Activities of nitrate assimilation and nitrate reduction were measured 50 cm above the ocean floor (5,845 m and 5,207 m) by an in situ 15N tracer technique at stations in the subtropical (28o29.8'N; 144~ and subarctic (44olO.2'N; 154~ western North Pacific Ocean. Nitrate assimilation ranged from 0.009 to 0.11 ~g-at N/ 1/day, and nitrate reduction from 0 to 0.42 Dg-at N/l/day in the presence of added peptone and yeast extract. Nitrate assimilation was higher than nitrite formation at the southern station, but the reverse was the case at the subarctic station. No correlation was observed between bacterial growth and nitrate metabolizing activities. Data are also presented on the effect of hydrostatic pressures upon nitrate metabolism by microbial populations in the surface waters.
Materials and Methods
Rubber bulbs (ca. 120 ml capacity) for J-Z bacteriological samplers (ZoBell and Morita, 1959) were used for collection and incubation of bottomwater samples. Rubber bulbs (2 to 3) were connected with glass tubing (outer diameter 5 mm, inner diamter 2 ram) (Figs. I and2). Two sets of samplers were attached to the frame of a deepsea pendulum-current meter (M. Okazaki, in preparation) approximately 50 cm above the bottom. Sampling of seawater was conducted by the action of a trigger lever on the current meter at Stations II (28o29.8'N; 144~ and 19 (44~ |54oO3'E). When the current meter landed on the ocean floor, the trigger lever (a, Fig. I) was forced upward about 30 cm. This action caused the attached copper wire (b, Fig. I) to break the curved portion of the glass tubing (c, Fig. I).
The operation of the trigger lever was checked photographically (Fig. 3).