Seasonal an latitudinal variations of column averaged volume mixing ratios of atmospheric CO2

Column-averaged volume mixing ratios of CO2 have been obtained by ground based high-resolution solar absorption spectrometry at Ny-Alesund (Spitsbergen, 79°N) in 20022003 and during two ship cruises (54°N34°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 CO2 column at Ny-Alesund is about 5 ppmv smaller than surface in situ data and 24 ppmv greater than model-predictions. The latitudinal gradient of column CO2 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 CO2 columns observed between 5°S15°S are attributed to a strong seasonal amplitude of CO2 over Central Africa.