VARIABILITY OF NITRATE CONCENTRATION IN NITROGEN-DEPLETED SUBTROPICAL SURFACE WATERS

Recent improvements in the analytical determination of nitrate and nitrite allow measurements of nanomolar concentrations in nitrogen-depleted surface waters, revealing variability not previously observable. The new methods allow direct observation of net nitrate consumption and production measured as changes in nitrate concentration over time in incubated samples of seawater. We find that nitrate concentrations in nitrogendepleted surface waters show regional differences, and sometimes diel differences. The variability in nitrate concentration reflects differences in atmospheric inputs, in physical forcing, as well as in the biological processes of nitrate uptake and nitrification. Examples are shown from the Southern California Bight (1986-1987), the equatorial Pacific (February-March, 1988), and the eastern subtropical Atlantic (March-April, 1989). © 1990 Springer-Verlag.