Coral reef origins of atmospheric dimethylsulfide at Heron Island, southern Great Barrier Reef, Australia

Abstract

Abstract. Atmospheric dimethylsulfide (DMS a ), continually derived from the world's oceans, is a feed gas for the tropospheric production of new sulfate particles, leading to cloud condensation nuclei that influence the formation and properties of marine clouds and ultimately the Earth's radiation budget. Previous studies on the Great Barrier Reef (GBR), Australia, have indicated coral reefs are significant sessile sources of DMS a capable of enhancing the tropospheric DMS a burden mainly derived from phytoplankton in the surface ocean; however, specific environmental evidence of coral reef DMS emissions and their characteristics is lacking. By using on-site automated continuous analysis of DMS a and meteorological parameters at Heron Island in the southern GBR, we show that the coral reef was the source of occasional spikes of DMS a identified above the oceanic DMS a background signal. In most instances, these DMS a spikes were detected at low tide under low wind speeds, indicating they originated from the lagoonal platform reef surrounding the island, although evidence of longer-range transport of DMS a from a 70 km stretch of coral reefs in the southern GBR was also observed. The most intense DMS a spike occurred in the winter dry season at low tide when convective precipitation fell onto the aerially exposed platform reef. This co-occurrence of events appeared to biologically shock the coral resulting in a seasonally aberrant extreme DMS a spike concentration of 45.9 nmol m −3 (1122 ppt). Seasonal DMS emission fluxes for the 2012 wet season and 2013 dry season campaigns at Heron Island were 5.0 and 1.4 µmol m −2 day −1 , respectively, of which the coral reef was estimated to contribute 4 % during the wet season and 14 % during the dry season to the dominant oceanic flux.

Quantification of dimethyl sulfide (DMS) production in the sea anemone <i>Aiptasia</i> sp. to simulate the sea-to-air flux from coral reefs

“…Taken together, this suggests that coral reefs likely continuously emit DMS at lower rates than the short-lived DMS "hotspots" of phytoplankton blooms in the North Atlantic (20.69 to 26.93 µmol m −2 SSA d −1 ; Holligan et al, 1993) or at high latitudes (21.87 µmol m −2 SSA d −1 ; Levasseur et al, 1994). Furthermore, our estimated sea-to-air flux from coral reefs is also often lower than the global oceanic flux that is calculated at 4.6 µmol m −2 SSA d −1 (equivalent to 19.6 Tg S yr −1 in Land et al, 2014) and is in agreement with earlier findings that suggest coral environments enhance the dominant oceanic DMS flux by just 4 % during the wet season and 14 % during the dry season (Swan et al, 2017). While our calculated fluxes refer to fully submersed reefs, it is important to note that tidally exposed corals such as the strongly DMS-producing Acropora spp.…”

“…Assuming a coral cover of 22 % in the Indo-Pacific (Bruno and Selig, 2007) and an average rugosity of 3 (Storlazzi et al, 2016), we can calculate a maximum flux of about 17.4 µmol DMS m −2 SSA d −1 , with the highest probabilities for fluxes ranging from 0.3 to 1.0 µmol DMS m −2 SSA d −1 . This flux is in good agreement with modelled fluxes based on continuous DMS measurements during the wet and dry seasons at Heron Island in the southern Great Barrier Reef that show coral-derived DMS fluxes of 0.2 µmol DMS m −2 SSA d −1 (Swan et al, 2017). Taken together, this suggests that coral reefs likely continuously emit DMS at lower rates than the short-lived DMS "hotspots" of phytoplankton blooms in the North Atlantic (20.69 to 26.93 µmol m −2 SSA d −1 ; Holligan et al, 1993) or at high latitudes (21.87 µmol m −2 SSA d −1 ; Levasseur et al, 1994).…”

“…(3000-11 000 µmol DMS m −2 SSA d −1 ) may provide substantial short 'bursts' of DMS to the atmosphere that last for several minutes during and after periods of aerial exposure (Hopkins et al, 2016). These bursts can be further enhanced when corals experience hypoosmotic stress from rain (Swan et al, 2017).…”

Dimethylsulfide and Coral Bleaching: Links to Solar Radiation, Low Level Cloud and the Regulation of Seawater Temperatures and Climate in the Great Barrier Reef

“…Mean aerosol particle concentrations averaged 3200 cm −3 and consisted of broad pulses of aerosol particles emitted in the morning and afternoon, with a small discrete aerosol burst at mid-day [26], a distribution similar to that measured for DMS a over coral reefs in the central GBR [28]. Periodic pulses of DMS a often occur over coral reefs during very low tides and rising tides [10] [28] [29] [30]. It is apparent that natural stress events (e.g.…”

“…[Adapted from Charlson et al 1987 [7] and Jones and Gabric, 2006 [8]]. Low tides and convective rainfall can increase the flux of DMS to the reef atmosphere, whilst wind speed over the ocean affects DMS transfer to the ocean atmosphere [9] [10].…”