Climatically-active trace gas emissions from the Antarctic seasonal ice zone – CGS-111

The Southern Ocean seasonal ice zone (SIZ) is a large and important biogeochemical province. Significant regional changes in the extent and duration of the Southern Ocean SIZ have been observed in recent decades (Vaughan et al., 2013; Stammerjohn et al., 2012), and further large changes are expected in the future in response to alterations in atmospheric temperatures and winds (Smith et al., 2014). These changes could have important implications for regional climate forcing as seasonal ice melt creates physiochemical conditions in the SIZ (Venables et al., 2013; Wang et al., 2014) that promote high rates of primary productivity at the ice edge (Taylor et al., 2013), leading to enhanced sea-air exchange of climate-active gases. As examples, the SIZ has very high fluxes of ozone depleting halogens including iodine & bromine (Hughes et al., 2012), and is suggested to be an emission ‘hot-spot’ for the cloud condensation nuclei (CCN) precursor dimethyl sulphide (DMS; Trevena & Jones, 2012) and the secondary organic aerosol (SOA) precursor isoprene (Meskhidze & Nenes, 2006; Hu et al., 2013).
It has been proposed that an expansion of the SIZ at high latitudes will promote increased emissions of climate-active gases such as DMS and that this will instigate regional climate-cooling effects (Levasseur, 2013). The SIZ is, however, a site of enhanced sea-air exchange of a range of climate-active gases, each of which will contribute to regional climate forcing. These gases and their breakdown products can also interact in the atmosphere. For example, von Glasow et al. (2004) show that tropospheric DMS levels are dramatically reduced in the presence of bromine oxides with potentially drastic changes in CCN formation. Hence, resulting climate forcing could be very different if a range of climate-active gases are simultaneously released from the SIZ. We are currently unable to quantify the net impact of Southern Ocean SIZ emissions on regional climate forcing as studies have, so far, focussed on only one or two groups of gases. It is essential that we now quantify emission rates of a range of key climate-active gases and understand the factors controlling their seawater concentrations so we can predict what, if any, SIZ-atmosphere-climate feedbacks will operate in the future.