Analysis of a 39-year continuous atmospheric CO2 record from Baring Head, New Zealand

[摘要] We present an analysis of a 39-year record of continuous atmosphericCO₂ observations made at Baring Head, New Zealand, filtered for steadybackground CO₂ mole fractions during southerly wind conditions. Wediscuss relationships between variability in the filtered CO₂ timeseries and regional to global carbon cycling. Baring Head is well situatedto sample air that has been isolated from terrestrial influences over theSouthern Ocean, and experiences extended episodes of strong southerly windswith low CO₂ variability. The filtered Baring Head CO₂ recordreveals an average seasonal cycle with amplitude of 0.95 ppm that is 13%smaller and 3 weeks earlier in phase than that at the South Pole. Seasonalvariations in a given year are sensitive to the timing and magnitude of thecombined influences of Southern Ocean CO₂ fluxes and terrestrial fluxesfrom both hemispheres. The amplitude of the seasonal cycle varies throughoutthe record, but we find no significant long-term seasonal changes withrespect to the South Pole. Interannual variations in CO₂ growth rate inthe Baring Head record closely match the El Niño-Southern Oscillation,reflecting the global reach of CO₂ mole fraction anomalies associatedwith this cycle. We use atmospheric transport model results to investigatecontributions to seasonal and annual-mean components of the observedCO₂ record. Long-term trends in mean gradients between Baring Head andother stations are predominately due to increases in Northern Hemispherefossil-fuel burning and Southern Ocean CO₂ uptake, for which thereremains a wide range of future estimates. We find that the postulated recent reduction in the efficiency of Southern Oceananthropogenic CO₂ uptake, as a result of increased zonal winds, is too small to be detectableas significant differences in atmospheric CO₂ between mid to high latitude SouthernHemisphere observing stations.

[学科分类] 地球化学与岩石