Canadian High Arctic Research Articles

First palaeointensity data from the cryogenian and their potential implications for inner core nucleation age

SUMMARY The timing of inner core nucleation is a hugely significant event in Earth's evolution and has been the subject of intense debate. Some of the most recent theoretical estimates for the age of nucleation fall throughout the Neoproterozoic era; much younger than previously thought. A young inner core requires faster recent core cooling rates and a likely hotter early core; knowledge of its age would be invaluable in understanding Earth's thermal history and total energy budget. Predictions generated by numerical dynamo models need to be tested against such data, but records are currently much too sparse to constrain the event to a precise period of time. Here, we present results from 720 Ma dolerite dykes (and one sill) from the Franklin Large Igneous Province, which fall within a crucial 300 Myr gap in palaeointensity records. This study uses three independent techniques on whole rocks from 11 sites spread across High Arctic Canada and Greenland to produce virtual dipole moments ranging from 5 to 20 ZAm2 (mean 11 ZAm2); almost one order of magnitude lower than the present-day field. These weak-field results agree with recent ultralow palaeointensity data obtained from Ediacaran rocks formed ∼150 Myr later and may support that the dynamo was on the brink of collapse in the Neoproterozoic prior to a young inner core formation date.

Holocene ice wedge formation in the Eureka Sound Lowlands, high Arctic Canada

AbstractIce wedges are ubiquitous periglacial features in permafrost terrain. This study investigates the timing of ice wedge formation in the Fosheim Peninsula (Ellesmere and Axel Heiberg Islands). In this region, ice wedge polygons occupy ~50% of the landscape, the majority occurring below the marine limit in the Eureka Sound Lowlands. Numerical simulations suggest that ice wedges may crack to depths of 2.7–3.6 m following a rapid cooling of the ground over mean winter surface temperatures of −18°C to −38°C, corresponding to the depth of ice wedges in the region. The dissolved organic carbon (DOC)/Cl molar ratios suggest that the DOC in the ice wedges is sourced from snowmelt and not from leaching of the active layer. Based on 3214CDOCmeasurements from 15 ice wedges, the wedges were likely developing between 9000–2500 cal yr BP. This interval also corresponds to the period of peat accumulation in the region, a proxy of increased moisture. Considering that winter air temperatures remained favorable for ice wedge growth throughout the Holocene, the timing of ice wedge formation reflects changes in snowfall. Overall, this study provides the first reconstruction of ice wedge formation from a high Arctic polar desert environment.

Genomic evidence for sulfur intermediates as new biogeochemical hubs in a model aquatic microbial ecosystem

BackgroundThe sulfur cycle encompasses a series of complex aerobic and anaerobic transformations of S-containing molecules and plays a fundamental role in cellular and ecosystem-level processes, influencing biological carbon transfers and other biogeochemical cycles. Despite their importance, the microbial communities and metabolic pathways involved in these transformations remain poorly understood, especially for inorganic sulfur compounds of intermediate oxidation states (thiosulfate, tetrathionate, sulfite, polysulfides). Isolated and highly stratified, the extreme geochemical and environmental features of meromictic ice-capped Lake A, in the Canadian High Arctic, provided an ideal model ecosystem to resolve the distribution and metabolism of aquatic sulfur cycling microorganisms along redox and salinity gradients.ResultsApplying complementary molecular approaches, we identified sharply contrasting microbial communities and metabolic potentials among the markedly distinct water layers of Lake A, with similarities to diverse fresh, brackish and saline water microbiomes. Sulfur cycling genes were abundant at all depths and covaried with bacterial abundance. Genes for oxidative processes occurred in samples from the oxic freshwater layers, reductive reactions in the anoxic and sulfidic bottom waters and genes for both transformations at the chemocline. Up to 154 different genomic bins with potential for sulfur transformation were recovered, revealing a panoply of taxonomically diverse microorganisms with complex metabolic pathways for biogeochemical sulfur reactions. Genes for the utilization of sulfur cycle intermediates were widespread throughout the water column, co-occurring with sulfate reduction or sulfide oxidation pathways. The genomic bin composition suggested that in addition to chemical oxidation, these intermediate sulfur compounds were likely produced by the predominant sulfur chemo- and photo-oxidisers at the chemocline and by diverse microbial degraders of organic sulfur molecules.ConclusionsThe Lake A microbial ecosystem provided an ideal opportunity to identify new features of the biogeochemical sulfur cycle. Our detailed metagenomic analyses across the broad physico-chemical gradients of this permanently stratified lake extend the known diversity of microorganisms involved in sulfur transformations over a wide range of environmental conditions. The results indicate that sulfur cycle intermediates and organic sulfur molecules are major sources of electron donors and acceptors for aquatic and sedimentary microbial communities in association with the classical sulfur cycle.-hYdWkMRSgNRZXNRu4CdmLVideo abstract

Water column gradients beneath the summer ice of a High Arctic freshwater lake as indicators of sensitivity to climate change

Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at > 150% saturation in a mid-water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime.

Flexibility in migratory strategy contrasts with reliance on restricted staging and overwintering grounds for Sabine’s gulls from the Canadian High Arctic

Abstract Sabine’s gulls (Xema sabini) undertake the longest migration of any gull, a trans-equatorial journey between Arctic breeding and southern hemisphere wintering areas. For such long-distance migrants, quantifying within- and between-individual variation in migratory strategy is key towards understanding resilience to environmental variability encountered over migration. We tracked 22 birds on 32 migrations from the Canadian Arctic to evaluate strategies and quantify flexibility among individuals and years. All birds undertook extended stopovers in a geographically-restricted staging area halfway through migration in the California Current System in both directions. Individuals were otherwise flexible in most aspects of migration but were repeatable in arrival date and duration of the southbound staging phase. Routes taken during southbound migration and overlap in overwintering areas were significantly larger within the same year than among years. Overall, birds showed high individual flexibility in migratory strategies but made similar decisions to one another in the same years. Every year, all birds showed repeatable, consistent reliance on the staging grounds as a key stopover site in both directions. This suggests Sabine’s gulls adjust to environmental change in many aspects of their migration but may be vulnerable to climate change and other anthropogenic influences during critical stages of the journey.

Fatty acids and stable isotope signatures of first-year and multiyear sea ice in the Canadian High Arctic

Ice algae are critical components to the lipid-driven Arctic marine food web, particularly early in the spring. As little is known about these communities in multiyear ice (MYI), we aimed to provide a baseline of fatty acid (FA) and stable isotope signatures of sea-ice communities in MYI from the Lincoln Sea and compare these biomarkers to first-year ice (FYI). Significant differences in the relative proportions of approximately 25% of the identified FAs and significantly higher nitrogen stable isotope values (δ15N) in bottom-ice samples of FYI (δ15N = 6.4 ± 0.7%) compared to MYI (δ15N = 5.0 ± 0.4%) reflect different community compositions in the two ice types. Yet, the relative proportion of diatom- and dinoflagellate-associated FAs, as well as their bulk and most of the FA-specific carbon stable isotope compositions (δ13C) were not significantly different between bottom FYI (bulk δ13C: –28.4% to –26.7%, FA average δ13C: –34.4% to –31.7%) and MYI (bulk δ13C: –27.6% to –27.2%, FA average δ13C: –33.6% to –31.9%), suggesting at least partly overlapping community structures and similar biochemical processes within the ice. Diatom-associated FAs contributed, on average, 28% and 25% to the total FA content of bottom FYI and MYI, respectively, indicating that diatoms play a central role in structuring sea-ice communities in the Lincoln Sea. The differences in FA signatures of FYI and MYI support the view that different ice types harbor different inhabitants and that the loss of Arctic MYI will impact complex food web interactions with ice-associated ecosystems. Comparable nutritional quality of FAs, however, as indicated by similar average levels of polyunsaturated FAs in bottom FYI (33%) and MYI (28%), could help to ensure growth and reproduction of ice-associated grazers despite the shift from a MYI to FYI-dominated sea-ice cover with ongoing climate warming.

Narwhal Abundance in the Eastern Canadian High Arctic in 2013

In summer, narwhals (Monodon monoceros) migrate from Baffin Bay to northeastern Canada and northwest Greenland, where they are hunted by Inuit for subsistence. To prevent localized depletion, management of narwhals is based on summer stocks. The High Arctic Cetacean Survey (HACS), conducted in August 2013, was the first survey to estimate abundance of all 4 Canadian Baffin Bay narwhal summer stocks, as well as putative stocks in Jones Sound and Smith Sound, in the same summer. Narwhal abundance was estimated using a double-platform aerial survey. Distance sampling methods were used to estimate detection probability away from the track line. Mark-recapture methods were used to correct for the proportion of narwhals missed by visual observers on the track line (i.e., perception bias). We used a data-driven approach to identify single and duplicate sightings, using 4 covariates to compare differences in sightings made by front and rear observers based on: time of sighting, declination angle, group size, and species identity. Abundance in fjords was estimated using density surface modelling to account for their complex shape and uneven coverage. Estimates were corrected for availability bias (narwhals that are not available for detection because they are submerged when the aircraft passes overhead) using a new analysis of August dive behaviour data from narwhals equipped with satellite-linked time depth recorders. Corrected abundance estimates were 12,694 (95% CI: 6,324–25,481) for the Jones Sound stock; 16,360 (95% CI: 3,833–69,836) for the Smith Sound stock; 49,768 (95% CI: 32,945–75,182) for the Somerset Island stock; 35,043 (95% CI: 14,188–86,553) for the Admiralty Inlet stock; 10,489 (95% CI: 6,342–17,347) for the Eclipse Sound stock; and 17,555 (95% CI: 8,473–36,373) for the East Baffin Island stock. Total abundance for these 6 stocks was estimated at 141,908 (95% CI: 102,464–196,536). Sources of uncertainty arise from the high level of clustering observed, in particular in Admiralty Inlet, Eclipse Sound, and East Baffin Island, as well as the difficulty in identifying duplicate sightings between observers when large aggregations were encountered.

RADARSAT-2 Derived Glacier Velocities and Dynamic Discharge Estimates for the Canadian High Arctic: 2015–2020

RADARSAT-2 imagery collected each winter from 2015/2016 to 2019/2020 is used to quantify and characterize the variability in the motion of, and the discharge from, the major marine-terminating ice masses of the Queen Elizabeth Islands (QEI: Devon, Ellesmere and Axel Heiberg Islands) in the Canadian High Arctic. The majority of the glaciers did not experience significant variations in flow speeds over the observation period, and for most that did the variations are attributed to pulse and surge processes. However, there are exceptions where the velocity record indicates continued acceleration of the glaciers by processes that appear distinct from surging or pulsing, such as dynamic thinning. These include Trinity and Wykeham glaciers (Prince of Wales Icefield) and Belcher Glacier (Devon Ice Cap). The combination of surface velocities with ice thicknesses indicates that average ice discharge to the ocean for the QEI over the observation period was 2.78 ± 0.52 Gt a−1 (ranging between ∼2.37 ± 0.48 Gt a−1 and ∼3.20 ± 0.55 Gt a−1), ∼50% of which was channeled through the Trinity-Wykeham glacier basin alone. The results presented here, combined with those of previous studies, provide a comprehensive record of ice motion and discharge from the QEI between 2008 and 2020.

The littoral zone of polar lakes: inshore–offshore contrasts in an ice-covered High Arctic lake

In ice-covered polar lakes, a narrow ice-free moat opens up in spring or early summer, and then persists at the edge of the lake until complete ice loss or refreezing. In this study, we analyzed the horizontal gradients in Ward Hunt Lake, located in the Canadian High Arctic, and addressed the hypothesis that the transition from its nearshore open-water moat to offshore ice-covered waters is marked by discontinuous shifts in limnological properties. Consistent with this hypothesis, we observed an abrupt increase in below-ice concentrations of chlorophyll a beyond the ice margin, along with a sharp decrease in temperature and light availability and pronounced changes in benthic algal pigments and fatty acids. There were higher concentrations of rotifers and lower concentrations of viruses at the ice-free sampling sites, and contrasts in zooplankton fatty acid profiles that implied a greater importance of benthic phototrophs in their inshore diet. The observed patterns underscore the structuring role of ice cover in polar lakes. These ecosystems do not conform to the traditional definitions of littoral versus pelagic zones but instead may have distinct moat, ice-margin, and ice-covered zones. This zonation is likely to weaken with ongoing climate change.

Measurements of Tropospheric Bromine Monoxide Over Four Halogen Activation Seasons in the Canadian High Arctic

AbstractBromine explosions and corresponding ozone depletion events are common in the Arctic spring. The snowpack on sea ice and sea salt aerosols (SSA) are both thought to release bromine, but the relative contribution of each source is not yet known. Furthermore, the role of atmospheric conditions is not fully understood. Long‐term measurements of bromine monoxide (BrO) provide useful insight into the underlying processes of bromine activation. Here we present a 4‐year data set (2016–2019) of springtime BrO partial columns retrieved from Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS) measurements in Eureka, Canada (80.1°N, 86.4°W, 610 m asl). Due to the elevation of the measurement site, the instrument often measures BrO in the free troposphere, except during strong wind episodes and storms that generate a deep boundary layer. Enhanced vertical mixing due to strong winds leads to increasing BrO values and reduced ozone depletion. We find that BrO enhancements show two modes differentiated by local wind direction and air mass history. Longer time spent by the airmass in first‐year sea ice areas corresponds to increased BrO for one of these modes only. Furthermore, we argue that snow on multiyear ice might also contribute to bromine release. High aerosol optical depth is required to maintain lofted BrO, and we show that the presence of coarse‐mode aerosols (>0.5 μm, likely SSA) is a necessary and sufficient condition for observing BrO at our elevated measurement site in Eureka. This work highlights the importance of considering variable local conditions when characterizing bromine activation.

Biotic interactions govern the distribution of coexisting ungulates in the Arctic Archipelago – A case for conservation planning

Climate change and biodiversity loss underscore the need for conservation planning, even in remote areas. Species distribution models (SDMs) can help identify critical habitat for reserve design and selection, and have quickly advanced to the fore of ecological inquiry. Such models are typically dominated by abiotic factors, following the Eltonian Noise Hypothesis (ENH) that physical features set the limits of species distributions. Nevertheless, recent studies challenge this notion and highlight the importance of biotic interactions. Resolving this discrepancy could have significant implications for conservation and ecological understanding. To test these ideas, we built distribution models for two large herbivores, muskoxen (Ovibos muschatus) and Peary caribou (Rangifer tarandus pearyi), systematically observed across a vast spatial extent – 65 islands spanning 800,000 km2 in the Canadian High Arctic. To test the ENH we fit SDMs with two sets of predictors: (1) abiotic only (i.e. topographic, climatic) and (2) abiotic + biotic (i.e. vegetation communities, distance-to-heterospecifics). We evaluated these models and spatially estimated habitat suitability for each species. We found both sets of models had good predictive ability, although biotic variables (i.e. proportion of grass-lichen-moss) improved model performance and substantially narrowed areas of high habitat suitability. Niche overlap between caribou and muskoxen was moderate and highly suitable areas were spatially disjunct between species and largely outside protected areas. These results fail to support the ENH. Our study implies that biotic features, although often overlooked, may be important to the performance of SDMs and vital in identifying priority areas for conservation. For these large herbivores, reflecting trophic interactions in SDMs was essential when estimating areas of conservation value. Our approach helps prepare the way for improved projections regarding the prospects for wildlife while laying the foundation for biologically relevant protected areas.

Zircon geochronology and geochemistry of the Ward Hunt pluton, Pearya terrane, Canadian High Arctic: Insights into its age, origin, and circum-Arctic Timanide connections

The northern margin of the Neoproterozoic Timanide Orogen is truncated by Paleozoic deformation of the Caledonian Orogen. Evidence for dispersion of terranes affected by the Timanide Orogen is documented through contemporaneous tectonothermal activity, and by detrital zircon in sedimentary rock from across the Arctic Ocean margins. However, directly tying these terranes to the Caledonide realm is hindered by the paucity of appropriate events in proximal terranes. The Ward Hunt Pluton, a previously undated syenite–monzodiorite intrusion located on Ward Hunt Island, northern Pearya terrane, yields a crystallization age of 542 ± 2 Ma. Trace-element data from the igneous zircon suggest that the pluton intruded older metasedimentary rocks of the terrane as part of a volcanic arc system, indicated by juvenile Hf isotopic signatures and trace-element data. The data support links between the Pearya terrane and other Neoproterozoic–Cambrian arc systems, such as those proposed in Arctic Alaska-Chukota and the Alexander terrane.

Microbial Metabolic Redundancy Is a Key Mechanism in a Sulfur-Rich Glacial Ecosystem.

Biological sulfur cycling in polar, low-temperature ecosystems is an understudied phenomenon in part due to difficulty of access and the dynamic nature of glacial environments. One such environment where sulfur cycling is known to play an important role in microbial metabolisms is located at Borup Fiord Pass (BFP) in the Canadian High Arctic. Here, transient springs emerge from ice near the terminus of a glacier, creating a large area of proglacial aufeis (spring-derived ice) that is often covered in bright yellow/white sulfur, sulfate, and carbonate mineral precipitates accompanied by a strong odor of hydrogen sulfide. Metagenomic sequencing of samples from multiple sites and of various sample types across the BFP glacial system produced 31 metagenome-assembled genomes (MAGs) that were queried for sulfur, nitrogen, and carbon cycling/metabolism genes. An abundance of sulfur cycling genes was widespread across the isolated MAGs and sample metagenomes taxonomically associated with the bacterial classes Alphaproteobacteria and Gammaproteobacteria and Campylobacteria (formerly the Epsilonproteobacteria). This corroborates previous research from BFP implicating Campylobacteria as the primary class responsible for sulfur oxidation; however, data reported here suggested putative sulfur oxidation by organisms in both the alphaproteobacterial and gammaproteobacterial classes that was not predicted by previous work. These findings indicate that in low-temperature, sulfur-based environments, functional redundancy may be a key mechanism that microorganisms use to enable coexistence whenever energy is limited and/or focused by redox chemistry.IMPORTANCE A unique environment at Borup Fiord Pass is characterized by a sulfur-enriched glacial ecosystem in the low-temperature Canadian High Arctic. BFP represents one of the best terrestrial analog sites for studying icy, sulfur-rich worlds outside our own, such as Europa and Mars. The site also allows investigation of sulfur-based microbial metabolisms in cold environments here on Earth. Here, we report whole-genome sequencing data that suggest that sulfur cycling metabolisms at BFP are more widely used across bacterial taxa than predicted. From our analyses, the metabolic capability of sulfur oxidation among multiple community members appears likely due to functional redundancy present in their genomes. Functional redundancy, with respect to sulfur-oxidation at the BFP sulfur-ice environment, may indicate that this dynamic ecosystem hosts microorganisms that are able to use multiple sulfur electron donors alongside other metabolic pathways, including those for carbon and nitrogen.

Extreme warming and regime shift toward amplified variability in a far northern lake

AbstractMean annual air temperatures in the High Arctic are rising rapidly, with extreme warming events becoming increasingly common. Little is known, however, about the consequences of such events on the ice‐capped lakes that occur abundantly across this region. Here, we compared 2 years of high‐frequency monitoring data in Ward Hunt Lake in the Canadian High Arctic. One of the years included a period of anomalously warm conditions that allowed us to address the question of how loss of multi‐year ice cover affects the limnological properties of polar lakes. A mooring installed at the deepest point of the lake (9.7 m) recorded temperature, oxygen, chlorophyll a (Chl a) fluorescence, and underwater irradiance from July 2016 to July 2018, and an automated camera documented changes in ice cover. The complete loss of ice cover in summer 2016 resulted in full wind exposure and complete mixing of the water column. This mixing caused ventilation of lake water heat to the atmosphere and 4°C lower water temperatures than under ice‐covered conditions. There were also high values of Chl a fluorescence, elevated turbidity levels and large oxygen fluctuations throughout fall and winter. During the subsequent summer, the lake retained its ice cover and the water column remained stratified, with lower Chl a fluorescence and anoxic bottom waters. Extreme warming events are likely to shift polar lakes that were formerly capped by continuous thick ice to a regime of irregular ice loss and unstable limnological conditions that vary greatly from year to year.

The identification of sulfide oxidation as a\xa0potential metabolism driving primary production on late Noachian Mars

The transition of the martian climate from the wet Noachian era to the dry Hesperian (4.1–3.0 Gya) likely resulted in saline surface waters that were rich in sulfur species. Terrestrial analogue environments that possess a similar chemistry to these proposed waters can be used to develop an understanding of the diversity of microorganisms that could have persisted on Mars under such conditions. Here, we report on the chemistry and microbial community of the highly reducing sediment of Colour Peak springs, a sulfidic and saline spring system located within the Canadian High Arctic. DNA and cDNA 16S rRNA gene profiling demonstrated that the microbial community was dominated by sulfur oxidising bacteria, suggesting that primary production in the sediment was driven by chemolithoautotrophic sulfur oxidation. It is possible that the sulfur oxidising bacteria also supported the persistence of the additional taxa. Gibbs energy values calculated for the brines, based on the chemistry of Gale crater, suggested that the oxidation of reduced sulfur species was an energetically viable metabolism for life on early Mars.

Pulsed food resources affect reproduction but not adult apparent survival in arctic foxes.

As top or mesopredators, carnivores play a key role in food webs. Their survival and reproduction are usually thought to be influenced by prey availability. However, simultaneous monitoring of prey and predators is difficult, making it challenging to evaluate the impacts of prey on carnivores' demography. Using 13years of field data on arctic foxes Vulpes lagopus in the Canadian High Arctic and a capture-recapture multi-event statistical approach, we investigated the hypothesis that increases in lemming abundance (a cyclic and unpredictable food source) and goose colony proximity (a stable but spatially and temporally limited food source) would be associated with increased apparent survival and reproduction probabilities of adults. Adult apparent survival varied greatly across years (0.13-1.00) but was neither affected by lemming nor goose variations in abundance. However, reproduction probabilities were strongly influenced by both lemming abundance and access to the goose colony. A fox breeding in the best conditions of food availability (year of high lemming density inside the goose colony) had a reproduction probability four times higher than one experiencing the worst conditions (year of low lemming density outside the goose colony). Breeding status of individuals also played a role, with breeders having a 10-20% higher probability of survival and 30% higher probability of reproduction the following year than non-breeders. As the Arctic ecosystem changes due to increased temperatures and species ranges, this study will allow better predictions of predator responses to management or environmental changes and a better understanding of ecosystem functioning.

Seismic anisotropy of the Canadian High Arctic: Evidence from shear-wave splitting

The Canadian High Arctic preserves a long and complex tectonic history, including craton formation, multiple periods of orogenesis, extension and basin formation, and the development of a passive continental margin. We investigate the possible preservation of deformational structures throughout the High Arctic subcontinental lithosphere using measurements of seismic anisotropy from shear wave splitting at 11 seismograph stations across the region, including a N-S transect along Ellesmere Island. The majority of measurements indicate a fast-polarisation orientation that parallels tectonic trends and boundaries, suggesting that lithospheric deformation is the dominant source of seismic anisotropy in the High Arctic; however, a sub-lithospheric contribution cannot be ruled out. Beneath Resolute in the central Canadian Arctic, distinct back-azimuthal variations in splitting parameters can be explained by two anisotropic layers. The upper layer is oriented E–W and correlates with tectonic trends and the inferred lithospheric deformation history of the region. The lower layer has a ∼NNE–SSW orientation and may arise from present-day convective mantle flow beneath locally-thinned continental lithosphere. In addition to inferences of anisotropic structure beneath the Canadian High Arctic, measurements from the far north of our study region suggest the presence of an anisotropic zone in the lowermost mantle beneath northwest Alaska.

Reproduction of a bathyal pennatulacean coral in the Canadian Arctic

While reproduction in deep-sea corals remains incompletely understood, there is a particularly crucial shortage of information related to corals living in deep waters of the Arctic Ocean. In the present study, colonies of the deep-sea pennatulacean coral Umbellula encrinus were collected in Baffin Bay (High Canadian Arctic) at bathyal depths between 2006 and 2010. From examination of gamete sizes, maturity levels and densities at several time points, U. encrinus was determined to be a gonochoric species with an equal sex ratio and a broadcast-spawning strategy. Fully mature oocytes measured between 800 and 950 μm in diameter, consistent with lecithotrophic larval development. Potential fecundity was ~4200 mature oocytes colony−1 and ~5300 mature spermatocysts colony−1. Gametogenesis was synchronous between sexes; a single main cohort of oocytes and spermatocysts was seen to increase in size throughout the year. Gametogenetically mature colonies were detected in late June during the earliest possible spring samplings. Spent colonies were detected in July and August. Early stages of gametogenesis appeared in early September shortly after the spawning months and more advanced growth stages occurred in late September and early November, after which time sampling was prevented by ice cover. The spawning season in U. encrinus appears to occur once a year, closely following the disappearance of the ice cover, when chlorophyll-a in Baffin Bay increases. The initiation of gametogenesis coincides with a period of sustained phytoplankton production and continues until the entire bay freezes over in fall. Since mature gametes were found in both male and female colonies just after the spring melt, gamete maturation likely continues under the ice. Both depth and latitude were shown to impact gamete development and fecundity in U. encrinus, with more advanced and fertile colonies occurring in deeper water and at higher latitudes.

Extreme Viral Partitioning in a Marine-Derived High Arctic Lake.

High-latitude, perennially stratified (meromictic) lakes are likely to be especially vulnerable to climate warming because of the importance of ice in maintaining their water column structure and associated distribution of microbial communities. This study aimed to characterize viral abundance, diversity, and distribution in a meromictic lake of marine origin on the far northern coast of Ellesmere Island, in the Canadian High Arctic. We collected triplicate samples for double-stranded DNA (dsDNA) viromics from five depths that encompassed the major features of the lake, as determined by limnological profiling of the water column. Viral abundance and virus-to-prokaryote ratios were highest at greater depths, while bacterial and cyanobacterial counts were greatest in the surface waters. The viral communities from each zone of the lake defined by salinity, temperature, and dissolved oxygen concentrations were markedly distinct, suggesting that there was little exchange of viral types among lake strata. Ten viral assembled genomes were obtained from our libraries, and these also segregated with depth. This well-defined structure of viral communities was consistent with that of potential hosts. Viruses from the monimolimnion, a deep layer of ancient Arctic Ocean seawater, were more diverse and relatively abundant, with few similarities to available viral sequences. The Lake A viral communities also differed from published records from the Arctic Ocean and meromictic Ace Lake in Antarctica. This first characterization of viral diversity from this sentinel environment underscores the microbial richness and complexity of an ecosystem type that is increasingly exposed to major perturbations in the fast-changing Arctic.IMPORTANCE The Arctic is warming at an accelerating pace, and the rise in temperature has increasing impacts on the Arctic biome. Lakes are integrators of their surroundings and thus excellent sentinels of environmental change. Despite their importance in the regulation of key microbial processes, viruses remain largely uncharacterized in Arctic lacustrine environments. We sampled a highly stratified meromictic lake near the northern limit of the Canadian High Arctic, a region in rapid transition due to climate change. We found that the different layers of the lake harbored viral communities that were strikingly dissimilar and highly divergent from known viruses. Viruses were more abundant in the deepest part of the lake containing ancient Arctic Ocean seawater that was trapped during glacial retreat and were genomically unlike any viruses previously described. This research demonstrates the complexity and novelty of viral communities in an environment that is vulnerable to ongoing perturbation.

The Limits of Empirical Electron Density Modeling: Examining the Capacity of E‐CHAIM and the IRI for Modeling Intermediate (1‐ to 30‐Day) Timescales at High Latitudes

AbstractThe Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM) is a new empirical 3‐D electron density model intended as an alternative to the use of conventional standards, such as the International Reference Ionosphere (IRI), at high latitudes (above 50°N). In this study, we have manually scaled a year of data from two Canadian High Arctic Ionospheric Network (CHAIN) ionosondes. Using this high‐quality data, we examine the behavior of the polar cap ionosphere under disturbed geomagnetic conditions and assess the capacity of E‐CHAIM to model polar cap F2‐peak electron density variability on “weather‐like,” intermediate timescales (1–30 days). This is a particularly challenging environment for monthly median empirical models due to the regular occurrence of variations about the monthly mean of up to 2 MHz. We demonstrate in this study that E‐CHAIM's storm model is capable of explaining 4 to 25% of polar cap foF2 variance at 1‐ to 30‐day timescales and 5 to 50% of the amplitude of that variability, while the IRI's Storm‐Time Ionospheric Correction Model (STORM) only explains 0.2 to 9% of the variance at these timescales and no more than 5% of their amplitude. While the IRI's STORM model provided no measurable improvement over the monthly median, E‐CHAIM's storm parameterization was able to improve overall root‐mean‐square errors by 0.05 to 0.1 MHz over its quiet time model. The overall improvement through the use of storm foF2 parameterizations is found to be limited, but measurable, particularly during storm periods, where an average improvement in root‐mean‐square error of 20% is observed.