This assessment report presents the results of the 2018 Arctic Monitoring and Assessment Programme (AMAP) assessment of Arctic Ocean Acidification. This is the second such assessment dealing with ocean acidification from an Arcticwide perspective, and complements several assessments that AMAP has delivered over past years concerning the effects of climate change on Arctic ecosystems and people. The main objectives of this assessment were to: •• Update the understanding of chemical and biological responses to ocean acidification since the first Arctic Ocean acidification assessment in 2013. •• Evaluate how ecological frameworks may respond to ocean acidification. •• Research socioeconomic and cultural consequences of ocean acidification at selected case study regions. •• Report on how Arctic Ocean acidification may impact on downstream global systems. •• Deliver guidance for management of change. AMAP is a group working under the Arctic Council. The Arctic Council Ministers have requested that AMAP: •• Produce integrated assessment reports on the status and trends of the conditions of the Arctic ecosystems. •• Identify possible causes for the changing conditions. •• Detect emerging problems, their possible causes, and the potential risk to Arctic ecosystems including indigenous peoples and other Arctic residents. •• Recommend actions required to reduce risks to Arctic ecosystems. This assessment report provides the scientific basis and validation for the statements and recommendations made in the AMAP Arctic Ocean Acidification: Assessment Summary for Policy-makers that will be delivered to Arctic Council Ministers at their meeting in Rovaniemi, Finland in May 2019. It includes extensive background data and references to the scientific literature. The summary for policy-makers report contains recommendations that focus mainly on policyrelevant actions concerned with addressing the consequences of ocean acidification in the Arctic, while the conclusions and recommendations presented in this report cover issues of a more scientific nature, such as proposals for filling gaps in knowledge, and recommendations relevant to future monitoring and research work. This assessment was conducted between 2014 and 2018 by an international group of over 40 experts. Lead authors were selected based on an open nomination process coordinated by AMAP. A similar process was used to select international experts who independently reviewed this report. Published Refereed Current 14.3 Inorganic carbon Manual (incl. handbook, guide, cookbook etc)