Linking the Arctic Ocean and clouds - bubble and aerosol flux measurements from ASCOS

The Arctic Summer Cloud Ocean Study (ASCOS) project aimed to study the many interlinked processes that couple the central Arctic Ocean and sea ice with low level stratiform clouds – a key component of the Arctic climate system. One of the hypotheses that ASCOS set out to test was that biological material within the waters of open leads in the ice found their way into the atmospheric boundary layer where they acted as cloud condensation nuclei. In the open ocean bursting bubbles – generated by breaking waves – provide an efficient mechanism for the ejection of droplets of sea water into the air. The typically low wind speeds and short open water fetch within leads in the central Arctic means that breaking waves are likely to be rare, and the extent of bubbles within the lead waters was previously unknown. Optical measurements of bubble populations within a lead during ASCOS demonstrated significant numbers of small bubbles, in concentrations comparable to those in the open ocean under low to moderate wind speeds, but very few larger bubbles. Here we present size spectra of the measured bubble populations, estimate the flux to the surface, and discuss a potential generation mechanism. We also present direct eddy covariance measurements of the total aerosol number flux over the same open lead and assess their potential to account for observed changes in mean aerosol loading.