Measurements of atmospheric O 2 in relation to the ocean carbon cycle Ralph Keeling Scripps Institution of Oceanography

The carbon cycle

Mauna Loa (black) South Pole (red) Northern and Southern CO 2 records Where is the signal of the oceans in these data?

CO 2 variability Land biosphere dominates CO 2 variability on all time scales except long term. Advances from using inverse models of atmospheric CO 2 data (e.g. CarbonTracker) are mostly limited to short-term fluxes on land. Large uncertainties still surround long-term fluxes. Atmospheric CO 2 data alone cannot yield much new insight into ocean biogeochemistry.

Ocean CO 2 uptake: H 2 O + CO 2 + CO 3 = ↔ 2HCO 3 - B F O Z Z ΔCO 2 = F – O – B ΔO 2 = -1.4F + 1.1B +Z ΔO ΔCO 2 = -0.3F -1.1O + Z Atmospheric CO 2 & O 2 budgets ΔAPO = “Atmospheric Potential Oxygen”

Northern and Southern APO records Ocean dominates APO variability on all time scale except long term. Long-term trend in APO dominated by fossil-fuel and ocean CO 2 uptake. Shorter-term variability mostly related to air-sea O2 exchanges.

Stations with atmospheric O 2 observations

Fossil-fuel corrected APO trend

Cape Grim Trend Any trend in amplitude is less than 1% per year. No evidence of large changes over the past 2 decades.

Cape Grim Observatory, 41°S

Seasonal Cycles of Air-Sea O 2 exchange

Seasonal air-sea O 2 fluxes JUNE DECEMBER Southern Hemisphere Northern Hemisphere

What are we headed in ocean biogeochemistry data assimilation? Joint ocean/atmosphere/land biosphere data assimilation Assimilations that optimize processes controlling fluxes rather than the fluxes themselves. Enhance ocean modeling component to assimilate changing ocean physics (e.g. Argo data, etc). Assimilation of CO 2, O 2, pCO 2, ocean color