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The ocean plays a central role in climate change mitigation and adaptation. However, climate and ocean policies have been historically siloed. After decades of slow convergence, the Ocean and Climate Change Dialogue, decided at COP25 and launched online in December 2020, was the first forum for Parties and non-Party stakeholders to the UNFCCC to give their perspectives on how the climate regime should address ocean-related mitigation and adaptation. The Ocean Dialogue was informed by 47 prior open submissions provided by a broad swath of actors from across the UN system and from civil society, including traditional and youth voices. Our analysis of the submissions demonstrates a political evolution towards the nexus among climate, ocean, and biodiversity regimes. The submissions uniformly acknowledge that ocean and climate systems are inextricably linked, and that consideration of ocean-based action will strengthen climate action and vice versa. Salient themes of the submissions include changing ocean impacts, carbon sinks and blue carbon opportunities, and the need for ecosystem resilience, biodiversity management and improved understanding of normative and institutional frameworks. There is a strong call to recognize the interconnectedness of the biophysical world. Similar themes emerged during the actual Ocean Dialogue and the subsequent informal meeting on next steps. The main message conveyed is the dire necessity to implement strong stewardship and good governance of the blue planet in a disrupted climate using cooperative and concrete actions. This analysis highlights the need for a continued transdisciplinary international dialogue on the ocean and climate change which elevates the ocean-climate-biodiversity nexus via collaborative science, finance, and policy. Key policy insights Ocean and marine ecosystem impacts of climate change were widely acknowledged, and referenced by ninety-one percent of submissions. After decades of slow integration of ocean into climate policy, the Ocean Dialogue submissions acknowledge that climate policy must address linkages with the ocean and its biodiversity. Concerns include changing ocean impacts, carbon sinks and blue carbon opportunities, and the need for ecosystem resilience, biodiversity management and increased institutional interactions. Continuation of this Dialogue, with strengthened collaboration between States and non-state actors, may give rise to multilateral and multilevel decision-making toward sustainable climate, ocean and biodiversity action.

Antarctica is estimated to contain as much as a quarter of earth's marine methane, however we have not discovered an active Antarctic methane seep limiting our understanding of the methane cycle. In 2011, an expansive (70 m × 1 m) microbial mat formed at 10 m water depth in the Ross Sea, Antarctica which we identify here to be a high latitude hydrogen sulfide and methane seep. Through 16S rRNA gene analysis on samples collected 1 year and 5 years after the methane seep formed, we identify the taxa involved in the Antarctic methane cycle and quantify the response rate of the microbial community to a novel input of methane. One year after the seep formed, ANaerobic MEthane oxidizing archaea (ANME), the dominant sink of methane globally, were absent. Five years later, ANME were found to make up to 4% of the microbial community, however the dominant member of this group observed (ANME-1) were unexpected considering the cold temperature (−1.8°C) and high sulphate concentrations (greater than 24 mM) present at this site. Additionally, the microbial community had not yet formed a sufficient filter to mitigate the release of methane from the sediment; methane flux from the sediment was still significant at 3.1 mmol CH4 m−2 d−1. We hypothesize that this 5 year time point represents an early successional stage of the microbiota in response to methane input. This study provides the first report of the evolution of a seep system from a non-seep environment, and reveals that the rate of microbial succession may have an unrealized impact on greenhouse gas emission from marine methane reservoirs.