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Aquatic Microbial Ecology

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AME 56:133-145 (2009)  -  DOI:

Net and gross oxygen production from O2/Ar, 17O/16O and 18O/16O ratios

Boaz Luz*, Eugeni Barkan

The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

ABSTRACT: In aquatic systems, variations in the O2/Ar ratio and in the 17O anomaly (17Δ, calculated from 17O/16O and 18O/16O) are affected by both physical and biological processes. Laboratory observations suggest that 17Δ is independent of respiration rate, in contrast to the O2/Ar ratio. This makes it possible to determine gross O2 production from measurements of 17O/16O and 18O/16O of dissolved O2, while the O2/Ar ratio can be applied to estimate net O2 production. We demonstrate how biological and physical forcing modifies the O2/Ar ratio and 17Δ during the day and at night in a coral reef near Eilat. This field study confirmed our hypothesis that 17Δ of dissolved O2 (17Δdis) is affected by photosynthesis, ocean dynamics and air–water gas exchange, but not by respiration. We also show, for the first time, a detailed record of 17Δ responses to biological fluxes and subtropical ocean dynamics on a seasonal scale. The measurements were conducted in the Atlantic Ocean near Bermuda during monthly cruises of the Bermuda Atlantic Time-series Study (BATS) from March 2000 to January 2001. With the formation of the seasonal thermocline, 17Δdis significantly increased below the oceanic mixed layer, reflecting the seasonal integration of photosynthesis in the thermocline. Hence, 17Δdis accumulation may be used to calculate the overall rate of photosynthesis below the mixed layer. We used the O2/Ar ratio and 17Δdis to estimate net and gross O2 production (NOP and GOP) and directly compared them with production values derived from 14C incubations. In general, GOP based on 17Δdis was several times greater than production determined via 14C fixation [P(14C)], which in turn was somewhat greater than NOP based on the O2/Ar ratio. The NOP/GOP ratio was 0.08 to 0.21. This implies that the observed high GOP/P(14C) ratios result mainly from rapid cycling of O2 between photosynthesis and O2 uptake mechanisms.

KEY WORDS: Gross production · Net production · Community production · Oxygen isotopes · O2/Ar ratio · Bermuda Atlantic Time-series Study · Coral reef

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Cite this article as: Luz B, Barkan E (2009) Net and gross oxygen production from O2/Ar, 17O/16O and 18O/16O ratios. Aquat Microb Ecol 56:133-145.

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