C^** Technique 



The carbon 14 method described by Stee- 

 mann-Nielsen (1952) has beenused exclusively 

 in these studies for the measurement of phyto- 

 plankton photosynthesis. 



The C^* was prepared from BaC" O3 in the 

 manner described by Steemann-Nielsen, ex- 

 cept that sulfuric acid was the acidifying agent 

 and that glass -redistilled water rather than 

 artificial sea water was the solvent for the 

 NajC^'^Oj. 



Two strengths of C-'-'^ were used. One con- 

 tained about 8 to 9 *ic. (microcurie) per mil- 

 liliter and the other about 1 to Z tic. per 

 milliliter. These solutions were adjusted to a 

 pH of 10.0 to 10.5, filtered through an HA or 

 PH Millipore filter, and placed in 1-, 5-, and 

 10-ml. glass ampules. The ampules were 

 sealed with cross-fire burners, inverted in a 

 solution of dye, and autoclaved for 30 minutes 

 at 15 lbs./in.2 pressure. Any ampules with 

 faulty seals were detected by the presence of 

 dye in the C-'-'^ solution and were discarded. 



Sample activity was measured by a Nuclear 

 Chicago Scaler (Model I6IA) with an automatic 

 sample changer (Nuclear Chicago, Model 

 CllOB) and Model D47 gas flow chamber 

 equipped with a Micromil window. Each sample 

 was counted until at least 1 ,280 disintegrations 

 (usually 2,560) had been detected, including 

 background (which averaged about 1 8 counts per 

 minute). Two carbon 14 standards and at least 

 two backgrounds were counted with each series 

 of 30 samples. The activity of the standards 

 was followed closely, and the samples re- 

 counted if the instrument showed any mechan- 

 ical aberration. The instrument was judged to 

 have malfunctioned whenever the disintegra- 

 tions per minute of one of the standard samples 

 exceeded two standard deviations of the mean 

 count of the standard. The mean value of the 

 standard was determined from 50 separate 

 measurements of the standard during which at 

 least 5,120 disintegrations were detected. One 

 would expect on the basis of chance alone to 

 have this limit exceeded in about 5 percent 

 of the cases. Nonetheless, samples were 

 rerun if this 2-standard-deviation linnit was 

 exceeded, for such a deviation might indicate 

 instrument malfunction. 



Computation of carbon uptake from the tracer 

 uptake was made in the conventional manner 

 (Steemann-Nielsen, 1952). The carbon dioxide 

 content of the water was assumed tobe constant 

 (90 milligrams per liter) at all stations. Cor- 

 rections for the isotope effect were made on all 

 samples but the respiration correction was not 

 made. Generally the dark-bottle uptake was 

 10 percent or less than the light-bottle uptake, 

 although the ratio of dark- to light-bottle 

 uptake was sometimes appreciably higher, 

 occasionally equaling 0.8 to 1.0. For instance, 

 on SCOT Expedition (Blackburn et al., 1962), 

 where this condition was particularly evident. 



8 of 31 productivity stations showed a high 

 ratio. The rather erratic appearance of such 

 results and the fact that the uptake in surface 

 and deep samples was somewhat high suggests 

 that on some occasions washing and rinsing of 

 the glassware left appreciable quantities of 

 bacteria in the incubation bottles. In other 

 situations SCOT Expedition stations 30, 74, 

 76, and 79) the ratio in the deepest samples 

 was reasonable, and only the surface samples 

 exhibited a high ratio. This erratic finding 

 suggests that the occasional C ampule con- 

 tained particulate radioactive material. 



Whenever the productivity index (light bottle 

 C-'-'^ uptake/chlorophyll^) fell in the range 2-8 

 per hour, the light-bottle data were used even 

 if the dark-bottle uptake was unreasonably 



high. ^^ 



The standardization of the C was carried 

 out by the method of Steemann-Nielsen (per- 

 sonal comnnunication). 



Standard solutions: 



(1) 0.1 M NaOH and 0.1 M NaNOj 



(2) 0.05 M Na2C03 



(3) 0.1 M BaCl2 • 2H2O 



One to three ampules from the same batch 

 of carbon 14 solution were taken at random 

 and the contents mixed together. Generally 1 

 ml. of this solution was diluted to 100 ml, with 

 distilled water, although the exact volume was 

 varied somewhat according to the activity of 

 the carbon 14 solution. Between 20 and 40 ml, 

 of this diluted carbon 14 stock solution was 

 placed in a 200-ml, volumetric flask. CO2 -free 

 distilled water was added to give a total volume 

 of 60 ml. Next, 20 ml. of Standard Solution 

 1 were added, followed by 40 ml. of Standard 

 Solution 2. The mixture was well shaken, and 

 finally 80 ml. of Standard Solution 3 were 

 added. The resultant precipitate was kept in 

 constant motion with a magnetic stirrer during 

 the preparation of the filters, and the flask 

 kept tightly stoppered except during withdrawal 

 of aliquots. 



Known volumes of the precipitate suspension 

 were withdrawn with wide -bore pipettes and 

 added to weighed 25. 4-mm. -diameter HA Mil- 

 lipore filters. The filter assembly was agitated 

 by hand while suction was applied to help in- 

 sure an even distribution of the precipitate 

 on the filter surface. The precipitate was 

 rinsed with 10 ml. of 0.001 M BaCl2 • 2H2O 

 while the filter assembly was again agitated. 

 The filters were placed in labelled perforated 

 cardboard pill boxes, and the boxes in turn 

 were placed in a vacuum desiccator over 

 freshly dehydrated silica gel. After drying 

 (24-36 hrs.), the filters were weighed and the 

 activity was measured with the counting equip- 

 ment described above. 



The volume of precipitate used in the stand- 

 ardization varied somewhat, but generally each 

 of the 0.1-, 0.2-, 0,6-, and 0.8- ml. aliquots was 

 duplicated, wheras 1 .0-, 2.0-, 3.0-, and 5.0-ml. 



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