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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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... Large pulses of warm and salty Atlantic Water (AW) have been increasing in the fjords along the North/West Svalbard Archipelago over the last three decades (Skogseth et al., 2020). The combination of AW with increased air temperatures (e.g. ...
... The combination of AW with increased air temperatures (e.g. Winter trend of +3°C dec -1 ; Maturilli et al., 2019) have severely restricted sea-ice formation (Kongsfjorden: Cottier et al., 2007;Tverberg et al., 2019;Isfjorden: Muckenhuber et al., 2016;Skogseth et al., 2020;Gronfjorden: Zhuravskiy et al., 2012). Pronounced warming in the temperature of AW inflow (3.1) itself has been recorded during the summer from 1912 to 2019 (Bloshkina et al., 2021). ...
... Atlantic Water (AW), which is warmer and more nutrient rich than Arctic waters, is circulated to Svalbard via the Fram Strait as part of the West Spitsbergen Current (WSC) where it forms much of the bottom layer of the West Svalbard fjords in summer. However, starting in 2006, AW has begun occupying much more of the water column (Tverberg et al., 2019;Skogseth et al., 2020), a process referred to as "Atlantification". This occurs in part due to changes to patterns of the wind stress field in the area (Pavlov et al., 2013) and the wandering of large-scale ocean currents. ...
Fjord systems are transition zones between land and sea, resulting in complex and dynamic environments. They are of particular interest in the Arctic as they harbour ecosystems inhabited by a rich range of species and provide many societal benefits. The key drivers of change in the European Arctic (i.e., Greenland, Svalbard, and Northern Norway) fjord socio-ecological systems are reviewed here, structured into five categories: cryosphere (sea ice, glacier mass balance, and glacial and riverine discharge), physics (seawater temperature, salinity, and light), chemistry (carbonate system, nutrients), biology (primary production, biomass, and species richness), and social (governance, tourism, and fisheries). The data available for the past and present state of these drivers, as well as future model projections, are analysed in a companion paper. Changes to the two drivers at the base of most interactions within fjords, seawater temperature and glacier mass balance, will have the most significant and profound consequences on the future of European Arctic fjords. This is because even though governance may be effective at mitigating/adapting to local disruptions caused by the changing climate, there is possibly nothing that can be done to halt the melting of glaciers, the warming of fjord waters, and all of the downstream consequences that these two changes will have. This review provides the first transdisciplinary synthesis of the interactions between the drivers of change within Arctic fjord socio-ecological systems. Knowledge of what these drivers of change are, and how they interact with one another, should provide more expedient focus for future research on the needs of adapting to the changing Arctic.
... By contrast, there has been numerous observations of intrusions of AW onto the West Spitsbergen Shelf and into the fjords of the west coast of Spitsbergen, in particular during winter, switching the hydrography from an Arctic to an Atlantic dominated system with reduced to non-existent sea ice Nilsen et al., 2008Nilsen et al., , 2016Skogseth et al., 2020;Tverberg et al., 2019). The occurrence of these intrusions is reported to have increased during the recent decades in response to changes in the atmospheric circulation around Svalbard, especially regarding winter cyclones (Francis & Vavrus, 2012;Nilsen et al., 2016). ...
... We conclude that the observed positive wind stress curl anomaly over Svalbardbanken and Storfjordrenna set up conditions prone for a migration of the flow (i.e., a migration of the PF) toward shallower depth. Once a depth shallower than 120 m (the sill depth) has been reached, obstacles to the progression into Storfjorden are much diminished, similarly to what has happened along the West Spitsbergen Shelf (Skogseth et al., 2020). ...
Storfjorden, Svalbard, hosts a polynya in winter and is an important source region of Brine‐enriched Shelf Water (BSW) that, if dense enough, feeds the Arctic Ocean deep water reservoir. Changes in the BSW production may thus have far‐reaching impacts. We analyze the water mass distribution and circulation in Storfjorden and the trough south of it, Storfjordrenna, using hydrographic sections occupied in July 2016, following a winter characterized by the lowest ice coverage recorded in the Barents Sea. These observations reveal an unusual hydrographic state, characterized at the surface by the near absence of Melt Water and Storfjorden Surface Water, replaced by a saltier water mass. At depth, BSW (maximum salinity of 34.95) was found from the bottom up to 90 m, above the 120‐m deep sill at the mouth to Storfjordrenna. However, no gravity driven overflow was observed downstream of the sill: the dome of BSW remained locked over the depression in a cyclonic circulation pattern consistent with a stratified Taylor column. Observations further reveal a previously unreported intrusion of Atlantic Water (AW) far into the fjord, promoting isopycnal mixing with entrapped Arctic Water. This intrusion was possibly favored by positive wind stress curl anomalies over Svalbardbanken and Storfjordrenna. The bottom plume exiting Storfjordrenna was weak, carrying Polar Front Water rather than BSW, too light to sink underneath the AW layer at Fram Strait. Whether Storfjorden switched durably to a new hydrographic state, following the observed Atlantification of the Barents Sea after 2005, remains to be established.
... It has previously been recorded in the White Sea, the Barents Sea including Franz-Josef land, the Kara Sea, and the Bering Sea [33,34,[69][70][71]. Svalbard waters have suitable habitat conditions for the mentioned species, and this new record is not surprising, especially during the period of ongoing global warming when the stronger inflow of Atlantic water into the Barents Sea leads to shifts in local circulation patterns [72,73], including the West Spitsbergen shelf area [74], thus promoting larval drift and range expansion of aquatic animals [75]. ...
... Over the past decades, various manifestations of warming have been registered in the Arctic, including rapid sea ice edge retreat, seasonal shifts in phytoplankton blooms, relatively warmer summer waters, and enhanced winter convection [89,90]. The Isfjorden system is also affected by the inflow of Atlantic water, and the local benthic communities, including those in Grønfjorden, are currently being affected by elevated temperatures and wind forcing [74]. The role of the thermal regime in shaping bryozoan communities of Grønfjorden is well illustrated by the results of our cluster analysis; SR and biomass of bryozoans were significantly higher at colder (Cluster 2) than at warmer stations (Cluster 1). ...
Despite significant research efforts focused on benthic assemblages in West Spitsbergen, there is a lack of knowledge regarding the shallow water bryozoan communities in Grønfjorden, a glacier fjord belonging to the Isfjorden system, Norway. Here, we studied species composition, richness, distribution, and biomass of bryozoans in the intertidal and upper subtidal zones of Grønfjorden in summer. We found 62 bryozoan species, among which Celleporella hyalina (Linnaeus, 1767), Harmeria scutulata (Busk, 1855), and Tegella arctica (d’Orbigny, 1853) were most prevalent while the highest contributions to the total biomass were registered for Eucratea loricata (d’Orbigny, 1853), Tricellaria gracilis (Van Beneden, 1848), Turbicellepora incrassata (Lamarck, 1816), and Tricellaria ternata (Ellis and Solander, 1786). Alpha-diversity varied from 1 to 50 averaging 15.1 ± 2.6 species. Bryozoan biomass ranged from 0.008 to 10.758 g m–2 with a mean value of 2.67 g m–2 being lower than in the central and northern parts of the Barents Sea. For the first time, we registered the presence of the circumpolar bryozoan Amathia arctica in Svalbard waters probably as a result of stronger advection of Atlantic water into the fjord. Cluster analysis revealed two groups, mainly composed of stations in colder and warmer waters. A relatively high proportion of outlying stations reflected habitat heterogeneity in Grønfjorden. Redundancy analysis indicated that bryozoan diversity and biomass were strongly negatively associated with temperature. A positive relationship was found between bryozoan biomass and the proportional contribution of macrophytes to a pool of substrates. Our study provides a reference point for further monitoring of changing marine ecosystems at high latitudes.
... Besides the inflow of oceanic water, there is a rich discharge of fresh waters, mainly formed from river runoff, as well as calving and melting of glaciers (Svendsen, 1959;Nilsen et al., 2008) located mostly in the inner part and the north shore of Isfjorden (Nilsen et al., 2008;Fraser et al., 2018). Isfjorden has been largely sea ice-free in winter for the last decade (Muckenhuber et al., 2016;Skogseth et al., 2020;Medelytė et al., 2022). ...
Although studies of the Arctic region have a long history there are still many aspects that require research.
Benthic species are important in the studies of environmental impact. However, there is currently very little
understanding of what factors drive the process of benthic larval recruitment and assemblage development. This
field study, conducted in Isfjorden (Svalbard) from summer 2016 to summer 2017, investigated the seasonal
trends in the development of benthic assemblages through the use of settlement plates fixed at different depths (6
and 12 m) and in different orientations. Replicate plates were additionally installed with and without cages to
account for the potential impact of predation. Species richness displayed clear seasonal changes, with the highest
number of species colonizing the plates was observed in the autumn. The abundance of recruits (particularly
Cirripedia) peaked in the summer months. In contrast, both species abundance and richness were much lower
over winter and spring, although evidence of recruitment over winter was found. The winter plates were
dominated by Lithothamnion sp., red encrusting alga which is very low-light adapted and may have started to
already settle in February. Organisms abundance was influenced by the interaction of season and cage treatment,
demonstrating a degree of predation, whereas plate orientation was the key driver of assemblage structure.
Depth, on the other hand, had a very limited impact on both recruits’ abundance and species richness. This study
highlights the importance of seasonality in the context of larval recruitment and is one of the first to provide
insights into the process of early benthic species colonization of rocky substrates, which are common in Arctic
coastal habitats.
... According to Constable et al. (2022), the SST in Arctic regions is predicted to increase drastically by the end of the century. At a warming rate of 0.7 C per decade, a mean summer SST of 11 C will be reached in $ 100 years (Skogseth et al. 2020), although extreme temperature events will reach 11 C earlier. While the Arctic endemic marine vegetation is likely to be lost (Bringloe et al. 2020), a poleward expansion of temperate kelp species is projected (Krause-Jensen et al. 2020;Assis et al. 2022). ...
Kelps act as ecosystem engineers on many polar rocky shore coastlines. The underwater light climate and temperature are the main drivers for their vertical and latitudinal distribution. With temperatures rising globally, an Arctic expansion of temperate kelp species and an accelerating glacial melt is predicted. It was our aim to investigate the effects of retreating glaciers and rising temperatures on the potential habitat of kelps in Arctic fjords. We analyzed the underwater light climate of areas being influenced by different stages of glacial retreat (sea‐terminating glacier, land‐terminating glacier, coastal water) in Arctic Kongsfjorden. We observed reduced light intensities and a changed spectral composition in glacial meltwater plumes, potentially resulting in an upward shift of the lower depth limit of kelp, counteracting the predicted biomass increase in the Arctic. Furthermore, we studied temperature‐related changes in light‐use characteristics in two kelp species (Alaria esculenta, Saccharina latissima) at 3°C, 7°C, and 11°C. Rising temperatures lead to a significant increase of the compensation irradiance of A. esculenta. The dark respiration of S. latissima increased significantly, correlating with a decreasing carbon content. We detected no differences in photosynthetic rates, although the chlorophyll a concentration of A. esculenta was ~ 78% higher compared to S. latissima. Ultimately, temperature‐induced changes in kelps light‐use characteristics might lead to a changed species composition, as we found A. esculenta better adapted to polar conditions. We conclude that the deterioration of the underwater light climate and the temperature increase may drive substantial changes of the future Arctic kelp forest structure.
... Hydrography of the Spitsbergen fjords has been the subject of many publications (Pavlov et al., 2013;Promińska et al., 2017;Promińska et al., 2018;Skogseth et al., 2020), indicating a very large spatial and inter-annual variability of S in these areas, depending on the domination of the Sørkapp Current or the West Spitsbergen Current on the West Spitsbergen Shelf. Moreover, based on high-resolution CTD measurements collected between 2001 and 2015, Promińska et al. (2017) observed an increase in variability of temperature and salinity in recent years and generally strong influence of freshwater supply from land (rivers, melting glaciers) shaping S in the surface layer. ...
... A recent study demonstrates that Isfjorden, a wide fjord bounding Nordenskiöld Land to the north, experienced a shift at the beginning of the twenty-first century. The warm Atlantic Water layer increased its thickness and is now observed higher up the water column (Skogseth et al. 2020;Bloshkina, Pavlov, and Filchuk 2021). Numerical modeling of the heat fluxes has shown that half of the Atlantic Water heat loss in the Isfjorden Trough occurs as heat loss to the atmosphere, influencing the local terrestrial climate (Nilsen et al. 2016). ...
The first seven years (2013/14–2019/20) of annual and seasonal mass-balance monitoring on the glacier Vestre Grønfjordbreen (16.4 km2), located south of the town of Barentsburg on Spitsbergen, Svalbard, are presented. This part of the archipelago is one of the least glaciated on Svalbard and at the same time it experiences the most prominent glacier retreat within the last few decades. The annual mass balance of Vestre Grønfjordbreen is negative, ranging from −0.60 ± 0.18 to −2.01 ± 0.26 m w.e. The results of direct observations are compared with the geodetic mass balance for the same period (July 2015 through end of summer 2019) to identify systematic bias in the record. As the mismatch between cumulative mass balances, defined by the glaciological method (−5.66 ± 0.47 m w.e.) and computed from geodetic differencing (−5.52 ± 0.40 m w.e.), lies within the uncertainty limits, no calibration of the mass-balance series is needed. From the results of a ground-penetrating radar (GPR) survey (spring 2019), which confirmed the polythermal glacier structure, a total glacier volume of 1.987 ± 0.139 km3 was found, meaning that the cumulative mass loss during the reported seven-year period equals 8 ± 1% of the total glacier mass. Observed annual ice-flow velocities, varying from 0.50 ± 0.10 to 4.50 ± 0.10 m year−1, are consistent with low mean bed and surface slopes (5° and 8°, respectively). Correlations of mass-balance values with meteorological observations at the Barentsburg weather station are mediocre, possibly due to anomalous values recorded for 2015/16: the negative mass-balance peak reported for the other land-terminating Svalbard glaciers was not observed at Vestre Grønfjordbreen.
... Today, the archipelago of Svalbard is one the fastest warming areas of the Arctic Ocean, experiencing an increase in the melting of their glaciers and a rise in the temperature of ocean water circulating along its continental margin (Meleshko et al., 2004;Førland et al., 2013;Skogseth, 2020). This fact may provide adequate conditions to trigger unloading earthquakes and to increase pore water pressure by gas hydrate breakdown, which can destabilize slope sediments (Solheim et al., 2005;Berndt et al., 2009), i.e. the occurrence of landslides and tsunamis in the near future. ...
A modelling approach to understand the tsunamigenic potentiality of submarine landslides will provide new perspectives on tsunami hazard threat, mostly in polar margins where global climatic change and its related ocean warming may induce future landslides. Here, we use the L-ML-HySEA (Landslide Multilayer Hyperbolic Systems and Efficient Algorithms) numerical model, including wave dispersion, to provide new insights into factors controlling the tsunami characteristics triggered by the Storfjorden LS-1 landslide (southwestern Svalbard). Tsunami waves, determined mainly by the sliding mechanism and the bathymetry, consist of two initial wave dipoles, with troughs to the northeast (Spitsbergen and towards the continent) and crests to the south (seawards) and southwest (Bear Island), reaching more than 3 m of amplitude above the landslide and finally merging into a single wave dipole. The tsunami wave propagation and its coastal impact are governed by the Storfjorden and Kveithola glacial troughs and by the bordering Spitsbergen Bank, which shape the continental shelf. This local bathymetry controls the direction of propagation with a crescent shape front, in plan view, and is responsible for shoaling effects of amplitude values (4.2 m in trough to 4.3 m in crest), amplification (3.7 m in trough to 4 m in crest) and diffraction of the tsunami waves, as well as influencing their coastal impact times.
... The Spitsbergen, the largest island of the Svalbard Archipelago presently covered with glaciers of about 57%, is composed of numerous fjords, which are seasonally (winter) sea ice-covered [8] . Over the last decades, fjords located on the west coast of Spitsbergen have experienced signi cant changes in hydrographic settings due to the strengthened West Spitsbergen Current (WSC), which brings warm and saline Atlantic water into the fjords [9][10][11] . Moreover, recent increases in air temperature and precipitation in the Svalbard archipelago have caused a shrink of marine and land-terminating glaciers in size, causing an increase in freshwater discharge and the release of large amounts of terrestrial OC [12][13][14][15] . ...
Svalbard fjords are hotspots of organic carbon (OC) burial because of their high sedimentation rates. To identify sedimentary OC sources in Arctic fjords, we investigated surface sediments collected from eight Svalbard fjords using bulk and molecular geochemical parameters. All fjord surface sediments investigated were depleted in ¹⁴ C org (–666.9 ± 240.3‰, n = 28), suggesting that more recently fixed terrestrial and marine biomass is not the only contribution to the sedimentary OC. However, the source could not be determined by the most commonly used bulk indicators (i.e., N org /TOC ratio and δ ¹³ C org ) in the Arctic realm. Thus, we applied a three-endmember model based on Δ ¹⁴ C org and lignin phenols to disentangle the relative contributions of petrogenic, subglacial, and marine OC to the sedimentary OC pool. The fjord sediments (n = 48) comprised on average of 79.3 ± 26.1% petrogenic OC, 17.7 ± 26.2% subglacial OC, and 3.0 ± 2.5% marine OC. This three-end-member approach highlights the substantial contribution of petrogenic and subglacial OC to the present-day sedimentary OC in Svalbard fjords. Accordingly, under predicted warming worldwide, accelerated contributions of petrogenic and subglacial OC to fjords can be expected as a consequence of rapid glacier retreat, which may play an important role in the active carbon cycle as a potential CO 2 source to the atmosphere.
... Impacts of cryosphere retreat in the surrounding marine environment vary in magnitude and scale. They include, but are not restricted to, both habitat loss and expansion, increased stratification of the water column (de Andrés et al. 2020), changes in underwater light regime, general circulation, transport of sediment and nutrients (Sundfjord et al. 2017, Skogseth et al. 2020) and increased ice-scouring (Gutt 2001, Barnes and Souster 2011a). All these are sources of ecological disturbance to the pelagic and benthic biocenosis associated with glacial and periglacial environments. ...
Marine ice is retreating in many sectors of Earth’s polar and subpolar regions. The rates are unprecedented, generating great concern in both scientific and public communities. Despite the expected serious implications, we lack a comprehensive understanding of how ice loss and related processes control marine biota and interactions at different spatiotemporal scales under multiple environmental stressors and drivers of change. We systematically review existing knowledge on how the losses of ice shelves, sea ice, and glaciers affect polar marine biocenosis. We include in situ, remote sensing, and modelling studies on sea ice biota, phyto- and zooplankton, fish, seabirds, phyto- and zoobenthos and marine mammals, covering a time span of three decades (1991-2022). We apply a qualitative ecosystem‐based risk assessment to assess the individual and cumulative response of ecosystem components and related ecosystem services. The most threats and opportunities are expected to manifest in the shallow coastal zones. They include loss of ice habitat, water column darkening due to sediment input with meltwater, increased sedimentation rates, and mechanical damage due to ice scouring, but also gain of marine habitat, lightening of the water column and nutrient input with meltwater. The cumulative score of all the stressors shows that marine ice loss will lead to autotroph-dominated polar marine systems with detrimental effects on secondary producers, i.e. zooplankton and zoobenthos, and sea ice-obligate species. Although similar stressors are recognised for polar and subpolar regions, some processes may differ in magnitude. This overview aims to provide summarised knowledge to inform science-based solutions for conservation and climate mitigation actions.
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.