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Variability and decadal trends in the Isfjorden (Svalbard) ocean climate and circulation – An indicator for climate change in the European Arctic
Abstract and Figures
Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 °C 10yr⁻¹) and summer (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1°C 10yr⁻¹). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10yr⁻¹) and summer (0.7 ± 0.1 °C 10yr⁻¹). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10yr⁻¹) and summer (0.07 ± 0.05 10yr⁻¹) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate.
In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.
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... Atlantification, which refers to increased influence of warm and saline Atlantic Water (AW), is contributing to the sea-ice decline and enhanced warming in the Arctic (Muckenhuber et al., 2016;Onarheim et al., 2014;Pavlov et al., 2013). Observations in Svalbard fjords from last two decades show fractions of AW and Transformed AW (TAW) in the water column in several years (Bloshkina et al., 2021;De Rovere et al., 2022;Divya et al., 2021;Skogseth et al., 2020). Strzelewicz et al. (2022) estimated an 8% per annum increase of AW volume fraction on the shelf south-west of Spitsbergen during 1999-2020. ...
... Resultant convective overturning makes the entire water column nearly homogeneous (Cottier et al., 2010). This typical annual cycle is changing to Winter Open type with no sea-ice and intrusion of AW during winters (Skogseth et al., 2020;Tverberg et al., 2019). The AW cools and forms the bottom layer, inducing AW advection at shallower depths in the subsequent summer (Skogseth et al., 2020;Tverberg et al., 2019). ...
... This typical annual cycle is changing to Winter Open type with no sea-ice and intrusion of AW during winters (Skogseth et al., 2020;Tverberg et al., 2019). The AW cools and forms the bottom layer, inducing AW advection at shallower depths in the subsequent summer (Skogseth et al., 2020;Tverberg et al., 2019). ...
Atlantic‐type hydrography is becoming more dominant in the Svalbard fjords. Advected warm waters affect sea‐ice formation and melting rates of tidewater glaciers. Therefore, it is important to study hydrographic variability in fjords. Here, we use hydrographic data from Hornsund fjord to investigate the presence of warm water masses close to tidewater glaciers. Data span from May to October of 2015–2023 and cover several inner basins: Brepollen, Samarinvågen, Burgerbukta West, and Burgerbukta East, in addition to the main fjord. Average temperatures above 2° C are observed during August–October in the surface–50 m layer of all the inner basins, and during September–October in the 50 m–bottom layer of all the inner basins except Burgerbukta East. The surface–50 m layer of both Burgerbukta basins is colder and fresher compared to Brepollen, despite Burgerbukta basins being closer to the fjord mouth. These spatial differences likely arise from counter‐clockwise currents that advect warm and saline shelf waters to Brepollen along the southern side of the fjord, and relatively cold and fresh mixed shelf‐fjord waters to Burgerbukta as they exit along the northern side of the fjord. Burgerbukta East is the coldest and freshest inner basin. The differences between the two Burgerbukta basins suggest a strong influence of underwater sills and site‐specific environmental processes such as glacier ablation and local circulation on the water properties. Observed differences in the water temperatures of these closely‐spaced inner basins match the spatial variability in the glacier retreat rates, and indicate the importance of ocean forcing for the ice mass loss.
... The interaction between AW and ArW occurs on the shelf, where the latter is transported northwards by the Spitsbergen Polar Current, resulting in the formation of the West Spitsbergen Polar Front along the density gradient between the two water masses [40]. Consequently, the western and eastern regions of Western Svalbard exhibit distinct thermohaline characteristics [41]. This area, therefore, is suitable for assessing the effects of differing environmental conditions on benthic animals. ...
... Most stations were sampled in the Isfjorden and Storfjorden systems ( Figure 1). Isfjorden, the largest fjord in western Spitsbergen, has a mean width of 24 km and extends approximately 100 km from its opening to the head of the side fjord, Billefjorden [41]. Encompassing a total area of 3084 km 2 and a volume of 390 km 3 , its main basin (Isfjorden proper) is 70 km long and 200-300 m deep, oriented in a southwest-northeast direction, creating a 60 • clockwise angle relative to the north direction. ...
... Svalbard waters exhibit considerable heterogeneity in terms of habitat conditions, including variations in temperature, salinity, sediments, and related properties such as primary production and carbon flux from upper water layers to the seafloor [41,47]. Near-bottom water layers are occupied by different types of water masses, resulting in favorable or less favorable conditions for bivalve mollusks. ...
Ongoing warming in the Arctic has led to significant sea-ice loss and alterations in primary production, affecting all components of the marine food web. The considerable spatial variability of near-bottom environments around the Svalbard Archipelago renders the local fjords promising sites for revealing responses of benthic organisms to different environmental conditions. We investigated spatial variations in abundance, biomass, and growth parameters of the common bivalve Macoma calcarea in waters off western Spitsbergen and identified two distinct groups of this species: one composed mainly of cold-water stations from Storfjorden (Group I) and the other comprising warmer-water stations from Grønfjorden and Coles Bay (Group II). Within these groups, the mean abundance, biomass, production, and mortality accounted for 0.2 and 429 ind. m −2 , 20 and 179 g m −2 , 18.5 and 314 g m −2 year −1 , and 0.22 and 0.10 year −1 respectively. The size-frequency and age-frequency distributions were biased towards smaller and younger specimens in Group I, while Group II displayed more even distributions. The maximum ages were 11 and 21 years, respectively. The mollusks from cold water were significantly smaller than their same-aged counterparts from warmer water. Two groups of Macoma were identified: slow-growing individuals with a rate of 1.4 mm and fast-growing individuals with a growth rate of 1.8 mm. Most population parameters were higher than those observed in the Pechora, Kara, and Greenland Seas. Redundancy analysis indicated water temperature as the main driving factor of abundance and biomass, while the latter was also influenced by the presence of pebbles. Our findings provide new insights into the growth patterns and spatial distribution of Macoma at high latitudes and confirm that this species can serve as a reliable indicator of environmental conditions.
... Consequently, the vertical stratification, optical properties, nutrient availability and chemical composition of seawater are changing (Murray et al., 2015;Moskalik et al., 2018;Błaszczyk et al., 2019). Because the Arctic and Atlantic waters host different species of zooplankton and fish, the changing environment has potentially prominent consequences for marine ecosystems in the West Spitsbergen fjords (Meire et al., 2017;Hopwood et al., 2020;Trudnowska et al., 2020;Stempniewicz et al., 2021). ...
... Simultaneously, atmospheric forcing during winter has become more favorable for the flooding of Atlantic Water and less favorable for the presence of the Arctic Water on the West Spitsbergen shelf Goszczko et al., 2018;Strzelewicz et al., 2022). Together, these changes have enabled larger volumes of the waters with Atlantic origin to be more frequently observed in Isfjorden and Kongsfjorden, especially during winter (Cottier et al., 2007;Nilsen et al., 2016;Tverberg et al., 2019;Skogseth et al., 2020;De Rovere et al., 2022). Strzelewicz et al. (2022) did not identify a trend in the presence of Atlantic waters in Hornsund, although they noted a decrease in the presence of Winter Cooled Water. ...
... The five fjord arms -Hansbukta, Vestre Burgerbukta and Austre Burgerbukta in the north, Brepollen in the east, and Samarinvågen in the south (Fig. 1c) -are separated from the main basin by shallow sills originating from glacial deposits of moraines; therefore, the warm and deep inflows into the main basin of Hornsund may only have a limited influence on the glacier termini (Arntsen et al., 2019). It has been observed that the Winter Cooled Water typically persists in the deep depressions of the bays long into the summer; hence, the bays can be regarded as an archive of conditions prevailing during the previous winter (Promińska et al., 2018;Skogseth et al., 2020). ...
Several climate-driven processes take place in the Arctic fjords. These include ice–ocean interactions, biodiversity and ocean circulation pattern changes, and coastal erosion phenomena. Conducting long-term oceanographic monitoring in the Arctic fjords is, therefore, essential for better understanding and predicting global environmental shifts. Here we address this issue by introducing a new hydrographic dataset from Hornsund, a fjord located in the southwestern part of the Svalbard archipelago. Hydrographic properties have been monitored with vertical temperature, salinity and depth profiles in several locations across the Hornsund fjord from 2015 to 2023. From 2016 onward, dissolved oxygen and turbidity data are available for the majority of casts. The dataset contributes to the so far infrequent observations, especially in spring and autumn, and extends the observations, typically concentrated in the central fjord, to the areas adjacent to the tidewater glaciers. Because sediment discharge from glaciers and land is an inseparable part of the glacier–ocean interactions, the suspended sediment concentration in the water column and the daily sedimentation rate adjacent to the tidewater glaciers are monitored with regular water sampling and bottom-moored sediment traps. Here we present the planning and execution of the monitoring campaign from the collection of the data to the postprocessing methods. All datasets are publicly available in the repositories referred to in the “Data availability” section of this paper.
... According to typical cyclonic water circulation in the Isfjord system (Skogseth et al., 2020), water will flow in the following sequence for the stations being studied IF1 -AF3 -AF1 -AF2 -SF2 -TF1 -TF2 -SF1 -IF2 ( Figure 1). However, wind direction can alter this circulation of the surface layer. ...
... Lower panel: map of Isfjorden; red squares represent studied polygons that consisted of 2-4 net transects on the sea surface (grey circles) with simultaneous pumping of water from the subsurface. Currents inside Isfjorden are shown by arrows, modified from (Skogseth et al., 2020). Areas of Longyearbyen city and Svalbard airport are marked on the map with red colour. ...
Little is known about the role of remote and sparsely populated Arctic coastal zones in the microplastic cycle. Distribution of microplastics was studied in the Svalbard fjords in June – July 2022 with the main goal of assessing rivers’ role in the fate of microplastic in Arctic coastal waters. Surface microplastics (0 – 20 cm depth, 500 – 5000 µm size) were sampled with a neuston net in triplicate per study site in parallel with sampling of subsurface microplastics with a pump system (1.5 m depth, 100 – 5000 µm size). The central part of Isfjorden and its several branches covering populated and unpopulated fjords were studied; the sampling was conducted during an intense riverine discharge in all studied sites. Maximum abundance of surface microplastics (71,400 items/km² or 0.19 iterms/m³, 0.19 mg/m³) was found along the river plume border in the middle of populated Adventfjorden indicating importance of both local sources and surface hydrodynamics in the formation of microplastics accumulation hotspots. All other unpopulated fjords were free of the floating on the sea surface microplastics as river discharge prevented transport of microplastics inside the fjords. The highest concentration of subsurface microplastics was found in the central part of Isfjorden and the lowest – in river plume waters, which also indicates the removal of microplastics from the inner part of fjords during an intensive river discharge. Our results may suggest that Arctic rivers flowing through unpopulated areas bring clean water and thereby reduce level of microplastic pollution in the coastal waters. In contrast to the rest of the world’s ocean, rivers are not the main source of microplastic pollution in the Arctic Ocean.
... The two study stations, northern-N (78° 22,585′ N; 14° 46,929′ E) and southern-S (78° 11,299′ N; 15° 08,685′ E; Fig. 1), differ in their environmental conditions, mostly due to the anticlockwise circular movement of sea water, which flows from the shelf along the southern coast and exits on the northern side 33 , as well as the distance from tidewater glaciers, bathymetric conditions and seabed characteristics. Station N is more Arctic in nature with slightly lower sea water temperatures, more sea ice present and more fresh water from melting glaciers 23 . ...
... The higher light intensities and slightly greater sea temperature at Station S than at Station N were primarily due to the exposure of cold, turbid glacial water at the northern location (Fig. 1 23 ). The fjord circulation is counterclockwise in Isfjorden, in which surface waters flow along the southern side to the northern side before leaving the fjord and continuing northwards due to the south-north flowing coastal current and the Coriolis effect 33 . The greater number of algal recruits at Station S (Fig. 3) is most likely the result of variability in environmental conditions connected to the presence of different water masses, of Atlantic and Arctic origin, flowing from the shelf and continuing along the southern coast of Isfjorden (see Fig. 1), with a depth-averaged current near our study site S varying between 0 and 35 cm s −133 . ...
Benthic organisms typically possess a planktonic propagule stage in the form of larvae or spores, which enables them to spread over large distances before settlement, and promotes tight pelago-benthic coupling. However, factors driving dispersal and epibenthos recruitment in shallow hard-bottom Arctic communities are poorly known. We therefore conducted a year-round in situ colonization experiment in Isfjorden (Svalbard), and found out that variation in early-stage epibenthic assemblages was explained by the combination of: abiotic (45.9%) and biotic variables (23.9%), and their interactions (30.2%). The upward-facing experimental plates were dominated by coralline algae, and this is the first study showing that at high latitudes coralline algae Lithothamnion sp. settle in high numbers on available substrates during the polar night in winter. The downward-facing plates, which had much less exposure to light, contained more diverse organisms, with a predominance of polychaetas and bryozoans. However, in summer, the barnacle Semibalanus balanoides outcompeted all the other recruits, as a result of massive occurrence of meroplanktonic Cirripedia larvae, triggered by the phytoplankton bloom. In conclusion, the rate and success of epibenthic settlements were dependent mostly on light availability and temperature, suggesting that larval settlement will be impacted by global warming with some taxa benefitting, while others losing.
... Numerous large breeding colonies of seabirds are situated on mountain slopes and islands within Isfjorden. Hydrological conditions within Isfjorden exhibit dynamic equilibrium between thermally contrasting large water masses, but due to climate change, they are increasingly influenced by "Atlantification", characterized by stronger advection of warmer, highly saline waters from lower latitudes (IPCC, 2022;Skogseth et al., 2020). Surface water typically freezes in winter for several months, especially in the innermost parts of the fjords; however, in recent years, some winters have remained ice-free in this area (Nilsen et al., 2008;Ostaszewska et al., 2017). ...
Artificial light at night (ALAN) has global impacts on animals, often negative, yet its effects in polar regions remains largely underexplored. These regions experience prolonged darkness during the polar night, while human activity and artificial lighting are rapidly increasing. In this study, we analyzed a decade of citizen science data on light‐sensitive seabird occurrences in Longyearbyen, a High‐Arctic port settlement, to examine the impact of environmental factors including ALAN during polar night. Our investigation incorporated remote sensing data on nighttime lights levels, sea ice presence, and air temperature measurements from local meteorological station. Our findings reveal that artificial light may potentially impact seabird diversity in this region, with overall diversity decreasing alongside light intensity. However, the relationship between artificial light and seabird diversity was not uniformly negative; individual species exhibited varied responses. We also detected a correlation between artificial light and air temperature, emphasizing the complexity of environmental interactions. Notably, the piscivorous Black Guillemot (Cepphus grylle), the dominant species in Longyearbyen during the polar night, showed increased contribution in the local seabird assemblage with higher light levels. In contrast, the zooplanktivorous Little Auk (Alle alle) exhibited reduced contribution with higher light intensity and increased presence with higher air temperatures. We hypothesize that these differing responses are closely tied to the distinct dietary habits, varying sensitivity to artificial light due to individual adaptations, and overall ecological flexibility of these species, underscoring the need for further research. This study, which uniquely combines citizen science with remote sensing data, represents the first effort to systematically assess the effects of artificial lighting on seabirds during the polar night. The findings underscore the potential importance of this issue for seabird conservation in polar regions.
... Climate change as a driver of shifting species distribution and occurence should also be considered. Isfjorden has been experiencing a shift in water masses over the last two decades, with an expanding layer of Atlantic water, higher sea surface temperatures and an increasing stratification (Skogseth et al. 2020). Temperature and stratification are important drivers of picoplankton community composition and distribution (Hörstmann et al. 2024, Loïc et al. 2024, and might explain the difference between 2011 and 2022/2023. ...
The newly discovered phylum Picozoa, with only one known species, appears widespread but remains poorly understood. Water samples from Isfjorden, Spitsbergen, and previous years were analyzed to identify local species and build a phylogenetic tree, aiming to clarify Picozoa’s diversity and ecological role in ocean ecosystems.
... Global warming is a main driver of global biodiversity loss and leads to the redistribution of species worldwide (Sunday et al., 2012;Wilson et al., 2019). Compared to the global average, Arctic regions have warmed nearly four times faster over the last four decades (Rantanen et al., 2022), with similar trends observed in air temperature and sea surface temperature (SST; Skogseth et al., 2020). The rapid temperature increase particularly threatens polar coastal ecosystems, which form an ecologically exceptional environment with a unique biological diversity (Bringloe et al., 2020). ...
Due to global rises in temperature, recent studies predict marine species
shifting toward higher latitudes. We investigated the impact of interacting
abiotic drivers on the distribution potential of the temperate kelp Laminaria
hyperborea. The ecosystem engineering species is widespread along
European coasts but has not yet been observed in the High Arctic, although
it can survive several months of low temperatures and darkness. To
investigate its ability to extend northward in future, we conducted a long-term
multifactorial experiment with sporophytes from Porsangerfjorden,
Norway—close to the species' documented northernmost distribution margin.
The samples were exposed to three different photoperiods (PolarDay,
LongDay, and PolarNight) at 0°C, 5°C, and 10°C for 3 months. Optimum
quantum yield of photosynthesis (Fv/Fm), dry weight, pigments, phlorotannins,
and storage carbohydrates were monitored. Both physiological and
biochemical parameters revealed that L. hyperborea was strongly influenced
by the different photoperiods and their interaction with temperature,
while temperature alone exerted only minor effects. The Fv/Fm data were
integrated into a species distribution model to project a possible northward
expansion of L. hyperborea. The combination of extended day lengths and low temperatures appeared to be the limiting reason for northward spread
of L. hyperborea until recently. However, with water temperatures reaching
10°C in summer, this kelp will be able to thrive also in the High Arctic.
Moreover, no evidence of stress to Arctic winter warming was observed.
Consequently, L. hyperborea has a high potential for spreading northward
with further warming which may significantly affect the structure and function
of Arctic ecosystems.
The Arctic is warming twice as fast as anywhere else on the planet, in the European Arctic mainly driven by exalted Atlantic Water inflow. Microbial eukaryotes are diverse and essential to the functioning of marine ecosystems, thus environmental perturbations altering their communities influence the entire ecosystem. To study seasonal and interannual variation and the potential effects of Atlantification, a long-term marine time series has been established in Isfjorden-Adventfjorden (IsA), West Spitsbergen. We here present three years of high-resolution data including hydrography, nutrients, photosynthetic biomass, flow cytometry and community composition of microbial eukaryotes (0.45–10μm, based on Illumina metabarcoding of 18S rDNA and rRNA). The timing, magnitude and species composition of the spring bloom varied interannually, with the more Atlantic spring 2014 being distinctly different from the two other years. A strong recurring seasonal pattern was evident in biodiversity, cell abundances and community composition. Winter communities were characterized by high alpha diversity and very low cell numbers with a dominance of heterotrophic and parasitic taxa. Despite large intra- and interannual differences in communities during the productive time of the year, winter communities were always highly similar, suggesting that the polar night represents a strong environmental forcing that resets the microbial communities.
Observational data covering currents and temperature through two contrasting autumn to spring periods (2010/2011 and 2013/2014) at the constricted entrance to the inner basin of the Hornsund fjord, Svalbard, are investigated. This fjord is presently undergoing significant changes, manifested by reduction of the seasonal sea ice cover and retreating tidewater glacier fronts. The data set presented here shows how local wind, tides, and longer period current fluctuations allow warm water of Atlantic origin to reach the innermost basin of the fjord. While the forcing factors of the exchange mechanisms are not seen to vary much between the two studied seasons, the effect of wind events on exchange is assumed to be modified by local stratification and sea ice concentration. The resulting heat transport depends on availability of heat in the central part of the fjord. The observations indicate that available heat in autumn and winter 2013/2014 effectively hindered formation of a stable sea ice cover. While the present data set does not enable direct quantification of the role of oceanic heat in tidewater glacier melting, we find that the net retreat of glacier fronts was 10 times larger in the warm (ocean) period 2013/2014 compared to the colder 2010/2011.
This report was commissioned by the Norwegian Environment Agency in order to provide basic information for use in climate change adaptation in Svalbard. It includes descriptions of historical, as well as projections for the future climate development in the atmosphere, hydrosphere, cryosphere and ocean, and it includes effects on the physical nature e.g. on permafrost and various types of landslides and avalanches. The projections for the future climate are based on results in the IPCCs fifth assessment report. The report is to a large degree an assessment of existing literature and model results. New results from atmosphere, ocean and hydrological models are, however, also presented. The report may be downloaded from the Norwegian Centre for Climate Service's web portal www.klimaservicesenter.no.
Many marine species are known to change their distribution in response to changing climatic conditions. One such example is the blue mussel Mytilus spp., spreading northward coincident with an increase in ocean temperatures. On Svalbard, the first living specimens of Mytilus spp. were discovered in 2004. Here we present an analysis of the current distribution of Mytilus spp. on Svalbard, with a focus on the west coast of Spitsbergen where strong Atlantification has been documented over the last few decades. We conducted diver-based surveys to develop a distributional map and to compare the current distribution with that of the Holocene. Furthermore, we investigate the recent history of recruitment of mussels on Svalbard to help identify invasion pathways. Our results show that blue mussels have been present on the archipelago at least since 2000 and are widespread along the west coast today. We also present evidence of local reproduction in one of the sites explored.
The fjords that connect Greenland's glaciers to the ocean are gateways for importing heat to melt ice and for exporting meltwater into the ocean. The transport of heat and meltwater can be modulated by various drivers of fjord circulation, including freshwater, local winds, and shelf variability. Shelf-forced flows (also known as the intermediary circulation) are the dominant mode of variability in two major fjords of east Greenland, but we lack a dynamical understanding of the fjord's response to shelf forcing. Building on observations from east Greenland, we use numerical simulations and analytical models to explore the dynamics of shelf-driven flows. For the parameter space of Greenlandic fjords, we find that the fjord's response is primarily a function of three nondimensional parameters: the fjord width over the deformation radius (W/Rd), the forcing time scale over the fjord adjustment time scale, and the forcing amplitude (shelf pycnocline displacements) over the upper-layer thickness. The shelf-forced flows in both the numerical simulations and the observations can largely be explained by a simple analytical model for Kelvin waves propagating around the fjord. For fjords with W/Rd > 0.5 (most Greenlandic fjords), 3D dynamics are integral to understanding shelf forcing-the fjord dynamics cannot be approximated with 2D models that neglect cross-fjord structure. The volume flux exchanged between the fjord and shelf increases for narrow fjords and peaks around the resonant forcing frequency, dropping off significantly at higher- and lower-frequency forcing.
Progressing warming in the Arctic and increased extreme weather events can significantly influence the hydrography of Svalbard fjords, leading to changes towards more Atlantic-type waters in the fjords. In this paper, we look into the hydrographic conditions in Hornsund, the southernmost fjord on the west coast of Svalbard, by analysing high-resolution CTD measurements collected in July during cruises with the RV Oceania between 2001 and 2015. These observations revealed high interannual variability in temperature, salinity and distribution of water masses, mainly due to differences in timing of the transition between winter and summer conditions but also as a result of changing environmental factors such as air temperature and sea-ice cover. Hornsund shows weak Atlantic Water occupation, probably due to strong influence of the Sørkapp Current along the southern coast of Spitsbergen. The main basin of the fjord was much more influenced by waters entering the fjord from outside than the inner basin, Brepollen, which was mainly characterized by the presence of locally formed Winter Cooled Water (WCW). The amount and properties of WCW in Brepollen revealed high variability after 2006, and no WCW in July 2012. The results of our study show that Hornsund is highly variable and susceptible to recently observed atmospheric and oceanic extreme events in the Svalbard region.
The decline in the floating sea ice cover in the Arctic is one of the most striking manifestations of climate change. In this review, we examine this ongoing loss of Arctic sea ice across all seasons. Our analysis is based on satellite retrievals, atmospheric reanalysis, climate-model simulations and a literature review. We find that relative to the 1981–2010 reference period, recent anomalies in spring and winter sea ice coverage have been more significant than any observed drop in summer sea ice extent (SIE) throughout the satellite period. For example, the SIE in May and November 2016 was almost four standard deviations below the reference SIE in these months. Decadal ice loss during winter months has accelerated from −2.4 %/decade from 1979 to 1999 to −3.4%/decade from 2000 onwards. We also examine regional ice loss and find that for any given region, the seasonal ice loss is larger the closer that region is to the seasonal outer edge of the ice cover. Finally, across all months, we identify a robust linear relationship between pan-Arctic SIE and total anthropogenic CO₂ emissions. The annual cycle of Arctic sea ice loss per ton of CO₂ emissions ranges from slightly above 1 m² throughout winter to more than 3 m² throughout summer. Based on a linear extrapolation of these trends, we find the Arctic Ocean will become sea-ice free throughout August and September for an additional 800 ± 300 Gt of CO₂ emissions, while it becomes ice free from July to October for an additional 1400 ± 300 Gt of CO₂ emissions.
The Kongsfjorden conductivity, temperature and depth (CTD) Transect has been monitored annually since 1994. It covers the full length of the fjord and the shelf, and the upper part of the shelf slope outside Kongsfjorden. In addition to CTD profiles, data from vessel-mounted Acoustic Doppler Current Profiler (ADCP) and moorings have been collected. Previous studies noted that Atlantic Water (AW) from the West Spitsbergen Current was observed in the fjord every summer, but to a varying extent. The prolonged monitoring provided by the Kongsfjorden Transect data set examined here reveals continuous variations in AW content and vertical distribution in the fjord, both on seasonal and inter-annual timescales. Our focus in this paper is on this variable content of AW in Kongsfjorden, the forcing mechanisms that may govern the inflow of this water mass, and its distribution in the fjord. We classify three winter types linked to three characteristic scenarios for winter formation of water masses. During the historically typical winters of type “Winter Deep”, deep convection, often combined with sea ice formation, produces dense winter water that prevents AW from entering Kongsfjorden. Summer inflow of AW starts when density differences between fjord and shelf water allows for it, and occurs at some intermediate depth. During winters of type “Winter Intermediate”, AW advects into the fjord along the bottom via Kongsfjordrenna. Winter convection in Kongsfjorden will then be limited to intermediate depth, usually producing very cold intermediate water. Deep AW inflow continues during the following summer. A winter of type “Winter Open” seems to develop when open water convection produces very dense shelf water, and AW winter advection into Kongsfjorden occurs at the surface. Summer AW inflow is rather shallow after such winters. We find that variations between Winter Deep and Winter Intermediate winters are due to inherent natural variability. However, the Winter Open winters seem to be a consequence of the general trend of atmospheric and oceanic warming, and, more specifically, of the decreasing sea ice cover in the Arctic region. The Winter Open winters have all occurred after an unusual flooding of AW onto the West Spitsbergen shelf in February 2006.
Zooplankton in Kongsfjorden, Svalbard, is shaped by irregular advection of seawater from the West Spitsbergen Current as well as input of freshwater of glacial and riverine origin. The zooplankton community reflects contributions of Arctic vs. Atlantic water masses in the fjord, and is changing with increasing tem- perature and declining sea ice. Here, we review zooplankton studies from Kongsfjorden, and present new data from a 20-year time series (1996–2016) of zooplankton abundance/biomass in the fjord based on annual surveys during sum- mer. During the last decade, the marine environment of the West Spitsbergen Shelf and adjacent fjords has undergone changes with increasing temperatures and vol- ume of inflowing Atlantic Water and declining sea ice. Annual monitoring of meso- zooplankton since 1996 has shown high seasonal, spatial, and inter-annual variation in species abundance and biomass, and in the proportion of Atlantic and Arctic species. Inter-annual variations in species composition and abundance demonstrate fluctuating patterns related to changes in hydrography. “Warm years” in Kongsfjorden were characterized by higher abundances of Atlantic species, such as Calanus fin- marchicus, Oithona atlantica, Thysanoessa longicaudata and Themisto abyssorum. Other krill species, particularly Thysanoessa inermis and to a lesser extent T. longi- caudata, increased in abundance during the warming period in 2006–2007, mainly in the inner basin. “Cold years”, on the other hand, were characterized by higher abundance of Themisto libellula. There was no clear impact, however, of changes in environmental factors on the abundance or biomass of the Arctic species Calanus glacialis suggesting that the changes in environmental conditions have not reached critical levels for this species. The long-term zooplankton data demonstrate that some Atlantic species have become more abundant in the Kongsfjorden’s pelagic realm, suggesting that they may benefit from increasing temperature, and also that the total biomass of zooplankton has increased in the fjord implying potentially higher secondary production.
The ecosystem role of Arctic microbial communities is still largely unknown. Based on a time-series study at the IsA station (West Spitsbergen), the seasonality and contribution of pelagic protists to the vertical flux was investigated at 7 time points during 2011−2012. The hydrography of this high-Arctic fjord was evaluated to identify impacts on the community compo- sition during the different seasons. Protists (<10 μm and >10 μm) were sampled at 4 depths from the water column and from short-time sediment traps, and investigated by 454 next-generation sequencing of the V4 region of the 18S ribosomal DNA. An advective event during winter, ex- changing the cold and less saline water mass with warmer and saline Atlantic Water, was poten- tially responsible for an abrupt shift in the protist composition in March. Small cells (<10 μm) con- tributed significantly to the vertical flux during autumn and winter, while larger bloom taxa (e.g. diatoms) predominated the water and traps during spring. Parasitic species, such as MALV 1a and Chytriodinium sp., were also detected in the traps, possibly being transported along with their hosts. Vertical export of Arctic pelagic protists is not limited to the productive period; however, the contribution of small taxa that are important contributors in this study seems to be seasonally influenced and may alter the flux efficiency. Molecular tools revealed new taxa contributing to the vertical export, but also identified new potential mechanisms exemplified by parasite-host- induced transport, spurring increased attention onto parasitism in the study of carbon cycles and vertical flux.
A realistic numerical model was constructed to simulate the oceanic conditions and circulation in a large southeast Greenland fjord (Kangerdlugssuaq) and the adjacent shelf sea region during winter 2007–2008. The major outlet glaciers in this region recently destabilized, contributing to sea level rise and ocean freshening, with increased oceanic heating a probable trigger. It is not apparent a priori whether the fjord dynamics will be influenced by rotational effects, as the fjord width is comparable to the internal Rossby radius. The modeled currents, however, describe a highly three-dimensional system, where rotational effects are of order-one importance. Along-shelf wind events drive a rapid baroclinic exchange, mediated by coastally trapped waves, which propagate from the shelf to the glacier terminus along the right-hand boundary of the fjord. The terminus was regularly exposed to around 0.5 TW of heating over the winter season. Wave energy dissipation provoked vertical mixing, generating a buoyancy flux which strengthened overturning. The coastally trapped waves also acted to strengthen the cyclonic mean flow via Stokes' drift. Although the outgoing wave was less energetic and located at the opposite sidewall, the fjord did exhibit a resonant response, suggesting that fjords of this scale can also exhibit two-dimensional dynamics. Long periods of moderate wind stress greatly enhanced the cross-shelf delivery of heat toward the fjord, in comparison to stronger events over short intervals. This suggests that the timescale over which the shelf wind field varies is a key parameter in dictating wintertime heat delivery from the ocean to the ice sheet.