Juranek, L.W.^1*, E. Barkan², B. Luz² and P. D.Quay¹

¹ University of Washington, School of Oceanography, Box 355351, Seattle, WA 98195, USA, Tel: 206-543-4511, Fax: 206-685-3351, E-mail: juranek@ocean.washington.edu and ²Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel

Gross primary productivity rates at HOT and BATS determined by the triple isotope composition of dissolved oxygen

Time-series studies have made a substantial contribution to our understanding of surface ocean processes, but some fundamental rates, such as Gross Primary Productivity (GPP), are still not well quantified. Recently the triple isotope composition of dissolved O₂ in situ has been shown to provide a measure of GPP that is unaffected by autotrophic or heterotrophic respiration. When compared with other estimates of PP at HOT and BATS, the triple isotope method has been shown to yield up to 4 times the ¹⁴C- derived rates while agreeing well with ¹⁸O bottle incubations. At BATS, the gross O₂ production calculated for March 2000 to January 2001 ranged between 41 and 125 mmol O₂ m^-2 d^-1, and the annual rate was about double the ¹⁴C annual rate. In preliminary measurements at HOT, O₂ production has been observed on two occasions to be roughly twice the ¹⁴C integrated production in the mixed layer; 92±46 mmol O₂ m^-2 d^-1 in June 2001 and 122±39 mmol O₂ m^-2 d^-1 in February 2002. The rates of GPP derived from the triple isotopes are representative of the mixed layer alone. The overall rates in the photic zone must be greater due to production in the thermocline. A comparison of the measurements to each other and to other core measurements will be discussed.