in 0-100 m layer 



Station 115 Station 1 16 Siaiton H7 Siaiion 1 18 SlMion 1 19 StMion 120 



.U 



n h _Q 



Suiiiin 1 15 Sluiion I Ift Station 1 17 Suihon I IH Suimn 1 19 SlMion 120 



in 500-2.000 m layer 



D 



Sluiion I IK Suimn ll>) 



I I BjLlcnjI priwluumn 

 Klug C/l/duy [v]] Orgunn nulla dcgrjduiii] 



Fig. 4. Bacterial production and organic-matter degradation in the equatorial 

 Pacific. 



104.4 jag C 1 ' d ' at Station 1 19. The average rate of bacterial 

 organic matter degradation in the0-100-m layer in this part of 

 the Pacific equaled 75.5 ug C 1 ' d '. The P/B coefficient for 

 microflora in the 0-100-m layer averaged 2.9, which was 

 somewhat higher than the value previously obtained by Sorokin 

 (1973). The average value of the P/D coefficient was 0.31. 



Maximum microfloral activity in the 0-100-m layer 

 occurred at a depth of 25 m. The rate of assimilation in darkness 

 here attained a level typical of mesotrophic waters, averaging 

 1.94 ugC I'd'. The respiratory oxygen uptake by microflora 

 also showed peak values, averaging 0.28 mg/1 — a finding that 

 is in good agreement with that of Sorokin ( 1973). The rate of 

 bacterial degradation of organic matter in the euphotic zone 

 reached maximum levels on the order of 103.9 ug C 1 ' d ' 

 (Fig. 4). 



The activity of microflora in the 100-250-m layer was 

 somewhat lower compared with the euphotic zone. The rate of 

 CO, assimilation in darkness averaged 1.10 |ig C 1' d'. 

 Bacterial biomass production was lower than in the top layer by 

 an average factor of 1.2. The bacterial degradation rate 

 averaged 58.0 Ug C 1 ' d '. The P/B coefficient was 2.2, the 

 P/D coefficient, 0.3 1 . 



Bacterial activity diminished sharply at depths exceeding 

 250 m. The rate of bacterial biomass production in the 

 500-2, 000-m layer was. on the average, almost five 

 times lower compared with the upper layers of the water 

 column, ranging from 2.5 to 5.5 |lg C 1 ' d ' and averaging 

 4.2 ug C 1 ' d "'. The bacterial degradation rate decreased more 

 than fivefold compared with that of the euphotic zone. This 

 decreased rate of degradation was clearly attributable to lower 

 temperatures. The P/B coefficient in the 500-2,000-m layer 

 was 0.7. The water column at 500-2,000 m was found to 

 include two layers of heightened activity, one at 1,000 m, the 

 other at 2,000 m. However, bacterial production and degradation 

 rates in these maximum-activity layers did not attain the 

 average values characteristic of the top layer. 



The next transect lay along 10°N in the western Pacific 

 (Frontispiece). The waters in this area exhibited lower 

 productivity as compared with those of the equatorial portion 

 of the central Pacific. The level of development of 



microbiocoenoses at most of the stations corresponded to the 

 upper limit of productivity for oligotrophic waters. The bacterial 

 population density in the 0-100-m layer ranged from 129 to 

 545 x 10 1 cells/ml 1 (Figs. 5-7). The highest bacterioplankton 

 concentration occurred at Station 123, where the average count 

 and biomass reached 387 x 10-' cells/ml ' and 8.7 ug C 1 ' d '. 

 The highest microfloral activity was observed at Station 121, 

 where the rate of CO, assimilation by bacterioplankton averaged 

 1.76 Ug C 1 ' d "', which corresponds to the upper limit for 

 oligotrophic waters. The lowest microfloral activity was noted 

 at Station 122. The daily rate of CO, assimilation in darkness 

 here was 3.4 times less than at the preceding station. 



Bacterial biomass production in the 0- 1 00-m layer ranged 

 from 2.1 to 52 ug C 1 ' d ' (Fig. 8). The oxygen uptake due to 

 bacterioplankton respiration averaged 0.12 mg/1. The rate 

 of organic matter degradation by bacteria lay in the 

 27-94-ug C 1' d ' range, with an average value of 

 47 ug C 1 ' d '. The P/B coefficient was 2.3. 



The portion of the water column lying below the 

 thermocline (150-500 m) exhibited relatively low bacterial 

 population levels. The total bacteria counts here ranged from 

 109 to 492 x 10' cells/ml', the biomass from 3.9 to 

 7.7 ug C 1 ' d "'. The mean bacteria count and biomass for the 

 150-500-m layer turned out to be 237 x 10- cells/ml' 

 and 5.3 Ug C 1' d ', respectively. The microfloral activity 

 was somewhat lower than in the supernatant 100 m of the 

 water column. The rate of CO, assimilation by bacteria in 

 darkness ranged from 0.12 to 1.36 ug C 1' d\ averaging 

 0.62 ug C 1 ' d ' . The most intense microfloral activity occurred 

 at Station 125, where the mean CO, assimilation rate reached 

 0.78 ug C 1 ' d ' . The lowest rate of 0.47 ug C 1 ' d ' corresponded 

 to Station 122. 



The bacterial biomass production rate turned out to be 1 .5 

 times lower than in the 0-100-m layer. Oxygen uptake due to 

 bacterioplankton respiration in the 150-500-m layer averaged 

 0.08 mg/1, indicating a relatively low rate of degradation. The 

 degradation rate OB ranged from 25 to 42 ug C 1' d '. with an 

 average value of 33 ug C 1 ' d '. 



A trend towards increased bacterial population densities 

 was noted in the deeper ( 1 .000-2,000 m) portion of the water 

 column. For example, the total bacteria counts at 2,000 m 

 for Stations 1 2 1 and 1 22 were much higher than further up 

 the water column. Some increase in bacterioplankton 

 concentrations was likewise noted at 1,500 m at Stations 123 

 and 125. The average total bacterial count and biomass for 

 the 1,000-2,000 m layer was 281 x 10' cells/ml' and 

 6.3 ug C I ' d '. respectively. These values were quite closely 

 comparable with the data for the 0-100-m layer. 



The results showed that microfloral activity in the 

 deeper portions of the water column was suppressed by 

 low temperatures and high pressures. The rates of CO, 

 assimilation by bacteria in darkness for the 1 ,000-2,000-m 

 layer ranged from 0.11 to 0.42 ug C 1' d ', averaging 

 0.22 ug C 1 ' d '. Bacterial biomass production was, on the 

 average. 2.8 times lower than in the 150-500-m layer. 

 Oxygen uptake due to bacterioplankton respiration averaged 

 0.03 mg/1. The rate of degradation of organic matter was 

 minimal, the average value for the layer being 12 ug C 1 ' d '. 

 The P/B coefficient was 0.5. 



209 



