Research
Ocean carbon levels and their influence on marine life
Voyage update 1 - From the log of Southern Surveyor' Chief Scientist,
Tom Trull, 3 April 2006.
Ups and Downs from the Sub-Antarctic Zone onboard Southern Surveyor
Voyage SS03/2006
On Tuesday, March 28 we sailed in glorious weather to start measuring
the Sub-Antartic biogeochemical cycles that control carbon transfers
from the atmosphere through the surface ocean to the deep sea.
Our first task was five hours south of Hobart where we successfully
'spoke' to the previously unresponsive PULSE-Test-2 mooring but
with night falling, we left it in the water for recovery by small
boat from Hobart.
Wednesday dawned grey with rising winds and our use of the CTD,
a highly-sophisticared deep ocean measuring instrument, around lunchtime
was to be our last 'over-the-side' operation for several days. We
had sailed into a classic subAntarctic Zone low pressure system
that brought sustained southwesterlies of 30 to 40 knots and mounting
seas.
Attendance at meals dropped, competition for beanbags rose, and
we steamed in a SWATH mapping grid searching for a flat spot for
the PULSE mooring deployment. It's remarkable how 30 hours of searching
turned our first 'Good God that's hilly!' reaction to our altimetry
- identified initial target into 'well I guess its the best we've
got!
Finally on Saturday the wind dropped back below 30 knots and we
managed a CTD cast by midday, but with the deck still rolling waiting
we waited until 2am Sunday to start our PULSE deployment. PULSE
is an experimental mooring design with a stiff lower section that
rises to about 160m below the surface, topped by a loating/sinking
S-shaped section that rises to the instrument packages suspended
below a surface float by thick elastic rubber lengths that protect
the instruments from wave stresses.
PULSE deployment required us to hit the target depth to within
50 meters - precisision deployment in fact, in those conditions.
Imagine flying four kilometers above Hobart trailing a string
of instruments in a line 4km behind you, while you pick a place
to let go of your one tonne weight to hit a spot on the ground that
would guarantee your depth to within 50 metres. A considerable challenge
to say the least.
Oh yes, don't forget the parachute on the weight so that the drop
acceleration doesn't rip the whole string apart as all the elements
are pulled below the surface!
With great coordination between the bridge, the aft-deck, and the
operations room we popped the chute and dropped the weight in water
just 20m deeper than our target depth. Because our weather window
was fading fast we could not wait for the 1.5 hour it would take
the mooring to sink to the bottom to verify its position on arrival.
Today (Monday) we are re-spooling the sub-Antarctic Zone mooring
for redeployment and then we will return to the PULSE site to see
if our drop landed where we hoped or if our chute was a kite that
carried us off target.
More info on this voyage: download
voyage plan as PDF [164kb]
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9/10/06
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