Decadal increase in Arctic dimethylsulfide emission

Abstract

Dimethylsulfide (DMS), a gas produced by marine microbial food webs, promotes aerosol formation in pristine atmospheres, altering cloud radiative forcing and precipitation. Recent studies suggest that DMS controls aerosol formation in the summertime Arctic atmosphere and call for an assessment of pan-Arctic DMS emission (EDMS) in a context of dramatic ecosystem changes. Using a remote sensing algorithm, we show that summertime EDMS from ice-free waters increased at a mean rate of 13.3 ± 6.7 Gg S decade−1 (∼33% decade−1) north of 70°N between 1998 and 2016. This trend, mostly explained by the reduction in sea-ice extent, is consistent with independent atmospheric measurements showing an increasing trend of methane sulfonic acid, a DMS oxidation product. Extrapolation to an ice-free Arctic summer could imply a 2.4-fold (±1.2) increase in EDMS compared to present emission. However, unexpected regime shifts in Arctic geo- and ecosystems could result in future EDMS departure from the predicted range. Superimposed on the positive trend, EDMS shows substantial interannual changes and nonmonotonic multiyear trends, reflecting the interplay between physical forcing, ice retreat patterns, and phytoplankton productivity. Our results provide key constraints to determine whether increasing marine sulfur emissions, and resulting aerosol–cloud interactions, will moderate or accelerate Arctic warming in the context of sea-ice retreat and increasing low-level cloud cover.

Phytoplankton and dimethylsulfide dynamics at two contrasting Arctic ice edges

“…The taxonomic composition of the drifting under-ice bloom at station 305E was also dominated by pennate diatoms, but with lower total cell abundance (0.48 × 10 6 cells L −1 at 305E) compared to the two other Barrow Strait stations (> 2.00 × 10 6 cells L −1 at 304 and 305, data not shown), as well as slightly different species. The phytoplankton assemblage at 305E was similar to the one previously described by Galindo et al (2014) for the underice bloom developing at a shallow station (50 m) in Allen Bay in 2011, located ca. 15 km west of 305E.…”

“…The dominance of the phytoplankton assemblage by pennate diatoms in the Barrow Strait region (BS transect station 305E as well as stations 304 and 305; see Fig. 1) suggests that the release of ice-associated algae (sympagic) likely contributed to the seeding of the under-ice bloom, as observed during similar under-ice blooms in the Barrow Strait region (Fortier et al, 2002;Galindo et al, 2014). These results agree with studies emphasizing the importance of ice algal communities as a seeding source during spring over oceanic regions when algal abundance in the water column is low (e.g., Arctic Ocean north of Svalbard by Kauko et al, 2018;Frobisher Bay in Davis Strait by Hsiao, 1992).…”

“…2 µg Chl a L −1 ) was lower than the maximum value of ca. 10 µg L −1 reported by Galindo et al (2014) during under-ice blooms at the end of June 2011. The 5-times-higher biomass measured during Galindo's study suggest that turbulent mixing could bring additional nutrients to the under-ice bloom closer to shore.…”

“…Global empirical relationships between DMS and other biogeochemical and physical variables are often inconsistent and difficult to establish (Kettle et al, 1999). The Arctic, in particular, displays important patchiness in drivers of DMS dynamics (Galí and Simó, 2010;Galindo et al, 2014;Jarníková et al, 2018), associated in great part with the presence of ice and its role in seeding under-ice algal blooms. The melt of sea ice and snow covers also influences surface water stratification and the ensuing shifts in salinity, temperature, and solar radiation doses experienced by potential DMS-producing communities.…”

“…These ice-edge blooms could account for up to 50 % of the annual primary production in the Arctic Ocean (Perrette et al, 2011) and represent the greatest supply of energy to the marine Arctic ecosystem (Wassmann et al, 2008). Later in the growing season, phytoplankton blooms can also develop under the ice as light penetration through the ice pack is heightened due to snow melting, ice thinning, and the development of melt ponds (Fortier et al, 2002;Mundy et al, 2007;Arrigo et al, 2012;Galindo et al, 2014). The gradual loss of perennial sea ice, induced by climate change, is thus expected to influence the phenology of ice-edge blooms and the associated biogeochemical cycling of elements such as carbon, nitrogen, and sulfur.…”