Nitrous oxide, a potent greenhouse gas, accumulates in regions of the ocean that are low in dissolved oxygen. We used a novel combination of chemical tracers to determine how nitrous oxide is produced in one of these regions, the eastern tropical North Pacific Ocean. Our experiments showed that the two most important sources of nitrous oxide under low-oxygen conditions are denitrification, an anaerobic process, and a novel “hybrid” process performed by ammonia-oxidizing archaea.

Wastewater treatment plants (WWTPs) are known to be hotspots of greenhouse gas emissions. However, the impact of WWTPs on the emission of the greenhouse gas N₂O in downstream aquatic environments is less constrained. We found spatially and temporally variable but overall higher N₂O concentrations and fluxes in waters downstream of WWTPs, pointing to the need for efficient N₂O removal in addition to the treatment of nitrogen in WWTPs.

We assess the representation of the plant response to surface water in a global atmospheric chemistry model. This sensitivity is crucial for the return of precipitation back into the atmosphere and thus significantly impacts the representation of weather as well as air quality. The newly implemented response function reduces this process and has a better comparison with satellite observations. This yields a higher intensity of unusual warm periods and higher production of air pollutants.

We report the first benthic foraminifera with a composite test (i.e. shell) made of opal, which coats the inner part of the calcitic layer. Using comprehensive techniques, we describe the morphology and the composition of this novel opal layer and provide evidence that the opal is precipitated by the foraminifera itself. We explore the potential precipitation process and function(s) of this composite test and further discuss the possible implications for palaeoceanographic reconstructions.

The approach presented is original in its coupling between field observations and airborne lidar observations. It has been applied to an instrumented reference forest site in the south of France, which is heavily impacted by climate change. It leads to the evaluation of tree heights and ends with assessments of aerial and root carbon stocks. A detailed assessment of uncertainties is presented to add a level of reliability to the scientific products delivered.

Understanding the drivers of forest productivity is key for accurately assessing forests’ role in the global carbon cycle. Yet, despite significant research effort, it is not fully understood how the productivity of a forest can be deduced from its stand structure. We suggest tackling this problem by identifying the share and structure of immature trees within forests and show that this approach could significantly improve estimates of forests’ net productivity and carbon uptake.

Understanding the link between climate and carbon fluxes is crucial for predicting how climate change will impact carbon sinks. We estimated carbon dioxide (CO₂) fluxes from deadwood in tropical Australia using wood moisture content and temperature. Our model predicted that the majority of deadwood carbon is released as CO₂, except when termite activity is detected. Future models should also incorporate wood traits, like species and chemical composition, to better predict fluxes.

Terrestrial biosphere models can either prescribe the geographical distribution of biomes or simulate them dynamically, capturing climate-change-driven biome shifts. We isolate and examine the differences between these different land cover implementations. We find that the simulated terrestrial carbon sink at the end of the 21st century is twice as large in simulations with dynamic land cover than in simulations with prescribed land cover due to important range shifts in the Arctic and Amazon.

How do perpetually slower and warmer oceans sequester carbon? Compared to the preindustrial state, we find that biological productivity declines despite warming-stimulated growth because of a lower nutrient supply from depth. This throttles the biological carbon pump, which still sequesters more carbon because it takes longer to return to the surface. The deep ocean is isolated from the surface, allowing more carbon from the atmosphere to pass through the ocean without contributing to biology.

In the Arctic tundra, climate change is transforming the landscape, and this may impact wildlife. We focus on three nesting bird species and the islets they select as refuges from their main predator, the Arctic fox. A geomorphological process, ice-wedge polygon degradation, was found to play a key role in creating these refuges. This process is likely to affect predator–prey dynamics in the Arctic tundra, highlighting the connections between nature's physical and ecological systems.

Our research is the first to measure dissolved NO concentrations in temperate estuarine waters, providing insights into its distribution under varying conditions and enhancing our understanding of its production processes. Dissolved NO was supersaturated in the Elbe Estuary, indicating that it is a source of atmospheric NO. The observed distribution of dissolved NO most likely resulted from nitrification.

The occurrence of unstable equilibrium points (EPs) could impede the applicability of microbial-explicit soil organic carbon models. For archetypal model versions we identify when instability can occur and describe mathematical conditions to avoid such unstable EPs. We discuss implications for further model development, highlighting the important role of considering basic ecological principles to ensure biologically meaningful models.

We investigate the effects of mineral grain size and seawater salinity on magnesium hydroxide dissolution and calcium carbonate precipitation kinetics for ocean alkalinity enhancement. Salinity did not affect the dissolution, but calcium carbonate formed earlier at lower salinities due to the lower magnesium and dissolved organic carbon concentrations. Smaller grain sizes dissolved faster but calcium carbonate precipitated earlier, suggesting that medium grain sizes are optimal for kinetics.