Scientific publications

How the Antarctic Ice Sheet responds to climate change depends largely on how easily the ice slides over the ground beneath it – a process that is still not fully understood.

By combining satellite observations of ice motion with seismic measurements and information from sediment cores, this study links conditions at the base of the ice to different sliding laws, that is, models describing how ice moves over its underlying surface. The results show that parts of Pine Island Glacier in West Antarctica slide with low friction, providing important insights that can help improve projections of future sea-level rise.

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Authors:
Hank, K., Arthern, R. J., Williams, C. R., Brisbourne, A. M., Smith, A. M., Smith, J. A., Wåhlin, A., and Anandakrishnan, S

Journal:
EGUsphere

DOI:
https://doi.org/10.5194/egusphere-2025-764

Nitrous oxide (N₂O) is a powerful greenhouse gas, yet its role in fjord systems has remained poorly understood, especially at high latitudes. In this study, researchers measured exchanges of N₂O between the sea and the atmosphere in six fjords across Sweden, Iceland and Greenland, covering temperate, subarctic and Arctic environments.

The results show that fjords behave very differently. Fjords in Sweden and Iceland acted as sources of N₂O to the atmosphere, while the Greenland fjord instead absorbed N₂O from the air. Elevated emissions were linked to low-oxygen waters and aquaculture activity, whereas uptake in Greenland may be influenced by dilution from glacier meltwater. Although fjords contribute a relatively small share of global coastal N₂O emissions, the study shows that these emissions partially offset the ability of fjords to store carbon, highlighting the complex role of fjords in the climate system.

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Authors: Politi, T., Yau, Y.Y., Santos, I.R., Cabral, A., Cheung, H.L.S., Majtényi-Hill, C., Ulfsbo, A., Wåhlin, A., Bonaglia, S

DOI-number: https://doi.org/10.1029/2024GL111624

AMIGOS-3 is an automated observation system developed to study interactions between the atmosphere, ice and ocean in polar regions. The system is deployed directly on floating ice and can operate unattended for several years, continuously collecting data on weather conditions, ice motion and ocean properties beneath the ice.

By combining ocean sensors, GPS, cameras and fibre-optic temperature measurements, AMIGOS-3 provides detailed time series of temperature, salinity, currents and conditions at the ice–ocean interface. Part of the data is transmitted via satellite, allowing researchers to monitor measurements and manage the system remotely. Two stations installed on the eastern part of Thwaites Glacier in Antarctica delivered valuable data between 2020 and 2022, contributing to improved understanding of climate processes, ice dynamics and ocean conditions in a rapidly changing region.

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Authors:
Scambos, T. A., White, T., Wallin, B., Truffer, M., Collao-Barrios, G., Kratt, C., Tyler, S., Pettit, E. C., Wild, C. T., Arora, S., Edwards, S., Fotherby, R., Meha, C., Soltys, J., Tomlinson, E., Weatherby, R., Ross, R., Wåhlin, A., Dotto, T. S., Alley, K., Muto, A

Journal:
Journal of Glaciology

DOI:
10.1017/jog.2024.96

Not yet published paper 

The scientific article had not yet been published as of 19 January 2026.

Authors:
Tom A. Jordan, Karen J. Heywood, Anna Wåhlin, Robert Hall, Atsuhiro Muto, Pierre Dutrieux, Kelly Hogan, James Girton, Karen Alley, Erin Pettit

Journal:
Solid Earth (EGU – Solid Earth)

DOI link:
https://www.solid-earth.net/

The seafloor is an important source of nutrients and dissolved carbon to the ocean, but these fluxes are often difficult to measure over large areas. In this study, the naturally occurring tracer radium-224 was used to investigate how nutrients are mixed from the seabed into the water column in the Baltic Sea, where deep waters are often low in oxygen.

Measurements from 50 stations across the Baltic Sea show that both radium and dissolved silica reach their highest concentrations close to the seafloor in deep, anoxic basins. By analysing these patterns, the researchers were able to estimate vertical mixing and nutrient fluxes that are consistent with previous smaller-scale studies. When scaled up to the entire Baltic Sea, the results reveal that silica released from sediments far exceeds riverine inputs, demonstrating that the seafloor is a much larger nutrient source than previously assumed.

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Authors:
McKenzie; Aprajita Singh Tomer; Tibaud Cardis; Claudia Majtényi Hill; Beata Szymczycha; Per O. J. Hall; Shibin Zhao; Stefano Bonaglia; Michael Böttcher; Isaac R. Santos

Journal:
Limnology and Oceanography

DOI:
10.1002/lno.70126

Marine sediments are an important long-term carbon sink, burying large amounts of organic carbon each year, particularly along continental margins. It has long been assumed that organic carbon is preserved more efficiently in sediments underlying oxygen-poor bottom waters, as degradation is expected to proceed more slowly under such conditions. However, recent observations from the Baltic Sea show that this is not always the case.

In this study, researchers investigated sediments in the Western Gotland Basin, where bottom waters have been anoxic for extended periods but organic carbon is nevertheless degraded at high rates. The results show that the sediments receive large inputs of organic material relative to the amount of mineral particles available to protect the carbon. Because much of the carbon is not bound to mineral surfaces, it remains highly reactive despite the lack of oxygen. The study demonstrates that anoxia alone does not guarantee efficient carbon burial and highlights the importance of interactions between organic matter and sediment composition for long-term carbon storage in marine sediments.

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Authors:
Placitu, S. J.; van de Velde, A.; Hylén, A.; Eriksson, M.; Hall, P. O. J.; Bonneville, S.

Journal:
Biogeosciences

DOI:
https://doi.org/10.5194/bg-22-8065-2025

The recycling of phosphorus in seafloor sediments is a key process driving eutrophication, particularly in the Baltic Sea, which has a long history of nutrient enrichment. This study presents a comprehensive dataset of benthic phosphorus fluxes based on in situ measurements collected over 20 years across large parts of the Baltic Sea.

The results show that the release of dissolved inorganic phosphorus from the seabed varies strongly between regions and is closely linked to oxygen depletion in bottom waters and the amount of organic matter in the sediments. Phosphorus fluxes generally increase from coastal areas towards the deeper central basins, and repeated measurements demonstrate how rapidly changes in oxygen conditions can affect phosphorus release. When scaled up to the entire Baltic Sea, the findings reveal that sediments constitute a major internal source of phosphorus, which can sustain eutrophication even when inputs from land are reduced. The dataset therefore provides an important foundation for future research as well as for marine management and policy.

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Authors:
Hylén; Nils Ekeroth; Hannah Berk; Andy Dale; Mikhail Kononets; Wytze K. Lenstra; Aada Palo; Anders Tengberg; Sebastiaan van de Velde; Stefan Sommer; Caroline P. Slomp; and Per O. J. Hall (2025)

Journal:
Earth System Science Data

DOI:
https://doi.org/10.5194/essd-17-6423-2025

This dataset brings together extensive measurements of water chemistry and isotopes from across the Baltic Sea, collected during two major research campaigns. The first was a roughly 5,000-kilometre expedition aboard the research vessel R/V Skagerak in 2023, during which surface waters and the water column were continuously monitored and sampled. The second campaign was carried out in 2024 and involved land-based sampling of groundwater, rivers and nearshore waters to better capture inputs from land to sea.

Together, the data provide a detailed picture of how nutrients, carbon, gases and water are transported and transformed between land, sea and atmosphere in the Baltic Sea. All data are openly available and form the basis for forthcoming scientific publications. The dataset is also a valuable resource for researchers studying coastal seas, submarine groundwater discharge and biogeochemical processes in estuaries.

Link to the publication

Authors:
McKenzie; Claudia Majtényi-Hill; Linnea Henriksson; Wilma Ljungberg; Gloria M. S. Reithmaier; Luiz C. Cotovicz Jr.; Jannine M. Lencina-Avila; Nico Mitschke; Michael Böttcher; Beata Szymczycha; Adam Ulfsbo; Aprajita S. Tomer; Tibaud Cardis; Per O. J. Hall; Ceylena Holloway; Júlia Rodriguez Puig; Solveig Börjesson; Yvonne Y. Y. Yau; Shibin Zhao; Henry L. S. Cheung; Stefano Bonaglia; Tobia Politi; Linda Zetterholm; Nicolai Verbücheln; Iris Schmiedinger; Gregor Rehder; Thorsten Dittmar; Mats Tysklind; Pedro A. Inostroza; Ana Tronholm; and Isaac R. Santos

Journal:
Scientific Data

DOI:
https://doi.org/10.1038/s41597-025-06217-9

Recreational boating is widespread in Sweden, with around 850,000 leisure boats in use, yet its impact on the marine environment is still not fully understood. Along the Swedish west coast, sheltered archipelagos and fjords with limited tidal influence provide favourable conditions for detecting pollution linked to boat traffic.

This study investigated polycyclic aromatic hydrocarbons (PAHs) from boat exhausts in water and surface sediments in both a busy harbour and a relatively pristine fjord. By combining chemical analyses with data on boat traffic and water residence times, the results show that recreational boating can increase PAH concentrations by up to 40 per cent. For the first time, a clear chemical fingerprint of emissions from leisure boats was identified in coastal marine environments. While PAH concentrations in the water remained below environmental quality standards, guideline values in some sediments were exceeded by more than five times. The study demonstrates that recreational boating is a significant source of PAH pollution in coastal areas and should be considered in future environmental management and mitigation efforts.

Authors:
Nordberg, K.; Björk, G.; Abrahamsson, K.; Josefsson, S.; Lundin, L.

Journal:
Chemosphere

DOI:
https://doi.org/10.1016/j.chemosphere.2024.143910

Microscopic organisms known as foraminifera are increasingly used to assess environmental conditions in coastal seas. They are at least as effective as larger bottom-dwelling animals that are commonly used in environmental monitoring today, but offer several advantages. Foraminifera respond rapidly to environmental change, occur in large numbers even in small sample volumes, and have hard shells that can be preserved over long periods of time. This makes them valuable both for present-day environmental monitoring and for reconstructing past environmental conditions.

A major challenge is that identifying foraminifera species has traditionally relied on manual examination under a microscope, a process that is time-consuming, uncertain and highly dependent on specialised expertise. By using deep learning, a form of machine learning, computers can instead be trained to recognise subtle differences in shell morphology. This opens up new possibilities for faster, more reliable and more automated environmental analyses, with great potential for the future of marine monitoring.

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Authors:
Plavetić, M.; Yi Hsiang, A.; Josefson, M.; Hulthe, G.; Polovodova Asteman, I.

Journal:
Journal of Micropalaeontology

DOI:
https://doi.org/10.5194/jm-44-693-2025

Fjords are important sites for the long-term burial of organic carbon and therefore play a central role in the global carbon cycle. Traditionally, efficient carbon burial has often been linked to oxygen-poor bottom waters, but recent research shows that fjords can store large amounts of carbon even when bottom waters are oxygenated.

In this study, researchers investigated how organic carbon is supplied, degraded and preserved in sediments in fjords in eastern Iceland, where bottom waters are well oxygenated. The results show that most of the carbon preserved in the sediments is of marine origin rather than derived from land. Despite some degradation of organic material, a large fraction of marine carbon is efficiently buried in the sediments. The study demonstrates that Icelandic fjords act as effective carbon sinks and that oxygen-rich conditions do not necessarily limit the long-term burial of organic carbon.

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Authors:
Watts, E. G.; Zautcke, K.; Santos, I.; Smeaton, C.; Ljungberg, W.; Cheung, H. L. S.; Bonaglia, S.; Politi, T.; Liu, Z.; Bianchi, T. S.

Journal:
Estuaries and Coasts

DOI:
https://doi.org/10.1007/s12237-025-01582-5

Nitrogen is a fundamental nutrient that regulates marine productivity and, in turn, the ocean’s capacity to store carbon. Fjords are already recognised as important sites for carbon sequestration, but their role in the global nitrogen cycle has so far been poorly quantified. This study shows that fjords are major hotspots for nitrogen burial, accounting for up to 18 per cent of all nitrogen buried in marine sediments, despite covering only around 0.1 per cent of the ocean surface.

The results demonstrate that long-term burial in sediments is the dominant nitrogen loss pathway in fjords, exceeding microbial processes that are often considered the main nitrogen sinks in the ocean. Microbial nitrogen loss is instead more important in fjords with anoxic waters and is also influenced by temperature and nutrient availability. Overall, the study highlights fjords as providers of an important ecosystem service by efficiently removing excess nitrogen over long timescales. As the climate warms, particularly in polar regions, both nitrogen burial and microbial nitrogen loss are expected to intensify, with implications for nutrient cycling in fjords and the global ocean.

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Authors:
Cheung, H.; Levin, L.; Smeaton, C.; Politi, T.; Thamdrup, B.; Santos, I.; Bonaglia, S.

Journal:
Research Square

DOI:
https://doi.org/10.21203/rs.3.rs-7808814/v1

Methane is a powerful greenhouse gas, but how much of it actually reaches the atmosphere from coastal seas remains uncertain. In this study, methane production and breakdown near the seafloor were investigated across the entire Baltic Sea, using measurements of methane concentrations and isotopes along gradients in oxygen and salinity.

The results show that methane concentrations are highest close to the seabed in low-oxygen waters, identifying sediments as a major source. At the same time, only a small fraction of this methane reaches the atmosphere. Instead, around half of the methane produced in sediments is consumed by microorganisms in bottom waters before it can be transported upwards. The study therefore demonstrates that methane oxidation near the seafloor is highly effective and plays a crucial role in limiting methane emissions from the Baltic Sea to the atmosphere.

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Authors:
Henriksson, L.; McKenzie, T.; Yau, Y. Y. Y.; Cheung, H. L. S.; Majtényi-Hill, C.; Ljungberg, W.; Tomer, A. S.; Bonaglia, S.; Santos, I. R.

Journal:
Limnology and Oceanography

DOI:
https://doi.org/10.1002/lol2.70081