Final Situation Report, NB Palmer Cruise 96-4A;   November 8, 1996


 
      The R.V. NB Palmer  completed its science activities yesterday by
 the retrieval of an in situ productivity array from the ice, and thus
 concluded the first Process Study of AESOPS.  In large part the
 objectives of the project were successfully addressed, and the onset
 of the bloom and its associated carbon dynamics were observed in
 detail.
 
      The week began with a "log station" at Site Minke in the
 southeastern sector of the Ross Sea.  During that station (which was
 covered with a sheet of 1.4 m ice) a strong pressure ridge formed
 during our operations, making it impossible for sampling to continue
 at that location.  The operation in the water (thorium sampling via in
 situ pumps) was promptly terminated, but ice caused some damage to two
 of the pumps upon retrieval.  An in situ productivity array was also
 retrieved, and the ship moved ca. 0.8 nm to an area where the ice
 exerted less pressure, and the station operations continued.  We
 transited back to Site Orca in the southcentral Ross Sea, completed
 another "long station", and occupied stations along 76 deg. 30 min. S
 every two degrees longitude back towards Minke, where the final
 station was occupied.

      One of the features which we observed was that the seasonal
 phytoplankton increase was beginning.  Chlorophyll levels increased to
 ca.  0.5 ug/l, pCO2 concentrations dropped from 460 to ca. 420 uM, and
 nitrate concentrations were reduced to slightly less than 30 uM.
 Dissolved organic carbon concentrations remained low and constant, and
 bacterial biomass and activity were low.  Although growth had begun,
 the rates and biomass observed are far lower than would be observed in
 a few weeks time.  However, the data collected will provide a complete
 assessment of the carbon dynamics of the onset of the seasonal
 phytoplankton bloom.

      Experimental work initiated during Process I was also concluded.
 These included trace metal additions to assess the role of metal
 limitation of phytoplankton growth, organic carbon additions to
 quantify the efficiency and rates of organic matter turnover, and
 large volume Phaeocystis growth experiments to understand the growth
 and development of this important species.  All of these experiments
 will add to our knowledge of the mechanisms which control primary
 productivity in the surface layer, and ultimately the flux of organic
 matter to depth.

      Scientists in NBP96-4A are awaiting off-load in the McMurdo Sound
 area and transfer to McMurdo Station for redeployment back to the US.
 Along with the scientists, many samples will be carried to insure the
 immediate analysis of this cruise's data.  The scientists are highly
 appreciative of the efforts of the ECO officers and crew, as well as
 ASA personnel, in making this cruise a safe and productive investigation.

 Submitted:     Walker Smith, Chief Scientist