The Planetary Boundaries (PB) framework, first introduced in 2009, has become one of the most influential conceptual tools in Earth system science for defining a 'safe operating space for humanity'. It identifies nine critical Earth system processes, including climate change, biosphere integrity, and ocean acidification, and proposes quantitative boundaries beyond which humanity risks triggering irreversible environmental changes. Despite the ocean covering 71% of Earth's surface and playing a fundamental role in regulating climate, sequestering carbon, and maintaining global biogeochemical cycles, its representation within the PB framework remains notably limited. Only one boundary, ocean acidification, explicitly addresses marine systems, and even this focuses primarily on surface ocean chemistry. The ocean interior, deep-sea processes, subsurface biogeochemistry, large-scale circulation patterns, and marine functional diversity are largely absent. This gap is not merely conceptual. As ocean industrialization accelerates, through deep-sea mining, high-seas fisheries, and the expanding 'blue economy', the need to understand how these activities impact planetary-scale stability becomes increasingly urgent. Meanwhile, the current governance landscape remains fragmented, with different ocean issues addressed under different regimes, lacking a coherent framework to guide decision-making. Against this backdrop, this forum chaired by Professor Minhan Dai of Xiamen University brings together leading scholars in marine and Earth system science to address a pressing question: How can marine processes and ecosystems be effectively incorporated into the PB framework, and what would this mean for science, governance, and sustainability? Deliang Chen Professor, Department of Earth System Science, Tsinghua University, China Sam Dupont Senior Lecturer, Department of Biological & Environmental Sciences, University of Gothenburg, Sweden Minhan Dai (Chair) Professor, College of Ocean and Earth Sciences, Xiamen University, China Ellycia Harrould-Kolieb Lecturer, School of Agriculture, Food and Ecosystem Sciences, University of Melbourne, Australia Ariel Pezner Chancellor's Research Fellow, University of Technology, Australia.
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