Net and gross production in the Ross Sea as determined by incubation experiments and dissolved O 2 studies

Abstract

We report net and gross production rates for samples from three JGOFS cruises to the Ross Sea during spring–autumn 1996–1997. We summarize continuous electrode measurements of mixed-layer O 2 supersaturation taken during January 1997, and use these to calculate air-sea O 2 fluxes and upper ocean net production. We also calculate net production rates from changes in the 0–80 m inventories of dissolved nitrate. Net C production rates during summer (January–February 1997), inferred from bottle incubations and O 2 supersaturation, are 60 and 56 mmol m −2 day −1, respectively. These values agree well with net production values from November 1 to February 6 estimated from the decrease in the nitrate inventory of the upper water column, 108 mmol m −2 day −1. Depth-integrated gross C production measured on the summer cruise averaged 185 mmol m −2 day −1. High values of net C production, gross C production, and net/gross ratio (0.32) confirm earlier studies (e.g., Smith and Gordon, Geophysical Research Letters 24 (1997) 233–236) concluding that net and gross rates of carbon production are very high during the spring and summer. δ 18O values of dissolved O 2 also demonstrate that C and O 2 are rapidly cycled metabolically even when mixed-layer O 2 concentrations are close to saturation.