US JGOFS Antarctic Environments Southern Ocean Process Study (AESOPS) Palmer Leg 97-01; January-February 1997 Documentation for: The Trace Metal Rosette 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 the trace metal rosette that was equipped with 8 ~30-liter "Go-Flo" bottles during Palmer leg 97-01 (January-February, 1997). Dr. John Marra of the Lamont Doherty Earth Observatory of Columbia University was the chief scientist during this leg (jmarra@ldeo.columbia.edu). This cruise was the second 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. At times, bottle "firing" and data acquisition/processing problems also complicated the interpretation of the data from the trace metal rosette, and the trace metal rosette data from this leg underwent significant post-cruise editing. 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. IN ADDITION, IT SHOULD BE NOTED THAT SOME OF THE INITIAL TRACE METAL DATA ROSETTE DATA PRODUCED DURING THE CRUISE CONTAINED SIGNIFICANT DATA ACQUISITION AND PROCESSING ERRORS. 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 degrees 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. 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, BUT THE RELATIVELY CALM CONDITIONS ON THIS CRUISE MAY HAVE PREVENTED COMPLETE FLUSING OF THE GO-FLO BOTTLES DESPITE THE 30 SECOND SOAK TIME. NORMALLY, INCOMPLETE FLUSHING WOULD MEAN THAT THE BOTTLE CONTAINED A MIXTURE OF WATER FROM THE DESIRED SAMPLING DEPTHS AND FROM DEEPER DEPTHS. EXAMINATION OF PAIRED BOTTLE AND CTD SALINITIES FROM THE HYDROGRAPHIC ROSETTE SUGGESTED THAT INCOMPLETE FLUSHING OF THE 10 LITER BULLISTER BOTTLES USED ON THAT ROSETTE OFTEN CREATED MIXTURES OF WATER WITH EFFECTIVE DEPTHS A FEW METERS DEEPER THAN THE ACTUAL SAMPLING DEPTH. IN THE CASE OF THE HYDROGRAPHIC ROSETTE MOST OF THESE OFFSETS WERE LESS THAN 5 METERS, BUT FLUSHING OF THE 30 LITER GO-FLO BOTTLES ON THE TRACE METAL ROSETTE MAY HAVE BEEN POORER. PAIRED CTD AND BOTTLE SALINITY DATA MAY BE OF SOME HELP IN ADDRESSING THIS FLUSHING PROBLEM BUT THE CTD DATA FROM THE TRACE METAL ROSETTE HAVE NOT YET BEEN CORRECTED FOR "SPIKING" THAT CAN OCCUR IN GRADIENTS AND FOR AN OFFSET OF ABOUT 0.02 TO (BOTTLE SALINITIES MINUS TRACE METAL CTD SALINITIES) IN THE TRACE METAL CTD DATA. Salinity: Salinities were determined with Guildline Autosal salinometers using JGOFS protocols. 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 trace metal rosette's CTD salinities which are also reported here in the absence of significant flushing or spiking problems (see above). Freezing in the Go-Flo bottles can also cause bottle salinities to be higher than the CTD values, but the cruise notes do not suggest that this was a problem on this leg. 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. 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. During an earlier Palmer Leg (96-04a) nutrient standards provided by Dr. Gordon's group were compared with standards from the Ocean Data Facility (ODF) Group at Scripps and with standards purchased from Ocean Scientific International (OSI) Leg 96-04a. 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. Because of the concentration of effort over the Ross Sea shelf and the season, significant amounts on nitrite and ammonium could occur throughout the water column. Therefore, the usual method of looking at deep-water values to assess nitrite and ammonium baselines could not be employed. Thus, there may be some baseline uncertainties in nitrite and ammonium concentrations that would result in 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 unlikely to effect the results reported here by more than ~1%. Because of the low nitrite concentrations and Cd column efficiencies that appeared to be always greater that 95%, the nitrate data from this cruise are not significantly affected 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