Response to Mary

Hi Mary:
Interested in the finer details? Each piece of equipment is attached to
wire cable which is controlled by a winch. The CTD travels to the
seafloor fastest, at 40 meters per minute. It comes up a bit more slowly
with stops at the depths where we want to trigger the Niskin bottles—that
means we send an electronic signal for the ends of the bottles to close.

Most of the coring equipment travels down at a rate of 30 meters per
minute. Once it is near the bottom we slow down a bit to allow the bridge
to position the boat so that the wire angle is good and our speed over
ground is zero. Then the winch operator lets out wire until the tension
on the wire indicates that the corer has hit bottom. Additional wire is
fed out to make sure the corer has time to trigger (we don’t want a swell
to yank it out prematurely). Then the gear is pulled out at 10-20 meters
per minute and it gradually speeds up for the trip to the surface. We
generally plan on 2 full hours for coring.

The trawls go down fast, too, at 30 meters per minute. A lot of extra
wire is released on trawl deployments. Then the otter trawl is on the
bottom for about 20 minutes as the bridge keeps the boat moving forward as
slowly as possible. It comes up at about 20 meters per minute. If it
comes up too fast the animals would squeeze against the net. There is
often a protective ball of mud in the net to help protect the critters.


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