CAREER: Future Oxygen minimum zones in Indo-Pacific Ocean: ventilation, biogeochemical feedbacks and risk of coastal dead zones

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Among the many consequences of global warming and other human impacts on the oceans are a general decrease in seawater oxygen concentrations and, in some areas, pronounced expansion of ocean oxygen minimum zones (OMZs) and coastal “dead zones.” The Indian and Pacific Oceans are areas of particularly large OMZs, and coastal waters surrounding densely populated countries in the Indian Ocean are prone to dead zones. OMZ expansion and coastal dead zones threaten marine life, including valuable species for local populations and ecosystem services such as fisheries and tourism. Larger OMZs would also produce more nitrous oxide, a potent greenhouse gas. Despite this importance, there is no consensus on how these threats will evolve in the future. This CAREER award will use Earth system models (ESMs) to examine the suite of physical, chemical, and biological processes that combine to produce OMZs and dead zones, and study how natural processes and human activities change them. The lead investigator will develop an educational activity on climate change and mitigation at the middle-school level. This activity will guide teachers and students to explore the effects of human activities, and mitigation strategies including thought- provocative mitigation plans such as "a cyclist planet". It will be tested with local middle-school teacher and students and shared publicly on a peer-reviewed web platform. Numerous studies in the past twenty years have highlighted strong discrepancies in future projections of OMZs. One challenge to refine these projections is that prior mechanistic work generally considered sub-regions of OMZs or the effect of one physical or biological mechanism in isolation. This project will build upon and expand this body of work to provide a comprehensive understanding that connects ventilation pathways and biogeochemical feedbacks to the OMZs at the scale of the Indo-Pacific basin, including largely overlooked key processes such as the Indonesian Throughflow or anthropogenic aerosol deposition (Objectives 1 and 2). This project will harness the state-of-the-art ESM ensemble from the Coupled Model Intercomparison Project 6 (CMIP6) and novel ocean biophysical models in combination with existing observational constraints with the aim to narrow down future OMZ projections. This project will also assess for the first time the risk of coastal dead zones in the Indian Ocean, using a high-resolution regional bio-physical model that incorporates the wide range of key natural and anthropogenic processes, from local (river discharge, eddies) to global (OMZ expansion, monsoon changes) scales (Objective 3).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.