Atmospheric CO2 concentrations and δ13C values between New Zealand and Antarctica, 1998 to 2010: some puzzling results

Abstract

ABSTRACTFrom 1998 to 2010, during eight cruises of the M/V Italica between New Zealand and Antarctica, sets of flask air samples were collected and atmospheric CO2 concentrations were recorded. The δ13C of CO2 from the 1998 to 2003 air samples have already been published and show large interannual variability and an increasing frequency of 13C-depleted samples. These results were related to a mosaic of areas with positive air–sea fluxes. We report here δ13C results from air samples collected from four further cruises. δ13C values obtained during the 2004/2005 cruise show an inexplicable saw-toothed distribution. Air samples from the 2005/2006 cruise have δ13C values which match previous sets of samples (1998 to 2004) and show more frequent and more negative isotopic events. From 2006 until 2009, further samples could not be collected. However, during December 2009 and January 2010, two more sets of air samples were collected, the δ13C values of which greatly differ from previous results, being absolutely homogeneous and paralleled by flat CO2 concentrations. The results of these last two sets of air samples may be due either to fortuitous environmental conditions or to an improbable and substantial change in oceanic and atmospheric conditions in this section of the circumpolar area.