HR: 0800h
AN: B51C-0231    [Abstracts]
TI: Seasonal variation of carbon-14 in atmospheric carbon dioxide at Point Barrow, Alaska: Observations and modeling
AU: * Krakauer, N Y
EM: niryk@caltech.edu
AF: California Institute of Technology, MC 100-23 1200 E California, Pasadena, CA 91125 United States
AU: Xu, X
EM: xxu@uci.edu
AF: University of California at Irvine, Earth System Science, Irvine, CA 92697 United States
AU: Trumbore, S E
EM: setrumbo@uci.edu
AF: University of California at Irvine, Earth System Science, Irvine, CA 92697 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: University of California at Irvine, Earth System Science, Irvine, CA 92697 United States
AB: Δ¹⁴C is an isotopic ratio uniquely suited for discriminating between fossil and biosphere carbon emissions, but few long-term measurement series exist. We have measured Δ¹⁴C in about 2 air samples monthly from the Point Barrow Observatory, Alaska (71°N, 157°W) since July 2003 with precision of around 2‰. In this period, Δ¹⁴C decreased by 7‰/year, to ~57‰ in mid-2005. We find a seasonal cycle in Δ¹⁴C with a broad minimum in January-June, a maximum in September and an amplitude of 6‰. Compared with these observations, simulations with the Model of Atmospheric Transport and Chemistry (MATCH) predict a seasonal cycle with broadly similar phase, with seasonality in fossil and biosphere CO₂ emissions predicted to make about equal contributions. However, the simulated seasonal cycle has ~70% the observed amplitude, and it has Δ¹⁴C starting to increase earlier in the spring than observed. The shape of the observed cycle suggests a larger biosphere contribution, possibly due to either longer carbon mean residence time (so that respired carbon contains more bomb Δ¹⁴C) or higher net primary production in the region, than assumed in our simulation. We plan to use our measurements from Point Barrow and elsewhere in North America to test the regional carbon balance inferred from inverse modeling using only measurements of the CO₂ concentration and δ¹³C.
DE: 0322 Constituent sources and sinks
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Biogeosciences [B]
MN: Fall Meeting 2005