Collecting the pole compass early today marked the completion of what we are calling the 'eastern' CEAMARC sampling stations. The central and northern reach of our grid marks out the 'Climate of Antarctica and Southern Ocean' (CASO) stations which we will work through over the coming week before another CEAMARC burst to the west off Dumont d'Urville on the continent.
As well as CTD sampling, the CASO team is gathering information on the speed and direction of water currents from polynya moorings. These Acoustic Doppler Current Profilers are deployed some 135 miles from the South Magnetic Pole but still fall within its influence, so a special "pole compass" is used as a kind of calibrator to correct their data.
Retrieval of the pole compass is quite a feat. The equipment is anchored to the seafloor for its week of work. The ship returns to the same position - ideally when visibility is good and the sea is calm and a remarkable sequence of cooperation and coordination occurs.
The technical engineer in the aft winch room above the trawl deck 'pings' the equipment electronically causing it to be releases from the anchor. On the bridge, all available sets of eyes scan the ocean for the tell tale yellow buoys that will bob up with the equipment after a five or ten minute ascent from 1200m below. There are a lot of if's. It might not release correctly. It might be carried by the current or concealed by waves.This one comes up portside, very close to the ship.
The ninety-five metre, seven thousand tonne icebreaker is maneuvered delicately alongside a cluster of buoys the size of a bunch of party balloons. They are joined to another float carrying the equipment. There's a length of floating line to grab. If the bridge can see the buoys, the trawl deck can't. When the trawl deck has the float in sight the bridge has lost view. The radios crackle to and fro with information and the ship carefully brushes by the floating procession so the crew on the trawl deck can haul it in with a grappling hook.
It's a textbook operation. A missed pick up would mean a lost hour for each repositioning of the ship for another try.
What's more, Steve reports that the equipment has performed the data collection it was asked to.
Pic: retrieving the pole compass
Margot Foster is a journalist currently on board the Australian Aurora Australis, an Australian research vessel currently participating in the Census of Antarctic Marine Life (CAML, IPY project 53). She works with the Australian Broadcasting Corporation (ABC).