Concentrations and C-delta 13 values of atmospheric CO2 from oceanic atmosphere through time: polluted and non polluted areas

CO2 is one of the primary agents of glocal climate changes. the increase of atmospheric CO2 concentration is essentially related to human-induced emissions and particularly to the burning of fossil fuel whos C-delta 13 values are quite negative. Consequently, an increase of the CO2 concentration in the atmosphere should be paralleled by a decrease of its C-delta13. Continuous and/or spot measurements of CO2 concentrations were repeatedly carried out during the last decade and in the same period of the year along hemispheric courses from Italy to Antarctica on a vessel of the Italian national research program in Antarctica. During these expeditions, discrete air samples were also collected in 4-liter Pyrex flasks in order to carry ot precise carbon isotope analyses on atmospheric CO2 from different areas, including theoretically clean open ocean areas, with the main purpose of comparing these open ocean results with the results obtained by the National Oceanic and Atmospheric Administration /World Metorological Organization (NOAA/WMO) at land-based stations. According to the data obtained for these two variables, a relatively large atmospheric pollution is apparent in the Mediterranean area where the CO2 concentration has reached the value of 384 ppmv, while quite negative C-delta 13 values have been measured only occasionally.In this area, southerly winds probably help to reduce the effect of atmospheric pollution even though, despite a large variability of CO2 concentrations, these values are consistently higher than those measured in open ocean areas by a few ppmv to about 10 ppmv. A marked, though non continuous, pollution is apparent in the area of the Ba-el-Mandeb strait where C-delta 13 values considerably more negative than in the Central and Sourhter Red Sea were measured. The concnetration of atmospheric CO2 over the Central Indian Ocean increased from about 361 ppmv at the end of 1996 to about 373 ppmv at the end of 2003 (mean grwoth rate of about 1.7 ppmv yr-1 (yr to the minus 1) in excellent agreement with the NOA/WMO data from land-based stations). Simultaneously, the mean C-delta 13 value of atmospheric CO2 over the Central Indian Ocean (Equator) decreased from -7.92 per mille at the end of 1998 to -8.22 per mille at the end of 2003; the mean decrease rate being about -0.06 per mille yr-1 (yr to the minus 1). This rate as wellas that calculated at 12°S(-0.05 per ille yr-1 (yr to the minus 1)) are not far from the rates that may be calculate according to the data from the nearest NOAA sites (Croset and Mahe islands); the rates calculated south of Australia and between Tasmania and New Zealand are almost identical to those calculated according to the data from Cape Grim NOAA site (Tasmania).