Soil CO2 flux baseline in an urban monogenetic volcanic field: the Auckland Volcanic Field, New Zealand

Abstract

The Auckland Volcanic Field (AVF) is a dormant monogenetic basaltic field located in Auckland, New Zealand. Though soil gas CO fluxes are routinely used to monitor volcanic regions, there have been no published studies of soil CO flux or soil gas CO concentrations in the AVF to date or many other monogenetic fields worldwide. We measured soil gas CO fluxes and soil gas CO concentrations in 2010 and 2012 in varying settings, seasons, and times of day to establish a baseline soil CO flux and to determine the major sources of and controlling influences on Auckland's soil CO flux. Soil CO flux measurements varied from 0 to 203 g m day, with an average of 27.1 g m day. Higher fluxes were attributed to varying land use properties (e.g., landfill). Using a graphical statistical approach, two populations of CO fluxes were identified. Isotope analyses of δCO confirmed that the source of CO in the AVF is biogenic with no volcanic component. These data may be used to assist with eruption forecasting in the event of precursory activity in the AVF, and highlight the importance of knowing land use history when assessing soil gas CO fluxes in urban environments.