Fjord Ecosystems Research Articles

The Effect of Salmon Food-Derived DOM and Glacial Melting on Activity and Diversity of Free-Living Bacterioplankton in Chilean Patagonian Fjords.

Fjord ecosystems cycle and export significant amounts of carbon and appear to be extremely sensitive to climate change and anthropogenic perturbations. To identify patterns of microbial responses to ongoing natural and human-derived changes in the fjords of Chilean Patagonia, we examined the effect of organic enrichment associated with salmon aquaculture and freshening produced by glacial melting on bacterial production (BP), extracellular enzymatic activity (EEA), and community diversity of free-living bacterioplankton. We assayed the effects of salmon food-derived dissolved organic matter (SF-DOM) and meltwaters through microcosm experiments containing waters from Puyuhuapi Fjord and the proglacial fjords of the Southern Patagonia Icefield, respectively. Rates of BP and EEA were 2 times higher in the presence of SF-DOM than in controls, whereas the addition of autochthonous organic matter derived from diatoms (D-DOM) resulted in rates of BP and EEA similar to those measured in the controls. The addition of SF-DOM also reduced species richness and abundance of a significant fraction of the representative taxa of bacterioplankton of Puyuhuapi Fjord. In the proglacial fjords, bacterioplankton diversity was reduced in areas more heavily influenced by meltwaters and was accompanied by moderate positive changes in BP and EEA. Our findings strongly suggest that SF-DOM is highly reactive, promoting enhanced rates of microbial activity while could be influencing the diversity of bacterioplankton communities in Patagonian fjords with a strong salmon farming activity. These findings challenge the traditional view of phytoplankton production as the primary source of labile DOM that fuels heterotrophic activity in coastal ecosystems impacted by anthropogenic organic enrichment. Given the intensive local production of salmon, we analyze the significance of this emerging source of rich “allochthonous” organic substrates for autotrophic/heterotrophic balance, carbon exportation, and hypoxia in Patagonian fjords. The effect of human DOM enrichment can be enhanced in proglacial fjords, where progressive glacial melting exerts additional selective pressure on bacterioplankton diversity.

New evidence for the establishment of coastal cod Gadus morhua in Svalbard fjords

The Arctic is experiencing increasing water temperatures, leading to a northward shift of Atlantic species into Arctic waters. Arctic marine ecosystems are therefore subject to substantial changes in species distributions and occurrence due to anthropogenic climate change. Atlantic cod is one of the most important commercial fish species in the northern seas. The largest known stock is the migrating Northeast Arctic cod (NEAC) that is distributed along the Norwegian coast, the Barents Sea and off Svalbard. Atlantic cod in Svalbard waters are generally reported in the literature as belonging to the NEAC ecotype. The more stationary coastal cod (CC) spawn together with NEAC in the Lofoten region and several other areas along the Norwegian coast. The aim of this study was to investigate the population structure of Atlantic cod in Svalbard waters. We used single nucleotide polymorphic (SNP) markers, the pantophysin locus (Pan I) and otolith structure to categorize the 2 cod ecotypes collected in Svalbard fjords between 2017 and 2019. Our results show that both NEAC and CC appear in Svalbard fjords and revealed that 0-group and adult CC individuals caught in Svalbard fjords differ genetically from those along the Norwegian coast, indicating a separation into a local Svalbard CC population. The establishment of CC in Svalbard fjords may be another keystone of the ongoing borealization of the Arctic, with consequences for the local Arctic fjord ecosystem.

Patterns of Benthic Communities in Arctic Fjords (Novaya Zemlya Archipelago, Kara Sea): Resilience vs. Fragility

Despite a large number of studies, a detailed overall picture of benthic communities zonation in the Arctic fjords is currently lacking. Our study aimed to find out whether there is a universal model for the distribution of benthic communities based on the structural features of the fjords. We examined benthic macrofaunal communities in fjords with various environmental settings on the eastern coast of Novaya Zemlya Archipelago, Kara Sea. The material was collected during five cruises undertaken from 2013 to 2016. A total of 50 stations located in the five fjords were taken. In all five fjords, macrofauna had a similar composition assembled from a regional species pool, with a predominance of species tolerant to glacial sedimentation and fluctuations in temperature and salinity. Benthic communities changed consistently along the axis of the bay from the outer slope to the inner parts. Biodiversity and quantitative characteristics of the macrofauna decreased along the environmental gradient related to terrigenous and glacial runoff, consistent with patterns reported in other studies of Arctic glacial fjords. The most impoverished communities were dominated by bivalvePortlandia arcticaand isopodSaduria sabini. At the same time, fjord walls and sills, characterized by low sedimentation rates, strong currents and the presence of ice-rafted debris, were inhabited by patchy distributed benthic communities dominated by species confined to hard substrates. In general, the distribution of communities corresponded to five zones: depleted inner periglacial areas, the upper subtidal belt with stony substrates, deep inner semi-isolated basin, outer non-isolated basins and upper slope transitioning to lower slope. Our study can provide a reference point for monitoring changes in fjord ecosystems in response to climate change and the potential impact of human activities.

Feeding of Aulacomya atra Under Different Organic Matter Sources (Autochthonous and Allochthonous) in a Chilean Patagonia Fjord Ecosystem

Aulacomya atra is an active suspension feeder, spatially dominant in the shallow-water hard-bottom benthic communities of the Chilean Patagonia fjords. In this region, the vertical flux of autochthonous organic matter (OM) reaching the benthos is augmented by allochthonous OM both from a terrestrial origin and from intensive salmon farming. This mixed pool of OM represents a potential source of food for a variety of benthic consumers, but to date little is known about the degree of utilization of these materials by filter feeders organisms. In this context, feeding experiments on A. atra in Puyuhuapi Fjord, Chilean Patagonia, were conducted during summer and winter 2018–2019. These experiments were designed to determine ingestion rates (IR) of A. atra fed with autochthonous (bacterial and microplanktonic community) and allochthonous (salmon food pellet) OM. Additionally, samples of A. atra tissues and suspended particulate organic matter (SPOM) were taken from the study area for stable isotope analysis. Data from laboratory experiments indicated that A. atra can feed on both autochthonous and allochthonous OM, but higher IR were detected in individuals fed with salmon food pellets. Because the IR is sensitive to food particle density rather than specific type of food, diet preferences of A. atra in feeding experiments could not be determined. Stable isotope analyses indicate that A. atra in natural environment preferentially exploits food with an isotopic signal corresponding to autochthonous OM, highlighting the primary role of phytoplankton carbon in their diet. Extensive utilization of terrestrially derived OM is therefore unlikely, although utilization of OM derived from salmon farming is not precluded because of the overlap in isotopic signal between food pellets and marine plankton.

Hard-Bottom Megabenthic Communities of a Chilean Fjord System: Sentinels for Climate Change?

Chilean Patagonia hosts one of the extensive fjord systems in the world, spanning more than 1,600 km between 41 and 55°S, and with a complex geomorphology and hydrography that supports rich and unique assemblages of marine fauna. The biodiversity of benthic organisms is possibly further enhanced by the geographic position of the region that extends far south into subantarctic waters. However, we currently lack an exhaustive picture of the zonation and ecological functioning of the benthic communities within Chilean fjords. The present study provides a detailed examination of the hard substrata megabenthic communities inhabiting the Puyuhuapi and Jacaf fjord system, in the Aysén Region of Chile. Fifty-nine stations scattered along these fjords were explored through SCUBA diving surveys, at depths between 5 and 30 m, and 16 stations were characterized in terms of benthic cover and diversity using replicated underwater photography. Ten hard bottom megabenthic communities were identified within the fjords, with some communities newly described for this region. Community composition varied both along-fjord, and with depth, and was apparently driven by variation in environmental properties. Our characterization of these fjord communities improves overall knowledge of the functioning of the fjords, and provides a useful baseline against which future anthropogenic pressures can be assessed. Future shifts in bathymetric and geographical distributions might indicate detrimental effects of climate changes, and we therefore propose that characteristic communities could be adopted as “sentinels” for overall environmental status of these unique fjord ecosystems. In this regard, detailed mapping of the distribution of megabenthic communities can provide a fundamental tool that assists in best management practices for these ecosystems.

Depth-Dependent Diversity Patterns of Rocky Subtidal Macrobenthic Communities Along a Temperate Fjord in Northern Chilean Patagonia

Understanding the distribution of biodiversity along environmental gradients allows us to predict how communities respond to natural and anthropogenic impacts. In fjord ecosystems, the overlap of strong salinity and temperature gradients provides us with the opportunity to assess the spatial variation of biodiversity along abiotic environmental gradients. However, in Northern Chilean Patagonia (NCP), a unique and at the same time threatened fjord system, the variation of macrobenthic communities along abiotic environmental gradients is still poorly known. Here, we tested whether macrobenthic species diversity and community structure followed systematic patterns of variation according to the spatial variation in salinity and temperature in Comau Fjord, NCP. A spatially extensive nested sampling design was used to quantify the abundance of subtidal macrobenthic species along the fjord axis (fjord sections: head, middle, and mouth) and a depth gradient (0–21 m). The vertical structure of the water column was strongly stratified at the head of the fjord, characterized by a superficial (depth to ca. 5 m) low-salinity and relatively colder layer that shallowed and decayed toward the mouth of the fjord. The biotic variation followed, in part, this abiotic spatial pattern. Species richness peaked at high salinities (>27 psu) between 5 and 10 m in the head section and between 15 and 21 m in the middle and mouth sections. Diversity and evenness were also highest at these salinities and depth ranges in the head and middle sections, but at shallower depth ranges in the mouth. Information theory-based model selection provided a strong empirical support to the depth- and section-dependent salinity, but not temperature, effects on the three biodiversity metrics. Erect algae and the edible mussel Aulacomya atra numerically dominated in shallow water (0–3 m) at the head and the middle of the fjord, coinciding with the horizontal extension of the low-density water layer—these taxa were further replaced by the crustose algae Lithothamnion sp. and deep-dwelling suspension filters (e.g., corals, polychaetes, and sponges) along depth gradient. Macrobenthic biodiversity correlated, therefore, with the influence of freshwater inputs and the density-driven stratification of the water column in this ecosystem. The spatially variable (across both, horizontal and vertical fjord axes) thresholds observed in our study question the widely accepted pattern of increasing biodiversity with increasing distance from the head of estuarine ecosystems. Finally, non-linear environmental stress models provide us a strong predictive power to understand the responses of these unique ecosystems to natural and anthropogenic environmental changes.

Early spring subglacial discharge plumes fuel under-ice primary production at a Svalbard tidewater glacier

Abstract. Subglacial upwelling of nutrient-rich bottom water is known to sustain elevated summer primary production in tidewater-glacier-influenced fjord systems. However, the importance of subglacial upwelling during the early spring season has not been considered yet. We hypothesized that subglacial discharge under sea ice is present in early spring and that its flux is sufficient to increase phytoplankton primary productivity. We evaluated the effects of the submarine discharge on primary production in a seasonally fast-ice covered Svalbard fjord (Billefjorden) influenced by a tidewater outlet glacier in April and May 2019. We found clear evidence for subglacial discharge and upwelling. Although the estimated bottom-water entrainment factor (1.6) and total fluxes were lower than in summer studies, we still observed substantial impact on the fjord ecosystem and primary production at this time of the year. The subglacial discharge leads to a salinity-stratified surface water layer and sea ice formation with low bulk salinity and permeability. The combination of the stratified surface layer, a 2-fold higher under-ice irradiance due to thinner snow cover, and higher N and Si concentrations at the glacier front supported phytoplankton primary production 2 orders of magnitude higher (42.6 mg C m−2 d−1) compared to a marine reference site at the fast-ice edge. Reciprocal transplant experiments showed that nutrient supply increased phytoplankton primary production by approximately 30 %. The brackish-water sea ice at the glacier front with its low bulk salinity contained a reduced brine volume, limiting the inhabitable brine channel space and nutrient exchange with the underlying seawater compared to full marine sea ice. Microbial and algal communities were substantially different in subglacial-influenced water and sea ice compared to the marine reference site, sharing taxa with the subglacial outflow water. We suggest that with climate change, the retreat of tidewater glaciers in early spring could lead to decreased under-ice phytoplankton primary production. In contrast, sea ice algae production and biomass may become increasingly important, unless sea ice disappears first, in which case spring phytoplankton primary production may increase.

Abundance, habitat use and food consumption of seabirds in the high-Arctic fjord ecosystem

To monitor the rapid changes occurring in Arctic ecosystems and predict their direction, basic information about the current number and structure of the main components of these systems is necessary. Using boat-based surveys, we studied the numbers and distribution of seabirds foraging in Hornsund (SW Spitsbergen) during three summer seasons. The average number of seabirds foraging concurrently in the whole fjord was estimated at 28,000. Little Auks Alle alle were the most numerous, followed by Northern Fulmars Fulmarus glacialis, Brünnich’s Guillemots Uria lomvia and Black-legged Kittiwakes Rissa tridactyla. The pelagic zone was exploited by some 75% of the birds. Their density was the highest (> 400 ind. km−2) in the tidewater glacier bays, where kittiwakes were predominant, and the lowest in the coastal glacier bays. The seabirds in Hornsund daily consumed c. 12.7 tons of food, i.e. c. 0.2% of the summer mesozooplankton and fish standing stocks available in the fjord. This food consisted primarily of copepods, amphipods and molluscs (c. 70%), whereas fish made up < 15%. More than 50% of this biomass was ingested by pursuit divers, while surface feeders took c. 29% and benthophages c. 13%. About three-quarters of the food biomass was taken from the pelagic zone. This paper describes, for the first time in quantitative terms, the structure and function of a seabird community foraging in an Arctic fjord. It also provides a baseline for future studies on climate-induced changes in the importance of seabirds in the Arctic food web.

Potentially bioavailable iron produced through benthic cycling in glaciated Arctic fjords of Svalbard

The Arctic has the highest warming rates on Earth. Glaciated fjord ecosystems, which are hotspots of carbon cycling and burial, are extremely sensitive to this warming. Glaciers are important for the transport of iron from land to sea and supply this essential nutrient to phytoplankton in high-latitude marine ecosystems. However, up to 95% of the glacially-sourced iron settles to sediments close to the glacial source. Our data show that while 0.6–12% of the total glacially-sourced iron is potentially bioavailable, biogeochemical cycling in Arctic fjord sediments converts the glacially-derived iron into more labile phases, generating up to a 9-fold increase in the amount of potentially bioavailable iron. Arctic fjord sediments are thus an important source of potentially bioavailable iron. However, our data suggests that as glaciers retreat onto land the flux of iron to the sediment-water interface may be reduced. Glacial retreat therefore likely impacts iron cycling in coastal marine ecosystems.

Genetic Conservation Management of Marine Resources and Ecosystems of Patagonian Fjords

The Chilean fjord region includes many remote and poorly known areas where management plans for the marine living resources and conservation strategies are urgently needed. Few data are available about the spatial distribution of its marine invertebrate fauna, prevalently influenced by complex interactions between biotic and abiotic factors, animal behavior and human activities. Patagonian fjords are a hotspot for finfish aquaculture, elevating Chile to the world’s second producer of farmed salmon, after Norway, a condition that emphasizes the necessity to develop strategies for a sustainable aquaculture management. The present study focuses on the emblematic cold-water coralDesmophyllum dianthus, dwelling the Comau Fjord from shallow to deep waters, with the aim to illustrate population structure, demography and adaptation of the species and its potential use for the development of a sustainable conservation and management plan for human activities. The analyses of microsatellite loci ofD. dianthusindividuals from four sampling localities along horizontal and vertical gradients of Comau Fjord, lead to identify them as a panmictic population. The results also contributed to consider a careful examination of the synchrony between the temporal and spatial variations of environmental factors and the biological cycle of the species as key role player in the inference of autecology of the species. The discussion stresses the importance of molecular analyses as extremely helpful tools for studies focusing on remote areas and non-model organisms, where logistic difficulties and limited scientific knowledge hamper a better management and conservation of marine resources, and in particular the relevance of multidisciplinary approaches to reduce the extensive knowledge gap on the remote fjord ecosystems of Patagonia. This study also highlights the importance of oceanographic information in the entire process of the analyses and interpretation of genetic results.

Bioenergetic traits of three keystone marine species in the food web of a pristine Patagonian fjord

The Patagonian fjords are high-latitude aquatic ecosystems, highly sensitive to climate change and play a key role in the exchange of organic matter and carbon flows between terrestrial and marine environments. The bioenergetic composition of species living in these ecosystems are fundamental to understanding the distribution, seasonal variations, and exchange of organic matter within benthic communities. This study reports on the bioenergetic characteristics (lipids, protein, glucose, and energy content) of three keystone species with different life-style and feeding habits: a benthic sea star (Ctenodiscus australis); squat lobster (Munida gregaria); and a Patagonian notothenioid (Eleginops maclovinus). Samples were obtained from the Yendegaia Fjord (54°40'S - 68°50′W) in Chilean Patagonia. Our results indicate that M. gregaria has higher concentrations of lipids, proteins, glucose, and total energy compared to either E. maclovinus or C. australis. The predominance of lipids in all species is possibly related to physiological characteristics and feeding strategies. Also, may be associated with the availability of food and environmental conditions typical of a fjord ecosystem and the reproductive stage in that they were collected. These results suggest that marine animals inhabiting glacially influenced environments with low temperature and low productivity, requires a convergent physiological strategy characterized by high levels of energy storage (i.e. lipids) for metabolism and key bioenergetic processes such as growth and reproduction.

Subglacial permafrost dynamics and erosion inside subglacial channels driven by surface events in Svalbard

Abstract. Cold glacier beds, i.e., where the ice is frozen to its base, are widespread in polar regions. Common theories state that stable permafrost should exist under glacier beds on shorter timescales, varying from years to decades. Presently, only a few direct measurements of both subglacial permafrost and the processes influencing its thermal regime exist. Here, we present subglacial permafrost and active layer measurements obtained from within the basal drainage systems of two cold-based glaciers on Svalbard during the summer melt season. Temperature observations were obtained from subglacial sediment that was accessed through the drainage systems of the two glaciers in the previous winters. The temperature records cover the periods from spring to autumn in 2016 and 2019 at the glaciers Larsbreen and Tellbreen in central Svalbard. The ground temperature below Larsbreen indicates colder ground conditions, whereas the temperatures of the Tellbreen drainage system show considerably warmer conditions, close to the freezing point. We suggest the latter is due to the presence of liquid water all year round inside the Tellbreen drainage system. Both drainage systems investigated show an increase in subglacial sediment temperatures after the disappearance of snow bridges and the subsequent connection to surface meltwater supply at the start of the summer melt season. Temperature records show influence of sudden summer water supply events, when heavy melt and rain left their signatures on the thermal regime and the erosion of the glacier bed. Observed vertical erosion can reach up to 0.9 m d−1 at the base of basal drainage channels during summer. We also show that the thermal regime under the subglacial drainage systems is not stable during summer but experiences several freeze–thaw cycles driven by weather events. Our results show the direct importance of heavy melt events and rain on the thermal regime of subglacial permafrost and the erosion of the glacier bed in the vicinity of subglacial drainage channels. Increased precipitation and surface melt, as expected for future climate, will therefore likely lead to increased degradation of subglacial permafrost, as well as higher subglacial erosion of available sediment around the preferential hydrological paths. This in turn might have significant impacts on proglacial and fjord ecosystems due to increased sediment and nutrient input.

Mercury bioaccumulation pathways in tusk (Brosme brosme) from Sognefjord, Norway: Insights from C and N isotopes.

Seafood is the main source of methylmercury (MeHg) exposure for humans and elevated total mercury (Hg) concentrations have been reported in marine fish from Norwegian fjords compared with offshore areas. Hg in tusk fillets (n=201) and liver samples (n=177) were measured in individuals from different habitats including offshore, coastal area, outer and inner Sognefjord. Specifically, the effects of habitat, energy sources and trophic complexity on Hg bioaccumulation pathways in tusk (Brosme brosme) were investigated using stable isotopes of carbon (δ13C) and nitrogen (δ15N). The concentrations of Hg in tusk increased from offshore towards inner Sognefjord. While Hg concentrations in sediment were at background levels, tusk fillet samples from 7 of 8 sites in Sognefjord had higher Hg levels than the maximum level set by European Union. Based on these findings, human consumption advice for tusk from Sognefjord was issued by the Norwegian Food Safety Authority. δ13C values in tusk successfully discriminated individuals from different habitats and were positively correlated to Hg concentrations in tusk across individuals, sites and habitats, outlining the potential importance of terrestrial carbon and most likely the atmospheric deposition of Hg from the catchment to the overall Hg bioaccumulation and exposure regime in tusk. Additionally, we postulate that the effects of terrestrial carbon sources increased towards inner Sognefjord and likely influenced Hg bioavailability throughout the food web. In contrast, δ15N values were patchy throughout the fjord system and although trophic position explained some of the Hg variation between individual fish, it was not correlated with Hg variation across sites and habitats. Our results suggest that tusk can accumulate high levels of Hg in fjord ecosystems and that catchment runoff is likely an important driver of Hg bioaccumulation in this species.

Biodiversity, community structure and ecosystem function on kelp and wood falls in the Norwegian deep sea

Fjordic systems in temperate and Arctic regions often feature extensive kelp forests at their shallow coastal margins as well as extensive terrestrial forests. Detrital export from these shallow-water and terrestrial ecosystems is an important source of carbon for deep-sea communities in the form of kelp and wood falls. Benthic landers with experimental substrates (wood blocks and kelp parcels) were deployed for 10 mo at a depth of 530 m in a deep Norwegian fjord to investigate and compare macro- and megabenthic community structure, biodiversity and ecosystem functioning on kelp and wood falls. Results revealed that while wood and kelp falls can support a similar number of species and abundance of fauna, they support significantly different faunal communities. Biomass and secondary production on both wood and kelp substrates were significantly greater than in the control samples. Secondary production estimates were similar or higher than those reported from soft-sediment ecosystems at shallower European marine sites. Biological trait analysis showed that macrofaunal assemblages were distinct between the kelp and wood, providing evidence for differences in ecosystem function between the substrates. This case study from a deep-sea fjord in Norway provides clear evidence that while wood and kelp organic falls can support similar abundances of fauna, the associated benthic biodiversity, community structure and ecosystem functioning can be dramatically different between these substrates. The work presented here aims to provide information that is useful in assessing the extent of anthropogenic impacts on deep fjord ecosystems with respect to informing future conservation and management strategies.

Water column circulation drives microplastic distribution in the Martínez-Baker channels; A large fjord ecosystem in Chilean Patagonia

We investigated the distribution of microplastics in the water column along a large remote estuarine system located between the Northern and Southern Patagonian Ice Fields in Chilean Patagonia, and connected with the Pacific Ocean through the Gulf of Penas. Microplastic particles were found in all samples, with abundances ranging from 0.1 to 7 particles/m3. Polymers identified were principally acrylics, PET, and cellophane.The average abundance of microplastics in surface waters was similar along the whole estuary (0.4 ± 0.3 particles/m3) with acrylics and epoxy resins being more abundant near Caleta Tortel, the only small village in the area. The observed higher abundance of microplastics in the deeper waters towards the Gulf of Penas points to intrusions of subsurface waters transporting plastic particles from the ocean into the channel system. This underlines the potential of ocean currents in transporting plastic pollution into pristine fjords and channels in Chilean Patagonia.

Intense deposition and rapid processing of seafloor phytodetritus in a glaciomarine fjord, Andvord Bay (Antarctica)

The West Antarctic Peninsula (WAP) region encompasses numerous fjords known to be hotspots of benthic biodiversity and biomass. These ecosystems are undergoing rapid climate warming and oceanographic change; consequent glacial melt and retreat may dramatically alter benthic communities and ecosystem functions in WAP fjords. In addition, there is extreme variability in seasonal productivity and phytodetrital food input to the deep shelf benthos of the WAP. Here we document the flux and utilization of phytodetritus at 530 m depth in Andvord Bay, a WAP glaciomarine fjord, using seafloor time-lapse images spanning a 10-month period, from December 2015 to September 2016. To explore the relationship between sea-surface conditions and detrital export, we developed a color-based method to quantify seafloor phytodetritus cover in time-lapse images, and correlated phytodetritus cover with sea-ice cover and surface wind speed. During the most rapid period of phytodetritus accumulation in early January 2016, approximately 3 cm of phytodetritus was deposited on the fjord floor over six days, representing a large input of organic carbon to the benthos. The timing of this rapid export event was not related to overlying wind conditions and occurred when the fjord was ice-free. To assess the response of the megafaunal community, we measured fecal-pellet production by the dominant surface deposit-feeder, the ampharetid polychaete Amythas membranifera. The deposit-feeding rate of A. membranifera increased substantially during high seafloor phytodetritus cover and returned to background levels for the rest of the autumn and winter. Ampharetids and mobile megafauna were observed to feed throughout the entire time-series, including beneath winter sea ice, suggesting that the delivery of phytodetritus from surface phytoplankton blooms in spring/summer sustains these abundant populations year-round with a sediment food bank. A. membranifera can reach densities of >37 m−2 and, as a population, processes a volume equivalent to the top 1.05 cm of sediment annually. The maximum individual feeding rates measured are comparable to some temperate intertidal deposit feeders. Nonetheless, phytodetritus on 31–73% of the seafloor was consumed by macrofauna or microbial populations not visible in time-lapse photographs, suggesting that recently deposited phytodetritus is processed primarily by these smaller size classes. This study demonstrates the seasonal coupling and subsequent decoupling of detritivore activity in response to a massive detrital deposition event in a deep, subpolar WAP fjord. This work indicates that both megafaunal deposit feeders and smaller size classes play important roles in processing labile organic matter in WAP fjord ecosystems.

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 ± 15 ng g−1) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km3 yr−1) and organic carbon accumulation rates (9.3 ~ 49.4 g m−2 yr−1) were elevated compared to other fjords. Furthermore, the δ13C (–27 ~ –24‰) and δ34S values (–10 ~ 15‰) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more OM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems.

Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord

Environmental change can have a significant impact on biogeochemical cycles at high latitudes and be particularly important in ecologically valuable fjord ecosystems. Seasonality in biogeochemical cycling in a sub-Arctic fjord of northern Norway (Kaldfjorden) was investigated from October 2016 to September 2018. Monthly changes in total inorganic carbon (CT), alkalinity (AT), major nutrients and calcium carbonate saturation (Ω) were driven by freshwater discharge, biological production and mixing with subsurface carbon-rich coastal water. Stable oxygen isotope ratios indicated that meteoric water (snow melt, river runoff, precipitation) had stratified and freshened surface waters, contributing to 81% of the monthly CT deficit in the surface layer. The timing and magnitude of freshwater inputs played an important role in Ω variability, reducing AT and CT by dilution. This dilution effect was strongly counteracted by the opposing effect of primary production that dominated surface water Ω seasonality. The spring phytoplankton bloom rapidly depleted nitrate and CT to drive highest Ω (~2.3) in surface waters. Calcification reduced AT and CT, which accounted for 21% of the monthly decrease in Ω during a coccolithophore bloom. Freshwater runoff contributed CT, AT and silicates of terrestrial origin to the fjord. Lowest surface water Ω (~1.6) resulted from organic matter remineralisation and mixing into subsurface water during winter and spring. Surface waters were undersaturated with respect to atmospheric CO2, resulting in modest uptake of –0.32 ± 0.03 mol C m–2 yr–1. Net community production estimated from carbon drawdown was 14 ± 2 g C m–2 yr–1 during the productive season. Kaldfjorden currently functions as an atmospheric CO2 sink of 3.9 ± 0.3 g C m–2 yr–1. Time-series data are vital to better understand the processes and natural variability affecting biogeochemical cycling in dynamic coastal regions and thus better predict the impact of future changes on important fjord ecosystems.

Bacterial community structure of a glacio-marine system in the Arctic (Ny-Ålesund, Svalbard)

The bacterial community composition of a valley glacier in Svalbard, its pro-glacial channels, and the associated downstream fjord ecosystem was investigated so as to figure out the degree to which downslope transport of microbes from the glacier systems along a hydrological continuum impose an effect on the patterns of diversity in the fjord system. A combination of culture based and high-throughput amplicon sequencing approach was followed which resulted in significant variation (R = 0.873, p = 0.001) in the bacterial community structure between these ecosystems. Dominance of sequences belonging to class β-Proteobacteria was seen in the glacier snow, ice and melt waters (MW) while a relatively higher abundance of OTUs belonging to α-Proteobacteria and Verrucomicrobiae demarcated the fjord waters. Similarity percentage (SIMPER) analysis of the Operational Taxonomic Units (OTUs) showed that OTU 1,105,280 (9.15%) and OTU 331 (6.5%) belonging to Burkholderiaceae (β-proteobacteria) and OTU 101,660 (5.76%) and OTU 520 (5.07%) belonging to Rhodobacteraceae (α-proteobacteria) contributed maximum to the overall dissimilarity between the sampling sites. The bacterial community from the MWs were found to be true signatures of the glacier ecosystem while the Kongsfjorden bacterial fraction mostly represented heterotrophic marine taxa influenced by warm Atlantic waters and presence of organic matter. Significant presence of unknown taxa in the MWs suggests the need to study such unexplored, transient niches for a better understanding of the associated microbial processes. Among the various environmental parameters measured, nutrients (NO3− and SiO42−) were found to exhibit strong association with the MW bacterial community while temperature, trace metals, Cl− and SO42− ions were found to influence the fjord bacterial community. The significant differences in the bacterial community composition between the glacier and the fjord ecosystem suggest the unique nature of these systems which in turn is influenced by the associated environmental parameters.

The spatial distribution of phytoplankton pigments in the surface sediments of the Kongsfjorden and Krossfjorden ecosystem of Svalbard, Arctic

Kongsfjorden–Krossfjorden twin fjord ecosystem in Svalbard (Arctic), is facing enhanced warm Atlantic water intrusion from ocean as well as intensified melting from glaciers. It is an interesting ecosystem to study phytoplankton productivity under the two opposing processes. For phytoplankton productivity, pigments are used as potential photosynthetic biomass indicators and taxonomic biomarkers. However, due to labile nature of pigments, degradation — preservation distribution must be investigated to form essential framework for biomarker studies. With this motivation, we have undertaken the present work to study the spatial distribution of surface sedimentary pigments in the twin-fjord ecosystem. The pigments were analysed using high-performance liquid chromatography coupled with diode array detector. A total of fifteen pigments were identified, which belonged to different classes — chlorophylls, pheopigments and carotenoids. Chlorophyll-a and pheophorbide-a were major pigments with concentration up to 700–800 ng g−1 dry weight of sediment. Among carotenoids, fucoxanthin, diatoxanthin and prasinoxanthin were abundant with maximum concentration recorded up to 400–600 ng g−1 dry weight. The distribution of the pigments varied significantly between the two fjords as well as in different regions of the fjord. Most of the pigments were significantly high in their concentration at Krossfjorden stations. Within Kongsfjorden, outer region showed higher concentration of pigments than inner. However, preservation was lesser for the outer fjord pigments than inner as confirmed by various pigment indices. Further, the overall distribution of phytoplankton communities derived from taxonomic biomarker pigments in Kongsfjorden–Krossfjorden sediments, was coherent with that of water during spring and summer. The distribution was dominated by diatoms, dinoflagellates, prasinophytes and prymnesiophytes. The surface sedimentary pigments were found capable of providing information about phytoplankton biomass and composition under environmental conditions existing in the region.