1. Long-term observations of atmospheric O 2 :CO 2 ratios over the Southern Ocean Britton Stephens (NCAR), Ralph Keeling (Scripps), Gordon Brailsford (NIWA), Andrew Manning (UEA), Sara Mikaloff-Fletcher (NIWA), Prabir Patra (JAMSTEC), Jonathan Bent (Scripps), Colm Sweeney (NOAA/CU)

2. Measurements of atmospheric O 2 are valuable because: Solubility and biological processes have strong and reinforcing effects on atmospheric O 2 Solubility, biological, and anthropogenic effects have distinct O 2 :CO 2 signatures The atmosphere integrates over large ocean regions Future changes will involve subtle combinations of all processes However, applications to date have been limited Southern Ocean air-sea CO 2 and O 2 fluxes 75 S 65 S55 S  O 2 /N 2 (per meg) = [(O 2 /N 2 ) sample /(O 2 /N 2 ) reference - 1] x 10 6

3. Basic problem: Quantitatively relating atmospheric variations in O 2 and CO 2 to underlying ocean processes continues to be limited by errors in atmospheric transport models Southern Ocean strategy: Find ways to use atmospheric data to constrain fluxes and test ocean models that are independent of atmospheric transport models Seasonal cycle amplitude from 9 TransCom models forced with identical seasonal ocean O 2 fluxes [T. Blaine, Dissertion, 2005]

4. Idea 1: Look at zonally and vertically integrated O 2 concentrations Idea 2: Look at O 2 :CO 2 ratios in concentration measurements 001 Poster B1538: Jonathan Bent et al. Assessing biogeochemical models with high-resolution airborne observations of the O 2 /N 2 ratio over the Southern Ocean [Stephens et al., Tellus 2003] January 2009 Drake Passage October 1998

5. SeaWiFS Summer Chlorophyll a Southern Ocean atmospheric O 2 observations SPO CGO PSA AMS SYO MCQ BHD Scripps flask Princeton flask NIWA in situ

6. Model and data products evaluated Dissolved-gas climatologies Seasonal ocean O 2 and N 2 : Garcia and Keeling, 2001 Ocean CO 2 : Takahashi et al., 2002 and 2009 Ocean inversions Mean ocean O 2 : Gruber et al., 2001 Mean ocean N 2 : Gloor et al., 2001 Fossil-fuel fluxes CO 2 and O 2 : CDIAC and EDGAR Ocean biogeochemistry models ORCA-PISCES-T: Le Quere et al. 2007 CCSM-3: Doney et al. 2009 Atmospheric inversions CO 2 ACTM 64 reg: Patra et al., 2011 Atmospheric transport models ACTM (~ 2.8°): Patra et al., 2009 TM3 (4° x 5 °) : Heimann and Körner, 2009

11. In general, O 2 and CO 2 PSA-SPO gradients are uncorrelated, and CO 2 gradients are often too small. The Garcia and Keeling O 2 fluxes have about a 1-month phase lead (by design) Takahashi 2009 CO 2 fluxes are an improvement but may still overestimate uptake in late summer (data coverage? coarse grid? gas- exchange formulation?) The O 2 :CO 2 correlations are worse in the models ORCA-PISCES-T appears to have CO 2 flux in wrong direction (uptake) in early winter and no CO 2 uptake in summer CCSM-3 appears to overestimate CO 2 outgassing in early winter Limitations in biological submodels and/or lack of eddy-mixing may be important What’s going on with the climatologies and models?

12. Baring Head, New Zealand: 10 years of O 2 :CO 2 ratios in synoptic variations during steady-CO 2 Southerly wind episodes +

13. June 2012 initiation of shipboard O 2 and CO 2 measurements will greatly increase Southern Ocean data coverage R/V Lawrence M. Gould Sweeney et al., 004 Poster B2052

14. Summary Atmospheric O 2 and CO 2 measurements have potential for testing surface-data based and ocean biogeochemistry model fluxes in the Southern Ocean Monthly surface gradient (PSA-SPO) O 2 :CO 2 ratios suggest that both pCO 2 climatologies and model seasonal CO 2 fluxes still require improvement in the Southern Ocean High hopes for O 2 :CO 2 ratios measured in synoptic variations in Drake Passage isolated from terrestrial influences strong signals model predictions of synoptic ratios well-behaved