Sensitivity Study of Atmospheric DMS Simulated in WRF-Chem to Various Oceanic DMS Fields Over the South West Pacific

Marine emission of the volatile gas dimethyl sulfide (DMS) is the most substantial source of natural sulfur in the global atmosphere. DMS is believed to play a significant role in the Earth's climate system as a precursor to new particle formation and cloud condensation nuclei in the pristine marine atmosphere. To simulate the global distribution of seawater DMS, atmospheric models use DMS climatologies. In this study, we tested the sensitivity of atmospheric DMS concentrations over the Southwest Pacific Ocean, simulated with the WRF-Chem regional model, to five seawater DMS climatologies developed over the last two decades together with seawater DMS inferred from a recently developed relationship from nanophytoplankton satellite retrievals. Comparisons with in situ observations recently obtained in the Southwest Pacific and the Southern Ocean revealed that oceanic DMS climatologies are less accurate for latitudes south of 65°S than between 40°S and 65°S. In addition, in our study area, the spatial distribution of marine DMS is more accurately reproduced in the 40–65°S latitudes when deduced from a surface ocean biological variable, particularly when using a recently derived relationship from nanophytoplankton satellite retrievals, rather than from observation-based climatologies. Simulated atmospheric DMS levels were sensitive to the oceanic DMS climatology used but the atmospheric DMS concentration variability was mostly dependent on the atmospheric dynamics. Atmospheric DMS concentrations and variability measured off the New-Zealand coast are fairly well reproduced in WRF-Chem using accurate phytoplanktonic assemblages and the nanophytoplankton-related seawater DMS concentration.