Abstract

The Southern Ocean represents 40% of the global ocean anthropogenic CO2 uptake. The strength of this sink is determined by a delicate balance between opposing biogeochemical processes: the upwelling of deep water rich in dissolved inorganic carbon and the drawdown of anthropogenic CO2 by biological production. Monitoring these processes is an inherently difficult task given the scarcity of observations and thus is the source of much scientific debate. Due to compounding physical, biological and chemical factors, the air-sea flux of CO2 is dampened and therefore difficult to detect. In this talk I will discuss how the addition of atmospheric O2 observations circumvents these problems and allows one to detect a much larger signal from the carbon cycle processes that drive air-sea CO2 fluxes.

I will present the first year of data from a very recent installation of a fully automated, continuous atmospheric O2 and CO2 measurement system at the Clean Air Sector Laboratory (CASLab) at the Halley Research Station, Antarctica, in collaboration with the British Antarctic Survey. I will present the seasonal cycle in atmospheric potential oxygen (APO = O2 + 1.1CO2), which is conservative with respect to terrestrial biosphere processes and therefore largely represents the seasonality of the above mentioned Southern Ocean carbon cycle processes. I compare this to other APO stations across the Southern Ocean and to modelled APO at the measurement site and comment on the significance of the differences. Finally, I interpret synoptic scale variability in APO in conjunction with other atmospheric species observed at the CAS Lab, by utilising air mass history “footprints” derived from the NAME (Numerical Atmospheric dispersion Modelling Environment) atmospheric transport model. From this one can discern different air masses deriving off the Southern Ocean where marine biological productivity dominates air-sea gas exchange of O2, or, conversely, where deep ocean ventilation dominates.