Arctic Fjord Research Articles

Biochemical composition of particles shape particle-attached bacterial community structure in a high Arctic fjord

Kongsfjorden, a high Arctic fjord was used as a model site to test the hypothesis that source and biochemical composition of particulate organic matter (POM) exert strong selective pressure on particle-attached bacterial community than their free-living counter parts. For this subsurface water samples were collected along the particle density gradient in Kongfjorden. Microbial communities were size fractionated into free-living (FL, 0.2–3 μm) and particle-attached (PA, >3 μm), and V3-V4 16S rRNA gene amplicon sequencing was used for evaluating bacterial community composition. Further, elemental (C/N), isotopic (δ13C) and biochemical composition (carbohydrates, proteins and lipids) of POM were also determined. Clear niche segregation among PA and FL communities was observed, except at a location close to Open Ocean. Higher alpha diversity was recorded in majority of the PA communities as compared to the FL. δ13C (‰) and particulate-carbohydrate (P-CHO) content of POM strongly influence PA bacterial community composition, which was composed primarily of complex biopolymers/carbohydrates degrading bacterial taxa, in particular members of phyla Verrucomicrobia and Bacteroidetes. In addition, glacial meltwater influx and particulate organic carbon (POC) influence FL bacterial community structure. Thus, it appears that particles act as direct substrates for bacterial utilization and select particle-attached bacterial community with specific structure and function while dissolved organic carbon (DOC) plume around the particles select for some specialized free-living bacteria. Further, our results suggest that PA bacterial community can act as ecological indicator for the availability and turnover of complex polymeric substrates in high Arctic fjord environment.

Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments

Selection by the local, contemporary environment plays a prominent role in shaping the biogeography of microbes. However, the importance of historical factors in microbial biogeography is more debatable. Historical factors include past ecological and evolutionary circumstances that may have influenced present-day microbial diversity, such as dispersal and past environmental conditions. Diverse thermophilic sulfate-reducing Desulfotomaculum are present as dormant endospores in marine sediments worldwide where temperatures are too low to support their growth. Therefore, they are dispersed to here from elsewhere, presumably a hot, anoxic habitat. While dispersal through ocean currents must influence their distribution in cold marine sediments, it is not clear whether even earlier historical factors, related to the source habitat where these organisms were once active, also have an effect. We investigated whether these historical factors may have influenced the diversity and distribution of thermophilic endospores by comparing their diversity in 10 Arctic fjord surface sediments. Although community composition varied spatially, clear biogeographic patterns were only evident at a high level of taxonomic resolution (>97% sequence similarity of the 16S rRNA gene) achieved with oligotyping. In particular, the diversity and distribution of oligotypes differed for the two most prominent OTUs (defined using a standard 97% similarity cutoff). One OTU was dominated by a single ubiquitous oligotype, while the other OTU consisted of ten more spatially localized oligotypes that decreased in compositional similarity with geographic distance. These patterns are consistent with differences in historical factors that occurred when and where the taxa were once active, prior to sporulation. Further, the influence of history on biogeographic patterns was only revealed by analyzing microdiversity within OTUs, suggesting that populations within standard OTU-level groupings do not necessarily share a common ecological and evolutionary history.

Virtual Reality in Cartography: Immersive 3D Visualization of the Arctic Clyde Inlet (Canada) Using Digital Elevation Models and Bathymetric Data

Due to rapid technological development, virtual reality (VR) is becoming an accessible and important tool for many applications in science, industry, and economy. Being immersed in a 3D environment offers numerous advantages especially for the presentation of geographical data that is usually depicted in 2D maps or pseudo 3D models on the monitor screen. This study investigated advantages, limitations, and possible applications for immersive and intuitive 3D terrain visualizations in VR. Additionally, in view of ever-increasing data volumes, this study developed a workflow to present large scale terrain datasets in VR for current mid-end computers. The developed immersive VR application depicts the Arctic fjord Clyde Inlet in its 160 km × 80 km dimensions at 5 m spatial resolution. Techniques, such as level of detail algorithms, tiling, and level streaming, were applied to run the more than one gigabyte large dataset at an acceptable frame rate. The immersive VR application offered the possibility to explore the terrain with or without water surface by various modes of locomotion. Terrain textures could also be altered and measurements conducted to receive necessary information for further terrain analysis. The potential of VR was assessed in a user survey of persons from six different professions.

Coastal waters freshening and extreme seasonality affect organic matter sources, quality, and transfers in a High Arctic fjord (Young Sound, Greenland)

Arctic benthic ecosystems are expected to experience strong modifications in the dynamics of primary producers and/or benthic-pelagic coupling under climate change. However, lack of knowledge about the influence of physical constraints (e.g. ice-melting associated gradients) on organic matter sources, quality, and transfers in systems such as fjords can impede predictions of the evolution of benthic-pelagic coupling in response to global warming. Here, sources and quality of particulate organic matter (POM) and sedimentary organic matter (SOM) were characterized along an inner-outer gradient in a High Artic fjord (Young Sound, NE Greenland) exposed to extreme seasonal and physical constraints (ice-melting associated gradients). The influence of the seasonal variability of food sources on 2 dominant filter-feeding bivalves (Astarte moerchi and Mya truncata) was also investigated. Results revealed the critical impact of long sea ice/snow cover conditions prevailing in Young Sound corresponding to a period of extremely poor and degraded POM and SOM. Freshwater inputs had a very local impact during summer, with relatively more degraded POM at the surface compared to bottom waters that were less nutritionally depleted but more heterogeneous among the sampled stations. Terrestrial inputs contributed to the SOM composition but showed a large variability along the fjord. Finally, diet analyses underlined the contrasted nutritional conditions, showing much higher lipid reserves in A. moerchi than in M. truncata during winter. Under a scenario with increased freshwater input, such results suggest a decline in organic matter quality and production in Young Sound, with subsequent impacts on benthic food webs.

Seasonal changes in foraminiferal assemblages along environmental gradients in Adventfjorden (West Spitsbergen)

Foraminifera are numerically abundant components of the benthic fauna; thus, they are very important compounds in glaciomarine environments. However, ongoing oceanographic changes may influence their distribution, abundances and diversity differently at different times of the year. In the present study, we aimed to assess seasonal environmental changes in an Arctic fjord (Adventfjorden, W Spitsbergen) and the structure and distribution of benthic foraminiferal assemblages during four seasons (January, May, August, November). The study revealed that the benthic foraminiferal assemblages in Adventfjorden are susceptible to environmental changes related to enhanced inflow of shelf-transformed water (STW). We distinguished three zones in the fjord: (1) the deeper outer part influenced by STW, with living specimens staying in the few uppermost layers of sediment, (2) the shallower interior influenced by freshwater outflows and high sediment load, resulting in the dominance of opportunistic glaciomarine taxa constantly buried in the sediment, and (3) the central part, where the seasonal variation in the foraminifera assemblage reflects the interplay between the influence of riverine inputs and STW. Our study also revealed that the presence of STW in Adventfjorden favours an early spring appearance of juvenile foraminifera; however, the majority of the specimens are later withered and do not contribute to the summer pool of mature individuals. On the other hand, the majority of the mature specimens can survive during the winter because of sufficient organic matter stocks and year-long ice-free conditions.

Spring Succession and Vertical Export of Diatoms and IP25 in a Seasonally Ice-Covered High Arctic Fjord

The biomarker IP25 and fossil diatom assemblages preserved in seafloor sediments are commonly used as proxies for paleo Arctic sea-ice reconstructions, but how their production varies over the seasons and is exported to the sediment remains unclear. We analysed IP25 concentrations and diatom assemblages from a five-week consecutive series of sea-ice cores and compared the results with sediment trap and surface sediment samples collected at the same site in the Young Sound fjord, Northeast Greenland. Our aim was to investigate the dynamics of diatom colonization of the spring sea ice and the in-situ production of IP25. Additionally, selected diatom taxa observed in the sea-ice samples were isolated from in-ice assemblages and their lipid composition was analysed via gas chromatography-mass spectrometry. We confirm that Haslea spicula (and not the closely related species H. crucigeroides) is an IP25-producer. All three known IP25-producing taxa (Haslea spicula, H. kjellmanii and Pleurosigma stuxbergii var. rhomboides) were present in Young Sound sea ice and the low IP25 concentrations measured in the sea ice (0.44-0.72 pg mL-1) were consistent with the low abundance of these source species (0.21-9.66 valves mL-1). Total sympagic diatom production also remained very low (21-985 valves mL-1), suggesting that the fjord’s sea ice did not provide an optimal physical-chemical environment for diatoms to thrive. Temporal changes in the sympagic diatom community were also observed, with an early presence of the pelagic Thalassiosira hyperborea and subsequent dominance of pennate taxa, including Nitzschia and Navicula species, Fossula arctica and Stauronella arctica. The assemblages observed during and after the seasonal ice melt consisted primarily of Fossula arctica, Fragilariopsis oceanica, Thalassiosira antarctica var. borealis (resting spores) and Chaetoceros spp. (vegetative cells and resting spores). The seafloor sediment assemblages largely reflected the melt and post-melt planktic production and were dominated by the resting spores of the centric Chaetoceros spp. and Thalassiosira antarctica var. borealis, and the pennate Fragilariopsis oceanica, Fossula arctica and Fragilariopsis reginae-jahniae. This study documents that IP25 is produced in Young Sound, and that the weak fingerprint of sea-ice in the sediment appears to be primarily due to the limited sea ice diatom biomass.

Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord

AbstractArctic waters are often enriched with terrestrial dissolved organic matter (DOM) characterized by having elevated visible wavelength fluorescence (commonly termed humic‐like). Here, we have identified the sources of fluorescent DOM (FDOM) in a high Arctic fjord (Young Sound, NE Greenland) influenced by glacial meltwater. The biological transformation of FDOM was further investigated using plankton community size‐fractionation experiments. The intensity of ultraviolet fluorescence (commonly termed amino acid‐like) was highly variable and positively correlated to bacterial production and mesozooplankton grazing. The overall distribution of visible FDOM in the fjord was hydrographically driven by the high‐signal intrusion of Arctic terrestrial DOM from shelf waters and dilution with glacial runoff in the surface waters. However, the high‐intensity visible FDOM that accumulated in subsurface waters in summer was not solely linked to allochthonous sources. Our data indicate that microbial activity, in particular, protist bacterivory, to be a source. A decrease in visible FDOM in subsurface waters was concurrent with an increase in bacterial abundance, indicating an active bacterial uptake or modification of this DOM fraction. This was confirmed by net‐loss of visible FDOM in experiments during summer when bacterial activity was high. The degradation of visible FDOM appeared to be associated with bacteria belonging to the order Alteromonadales mainly the genus Glaciecola and the SAR92 clade. The findings provide new insight into the character of Arctic terrestrial DOM and the biological production and degradation of both visible and UV wavelength organic matter in the coastal Arctic.

Enhanced Air\u2013Sea Exchange of Heat and Carbon Dioxide Over a High Arctic Fjord During Unstable Very-Close-to-Neutral Conditions

Eddy-covariance measurements made in the marine atmospheric boundary layer above a high Arctic fjord (Adventfjorden, Svalbard) are analyzed. When conditions are unstable, but close to neutral −0.1 < z/L < 0, where z is the height, and L is the Obukhov length, the exchange coefficient for sensible heat CH is significantly enhanced compared with that expected from classical surface-layer theory. Cospectra of the vertical velocity component (w) and temperature (T) reveal that a high-frequency peak develops at f ≈ 1 Hz for z/L > − 0.15. A quadrant analysis reveals that the contribution from downdrafts to the vertical heat flux increases as conditions become close to neutral. These findings are the signature of the evolving unstable very-close-to-neutral (UVCN) regime previously shown to enhance the magnitude of sensible and latent heat fluxes in the marine surface layer over the Baltic Sea. Our data reveal the significance of the UVCN regime for the vertical flux of the carbon dioxide (CO2) concentration (C). The cospectrum of w and C clearly shows how the high-frequency peak grows in magnitude for z/L > − 0.15, while the high-frequency peak dominates for z/L > − 0.02. As found for the heat flux, the quadrant analysis of the CO2 flux shows a connection between the additional small-scale turbulence and downdrafts from above. In contrast to the vertical fluxes of sensible and latent heat, which are primarily enhanced by the very different properties of the air from aloft (colder and drier) during UVCN conditions, the increase in the air–sea transfer of CO2 is possibly a result of the additional small-scale turbulence causing an increase in the water-side turbulence. The data indicate an increase in the gas-transfer velocity for CO2 for z/L > − 0.15 but with a large scatter. During the nearly 2 months of continuous measurements (March–April 2013), as much as 36% of all data are associated with the stability range −0.15 < z/L < 0, suggesting that the UVCN regime is of significance in the wintertime Arctic for the air–sea transfer of heat and possibly also CO2.

The Molecular Fingerprint of Fluorescent Natural Organic Matter Offers Insight into Biogeochemical Sources and Diagenetic State.

Investigating the biogeochemistry of dissolved organic matter (DOM) requires the synthesis of data from several complementary analytical techniques. The traditional approach to data synthesis is to search for correlations between measurements made on the same sample using different instruments. In contrast, data fusion simultaneously decomposes data from multiple instruments into the underlying shared and unshared components. Here, Advanced Coupled Matrix and Tensor Factorization (ACMTF) was used to identify the molecular fingerprint of DOM fluorescence fractions in Arctic fjords. ACMTF explained 99.84% of the variability with six fully shared components. Individual molecular formulas were linked to multiple fluorescence components and vice versa. Molecular fingerprints differed in diversity and oceanographic patterns, suggesting a link to the biogeochemical sources and diagenetic state of DOM. The fingerprints obtained through ACMTF were more specific compared to traditional correlation analysis and yielded greater compositional insight. Multivariate data fusion aligns extremely complex, heterogeneous DOM data sets and thus facilitates a more holistic understanding of DOM biogeochemistry.

Population Dynamics of Bacterioplanktonic Component Associated with the Phytoplankton Biomass in Kongsfjorden, an Arctic Fjord

Population Dynamics of Bacterioplanktonic Component Associated with the Phytoplankton Biomass in Kongsfjorden, an Arctic Fjord

Hyperbenthic food-web structure in an Arctic fjord

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 603:29-46 (2018) - DOI: https://doi.org/10.3354/meps12713 Hyperbenthic food-web structure in an Arctic fjord Maeve McGovern1,2,3,4,6,*, Jørgen Berge2,3, Beata Szymczycha5, Jan Marcin Węsławski5, Paul E. Renaud1,2 1Akvaplan-niva, Fram Centre for Climate and the Environment, 9296 Tromsø, Norway 2University of Tromsø, 9027 Tromsø, Norway 3University Centre in Svalbard, 9171 Longyearbyen, Norway 4Nord University, Faculty of Biosciences and Aquaculture, Postbox 1490, 8049 Bodø, Norway 5Institute of Oceanology PAS, ul. Powstancow Warszawy 55, 81-712 Sopot, Poland 6Present address: Norwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo, Norway *Corresponding author: maeve.mcgovern@niva.no ABSTRACT: Current knowledge of the Arctic marine ecosystem is based primarily on studies performed during the polar day on the pelagic and benthic realms. Both the polar night and the hyperbenthic layer remain as substantial knowledge gaps in our understanding of the marine system at high latitudes. This study investigated the hyperbenthic food web in Kongsfjord, a high-latitude, ice-free fjord, in September 2014 and January 2015. The hyperbenthic food web was analyzed using a multi-biomarker approach including stable isotopes of carbon and nitrogen as well as fatty acid profiles of a variety of hyperbenthic taxa. While results suggested no difference in biomarker composition between September and January, they indicated a division in the sampled hyperbenthic species assemblage between pelagic and benthic feeders in both sampling periods. The presence of these 2 food-web pathways may have implications for maintaining higher trophic levels through the polar night, thereby enhancing stability in the Kongsfjord system. KEY WORDS: Hyperbenthos · Suprabenthos · Benthic-boundary layer zooplankton · Kongsfjord · Stable isotopes · Fatty acids · Benthic-pelagic coupling Full text in pdf format PreviousNextCite this article as: McGovern M, Berge J, Szymczycha B, Weęsławski JM, Renaud PE (2018) Hyperbenthic food-web structure in an Arctic fjord. Mar Ecol Prog Ser 603:29-46. https://doi.org/10.3354/meps12713 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 603. Online publication date: September 17, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Calanus finmarchicus diel and seasonal rhythmicity in relation to endogenous timing under extreme polar photoperiods

Changing environmental conditions cause poleward distribution shifts in many marine organisms including the northern Atlantic key zooplankton species Calanus finmarchicus. The copepod has diel cycles of vertical migration and feeding, a seasonal life cycle with diapause in winter and a functioning circadian clock. Endogenous clock mechanisms control various aspects of rhythmic life and are heavily influenced by environmental light conditions. Here we explore how the extreme seasonal change in photoperiod (day length) in a high Arctic fjord affects circadian clock functioning as well as diel and seasonal cycles in C. finmarchicus. Expression of clock genes was measured in the active life phase at the end of midnight sun, in early diapause when photoperiod was ~12 h, and in late diapause during the polar night. While the clock maintained diel rhythmicity under extremely long photoperiods, it became arrhythmic during diapause. This was probably not due to a lack of light but was related to the physiological state of diapause. Seasonal expression analyses of 35 genes show distinct patterns for each investigated life phase. C. finmarchicus is able to maintain diel clock rhythmicity at photoperiods close to 24 h, and it is discussed how this may be related to the nature of the marine environment. The work also evaluates the potential negative consequences of rigid clock-based seasonal timing in a polar environment exposed to climate change and with high interannual variability.

Quantifying the impact of solid-phase extraction on chromophoric dissolved organic matter composition

Advancing our understanding of the behaviour of dissolved organic matter (DOM) in aquatic environments necessitates efforts to combine complementary analytical data sets. However, some analytical measurements require sample pre-treatment, while others are carried out on bulk water samples, and it remains unclear if the resulting data sets can be compared. Here, we investigated the impact of solid-phase extraction with PPL resins on DOM optical properties. In samples from contrasting Arctic fjords, extraction efficiencies based on optical properties varied spectrally with averages between 31 ± 13% at 411 nm and 40 ± 12% at 363 nm for chromophoric DOM. Similarly, the extraction efficiency for specific fluorescence components varied between 37 ± 16% and 58 ± 18%. Solid-phase extraction also decreased S275–295, fluorescence index, and the freshness index, but increased S350–400, and apparent fluorescence quantum yields, indicating that the extraction process was qualitatively selective. Six fluorescence components identified independently in bulk water samples and extracted DOM using parallel factor analysis exhibited different behaviours. Three had identical spectral properties before and after extraction, although their extraction efficiencies varied with water mass characteristics and DOM composition, whereas three other components appeared to change after extraction. With the exception of one fluorescence component, the dynamics of optical properties in bulk water samples were not accurately reflected by DOM extracts. These results indicate that solid-phase extraction imparts a qualitative selectivity that leads to the homogenization of DOM extracts relative to their original samples. Efforts to integrate chemical information from different analytical methods should prioritize comparisons of measurements obtained on the same samples.

Warming in the Arctic Captured by productivity variability at an Arctic Fjord over the past two centuries.

Arctic fjords feature among some of the most climate-sensitive regions on the planet. The site of this study–Kongsfjorden–is one such fjord in which sedimentation and sediment geochemistry reflect climate-mediated changes in glacial melt and marine primary productivity. Here, we have shown that the fjord is particularly sensitive to the changing melt dynamics of the surrounding glaciers which are a direct consequence of warming/cooling in the region and is reflected in the productivity at the fjord. Warming increases meltwater influx into the fjord leading to enhanced turbidity which results in lower productivity. A multi-proxy study (sedimentary organic matter content, carbon and nitrogen isotope ratios, and microfossil abundance) using a 21 cm long sediment core from the Kongsfjorden helped us reconstruct warming driven melt-dynamics history for the past two centuries. Proxy data show a general decreasing trend in productivity along with a few excursions over the last two centuries. Warming driven glacial-melt dynamics appears to be the dominant control on productivity throughout the span of the core.

Bacterial Response to Permafrost Derived Organic Matter Input in an Arctic Fjord

The warming of the Arctic causes increased riverine discharge, coastal erosion, and the thawing of permafrost. Together, this is leading to an increased wash out of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems. This tDOM may be anticipated to affect both carbon and nutrient flow in the microbial food web and microbial community composition, but there are few studies detailing this in Arctic marine ecosystems. We tested the effects of tDOM on the bacterial community composition and net-growth by extracting DOM from the active layer of permafrost soil and adding the aged tDOM concentrate to a natural microbial fjord community (Kongsfjorden, NW Svalbard). This resulted in an increased carbon load of 128 µM in the tDOM treatment relative to the control of 83 µM DOC. We observed changes in community composition and activity in incubations already within 12 hours where tDOM was added. Flow cytometry revealed that predominantly large bacteria increased in the tDOM treated incubations. The increase of this group correlated with the increase in relative abundance of the genus Glaciecola (Gammaproteobacteria). Glaciecola were initially not abundant in the bacterial community (0.6%), but their subsequent increase up to 47% after four days upon tDOM addition compared to 8% in control incubations indicates that they are likely capable of degrading permafrost derived DOM. Further, according to our experimental results we hypothesize that the tDOM addition increased bacterivorous grazing by small protists and thus tDOM might indirectly also effect higher trophic levels of the microbial food web.

Functional Characterization of a New Cold-Adapted β-Galactosidase from an Arctic Fjord Sediment Bacteria Enterobacter ludwigii MCC 3423

In the present study, a new cold-adapted β-galactosidase, BgalEL isolated from the fjord sediment bacteria, Enterobacter ludwigii MCC 3423, was purified and characterized. The phylogenetic analysis of partial sequence of bgalEL gene revealed 99% relatedness of the enzyme to Enterobacter cloacae β-galactosidase. BgalEL is a homotetramer with molecular weight 465 kDa composed of ~ 116.42 kDa subunits. The optimal pH range and temperature for maximum hydrolytic activity on ONPG were 7.0–8.0 and 45 °C respectively. BgalEL was stable at pH ranges 6.0–8.0. The Km and Vmax for BgalEL were recorded as 2.03 mM and 49.3 U mg−1 respectively. The product formation by BgalEL was modelled with various degradation kinetic models and zeroth was found as model was best-fitted model. The kinetic half-life period of ONPG was noted as 9.0 × 10−4. The presence of K+, Mg2+ and Mn2+ at 10 mM concentrations stimulated BgalEL activity by 31 ± 3.9, 34 ± 1.2 and 42 ± 1.9% respectively. It was interesting to see that BgalEL was least affected by the hydrolytic products, glucose and galactose. Noteworthy, effect of Ca2+ ions on BgalEL activity was negligible at concentrations of 10 mM. BgalEL hydrolyzed lactose in milk at refrigerated temperature and also displayed transglycosylation potential in the presence of substantial concentrations of lactose at 40 °C. Finally, this is the first report with such a detailed characterization of β-galactosidase enzyme from a gram-negative bacterium isolated from the Arctic region. In light of the above mentioned properties, we thus recommend the enzyme BgalEL for the large scale production lactose free milk for the safe consumption in lactose-intolerance and the prebiotic galactooligosaccharides as supplement for infant food formulas.

Ambient noise field and propagation in an Arctic fjord Kongsfjorden, Svalbard

Ambient noise field and propagation in a glacierized Arctic fjord, Kongsfjorden is investigated using time series measurements of noise and Conductivity Temperature Depth (CTD) measurements between July 2015–April 2016. The hydrophone recorded noise for 10 months, with a duty cycle of 1 min every 3 h, covering summer, fall, winter and spring season. Noise field is seen to be variable with highest levels recorded during summer-fall (112 dB at 0.125 kHz) after which there is a decrease in maximum recorded noise levels. The spectral distribution of noise deviates from the theoretical Gaussian assumption, at varying degrees over the frequency band (0.125–4 kHz). Low frequency band is dominated by marine traffic during summer and fall, and ice wave interactions during winter and spring months. Propagation studies reveal variable nature in propagation with different scenarios observed between seasons. During the summer, refracted paths are observed and a weak channel is formed around the sound channel axis (∼100 m), and a well defined surface duct is revealed during the fall (depth of ∼60 m), characterized by a lower half channel bounded by the sea surface and the sonic layer depth. Surface duct propagation is common in winter with an upward profile and weakens with the onset of spring, as a consequence of the hydrology at the region. The studies will be useful in the context of climate change owing to the critical location of Kongsfjorden which is more prone to experience ongoing warming.

Increased occurrence of the jellyfish Periphylla periphylla in the European high Arctic

The jellyfish Periphylla periphylla, which can have strong ecological impacts on its environment, is ubiquitous in the Norwegian Sea and its range was predicted to extend northwards. The occurrence of P. periphylla in the northern Barents Sea increased since 2014 and, for the first time, several individuals were collected within a high Arctic fjord (> 78°N) in western Spitsbergen in January 2017. The low solar irradiance prevailing during the polar night and an increased inflow of relatively warm Atlantic water in the European Arctic since the last decade likely provide suitable conditions for the medusa to colonize Svalbard’s fjords during the winter months. However, light avoidance constrains the photophobic P. periphylla to deeper offshore areas during the midnight sun period. The current occurrence of P. periphylla in high Arctic fjords during the polar night will have a limited impact on marine ecosystems in the short term, but long-term effects are more uncertain if its abundance continues to increase.

Wahlenbergfjord, eastern Svalbard: a glacier‐surrounded fjord reflecting regional hydrographic variability during the Holocene?

Exceptionally high sedimentation rates in Arctic fjords provide the possibility to reconstruct environmental conditions in high temporal resolution during the (pre‐)Holocene. The unique geographical location of Svalbard at the intersection of Arctic and Atlantic waters offers the opportunity to estimate local (mainly glacier‐related) vs. regional (hydrographic) variabilities. Sedimentological, micropalaeontological and geochemical data from the very remote, glacier‐surrounded Wahlenbergfjord in eastern Svalbard provides information on glacier dynamics, palaeoceanographic and sea‐ice conditions during the Holocene. The present study illustrates a high meltwater discharge during the summer insolation maximum (c. 11.3–7.7 ka) when the intrusion of upwelled relatively warm Atlantic‐derived waters led to an almost open fjord situation with reduced sea ice in summer. Around 7.7 ka, a rapid hydrographic shift occurred: the dominance of inflowing Atlantic‐derived waters was replaced by a stronger influence of Arctic Water reflecting regional palaeoceanographic conditions evident in the benthic foraminiferal fauna also at Svalbard's margins. Neoglacial conditions characterized the late Holocene (c. 3.1–0.2 ka), when glaciers probably advanced as cold atmospheric temperatures were decoupled from the advection of relatively warm intermediate waters probably caused by an extending sea‐ice coverage. Accordingly, our data show that even a remote, glacier‐proximal study site reflects rapid as well as longer‐term regional changes.

Morphological characterization of submarine slope failures in a semi-enclosed fjord, Frobisher Bay, eastern Canadian Arctic

Abstract Submarine slope failures in the nearshore waters of SE Baffin Island, eastern Canadian Arctic, present a challenge to coastal and seabed development. Submarine slope failures are a known geohazard in fjords in Norway, Chile, Alaska, British Columbia and elsewhere, but have received little attention in the coastal waters of Arctic Canada. Over the past 6 years, there has been a rapid expansion of multibeam echosounder (MBES) mapping in Canadian Arctic fjords, leading to the discovery of many submarine slope failures. One area that has been mapped in detail is inner Frobisher Bay. This macrotidal, seasonally ice-covered, semi-enclosed embayment has a glacially scoured bed, ice-contact deposits, including recessional moraines, and stratified glaciomarine and post-glacial silts and clays with abundant dropstones. The prevalence of submarine slope failures in the inner bay (one per 20 km 2 ) appears to be anomalous. To date, MBES mapping has imaged at least 246 failures, ranging in size from 0.007 to 2.1 km 2 and all within the glaciomarine and post-glacial succession. Morphometric analysis of these features based on high-resolution MBES bathymetry provides an insight into their spatial distribution, relative chronology, triggers and flow characteristics; factors essential to understanding the mechanisms underlying their abundance in this Canadian Arctic fjord.