Seasonal and latitudinal variations of column averaged volume‐mixing ratios of atmospheric CO₂

Column‐averaged volume mixing ratios of CO 2 have been obtained by ground based high‐resolution solar absorption spectrometry at Ny‐Alesund (Spitsbergen, 79°N) in 2002–2003 and during two ship cruises (54°N–34°S) on the Atlantic in 2003. Precisions are better than 0.4% at Ny‐Alesund and better than 0.6% for the cruises. The observed 11 ppmv (part per million by volume) seasonal amplitude of the CO 2 column at Ny‐Alesund is about 5 ppmv smaller than surface in situ data and 2–4 ppmv greater than model‐predictions. The latitudinal gradient of column CO 2 inferred from shipborne measurements is less than 2 ppmv in Oct/Nov 2003. During the cruise in Jan/Feb 2003 the observed latitudinal variation is about 7 ppmv. This strong variation is caused by pollution events (biomass burning) and natural variations. Low CO 2 columns observed between 5°S–15°S are attributed to a strong seasonal amplitude of CO 2 over Central Africa.