Do Atmospheric Measurements of Trace Gases Inform us on the Dynamics of Carbon Exchange During Spring and Fall at High Northern Latitudes? (Invited)

Quantitative understanding of atmospheric carbon sources and sinks is necessary to develop a reasonable strategy to mitigate the potential influence of CO2 and CH4 on climate. High northern latitudes, which are warming at twice the globally averaged rate, are especially vulnerable to climate change. Large stores of carbon there, if released to the atmosphere, would provide strong positive feedbacks on climate. Northern ecosystems clearly contribute to the observed signals in atmospheric CO2 and CH4 at high northern latitudes. For example, emissions from northern wetlands contribute to an annual CH4 seasonal cycle with a peak-to-peak amplitude of ~50 ppb. Our ability to simulate the CH4 seasonal cycle with a chemical transport model was improved by recent measurements of a fall “freeze-in” burst of CH4 from tundra in Greenland. When these emissions were included for all similar ecosystems, agreement between simulated and observed seasonal cycles improved, particularly in autumn. Other processes may also be important. For CO2, seasonal cycle peak to peak amplitudes at high northern latitudes are ~15 ppm, but only ~3 ppm of that amplitude results from carbon exchange in high latitude ecosystems. It is not clear then if observed asymmetry in the shape of the seasonal cycle is related to unknown Arctic biospheric processes or transport of signals from mid-latitudes. Contributions of high northern latitude ecosystems to observations of atmospheric CO2 and CH4 will be described. Emphasis will be placed on current limitations of constraining the carbon cycle at high northern latitudes using atmospheric observations, especially on our ability to explain carbon dynamics in the spring and fall. It is already clear that a denser atmospheric observing network is needed in the Arctic to identify new processes and test them in models.