Relationship between continuous aerosol measurements and firn core chemistry over a 10-year period at the South Pole

Before ice core chemistry can be used to estimate past atmospheric chemistry it is necessary to establish an unambiguous link between concentrations of chemical species in the air and snow. For the first time a continuous long-term record of aerosol properties (aerosol light scattering coefficient, sigma(sp) and Angstrom exponent, (a) over circle) at the South Pole are compared with the chemical record from a high resolution firn core (similar to 10 samples per year) covering the period from 1981 to 1991. Seasonal signals in (a) over circle, associated with winter minima due to coarse mode seasalt and summer maxima due to accumulation mode sulfate aerosol, are reflected in the firn core SO42-/Na+ concentration ratio. Summertime ratios of sigma(sp) and aerosol optical depth, tau, to corresponding firn core sulfur concentrations are determined and the 'calibrations' are applied to sulfur concentrations in snowpits from a previous study. Results show that sigma(sp) estimates from snowpit sulfur concentrations are in agreement with atmospheric measurements while tau estimates are significantly different, which is likely due to the lack of understanding of the processes that mix surface air with air aloft.