Date: Tue, 03 Mar 1998 15:18:39 -0500

 

The following was received via fax from the Revelle this morning:

Feb. 28
As we were sending our last report the skies cleared and the winds
died.  We enjoyed almost 36 h of winds of only a few knots and clear,
and a few hours of sunny skies for parts of two days.  If this doesn't
fuel a bloom, what will?  As we left Mooring 4 (St. 7 for us), a
BLOOMIN' CONTEST was started to guess the latitude of the peak of the
bloom as determined from the underway fluorometer.  That night the
Aurora Austrailus put on a show for us as the pale lights waxed and
waned rapidly across the sky.

It was still calm the morning of 2/27 as we started to sample at
Mooring 5 (St. 9; 66S), but we started to get a few snow flakes that
grew to a light flurry and then the snow ceased.  It is definitely
surreal to deploy equipment when it is snowing, the sun is faintly
piercing through the clouds in the distance, a huge iceberg is nearby,
air temp is 0, the water is 1C, and we are looking for a plankton
bloom!  In the afternoon the winds kicked up to 20 kts, and by the next
afternoon the winds were back up to our familiar 30-40 kts.  Giant
icebergs hovered nearby at moorings 4 & 5.

Particle concentrations increased markedly at mooring 5 - the highest
we have had for the cruise, although fluorescence didn't exceed the
values measured at mooring 1.  Everyone reported more phytoplankton and
zooplankton in the water.  Yet the surface silica was up to 50 umol/kg
at this station.  S. Rubin's plot of the underway pCO2 showed much
higher surface values than along any of the 4 Survey II transects, and
values at mooring 5 (350 uatm) were as high as those reached south of
the bloom during Survey II.  It seemed possible that the bloom had
ended and that our task was to monitor the system as it progressed
after the bloom.  Still, we felt it was important to head further south
to see if there were any indications of blooming waters and to then to
do a long station in what appeared to be prebloom waters.  Why
hydrographic conditions prevail there?  What species and abundance of
phytoplankton, bacteria and zooplankton could be found and what were
their growth and grazing rates? Why wasn't it blooming?  After
Mooring 5 plans were to do hydro stations at 67.5, 69 and 70.5S to
assess conditions.  With our first report went a request to look at
SeaWiFS images to check for bloom conditions to the south since we had
some open skies.  This afternoon (2/28) Greg Mitchell sent a cartoon of
conditions from 160-180W and 50-72S, and it appeared that the best was
yet to come (thanks Greg and Walker!).

We are finishing the Mooring 5 station and will head south, although it
seems that we will not get to prebloom waters before we have to turn
around.  It is great to see that the chlorophyll highs and lows in the
SeaWiFS image match so well the highs and lows in the locations we have
sampled so far.  it is also reassuring to have information about what
lies ahead.

Evening
We have suspended over the side sampling at this site as winds are
gusting over 40 kts and the seas are heavy, so we are heading south.  A
sad note is that the primary productivity array was being recovered
under these rough conditions a few hours ago and only some of the
surface bottles and a PAR sensor were recovered before the line was
severed by the screw and Neptune extracted his dues.  One good in situ
deployment has been obtained and there is still enough equipment left
to try another floating array.  Most incubations, however, will be
restricted to the deck for the remaining stations, and right now we
have to request permission from the bridge to retrieve bottles from the
incubators due to the rough seas.

3/1, St. 10
We left St. 9 early because the weather was so bad we couldn't work over
the side.  It was rough all night.  They used night glasses on the
bridge to look for ice.  We came to the next hydro station (67.5S) just
after breakfast.  it was marginal for the CTD, but we got it in and
out, and didn't try the TMR.  The mixed layer was only 50 m.  Beam
attenuation was low and pCO2 high, yet silica was also still high (55
umol/kg).  According to the SeaWiFS image this should be in an area of
moderate (0.1-0.5 mg/m3) chlorophyll concentrations, but the image was
a composite from 10-15 days ago.  The icebergs at the last two stations
had been moving NE, so we assumed that the water in the SeaWiFS image
was moving ion the same direction and decided to steam SSE to look for
the bloom.  As we headed for 69S there were a couple of 20 km patches
with higher particle concentrations and lower pCO2.  Icebergs were
becoming abundant and Sunday morning we passed 1 mile from one very
tall berg we called the Cathedral because of the tall spire on one
side.  As night approached, visibility became very limited and the
sudden appearance of several small pieces of ice led us to stop for the
night and do what sampling we could with the intent of moving southeast
at daylight.


3/2
Daylight came along with pea soup fog- low visibility.  After waiting a
while for it to burn off, we steamed on a course of 145 deg.  The fog
cleared and we moved faster.  Fluorescence and beam attenuation started
to increase and pCO2 dropped.  Things really changed around noon and by
1500 fluorescence was twice as high as anything we had seen south of
the front.  pCO2 drooped to 270 uatm- by far the lowest of the cruise.
Surely this was the bloom.  However, our fourth rapid "bloom barometer"
was Helen Quinby's fluorescence microscope evaluations of the plankton
assemblage from the underway water samples.  "This is not the bloom"
she announced, and we moved on.  Fluorescence started to decrease, and
the fog had thickened, slowing us to 5 kts.  It was an opportune time
to start a long station, so measurements began at 70 deg., 24'S,
165deg, 55'W. There are plenty of Phaeocystis in the water, and some
healthy diatoms, but no species dominate as one might expect in a
bloom.  Silica, nitrate and phosphate have dropped slightly, but are
still high (silica is still at 55 umol/l).  The area is clearly patchy
as we sit here and the surface 50 m of water moves E or NE (based on
the ADCP), but all values are more extreme than anything else seen
south of the front.  As we speculated earlier, it may be that when
large areas of water suddenly were freed of ice, the bloom became much
more patchy rather than "burning" steadily southward.  Based on the
nutrients, fluorescence, and plankton assemblages, the system seems
more complicated than on earlier cruises.  Fortunately, the weather has
been excellent for 2 days (10-20 kt winds) and we hope to sneak south a
few more miles to see what is on the other side of the peak before we
return north.  Lots of good measurements are being made and report some
of those next time.

Wilf Gardner
Chief Scientist