US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS)

Palmer Leg 96-04a; October-November 1996

Documentation file for: TRACE METAL Rosette Hydrographic Bottle Data 
LEG 96-04a

L.A. Codispoti (lou@ccpo.odu.edu)
Old Dominion University,  June 1998



General Comments:

This "readme" file pertains to the salinity, dissolved oxygen, and nutrient
data taken from sampling bottles with the trace metal rosette that was equipped
with 8 ~30-liter "Go-Flo" 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).  The CTD system on the trace
metal 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 obtaining hydrographic
(salinity, oxygen, and nutrient) data.  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.  At times, bottle "firing" problems also complicated
the interpretation of the data from the trace metal rosette.  BECAUSE THESE
DATA FROM THE TRACE METAL ROSETTE ARE NOT OF THE SAME QUALITY AS THE DATA FROM
THE HYDROGRAPHIC ROSETTE, THEY SHOULD BE MAINTAINED IN A SEPARATE FILE.

Some questionable data are not included in this report.  These data 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) The weights of the
potassium iodate 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%.  2) 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.  3) 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.  4) 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.  5) Duplicate oxygen samples were not routinely drawn.  6) The JGOFS
protocols do not describe an automated technique for the determination of
ammonium concentrations.  We employed the Berthelot reaction using a method
somewhat similar to that described by Whitledge et al. (1981, Whitledge, T.E.,
Malloy, S.C., Patton, C.J. and Wirick, C.D. Automated Nutrient Analyses in
Seawater. Brookhaven National Laboratory Rept. BNL 51398, 216pp.).  Details on
this method can be obtained from Dr. Louis I. Gordon (lgordon@orst.oce.edu).


Temperature:

The temperature data associated with each bottle depth were taken by the CTD
system during the bottle tripping process.


Sampling:

The samples in this report were taken from ~30 liter Go-Flo bottles. 

Bottles were generally held at the sampling depth for at least 30 seconds
before tripping. 


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. 
These bottle salinities were in general about 0.02 higher than the CTD
salinities which are also reported here except in cases where freezing in the
Go-Flo bottles caused the differences to be greater.  


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 here
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 here 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

lou@ccpo.odu.edu