A52C-04
Empirically constrained estimates of Alaskan regional Net Ecosystem Exchange of CO2, 2012-2014

Friday, 18 December 2015: 11:05
3006 (Moscone West)
Roisin Commane1, Jakob Lindaas1, Joshua Simon Benmergui2, Kristina A Luus3, Rachel Ying-Wen Chang4, Scot M Miller1, John Henderson5, Anna Karion6, John B Miller6, Colm Sweeney6, Charles E Miller7, John C Lin8, Walter C Oechel9, Donatella Zona9, Eugenie Susanne Euskirchen10, Hiroki Iwata11, Masahito Ueyama12, Yoshinobu Harazono13, Sander Veraverbeke14, James Tremper Randerson14, Bruce C Daube1, Jasna Vellovic Pittman15 and Steven C Wofsy1, (1)Harvard University, Cambridge, MA, United States, (2)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (3)Max Planck Institute for Biogeochemistry, Jena, Germany, (4)Dalhousie University, Halifax, NS, Canada, (5)Atmospheric and Environmental Research, Lexington, MA, United States, (6)NOAA Boulder, ESRL, Boulder, CO, United States, (7)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (8)University of Utah, Salt Lake City, UT, United States, (9)San Diego State University, San Diego, CA, United States, (10)University of Alaska Fairbanks, Fairbanks, AK, United States, (11)Shinshu University, Matsumoto, Japan, (12)Osaka Prefecture University, Sakai, Japan, (13)Osaka Prefecture University, Graduate School of Life and Environmental Sciences, Sakai, Japan, (14)University of California Irvine, Department of Earth System Science, Irvine, CA, United States, (15)NorthWest Research Associates Bellevue, Bellevue, WA, United States
Abstract:
We present data-driven estimates of the regional net ecosystem exchange of CO2 across Alaska for three years (2012-2014) derived from CARVE (Carbon in the Arctic Reservoirs Vulnerability Experiment) aircraft measurements. Integrating optimized estimates of annual NEE, we find that the Alaskan region was a small sink of CO2 during 2012 and 2014, but a significant source of CO2 in 2013, even before including emissions from the large forest fire season during 2013. We investigate the drivers of this interannual variability, and the larger spring and fall emissions of CO2 in 2013.

To determine the optimized fluxes, we couple the Polar Weather Research and Forecasting (PWRF) model with the Stochastic Time-Inverted Lagrangian Transport (STILT) model, to produce footprints of surface influence that we convolve with a remote-sensing driven model of NEE across Alaska, the Polar Vegetation Photosynthesis and Respiration Model (Polar-VPRM). For each month we calculate a spatially explicit additive flux (∆F) by minimizing the difference between the measured profiles of the aircraft CO2 data and the modeled profiles, using a framework that combines a uniform correction at regional scales and a Bayesian inversion of residuals at smaller scales. A rigorous estimate of total uncertainty (including atmospheric transport, measurement error, etc.) was made with a combination of maximum likelihood estimation and Monte Carlo error propagation. Our optimized fluxes are consistent with other measurements on multiple spatial scales, including CO2 mixing ratios from the CARVE Tower near Fairbanks and eddy covariance flux towers in both boreal and tundra ecosystems across Alaska. For times outside the aircraft observations (Dec-April) we use the un-optimized polar-VPRM, which has shown good agreement with both tall towers and eddy flux data outside the growing season. This approach allows us to robustly estimate the annual CO2 budget for Alaska and investigate the drivers of both the seasonal cycle and the interannual variability of CO2 for the region.

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