JC010: Mud volcanoes and submarine canyons


Cruise diary

Day 11: Sunday 1 July 2007
Position: 44°01.11N 11°03.09W (Google Earth reference: 44 01’1”N 11 03’09”W)
Weather: Cloudy

Richard writes:

"Whilst in transit from Portuguese to Irish waters, things got a bit messy. As we were ‘steaming’, there was no work for the scientists to do that necessitated staying up at night, so during my shift I tried to catch up on some sleep. It was pretty hard to sleep however as the ship was rocking from side to side, quite violently at times. Thankfully the ship has a stabilisation system so that it prevents too much rocking, but this is quite noisy whilst in operation, from my cabin anyway.

Despite this, during the night my cabin started to come alive… The first thing to start moving was the curtain. Now I don’t have a porthole (‘window’) but every cabin has a curtain behind the door so that you can leave your door open, but drawing the curtain to give more privacy. It started to open then close, open, then close... The cupboard and wardrobe doors (I should have had them on the latches) were next, followed by just about everything in my cabin!  Quite a big roll of the ship lead to my phone (that is ‘desk ‘phone’, not mobile) and lamp flying off the desk, bouncing off the wall and then, along with my other belongings sliding from wall to wall as the ship lurched from side to side. If I had videoed it, it would have resembled something from a horror movie, all these objects seemingly moving about by themselves…

Similar goings on had happened all over the ship - plaques had come off the wall in the bar area and chairs were all over the place. The galley wasn’t much better, so I was pretty impressed that the catering team still managed to have breakfast on time. I have no idea how they managed to cook it – I could barely stand!"

Anyway, here are some photos:

Chairs stowed away in the galley...

...and in a less orderly fashion in the lab!

Richard hangs on whilst writing his diary!

Andy serenely reads, apparently oblivious to the tempest

Watertight doors shut...just in case!

I have been trying to think of how best to describe what people look like as they are walking about on the ship. I know you lot will be too young to remember it (actually so am I, but I have seen it since…), but if you look up the Michael Jackson video for ‘Thriller’ on YouTube, you can get an idea of what people look like as they walk about on the ship – leaning from side to side so as to try and stay on their feet!

Tina writes:

Last night the dishwasher in the bar made a leap towards freedom.  It was captured just before it left the bar and took of down the corridor.  Of course it should not have happened - it was securely fastened in place under the counter but somehow during rough waters over night it worked its way loose and headed for freedom. I slept through it all.  Typical...The first bit of rough weather and I’m sleeping like a baby! 

Left: The ship rolling in the waves

While we are in transit (moving between survey points)  Doug and Veerle  were trying to work out what to do and where. You could just stop the boat and drop the megacorer over the side, but if you haven’t researched the location you could spend hours collecting core samples and not get any thing useful.  Hours are spent researching where the ship should stop and what equipment should be deployed at each location.  Ultimately it saves time.

One method used to map the sea floor is swath bathymetry data.  This is an echo sounding technique. In echo sounding a blip of sound is sent to the ocean floor, when it reaches the floor it is reflected and returns, a receiver, capable of hearing the signal, listens for the sound.  The receiver measures the time between sending the signal and it being reflected then arriving back.  The further away the seabed the longer it takes for the signal to return to the receiver.  So if we know how quickly sound travels in water we can work out how far away the bottom is.

Left: Map of the seabed from swath data.

It goes like this:

Sound travels in water at a rate of 1500 meters every second.  So if the initial sound signal (ping) takes 4 seconds to return to the receiver we know the sound has travelled 6000metres (4 x 1500).  BUT this is to the seabed and back again so the distance to the seabed is only half this distance, 3000metres. 

Of course, it is not actually as simple as this! Depending how deep you go the speed of sound changes, at the surface it is around 1494metres per second while at depths of around 4000m it could be as much as 1533 metres per second.  These small differences make BIG differences when you are working at the levels of accuracy the scientist have to work at.  So before calculating the depth from echo sounding data you need to measure the speed of sound.  They can do this with a sound velocity probe, or if this is not available they can use the CTD probe  to measure temperature and salinity and from this calculate the speed of sound.

Then just to make it more complicated, for swath bathymetry data a signal is sent out through an arc of 120o  the returning echo is picked up by 128 receivers and a bit of complicated maths does the calculations to work out the depth.

A more detailed guide to swath bathymetry is coming soon..."

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