Ozone in the Boundary Layer air over the Arctic Ocean: Measurements During the TARA Expedition.

It is now well established that after sunrise in polar regions, the atmospheric boundary layer experiences episodes where dramatic loss of ozone can be observed. Virtually all measurements in this respect have been made at coastal observatories on land, but there is strong evidence to surmise that such episodes originate over the frozen ocean. Satellite measurements (GOME, SCIAMACHY, OMI) invariably indicate large areas over the ocean with increased concentrations of BrO which can be interpreted as a smoking gun for ozone depletion processes, but no systematic in-situ measurements of ozone do exist to corroborate the satellite data. The TARA expedition (www.taraexpeditions.org) (IPY project # 238) has enabled us for the first time to make long term ozone measurements in the surface air over the Arctic Ocean, and we report here the first results. As expected ozone was found to be stable at approx. 35 ± 5 nmol~mol-1 during the winter, but shortly after local sunrise in mid March, large depletions of ozone were observed which lasted until well into June. A particularly long episode (> 15 days) of virtually no ozone (mole fraction below or near 1 nmol~mol-1) was experienced during late April. 10-day back trajectories were calculated in an attempt to obtain more insight into the potential origin of the depletion episodes. To place the TARA ozone data into context we will compare the data with land based and satellite observations in 2007 when they become available, as well as the limited record of previous observations made from ice islands. Taking all evidence together it is plausible to speculate that large areas over the Arctic Ocean are devoid of ozone in the atmospheric boundary layer in the first months after polar sunrise, and that if anything, this will increase in the coming years. We speculate what the implications might be. This work is a contribution to IPY project #038 (OASIS, Ocean Atmosphere Sea-Ice and Snow interactions in polar regions), sponsored by the Canadian Federal Government Program for the IPY (project OASIS-CANADA).