Final Cruise Report for the AESOPS Sediment Trap Mooring Cruise

It is often said that timing is everything.  This cliche certainly
proved to be true for the AESOPS sediment trap mooring leg.  Being able
to deploy seven moorings in less than two weeks while covering nearly
2000 miles of ocean is an accomplishment that in retrospect involved a
large measure of good fortune.  Given the difficulties and weather
trials of previous legs, we had reason to believe that our one day of
weather contingency would prove inadequate.  But, there were times on
this cruise when wind and sea conditions, if not temperatures, were
more akin to the Tropic of Capricorn than the Antarctic Circle.
Captain Borkowski and his mates were often shaking their heads in
wonder as we began day after day under excellent conditions.  The head
shaking continued through the final mooring deployment as a squall blew
through sunny skies and a rainbow appeared off the fantail, just before
the last anchor went over--a fitting symbol of how lucky we had been.
As it turned out, the fair weather window closed that evening, and we
then encounted a low pressure system with 50 knot winds.  The winds
have slackened slightly after two days of steaming towards Lyttleton,
but conditions are still unfavorable for mooring deployments.  However,
with our moorings already in the water we are content to feast on
Thanksgiving dinner with all the trimmings (three kinds of pie) and
celebrate in the 02 lounge late into the evening.  We see now how
important it was for us to leave the ice edge two days ahead of
schedule.  Had we not done that, currently we would be sitting out the
storm at one of the mooring sites and sending e-mails requesting more
ship time.

Although the three anchor-first mooring deployments within the
ice-covered sites were an immense challenge, the four anchor-last
deployments that were up to 4500 m long and heavily instrument laden,
were no piece of cake.  But, thanks to the skill of the core mooring
group from WHOI and OSU (Steve Manganini, John Billings, Larry
Costello, Chris Moser, Kathryn Brooksforce, Tom Gann, and Brendan
Hart), the efforts of Jon Alberts and several ASA marine techs, and
numerous others in the scientific party, the deployments were both safe
and smooth.  In all, we deployed 32 sediment traps and trap arrays,
numerous current meters, and transmissometers.   The bulk of the
sediment traps were of the WHOI design with 21 and 13 cup carousels
that generally provide 17 day sampling resolution.  Eight trap arrays
(three traps each) from the UW-Skidaway-Stony Brook consortium that
were designed for organic chemical studies, have "swimmer-exclusion
valves".  Two OSU time-series traps that were designed for high flux
conditions and trace element studies were deployed in the Ross Sea.

The SeaBeam maps collected by Bob Anderson's Site Survey Cruise were an
essential part of our success.  Because the Polar Frontal Zone lies
within rugged topography, we would have been gambling under poor odds
to place moorings without these detailed images of the seafloor.  The
outstanding efforts of Suzanne O'Hara made it possible to obtain more
detailed versions of the original maps that proved critical for
defining the final placements of the moorings.  She also trained a team
of tireless "ping editors" whose efforts made it possible to transform
our additional surveys into near-final maps.  Although I was impressed
by the capabilities of the SeaBeam system for producing beautiful,
detailed maps, I also developed a new realization of the amount of
human effort required to produce acceptable results.

CTD casts, water sampling for CO2, nutrients, and stable carbon
isotopes were done at each station.  In addition, in situ filtrations
at various depths were carried out at every site to define the organic
and trace element composition of suspended particles.  Upper water
column net tows were conducted at each station to obtain samples for
organic chemical analyses.

Underway sampling and measurements, while ineffective in the ice,
worked well in the open waters north of 64.6 degrees S.  Sea surface
temperature rose sharply by nearly three degrees around 61 degrees S.
This jump, which was at a latitude similar to where sharp changes in
SST and silica occurred during the Site Survey Cruise, may have marked
the Polar Front during our transit.  This transition was marked by high
surface fluorescence and pCO2 values well below atmospheric, indicating
greater productivity.  North of the temperature jump, fluorescence
dropped and pCO2 values rose to above atmospheric values.  Further
north, at 57 degrees  another temperature jump of greater than two
degrees was also accompanied by increases in fluorescence and decreases
in pCO2.  Just north of this change in SST, fluorescence rose and pCO2
values reached the lowest values observed on the transit.

The placement of our moorings along the 170 transect appears to be
favorable for defining the influence of these frontal zones.  Mooring 5
at 66 S, currently south of open water, will define fluxes influenced
by meltback of seasonal ice.  Mooring 4 at 63 S is south of the PFZ,
while mooring 3 (60 S) is just  north of the current PFZ position.
Mooring 2 (57 S) is south of the more northerly front (the Subantarctic
Front?), while mooring 1 (53 S) is north of this front.

Special thanks goes to Captain Borkowski and his fine crew who showed
us that the R/V Palmer can both crack ice and ride well in the rough
seas of the Southern Ocean.  The food has been excellent, and we all
look forward to returning in 15 months to examine the story that will
be revealed by our temporal and spatial record of particle fluxes in
this part of the world's oceans.

Jack Dymond for the 17 other scientists on the AESOPS Sediment Trap
Mooring Cruise (NBP 96-5)