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Reaching the Paris Agreement targets to limit global warming to 1.5 or 2°C implies not only reducing emissions, but also active carbon dioxide removal from the atmosphere. While land-based carbon dioxide removal or negative emission technologies have received most attention, ocean solutions are increasingly being considered. Ocean alkalinity enhancement (OAE), or alkalinization, is one promising ocean-based carbon dioxide technology. However, any new carbon dioxide removal technique needs thorough investigations for its effectiveness, longevity, benefits and lack of disbenefits, financial viability, social acceptance and governability. The paper by Bach is a nice illustration of the type of research that must be done if we are to consider large scale application of OAE. It focuses on the additionality problem of ocean alkalinity enhancement, specifically it investigates how the addition of alkalinity modifies the natural alkalinity cycle and in that way the efficiency of carbon dioxide sequestration.

The study covers a relevant contemporary topic (wildfire) and focusses on the recent major European summer of wildfires. The authors demonstrate that the assessment of burned area alone is not enough to fully characterize the impact of fires. Novel methods to assess burned area and above ground biomass losses are described to provide a more informative impact-based characterization of fires.

Arctic greenhouse gas fluxes are key for climate feedback but the Arctic greenhouse gas balance is poorly constrained due to a limited understanding of the spatial variation in these fluxes. This study combines extensive chamber-based flux measurements and remote sensing data to develop a machine-learning model to predict greenhouse gas fluxes across a tundra landscape in Finland. The analysis revealed that the system was a net greenhouse gas sink and showed widespread CH4 uptake in upland vegetation types, almost surpassing the high wetland CH4 emissions at the landscape scale.

This is an excellent review of gross primary production (GPP) and net community production (NCP) measurements in the world's oceans using a new fleet of autonomous ocean-going instruments called biogeochemical-Argo (BGC-Argo) floats. The number of BGC-Argo floats has recently been surging with their users, so this review is timely and helpful for many oceanographers and biogeochemists to understand the advantages and challenges in the measurements of GPP and NCP in the oceans with the recently emerged technology.

This study presents an interesting finding that, when climatic conditions are dry, the direction of soil evaporation from soil to sky can reverse where atmospheric vapor adsorbs downward into the soil. This increased soil moisture input from the atmosphere serves as a non-precipitation water source. The authors show evidence for this process with lysimeters and also demonstrate that this soil adsorption process shows up in commonly used eddy covariance measurements.

This important study evaluates the impacts of enhanced olivine weathering on globally relevant phytoplankton species. Results from the study indicate that olivine dissolution products are unlikely to negatively impact the six phytoplankton species tested and may even enhance growth under certain conditions. Studies examining the safety of ocean alkalinity enhancement are urgently needed as interest in deploying this strategy for carbon dioxide removal is increasing.

This study documents the formation of Fe, Mn and Si amorphous mineral phases by very small cyanobacteria living in oxic, alkaline lakes. This finding has implications for using sedimentary Fe/Mn enrichments as a proxy for redox cycling in the past and extends the documented evidence for biomineralization of Si-rich phases.