Overview of the antarctic circumnavigation expedition: Study of preindustrial-like aerosols and their climate effects (ACE-SPACE)

The first results from ACE-SPACE highlight that the Southern Ocean is a region with highly heterogeneous aerosol properties. The areas around the strong westerly wind belt are characterized by significant sea spray contributions to the total particle and CCN number concentrations in the MBL. Future work will link detailed wave and wind observations to sea spray production. In the Ross and Amundsen Sea polynyas (leg 2), biogenic emissions appear to play an important role for CCN abundance. There are a number of open questions associated with this observation. First, even though this particular region was probed during a phytoplankton bloom period, it was not the only region with microbial activity but showed the clearest link to high CCN concentrations. Hence, either DMS production from dimethylsulfoniopropionate in the water and/or DMS fluxes into the atmosphere were enhanced. Second, the major pathway of how MSA is added to the particle phase remains to be identified. There are two possibilities: It can condense from the gas into the particle phase, or it can be added during cloud processing. The latter process would be consistent with the reduced efficiency of wet removal because of droplet evaporation or snowflake sublimation in the cold and dry airmasses from Antarctica. Our results also indicate that the absence of MSA-related processes in the aerosol model could explain the underestimation of CCN concentration, particularly in high aerosol-MSA regions. Given that the number of CCN influence Nd, this is an important issue to solve, especially close to the coast of Antarctica where clouds could impact the surface snow mass balance by influencing both the surface energy budget and precipitation. Further studies are planned that more closely investigate the linkages between CCN number concentrations and model simulations that take DMS emissions fluxes and particle phase MSA into account. A comparison of satellite-retrieved Nd90 and ship-based measurements of CCN s