Coupling between dimethylsulfide emissions and the ocean - atmosphere exchange of ammonia

Abstract

Environmental context. Dimethylsulfide (DMS) is recognised as a potentially significant climate-forcing gas, owing to its role in particle and cloud formation in the marine atmosphere, where it is the dominant source of acidity. Ammonia, the dominant naturally occurring base in the atmosphere, plays an important role in neutralising particles formed from DMS oxidation products and may even enhance the formation rate of new particles. A biogeochemical coupling has previously been proposed between DMS and ammonia fluxes from the ocean to the atmosphere, in the form of coproduction of the two gases in seawater. We revise this suggestion by introducing the concept of 'co-emission' of the gases, where DMS emission controls the rate of emission of ammonia from the ocean by acidifying the atmosphere. Abstract.A strong correlation between aerosol ammonium and non-sea salt sulfate is commonly observed in the remote marine boundary layer. It has been suggested that this relationship implies a biogeochemical linkage between the nitrogen (N) and sulfur (S) cycles at the cellular biochemical level in phytoplankton in the ocean, or a linkage in the atmosphere (see P. S. Liss and J. N. Galloway, Interactions of C, N, P and S biogeochemical cycles and global change (Springer, 1993), and P. K. Quinn et al. in J. Geophys. Res. -Atmos. 1990, 95). We argue that an oceanic linkage is unlikely and draw on mechanistic and observational evidence to make the argument that the atmospheric connection is based on simple physical chemistry. Drawing on an established analogous concept in terrestrial trace gas biogeochemistry, we propose that any emission of dimethylsulfide (DMS) from the ocean will indirectly influence the flux of NH 3 from the ocean, through the neutralisation of acidic DMS oxidation products and consequent lowering of the partial pressure of NH 3 in the atmosphere. We present a simple numerical model to investigate this hypothesised phenomenon, using a parameterisation of the rate and thermodynamics of gas-to-particle conversion of NH x and explicitly modelled oceanatmosphere NH 3 exchange. The model indicates that emission of acidic sulfur to the atmosphere (e.g. as a product of DMS oxidation) may enhance the marine emission of NH 3 . It also suggests that the ratio of ammonium to non-sea salt sulfate in the aerosol phase is strongly dependent on seawater pH, temperature and wind speed -factors that control the ocean-atmosphere ammonia flux. Therefore, it is not necessary to invoke a stoichiometric link between production rates of DMS and ammonia in the ocean to explain a given ammonium to non-sea salt sulfate ratio in the aerosol. We speculate that this mechanism, which can provide a continuous resupply of ammonia to the atmosphere, may be involved in a series of biogeochemical-climate feedbacks. His research interests are biogeochemical cycles taking place both within and between the ocean and its overlying atmosphere, with a focus on biogenic trace gases. He is currently working with Peter Liss as part of the Surfac...

Aerosol and snow transfer processes: An investigation on the behavior of water-soluble organic compounds and ionic species

“…Ammonium was mainly distributed in the <0.49 mm fraction (Fig. S2), suggesting that its main source was the ocean (Jickells et al, 2003;O'Dowd et al, 2004;Johnson and Bell, 2008). The ionic composition, concentration and particle size distributions were similar to data obtained from the same sampling site during the austral summer of 2010e11 (Barbaro et al, 2017).…”

Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean

“…Note that measured R NS in the SO region is always far from complete neutralization of sulfate aerosol; accordingly, the availability of acidic sulfate aerosol does not stoichiometrically limit the atmospheric NH 4 þ concentration. The measured R NS values fit with results of the co-emission model by Johnson and Bell (2008) Referring to the typically R NS value of 0.3 within the MBL source region relevant for the interior of Antarctica, an almost one order of magnitude depletion of this ratio is needed to achieve the values observed at EDML and EDC. The R NS of ammonium sulfate aerosol in an isolated, marine air mass traveling over the ice sheet is expected to steadily decrease as nssSO 4 2À builds up from the SO 2 (DMS) precursor, whereas the extremely low atmospheric NH 3 level (with respect to NH 4 þ ) may be neglected for subsequent NH 4 þ formation.…”

“…Physical conditions of the ocean surface strongly influence the emission of DMS during algal blooms (Andreae et al, 2003) and subsequently the production of sulfur aerosol and the flux of NH 3 (Johnson and Bell, 2008) out of the ocean surface. Iron fertilization experiments showed that diatoms, which only produce low amounts of DMSP, are outgrowing other phytoplankton species when nutrient supply is increased (Martin et al, 1989;Coale et al, 1996;Riseman and DiTullio, 2004).…”

Spatial and temporal variability of snow chemical composition and accumulation rate at Talos Dome site (East Antarctica)

“…Sulfuric acidity is partially or totally neutralized by NH 3 , giving (NH 4 )HSO 4 and (NH 4 ) 2 SO 4 , respectively (e.g. Johnson and Bell, 2008). The limiting factor of this neutralization usually is the atmospheric concentration of ammonia.…”