Emerson, Steven, Allan Devol, Wendy Ruef and Charles Stump

P.O. 355351, School of Oceanography, University of Washington, Seattle, WA 98195, Tel: 206-543-0428, E-mail: emerson@u.washington

In situ diurnal oxygen measurements: a method for determining net primary production

We measured the diurnal changes of oxygen in the euphotic zone of the ocean at the Hawaii Ocean Time series (HOT) in the Subtropical North Pacific and in Puget Sound, WA. Measurements were made in situ every 1 to 4 hours over periods of six months to two years using a Clark oxygen sensor at a single depth on a mooring at HOT and using a profiling mooring in Puget Sound. The results are independent of long-term sensor drift because we determine diurnal differences for each individual day. At both locations there were significant advective effects that render the diurnal change of oxygen for individual days unreliable for interpretation as a local biological signal. In each case; however, the data, when averaged over hundreds of measurements, indicate very clear mean diurnal changes within the standard deviations of the means. The diurnal signals yield Net Primary Production values that are similar to Primary Production determined with ¹⁴C bottle assays. We believe this technique, coupled with estimates of the net oxygen mass balance determined using the same data, has the potential to measure both Net Primary Production and Net Community Production and hence the recycling efficiencies (e or f ratios). The method requires a depth distribution of oxygen sensors or a profiling mooring to determine the euphotic zone integrated biological signal.