Thorbjørn Joest Andersen

The turnover rate of microbial cells drops steeply by increasing depth in the seabed, in accordance with the decreasing rate of organic matter mineralization. Bacterial endospore formation and germination may take place concurrently, yet their coupling to the mineralization rates during burial is poorly understood. We used high‐resolution ¹⁴ C‐dating of coring sites on the Peru Margin to show that the upper 8.5 m of sediment had been lost due to landslides at one site, thereby exposing 13,500‐yr old sediment. Dynamic transport‐reaction modeling of sulfate and methane showed that these landslides took place several thousand years ago. We discovered that microbiological and biogeochemical data from the two sites could be combined to deconvolute the effect of sediment age on microbial turnover and organic matter mineralization. A D : L amino acid racemization model showed that the mean turnover time of both microbial biomass and bacterial endospores was a few hundred years. Detailed chrono‐stratigraphy combined with microbiological and geochemical data revealed a 10,000‐fold span of anaerobic mineralization rates across 25,000 yr of sediment age. The mean power consumption per cell of the subsurface microbial community could theoretically enable the calculated production by Firmicutes of one endospore per cell per 140–1400 years, thereby maintaining a constant stock of 10 ⁶ –10 ⁷ endospores cm ⁻³ over thousands of years. These results suggest that bacterial endospores continue to be produced and to germinate deep down in the subseafloor.

Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of seasonal ice bridges between Canada and Greenland that prevent the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation particularly evident in Kane Basin, which either freezes over or remains open during winter and spring, depending on ice-bridge dynamics. Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland's widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning the 18th century to the present, that we compare with Humboldt Glacier solid ice discharge and retreat since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and organic matter sources. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea-ice cover during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by a shift towards higher primary production from approximately 1950 CE to the present.

Tsunamigenic landslides represent a major geohazard in the fjord environments of central West Greenland, induced by steep topographic reliefs and changing Arctic conditions. A dramatic example occurred on June 17th 2017, when a slope failure on the south-facing wall of Ummiammakku Mountain released a 38-40 × 10⁶ m³ rock avalanche into Karrat Fjord. The event generated a displacement wave with local runup heights exceeding 90 m and propagated 32 km southwest to the settlement of Nuugaatsiaq, causing severe infrastructure destruction and four fatalities. In this study we have integrated swath bathymetry and seismic datasets, along with sediment core information, to map mass-transport deposits produced by the 2017 rock avalanche in Karrat Fjord. By integrating geophysical imaging, lithofacies descriptions, XRF geochemistry, grain-size distributions, and 210Pb-dating, this study delineates the channelized runout of the 2017 event.The increasing frequency of landslides in West Greenland has motivated new research into the climatic and cryospheric controls on slope instability. Although the region is tectonically stable with only minor earthquake activity, recent studies suggest a connection between warming climate, permafrost degradation, and enhanced slope failure. This hypothesis aligns with broader observations across polar margins that link rising temperatures, increased precipitation, and isostatic rebound with enhanced decreasing slope instability. Our findings demonstrate the value of high-resolution marine datasets for detecting offshore landslide deposits and contribute new insights into the temporal and spatial patterns of slope instability in a rapidly changing Arctic fjord system.

Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of a seasonal ice bridge between Canada and Greenland, that prevents the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation, particularly evident in Kane Basin, which either freezes over or remains open during winter and spring depending on ice-bridge dynamics. The Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland’s widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning from the 18th century to the present, that we compare with Humboldt Glacier frontal positions since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and the source of organic matter. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea ice during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by increased primary production from approximately 1950 CE to the present.

Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of a seasonal ice bridge between Canada and Greenland, that prevents the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation, particularly evident in Kane Basin, which either freezes over or remains open during winter and spring depending on ice-bridge dynamics. The Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland’s widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning from the 18th century to the present, that we compare with Humboldt Glacier frontal positions since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and the source of organic matter. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea ice during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by increased primary production from approximately 1950 CE to the present.

Plastics are deeply embedded in modern life, but their degradation releases micro- and nanoplastics (MNPs) into ecosystems. These persistent particles are found everywhere, from oceans to the human body, and raise growing concerns about environmental and human health, biodiversity, and sustainability implications. Despite increasing awareness, effective responses to MNP pollution remain limited by unresolved challenges in scientific monitoring, policymaking, and public engagement. Addressing these challenges, the summer school on "Microplastics: From Environmental Impact to Policy, Innovation, and Public Awareness" held in June 2025 in Geneva, Switzerland, exemplifies an innovative educational model. The program was multi- and interdisciplinary, action-oriented, internationally collaborative, and rooted in local contexts. Focusing on microplastic pollution in aquatic environments, it brought together participants from 15 countries to explore the nexus of science, policy, governance, innovation, and public engagement. This contribution reflects the summer school’s design and outcomes, highlighting its promise as a model for advancing next-generation environmental education as well as discussing some of the key challenges.

Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of a seasonal ice bridge between Canada and Greenland, that prevents the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation, particularly evident in Kane Basin, which either freezes over or remains open during winter and spring depending on ice-bridge dynamics. The Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland’s widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning from the 18th century to the present, that we compare with Humboldt Glacier frontal positions since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and the source of organic matter. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea ice during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by increased primary production from approximately 1950 CE to the present.

Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of a seasonal ice bridge between Canada and Greenland, that prevents the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation, particularly evident in Kane Basin, which either freezes over or remains open during winter and spring depending on ice-bridge dynamics. The Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland’s widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning from the 18th century to the present, that we compare with Humboldt Glacier frontal positions since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and the source of organic matter. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea ice during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by increased primary production from approximately 1950 CE to the present.

Salt marshes are known as one of the world’s most efficient ecosystems for carbon sequestration. At the same time they are vulnerable to ecosystem degradation due to climate-induced sea level rise (SLR). It is relatively poorly understood how marsh response to SLR may affect carbon sequestration rates. Here we present work based on some global to local-scale studies on organic carbon accumulation rates (OCAR, g C m-2 yr-1) in salt marsh sediment beds. First, based on a global dataset including 477 marsh sites, we find that the local SLR rate is the most important driver of OCAR among 12 investigated environmental variables. Overall, faster SLR favors higher OCAR values, which is interpreted to result from a positive feedback between SLR, more tidal inundation of marshes, higher tidal supply and deposition of sediments, and hence higher rates of sediment organic carbon (SOC) burial. Yet our global analysis shows OCAR values are also related to several other environmental variables. This illustrates the limits of global or regional-scale meta analyses to identify OCAR response to SLR, as also other environmental drivers vary between geographically distant sites. Therefore, secondly, we present results from two local-scale studies on OCAR, one in a so-called minerogenic marsh complex (i.e. SOC contents 35 %) in Maryland, USA. In the minerogenic system we quantified OCAR over the past four decades in two nearby marsh systems, with similar environmental conditions, but largely varying local relative SLR rates: one reference marsh with a SLR rate of ~2 mm.yr-1 versus a nearby marsh with accelerated relative SLR rate (~10 mm.yr-1) due to local land subsidence through gas extraction. Our results show OCAR values are on average twice as high in response to the accelerated SLR, with a more pronounced response (i.e. 63 % increase) on marginal marsh zones 30 m from creeks. We explain this as increased tidal sediment deposition and OCAR in response to faster SLR is more pronounced closer to creeks, as these are the source of tidal sediment supply. Further, in the organogenic marsh, we find OCAR values at 30 m from creeks. Moreover, our local case studies show interior marsh zones may experience vegetation die-back and conversion to shallow water ponds, which we interpret as a result of too low sediment accretion to keep pace with SLR. We highlight that the SOC response after marsh to pond conversion remains a key question. First analyses show lower SOC stability in response to higher SOC contents, suggesting that marsh degradation in response to SLR may trigger potentially higher SOC losses in organogenic marshes as compared to minerogenic marshes.