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

Graham Jones; Mark Curran; Hilton Swan; Elisabeth Deschaseaux

doi:10.4236/ajcc.2017.62017

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

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

Graham Jones, Mark Curran, Hilton Swan and Elisabeth Deschaseaux

American Journal of Climate Change, Vol.6(2), pp.328-359

2017

DOI: https://doi.org/10.4236/ajcc.2017.62017

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Abstract

Dimethylsulfide,

Low Level Cloud

Climate Feedback

Coral Bleaching

Coral reefs produce atmospheric dimethylsulfide (DMSa) which oxidises to non-sea-salt (nss) sulfate aerosols, precursors of cloud condensation nuclei (CCN) and low level cloud (LLC), reducing solar radiation and regulating sea surface temperatures (SSTs). Here we report measurements of solar radiation, SST, LLC, DMS flux, NH4 + , and rainfall before, during and after a major coral bleaching event at Magnetic Island in the central Great Barrier Reef (GBR). Measurements are compared with those made at the nearby fringing reef of Orpheus Island where coral bleaching did not occur. Extreme solar radiation levels occurred from November to late January and could have reflected cloud radiative effects that increased downwelling of solar radiation. High levels of LLC often coincided with high periodic fluxes of DMS from the unbleached coral reef at Orpheus Island (e.g. 14 - 20 µmol·m−2 ·d−1 ), in direct contrast to the very low fluxes of DMS that were emitted from the bleached, human-impacted Magnetic Island fringing reef (nd-0.8 µmol·m−2 ·d−1) when SSTs were >30˚C. Continuous SSTs measurements at the Magnetic Island reef revealed various heating and cooling periods, interspersed with stable SSTs. Cooling periods (negative climate feedback) ranged from −1˚C to −3˚C (7 day mean −1.6˚C), and often seemed to occur during low tides, periodic pulses of DMS flux and LLC, keeping SSTs < 30˚C. In contrast warming periods of +1˚C to +3˚C (positive climate feedback, 7 day mean +1.52˚C), seemed to occur during increasing tides, decreasing DMS flux and low to medium levels of LLC which increased solar radiation and caused SSTs over 30˚C and corals to bleach. Alternation between these two states or types of feedback is indicated in this research and may be a function of enhanced scattering of solar radiation from nss-sulfate aerosols that originate from oxidation of DMSa produced from the coral reefs in the GBR. The net radiative forcing from clouds can be as high as four times as large as the radiative forcing from a doubling of CO2 levels in the atmosphere, which needs to be taken into account when ascribing coral bleaching events in the GBR solely to GHG warming. Further studies are needed to more critically assess the importance of this GBR coral reef-cloud feedback to the climate of northern Australia and the western Pacific, where the greatest biomass of coral reefs occurs

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Title: Dimethylsulfide and Coral Bleaching: Links to Solar Radiation, Low Level Cloud and the Regulation of Seawater Temperatures and Climate in the Great Barrier Reef
Creators: Graham Jones - Southern Cross University
Mark Curran - Antarctic Climate and Ecosystems Cooperative Research Centre
Hilton Swan - Southern Cross University
Elisabeth Deschaseaux - Southern Cross University
Publication Details: American Journal of Climate Change, Vol.6(2), pp.328-359
Identifiers: 991012986298302368
Academic Unit: Faculty of Science and Engineering; Centre for Coastal Biogeochemistry
Language: English
Resource Type: Journal article

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

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