Bottle and Pumpcast Data from the 1988 Black Sea Expedition MBARI Technical Report No. 90-3 Gernot E. Friederich Louis A. Codispoti Carole M. Sakamoto Monterey Bay Aquarium Research Institute 160 Central Avenue Pacific Grove, CA 93950 408-647-3700 Introduction This report contains inorganic nutrient chemistry, sulfide and oxygen data collected during cruises 2 through 5 of the 1988 Black Sea Oceanographic Expedition aboard the R/V Knorr. Continuous nutrient and sulfide data were obtained in the upper 375 m using a pumped profiling system. Discrete samples were collected from rosette-CTD casts. The corresponding physical oceanographic data have been presented by White et al. (1989). Although all of the data reported has been edited at least twice, errors may remain. We encourage queries and plan to distribute updates on electronic media if there are any non-trivial changes. Analysts Cruise 2: G.E. Friederich 14 May - 28 May 1988 Cruise 3: G.E. Friederich 3 June - 16 June 1988 Cruise 4: L.A. Codispoti and 21 June - 8 July 1988 G.E. Friederich Cruise 5: L.A. Codispoti and 13 July - 29 July 1988 J. Christensen Pump Casts The profiling pump system was based on a prototype described by Friederich and Codispoti (1987). A hydraulic winch was used to deploy 400 m of cable to which the pump and a Seabird SBE-9/11 CTD were attached. The winch was designed to give smooth lowering speeds from near 0 to 20 m per min. Tests during very calm conditions indicated that lowering speeds less then 6 m per min did not resolve any additional water column structure in the region of the highest gradients. Consequently lowering speeds of 6-10 m per min were used for the profiles presented in this report. The center of the pump cable was a continuous nylon hose with an internal diameter of 6 mm. The hose was surrounded by a Kevlar strength member; electrical conductors for data and power transmission formed the next layer. A Dacron braid formed the outer jacket. The pump was a stainless steel and graphite positive displacement vane pump, coupled to a submersible deep well pump motor. The flow rate of about 4 l per min resulted in a travel time through the pump tubing of about 3 minutes. Delay times for the entire system including the time for each chemical analysis were derived for each cast. Most delay times were obtained by stopping the pump/CTD system for a short time during a profile and then matching the plateau generated in the chemical profile with that of the CTD pressure readings. A few delay times were derived by injecting enriched water into the pump intake while it was held in a tank on deck. Data was recorded to disk from all chemistry channels and from the CTD every three seconds during each cast. All pump data was averaged in 1 decibar (db) bins. The complete 1 db data files are available on disk. For the purpose of this report data are given in 2 db increments between the surface and 150 db and in 5 db increments below 150 db. Inorganic Nutrients Nutrient analysis of both the pump profiles and the bottle samples were made using a computer controlled (Hewlett-Packard Series 85) Alpkem Rapid Flow Analysis (RFA) system. Ammonium, nitrite, phosphate and dissolved silicon measurements were made using slight modifications of the methods described by Whitledge et al.(1981). Nitrate was measured using a slight modification of the method supplied by Alpkem which is based on the work of Patton (1982). In order to eliminate the interference of sulfide in the analysis of phosphate, dissolved silicon and ammonium; bottle samples from the anoxic zone were stripped with nitrogen for about 20 min. The amount of potassium antimony tartrate in the phosphate analysis was doubled in order to reduce sulfide interference. Nitrate levels decreased to undetectable levels just above the sulfide bearing waters and it was therefore not necessary to measure nitrate in the sulfidic waters. Nitrate analysis were occasionally performed on stripped samples from sulfide bearing waters near the oxic/anoxic interface to confirm the absence of nitrate in sulfidic water. During pump casts, the only precautions taken for sulfide interference were disconnecting the nitrate channel at about the depth were sulfide first appeared and the doubled potassium antimony tartrate concentration used in the phosphate analysis. Intercomparisons between pump and bottle data suggested that other precautions were not necessary for the sulfide concentrations encountered during pump casts. Sulfide Continuous sulfide determinations were made from the pump stream using a continuous flow adaptation of the method developed by Cline (1969). Samples from the rosette casts, however, could not be analyzed with this method since considerable loss of sulfide occurred in the interval between sampling and analysis (< 15 min.). Oxygen Dissolved oxygen concentrations in bottle samples were measured using the Chesapeake Bay version of the Winkler titration (Carpenter, 1965). During some pump casts the low concentration colorimetric method of Broenkow and Cline (1969) was employed at concentrations less than 25 æM on discrete samples collected during the pump cast. When collecting these samples the pump was held at selected depths for about 5 minutes to ensure complete flushing of the pump tube. CTD The CTD system on the pump package was a Seabird SBE-9/11 identical to the one used on the rosette system. During cruise 4 and 5 a Sea Tech transmissometer was added to the pump package. Each CTD data record taken during the pump casts consisted of an average of six scans taken over a period of 0.25 seconds. Data Quality CTD data listed with the bottle casts was taken from the upcast of the rosette-CTD system. These data have not been corrected for the drift of the CTD as given by White et al. (1988). The above omission should cause errors smaller than 0.0025 Deg. C in temperature and 0.005 ppt. in salinity During these cruises leaking bottles and out of sequence tripping of bottles on the rosette were encountered. We hope to have eliminated most of the data points plagued by these problems. The CTD system coupled to the pump was calibrated before the cruise but it was not possible to perform a post cruise calibration. Comparison with the rosette-CTD system and occasional salinity determinations of pumped water on an Autosal salinometer indicated that the data are reliable to at least .01 deg. C in temperature and .01 ppt. in salinity. Due to the large range of phosphate, dissolved silicon, ammonium and sulfide concentrations, the detection limit for these methods was larger than for more typical marine environments. Ammonium data in the oxygenated zone are unlikely to have any meaning since concentrations were of the same magnitude as the noise. An additional problem that degraded data quality was the interference of sulfide in the analysis of phosphate and to a lesser extent in the analysis of dissolved silicon and ammonium. The extra manipulation necessary to remove excess sulfide from the samples prior to analysis increased the risk of contamination and sample degradation. Another problem that effected some of the dissolved silicon data was the poor control of laboratory temperature which could vary as much as 15 deg. C over the course of a few hours. At all times at least two independent nutrient standards were maintained and intercomparisons of the various standards used during these cruises assured the absence of any systematic calibration errors. In addition to the full calibration curves, most analytical runs were accompanied by single point standards that could be used to correct drift due to such factors as temperature. In a few instances dissolved silicon data was normalized using deep samples from the same location as internal standards. Sulfide standards were titrated with thiosulfate and simultaneously analyzed in the RFA system. The estimates for accuracy given in the table below are a best estimate based on replicate standards, replicate deep samples, comparisons on isopycnal surfaces and our knowledge of various analytical problems encountered during these cruises. Richard Mortlock provided us with results from his high precision phosphate analysis to help in our assessment of data quality. These comparisons suggest: Detection High Range Analysis Range (æM) Limit (æM) Error (+/- æM) ---------------------------------------------------------------------- Ammonium 0 - 100 0.5 2 Nitrate 0 - 10 0.05 0.2 Nitrite 0 - 5 0.02 0.1 Phosphate 0 - 10 0.05 0.2 Silicon 0 - 350 2 10 Sulfide 0 - 200 1 10 At intermediate values the expected error should be between the detection limit and the high range error. Due to the method of assessment the high range error cannot be expressed as a statistical quantity, but it should be roughly equivalent to one standard deviation. Due to the configuration of the pumping system during cruise 5 a systematic offset appears to have been introduced to the ammonium profiles during cruise 5. The pump profiles on this disc have been corrected for this offset. Acknowledgements This research was supported by National Science Foundation grant OCE-8614400. Financial support was also provided by the Monterey Bay Aquarium Research Institute. We thank the crew of the R/V Knorr for their assistance during the field work and their help in the repair of mechanical problems. C. Goyet assisted with some of the initial colorimetric oxygen determinations. A.Gough's secretarial assistance is also much appreciated. References Carpenter, J.H. (1965) The Chesapeake Bay Institute technique for the Winkler dissolved oxygen method. Limnol. Oceanogr., 10, 141-143. Broenkow, W. W. and J.D. Cline (1969) Colorimetric determination of dissolved oxygen at low concentrations. Limnol. Oceanogr., 14, 450-454. Cline, J.D. (1969) Spectrophotometric determination of hydrogen sulfide in natural waters. Limnol. Oceanogr., 14, 454-458. Friederich, G. E. and L. A. Codispoti (1987) An analysis of continuous vertical nutrient profiles taken during a cold-anomaly off Peru. Deep-Sea Research 34, 1049-1065. Patton, C. J., Doctoral Dissertation, Michigan State University, 1982, pp. 87-121 White, G., M. Relander, J. Postal and J. W. Murray (1989) Hydrographic data from the 1988 Black Sea Oceanographic Expedition. University of Washington School of Oceanography Special Report No. 109. Whitledge, T. E., S. C. Malloy, C. J. Patton and C. O. Wirick (1981) Automated nutrient analysis in seawater. Brookhaven National Lab Report 51398, 216 pp. Table of Units Hydrocast Sequential cast number used by White et al.(1989) Pumpcast Sequential pumpcast number Latitude In degrees and decimal degrees Longitude In degrees and decimal degrees Date Greenwich Julian day and decimal day Depth Pressure in decibars Temperature In degrees Celsius Salinity In practical salinity units Sigma-t In kg per cubic meter Light transmission Per cent transmission at 660 nm Oxygen In milliliters of oxygen per liter at NTP or micro molar (ml O2/l = .0224 x æM) Low Conc. Oxygen Micro molar Phosphate Micro molar reactive phosphorous Dissolved Silicon Micro molar Nitrate Micro molar (corrected for nitrite) Nitrite Micro molar Ammonium Micro molar Sulfide Micro molar Null values -999 (any 0 in %transmission also indicates no data)