The nitrogen cycle of the Baltic Sea has received considerable attention over the past five decades mainly due to the ongoing expansion of oxygen-free zones. Here we present a summary of the present state of the nitrogen cycle in the Baltic Sea, identify open research questions and suggest a way forward to address the open questions with the aim to reduce uncertainties in projections of the future nitrogen cycle which, in turn, can advance and help management measures for ecosystem restoration.

Taliks, unfrozen ground within permafrost, sustain year-round biogeochemical processes, mobilizing carbon, nutrients, and contaminants through lateral and open taliks, while closed and isolated taliks confine reactions locally. In this manuscript, we argue that taliks represent a critical and overlooked driver of Arctic and sub-Arctic biogeochemical processes. We put forward three testable hypotheses to advance the study of talik biogeochemical functioning and we propose a related road map. 

Ocean alkalinity enhancement (OAE) is a proposed technology to remove CO₂ from the atmosphere. The effectiveness of OAE is determined by several physical, biological, and geochemical processes, many of which are poorly constrained and not typically considered in recent assessments. To help align research and improve estimates of OAE efficiency, we provide a framework describing these processes, identify major knowledge gaps, and highlight research priorities.

We examine the underlying challenges facing in situ measurements of chemical and biological analytes in seawater and makes a case for sample collection and subsequent laboratory analysis. Many analytes of biogeochemical importance are orders of magnitude scarcer than a needle in a haystack. We compare this challenge to biomedical diagnostics that rely primarily on sample collection and centralized laboratory analysis, despite greater financial investment and fewer engineering challenges.

Restoring wetlands and planting forests are both promoted to slow climate change, but they are often discussed as competing solutions. We argue that these options should be compared using a broader perspective that considers not only greenhouse gases released from soils, but also carbon stored in forests, wood products, and practical risks. Better-informed comparisons can help decision-makers choose the most suitable climate solution for each landscape.

Distributed data generation, or data collected from multiple sources and locations using standardized approaches and coordination among researchers, is powerful for scalable environmental knowledge. This paper helps readers understand options for distributed data generation, offers practical guidance for outreach, operations, and sharing outcomes, and explores how artificial intelligence can help address longstanding challenges.