JC010: Mud volcanoes and submarine canyons


Cruise diary

Day 14: Wednesday 4 July 2007
Position: 48o 25.921N  09o 56.433W  Whittard Canyon (Google Earth reference: 48 25’92”N 09 56’43”W)
Weather: Sunny with light cloud

Richard writes:

"Over the course of the day, Isis was involved in two dives. Dive 64 carried on from yesterday and was based around a video transect of the western wall of the Whittard Canyon, at a depth of 3000m, rising to 2000m. Push cores were also taken. There was lots of life - brittle stars, squat lobsters, rattail fish, anemones, sea pens, burrows (not sure what created them!), and also geographical features such as errosional furrows (which look like ripples).

Animal life (above) and geological features (below)

Dive 65, which will carry on into tomorrow morning, involved travelling between two points in which Isis would end up in relatively shallow waters (around 500m!).

Something I found interesting during this dive was that data from the CTD (along with knowledge of the currents) shows the scientists that the water flowing through this area is outflow from the Mediterranean Sea. Whereas warmer water will normally flow at the top of the sea, that from the Mediterranean has quite a lot of salt in it, making it more dense than the water in the sea it flows into. This means it flows along the seabed even though it is warmer than the water above it

Due to this, there must be both haloclines and thermoclines in the water. ‘Cline’ means change, ‘thermo’ obviously refers to temperature, and ‘halo’ to salt content – basically changes in temperature and salt content. These can happen very abruptly so that the change is noticable in a very small layer of water (look at the diagrams below – the ‘clines’ can be less than a few metres deep!). I was really interested in this as I have gone through thermoclines many times when diving. At the boundary between the two ‘sections’ of water, everything looks very streaky, just like when hot air rises from a road on a hot day or like looking through a bathroom window. It is quite pleasant going from cold to warm in a thermocline, but not so nice the other way round – it is a bit like stepping outside your warm house on a very cold winter’s day! The differences in the water in this part of the ocean mean that the plant and animal life is different to that normally found in these seas because of the different environment they experience.

Haloclines are useful in that they allow sea ice to form. As you have heard already, the salty water is more dense and so sinks. This means the colder water stays at the surface and so is able to freeze more easily. Thermoclines are the reason that lakes don’t freeze right to the bottom – once the ice forms on top, the most dense water (about 4oC) sinks to the bottom and stays there, and so doesn’t get cold enough to freeze. You just have to hope that the layer of ice is thick enough if you want to go skating on ..."

Tina writes:

"The last ROV survey is on the way, a storm is en route.  We are looking forward to celebrating Jacqui’s birthday tomorrow.  We had a fabulous Indian for supper (thanks Mark, Wally, Vikki and Jacqui). Here are a few photos to show what we have been up to over the past few days...

Belinda and Wsouter splitting cores

George and Belinda wrapping cores for storage

Preparing to bring the ROV in

Winching tohe ROV into the ship

Scientists turn artisits - preparing polystyrene cups for the next dive...

...the results - little and large!

Rhys washing down the multicorer

Deploying the CTD

So as we start packing away the kit and securing equipment that is not going to used again this trip there are mixed feelings.  Those who have been on board since May are looking forward to going home and seeing their families, those of us who have been here just over two weeks are feeling nostalgic, this time has been fun..."


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