For questions about GMD seminars, contact Julie Singewald, Phone: (303) 497-6074 or Ann Thorne, Phone: (303) 497-4600.

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Upcoming Seminars

Speaker: Dr. Britton Stephens, National Center for Atmospheric Research
Britton Stephens is a Scientist III in the Earth Observing Laboratory (EOL) of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. He received a Bachelor's degree in Earth and Planetary Sciences from Harvard University in 1993 and a Ph.D. in Oceanography from the Scripps Institution of Oceanography in 1999. Before joining NCAR in 2002, he completed a post-doctoral fellowship with the National Oceanic and Atmospheric Administration's Carbon Cycle and Greenhouse Gases group. His research has focused on developing and deploying new instruments for tower, ship, and aircraft-based observations of atmospheric O2 and CO2, and on synthesizing data sets and models to elucidate global carbon cycle processes. Britt's carbon-cycle interests span terrestrial ecology, oceanography, atmospheric dynamics, and climate change mitigation.
Date/Time: Thursday, September 21, 2017 02:00 PM
Location: David Skaggs Research Center, GC402 (multi-purpose room)
Title: Southern Ocean air-sea CO2 exchange inferred from airborne, shipboard, and surface station measurements of atmospheric O2 and CO2
The seasonal exchange of CO2 with the Southern Ocean is driven by strong opposing thermal and biological forces. Climatological air-sea CO2 flux estimates based on temporally and spatially sparse pCO2 measurements in the region predict seasonal exchange in phase with biological forcing but relatively muted in amplitude. In contrast, many Earth system models predict large seasonal cycles in Southern Ocean air-sea CO2 flux, in phase with biological forcing in some models but with opposite phase in others. Because air-sea O2 exchanges are positively correlated for thermal and biological influences, and not affected by buffering chemistry, seasonal air-sea O2 fluxes are considerably larger than their CO2 counterparts. Consequently, atmospheric O2 gradients are relatively unaffected by remote terrestrial and fossil influences and O2 fluxes are more robustly constrained by atmospheric measurements. Estimates of air-sea O2 fluxes validated against atmospheric O2, combined with O2:CO2 ratios in observed atmospheric gradients, can be used to constrain the magnitude and drivers of seasonal CO2 fluxes. I will present results from the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) Study, which collected extensive measurements of atmospheric O2, CO2, and related species over the Southern Ocean, using the NSF/NCAR Gulfstream V aircraft based out of Punta Arenas, Chile, during January and February 2016. This intensive airborne campaign leverages long-term in situ atmospheric O2 and CO2 measurements made over a latitudinal transect across the Drake Passage on the Antarctic Research and Support Vessel Laurence M. Gould (2012-2017), flask based measurements from Palmer Station Antarctica (PSA) and South Pole (SPO) from the Scripps Oxygen Network (1997-2016), and additional airborne observations from the HIPPO (2009-2011) and ATom (2016-2018) campaigns. Collectively, these measurements show consistently negative correlations between atmospheric O2 and CO2 gradients in both summer and winter, confirming the biological dominance of Southern Ocean seasonal CO2 exchange and allowing rejection of Earth system models that predict air-sea CO2 fluxes with opposite phase to biological forcing, and O2:CO2 ratios that suggest significantly greater seasonal amplitude in air-sea CO2 fluxes than has long been assumed from pCO2 measurements


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