Global simulations of the impact on contemporary climate of a perturbation to the sea-to-air flux of dimethylsulfide

Abstract

The sea-to-air flux of the biogenic sulfur (S) compound dimethylsulfide (DMS) is thought to constitute an important radiative impact on climate, especially in remote marine areas. Previous biogeochemical modelling analyses simulate medium to large changes in the sea-to-air flux of DMS in polar regions under warming scenarios. Here we assess the global radiative impact of such a prescribed change in DMS flux on contemporary climate using a low-resolution atmospheric general circulation model. This impact operates through the atmospheric oxidation of DMS to radiatively-active sulfate aerosols, which are known to both reflect incoming short-wave radiation and to affect the microphysical properties of clouds, for example, through an increase in cloud albedo. We use an atmospheric GCM with incorporated sulfur cycle, coupled to a mixed-layer ('q-flux') ocean, to estimate the climatic response to a prescribed meridionally-variable change in zonal DMS flux, as simulated in a previous modelling analysis. We compare baseline sulfur emissions (contemporary anthropogenic S and contemporary DMS sea-to-air flux), with contemporary anthropogenic S and a perturbed DMS flux. Our results indicate that the global mean DMS vertically integrated concentration increases by about 41 per cent. The relative increase in DMS annual emission is around 17 per cent in 70-80°N, although the most significant increase is in 50-70°S, up to 70 per cent. However, concentrations of atmospheric SO 2 and SO 4 2-increase by only about eight per cent. The oxidation of DMS by OH increases by about 20 per cent. Oxidation of SO 2 to SO 4 2 by H 2 O 2 increases seven per cent. The oxidation of SO 2 by O 3 increases around six per cent. Overall sulfur emissions increase globally by around 4.6 per cent.Global mean aerosol optical depth (AOD) increases by 3.5 per cent. Global mean surface temperature decreases by 0.6 K. There is a notable difference between the impacts in the southern and northern hemispheres. In general, most processes and chemical species related to the sulfur cycle show a larger increase in the southern hemisphere, except SO 2 and the oxidation of DMS by NO 3 . The global mean direct radiative forcing due to the DMS change is -0.05 Wm -2 with total forcing (direct + indirect effects) of -0.48 Wm -2 . This perturbation on DMS flux leads to a mean surface temperature decrease in the southern hemisphere of around 0.8 K, compared with a decrease of 0.4 K in the northern hemisphere.

Influence of dimethyl sulfide on the carbon cycle and biological production

“…Furthermore, the sign and strength of feedback loops involving different phytoplankton groups varies. The overall sign of the feedback disagrees with some previous studies (Bopp et al 2004;Gunson et al 2006;Gabric et al 2013). This discrepancy can be attributed to the coupling between a dynamic marine ecosystem module and the sulfur cycle mechanism adopted in the current simulations.…”

“…They found negligible changes in the direct effect and an indirect effect of -0.05 W/m 2 . Using the elevated DMS flux simulated by Gabric et al (2004) (3 9 CO 2 ), Gabric et al (2013) estimated the global mean direct effect due to the DMS perturbation to be -0.05 W/m 2 and the total radiative forcing to be -0.48 W/m 2 . Sensitivity simulations conducted by Gunson et al (2006) showed significant impacts on the net cloud radiative forcing of -2 and 3 W/m 2 due to doubling and halving the DMS flux, respectively.…”

Impacts of Shifts in Phytoplankton Community on Clouds and Climate via the Sulfur Cycle

“…Thomas et al (2011) showed 23.1% changes in aerosol optical depth (AOD) between simulations with and without oceanic DMS emissions over 30°S-75°S using a global aerosol-chemistry-cloud microphysics-climate model (ECHAM5-HAMMOZ). Another previous study suggested a weaker response of AOD to DMS perturbations, a 3.5% increase in AOD in response to a 14% increase in the oceanic sulfur emission (Gabric et al, 2013). Motivated by these studies, we compare modeled AOD to examine the sensitivity of direct effects to changes in ocean ecosystems through the sulfur cycle.…”

The Impact of Melting Ice on the Ecosystems in Greenland Sea

“…The oceanic CO 2 absorption capacity decreases, while oceanic CO 2 burden increases. Gabric et al (2013) used an atmospheric GCM with incorporated sulfur cycle, coupled to a mixed-layer ("q-flux") ocean, to estimate the climatic response to a prescribed meridionally variable change in zonal DMS flux. It is not well known that on the other hand, atmospheric aerosols have a cooling effect on global temperature.…”