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Research Voyages

MAPPING SEABED HABITATS OFF wEST AUSTRALIA SS07/05 Jul 05

[Introduction] [The Voyage] [The Voyagers] [Ship to shore]

Ship to shore

Day 7 - Controlling the Equipment
by Matt Sherlock

Some of the gear on board is large and it takes a bit of managing.

Our cameras and lights take a peek at the bottom.

The deep water camera sled.

It's early morning, on board Southern Surveyor, and we have just completed another video camera survey of the ocean floor at 400 metres depth. The winch is hauling the system back to the ship. Sitting in front of a computer screen, I watch as our carefully targeted images are transferred from the digital SLR camera, through 3 kilometers of optic fibre cable, to the safety of the hard disk just in front of me.

Watching on the video monitor, I can see a brightening glow as the camera system reaches the surface just behind the ship. It's well before sun up but the bright lights from the rear deck and 'A' frame penetrate some distance beneath the surface. The screen shows a churn
of bubbles and disturbed water from the ships propeller which is spinning just a few metres ahead. Suddenly the visual chaos ends as the camera system leaves the water and the colourful stern of the ship is in view.

I can see the deck crew, with long hooker poles extended, to latch safety lines to the frame providing a means of steadying the camera as is it brought on board. This time the ship is rolling a little and the camera is building up quite a swing making it difficult to get the ropes attached. Possibly the winch operator will need to drop it back into the water to ease the movement and avoid having it smash into the stern of the ship and cause camera damage. Suddenly however the swinging is eased as the lines are attached and secured. The camera moves smoothly through the air as the 'A' frame is retracted and system landed gently on deck.

The ships intercom is active again with discussions and instructions on exactly where the next sediment samples will be collected at this site. Through the deck beneath my feet I can feel the shudder as the propeller pitch is adjusted to increase speed and the 1.5 meter high Kort nozzle rotates to steer the ship towards the next site. Just outside there is a clatter as the sediment grab is loaded. A long lever arm is attached, to the centre of the grab, to compress the big loading springs and open the jaws. The mechanism latches, with a sharp metallic clunk, and the grab is 'armed'. Soon the ship is on station and ready for deployment.

The grab is lifted into the air, by the deployment cable, and is lowered gently over the side. It disappears quickly into the dark water. Once near the bottom, the grab is stopped briefly to allow it to settle, ensuring it is in the optimum orientation to capture a sample. Then the winch operator lowers quickly to have the grab strike the bottom activating the trigger and closing the jaws.

After hauling, the grab is landed back on board, and the inspection panels opened to recover the sample. Scientists busily photograph and bag a portion of the muddy sand for freezing. The samples are carefully inspected on board to enhance our geological and biological understanding of the site and its significance on the habitat of the region.

Now I can hear the clatter of the pneumatic gantry as the CTD (conductivity, temperature, depth) profiler is brought out on deck. This instrument comprises a suite of sensors for measuring various parameters in the ocean including temperature, salinity, fluorescence, dissolved oxygen and light levels.

The hydro chemist and technicians have been preparing the instrument for deployment. Special underwater sample bottles, attached to the CTD frame, have been cocked open and linked to their respective trigger releases. A technician issues the last instructions, from a computer terminal, to a self contained acoustic current profiler which hitches a ride on the CTD frame. This instrument uses acoustic pulses to measure and internally record the speed and direction of water currents, both above and below the CTD, as it moves through the water column.

From below, in the operations room, the operator signals that data is being received from the instrument through the 7000 meter conducting deployment cable. The cast begins and the system is lowered over the side of the vessel. Very accurate measurements are collected, many times per second on the way down, from the many sensors on the system. On the computer screens the ocean temperature measurement jitters in the third decimal place, it's measurement accuracy is better than 5 thousandths of a degree Celsius.

Just above the bottom, at 390 meters depth, the CTD winching is stopped and the first water bottle closure is initiated by the operator. A fraction of a second later the caps of the first sample bottle are released and snap shut to catch a sample of the water at that depth.

At regular intervals the CTD is stopped and more water samples are collected, all the while the intercom is exchanging messages between the winch driver and system operator. The groan from the hydraulic motors on the 'A' frame rams signals the system has returned from the 'deep'. The hydro chemist and technicians begin water sampling and analysis in the ship's chemistry lab.

The sun is just coming up now and we are moving, at speed, to the next study site, which is some miles away. This will be the routine now, for several days, as we move down the coast, towards Perth, stopping at selected survey sites along the way.

The sky is clear but the wind is blowing and the sea rising. Time to start some data backups and wander into the mess for breakfast.

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Updated: 29/03/07