JC010: Mud volcanoes and submarine canyons


 JC10



Cruise diary


Day 7: Wednesday 27 June 2007
Position: 38°22.454N 09°20.122W (Google Earth reference: 38 22’4”N 09 20’1”W)
Weather: Sunny with light cloud


Richard writes:

"Even though I said in yesterday’s blog that we would be heading off to the Irish margins, when I arrived for my shift I was told that the plan had changed. As I am from Northern Ireland myself, I wasn’t too surprised to hear that this was because the weather was a bit bad. Well, ok more than a bit bad – force 9 gales to be precise! If you are familiar with the Beaufort Scale from your Geography lessons, you are probably aware that the scale only goes as high as 12 (although typhoons can be described as higher than 12 in some countries). Apparently force 9 gales will produce waves of around 7m in height (roughly the size of a fully-grown man standing on a fully-grown giraffe's head!) and can cause light structural damage. Going back to my first diary entry on 23 June, a Force 7 gale was turning me a little green, so I was glad we were going to avoid the Force 9 gales! Check this page http://www.geology.wmich.edu/Kominz/windwater.html for photographs of the sea at different points on the Beaufort Scale.

So what does this mean for the cruise?  Well, Doug is having to work closely with the ship's master (captain) so they can figure out where the best place to go now is. He also has to work closely with the other scientists to develop a plan of attack for the scientific work as this will obviously have to change too.

Don’t forget to keep checking back for updates on our progress. We will be continuing to work off the Portuguese coast for a while and so your Google Earth plots will be criss-crossing a bit, so don’t think you are doing something wrong!

 

Today we:
Did an Agassiz Trawl
Sent down the Megacorer
Did a ROV dive to carry out reconnaissance of the sea bed in a shallow part of the sea canyon and collect push cores..."


Tina writes:

"Collecting a core sample is like taking a trip back into history.  On the core sample collected today (left) I could see quite a few different layers. I wanted to know what the darker layer was. 

One suggestion:  the dark layer was a layer of sediment carried into the sea during a massive volcanic eruption that occurred hundreds of years ago bringing dark volcanic ash to the sea which eventually settled out on the ocean floor.

Another suggestion:  The top layer is the layer where there is oxygen in the water, then, when the layer becomes darker the oxygen runs out. 


See if you can follow the chemistry:
Normally there is oxygen present in the top layers of sediment but the oxygen can not diffuse quickly into the lower layers.  However, there are still bacteria in the sediment needing some form of oxygen so that they can use the organic matter in the sediment for respiration.  So the bacteria look try to find oxygen in different places.  They find oxygen attached to minerals like iron oxide and manganese oxide and have to reduce these minerals to use the oxygen.  When this happens they can change insoluble iron (III) oxide into another form of reduced iron (II), which is soluble and free to diffuse through the sediment layers.  BUT if the dissolved iron (II) diffuses back up towards the surface layers again and comes into contact with oxygen, it reacts and changes back into the the insoluble iron (III) oxide again. Since iron (III) oxide is red/reddish and iron (II) compounds are darker you see a colour contrast. 

Difficult or what !!?

To find out who was right they would have to slice up the core.  If a volcanic eruption was responsible for the darker layer then the grains of sediment would look different from the other layers.  But if it is due to iron reduction, you would not expect to see any difference in the sediment types..."



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