Polar dimethylsulfide ( DMS ) production insensitive to ocean 1 acidification during shipboard microcosm experiments : a 2 meta-analysis of 18 experiments from temperate to polar 3 waters

Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in 12 atmospheric processes and climate. Therefore, it is important to increase our understanding of 13 how DMS production in these regions may respond to climate change. The polar oceans are 14 particularly vulnerable to ocean acidification (OA). However, our understanding of the polar 15 DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS 16 concentrations decreased with increasing acidity. Here, we report on our findings from seven 17 summertime shipboard microcosm experiments undertaken in a variety of locations in the 18 Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short 19 term OA on the net production of DMS by planktonic communities. This is in contrast to 20 similar experiments from temperate NW European shelf waters where surface ocean 21 communities responded to OA with significant increases in dissolved DMS concentrations. A 22 meta-analysis of the findings from both temperate and polar waters (n = 18 experiments) 23 reveals clear regional differences in the DMS response to OA. Based on our findings, we 24 hypothesise that the differences in DMS response between temperate and polar waters reflect 25 the natural variability in carbonate chemistry to which the respective communities of each 26 region may already be adapted. If so, future temperate oceans could be more sensitive to OA 27 2 resulting in a change in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS 28 emissions from the polar oceans may remain relatively unchanged. By demonstrating that 29 DMS emissions from geographically distinct regions may vary in their response to OA, our 30 results may facilitate a better understanding of Earth’s future climate. Our study suggests that 31 the way in which processes that generate DMS respond to OA may be regionally distinct and 32 this should be taken into account in predicting future DMS emissions and their influence on 33

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