The peak of my participation in the cruise arrived on the 30th of April, when Giuliana and I finally deployed the two sea gliders which we had lovingly lugged across the Southern Ocean. This brace of sleek, yellow, autonomous machines is planned to track one of the many "SOCCOM" floats that bob through the world's oceans. They will dive in a cross-shaped pattern centred on float #12888, taking regular measurements of temperature, conductivity, dissolved oxygen and fluorescence, at a high spatial resolution. Comparing this data to the coarser float data will help in the wider interpretation of the SOCCOM data sets, specifically to develop our understanding of the submesoscale (i.e. about 10 km length scale) contribution to carbon transport out of the surface ocean.
|Sea gliders 659 and 660 taste their first fresh air in front of Table Mountain.|
Oomph. Enough jargon. (See key-words at the bottom). Here's a picture of our gliders, SG 659 and SG 660 basking in the sun on the back-deck of the ship while in Cape Town, with Table Mountain watching over them from across the harbour.
During our days steaming across the Southern Ocean, the gliders could often be found like this: strapped against the railing of the deck, their antenna pointed up to the clear southern skies, awaiting satellite instructions with the patient loyalty of a hunting dog awaiting its masters whistle. Unfortunately, like even the best hunting dogs, our gliders were occasionally poorly behaved. This manifested itself in their sporadic reluctance to be turned on; an odd procedure which involves being rubbed in concentric circles with a magnetic (magic) wand. In the midst of freezing winds and a rolling ship, Giuliana or I would often have to crouch next to the glider, stroking their yellow bellies for what seemed an eternity. What divas!
Max celebrates a particularly stubborn glider finally turning on.
When finally deploying the gliders at 51.5 degrees south I was thrilled to be sent out in a small inflatable boat, the safest way to deploy our yellow friends. After 4 weeks without leaving the ship, the rest of the science crew were understandably envious of this chance at an escape. Third mate Todd, A.B. Bernadette and my pal Isa were aboard to drive the boat and help to deploy. We were lowered over the side of the ship at a precarious angle as the science crew looked on and waved goodbye to the first glider, SG 660. With a sudden splash and roar of the boats engines we were off. Todd raced away and soon the R.V. Thomas G. Thompson was just a grey blur in the soft sea mist. When 500 m away from the ship Isa and I lowered the glider into the ocean and held it still until it filled with water (quite a chilly affair…). Giuliana gave it the command to dive from the ship and we bid it farewell as it sunk on the first of many dives. We cheered and congratulated one another, the relief and excitement bubbling over!
We returned to the ship to collect the second glider, but unfortunately our engine overheated while leaving and we had to return slowly to the ship without having deployed. The silver-lining to this set-back was the opportunity for observation from close to the seas surface as we slowly made our way back. Beautiful sea birds swooped close to our heads and the proud stern of the Thompson cutting through the swelling seas was an impressive sight.
SG 659 had to be deployed from the crane of the ship instead and we quickly learnt why deploying by hand from a small boat is preferable… The glider swung dangerously close to the ship as it was lowered over the side. Thankfully, the pin was pulled and the glider dove gracefully into the water before this could happen. 10/10 from the onlooking judges! After a somewhat stressful deployment we were relieved and overjoyed to see them send back their data, as the files popped up on our laptops.
All that was left was to deploy SOCCOM float #12888, which Melissa did at the end of the CTD cast. The float, also called Silva, was named the beloved principal of the East Middle School Eagles. Since then we have seen data profiles come back from the float (access them here: www.mbari.org/science/upper-ocean-systems/chemical-sensor-group/soccomviz) and the gliders have been piloted from Caltech. For the next four months they will continue to float and glide together through the beautiful Southern Ocean!
Unfortunately for us, we are now making our way back to Cape Town, leaving the wilderness of these seas behind.
"SOCCOM" - Southern Ocean Carbon and Climate Observations and Modeling.
"Float" - 1.5 metre long conglomerate of sensors that float (what?!) freely in the ocean, sinking to 2000 m depth and bobbing back up again once every 5 days.
"Fluorescence" - light of a particular wavelength that is emitted by phytoplankton, gives a good indication chlorophyll content.