A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification

Frances E Hopkins,Philip D Nightingale,Gemma L Cripps,Sophie Richier,C Mark Moore,Stephen D Archer,John A Stephens

doi:10.5194/bg-17-163-2020

Abstract

Abstract. Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in atmospheric processes and climate. Therefore, it is important to increase our understanding of how DMS production in these regions may respond to climate change. The polar oceans are particularly vulnerable to ocean acidification (OA). However, our understanding of the polar DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS concentrations decreased with increasing acidity. Here, we report on our findings from seven summertime shipboard microcosm experiments undertaken in a variety of locations in the Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short-term OA on the net production of DMS by planktonic communities. This is in contrast to similar experiments from temperate north-western European shelf waters where surface ocean communities responded to OA with significant increases in dissolved DMS concentrations. A meta-analysis of the findings from both temperate and polar waters (n=18 experiments) reveals clear regional differences in the DMS response to OA. Based on our findings, we hypothesize that the differences in DMS response between temperate and polar waters reflect the natural variability in carbonate chemistry to which the respective communities of each region may already be adapted. If so, future temperate oceans could be more sensitive to OA, resulting in an increase in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS emissions from the polar oceans may remain relatively unchanged. By demonstrating that DMS emissions from geographically distinct regions may vary in their response to OA, our results may facilitate a better understanding of Earth's future climate. Our study suggests that the way in which processes that generate DMS respond to OA may be regionally distinct, and this should be taken into account in predicting future DMS emissions and their influence on Earth's climate.

Highlights

The trace gas dimethylsulfide (DMS) is a key ingredient in a cocktail of gases that exchange between the ocean and atmosphere
Chlorophyll a (Chl a) was variable in polar waters, exceeding 4 μg L−1 at South Sandwich and 2 μg L−1 at Greenland Ice-edge, whilst the remaining stations ranged from 0.2 μg L−1 (Weddell Sea) to 1.5 μg L−1 (Barents Sea) (Fig. 2)
We have shown that net DMS production by summertime polar open ocean microbial communities is insensitive to ocean acidification (OA) during multiple, highly replicated short-term microcosm experiments

Summary

Introduction

The trace gas dimethylsulfide (DMS) is a key ingredient in a cocktail of gases that exchange between the ocean and atmosphere. DMS and its oxidation products play vital roles in atmospheric chemistry and climate processes. These processes include aerosol formation pathways that influence the concentration of cloud condensation nuclei (CCN), with implications for Earth’s albedo and climate (Charlson et al, 1987; Korhonen et al, 2008a), and the atmospheric oxidation pathways of other key climate gases, including isoprene, ammonia and organohalogens Hopkins et al.: DMS production in polar waters is insensitive to ocean acidification

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