Abstract

Precise measurements of atmospheric O2 concentration can provide constraints on several aspects of the global carbon cycle. Seasonal variations in O2 concentration, driven in part by biological and physical cycles in the ocean, can be used to constrain seasonal net photosynthesis rates of marine biota. Interannual variations in O2 concentration, driven largely by O2 uptake by fossil fuel burning and O2 exchanges with land biota, can be used to partition the net global uptake of anthropogenic CO2 into oceanic and land biotic components. The latter application is potentially complicated, however, by interannual sources and sinks of O2 from the ocean. Model simulations are presented that suggest that interannually driven air–sea O2 exchanges may be several times larger on a mole-for-mole basis than interannually driven air–sea CO2 exchanges.

Introduction

It has recently become feasible to measure the atmospheric oxygen concentration to a degree of precision that allows for the detection of variations in the remote atmosphere (Keeling and Shertz, 1992; Bender et al., 1994; Bender et al., 1996; Keeling et al., 1996). These variations primarily reflect changes in O2 because N2 is constant to a very high level. Variations in O2 are caused primarily by production and consumption of O2 by photosynthesis, respiration, and combustion, and are thereby tied to the rate at which carbon is transformed between organic and inorganic forms.