Observation of a fast ozone loss in the marginal ice zone of the Arctic Ocean

[ 1] In both polar regions tropospheric ozone regularly decreases during springtime to negligible concentrations in the atmospheric boundary layer. Here we report the observation of a dramatic ozone depletion event in the atmospheric boundary layer in the vicinity of new ice fields in the marginal ice zone (MIZ) of the Arctic Ocean monitored by instrumentation on board the icebreaker RV Polarstern. The ozone mixing ratio decreased from approximately 40 to below 1 ppbV in less than 7 hours. The analyses of backward trajectories and the synoptic conditions indicate that the observed decrease was not caused by the transport of ozone-free air, but that the ozone depletion occurred locally. Accordingly, bromine oxide, which is formed during the photochemical destruction of ozone in the presence of reactive bromine compounds, was significantly enhanced: Bromine oxide concentrations of approximately 1.8 . 10(9) molecules cm(-3) are retrieved around the same location from SCIAMACHY satellite observations assuming a uniform vertical distribution within the boundary layer. The release of bromine in the MIZ where the new ice formation took place appears to be the most likely explanation for the activation of reactive bromine compounds and subsequent depletion of ozone. Since the conditions were favorable for the formation of frost flowers, we suggest that these are the most likely sources of the reactive bromine. However, contributions of heterogeneous reactions on other surfaces like the highly saline brine on the new ice, aerosols generated from frost flowers, and sea salt aerosols deposited on the snowpack on top of the sea ice cannot be ruled out.