to start a survey.

We saw real differences in bottom type and in the abundance of fish and invertebrates. Site AC2 seemed to have several times more fish than the shallower site AC1. And there seemed to be several bottom types depending on whether we were surveying in or out of the valleys. Of course it will take months of careful counting and analysis to determine if these first impressions are real findings.

Ian controls the winch
during the launch of MILET.
On the final site in this blog we went to a site called Seep A, where we thought there might be some natural oil and gas seepage. Here we wanted to concentrate our survey around the small area where the seep might be. At first we had some promising results. We got the camera to the bottom in about 1200 m of water and were able to just let the MILET drift over the seep. A few minutes into the first line, several us saw what looked like giant oil bubbles drifting up past the camera! But then they disappeared, we didn’t come across anything else, and we couldn’t be sure what we had seen.

So, we decided to try and double back over our previous site where we saw the suspected bubbles. Right away, things started going wrong. As soon as we asked the ship to turn, we drifted back over our cable so that it was going under the stern. This makes everyone a little nervous because of the awful possibility of somehow catching it in the propeller. The captain kept a cool head though and eased us out of danger. But then no matter how we turned, we couldn’t seem to get the MILET to drift back where we wanted it to. Finally, we had to haul the MILET almost all the way back to the surface and lower it down again to get things lined out.
MILET goes over the stern to start a survey.
Crowded conditions in the
main lab where we do
most of our work.
As we were approaching the bottom, we got the bright idea of replaying the video tape to see where the “bubbles” had appeared. Oops. In slow-motion, it turned out that what we had seen were swimming sea cucumbers, not oil bubbles at all. Then, at 2 am with everyone a bit tired and on-edge, we had a bizarre, but harmless issue. Flies buzzing around in the lab started landing on the touch screen of our imaging computer, which sounded warning chimes and even caused files to open. It was like the flies were taking over our work. Maybe they could do a better job.

Oh well, another hour or so and we’ll give the water samplers a 3am wake-up call and go sleep for a while.

Post Author:
Dr. Ian MacDonald

No comments:

Post a Comment