Thursday, March 11, 2010

Thursday 11 March, Day 56

Back to the mooring recovery.
At and between each mooring, we lowered some instruments attached on a metallic frame with 24 Niskin bottles (to take in situ water samples) to the bottom of the ocean. The instruments measure the conductivity, pressure and depth (CTD) of the water (salinity can be inferred from these), and the currents (using lowered Acoustic Doppler Current Profilers, or LADCPs). Here is the instrument package coming back to the surface:

and hauled onboard:

When we arrive on a mooring position, we lower an acoustic device in the water to "talk" to a device at the bottom of the mooring, called an acoustic release. This is one of the most important piece of equipment of a mooring, since if it does not open, we cannot retrieve the mooring! Last year we had some instances when we couldn't "talk" to the acoustic releases, or would send the release signal but nothing would happen, and we were not able to retrieve some moorings of other projects. Thankfully, all the releases worked perfectly for the SASSI moorings, and we were able to recover all of them!
Below is the top buoy of the deepest mooring after having reached the surface (the game is to be the first to spot it out after the release command has been sent to the acoustic release!):

The next game is to catch the retrieve line with a grapple:

But the line seemed to be stuck, so everybody gave a hand to pull it out:

They did not manage to pull the line in, but they managed to break the grapple! So Dave, the bosun, had to climb a ladder down to the water level to attach a shackle with another line on the buoy (falling in the water would not be a pleasant experience...):

Finally the mooring could be hauled onboard:

And we discovered why the retrieve line was stuck: it was completely tangled around the main mooring line! Everything on this mooring turned out to be tangled. Perhaps it is due to the length of the mooring (2000 m), or to the way it was deployed, "anchor-last", which means everything was floating in the water before the bottom weight (called the anchor) was dropped into the ocean, and since we could not move much because of the sea ice around the ship, the line was probably loose and making turns on itself...

(to be continued...)

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