Figure 5. Results of diel periodicity experiments showing nitrification rates from five depths in the photic zone at station 67–70, incubated under in situ light conditions or in complete darkness for 24 h.

(A) Surface photosynthetically active radiation (sPAR) during the experiment, with sampling intervals denoted by vertical hashed lines; (B) rates of nitrification at each sampling interval in surface waters (2 m) held at 90% sPAR or in the darkness; (C) from 5 m and held at 50% sPAR or in the dark; (D) from 10 m and held at 15% sPAR or in the dark; (E) from 20 m and held at 1% sPAR or in the dark; (F) and from 35 m and held at 0.1% sPAR or in the dark. Incubations were conducted in October of 2011 at station 67–70 in the Northeast Pacific. Error bars denote the standard deviation about the mean of duplicate samples.