We evaluate the variability of carbon dioxide and methane in the surface layer of the north-eastern basins of the Baltic Sea in 2018. We show that the shallower coastal areas have considerably higher spatial variability and seasonal amplitude of surface layer pCO₂ and cCH₄ than measured in the offshore areas of the Baltic Sea. Despite this high variability, caused mostly by coastal physical processes, the average annual air–sea CO₂ fluxes differed only marginally between the sub-basins.

Ocean alkalinity enhancement (OAE) is being evaluated as a carbon dioxide removal technology for climate change mitigation. With an experiment on species communities, we show that larval and juvenile fish can be resilient to the resulting perturbation of seawater. Fish may hence recruit successfully and continue to support fisheries' production in regions of OAE. Our findings help to establish an environmentally safe operating space for this ocean-based solution.

This study investigates dissolved organic carbon (DOC) export in headwater catchments. Results show small links between DOC, nitrates, and the iron cycle throughout the year, calling into question our current conceptualization of DOC export at the catchment scale. Indeed, this study evidences that the winter period, referred as a non-productive period in our current conceptual model, acts as an active period for DOC production in riparian soils and DOC export toward stream waters.

Many different processes produce nitrous oxide (N₂O), a potent greenhouse gas. Measuring the ratio of heavy and light nitrogen isotopes (¹⁵N/¹⁴N) for the non-exchangeable central and outer N atoms of N₂O helps to distinguish sources of N₂O. To accurately calculate the position-specific isotopic preference, we developed an expansion of the widely used Rayleigh model. Application of our new model to simulated and experimental data demonstrates its improved accuracy for analyzing N₂O synthesis.

Quantifying how much organic carbon is stored in seafloor sediments is key to assessing how human activities can accelerate the process of carbon storage at the seabed, an important consideration for climate change. This study uses seafloor sediment maps to model organic carbon content. Carbon estimates were 12 times higher when assuming the absence of detailed sediment maps, demonstrating that high-resolution seafloor mapping is critically important for improved estimates of organic carbon.

Recent studies described the precipitation of carbonates as a result of alkalinity enhancement in seawater, which could adversely affect the carbon sequestration potential of ocean alkalinity enhancement (OAE) approaches. By conducting experiments in natural seawater, this study observed uniform patterns during the triggered runaway carbonate precipitation, which allow the prediction of safe and efficient local application levels of OAE scenarios.

We tested the effects of warming, low salinity, and low irradiance on Arctic kelps. We show that growth rates were similar across species and treatments. Alaria esculenta is adapted to low-light conditions. Saccharina latissima exhibited nitrogen limitation, suggesting coastal erosion and permafrost thawing could be beneficial. Laminaria digitata did not respond to the treatments. Gene expression of Hedophyllum nigripes and S. latissima indicated acclimation to the experimental treatments.

Rising atmospheric CO₂ influences ocean carbon chemistry, leading to ocean acidification. Global warming introduces spatial patterns in the intensity of ocean acidification. We show that the most prominent spatial patterns are controlled by warming-driven changes in rainfall and evaporation, not by the direct effect of warming on carbon chemistry and pH. These evaporation and rainfall patterns oppose acidification in saltier parts of the ocean and enhance acidification in fresher regions.

Phytoplankton growth in the Southern Ocean (SO) is often limited by low iron (Fe) concentrations. Sea surface warming impacts Fe availability and can affect phytoplankton growth. We used shipboard  Fe clean incubations to test how changes in Fe and temperature affect SO phytoplankton. Their abundances usually increased with Fe addition and temperature increase, with Fe being the major factor. These findings imply potential shifts in ecosystem structure, impacting food webs and elemental cycling.

Natural organic matter (NOM) is often studied via Fourier transform mass spectrometry (FTMS), which identifies organic molecules as mass spectra peaks. The intensity of peaks is data that is often discarded due to technical concerns. We review the theory behind these concerns and show they are supported empirically. However, simulations show that ecological analyses of NOM data that include FTMS peak intensities are often valid. This opens a path for robust use of FTMS peak intensities for NOM.

We analysed sea surface temperature (SST) proxy and plankton biomarkers in sediments that accumulate sinking material signatures from surface waters in the central Arabian Sea (21°–11° N, 64° E), a tropical basin impacted by monsoons. We saw a north–south SST gradient, and the biological proxies showed more organic matter from larger algae in the north. Smaller algae and zooplankton were more numerous in the south. These trends were related to ocean–atmospheric processes and oxygen availability.