Disparities in ocean carbon sink estimates derived from observations and models raise questions about our ability to accurately assess its magnitude and trend. Surface ocean pCO2-data based carbon uptake inferences are systematically higher than estimates based on global ocean biogeochemical models. River carbon inputs and carbon burial in sediments contribute largely to this difference. Hence, it is critical to accurately constrain riverine carbon inputs (in the form of inorganic and organic carbon) and burial of organic and inorganic carbon in oceanic sediments. These are non-trivial task because part, but not all, of the organic carbon delivered by rivers is degraded to inorganic carbon and because of carbonate-system re-equilibrations, including calcium carbonate precipitation and dissolution. The Planchat et al. paper presents a simple conceptual model and explores its value using full scale ocean biogeochemical models. The resulting framework is useful for future model intercomparisons and for revising pre-industrial air-sea carbon fluxes when new carbon and alkalinity budgets become available.

The role of Artisanal Small-scale Gold Mining emissions and the uptake of Hg in biota are key research questions in global Hg cycling. The presented work focuses on an understudied region in Nigeria. It results from a successful international collaboration with local researchers from a region with high Artisanal Small-scale Gold Mining emissions and deserves the attention of the scientific community.

This study represents a pioneering step in the development of in situ monitoring, reporting, and verification (MRV) frameworks for ocean alkalinity enhancement (OAE), a leading marine carbon dioxide removal strategy. The authors conducted one of the first open-ocean rhodamine tracer release experiments explicitly designed to simulate alkalinity enhancement, demonstrating a scalable and practical approach for tracking the fate of alkalinity additions in dynamic marine environments. By moving beyond theoretical modeling and implementing real world testing, this work establishes a critical methodological foundation for future field trials and offers a replicable strategy for validating carbon removal through OAE.

This paper maps the safe operating space of marine ecosystems in various metrics, including physical (e.g. temperature, heatwaves, sea-ice, etc), ocean acidification (saturation state), oxygen availability and pelagic ecosystem system functioning (e.g. biomass and production). It provides guidance how different emission scenario are likely to impact marine ecosystems.

This paper reports the alarming increase in wildfires in the Amazon rainforest during the severe 2023/2024 drought leading to an increase in large-scale forest degradation. It is highly relevant as the fire-driven forest degradation impacted also intact forests and released large amounts of carbon dioxide to the atmosphere pushing the Amazon rainforest closer to a potential tipping point.