The United Nations Decade of Ocean Science for Sustainable Development 2021-2030 (the 'Ocean Decade') is poised to stimulate new cooperation for ocean science, but makes no mention of conflict or peace. We contend that this is a missed opportunity, and use an environmental peacebuilding typology to review how ocean science has historically contributed to peace. Such considerations are timely in the context of an increasingly complex and multidimensional ocean risk landscape, due among other things to unprecedented growth in the extent and intensity of ocean uses, and increasing conflict potential as the ocean becomes a more crowded and coveted place. We conclude by proposing the Ocean Decade Implementation Plan be appended to include an eighth intended outcome: 'A Peaceful Ocean'.