Coral Reef Emissions of Atmospheric Dimethylsulfide and the Influence on Marine Aerosols in the Southern Great Barrier Reef, Australia

R L Jackson,H B Swan,M T Woodhouse,E S M Deschaseaux,R Cropp,A J Gabric,G B Jones

doi:10.1029/2019jd031837

Abstract

AbstractVariability in atmospheric dimethylsulfide (DMSa) and the potential influence on atmospheric aerosols was investigated at Heron Island in the southern Great Barrier Reef (GBR), Australia. This work compiles previously published DMSa data (reported in Swan, Jones, Deschaseaux, & Eyre, 2017, https://doi.org/10.5194/bg‐14‐229‐2017), with additional surveys of DMSa, atmospheric particle number concentration, and other oceanic and atmospheric data sets. DMSa was higher in summer (mean 3.2 nmol m−3/78 ppt) than winter (mean 1.3 nmol m−3/32 ppt), reflective of seasonal shifts in phytoplankton biomass and emissions from corals in the southern GBR. Seasonally extreme spikes in DMSa were detected during low tide and low wind speed, supporting findings that the coral reef can be an important source of DMSa above background oceanic emissions. A significant link was present between DMSa and aerosol concentration (ranging from 0.5 to 2.5 μm) during calm, daylight hours, when conditions were optimal for the local oxidation of DMSa to sulfate aerosol precursors. This link may reflect condensational growth of existing fine particles (< 0.5 μm), which is the dominant pathway by which biogenic trace gases influence aerosols in the marine boundary layer. Aerosol concentration significantly correlated with reduced surface solar irradiance and sea surface temperature, which is potential evidence of a local negative feedback mitigating coral physiological stress. These findings provide a step toward a better understanding of the processes influencing DMSa and aerosol concentrations and of the consequences for the local radiative balance over coral reefs; an increasingly important topic with ongoing ocean warming and coral bleaching.

Highlights

In the clean marine boundary layer (MBL) biogenic sulfates contribute to marine biogenic aerosol (MBA) formation and growth (Gabric et al, 2013; Korhonen et al, 2008; Modini et al, 2009; Sanchez et al, 2018)
Our results support previous findings that the coral reef is a strong source of DMSa above the background oceanic signal during calm conditions, at low tide
The diel DMSa cycle varied between season at Heron Island, with daily maximums occurring at midday in winter, yet daily minimums at midday in summer

Summary

Introduction

In the clean marine boundary layer (MBL) biogenic sulfates contribute to marine biogenic aerosol (MBA) formation and growth (Gabric et al, 2013; Korhonen et al, 2008; Modini et al, 2009; Sanchez et al, 2018). Reported concentrations of dimethylated sulfur compounds are typically higher in zooxanthellate corals than in other marine producers (Broadbent et al, 2002; Swan, Deschaseaux, et al, 2017). Corals and their endosymbiotic zooxanthellae upregulate the biosynthesis of dimethylsulfoniopropionate (DMSP) during physiological stress caused by elevated sea surface temperature (SST) and irradiance, hyposalinity with rainfall or riverine discharge, and aerial exposure at low tide (Deschaseaux, Jones, et al, 2014; Hopkins et al, 2016; Jones et al, 2014; Raina et al, 2013). Zooxanthellate corals harbor several genetically distinct types of dinoflagellates, distinguished as zooxanthellae Clades (A–H), and DMSP biosynthesis varies between coral species and JACKSON ET AL

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