IN-SITU MEASUREMENT OF DISSOLVED NITROGEN AND OXYGEN IN THE OCEAN

Motivated by the need to separate changes in dissolved gas concentrati ons due to air-sea fluxes from biological production, a novel method o f inferring dissolved nitrogen in the ocean is described. The method r equires a local measurement of gas tension, dissolved oxygen, water te mperature and salinity. Such instrumentation has been developed and te sted at sea. Preliminary open ocean data are presented. The measuremen ts during periods of low wind speed show a clear diurnal dissolved oxy gen signal, incorporating biological photosynthetic response, solar he ating and nocturnal convective mixing. The diurnal variability of the inferred nitrogen signal is approximately 10% that of the measured oxy gen diurnal variability. The nitrogen diurnal variability is attribute d to a 10 m separation between the primary measurements of gas tension and dissolved oxygen rather than any intrinsic change in dissolved ni trogen. These results are, however, consistent with the relative insen sitivity of dissolved gaseous nitrogen to biological activity compared to that of dissolved oxygen. The open ocean results give good evidenc e for the integrity of the measurement scheme and indicate the potenti al for simultaneous measurement of dissolved nitrogen and oxygen in th e study of biological cycling as well as gas transfer in the upper oce an.