CO2-Variation over the Baltic Sea

Abstract: The increasing levels of the greenhouse gas carbon dioxide (CO2) in the Earths atmosphere, caused by human release of CO2, has made it desirable to understand the factors determining the CO2-variation because of CO2’s warming effect on the Earths temperature which will change the premises of all life on earth. The purpose of this investigation is to understand the effects of the largest factors of influence on the CO2-concentration - like sea, vegetation and anthropogenic outlets - in the Baltic Sea region, and possible surprises from the results. To be able to do this only from CO2-measurements some assumptions have to be done as starting point. Such are that, besides from the yearly trend of the CO2-concentration and the variation of oceanic influence, monthly variation only is caused by vegetation and that the yearly offset in CO2-levels only is affected by anthropogenic outlets. These factors are together called the local season and will be used for evaluation of the CO2-values for each site. This analysis is done for eight sites surrounding the Baltic Sea region and is compared with results from the site of Östergarnsholm, an island in the Baltic Sea east of Gotland. The results show that stations with high vegetational influence has high amplitudes for the local season compared to sites more influenced by sea. This also makes the amplitude to be connected with latitude since sites with longer growing season is surrounded by higher density of vegetation. The minimum for the local season is also dependent on the growing season, since it occurs when the vegetational consumption is largest. Peaks in the local season can be seen in connection with the maximum decay of the natural vegetation in the early winter months, and with the planting and harvest season for agricultural land. Considering the effect from anthropogenic influence a clear connection in the offset of the local season can be seen, with higher offsets for sites of higher anthropogenic influence and vice versa. Anthropogenic influence also seems to give raised values in summer for the local season, indicating that the variation of the local season cannot be simply connected to only vegetational influence. For variability, higher values in the summer months are seen for the anthropogenic sites, while in winter the variability is more similar for all sites. This might be connected with a higher degree of local influence during summers, which for anthropogenic stations leads to high variability due to inhomogenous surroundings. For Östergarnsholm we get higher amplitude for the local season than expected, this is partly due to unrepresentatively high amplitudes for the seasons used, but also probably to some degree of underestimation of the vegetational influence. Due to correction of the offset it was not possible to draw any conclusions from this factor, but rather give suggestions of what the correction should be. When analysing the local season for different source areas by WD-classification we see the surprising property that the sector that should be most influenced by land, due to higher values in summer, has a lower amplitude than the sector most influenced by sea. Since it was suggested that anthropogenic influence gives raised values in summer this was suggested as an explanation.