Date: Tue, 20 Jan 1998 09:58:36 -0500


  January 16

        The ice images that arrived today via fax and confirm sea ice at
about  69 deg, 30 min south along 170 W. We won't be traveling south much
longer. We  have been steaming  from 57 S towing the OSU SeaSoar and
constructing real-time  vertical cross sections of temperature, salinity,
density, large particle  concentrations (via OPC) and a number of
fluorescence parameters (from two  flashpacks and an AC9).  As the fish
undulates up and down, it is like painting  a mural of the upper water
column which is 300 meters high and over 1,200  kilometers wide.  In
addition, underway surface water measurements of nutrients,  pCO2, metals,
oxygen, salinity, phytoplankton species composition and abundance,
extracted chlorophyll, silicate uptake, DOC, fluorescence, currents (via
APDC)  and all the IMAT parameters, add richness to this painting.  The
picture that is  emerging is different from the first Survey cruise, now
three months ago, but  when taken together with the underway Process I
data, suggests an interesting  story.

        We had expected to see a strong surface manifestation of the APFZ
just  south of the subsurface expression detected between 60.5 and 61 S.
During  Survey I, surface water temperatures dropped almost 4 degrees
within sixty  kilometers, but nothing of the kind was to be seen.  Overall
surface water  temperatures are 2 degrees warmer north of the front and
there is a gradual  monotonic decrease in temperature dropping only 2
degrees C over the last three  hundred miles. Over this distance there is a
thin 20-30 m mixed layer overriding  a strong thermocline.  Presumably the
calm weather during Process I allowed for  the stratification of this water
column. Because of the lack of a strong frontal  system, the distance to
the sea ice, (where no "front" is guaranteed) and a  decreasing undulation
amplitude of the SeaSoar (decreasing travel of the push  rods on the
SeaSoar wings),  a decision to stop the SeaSoar at 2030 was made  this
morning. Silicates are back to 60 micromolar at this southernmost station.

 January 20

        We have pursued the notion that the transect south represents a
trip  backwards in time, relative to bloom formation, and we have
identified a region  of high plant biomass at about 64 deg 50 min S where
chlorophyll levels reached  2.7 micrograms per liter, pCO2 drops to 230
ppm, there is about a 7 micromolar  drawdown in nitrate and a strong
(almost two order of magnitude) gradient in  silicate!  Here the ocean is
green, for miles (it looks like someone dumped a  bunch of iron here).
Bottles lowered over the side can only be seen a few meters  underwater.
Long chains of chaetocerous and other diatoms clog the ring nets  and
Mocness, water samples processed with silver filters have almost too much
material to fit into the thorium detectors, and the main lab smells of
phytoplankton drying on filters in the oven.

        We are just beginning our third, in a series of, intensive vertical
profile station at 62 S on our transect northwards.  Some of the main
questions  driving our sampling strategy for this period have been: What
are the  differences between pre-bloom (67.5 S), bloom (64 50' S), and post
bloom (62 S)  waters?  What are the processes which act to control this
bloom?  What are the  differences in phytoplankton physiology and community
structure between these  regions? and  What turns the bloom on in the south
and off in the north?  An  examination of the Survey I and Process I
underway data indicate that this  feature has intensified in magnitude and
progressed southwards over the last  three months. The bloom is moving like
a wildfire consuming silicate as it  rages southwards.  What is curious is
that only a small amount of nitrate was  burned as the bloom passed.

        A sharp gradient in silicate from 2 micromolar at 64.8 S to over 50
at  65.5 S is found coincident with the bloom.  This silicate front has
migrated  about 5 degrees in the past three months. Values as low as 0.8
micromolar  are  scattered between values of one and two in the waters
south of  60 and north of  64.5, the region charred by the passing of this
bloom.  Where did the silicate  go and how did it leave without nitrate?
Nitrogen must be recycled much faster  that silicate in this system (no 1:1
drawdown here). But what turns the system  on and off? From the retreat of
the ice edge,  we postulate that the products of  melt water including
micronutrients and stratification serve to ignite the bloom  and silicate
or possibly iron limitation extinguish it.  We have initiated iron
enrichment experiments with waters collected south of the bloom, and will
collect water for another enrichment experiment tomorrow from waters north
of  the bloom.  We seek to see if a little iron will rekindle the blaze, we
will  also try to clean up some silicate for a comparable enrichment
experiment.

        Following this station, we will begin the first of two SeaSoar grid
surveys of the APFZ in the vicinity of 60.5 S.  This will last for
approximately  4.6 days and will be followed by another series of vertical
profile stations  within, and to the north of, the APFZ.  Time permitting,
I am strongly inclined  to revisit the bloom during this period, especially
if we can get the fast  repetition rate fluorometer to function properly.
The second series of vertical  profile stations will be followed by a
repeat of the first SeaSoar grid to  obtain a temporal description of the
physical dynamics of the frontal region. Spirits of both crew and
scientists are high, the weather is cold, wet and windy  but the seas are
cooperating.

        We hope you all are well in this new year.

Best regards,
Kenneth Coale
Chief Scientist JGOFS/AESOPS/APFZ Survey II