US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS)
 
Palmer Leg 97-01; January-February 1997

Documentation for: THE HYDROGRAPHIC BOTTLE DATA 


L.A. Codispoti (lou@ccpo.odu.edu)
Old Dominion University, November 1997

General Comments:

This "readme" file pertains to the salinity, dissolved oxygen, and
nutrient data taken from sampling bottles with the hydrographic
rosette that was equipped with 24 ~10-liter "Niskin-like" Bullister
Bottles made mostly of PVC and equipped with orange silicone o-rings
during Palmer leg 97-01 (January-February 1997). Dr. John Marra of
the Lamont Doherty Earth Observatory of Columbia University
(marra@lamont.ldeo.columbia.edu) was the chief scientist during this
leg. This cruise was the second process study leg of the U.S. JGOFS
program in the Southern Ocean (AESOPS). Several casts with a Trace
Metal clean rosette equipped with 8, 30-l Go-Flo bottles were also
taken during this leg, but they are not reported here because this
system was not designed to produce hydrographic data of "WOCE
quality".

Some questionable data are not included in this report. These data
together with data from the trace metal casts are retained in files at
Old Dominion University and are available upon request. In particular,
several casts had questionable bottle salinity (Autosal) data. In
addition, reactive silicate (a.k.a. silicate, silicic acid or
dissolved silicon) data from several casts have not been submitted
because of excessive baseline drift even though these data might be
useable for some purposes.

No units are given for salinity in this report because the most recent
definitions of salinity define it as a dimensionless number.  To
accommodate every preference, Winkler oxygen values are reported in
ml/l, micromolar and micromoles per kg.  The latter values can only be
calculated with a knowledge of the oxygen sample temperatures when the
samples were drawn. These "draw temperatures" are not reported here,
but can be obtained by contacting lou@ccpo.odu.edu.  Nutrient values
are reported in micromolar. They can be converted to micromoles per
kg, by combining laboratory temperature on the Palmer (approx. 21
deg C during this leg) and the salinity of the sample to compute
density and then dividing the value in micromolar by this number.

Methods:

In general, the methods employed for the bottle salinity, Winkler
dissolved oxygen, and nutrient analyses did not differ significantly
from those described in the JGOFS protocols that were distributed in
1994 (UNESCO, IOC Manual and Guide #29). Minor differences included
the following: 1) Sea Bird CTD systems and bottle carousels were
employed (SBE-9+ underwater units, SBE-11 deck units, SBE-32
carousels).  These units represent a newer generation of equipment
than the units described in the JGOFS protocols.  2) The weights of
the salts used for primary standards for dissolved oxygen were not
adjusted to an "in vacuo" basis as suggested in the protocols. It is
unlikely that this departure from procedure would cause significant
errors. Our calculations suggest that the maximum differences arising
from our decision to not correct to an "in vacuo" basis would be 0.02%
3) The protocols give one a choice of adjusting nutrient methods so
that calibration curves are strictly linear, or opting for more
response and taking into account non-linearities.  We choose the
former method.  4) No corrections were made for "carryover" between
nutrient samples run on the Technicon Autoanalyzer. Carryover effects
in our nutrient analyses are generally less than ~2% of the
concentration difference between adjacent samples, and were minimized
by arranging samples in depth order and by running duplicate samples
in some cases.  5) Calibration and re-calibration of volumetric ware
were not exactly as described in the JGOFS protocols.  6)Duplicate
oxygen samples were not routinely drawn.

Temperature:

The temperature data associated with each bottle depth were taken by
the CTD system during the bottle tripping process.  Consult the
companion CTD data report for this cruise to learn more about the CTD
system.

Sampling:

The samples in this report were taken from ~10 liter Bullister
bottles. 

Because there is little or no lag time between triggering a bottle and
bottle closure with the new SeaBird rosette systems, bottles were
generally held at the sampling depth for at least 30 seconds before
tripping. 

NOTE THAT THE MID-POINT OF THE SAMPLING BOTTLES WAS 0.8 METER ABOVE
THE CTD SENSORS.  THE DATA HAVE NOT BEEN CORRECTED FOR THIS OFFSET.

MORE IMPORTANTLY, THE CALM CONDITIONS ON THIS CRUISE MAY HAVE
PREVENTED COMPLETE FLUSHING OF THE BULLISTER BOTTLES DESPITE THE 30
SECOND SOAK TIME. EXAMINATION OF BOTTLE VS CTD SALINITIES IN GRADIENTS
SUGGEST THAT THE BOTTLES OFTEN RETAINED SOME DEEPER WATER WHEN
THEY WERE TRIPPED AND HAD EFFECTIVE DEPTHS A FEW METERS DEEPER THAN
THE CTD PROBE.  IN GENERAL, THE SALINITY DIFFERENCES COULD BE
EXPLAINED BY DEPTH OFFSETS OF 5 METERS OR LESS FROM THE CTD PROBE
ASSUMING THAT ALL OF THE WATER IN THE BOTTLE CAME FROM THE DEEPER
DEPTH. IN FACT, THE BOTTLE WOULD HAVE CONTAINED A BLEND OF WATER FROM
DEPTHS ABOVE AND BELOW THE CTD SENSOR BUT WITH AN APPARENT BIAS
TOWARDS THE DEEPER DEPTHS.  USUALLY THE DIFFERENCES IN EFFECTIVE DEPTH
WERE SIGNIFICANTLY LESS THAN 5 M, AND SHOULD HAVE LITTLE EFFECT ON THE
OXYGEN AND NUTRIENT DISTRIBUTIONS ARISING FROM THE BOTTLE DATA. BY
COMPARING BOTTLE AND CTD SALINITY DATA IN HIGH GRADIENT REGIONS, THE
USER CAN ASSESS THE IMPORTANCE OF THIS EFFECT FOR A PARTICULAR CAST.

Salinity:

Salinities were determined with Guildline Autosal salinometers. New
vials of standard sea-water were used to standardize before and at the
end of every run. Agreement between bottle salinities and the recently
calibrated sensors on the Sea Bird CTD systems was usually better than
0.01 (except in regions of strong gradients) before post-cruise data
processing which employs the bottle salinities to correct the CTD
salinities. More information on the quality of the salinity data are
given in the companion CTD report.  Both the CTD salinity data at the
time of bottle tripping and the salinities run on the Niskin bottle
samples with an Autosal salinometer are reported here.

Dissolved oxygen:

The Winkler dissolved oxygen set-up was built and supplied by the
SIO/ODF group.  This system is computer controlled and detects the
end-point photometrically.  Temperatures of the thiosulfate and
standard solutions are automatically monitored by this system.  


Nutrients:

Note that the terminology used to describe nutrients has become
somewhat loose over the years and that silicate=silicic acid,
dissolved silicon or reactive silicate, and phosphate=reactive
phosphorus.

Nutrient analyses were performed on a 5-channel Technicon II AA system
that was modified and provided by Dr. Lou Gordon of Oregon State
University.

The nutrient standards provided by Dr. Gordon's group were compared
with standards from the Ocean Data Facility Group at Scripps and with
standards purhased from Ocean Scientific International (OSI). The
results of these comparisons were good. Interested users may contact
Dr. Louis I. Gordon (lgordon@oce.orst.edu) if they are interested in
the details of these intercomparisons.  The only notable differences
were a tendency for the OSI silicate values to be ~1% high relative to
the OSU standards, and 4% low relative to OSU nitrite standards.  We
believe that the OSI nitrite standards may be in error, but in any
event nitrite values in the data reported from this leg were never
greater than 0.25 micromolar, so the error would be 0.01 micromolar or
less even if the OSI nitrite standards were correct. No ammonium
standards from OSI were available.  The maximum ammonium concentrations
on this leg was about 4 micromolar, so a 5% error in a standard (which
is unlikely) would cause a maximum error in ammonium of 0.2
micromolar. Because of the concentration of effort over the Ross Sea
shelf and the season, significant amounts of nitrite and ammonium could
occur throughout the water column, and the usual method of looking at
deep-water values to correct nitrite and ammonium baselines could not
be employed.  Thus, there may be some baseline uncertainties in nitrite
and ammonium concentrations that would induce errors of less than ~0.1
micromolar. Tests of the salt effect in the ammonium analysis during
this cruise suggested that it was unlikely to effect the results by
more than ~ 1%. Because of the low nitrite concentrations and Cd column
efficiencies that appeared to be always greater than 95%, the nitrate
data from this cruise are not significantly effected by changes in Cd
column efficiency.

Queries:

Questions about these data may be addressed to:

Dr. L.A. Codispoti
CCPO
Old Dominion University
Norfolk, VA 23529

lou@ccpo.odu.edu