Oceanographic regime and foraging behaviour structure compound-specific PFAS variability in arctic-atlantic guillemots

Transverse structure of tidal and exchange flows in a Magellan glacial fjord

Glacial meltwater is a major contributor to stratification in polar waters, particularly in glacial fjords where it is contained by fjord topography. Stratification from glacial meltwater input impacts both light and nutrient availability, altering the timing and magnitude of phytoplankton blooms and peak in secondary productivity. Ice conditions can further impede near-surface circulation and trap low-density meltwater plumes, amplifying stratification. Whilst stratification is a critical process in the initiation of phytoplankton blooms, reduced mixing can impede nutrient resupply in the euphotic zone, reduce productivity, and alter the formation processes of marine snow. Here, using a combination of optical and acoustic instrumentation, we investigated how different stratification conditions in two adjacent fjords of northwest Greenland (Petermann Fjord, PF, and Sherard Osborn Fjord, SOF) impact the vertical distribution of two key components of Arctic pelagic ecosystems: marine snow and copepods. We show that the amplified stratification caused by ice damming outside SOF was associated with lower indices of primary and secondary production. Stratification also reduced concentrations of marine snow and resulted in an altered vertical distribution of small sphere particles that were likely fecal pellets in the top 100 m of SOF. Zooplankton distributions in both fjords were centered below the fluorescence peak but were more tightly coupled with the chlorophyll maximum in SOF than in the well-mixed PF. Feeding conditions in SOF were poorer, while in the more productive PF zooplankton were distributed deeper where risks of predation are likely reduced. Although small and large copepod densities were comparable between fjords, the low numbers of nauplii in SOF further suggest mismatch conditions not suitable for their survival. We demonstrate that sea ice conditions are linked to local physical water column stratification that has cascading effects on productivity and the abundance, distribution, and types of marine snow and copepods. Future conditions in glacial fjords are not clear because thermal stratification and glacier runoff will increase, but the number of ice damming events could decrease.

Autonomous video-acoustic monitoring at the sea-floor can improve our understanding of poorly documented ecosystems and help interpret active or passive acoustic data, but it has been rarely carried out, particularly in the Arctic. This study deployed a video camera synchronized with a hydrophone, combined with red lights and other oceanographic instrumentation, on the bottom of a glacial fjord in Inglefield Bredning, northwest Greenland (to 260 m water depth). Through manual review and automatic analysis of high-frequency images (30 fps) and audios (96 kHz), the conditions and biodiversity near the sea-floor were quantified. The data revealed a highly turbulent environment with abundant suspended particles and fibers, with 88% of 478 detected organisms being Amphipoda, Copepoda, Hydrozoa, and Chaetognatha. Amongst the other observed animals were Decapoda, Liparidae, Pterotracheoidea, Ctenophora, and narwhals (Monodon monoceros). The number of marine snow particles was highly variable through time and could change up to twofold within several hours. The tide modulated the particle flow direction and speed. Overall, the results show that portable moorings with video recorders are an important tool for exploration of the Arctic seafloor.

Abstract Glacier ice melt, a key driver of sea level rise, depends on how the ocean currents interact with ice. The roughness and shape of the ice on scales smaller than 10 m are important and remain poorly understood due to a lack of observations. We investigate submarine ice roughness using fine-resolution multibeam sonar measurements from 13 grounded icebergs and a drone survey of a recently capsized floating iceberg in the temperate tidewater glacial fjord Xeitl Geeyi’ (LeConte Bay), Alaska. From these 14 icebergs, 55 gridded iceberg surfaces (20–40 cm resolution) were derived. We apply a spectral, scale-resolved approach to quantify iceberg roughness. Spectral analysis shows that 40 of these surfaces were dominated by vertically oriented channels with wavelengths ranging from 0.9 m to 3.7 m, likely shaped by buoyancy-driven meltwater plumes. Statistical analyses reveal a mean peak wavelength of 1.9 m, RMS height of 0.3 m, skewness of -0.3 and kurtosis of 4.3. Roughness at medium- to small-scales $\mathcal{O}$ (0.5-5 m) can nearly double the ice–ocean boundary surface area and, when combined with iceberg-scale morphology $\mathcal{O}$ (10 m), underscores the need to integrate realistic roughness and morphology parameters into melt models, which may improve melt predictions.

Abstract Greenland's glacial fjords serve as pathways for the transport of heat and freshwater between the continental shelf and the outlet glaciers of the Greenland Ice Sheet. Despite increasing attention from the research community, seasonal studies in Greenland fjords remain scarce. This is especially true for near‐surface measurements. Here, we present year‐round, near‐full water column velocity observations and water mass data in Nuup Kangerlua, a glacial fjord in southwest Greenland. In July, a strong exchange flow is present in the upper 200 m, coinciding with the presence of subglacial discharge waters in the upper 10–50 m. Fjord circulation remains active throughout the year. Net heat transport toward the glaciers is most pronounced in the glacial melt domain (upper 150 m) in summer, while the heat transport occurs mostly in deeper layers in the winter months. Episodic dense coastal inflows renew the deep water in the fjord and can profoundly increase or decrease fjord water temperatures depending on the timing and depth of the inflow. We estimate vertical diffusivity in deeper layers to be around during stagnant periods (i.e., when no inflows occur). This study underlines the importance of seasonal variations and episodic events in fjord current dynamics and associated heat transport as a potentially important control for the submarine melting of marine‐terminating glaciers.

Abstract. As global atmosphere and ocean temperatures rise and the Greenland Ice Sheet loses mass, the glacial fjords of Kalaallit Nunaat/Greenland play an increasingly critical role in our climate system. Fjords are pathways for freshwater from ice melt to reach the ocean and for deep, warm, nutrient-rich ocean waters to reach marine–terminating glaciers, supporting abundant local ecosystems that Greenlanders rely upon. Research in Greenland fjords has become more interdisciplinary and more observations are being collected in fjords than in previous decades. However, there are few long-term (> 10 years) datasets available for single fjords. Additionally, observations in fjords are often spatially and temporally disjointed, utilize multiple observing tools, and datasets are rarely provided in formats that are easily used across disciplines or audiences. We address this issue by providing standardized, gridded summer season hydrographic sections for Sermilik Fjord in Southeast Greenland, from 2009–2023. Gridded data facilitate the analysis of coherent spatial patterns across the fjord domain, and are a more accessible and intuitive data product compared to discrete profiles. We combined ship-based conductivity, temperature, and depth (CTD) profiles with helicopter-deployed eXpendable CTD (XCTD) profiles from the ice mélange region to create objectively mapped (or optimally interpolated) along-fjord sections of conservative temperature and absolute salinity. From the gridded data, we derived a summer season climatological mean and root mean square deviation, summarizing typical fjord conditions and highlighting regions of variability. This information can be used by model and laboratory studies, biological and ecosystem studies in the fjord, and provides context for interpreting previous work. Additionally, this method can be applied to datasets from other fjords helping to facilitate fjord intercomparison studies. The gridded data and climatological products are available in netCDF format at https://doi.org/10.18739/A28G8FK6D (Roth et al., 2025a). All original profile observations, with unique DOIs for each field campaign, are available through the Sermilik Fjord Hydrography Data Portal (https://arcticdata.io/catalog/portals/sermilik, last access: 7 November 2025) hosted by the Arctic Data Center (Straneo et al., 2025). The code used has also been made available to facilitate continued updates to the Sermilik Fjord gridded section dataset and applications to other fjord systems.

Abstract. Interactions between ice masses and the ocean are key couplings in the global climate system. In many cases, these interactions occur through glacial fjords, which are long, deep, and narrow troughs connecting the open ocean to marine-terminating glaciers. By controlling the fluxes of ocean heat towards the ice sheet and ice sheet freshwater towards the ocean, glacial fjords play an important role in modulating ice sheet mass loss and the impacts of freshwater on ocean circulation. Yet, these dynamics occur at small scales that are challenging to resolve in earth system models and hence are often ignored, represented in an ad-hoc manner, or studied using expensive high-resolution models that are limited in scope. Here, we propose a means of capturing glacial fjord dynamics at negligible computational expense in the form of a “reduced-physics” model (FjordRPM) that resembles a “1.5-dimensional” or box model. We describe the design and physical parameterisations in the model and demonstrate its ability to capture important modes of glacial fjord circulation by comparing it against a general circulation model in idealised and realistic simulations. We suggest that the model is a useful tool for understanding fjord dynamics and a promising approach for representing glacial fjord processes within large-scale models or climate and sea level projection efforts.

Abstract. High-frequency broadband scientific echosounders enable the monitoring of complex dynamics, via the rapid collection of high-resolution, near-synoptic observations of the water column and quantitative geophysical measurements. Here, we demonstrate the applicability and utility of broadband active acoustics systems to improve observational capabilities in high-latitude glaciated fjords. These isolated and challenging field locations are a critical environment, linking the terminal end of terrestrial ice fields to the broader ocean, undergoing complex changes due to accelerated high-latitude warming trends. Using broadband (160–240 kHz) acoustic data, collected in tandem with ground-truth measurements from a conductivity–temperature–depth (CTD) and microstructure probe, in Hornsund Fjord in southwest Svalbard, we address the following three topics: (1) variability in the thermohaline structure and mixing across different temporal and spatial scales, (2) identification and characterization of processes in play at dangerous glacier termini, and (3) remote estimation of dissipation rates associated with mixing. Through these analyses, we illustrate the potential of broadband echosounders as a reasonably priced, relatively straightforward addition to experimental field kits, well suited for field deployment in high-latitude fjords where observations are limited by the length of season and generally challenging conditions.

Abstract Grand Lake is a large 250 m deep fjord lake located in Labrador, Canada. Previous studies on short and shallow sediment cores identified seasonal hydrological signals and connections with North Atlantic modes of climate variability. This study presents a new 20 m composite sequence from the deepest basin of Grand Lake, providing high‐resolution insights into sedimentary processes over the last ca. 3300 years. As a potential key environmental archive for north‐eastern Canada, a region where high‐resolution palaeoclimate records are scarce, Grand Lake offers a unique opportunity to examine long‐term sedimentary and climatic interactions. Previous research did not examine temporal changes in sedimentary processes or the specific mechanisms driving mass sediment deposition, limiting the distinction and interpretation of climate controls on longer time scales. Here, sedimentological and geochemical characteristics are used to reconstruct sedimentation dynamics and erosional processes. Several rapidly deposited layers are characterised over changing depositional environments during the Late Holocene, from a phase when the lake was connected to the sea to a more stable state conducive to varve formation. A combination of end‐member modelling analysis, lithofacies descriptions and high‐resolution μ‐XRF proxies revealed density currents as the dominant sedimentation process. Their origins ranged from proximal sources (gully systems) to distal sources (tributary rivers), with contributions varying over time, reflecting the transition from a marine‐influenced system to a post‐glacial fjord lake. The results provide a framework for future palaeoclimate studies in the region by contributing to a better understanding of sedimentary dynamics in a deep glacial lake, with implications for regional palaeoclimate reconstructions. Additionally, this study highlights the broader applicability of statistical unmixing for interpreting grain‐size variations in both lacustrine and marine environments.

Abstract. Glacier retreat and mass loss in East Greenland have profound implications for global sea-level rise, making it crucial to understand the complex dynamics of glacier–ocean interactions. Currently, our knowledge of East Greenland glacial fjords is limited, and the processes occurring directly in front of these glaciers, particularly the fate of subglacial meltwater, remain poorly understood. In this study, conducted in Dickson Fjord, East Greenland, in August 2022, hydrographic and stable water isotope measurements at various depths and fjord locations were carried out, starting from the terminus of the marine-terminating glacier. Employing a drone-deployed ocean profiler, we obtained salinity and temperature profiles as close as 20 m from the glacier terminus. We found that the terminus is primarily in contact with a cold Polar Water layer, with temperatures ranging between −0.8 and −1.7 °C. Within this layer, we observed an increase in temperature close to the glacier terminus. In the surface water layer, we identified two distinct depleted water isotope signals originating from the glacier: one located at the surface and the other near the freshwater freezing line, separated by non-depleted water. Based on our findings, we hypothesise that subglacial meltwater undergoes freezing upon encountering the cold Polar Water at the terminus. The buoyant ice crystals (frazil) formed during this refreezing process would then ascend to the surface, where they encounter positive ocean temperatures and melt. This frazil ice crystal formation process would explain the temperature increase in the Polar Water layer (due to latent heat released during freezing) and the depleted water isotope signal around the freshwater freezing line.

Abstract Greenland's fjords are the gateways through which the Greenland Ice Sheet (GrIS) interacts with the open ocean. These fjords are projected to undergo significant change as glaciers retreat with implications ranging from impacts to local fisheries and infrastructure to global sea level rise. Icebergs discharged by marine‐terminating glaciers in these fjords progressively melt on their way out of the fjord. Studies have shown that the cooling/freshening of the water column by icebergs contributes to the fjord overturning circulation. However, the majority of these studies are focused on summer conditions when data exist, and little is known about the impact and melting of icebergs year‐round. Here, we use a realistic regional configuration of a numerical model (MITgcm) of Sermilik fjord in southeast Greenland, from 2015 to 2017, to show that iceberg melting occurs year‐round, is focused in the upper 100 m of the water column, and largely occurs in the mélange region near the glacier. Comparison with an identical run without icebergs shows that upwelling induced by subsurface iceberg melt drives a warming (°C) of the surface layer in spring/winter in the entire fjord. This mélange upwelling supports a year‐round overturning circulation. Overall, our findings emphasize that icebergs must be included in simulations of fjords in order to correctly simulate water properties and circulation, including upwelling and heat flux. Representing these dynamics accurately is critical for understanding the impacts of icebergs on glacial melt rates and the interactions between glacial fjords, the GrIS, and the open ocean.

Abstract. Arctic tidewater glaciers and ice shelves are undergoing rapid attrition, with warmer ocean temperatures playing an important role. However, the relationship between ocean temperature and ice structure retreat is complex and may change as the ocean warms and as the ice structure geometry evolves. In order to explore ice–ocean interactions and the impact of retreating ice structures in a glacial fjord, we use a numerical ocean model of Milne Fiord, which features an ice shelf and a tidewater glacier with a floating glacier tongue (part of which is detached). We model past, present, and potential future ice configurations. Our results reveal that the average submarine melting is negligible across the ice shelf (<2 cm a−1) but can dominate thinning rates (>20 cm a−1) at specific locations where the ice is thick (>50 m) along the seaward edge. Our simulations also indicate that the temperature of water reaching the grounding line does not vary significantly when the ice shelf and glacier tongue are removed. In addition, we carry out a series of simulations with increasing ocean temperature which reveal a quasi-linear relationship between ocean temperature and submarine melting at the grounding line. Using this relationship and ocean temperature predictions for different greenhouse gas emission scenarios (2020 to 2100), we estimate that Milne Glacier will continue to retreat for at least 50 years, solely in response to ocean forcing. This study highlights the vulnerability of ice structures in the Arctic, even in a region regarded as the Last Ice Area.

Fjords in the Arctic are changing rapidly due to multiple factors including increasing air temperatures, the influx of Atlantic Water (Atlantification), sea-ice loss, retreat of tidewater glaciers, increased freshwater discharges, pollution and tourism. Understanding how these changes affect ecosystem processes and functions and, thus, services to society is critical. Net Ecosystem Metabolism (NEM) offers a holistic measure of ecosystem functioning and services, reflecting the balance between autotrophic and heterotrophic processes and the sink/source role of an ecosystem for nutrients and carbon. Using a 10-year dataset we quantify the main nutrient sources and sinks in Kongsfjorden (Svalbard) and estimate NEM using a method based on mixing diagrams combined with an ocean circulation model. We show that Kongsfjorden is a nutrient and carbon sink primarily supported by nutrient inputs from the adjacent shelf sea with terrestrial run-off playing a secondary role. Given the ongoing changes in the Arctic, driven by global warming and its associated effects, we recommend monitoring NEM as an integrated measure of the state of coastal ecosystems, considering the disproportionately large role of coastal regions in the global carbon budget.

Abstract. The Greenland Ice Sheet has steadily lost mass over the past decades, presently representing the second-largest single contributor to global sea-level rise. In line with the rest of the Greenland Ice Sheet, the glaciers draining the northeast Greenland ice stream have been observed to retreat and thin. Here, we present a comprehensive study of processes affecting and being affected by the mass balance of marine-terminating and peripheral glaciers in northeast (NE) Greenland. Our focus is on the 79N Glacier (79NG), which hosts Greenland’s largest floating ice tongue. We provide new insight into the ice surface melt, the ice mass balance, glacier dynamics, the regional solid Earth response, the ocean-driven basal melt and the consequences of meltwater discharge into the ocean. Our study is based on field observations, remote sensing and simulations with numerical models of different complexity, most of them originating from the Greenland Ice Sheet–Ocean Interaction (GROCE) experiment. We find the overall negative climatic mass balance of 79NG to co-vary with summertime volumes of supraglacial lakes and show that the spatial pattern of the overall negative ice mass balance for NE Greenland is mirrored by the pattern of glacial-isostatic adjustment. We find near-coastal mass losses of both marine-terminating and peripheral glaciers in NE Greenland to be of a similar magnitude in the last decade. In contrast to the neighboring Zachariæ Isstrøm, 79NG – despite experiencing massive thinning of the floating tongue – has resisted an acceleration of ice discharge across the grounding line due to buttressing imposed by lateral friction of the 70 km long ice tongue in the narrow glacial fjord. Observations and models employed in this study are consistent in terms of melt rates occurring below the floating ice tongue. Our results suggest that the multidecadal warming of Atlantic Intermediate Water flowing into the cavity below the ice tongue – supplied by the recirculating branch of the West Spitsbergen Current in Fram Strait – is the main driver of the recent major increase in basal melt rates. We find that the meltwater leaving the cavity toward the ocean at subsurface levels quickly dilutes on the wide shelf. The study concludes by summarizing important estimates of changes to the state of the atmosphere, ice, land and ocean domains.

Long-lived species must balance allocation between reproduction and self-maintenance, and such a trade-off is expected to affect their foraging behavior. A bimodal foraging strategy, where individuals alternate between long trips for self-maintenance and short trips for offspring provisioning, may reflect this compromise. Using tracking data collected over three breeding seasons, we investigated the occurrence of a bimodal foraging strategy and inter-annual variation in foraging decisions among black-legged kittiwakes (Rissa tridactyla) breeding in Kongsfjorden, Svalbard. Kongsfjorden, a glacial fjord with six tidewater glacier fronts, provides close foraging opportunities to breeding sites. The continental shelf break outside the fjord offers another foraging area but involves higher commuting costs. We tested the hypothesis that breeding adults perform foraging trips outside the fjord for self-maintenance. We predicted that (1) adults were more likely to undertake foraging trips outside the fjord when their body condition was low and that (2) individuals foraging outside the fjord were likelier to improve their body condition than those foraging within. Our results indicate that kittiwakes in Kongsfjorden may adopt a bimodal foraging strategy during chick-rearing, but not every year. Contrary to our first prediction, we found no evidence that adult body condition affected the probability of foraging at distant sites. However, adults were more likely to maintain or improve body condition during outside-fjord foraging trips, supporting the hypothesis that long-distance trips can be used for self-maintenance. Overall, our results suggest that bimodal foraging is not a fixed characteristic of kittiwake foraging behavior and may be influenced by environmental conditions.

Recent rapid environmental changes along the Greenland coast have significantly impacted Arctic marine mammals. The melting of tidewater glaciers influences ocean environments and ecosystems, potentially changing the distribution and behavior of Arctic marine mammals. The ringed seal (Pusa hispida) is a keystone species in the Arctic marine ecosystem. In this study, four ringed seals were equipped with Argos conductivity-temperature-depth (CTD) satellite relay data loggers close to tidewater glaciers in the Thule area of northwestern Greenland to investigate the relationship between their behavior and the marine environment. All seals spent most of their time in the vicinity of tidewater glacier fronts during the open-water period. After that period, the two seals moved out of the glacial fjords due to the formation of land-fast ice and stayed in the North Water Polynya area, where sea ice was relatively thin and sparse during the ice-covered period. Furthermore, CTD data suggest that ringed seals mainly dove to the depths of the water inhabited by the polar cod (Boreogadus saida). These habitat use characteristics, associated with distribution of ice and prey species, could potentially affect the distribution and ecology of this species under future climate change.

Abstract The ocean supplies large quantities of thermal energy to tidewater glaciers, but the mechanisms behind the heat delivery are not fully understood. To examine heat flux dynamics in glacial fjords, we run an 8‐year realistic numerical simulation of Milne Fiord, validated with observations. We leverage the duration and spatial resolution of the simulation to calculate ice melt, offshore density variations, average fjord temperature, and heat fluxes at different locations along‐fjord. Correlations between these quantities reveal that heat fluxes near the grounding line (<5 km) are linked to buoyancy‐driven circulation while offshore forcing is linked to heat fluxes along the remainder of the fjord. Comparison to a simulation with constant offshore boundary conditions reveals that offshore forcing enhances the exchange between the coastal shelf and the fjord, increasing glacier melt rates by 18%. Including offshore forcing into numerical and box models of glacial fjords is essential for accurate melting predictions.

Abstract. Glacial fjords often contain ice mélange, a frozen conglomeration of icebergs and sea ice, which has been postulated to influence both glacier dynamics and fjord circulation through coupled mechanical and thermodynamic processes. Ice mélange meltwater can alter stratification of the water column by releasing cool fresh water across a range of depths in the upper layer of the fjord. This meltwater input can subsequently modify the depth at which the subglacial discharge plume reaches neutral buoyancy and therefore the underlying buoyancy-driven fjord circulation and heat exchange with warm ocean shelf waters. Despite a spate of recent modeling studies exploring these proposed feedbacks, we lack in situ observations quantifying changes to the water column induced by ice mélange meltwater. Here we use a novel dataset collected before and after the melt, breakup, and down-fjord transport of ephemeral ice mélange in front of Kangilliup Sermia (Rink Isbræ) to directly investigate the extent to which ice mélange meltwater can modify glacier-adjacent water properties. We find that even a short-lived ice mélange event (4 d) can cause substantial cooling (0.18 °C) and freshening (0.25 g kg−1) of the water column that leads to stratification change down to the depth of the outflowing discharge plume. We compare our observations to an adjacent fjord, Kangerlussuup Sermia, where ice mélange seldom forms in the summertime and show that the presence or absence of ice mélange melt creates fundamental differences in the upper-layer hydrography of the two areas. These observations provide critical constraints for and agreement with recent modeling studies that have suggested ice mélange meltwater needs to be included in ocean circulation models for glaciers with deep grounding lines and high ice fluxes, which are precisely the glaciers exhibiting the largest-magnitude terminus retreats at present.

Abstract Climate change is rapidly transforming the coastal margins of Greenland. At the same time, there is increasing recognition that marine‐terminating glaciers provide unique and critical habitats to ice‐associated top predators. We investigated the connection between a top predator occupying glacial fjord systems in Northwest Greenland and the properties of Atlantic‐origin water and marine‐terminating glaciers through a multiyear interdisciplinary project. Using passive acoustic monitoring, we quantified the summer presence and autumn departure of narwhals (Monodon monoceros) at glacier fronts in Melville Bay and modeled what glacier fjord physical attributes are associated with narwhal occurrence. We found that narwhals are present at glacier fronts after Greenland Ice Sheet peak summer runoff and they remain there during the period when the water column is becoming colder and fresher. Narwhals occupied glacier fronts when ocean temperatures ranged from −0.6 to 0.8°C and salinities between 33.2 and 34.0 psu at around 200 m depth and they departed on their southbound migration between October and November. Narwhals' departure was approximately 4 weeks later in 2019 than in 2018, after an extreme 2019 summer heatwave event that also delayed sea ice formation by 2 months. Our study provides further support for the niche conservative narwhal's preference for cold ocean temperatures. These results may inform projections about how future changes will impact narwhal subpopulations, especially those occupying Greenland glacial fjords.