Using Lagrangian flights and modeling to study O2 and CO2 fluxes over the Southern Ocean during the O2/N2 Ratio and CO2 Airborne Study (ORCAS).

The ORCAS (O2/N2 Ratio and CO2 Airborne Southern Ocean Study) was designed to add new observational constraints on summertime fluxes and controlling processes for carbon dioxide and oxygen with unprecedented spatial coverage over the Southern Ocean. One approach unique to these air-sea gas exchange studies involved using Lagrangian modeling to determine flight paths for sampling different biogeochemical regions in the Southern Ocean and defined Lagrangian flights to sample the same air mass as it transits the Drake Passage and the Argentine basin. We will discuss the Stochastic Time-Inverted Lagrangian Transport (STILT) modeling system as used in planning and analyzing flights. We will show the sensitivity of the entire campaign to the Southern Ocean and combine with the Community Earth System Model (CESM) and climatologies of air-sea exchange to directly compare aircraft observations with simulated values and discuss reasons for discrepancies. We also will show results from a 24-hour Lagrangian experiment that tightly constrains short-term air-sea gas exchange over the Palmer Antartctic Long Term Ecological Research Network (PALTER) grid.