Nitrite distributions and dynamics at Station ALOHA

John E. Dore and David M. Karl

Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, U.S.A.

(Received 5 September 1994; in revised form 12 April 1995; accepted 24 November 1995)

Abstract

We used a chemiluminescence method to measure nitrite concentrations in the water column at the U.S. JGOFS/WOCE time-series station, ALOHA (22 45'N, 158'W), from September 1989 to November 1993. We present a detailed time-series of nitrite in the upper 200 m in order to examine the dynamics of the primary nitrite maximum. Our results reveal a double-peaked structure to this feature that is consistent with a vertical separation of the reductive and oxidative microbial processes responsible for nitrite production. The possibility of using the nitrite content of this upper layer as an indicator of nitrogen export from the euphotic zone is explored and rejected.

Midwater nitrite profiles (200-1000 m) show a supra-exponential decrease in concentration with depth and reveal month-to-month variability. Nitrite concentrations in deep waters (1000-4800 m) are in the nanomolar-subnanomolar range, and are similar to Atlantic data, arguing against significant basin-scale differences in the deep nitrite pool. Deep profiles also show measurable variability on both monthly and annual timescales. We speculate that this deep variability may be associated with nitrate reduction by sinking phytoplankton cells.