Arctic Fjord Sediments Research Articles

Exploring bacterial diversity in Arctic fjord sediments: a 16S rRNA-based metabarcoding portrait.

The frosty polar environment houses diverse habitats mostly driven by psychrophilic and psychrotolerant microbes. Along with traditional cultivation methods, next-generation sequencing technologies have become common for exploring microbial communities from various extreme environments. Investigations on glaciers, ice sheets, ponds, lakes, etc. have revealed the existence of numerous microorganisms while details of microbial communities in the Arctic fjords remain incomplete. The current study focuses on understanding the bacterial diversity in two Arctic fjord sediments employing the 16S rRNA gene metabarcoding and its comparison with previous studies from various Arctic habitats. The study revealed that Proteobacteria was the dominant phylum from both the fjord samples followed by Bacteroidetes, Planctomycetes, Firmicutes, Actinobacteria, Cyanobacteria, Chloroflexi and Chlamydiae. A significant proportion of unclassified reads derived from bacteria was also detected. Psychrobacter, Pseudomonas, Acinetobacter, Aeromonas, Photobacterium, Flavobacterium, Gramella and Shewanella were the major genera in both the fjord sediments. The above findings were confirmed by the comparative analysis of fjord metadata with the previously reported (secondary metadata) Arctic samples. This study demonstrated the potential of 16S rRNA gene metabarcoding in resolving bacterial composition and diversity thereby providing new in situ insights into Arctic fjord systems.

Large contributions of petrogenic and aged soil-derived organic carbon to Arctic fjord sediments in Svalbard

Svalbard fjords are recognized as hotspots for organic carbon (OC) burial and storage due to their high sedimentation rates, which effectively trap terrestrial sediments and inhibit extensive OC remineralization. In this study, we investigated surface sediments (n = 48) from eight Svalbard fjords, along with bedrock (n = 17), soil (n = 28), and plant (n = 12) samples, to identify the sources of sedimentary OC in these fjords using geochemical parameters. All examined surface sediments from the fjords showed a depletion in 14Corg (− 666.9 ± 240.3‰), indicating that recently fixed terrestrial and marine biomass alone cannot account for the entire sedimentary OC pool. Conventional bulk indicators such as Norg/TOC ratio and δ13Corg were insufficient for fully determining the sources of sedimentary OC. Therefore, we employed a four-end-member approach, using Δ14Corg, δ13Corg, and lignin phenols to assess the relative contributions of petrogenic, soil-derived, plant-derived, and marine OC to the sedimentary OC pool. The analyzed fjord sediments consisted, on average, of 59.0 ± 28.1% petrogenic OC, 16.8 ± 12.1% soil-derived OC, 2.5 ± 2.2% plant-derived OC, and 21.8 ± 18.5% marine OC. This approach highlights the substantial contributions of petrogenic and aged soil-derived OC to present-day sedimentary OC in Svalbard fjords. Considering predicted global warming, accelerated inputs of petrogenic and soil-derived OC into fjords due to rapid glacier retreat may significantly impact the active carbon cycle and potentially contribute to CO2 emissions to the atmosphere, depending on burial efficiency.

Fossil organic carbon utilization in marine Arctic fjord sediments by subsurface micro-organisms

Rock-derived or petrogenic organic carbon has traditionally been regarded as being non-bioavailable and bypassing the active carbon cycle when eroded. However, it has become apparent that this organic carbon might not be so inert, especially in fjord systems where petrogenic organic carbon influxes can be high, making its degradation another potential source of greenhouse gas emissions. The extent to which subsurface micro-organisms use this organic carbon is not well constrained, despite its potential impacts on global carbon cycling. Here, we performed compound-specific radiocarbon analyses on intact polar lipid–fatty acids of live micro-organisms from marine sediments in Hornsund Fjord, Svalbard. By this means, we estimate that local bacterial communities utilize between 5 ± 2% and 55 ± 6% (average of 25 ± 16%) of petrogenic organic carbon for their biosynthesis, providing evidence for the important role of petrogenic organic carbon as a substrate after sediment redeposition. We hypothesize that the lack of sufficient recently synthesized organic carbon from primary production forces micro-organisms into utilization of petrogenic organic carbon as an alternative energy source. The input of petrogenic organic carbon to marine sediments and subsequent utilization by subsurface micro-organisms represents a natural source of fossil greenhouse gas emissions over geological timescales.

Metabolic responses of thermophilic endospores to sudden heat-induced perturbation in marine sediment samples.

Microbially mediated processes in a given habitat tend to be catalyzed by abundant populations that are ecologically adapted to exploit specific environmental characteristics. Typically, metabolic activities of rare populations are limited but may be stimulated in response to acute environmental stressors. Community responses to sudden changes in temperature and pressure can include suppression and activation of different populations, but these dynamics remain poorly understood. The permanently cold ocean floor hosts countless low-abundance microbes including endospores of thermophilic bacteria. Incubating sediments at high temperature resuscitates viable spores, causing the proliferation of bacterial populations. This presents a tractable system for investigating changes in a microbiome's community structure in response to dramatic environmental perturbations. Incubating permanently cold Arctic fjord sediments at 50°C for 216 h with and without volatile fatty acid amendment provoked major changes in community structure. Germination of thermophilic spores from the sediment rare biosphere was tracked using mass spectrometry-based metabolomics, radiotracer-based sulfate reduction rate measurements, and high-throughput 16S rRNA gene sequencing. Comparing community similarity at different intervals of the incubations showed distinct temporal shifts in microbial populations, depending on organic substrate amendment. Metabolite patterns indicated that amino acids and other sediment-derived organics were decomposed by fermentative Clostridia within the first 12–48 h. This fueled early and late phases of exponential increases in sulfate reduction, highlighting the cross-feeding of volatile fatty acids as electron donors for different sulfate-reducing Desulfotomaculia populations. The succession of germinated endospores triggered by sudden exposure to high temperature and controlled by nutrient availability offers a model for understanding the ecological response of dormant microbial communities following major environmental perturbations.

Tight benthic-pelagic coupling drives seasonal and interannual changes in iron‑sulfur cycling in Arctic fjord sediments (Kongsfjorden, Svalbard)

Glaciated fjords are dynamic systems dominated by seasonal events such as spring phytoplankton blooms and pulses of glacial sediment-bearing meltwater delivery. These fjords are also characterized by strong spatial gradients in environmental factors such as sedimentation rate and primary productivity from the glacier-influenced head to the marine-influenced mouth. Such seasonal variations and spatial gradients, combined with the ongoing influence of climate change, generate non-steady state conditions, which have a strong impact on the mineralization of organic carbon in the fjord sediments and the flux of nutrients from the seabed. In order to investigate the role of fjord seasonal events and variability on diagenetic cycling of iron (Fe) and sulfur (S), we sampled Kongsfjorden (Svalbard, 79°N) in the spring, mid-summer, and late summer. We investigated sediment structure and biogeochemistry, conducted laboratory experiments to determine reaction rates, and compared these findings to water column productivity and turbidity. We found that rapid sedimentation near the glacial input buried algal matter-rich layers that fueled sub-surface peaks in mineralization rates over multi-year timescales. Sulfate reduction rates were limited by organic carbon availability and competition with Fe-reducers, while Fe reduction was controlled by the availability of reactive Fe(III) oxides. Pore water Fe 2+ concentrations were influenced by sulfur cycling pathways and abiotic reactions such as carbonate precipitation and potentially reverse weathering. Seasonal changes in sedimentation and organic carbon supply caused lower sulfate reduction and sulfide production rates in spring, driving generally higher spring fluxes of Fe 2+ from the sediment. The results of this study reveal the potential for an increased benthic source of nutrients such as Fe with continued benthic remineralization over winter in Kongsfjorden. Interannual changes in primary productivity, which are likely to intensify with global warming, and shifts in glacial sediment delivery have immediate impacts on the benthic cycling of Fe and S in this tightly coupled system, with a long term trend likely toward decreased benthic Fe fluxes. With the glacial retreat and changes in productivity predicted due to climate change, glaciated fjords such as Kongsfjorden may become a less efficient carbon sink by burying less terrestrial and marine-sourced organic matter in the deep sediments. • Investigation of seasonal Fe-S-C cycling in Arctic fjord sediments and water column. • Results show benthic respiration and increased benthic Fe 2+ flux over winter. • Findings suggest that fjord sediments respond rapidly to water column changes. • With glacial retreat, fjords may produce less benthic Fe and sequester less carbon.

Climate-Associated Changes in Mercury Sources in the Arctic Fjord Sediments

Despite the large climatic fluctuations in the Arctic over the Holocene, the dominant mercury (Hg) sources and the potential changes in Hg sources associated with the climate remain unclear. Here, we use Hg isotopes to reconstruct changes in Hg sources and processes in two Svalbard fjord sediment cores spanning the Holocene. The Hg isotope ratios of the fjord sediment cores are similar to bedrock and Hg bound to terrestrial total organic carbon (TOC) but different from other sediment cores influenced by atmospheric Hg drawdowns via the sinking of marine particulate organic matter. The absence of significant Hg and TOC relationships indicates that bedrock erosion caused by glacier dynamics is the major Hg source to the fjord sediment rather than those bound to marine and terrestrial TOC. Measurable shifts in Hg sources are observed at regional cooling (4.3 ka) and during the Medieval Warm Period in the late Holocene. The negative shift in δ202Hg (by −0.5‰) at 4.3 ka from baseline (∼10 ka) is consistent with the rapid increase in glacier-mediated physical and chemical erosions of bedrock. The significant positive shifts in δ202Hg (by 0.5‰) in the late Holocene are explained by enhanced input of atmospheric Hg and its drawdown via the sinking of marine particulate organic matter and some anthropogenic influence, which suppressed the positive Δ199Hg and Δ200Hg shifts. This study suggests that Hg isotope ratios measured in sedimentary archives can be used to decipher climate and other local to global changes modifying Hg sources in the Arctic.

Bacterial community structure and functional profiling of high Arctic fjord sediments.

Kongsfjorden, an Arctic fjord is significantly affected by the glacier melt and Atlantification, both the processes driven by accelerated warming in the Arctic. This has lead to changes in primary production, carbon pool and microbial communities, especially that in the sediment. In this study, we have examined the bacterial community structure of surface (0-2cm) and subsurface (3-9cm) sediments of Kongsfjorden using the high throughput sequencing analysis. Results revealed that bacterial community structure of Kongsfjorden sediments were dominated by phylum Proteobacteria followed by Bacteroidetes and Epsilonbacteraeota. While α- and γ-Proteobacterial class were dominant in surface sediments; δ-Proteobacteria were found to be predominant in subsurface sediments. The bacterial community structure in the surface and subsurface sediments showed significant variations (p ≤ 0.05). Total organic carbon could be one of the major parameters controlling the bacterial diversity in the surface and subsurface sediments. Functional prediction analysis indicated that the bacterial community could be involved in the degradation of complex organic compounds such as glycans, glycosaminoglycans, polycyclic aromatic hydrocarbons and also in the biosynthesis of secondary metabolites.

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.

Distinct community composition and abundance of ammonia oxidizers in the high Arctic fjord sediments of Svalbard

Though the process and players of nitrification are important in the ecology and biogeochemistry of Arctic fjords; there are very limited studies available on the ecology of ammonia oxidizers. Hence, we studied the abundance, diversity, and niche separation of ammonia oxidizers in the surface sediment of two high Arctic fjords (Kongsfjorden and Krossfjorden) to explore their ecology in the Arctic system. Surface sediment samples were collected from eight stations (four stations from each fjord). The diversity and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were analyzed using ammonia monooxygenase A (amoA) gene from the sediment metagenome. Environmental variables including bottom temperature and salinity, and sediment characteristics such as total carbon (TC), total nitrogen (TN), total sulfur (TS), and total organic carbon (TOC), were measured. AOA were more abundant than AOB in most of the samples and AOA/AOB ratios ranged from 0.63 to 17.11. AOA were dominated by Nitrosopumilus lineage (67.5%), followed by Nitrososphaera lineage (32.2%). Most of the AOB were affiliated with Nitrosospira lineage (82.2%), and comparatively lesser contribution (18.2%) was observed for Nitrosomonas. We could not observe comammox bacteria in our samples. The distribution of ammonia oxidizers had a significant influence with the total nitrogen and total organic carbon content. Both AOA and AOB showed spatial variations in community composition within the fjords and between the fjords with a domination of freshwater/soil communities in the inner fjord stations. Freshwater and soil influx from glacial melt had a significant influence in controlling the environmental variables in the fjords which in turn regulated the distribution and niche selection of ammonia oxidizers.

Abundance and diversity of diazotrophs in the surface sediments of Kongsfjorden, an Arctic fjord

Diazotrophy in the Arctic environment is poorly understood compared to tropical and subtropical regions. Hence in this study, we report the abundance and diversity of diazotrophs in Arctic fjord sediments and elucidate the role of environmental factors on the distribution of diazotrophs. The study was conducted during the boreal summer in the Kongsfjorden, an Arctic fjord situated in the western coast of Spitsbergen. The abundance of nifH gene was measured through quantitative real-time PCR and the diversity of diazotrophs was assessed by nifH targeted clone library and next generation sequence analysis. Results revealed that the abundance of nifH gene in the surface sediments ranged from 2.3 × 106 to 3.7 × 107 copies g- 1. The δ-proteobacterial diazotrophs (71% of total sequence) were the dominant class observed in this study. Major genera retrieved from the sequence analysis were Desulfovibrionaceae (25% of total sequence), Desulfuromonadaceae (18% of total sequence) and Desulfobacteriaceae (10% of total sequence); these are important diazotrophic iron and sulfur-reducing bacterial clade in the Kongsfjorden sediments. The abundance of nifH gene showed a significant positive correlation TOC/TN ratio (r2 = 0.96, p ≤ 0.05) and total organic carbon (p ≤ 0.05) content in the fjord sediments. The higher TOC/TN ratio (4.24-14.5) indicated low nitrogen content organic matter in the fjord sediments through glacier runoff, which enhances the abundance and diversity of nitrogen fixing microorganisms.

Woeseiales transcriptional response to shallow burial in Arctic fjord surface sediment.

Distinct lineages of Gammaproteobacteria clade Woeseiales are globally distributed in marine sediments, based on metagenomic and 16S rRNA gene analysis. Yet little is known about why they are dominant or their ecological role in Arctic fjord sediments, where glacial retreat is rapidly imposing change. This study combined 16S rRNA gene analysis, metagenome-assembled genomes (MAGs), and genome-resolved metatranscriptomics uncovered the in situ abundance and transcriptional activity of Woeseiales with burial in four shallow sediment sites of Kongsfjorden and Van Keulenfjorden of Svalbard (79°N). We present five novel Woeseiales MAGs and show transcriptional evidence for metabolic plasticity during burial, including sulfur oxidation with reverse dissimilatory sulfite reductase (dsrAB) down to 4 cm depth and nitrite reduction down to 6 cm depth. A single stress protein, spore protein SP21 (hspA), had a tenfold higher mRNA abundance than any other transcript, and was a hundredfold higher on average than other transcripts. At three out of the four sites, SP21 transcript abundance increased with depth, while total mRNA abundance and richness decreased, indicating a shift in investment from metabolism and other cellular processes to build-up of spore protein SP21. The SP21 gene in MAGs was often flanked by genes involved in membrane-associated stress response. The ability of Woeseiales to shift from sulfur oxidation to nitrite reduction with burial into marine sediments with decreasing access to overlying oxic bottom waters, as well as enter into a dormant state dominated by SP21, may account for its ubiquity and high abundance in marine sediments worldwide, including those of the rapidly shifting Arctic.

Glacial influence on the iron and sulfur cycles in Arctic fjord sediments (Svalbard)

Arctic fjord sediments of Svalbard receive terrestrial material from glacial runoff and organic matter from marine primary productivity. Organic carbon mineralization proceeds primarily through sulfate and iron reduction in the fjord sediment. The ongoing retreat of glaciers in the high Arctic is altering the input of glacial material to the fjords, with unknown consequences for the iron and sulfur cycles in the fjord sediments. We measured sulfate reduction rates in sediment cores and analyzed porewater geochemistry, then compared these results to long-term sediment incubations to determine the rates of iron reduction and sulfide oxidation in three glacially influenced fjords on the west coast of Spitsbergen, Svalbard. Despite an abundance of glacially-sourced Fe(III)-oxide minerals, active sulfate reduction took place throughout the sediment. Analyses of the sulfur and oxygen isotopic composition of porewater sulfate and sulfate concentrations suggest that sulfide produced from biological sulfate reduction is reoxidized to sulfate. Long-term sediment incubations indicated sulfide oxidation at all three stations. The rate of sulfide oxidation was controlled by both the rate of sulfate reduction and the quantity and reactivity of Fe(III)-oxides. In our experimental incubations, we detected a decrease in Fe(III) content of the 0.5 M HCl and ascorbate-extractable fractions, but not in the 6 M HCl fraction, indicating that the highly reactive Fe(III) fraction is utilized by microorganisms and serves as the oxidant for sulfide oxidation. Our results show that sulfide oxidation in glacially-influenced fjord sediments is a wide-spread geochemical process. Further warming will drive glacial retreat onto land, where sediment-laden glacial meltwater will be altered during flow through proglacial streams and lakes before entering the marine environment. Fjord sediments will likely become more sulfidic, as glaciers deliver less particulate, highly-reactive metal oxides to the marine environment.

Complex Microbial Communities Drive Iron and Sulfur Cycling in Arctic Fjord Sediments.

Glacial retreat is changing biogeochemical cycling in the Arctic, where glacial runoff contributes iron for oceanic shelf primary production. We hypothesize that in Svalbard fjords, microbes catalyze intense iron and sulfur cycling in low-organic-matter sediments. This is because low organic matter limits sulfide generation, allowing iron mobility to the water column instead of precipitation as iron monosulfides. In this study, we tested this with high-depth-resolution 16S rRNA gene libraries in the upper 20 cm at two sites in Van Keulenfjorden, Svalbard. At the site closer to the glaciers, iron-reducing Desulfuromonadales, iron-oxidizing Gallionella and Mariprofundus, and sulfur-oxidizing Thiotrichales and Epsilonproteobacteria were abundant above a 12-cm depth. Below this depth, the relative abundances of sequences for sulfate-reducing Desulfobacteraceae and Desulfobulbaceae increased. At the outer station, the switch from iron-cycling clades to sulfate reducers occurred at shallower depths (∼5 cm), corresponding to higher sulfate reduction rates. Relatively labile organic matter (shown by δ13C and C/N ratios) was more abundant at this outer site, and ordination analysis suggested that this affected microbial community structure in surface sediments. Network analysis revealed more correlations between predicted iron- and sulfur-cycling taxa and with uncultured clades proximal to the glacier. Together, these results suggest that complex microbial communities catalyze redox cycling of iron and sulfur, especially closer to the glacier, where sulfate reduction is limited due to low availability of organic matter. Diminished sulfate reduction in upper sediments enables iron to flux into the overlying water, where it may be transported to the shelf.IMPORTANCE Glacial runoff is a key source of iron for primary production in the Arctic. In the fjords of the Svalbard archipelago, glacial retreat is predicted to stimulate phytoplankton blooms that were previously restricted to outer margins. Decreased sediment delivery and enhanced primary production have been hypothesized to alter sediment biogeochemistry, wherein any free reduced iron that could potentially be delivered to the shelf will instead become buried with sulfide generated through microbial sulfate reduction. We support this hypothesis with sequencing data that showed increases in the relative abundance of sulfate reducing taxa and sulfate reduction rates with increasing distance from the glaciers in Van Keulenfjorden, Svalbard. Community structure was driven by organic geochemistry, suggesting that enhanced input of organic material will stimulate sulfate reduction in interior fjord sediments as glaciers continue to recede.

Streptomyces artemisiae MCCB 248 isolated from Arctic fjord sediments has unique PKS and NRPS biosynthetic genes and produces potential new anticancer natural products

After screening marine actinomycetes isolated from sediment samples collected from the Arctic fjord Kongsfjorden for potential anticancer activity, an isolate identified as Streptomyces artemisiae MCCB 248 exhibited promising results against the NCI-H460 human lung cancer cell line. H460 cells treated with the ethyl acetate extract of strain MCCB 248 and stained with Hoechst 33342 showed clear signs of apoptosis, including shrinkage of the cell nucleus, DNA fragmentation and chromatin condensation. Further to this treated cells showed indications of early apoptotic cell death, including a significant proportion of Annexin V positive staining and evidence of DNA damage as observed in the TUNEL assay. Amplified PKS 1 and NRPS genes involved in secondary metabolite production showed only 82% similarity to known biosynthetic genes of Streptomyces, indicating the likely production of a novel secondary metabolite in this extract. Additionally, chemical dereplication efforts using LC–MS/MS molecular networking suggested the presence of a series of undescribed tetraene polyols. Taken together, these results revealed that this Arctic S. artemisiae strain MCCB 248 is a promising candidate for natural products drug discovery and genome mining for potential anticancer agents.

Relatively high antibiotic resistance among heterotrophic bacteria from arctic fjord sediments than water – Evidence towards better selection pressure in the fjord sediments

The objective of this study was to determine the prevalence of antibiotic resistance among aerobic heterotrophic bacteria and coliform bacteria from water and sediment of Kongsfjord. The study was based on the assumption that arctic fjord environments are relatively pristine and offer very little selection pressure for drug resistant mutants. In order to test the hypothesis, 200 isolates belonging to aerobic heterotrophic bacteria and 114 isolates belonging to coliforms were tested against 15 antibiotics belonging to 5 different classes such as beta lactams, aminoglycosides, quinolones, sulpha drugs and tetracyclines. Resistance to beta lactam and extended spectrum beta lactam (ESBL) antibiotics was considerably high and they found to vary significantly (p < 0.05) between heterotrophic and coliform bacteria. Though the coliforms showed significantly high level of antibiotic resistance against ESBL's extent and diversity of antibiotic resistance (as revealed by multiple antibiotic resistance index and resistance patterns), was high in the aerobic heterotrophic bacteria. Most striking observation was that isolates from fjord sediments (both heterotrophic bacteria and coliforms) in general showed relatively high prevalence of antibiotic resistance against most of the antibiotics tested, indicating to better selection pressure for drug resistance mutants in the fjord sediments.

Temperature response of denitrification and anaerobic ammonium oxidation rates and microbial community structure in Arctic fjord sediments.

The temperature dependency of denitrification and anaerobic ammonium oxidation (anammox) rates from Arctic fjord sediments was investigated in a temperature gradient block incubator for temperatures ranging from -1 to 40°C. Community structure in intact sediments and slurry incubations was determined using Illumina SSU rRNA gene sequencing. The optimal temperature (Topt ) for denitrification was 25-27°C, whereas anammox rates were optimal at 12-17°C. Both denitrification and anammox exhibited temperature responses consistent with a psychrophilic community, but anammox bacteria may be more specialized for psychrophilic activity. Long-term (1-2 months) warming experiments indicated that temperature increases of 5-10°C above in situ had little effect on the microbial community structure or the temperature response of denitrification and anammox. Increases of 25°C shifted denitrification temperature responses to mesophilic with concurrent community shifts, and anammox activity was eliminated above 25°C. Additions of low molecular weight organic substrates (acetate and lactate) caused increases in denitrification rates, corroborating the hypothesis that the supply of organic substrates is a more dominant control of respiration rates than low temperature. These results suggest that climate-related changes in sinking particulate flux will likely alter rates of N removal more rapidly than warming.

Filamentous sulfur bacteria, Beggiatoa spp., in arctic marine sediments (Svalbard, 79°N)

Fjord sediments on the west coast of the arctic archipelago Svalbard were surveyed to understand whether large filamentous sulfur bacteria of the genus Beggiatoa thrive at seawater temperatures permanently near freezing. Two sediments had abundant populations of Beggiatoa, while at six sites, only sporadic occurrences were observed. We conclude that Beggiatoa, although previously unnoticed, are widespread in these arctic fjord sediments. Beggiatoa ranged in diameter from 2 to 52 microm and, by those tested, stored nitrate in vacuoles at up to 260 mM. The 16S rRNA gene sequence of a 20-microm-wide filament is closely associated with other large, marine, nitrate-storing Beggiatoa. The Beggiatoa mostly occurred in the upper 2-5 cm of oxidized surface sediment between oxygen and the deeper sulfidic zone. In spite of a very low or an undetectable sulfide concentration, sulfate reduction provided abundant H(2)S in this zone. The total living biomass of Beggiatoa filaments at one study site varied over 3 years between 1.13 and 3.36 g m(-2). Because of their large size, Beggiatoa accounted for up to 15% of the total prokaryotic biomass, even though the filament counts at this site were rather low, comprising <1/10,000 of the bacterial numbers on a cell basis.

Contamination of arctic Fjord sediments by Pb–Zn mining at Maarmorilik in central West Greenland

This study focuses on heavy metal contamination of arctic sediments from a small Fjord system adjacent to the Pb–Zn “Black Angel” mine (West Greenland) to investigate the temporal and spatial development of contamination and to provide baseline levels before the mines re-opening in January 2009. For this purpose we collected multi-cores along a transect from Affarlikassaa Fjord, which received high amounts of tailings from 1973 to 1990, to the mouth of Qaumarujuk Fjord. Along with radiochemical dating by 210Pb and 137Cs, geochemical analyses of heavy metals (e.g. As, Cd, Hg, Pb, and Zn) were carried out. Maximum contents were found at 12 cm depth in Affarlikassaa. After 17 years the mine last closed, specific local hydrographic conditions continue to disperse heavy metal enriched material derived from the Affarlikassaa into Qaumarujuk. Total Hg profiles from multi-cores along the transect clearly illustrate this transport and spatial distribution pattern of the contaminated material.

Direct determination of nitrogen cycling rates and pathways in Arctic fjord sediments (Svalbard, Norway)

Results from a study of benthic nitrogen cycling in two Arctic fjords are presented. Intact sediment core incubations were used to quantify net fluxes of dissolved inorganic nitrogen, organic nitrogen, organic carbon, and oxygen across the sediment‐water interface. Rates of gross denitrification, anammox, nitrification, dissimilatory nitrate reduction to ammonium, and N2 fixation were quantified using core incubations and slurry experiments. Profiles of dissolved inorganic nitrogen in pore‐water, and organic carbon and nitrogen contents in the solid phase, were also obtained. Net nitrogen losses as N2, measured directly as changes in N2 : Ar, ranged from 152 µmol N m−2 d−1 to 453 µmol N m−2 d−1. Gross denitrification, as determined using 15N‐NO3− tracers, was 34–294 µmol N m−2 d−1. Rates of anammox ranged from 10 µmol N m−2 d−1 to 26 µmol N m−2 d−1 and contributed 5–23% of gross N2 generation. Nitrification rates were as high as 833 µmol N m−2 d−1 and sediments were a substantial source of nitrate to the water column (169–393 µmol N m−2 d−1 efflux). Uptake of ammonium (52–87 µmol N m−2 d−1), dissolved organic nitrogen (291‐486 µmol N m−2 d−1), and dissolved organic carbon (1313–2504 µmol N m−2 d−1) were observed. Nitrogen loss from the seafloor is shown to occur at rates comparable to temperate coastal environments and the sediments provide a substantial source of nitrate to the water column of Arctic fjords. In addition, anammox is confirmed as an important pathway in Arctic marine sediments, although N2 production is dominated by denitrification.

Direct determination of nitrogen cycling rates and pathways in Arctic fjord sediments (Svalbard, Norway)

Results from a study of benthic nitrogen cycling in two Arctic fjords are presented. Intact sediment core incubations were used to quantify net fluxes of dissolved inorganic nitrogen, organic nitrogen, organic carbon, and oxygen across the sediment-water interface. Rates of gross denitrification, anammox, nitrification, dissimilatory nitrate reduction to ammonium, and N2 fixation were quantified using core incubations and slurry experiments. Profiles of dissolved inorganic nitrogen in pore-water, and organic carbon and nitrogen contents in the solid phase, were also obtained. Net nitrogen losses as N2, measured directly as changes in N2 : Ar, ranged from 152 µmol N m−2 d−1 to 453 µmol N m−2 d−1. Gross denitrification, as determined using 15N-NO3− tracers, was 34–294 µmol N m−2 d−1. Rates of anammox ranged from 10 µmol N m−2 d−1 to 26 µmol N m−2 d−1 and contributed 5–23% of gross N2 generation. Nitrification rates were as high as 833 µmol N m−2 d−1 and sediments were a substantial source of nitrate to the water column (169–393 µmol N m−2 d−1 efflux). Uptake of ammonium (52–87 µmol N m−2 d−1), dissolved organic nitrogen (291-486 µmol N m−2 d−1), and dissolved organic carbon (1313–2504 µmol N m−2 d−1) were observed. Nitrogen loss from the seafloor is shown to occur at rates comparable to temperate coastal environments and the sediments provide a substantial source of nitrate to the water column of Arctic fjords. In addition, anammox is confirmed as an important pathway in Arctic marine sediments, although N2 production is dominated by denitrification.