Award: OCE-1316133

Along with global warming generated by human-driven enhanced emissions of carbon dioxide (CO2), ocean acidification is one of the most pressing environmental issues of our time. Driven by the dissolution of excess atmospheric CO2 into seawater, ocean acidity has increased by approximately 30% since pre-industrial times and is likely to increase by more than 100% by the year 2100. A great deal of attention has focused on how organisms will respond to the increasing acidity of the oceans. However, a consequence of ocean acidification that has received less attention is how the increasing acidity will impact the role the oceans play in buffering climate change. As a part of their metabolic processes planktonic microbial communities absorb and emit a suite of volatile compounds including gases, some of which exchange across the air-sea interface and influence atmospheric chemistry and climate. This project addressed how ocean acidification influences the production and transfer of dimethylsulfide (DMS) from the oceans to the atmosphere. In the atmosphere, DMS contributes to the formation of aerosol particles that seed the formation of clouds, effectively increasing the reflectivity of the Earth and thereby reducing global temperatures. If ocean acidification increased or decreased emissions of DMS from the ocean this has the potential to positively or negatively feedback on global warming. Our results from this study confirmed earlier studies by us and others that in combination, strongly indicate increasing ocean acidity is likely to decrease DMS emissions to the atmosphere with a potential to positively feedback on increases in global temperature. Specifically, our team from Bigelow Laboratory collaborated with scientists from GEOMAR in Germany and the University of Las Palmas in Gran Canaria, Spain, to carry out two major experiments involving the deployment of nine large scale (~50 m3) free floating, pelagic mesocosms in the sub-tropical oceanic waters of the Canary Islands. The first experiment had to be abandoned after storm force winds irretrievably damaged the mesocosms, two weeks into the experiment. A second attempt later in the year was successful and lasted 55 days. The results illustrated that DMS emissions may decrease by 5 to 33 % across the vast sub-tropical oceans by 2100, depending on which IPCC greenhouse gas emission scenario occurs. Our team also carried out two similar, smaller-scale experiments using waters from the Gulf of Maine and mesocosm facilities at Bigelow Laboratory. Following which, we took part in a UN-sponsored meeting held at the University of East Anglia, UK, in 2017, to compile information on the impact of ocean acidification on climate-active gases. Similar levels of decrease in DMS production due to acidification were reported in 10 of 13 similar mesocosm experiments in waters ranging from the Arctic, North Sea, the Baltic, the Sea of Japan, Gulf of Maine and our sub-tropical study. This level of consensus among experiments carried out in different oceans by different research teams is highly unusual and points to a pressing need to better understand the causes and consequences. A key aspect of our research has been to try to understand the processes that lead to decreased DMS production by planktonic communities in response to increased acidity. To address this issue, we examined whether alterations in the composition of microbial communities were responsible for the changing DMS emissions or whether the microbes changed the metabolic processes that lead to DMS production during mesocosm experiments. Unsurprisingly, being complex natural systems, both processes occur simultaneously in response to increased ocean acidity and the consensus among mesocosm experiments suggests the responses may occur throughout the global ocean. Our current challenge is how best to incorporate the metabolic and community responses observed in relatively short-term mesocosm experiments into mathematical models that address climate change and potential feedbacks due to ocean acidification over decades to centuries? To disseminate this information, we have presented our results to other scientists at five international symposia, including the ASLO Ocean Sciences meetings in 2015, 2017 and 2018. Project results were presented twice to the public as part of the grassroots public science initiative Caf? Scientifique, organized by Bigelow Laboratory each summer. In addition, the science has inspired a permanent large art installation and movie by Carter Shappy from the Maine College of Art and has inspired poetry including ?At last I know why I love cheese and beer? by R. David Drucker a summer visitor to our laboratory. Participation in the project has advanced the scientific experience and careers of a postdoctoral scientist, research associate, 4 undergraduate research students and been the subject of part of the teaching syllabus of the Fall Semester Program taught by Bigelow Laboratory for Colby College. Last Modified: 04/23/2019 Submitted by: Stephen Archer