Reviews and syntheses: Marine biogenic aerosols and the ecophysiology of coral reefs

Abstract

<p><strong>Abstract.</strong> Coral reefs are being threatened by global climate change, with ocean warming and acidification, compounded by declining water quality in many coastal systems, adversely affecting coral health and cover. This is of great concern as coral reefs provide numerous ecosystem, economic and social services. Corals are also recognized as being amongst the strongest individual sources of natural atmospheric sulfur, through stress-induced emissions of dimethylsulfide (DMS). In the clean marine boundary layer, biogenic sulfates contribute to new aerosol formation and the growth of existing particles, with important implications for the radiative balance. Evidence suggests that DMS is not only directly involved in the coral stress response, alleviating oxidative stress, but may create an <q>ocean thermostat</q> which suppresses sea surface temperature (SST) through changes to aerosol and cloud properties. This review provides a summary of the current major threats facing coral reefs and describes the role of dimethylated sulfur compounds in coral physiology and climate. The role of coral reefs as a source of climatically important compounds is an emerging topic of research however, the window of opportunity to understand the complex biogeophysical processes involved is closing with ongoing degradation of the world's coral reefs. The greatest uncertainty in our estimates of radiative forcing and climate change are derived from natural aerosol sources, such as marine DMS, which constitutes the largest flux of oceanic reduced sulfur to the atmosphere. Gaining a better understanding of the role of coral reef DMS emissions is crucial to predicting the future climate of our planet.</p>

CMIP6 projections of ocean warming and the impact on dimethylsulfide emissions from the Great Barrier Reef, Australia

“…Fischer & Jones, 2012). While it is not possible to distinguish between coral and algal-derived DMS w from observations of dissolved DMS concentration alone, increases in DMS-producing marine algae in degraded coral reef ecosystems (McCook and Diaz-Pilido, 2002;De'ath & Fabricius, 2010) could counteract a decline in coral-derived DMS w (as discussed in Jackson et al, 2020). More research is required to determine whether corals can acclimate to rising SST and how DMS w in coral reefs will be affected by changes in surface temperature, irradiance and coral-algal interactions.…”

“…Coral reefs are strong regional sources of biogenic sulfur through stress-induced emissions of dimethylsulfide (DMS). The atmospheric oxidation products of DMS are important sulfate aerosol precursor compound which can influence nonsea salt sulfate (nss-SO 4 ) aerosol properties (Gabric et al, 2013;Woodhouse et al, 2013;Fiddes et al, 2018;Sanchez et al, 2018;Jackson et al, 2020). It has been hypothesised that DMS emissions from coral reefs may facilitate aerosol nucleation and growth to cloud condensation nuclei (CCN), influencing the lifetime and albedo of low-level clouds (LLC) over coral reefs via aerosol direct and indirect effects on the radiation budget (Fischer & Jones, 2012;Jones, 2015;Jones et al, 2017).…”

“…Ocean warming poses one of the greatest threats to coral reefs (Ainsworth et al, 2016;Hughes et al, 2019). In addition to more frequent and severe coral bleaching events, warmer oceans may lead to a change in DMS production and emissions (Jackson et al, 2020). Given that DMS(P) production in the coral holobiont is upregulated in response to thermal stress (Raina et al, 2013), rising SST could increase coral DMS(P) biosynthesis.…”