Atmospheric CO2 concentrations and δ13C values during 2011-2012 voyage: Mediterranean, Atlantic Ocean, southern Indian Ocean and New Zealand to Antarctica

During the 2011-2012 hemispheric voyage of the M/V Italica from Italy to the Atlantic Ocean, southern Indian Ocean, New Zealand and Antarctica, atmospheric CO2 concentrations were continuously recorded and 52 air samples collected in 4-L Pyrex flasks for the measurement of the δ13C of atmospheric CO2. In the case of CO2 concentrations, new data include the following: 1) in the Adriatic, between Ravenna and Otranto, CO2 was never measured in order to avoid the expected heavy contribution from industrial plants; the 2011 measurements fully confirm this contribution; 2) in the Atlantic, along the Moroccan coast, high values of up to 415 ppmv were recorded, apparently due to considerable industrial development in Morocco; 3) minor CO2 concentrations were also recorded along other sections of the African coast north of the Equator, whereas relatively low constant values were recorded south of the Equator; 4) in the southern Indian Ocean, CO2 concentrations were measured almost along a parallel, yielding homogeneous values not much higher than the mean values recorded at NOAA stations in nearby areas. With only one exception, the δ13C values were systematically less negative than −9‰ (VPDB), the mean values for the three oceanic sections being the following: Atlantic Ocean −8.64 ± 0.20‰; Indian Ocean −8.54 ± 0.06‰; New Zealand to Antarctica −8.49 ± 0.02‰. A small but progressive increase in δ13C values with increasing latitude was in good agreement with the expected trend. The homogeneity of such values between New Zealand and Antarctica was remarkable, as these samples had been collected in particularly rough oceanic conditions with high winds. In spite of these particular environmental conditions these values were very close to those of samples collected in the same area in 2009 and 2010 in conditions of calm sea and low wind. This similarity contrasts sharply with the theory and models of air-sea gas exchange.