Patterns and Variability in Δ14C of CO2 in Northern Hemisphere Background Air
H.D. Graven1, T.P. Guilderson2 and R.F. Keeling1
1Scripps Institution of Oceanography (SIO), University of California at San Diego, La Jolla, CA 92093; 858-822-3362, E-mail: hgraven@ucsd.edu
2Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550
The development of applications that determine fossil fuel-derived CO2 and fossil fuel CO2 emissions using observations of Δ14C in atmospheric CO2 has advanced rapidly in recent years. The largest uncertainties associated with this method are contributed by measurement uncertainty and the specification of the “background” level of Δ14C, which provides the reference to which Δ14C dilution in polluted air is quantified. We will present measurements of Δ14C of CO2 in Northern Hemisphere background air from the Scripps CO2 Program’s flask sampling network that were conducted at Lawrence Livermore National Laboratory. Meridional gradients in background air are evident in comparisons of Δ14C observed at Mauna Loa and Kumukahi, Hawaii (20°N), La Jolla, California (33°N) and Point Barrow, Alaska (72°N) between 2001 and 2007. La Jolla typically shows the lowest Δ14C. Seasonal cycles of Δ14C with maxima in fall are evident, with the largest amplitudes at Point Barrow, on average. The observations also show substantial year-to-year variability. For example, very little seasonality was observed in 2002-03 at La Jolla. We will discuss the influences that are likely to contribute to the observed patterns and variability in Δ14C of Northern Hemisphere background air and the implications for quantifying fossil fuel-derived CO2 from Northern continents.
Figure 1. Measurements of Δ14C in CO2 from Northern Hemisphere flask sampling sites in the Scripps CO2 Program. Shown are smoothed curves for Point Barrow (PTB), La Jolla (LJO), Kumukahi (KUM) and Mauna Loa (MLO).