Abstract
Abstract. The ubiquitous marine trace gas dimethyl sulfide (DMS) comprises the greatest natural source of sulfur to the atmosphere and is a key player in atmospheric chemistry and climate. We explore the short-term response of DMS production and cycling and that of its algal precursor dimethyl sulfoniopropionate (DMSP) to elevated carbon dioxide (CO2) and ocean acidification (OA) in five 96 h shipboard bioassay experiments. Experiments were performed in June and July 2011, using water collected from contrasting sites in NW European waters (Outer Hebrides, Irish Sea, Bay of Biscay, North Sea). Concentrations of DMS and DMSP, alongside rates of DMSP synthesis and DMS production and consumption, were determined during all experiments for ambient CO2 and three high-CO2 treatments (550, 750, 1000 μatm). In general, the response to OA throughout this region showed little variation, despite encompassing a range of biological and biogeochemical conditions. We observed consistent and marked increases in DMS concentrations relative to ambient controls (110% (28–223%) at 550 μatm, 153% (56–295%) at 750 μatm and 225% (79–413%) at 1000 μatm), and decreases in DMSP concentrations (28% (18–40%) at 550 μatm, 44% (18–64%) at 750 μatm and 52% (24–72%) at 1000 μatm). Significant decreases in DMSP synthesis rate constants (μDMSP, d−1) and DMSP production rates (nmol d−1) were observed in two experiments (7–90% decrease), whilst the response under high CO2 from the remaining experiments was generally indistinguishable from ambient controls. Rates of bacterial DMS gross consumption and production gave weak and inconsistent responses to high CO2. The variables and rates we report increase our understanding of the processes behind the response to OA. This could provide the opportunity to improve upon mesocosm-derived empirical modelling relationships and to move towards a mechanistic approach for predicting future DMS concentrations.
Highlights
Dimethyl sulfide (DMS) is a ubiquitous marine trace gas derived from the breakdown of the algal osmolyte ß-dimethyl sulfoniopropionate (DMSP)
The bioassay results we present represent an “acclimatory” response characterised by the lack of ability of small phytoplankton (< 10 μm) to adapt to the altered carbonate chemistry
Our data are suggestive of an increase in stress-induced algal processes induced by the rapid changes to carbonate chemistry
Summary
Dimethyl sulfide (DMS) is a ubiquitous marine trace gas derived from the breakdown of the algal osmolyte ß-dimethyl sulfoniopropionate (DMSP). A variety of phytoplankton species produce DMSP, with the majority of production attributed to prymnesiophytes, dinoflagellates and diatoms (Stefels, 2000). DMSP is released from phytoplankton cells into the dissolved phase by active exudation or when cells are lysed during grazing, viral attack or senescence (Stefels et al, 2007). Once in this phase, marine bacteria play a vital role in the fate of DMSP in the surface oceans. Most DMSP released from phytoplankton is either catabolised by bacteria to produce DMS (Todd et al, 2007, 2009), or Published by Copernicus Publications on behalf of the European Geosciences Union
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