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The energy-efficient reductive tricarboxylic acid cycle drives carbon uptake and transfer to higher trophic levels within the Kueishantao shallow-water hydrothermal system

In acidic hot springs off Kueishantao, Campylobacteria fix CO₂ by using the reductive tricarboxylic acid (rTCA) cycle, causing them to have an isotopically heavier biomass. Here, we report extremely low isotopic fractionation (of almost 0 ‰), which has never been reported in environmental samples. Moreover, the crab Xenograpsus testudinatus relies up to 34 % on campylobacterial biomass, highlighting the dependency of complex life on microscopic Bacteria in harsh environments.

Composite model-based estimate of the ocean carbon sink from 1959 to 2022

The ocean is a major natural carbon sink. Despite its importance, estimates of the ocean carbon sink remain uncertain. Here, I present a hybrid model estimate of the ocean carbon sink from 1959 to 2022. By combining ocean models in hindcast mode and Earth system models, I keep the strength of each approach and remove the respective weaknesses. This composite model estimate is similar in magnitude to the best estimate of the Global Carbon Budget but 70 % less uncertain.

Toward more robust net primary production projections in the North Atlantic Ocean

Biogeosciences
DOI 10.5194/bg-22-841-2025
20 February 2025

The marine biogeochemistry components of Coupled Model Intercomparison Project phase 6 (CMIP6) models vary widely in their process representations. Using an innovative bioregionalization of the North Atlantic, we reveal that this model diversity largely drives the divergence in net primary production projections under a high-emission scenario. The identification of the most mechanistically realistic models allows for a substantial reduction in projection uncertainty.

What controls planktic foraminiferal calcification?

Biogeosciences
DOI 10.5194/bg-22-791-2025
17 February 2025

Planktic foraminifers are a plankton whose fossilised shell weight is used to reconstruct past environmental conditions such as seawater CO2. However, there is debate about whether other environmental drivers impact shell weight. Here we use a global data compilation and statistics to analyse what controls their weight. We find that the response varies between species and ocean basin, making it important to use regional calibrations and consider which species should be used to reconstruct CO2.

Assessment framework to predict sensitivity of marine calcifiers to ocean alkalinity enhancement – identification of biological thresholds and importance of precautionary principle

The environmental impacts of ocean alkalinity enhancement (OAE) are unknown. Our synthesis, based on 68 collected studies with 84 unique species, shows that 35 % of species respond positively, 26 % respond negatively, and 39 % show a neutral response to alkalinity addition. Biological thresholds were found from 50 to 500 µmol kg−1 NaOH addition. A precautionary approach is warranted to avoid potential risks, while current regulatory framework needs improvements to assure safe biological limits.

Efficiency metrics for ocean alkalinity enhancements under responsive and prescribed atmospheric pCO2 conditions

Marine CO2 removal (mCDR) is a promising technology for removing legacy emissions from the atmosphere. Its indirect nature makes it difficult to assess experimentally; instead one relies heavily on simulation. Many past papers have treated the atmosphere as non-responsive to the intervention studied. We show that even under these simplified assumptions, the increase in ocean CO2 inventory is equal to the equivalent quantity of direct CO2 removals occurring over time, in a realistic atmosphere.

Ensemble estimates of global wetland methane emissions over 2000–2020

This study assesses global methane emissions from wetlands between 2000 and 2020 using multiple models. We found that wetland emissions increased by 6–7 Tg CH4 yr-1 in the 2010s compared to the 2000s. Rising temperatures primarily drove this increase, while changes in precipitation and CO2 levels also played roles. Our findings highlight the importance of wetlands in the global methane budget and the need for continuous monitoring to understand their impact on climate change.

Particle fluxes by subtropical pelagic communities under ocean alkalinity enhancement

Ocean alkalinity enhancement (OAE) is a negative emission technology which may alter marine communities and the particle export they drive. Here, impacts of carbonate-based OAE on the flux and attenuation of sinking particles in an oligotrophic plankton community are presented. Whilst biological parameters remained unaffected, abiotic carbonate precipitation occurred. Among counteracting OAE’s efficiency, it influenced mineral ballasting and particle sinking velocities, requiring monitoring.

Microbial response to deliquescence of nitrate-rich soils in the hyperarid Atacama Desert

We studied unique nitrate-rich soils in the hyperarid Atacama Desert that form brines at night under high relative humidity. Despite providing water for microorganisms, these soils exhibit extremely low microbial activity, indicating that the high nitrate levels inhibit microbial life. On the other hand, enriched organic matter indicates their potential preservation. This research helps to understand the limits of life in extreme environments and aids in the search for signs of life on Mars.

Microbial strong organic-ligand production is tightly coupled to iron in hydrothermal plumes

Hydrothermally derived iron can be transported kilometers away from deep-sea vents, representing a significant flux of vital micronutrients to the ocean. However, the mechanisms that support the stabilization of dissolved iron remain elusive. Using electrochemical, spectrometry, and genomic methods, we demonstrated that strong ligands exert an important control on iron in plumes, and high-affinity iron-binding siderophores were identified in several hydrothermal plume samples for the first time

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