Johnson, K, S, MBARI, Moss Landing, USA, johnson@mbari.org
Coletti, L, , MBARI, Moss Landing, USA, coletti@mbari.org
Chavez, F, , MBARI, Moss Landing, USA, chfr@mbari.org

DIEL NITRATE CYCLES IN THE COASTAL OCEAN PREDICT ANNUAL PRIMARY PRODUCTION AND BIOMASS ACCUMULATION

Diel cycles of nitrate were regularly observed in surface waters using optical nitrate sensors deployed for several years on the M1 and M2 oceanographic moorings offshore of Monterey Bay, California. Nitrate was measured hourly with In Situ Ultraviolet Spectrophotometers (ISUS). The amplitude of the diel cycles correlated with rates of primary production measured by 14C uptake and they appear to be a direct measure of daily new primary production. The mean values of new primary production determined from diel nitrate cycles from 2002 to June 2004 were 80+/-9 and 47+/-5 mg C/m^3/d at M1 and M2, respectively (error limits are 95% CI). For comparison, the mean primary production values determined during visits to the mooring sites at 21 day intervals from 1989 to 2004 are 145+/-21 and 68+/-14 mg C/m^3/d. Phytoplankton biomass predicted from the diel nitrate uptake and a constant loss rate matched observations over the annual cycle. The implication is that arrays of chemical sensors can be used to estimate primary production and ecosystem processes over multiple temporal and spatial scales.