Abstract
Abstract. The marine biogenic gas dimethylsulfide (DMS) modulates climate by enhancing aerosol light scattering and seeding cloud formation. However, the lack of time- and space-resolved estimates of DMS concentration and emission hampers the assessment of its climatic effects. Here we present DMSSAT, a new remote sensing algorithm that relies on macroecological relationships between DMS, its phytoplanktonic precursor dimethylsulfoniopropionate (DMSPt) and plankton light exposure. In the first step, planktonic DMSPt is estimated from satellite-retrieved chlorophyll a and the light penetration regime as described in a previous study (Galí et al., 2015). In the second step, DMS is estimated as a function of DMSPt and photosynthetically available radiation (PAR) at the sea surface with an equation of the form: log10DMS=α+βlog10DMSPt+γPAR. The two-step DMSSAT algorithm is computationally light and can be optimized for global and regional scales. Validation at the global scale indicates that DMSSAT has better skill than previous algorithms and reproduces the main climatological features of DMS seasonality across contrasting biomes. The main shortcomings of the global-scale optimized algorithm are related to (i) regional biases in remotely sensed chlorophyll (which cause underestimation of DMS in the Southern Ocean) and (ii) the inability to reproduce high DMS ∕ DMSPt ratios in late summer and fall in specific regions (which suggests the need to account for additional DMS drivers). Our work also highlights the shortcomings of interpolated DMS climatologies, caused by sparse and biased in situ sampling. Time series derived from MODIS-Aqua in the subpolar North Atlantic between 2003 and 2016 show wide interannual variability in the magnitude and timing of the annual DMS peak(s), demonstrating the need to move beyond the classical climatological view. By providing synoptic time series of DMS emission, DMSSAT can leverage atmospheric chemistry and climate models and advance our understanding of plankton–aerosol–cloud interactions in the context of global change.
Highlights
Ocean-emitted gases and particles control the number, size distribution and composition of aerosols in remote oceanic areas (Brooks and Thornton, 2018)
This analysis systematically showed that (i) DMSPt was the best correlate of DMS (r = 0.46 to 0.65), and (ii) surface PARSAT and mean photosynthetically available radiation (PAR) in the mixed layer (PARMLD) were the best correlates of the DMS / DMSPt ratio (r = 0.35 to 0.67)
These correlation patterns remained across different binning levels, suggesting that DMS can be estimated, to first order, by the concentration of its phytoplanktonic precursor compound and by the PAR-dependent enhancement of DMSPt-to-DMS conversion
Summary
Ocean-emitted gases and particles control the number, size distribution and composition of aerosols in remote oceanic areas (Brooks and Thornton, 2018). These aerosols scatter sunlight and can act as cloud condensation nuclei that alter the radiative properties of clouds, both microscopic (cloud droplet number concentration and effective radius) and macroscopic (cloud abundance, albedo and lifetime). There is an urgent need to better understand and model the oceanic sources of aerosols, and to better resolve their variations at relevant spatial and temporal scales, from weekly to seasonal to interannual. With its emission currently estimated at 28 Tg S yr−1, it contributes about 70 % of natural sulfur emissions to the global atmo-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
