NBP96-04 Final Cruise report

Dear Colleague,

	You have already received a message from Jon Alberts pointing
out that we have completed the scientific portion of the AESOPS Site
Survey cruise, and noting that we experienced more than a little
misfortune at our last two stations.  The failure of the CTD wire
prevented us from collecting deep hydrocasts at our final two stations
(60 deg S and 57 deg S). Inextricably wrapping the trawl wire around
one screw during the penultimate over-the-side activity of the cruise
has slowed our return to port.

	Nevertheless, despite these setbacks, the bad weather at the
beginning of the cruise, and the unexpected ice conditions at 64 deg S,
the cruise has been far more a success than not.

	Bathymetric surveys were completed for the proposed sediment trap 
mooring sites at 64 deg S and 57 deg S, as well as the large-area survey 
between 60 S and 62 S spanning the Antarctic Polar Front.  

	JGOFS hydrographic software developed during the Arabian Sea
process study has been successfully transplanted to the Palmer and used
to conduct a pair of hydrocasts (one shallow and one deep) at 64S, 62S
and 61S.

	The new TM Clean Rosette has been tested and, after working out
minor last-minute bugs, is fully operational.  The first complete
sample cast with the Clean Rosette was completed at 61S, and the Clean
Rosette was used to provide two shallow casts each at 60S and 57S after
the primary rosette was rendered unusable.  Running the Clean Rosette
out of the Palmer's Wet Lab is a little cumbersome, but far preferable
to an alternative operation out on deck.

	MOCNESS tows were completed successfully at 62S, 61S, 60S and
57S.  BONGO tows were completed at 64S, 62S, 61S and 60S.

	Problems with the ADCP system software experienced at the
beginning of the cruise have been worked out, and we are now routinely
collecting ADCP data that will be used jointly for current velocities
and for mapping zooplankton distributions.

	Multicores with well-preserved sediment-water interfaces were
obtained at 64S and 62S.  A gravity core was collected at 57S.  Coring
attempts at 61S and 60S failed to recover sediments.  Of the sites
sampled, sediments at 62S appear visually to be most like the classical
diatom oozes of the Southern Ocean.  This is not surprising, as
historical data suggests that the zone of highest productivity, around
the APF, lies between 60S and 62S.

	Analysis of surface water samples shows classical patterns for
the Southern Ocean:  Nitrate decreases systematically from approx. 30
uM at 64S to approx. 15 uM at 50S, showing no detectable features
associated with the APF.  Dissolved silicate decreases from approx. 55
uM at 64S to approx. 6 uM north of 54S.  Unlike nitrate, however, the
concentration of silica drops abruptly at about 63S, and even more so
across the APF (approx. 61S).

	Through the entire region, from 50S to 64S, the ocean is a
source of CO2 to the atmosphere under late-winter conditions,
although we observed a minimum in PCO2 situated between the APF and the
ice edge.

	Beyond completing the Site Surveys, and the collection of
samples & data representative of winter conditions, the Site Survey
cruise has served as a shake-down for the hydrographic and nutrient
work to be carried out during subsequent process cruises.  We would
like to think that we have contributed in some small way to successful
and efficient Process cruises to follow us.

	The science party is most grateful to Capt. Borkowski, and the
ship's crew, for their efficient (and friendly!!) support of science
activities.  ASA personnel have been putting in extra hours helping us
work through problems during this cruise, and setting up an operation
that will support JGOFS through the upcoming Process cruises.

Regards,

Bob Anderson
Chief Scientist