Dimethylsulfide (DMS) fluxes from permeable coral reef carbonate sediments

Abstract

Dimethylsulfide (DMS) is a biogenic volatile organic compound of high interest as it can influence the Earth's climate by contributing to cloud formation in the atmosphere. Although DMS occurs at high concentrations in coral reef ecosystems, the role of permeable coral reef carbonate sediments as a source and sink of DMS to the surrounding seawater is unknown. Here, we report for the first time fluxes of dissolved DMS from permeable coral reef carbonate sediments over a full diel cycle obtained from benthic chamber deployments on the reef flat of Heron Island, southern Great Barrier Reef. Carbonate coral reef sediments were a substantial net diel source of DMS to the water column (mean 85.4 ± 13.2; range 42.3 ± 5.1 to 114 ± 4.7 nmol m−2 h−1), with rates similar to saltmarsh sediments. DMS effluxes were higher in the light under advective porewater flow, suggesting that DMS production in carbonate coral reef sediments is associated with photosynthesis by benthic microalgae. However, DMS effluxes decreased with advection at night, suggesting either greater DMS consumption or less DMS production under dark conditions. Similarly, dimethylsulfoniopropionate (DMSP), which is generally considered the main precursor of DMS, was mainly produced during the day. Net and dark methane (CH4) effluxes negatively correlated with net DMSP and dark DMS fluxes, respectively; suggesting that CH4 production via methanogenesis could be a sink for DMS and DMSP in carbonate coral reef sediments, especially under dark anoxic conditions. On Heron Island the permeable sands were estimated to contribute from about 22% to 44% of the benthic DMS emitted from the reef to the water column, which could represent an important portion of the yearly sea-to-atmosphere DMS fluxes. Permeable carbonate sediments should be considered further as a source of benthic DMS emitted from coral reefs and the broader continental shelf.