Scientists have studied the open ocean’s mesopelagic zone, extending from 200m-1000m depth, for more than 70 years. As renewed interest in this global ecosystem grows, divergent proposals and knowledge claims are being made on its current and future role in supporting human life. We use automated content analysis to identify 13 latent topics about the mesopelagic zone from 2,226 scientific abstracts and 4,066 tweets. Two dominant ideas emerge: (1) the exploitation of fish resources and (2) the potential of the mesopelagic zone as a carbon sink. We find that, in the absence of national or international governing institutions, science plays a de facto governing role by shaping how the ecosystem is known to the public and policymakers alike. These results indicate the need for new knowledge and governance arrangements that can broaden the range of meanings and knowledge needed to anticipate future uses of deeply uncertain ecosystems and resources.