US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS) Palmer Leg 97-08 November-December 1997 Documentation for: THE HYDROGRAPHIC BOTTLE DATA L.A. Codispoti (lou@ccpo.odu.edu) Old Dominion University, July 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 97-08 (November-December 1997). Dr. Walker Smith of the Virginia Institute of Marine Sciences (wos@vims.edu) was the chief scientist during this leg. This cruise was the fourth 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". These trace metal rosette data have been submitted to the U.S. JGOFS data base as a separate file. Some questionable data are not included in this report. These data together 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 instruments 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 method somewhat similar to 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.). Details about the ammonium method and about other aspects of the nutrient analyses protocols may be obtained by contacting Dr. Louis I. Gordon of Oregon State University (lgordon@oce.orst.edu). 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, 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 ~1 METER ABOVE THE CTD SENSORS. THE DATA HAVE NOT BEEN CORRECTED FOR THIS OFFSET. 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 6 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 LARGER APPARENT OFFSETS, BUT IT IS POSSIBLE THAT SOME OF THESE COULD ARISE FROM OTHER CAUSES SUCH AS ERRORS IN THE DETERMINATION OF SALINITY. 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. Dissolved oxygen: The Winkler dissolved oxygen apparatus 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 purchased 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 OSI nitrite standard signals to be 4% low relative to OSU nitrite standards. We believe that the OSI nitrite standards were in error, but in any event, nitrite concentrations in the water column observations rarely exceeded 0.25 micromolar, so any errors arising from systematic errors in standards are likely to be less than 0.01 micromolar. Because of the concentration of observations over the Ross Sea Shelf, 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. Cd column efficiencies appeared to be 97% or greater throughout this leg above). Because of the high Cd column efficiencies and low water column nitrite values (generally less than 0.25 micromolar), it was not necessary to correct for Cd column efficiency when subtracting nitrite values from the nitrate plus nitrite analyses to obtain nitrate concentrations. Queries: Questions about these data may be addressed to: Dr. L.A. Codispoti CCPO Old Dominion University Norfolk, VA 23529 lou@ccpo.odu.edu