Southern Ocean Emissions of DMS

The biogeochemical behaviour of the Southern Ocean is extremely complex and dynamic. The processes that effect this behaviour in the Southern Ocean are highly dependent on radiative (e.g. sunlight), chemical (e.g. nutrient availability) and biological (e.g. phytoplankton) constraints. We aim to assess how the Southern Ocean DMS emissions change when the underlying biological constraints on the production of DMS are altered across time and space.Using a nudged configuration of the atmosphere-only Earth System Model, UKESM1-AMIP, we performed two sets of four different 10-year simulations from 2009 – 2018. One set tested four different seawater DMS data sets (Anderson et al. 2001, Hulswar et al. 2022, Lana et al. 2011, ), while the other set tested four different DMS sea-to-air flux parameterisations (Goddijn-Murphy et al. 2016, Liss and Merlivat 1986, Nightingale et al. 2000, Wanninkhof 2014). Our goal is to evaluate the variability in each stage for atmospheric DMS formation using four sea-to-air parameterizations and four oceanic DMS sources.Using a quadratic sea-to-air flux (Wanninkhof (2014) and Nightingale et al. (2000)) provides high transfer velocities in DMS, creating a positive bias across most areas of the Southern Ocean, except for biologically productive areas, such as the high latitude regions. Although the Southern Ocean atmospheric DMS average corresponds well to observations using quadratic formulas, large areas of the Southern Ocean have lower measured atmospheric DMS than model simulations. Linear relationships between wind and flux are shown to be more realistic. We find that there is a greater range of outcomes from the different sea-to-air flux parameterizations (2.84 TgS Yr-1 to 7.44 TgS Yr-1) than from the different oceanic DMS datasets (3.37 TgS Yr-1 to 7.29 TgS Yr-1). This work highlights the need for Earth System Models to include a sea-to-air parameterization that is more appropriate for DMS, and for oceanic DMS datasets to capture the time-varying nature of biological activity. Such improvements would help provide more accurate and realistic simulations of DMS in the Southern Ocean.