US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS)
 
Palmer Leg 97-03; April-May 1997
 
Documentation for: THE HYDROGRAPHIC BOTTLE DATA 


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

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 97-03 (April-May 1997). Dr. Hugh Ducklow of the
Virginia Institute of Marine Sciences (duck@vims.edu) was the chief
scientist during this leg. This cruise was the third 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. 

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. 7) The JGOFS protocols do not
describe an automated technique for the analysis of ammonium
concentrations.  We employed the Berthelot reaction using a
modification of the method 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.).

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. NOTE THAT THE BULLISTER BOTTLE IN THE NUMBER 5 POSITION
(NB10B025) ON THE HYDROGRAPHIC ROSETTE WAS FOUND TO HAVE BLACK SPIGOT
O-RINGS UP TO AND INCLUDING STATION 16 CAST 6.  THIS SHOULD HAVE NO
EFFECT ON THE HYDROGRAPHIC DATA REPORTED HERE, BUT ANY BIOLOGICIAL
INCUBATION SAMPLES TAKEN FROM THIS BOTTLE COULD BE SUSPECT.

Because there is little or no lag time between triggering a bottle and
bottle closure with the new SeaBird rosette systems, our sampling
protocols request that bottles be 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 CONDITIONS ON THIS CRUISE OFTEN PREVENTED
COMPLETE FLUSHING OF THE BULLISTER BOTTLES DESPITE THE REQUESTED 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 APPARENT 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.  THERE WERE A FEW APPARENT OFFSETS OF ABOUT 10 METERS BUT THE
DIFFERENCES IN APPARENT DEPTH WERE SELDOM GREATER THAN 5 METERS AND IN
MOST CASES SIGNIFICANTLY LESS THAN 5 METERS. 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
0.02 (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, but we note that the initial
salinity data from the primary CTD sensors drifted by about 0.01
during this cruise. Both the corrected CTD salinity data collected 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.

During PALMER leg 96-04a, 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). Interested parties 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 signals to be ~1% high relative
to the OSU standards,and 4% low relative to OSU nitrite standards.  We
believe that the OSI nitrite standards were in error. NOTE THAT DURING
THIS LEG (PALMER 97-03), MAJOR PROBLEMS WERE ENCOUNTERED WITH NITRITE
STDS. WE HAVE CORRECTED THE NITRITE DATA TO AN ACCURACY OF ABOUT 10%
DURING POST-CRUISE DATA PROCESSING. SINCE WATER COLUMN NITRITE VALUES
WERE GENERALLY LESS THAN ~0.25 MICROMOLAR MAXIMUM REMAINING ERRORS IN
THE WATER COLUMN NITRITE DATA ARISING FROM THIS PROBLEM SHOULD BE ON
THE ORDER OF 0.02 TO 0.03 MICROMOLAR. Nitrate concentrations have been
adjusted for the changes in nitrite values since nitrate is obtained 
by subtracting nitrite from the results of the nitrate+nitrite
analysis. 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 for ammonium and less than ~0.02 micromolar for nitrite.
Tests of the salt effect in the ammonium analysis during this cruise
suggested that it was negligible for the water column values reported
here, but this may not be the case for specialized incubation and ice
samples. Most Cd column efficiencies appeared to be >95%, but
correction factors were applied to the data from stations 06 casts 03,
04, and 06 (Cd column efficiency = 0.7), and from station 19 cast 01
(Cd column efficiency = 0.86) because of low Cd column efficiencies and
the use of mixed working standards. These standards contained between
30 to 31 micromolar nitrate and between 1 to 2 micromolar nitrite
depending on the state of degradation of thenitrite standards which
were being oxidized to nitrate during this cruise (the nitrite problem
alluded to above).  Water column nitrite values were so low (generally
less than 0.2 micromolar) that it was not found necessary to correct
for Cd column efficiency when subtracting nitrite values from the
nitrate plus nitrite analyses to obtain nitrate concentratrions.

Queries:

Questions about these data may be addressed to:

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

lou@ccpo.odu.edu