US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS)

Palmer Leg 96-04a; October-November 1996

Documentation file for: THE HYDROGRAPHIC BOTTLE DATA 


L.A. Codispoti (lou@ccpo.odu.edu)
Old Dominion University, October 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 96-04a (October-November 1996). Dr. W. O. Smith of
the University of Tennessee was the chief scientist during this leg
(wosmith@utkux.utk.edu.  This cruise was the first 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". For example, the CTD system on this rosette was not
capable of the precision obtained from the system on the hydrographic
rosette, and Go-Flo bottles while superior for obtaining trace metal
clean samples, are not the bottles of choice for dissolved oxygen
values.  In addition, the handling system for the Trace Metal rosette
was cumbersome and, at times, freezing occurred in the water in the
Go-Flo bottles while this rosette was being "wrestled" into its wet
laboratory location.

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.

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, but this was
largely compensated for by comparing independent standards.            
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 or until the deck read-outs stabilized if this took more than
30 seconds.

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.

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.  Temperature of the thiosulfate and
standard solutions is 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 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 always
less than 0.25 micromolar, so the error would be <0.01 micromolar even
if the OSI nitrite standards were correct.  No ammonium standards were
available from OSI for intercomparison, but the ammonium concentrations
in the data reported from this leg are all quite low (<0.25 micromolar),
so it is unlikely that there will be any significant systematic errors
in excess of ~0.01 micromolar.  

The salinity of the low nutrient sea water
used to make nutrient standards was monitored during this cruise as was
the efficiency of the cadmium columns used in the nitrate analyses.  The
cadmium column efficiencies appeared to never fall below 97% during this
leg (PALMER96-04a).

Questions about these data may be addressed to:

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

e-mail:  lou@ccpo.odu.edu