Influence of transport and trends in atmospheric CO2 at Lampedusa

The study of the CO2 15-year records at Lampedusa (35 degrees 31'N,12 degrees 37'E) is presented in this work. Shortand long-term CO2 variability has been investigated. No significant diurnal variations are observable thus remarking the background character and representativeness of the observation site. The CO2 long-term trend shows a mean linear growth rate (GR) of 1.9 ppm yr(-1). The periodic behaviour of the time series has been analysed and the mean seasonal cycle amplitude has been found to be 8.72 ppm. The seasonal cycle amplitude shows a marked interannual variability. The lowest value of the seasonal cycle amplitude has been detected in 2003, in concomitance with the strong anomalous heat wave recorded in Europe. CO2 GR behaviour has been related to global processes such as El Nino Southern Oscillation (ENSO) and global temperature (T-g). The influence of ENSO event on GR is remarkable only during 1998. CO2 GR curve shows peaks in the periods 1995, 2001 and 2005 (1.9, 3.7, 3.2 ppm yr(-1) respectively) that are characterized by high T-g values and by intense biomass burning events. The anomalous decrease in the GR during the warm 2003 has been attributed to changes in the atmospheric circulation regime. Evaluation of the influence of transport on CO2 variability has been carried out using backward air-mass trajectory analysis and highlights the effect of the regional distribution of sources and sinks. The industrial activities and forests located in the Eastern European and Russian sector strongly affect the CO2 mixing ratio. The CO2 content of air-masses originating from this region is influenced in summertime by the high efficiency of the vegetation sink while in the winter period prevails the effect of industrial emissions. (C) 2009 Elsevier Ltd. All rights reserved.