The temporal and spatial distribution of enhanced boundary layer BrO concentrations in both hemispheres during 1997 is presented using observations of the Global Ozone Monitoring Experiment (GOME) on board the European research satellite ERS-2. BrO concentrations (up to 50 ppt) are the major cause for catalytic boundary layer ozone destruction typically observed during polar spring in both hemispheres. While autocatalytic mechanisms are most probably responsible for the release of the observed high concentrations of reactive bromine compounds, uncertainties still remain with respect to the primary release mechanisms and whether the autocatalytic reactions are taking place on sea-salt aerosol or the surface of sea ice. We find that enhanced boundary layer BrO concentrations correlate very well with ozone depletion events. Enhanced BrO concentrations are always found over or near to areas of frozen salt water (above sea ice or also above the frozen surface of the Caspian Sea) consistent with the assumption that such conditions are a prerequisite for the autocatalytic release of high BrO concentrations to the troposphere.