Søren Rysgaard

Coastal ecosystems are threatened by global change but remain understudied despite their importance for biodiversity and human society. For instance, most coastal studies and monitoring programs focus on a few groups of organisms owing to methodological limitations. However, high-throughput sequencing of environmental DNA (eDNA) now facilitates taxonomically broad studies of coastal biodiversity. Here, we conducted a very comprehensive study of coastal biodiversity patterns using multi-marker eDNA metabarcoding of nearly 1000 water and sediment samples covering the strong salinity gradient from the North Sea to the Baltic Sea. We included the major coastal habitat types and measured a range of environmental variables. Importantly, we found that across the tree of life: (i) salinity was the best predictor of community composition and richness, (ii) hard-bottomed habitats were coastal biodiversity hotspots regarding both species richness and unique sequences, and (iii) water and sediment samples harboured very different biological communities. Furthermore, we found geographically structured intraspecific genetic variation and detected 90 marine species not previously documented in Denmark. Our study suggests similar drivers of coastal biodiversity and community composition across the tree of life and demonstrates the potential of holistic eDNA biomonitoring for future management of coastal ecosystems locally and globally.

Greenland's ice loss is increasing across the ice sheet due to enhanced surface melting and accelerated glacier discharge, contributing to sea level rise and potentially altering ocean circulation and marine ecosystems. Fjords play a key role in this process by linking the ocean and ice sheet, but currently a limitation is that most fjords in Greenland lack observational data, especially seasonal data sets. Using glacier‐to‐coast hydrographic sections from the Ella Ø fjord complex in East Greenland, we document strong seasonal variability. Summer conditions are characterized by ice‐free, warmer, and fresher surface waters, with clear glacier meltwater and precipitation signals confined to the upper 50 m and primarily to the inner fjord. In winter, the fjord is ice covered, with colder and saltier surface waters, weaker turbidity that is dominated by basal melt at depth, and only small fractions of glacier meltwater and local meteoric water. The Polar Water layer is warmer close to the marine‐terminating glacier during both seasons, without corresponding change in salinity. The observed seasonal change in Polar Water thickness of 40 m is consistent with the proposed thinning of the Polar Water layer along the Northeast Greenland shelf since the 2000s, suggesting that longer‐term changes are superimposed on a strong seasonal variability. Given that most freshwater from the Arctic Ocean flows southward along the East Greenland coast, influencing regional and potentially large‐scale ocean circulation, it is important to gain more insight into its seasonal variability across multiple locations to evaluate the robustness of reported longer‐term changes.

Observations have shown a significant undersaturation of surface partial pressure of CO2 in Arctic fjords, resulting in a CO2-uptake during the ice-free summer period. However, few locations in the Arctic have been monitored sufficiently frequently to resolve the physical and biogeochemical processes that impact the seasonal CO2-uptake. Here we apply a three-dimensional biogeochemical ocean model of a high-Arctic fjord system to quantify the sensitivity of the seasonal CO2-uptake to changes in runoff and biological production. Tyrolerfjord/Young Sound (74°N) is the most well-described fjord along the east Greenland coast, and a comprehensive field campaign in 2014 provided validation data for the model. The seasonal CO2-uptake was almost linearly related to runoff, e.g., a 100% increase in runoff caused a 46% increase in the seasonal CO2-uptake. This was mainly due to the effect from surface salinity on the carbonate system. Biological production was also found to be of major importance, and a model scenario without biological production reduced the CO2-uptake by a factor of 2. Inorganic nutrients in runoff and the influence from tidal mixing only had a relatively small impact on the CO2-uptake. Carbonate compounds in runoff and wind forcing along the fjord were identified as sensitive and poorly understood elements for quantifying the CO2-uptake, and this increase the uncertainty on the estimated carbon sink for the fjord during the ice-free period of 1500 t C. The sensitivity to runoff indicates that increased melting from the Greenland Ice Sheet will cause a significant increase of the seasonal CO2-uptake in high-Arctic fjords.

Strong spatial and temporal gradients in salinity, temperature, and carbonate chemistry in Arctic coastal surface waters complicate the estimation of air-sea carbon dioxide (CO2) exchange, particularly during sea ice breakup. The present study evaluates the applicability of the widely used bulk flux model under such conditions. This approach assumes homogeneous surface conditions and no vertical pCO2 gradients in the bulk seawater. However, our observations in a stratified Arctic fjord reveal pronounced vertical variability in pCO2 within the upper water column, including non-linear gradients near the air-sea interface. This results in, widely varying flux estimates depending upon the depth of the pCO2 measurement used to establish air-sea disequilibrium. Importantly, similarly structured nonlinear pCO2 profiles were observed across distinct fjord systems and years, suggesting that this vertical heterogeneity may be a characteristic feature of Arctic stratification during sea ice breakup. We recommend incorporating both micrometeorological techniques and high-resolution vertical profiling in Arctic fjords to improve flux estimates of CO2 in this rapidly changing region.

Thermal springs are a rare but diverse feature of Greenland’s ice-free margins, with temperatures ranging from near freezing to over 60 °C. Greenland’s thermal springs host distinctive biological communities, from thermophilic microbial mats to unique vascular plant assemblages, representing important Arctic biodiversity hotspots. They hold cultural, ecological, and scientific importance, yet records are mostly scattered across historical literature, local knowledge, and isolated field reports. Here, we present the first comprehensive review and quality-controlled geodatabase of Greenland’s thermal springs, compiled from more than a century of scientific and historical sources, botanical surveys, Greenlandic placenames, satellite imagery, and field observations. The present database contains entries for 382 individual spring localities, providing names, coordinates, geological setting, thermal characteristics, and metadata on source reliability. We describe their geographic distribution, geological setting, and possible heat sources, which include radiogenic decay, residual magmatic heat, and exothermic chemical weathering. Besides a lack of recent visits and photo documentation of many thermal springs, this synthesis highlights substantial gaps in temperature, chemistry, and discharge measurements, underlining the need for systematic sampling and community-based monitoring. The open access database offers a foundation for future interdisciplinary research, supports conservation planning, and provides a baseline for assessing climate-driven changes in Greenland’s geothermal systems. Eqikkaaneq Puilasut kissartut Kalaallit Nunaata sermersuaqanngitsuani qaqutigoortuupput kisianni assigiinngisitaarlutik, qerisinnaanngajatsuniit 60°C-t sinnerlugit kissassusilinnut. Kalaallit Nunaanni puilasut kissartut immikkuullarissunik pinngortitap uumassusililernerinik assigiinngitsorpassuarnik peqarput kissartumi tappiorannartuniit naasunut tunngasunut pisunit, issittumilu uumassusilinnut pingaaruteqarluinnartumik inissisimasuullutik. Taakku kulturikkut, pinngortitami pissuseqatigiinnikkut ilisimatusarnikkullu pingaaruteqarluinnarput, taamaattorli oqaluttuarisaanermi atuakkiani sumiiffinni ilisimatusarnermik aammalu immikkoortunik misissuinerni, inuiaqatigiit ilisimasaannik apersuinernit allattorsimaffiit siaruaqqasuullutik. Uani siullerpaamik tamakkiisumik saqqummiunneqarput misissuinerit pitsaasutsimillu nakkutigineqartumik geodatabase Kalaallit Nunaanni silaannaap pissusaanik misissuinerit, ukiuni untritilillit sinnerlugit ilisimatusarnerni oqaluttuarisaanermillu tunngaveqartunik, naasorsiuussutsikkut misissuinernit, kalaallisut nunat aqqinit, qaammataasiamit assilisanit aammalu nunami misissuinernit katersorneqarsimasut. Maannamut paasissutissaavimmi puilasut ataasiakkaat 382-usut pillugit allattorsimaffiit ilaatinneqarput, tassanilu aqqit, naleqqat (koordinaatit), geologiskimi inissisimanerit, kissassutsit pissusiannit naleqqussarnerit aammalu qularnaveeqquserneqarnerinnut metadata-t allaaserineqarlutik. Uani nassuiarneqarput nunap assinganik siammasissuseqarneri, geologiskimi inissisimaneri kiisalu kissassutsimik pilersitsisinnaanneri. Taakkulu ilagalugit radiogenimik aserorterneqarneri, magmateskimik kissassusiup sinneri kiisalu eksotermiskimik kemiimut tunngasunik aakkiartornerit. Puilasut kissartut amerlasuut qanittukkut tikinneqarsimannginneri kiisalu assinik uppernarsiisarnernik amigaateqarnerit saniatigut ataatsimoortillugit isiginiarneqarnerini pingaaruteqarpoq kissassutsinut, kemimik aammalu aniatitsinermik misissuinerni annertuumik amigaateqarnernik ersersitsinissaq, tassanimi ataqatigiissumik misissueqqisaarinissat kiisalu inuiaqatigiinnit nakkutiginninnerit pisariaqartinneqarmata. Avammut ammasumik paasissutissaaveqarnerup siunissami tunngaviusumik ilisimatusarnissamut neqeroorutigaa innarlernaveersaarnissaannut pilersaarusiornernut misissuieqqissaarineqarsinnaaneq.

Strong spatial and temporal gradients in salinity, temperature, and carbonate chemistry in Arctic coastal surface waters complicate the estimation of air-sea CO₂ exchange, particularly during sea ice breakup. This study evaluates the applicability of the widely used bulk flux model under such conditions. The bulk approach assumes homogeneous surface conditions and linear vertical pCO₂ gradients. However, our observations in a stratified Arctic fjord reveal pronounced vertical variability in pCO₂ within the upper water column, including non-linear gradients near the air-sea interface. Micrometeorological measurements captured episodic upward CO₂ fluxes even when waters 1 m and below were CO₂-undersaturated. We hypothesize that transient, high-pCO₂ layers at ~0.1 m depth intermittently decouple the atmospheric exchange from subsurface waters, reversing the expected flux direction. These findings highlight the importance of resolving near-surface variability during the transition from ice-covered to open water conditions. We recommend incorporating micrometeorological techniques and high-resolution vertical profiling in Arctic fjords to improve flux estimates of CO₂ in this rapidly changing region.

Strong spatial and temporal gradients in salinity, temperature, and carbonate chemistry in Arctic coastal surface waters complicate the estimation of air-sea CO₂ exchange, particularly during sea ice breakup. This study evaluates the applicability of the widely used bulk flux model under such conditions. The bulk approach assumes homogeneous surface conditions and linear vertical pCO₂ gradients. However, our observations in a stratified Arctic fjord reveal pronounced vertical variability in pCO₂ within the upper water column, including non-linear gradients near the air-sea interface. Micrometeorological measurements captured episodic upward CO₂ fluxes even when waters 1 m and below were CO₂-undersaturated. We hypothesize that transient, high-pCO₂ layers at ~0.1 m depth intermittently decouple the atmospheric exchange from subsurface waters, reversing the expected flux direction. These findings highlight the importance of resolving near-surface variability during the transition from ice-covered to open water conditions. We recommend incorporating micrometeorological techniques and high-resolution vertical profiling in Arctic fjords to improve flux estimates of CO₂ in this rapidly changing region.

Marine-terminating glaciers play a significant role he loss of ice mass from Greenland. Iceberg calvings are thought to account for about half of Greenland ice mass loss. These events produce seismic waves (glacial earthquakes) recorded by global seismic networks and contain information such as the iceberg volume and the forces acting during the event. Previous work showed that seismic inversion, coupled to numerical modeling, can be used to decipher the glacial earthquake signal [Sergeant 2019]. However, the lack of consideration for the hydrodynamic forces applied onto the glacier leads to large uncertainties in the iceberg volume estimations. Therefore, based on previous work, a Computational Fluid Dynamics (CFD) model is employed to model the complex fluid/structure interaction between a capsizing iceberg and the ocean. The simulations match results from laboratory experiments with great accuracy (rotation kinematics, effect of calving type, hydrodynamic pressure, etc.) [De Pinho Dias 2025].In this presentation, we will show how the forces applied onto a simple model of Helheim glacier during an iceberg calving depend on geometrical parameters (iceberg height, aspect ratio, water depth, iceberg drop height). The pressure force exerted onto the glacier front has a significant magnitude of more than 50 % of the iceberg/glacier contact force which acts in the opposite direction.The forces are then converted into seismic signals and show a very good match with the signal recorded at 8 stations in Greenland.In addition, we will show the path of particle tracers advected by calving-induced water currents. Sergeant, A. et al. (2019) ‘Monitoring Greenland ice sheet buoyancy-driven calving discharge using glacial earthquakes’, Annals of Glaciology, 60(79), pp. 75–95. doi:10.1017/aog.2019.7. De Pinho Dias, N., Leroyer, A., Mangeney, A. and Castelnau, O., 2025. Fluid-structure modeling of iceberg capsize. Ocean Engineering, 336, p.121765. doi:10.1016/j.oceaneng.2025.121765