The sensitivity of Southern Ocean atmospheric dimethyl sulfide (DMS) to modeled oceanic DMS concentrations and emissions

Abstract

Abstract. The biogeochemical formation of dimethyl sulfide (DMS) from the Southern Ocean is complex, dynamic, and driven by physical, chemical, and biological processes. Such processes, produced by marine biogenic activity, are the dominant source of sulfate aerosol over the Southern Ocean. Using an atmosphere-only configuration of the United Kingdom Earth System Model (UKESM1-AMIP), we performed eight 10-year simulations for the recent past (2009–2018) during austral summer. We tested the sensitivity of atmospheric DMS to four oceanic DMS datasets and three DMS transfer velocity parameterizations. One oceanic DMS dataset was developed here from satellite chlorophyll a. We find that the choice of oceanic DMS dataset has a larger influence on atmospheric DMS than the choice of DMS transfer velocity. Simulations with linear transfer velocity parameterizations show a more accurate representation of atmospheric DMS concentration than those using quadratic relationships. This work highlights that the oceanic DMS and DMS transfer velocity parameterizations currently used in climate models are poorly constrained for the Southern Ocean region. Simulations using oceanic DMS derived from satellite chlorophyll a data, and when combined with a recently developed linear transfer velocity parameterization for DMS, show better spatial variability than the UKESM1 configuration. We also demonstrate that capturing large-scale spatial variability can be more important than large-scale interannual variability. We recommend that models use a DMS transfer velocity parameterization that was developed specifically for DMS and improvements to oceanic DMS spatial variability. Such improvements may provide a more accurate process-based representation of oceanic and atmospheric DMS, and therefore sulfate aerosol, in the Southern Ocean region.

Aerosol and Dimethyl Sulfide Sensitivity to Sulfate Chemistry Schemes

“…A. Bhatti et al (2023) identified a 171% spread in DJF atmospheric DMS from Southern Ocean DMS concentrations and emissions, whereas the spread identified from the simulations performed here during the same period and region is 48%. Although the emissions and concentrations drive much of the spatial and seasonal variability of atmospheric DMS, we demonstrate that differences in CMIP6 chemistry also have a profound influence on Southern Ocean atmospheric DMS.…”

“…A. Bhatti et al, 2023), we demonstrate the importance of choosing a sulfate chemical reaction scheme appropriately over the Southern Ocean. As a result, we investigate the global differences in chemical oxidation of DMS between each simulation.…”

“…A. Bhatti et al (2023). DMS emissions are calculated using the transfer velocity from Blomquist et al (2017).…”

“…A. Bhatti et al, 2023). Here, we examine the sensitivity of sulfate aerosol formation to the model's DMS and sulfate chemistry scheme.…”