Comparison of Microstructure of White Winter Fur and Brown Summer Fur of Some Arctic Mammals

Abstract Several species of Arctic mammals have brown hair in the summer and molt into a white pelage in the winter. It is unknown whether characteristics other than color of the hair also change during the color transition between seasons. We borrowed guard hair samples from museums to represent summer and winter pelages of five species: Alopex lagopus (Arctic fox), Lepus americanus (snowshoe hare), Lepus Arcticus (Arctic hare), Mustela erminea (ermine) and Mustela nivalis (least weasel). Micro-structural differences exist between the brown and white hairs. In general, white winter hairs had larger upper shaft medullas comprising more air-filled cells and smaller lower shafts. These structural changes may function in conservation of heat or in increasing light reflection to whiten the fur and aid as camouflage. © 1997 Published by Elsevier Science Ltd on behalf of The Royal Swedish Academy of Sciences.     

Urea Uptake and Carbon Fixation by Marine Pelagic Bacteria and Archaea during the Arctic Summer and Winter Seasons

How Arctic climate change might translate into alterations of biogeochemical cycles of carbon (C) and nitrogen (N) with respect to inorganic and organic N utilization is not well understood. This study combined ¹⁵N uptake rate measurements for ammonium, nitrate, and urea with ¹⁵N- and ¹³C-based DNA stable-isotope probing (SIP). The objective was to identify active bacterial and archeal plankton and their role in N and C uptake during the Arctic summer and winter seasons. We hypothesized that bacteria and archaea would successfully compete for nitrate and urea during the Arctic winter but not during the summer, when phytoplankton dominate the uptake of these nitrogen sources. Samples were collected at a coastal station near Barrow, AK, during August and January. During both seasons, ammonium uptake rates were greater than those for nitrate or urea, and nitrate uptake rates remained lower than those for ammonium or urea. SIP experiments indicated a strong seasonal shift of bacterial and archaeal N utilization from ammonium during the summer to urea during the winter but did not support a similar seasonal pattern of nitrate utilization. Analysis of 16S rRNA gene sequences obtained from each SIP fraction implicated marine group I Crenarchaeota (MGIC) as well as Betaproteobacteria, Firmicutes, SAR11, and SAR324 in N uptake from urea during the winter. Similarly, ¹³C SIP data suggested dark carbon fixation for MGIC, as well as for several proteobacterial lineages and the Firmicutes. These data are consistent with urea-fueled nitrification by polar archaea and bacteria, which may be advantageous under dark conditions.     

Potential for Mercury Reduction by Microbes in the High Arctic

The contamination of polar regions due to the global distribution of anthropogenic pollutants is of great concern because it leads to the bioaccumulation of toxic substances, methylmercury among them, in Arctic food chains. Here we present the first evidence that microbes in the high Arctic possess and express diverse merA genes, which specify the reduction of ionic mercury [Hg(II)] to the volatile elemental form [Hg(0)]. The sampled microbial biomass, collected from microbial mats in a coastal lagoon and from the surface of marine macroalgae, was comprised of bacteria that were most closely related to psychrophiles that had previously been described in polar environments. We used a kinetic redox model, taking into consideration photoredox reactions as well as mer-mediated reduction, to assess if the potential for Hg(II) reduction by Arctic microbes can affect the toxicity and environmental mobility of mercury in the high Arctic. Results suggested that mer-mediated Hg(II) reduction could account for most of the Hg(0) that is produced in high Arctic waters. At the surface, with only 5% metabolically active cells, up to 68% of the mercury pool was resolved by the model as biogenic Hg(0). At a greater depth, because of incident light attenuation, the significance of photoredox transformations declined and merA-mediated activity could account for up to 90% of Hg(0) production. These findings highlight the importance of microbial redox transformations in the biogeochemical cycling, and thus the toxicity and mobility, of mercury in polar regions.     

Ammonia-oxidizing Archaea in the Arctic Ocean and Antarctic coastal waters

We compared abundance, distributions and phylogenetic composition of Crenarchaeota and ammonia-oxidizing Archaea (AOA) in samples collected from coastal waters west of the Antarctic Peninsula during the summers of 2005 and 2006, with samples from the central Arctic Ocean collected during the summer of 1997. Ammonia-oxidizing Archaea and Crenarchaeota abundances were estimated from quantitative PCR measurements of amoA and 16S rRNA gene abundances. Crenarchaeota and AOA were approximately fivefold more abundant at comparable depths in the Antarctic versus the Arctic Ocean. Crenarchaeota and AOA were essentially absent from the Antarctic Summer Surface Water (SSW) water mass (0–45 m depth). The ratio of Crenarchaeota 16S rRNA to archaeal amoA gene abundance in the Winter Water (WW) water mass (45–105 m depth) of the Southern Ocean was much lower (0.15) than expected and in sharp contrast to the ratio (2.0) in the Circumpolar Deep Water (CDW) water mass (105–3500 m depth) immediately below it. We did not observe comparable segregation of this ratio by depth or water mass in Arctic Ocean samples. A ubiquitous, abundant and polar-specific crenarchaeote was the dominant ribotype in the WW and important in the upper halocline of the Arctic Ocean. Our data suggest that this organism does not contain an ammonia monooxygenase gene. In contrast to other studies where Crenarchaeota populations apparently lacking amoA genes are found in bathypelagic waters, this organism appears to dominate in well-defined, ammonium-rich, near-surface water masses in polar oceans.     

Impacts of Ocean Acidification on Sediment Processes in Shallow Waters of the Arctic Ocean

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO₂ and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO₂ covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study.     

Nematode and macrofaunal diversity in central Arctic Ocean benthos

Deep-sea diversity studies have revealed intriguing patterns on both local and regional scales, but there is insufficient evidence with which to evaluate these trends in the Arctic Ocean basin. We collected data on the diversity of benthic macrofauna and meiofaunal nematodes along two transects from the shelf margin to the North Pole. Contrary to prevailing paradigms, there was no change in diversity with depth between 1000 and 4273 m. There was a trend, however, toward reduced taxonomic richness for both macrofauna and nematodes with increasing latitude. Regional (β-) diversity differences were not observed for nematodes, but significant contrasts in Bray-Curtis similarity-based community structure of macrofauna were seen between the Eurasian and Amerasian Basins, as well as between the Lomonosov and Mendeleev Ridges. Since fauna within the deep Arctic Ocean appear to represent a single species pool, we suggest that both local (α-) and β-diversity may be determined by ecological processes in the Arctic, and are not the consequence of historical or evolutionary processes. Furthermore, insights gained from studies of benthic-pelagic coupling, known to play a significant role in determining benthic community structure and function at high latitudes, may also be useful in investigations of Arctic biodiversity. This model may be valuable in designing future studies of biodiversity, and for predicting potential impacts of climate change on diversity patterns.     

Benthic response to ice-edge-induced particle flux in the Arctic Ocean

With the aims of investigating the response of the smallest benthic biota to a strong ice-edge-related input of phytodetritus, and of registering supposed lateral transportation processes of phytodetrital matter with northerly direction under the ice, we analysed a number of abiotic and biotic parameters in surface sediments from the northern Fram Strait. Two transects of 14 stations in total were made. One transect, crossing the Fram Strait from the east to the west, followed mainly the ice edge. The second transect extended latitudinally in a northerly direction, starting in ice-free areas, passing the ice edge, and ending in heavy ice-covered areas, approximately 100 nm north of the ice edge. Stations along this transect were sampled at almost constant water depths to avoid depth-related influences in our investigations. Results showed the expected high phytodetritus concentrations in the ice-edge vicinity. Concentrations of sediment-bound plant pigments were approximately 5 times higher than in ice-covered areas, indicating a very strong phytodetritus input. With increasing distance from the highly productive areas at the ice edge, we found significantly decreasing concentrations of phytodetrital input to the seafloor in a northerly direction. Within the foraminiferans, generic diversity was clearly reduced in the area of strong phytodetritus deposition. Along the latitudinal transect, out of the direct ice-edge influence, foraminiferal diversities slowly increased within increasing distance from the ice edge. The integration of results from earlier foraminiferal investigations, from stations further to the north, indicates a once more decreasing diversity with continually decreasing food supply.     

Ocean currents shape the microbiome of Arctic marine sediments

Prokaryote communities were investigated on the seasonally stratified Alaska Beaufort Shelf (ABS). Water and sediment directly underlying water with origin in the Arctic, Pacific or Atlantic oceans were analyzed by pyrosequencing and length heterogeneity-PCR in conjunction with physicochemical and geographic distance data to determine what features structure ABS microbiomes. Distinct bacterial communities were evident in all water masses. Alphaproteobacteria explained similarity in Arctic surface water and Pacific derived water. Deltaproteobacteria were abundant in Atlantic origin water and drove similarity among samples. Most archaeal sequences in water were related to unclassified marine Euryarchaeota. Sediment communities influenced by Pacific and Atlantic water were distinct from each other and pelagic communities. Firmicutes and Chloroflexi were abundant in sediment, although their distribution varied in Atlantic and Pacific influenced sites. Thermoprotei dominated archaea in Pacific influenced sediments and Methanomicrobia dominated in methane-containing Atlantic influenced sediments. Length heterogeneity-PCR data from this study were analyzed with data from methane-containing sediments in other regions. Pacific influenced ABS sediments clustered with Pacific sites from New Zealand and Chilean coastal margins. Atlantic influenced ABS sediments formed another distinct cluster. Density and salinity were significant structuring features on pelagic communities. Porosity co-varied with benthic community structure across sites and methane did not. This study indicates that the origin of water overlying sediments shapes benthic communities locally and globally and that hydrography exerts greater influence on microbial community structure than the availability of methane.     

Phylogenetic composition of bacterioplankton assemblages from the Arctic Ocean

We analyzed the phylogenetic composition of bacterioplankton assemblages in 11 Arctic Ocean samples collected over three seasons (winter-spring 1995, summer 1996, and summer-fall 1997) by sequencing cloned fragments of 16S rRNA genes. The sequencing effort was directed by denaturing gradient gel electrophoresis (DGGE) screening of samples and the clone libraries. Sequences of 88 clones fell into seven major lineages of the domain Bacteria: alpha(36%)-, gamma(32%)-, delta(14%)-, and epsilon(1%)-Proteobacteria; Cytophaga-Flexibacter-Bacteroides spp. (9%); Verrucomicrobium spp. (6%); and green nonsulfur bacteria (2%). A total of 34% of the cloned sequences (excluding clones in the SAR11 and Roseobacter groups) had sequence similarities that were <94% compared to previously reported sequences, indicating the presence of novel sequences. DGGE fingerprints of the selected samples showed that most of the bands were common to all samples in all three seasons. However, additional bands representing sequences related to Cytophaga and Polaribacter species were found in samples collected during the summer and fall. Of the clones in a library generated from one sample collected in spring of 1995, 50% were the same and were most closely affiliated (99% similarity) with Alteromonas macleodii, while 50% of the clones in another sample were most closely affiliated (90 to 96% similarity) with Oceanospirillum sp. The majority of the cloned sequences were most closely related to uncultured, environmental sequences. Prominent among these were members of the SAR11 group. Differences between mixed-layer and halocline samples were apparent in DGGE fingerprints and clone libraries. Sequences related to alpha-Proteobacteria (dominated by SAR11) were abundant (52%) in samples from the mixed layer, while sequences related to gamma-proteobacteria were more abundant (44%) in halocline samples. Two bands corresponding to sequences related to SAR307 (common in deep water) and the high-G+C gram-positive bacteria were characteristic of the halocline samples.     

Seasonal occurrence of picocyanobacteria in the Greenland Sea and central Arctic Ocean

The seasonal occurrence of picocyanobacteria in the Greenland Sea and Arctic Ocean was investigated during four expeditions in May–June 1987 and 1988, August–October 1991, and November–December 1988 by epifluorescence microscopy. In early summer, the abundance of picocyanobacteria was related to water masses: they were nearly absent in polar water, whereas they occurred in high concentrations (up to 5470 cells ml^–1) in Atlantic Water. During autumn and beginning of winter, the abundances of picocyanobacteria remained around 10³ cells ml^–1. Their relative contribution to total picoplanktonic algal abundance increased from 0% during spring/summer to 70–80% in late autumn, as a result of a decrease in the abundance of eucaryotic picoalgae. Consequently, the impact of picocyanobacteria on Arctic epipelagic carbon and energy flow is of minor importance, and the strong contribution of picoplankton algae to biomass and primary productivity in Arctic seas has to be attributed to eucaryotic species.     

Inter-annual Fidelity to Summer Feeding Sites in Arctic Grayling

Inter-annual fidelity to summer feeding sites was assessed in adult Arctic grayling, Thymallus arcticus, in the Kuparuk River, Alaska using long-term (15 years) records of individually tagged fish. The Kuparuk River has been the site of a long-term fertilization experiment which allowed us to evaluate the effects of habitat quality on site fidelity. Fidelity to the entire 5km experimental reach, the reference or fertilized zone of the river and to specific river locations was examined. On average, 32% of the arctic grayling caught in the experimental reach were recaptured within the reach in subsequent years. Grayling that returned to the reach displayed strong fidelity to river zones as well as to specific sites on the river. More than half of the fish were recaptured within 300meters of the site where they were captured in previous years. There was no significant difference in fidelity to either the reference or the more productive fertilized zone. Unexpectedly, fidelity was unrelated to fish size (29–43cm TL) or previous summers growth. Strong site fidelity appears to be an adaptation to a short summer during which sufficient resources must be acquired to sustain the fish through the long (9 month) Arctic winter leaving little time to explore alternative locations.     

Phylogenetic Composition of Bacterioplankton Assemblages from the Arctic Ocean

We analyzed the phylogenetic composition of bacterioplankton assemblages in 11 Arctic Ocean samples collected over three seasons (winter-spring 1995, summer 1996, and summer-fall 1997) by sequencing cloned fragments of 16S rRNA genes. The sequencing effort was directed by denaturing gradient gel electrophoresis (DGGE) screening of samples and the clone libraries. Sequences of 88 clones fell into seven major lineages of the domain Bacteria: α (36%)-, γ (32%)-, δ (14%)-, and (1%)-Proteobacteria; Cytophaga-Flexibacter-Bacteroides spp. (9%); Verrucomicrobium spp. (6%); and green nonsulfur bacteria (2%). A total of 34% of the cloned sequences (excluding clones in the SAR11 and Roseobacter groups) had sequence similarities that were <94% compared to previously reported sequences, indicating the presence of novel sequences. DGGE fingerprints of the selected samples showed that most of the bands were common to all samples in all three seasons. However, additional bands representing sequences related to Cytophaga and Polaribacter species were found in samples collected during the summer and fall. Of the clones in a library generated from one sample collected in spring of 1995, 50% were the same and were most closely affiliated (99% similarity) with Alteromonas macleodii, while 50% of the clones in another sample were most closely affiliated (90 to 96% similarity) with Oceanospirillum sp. The majority of the cloned sequences were most closely related to uncultured, environmental sequences. Prominent among these were members of the SAR11 group. Differences between mixed-layer and halocline samples were apparent in DGGE fingerprints and clone libraries. Sequences related to α-Proteobacteria (dominated by SAR11) were abundant (52%) in samples from the mixed layer, while sequences related to γ-proteobacteria were more abundant (44%) in halocline samples. Two bands corresponding to sequences related to SAR307 (common in deep water) and the high-G+C gram-positive bacteria were characteristic of the halocline samples.     

The impact of ice melting on bacterioplankton in the Arctic Ocean

Global warming and the associated ice melt are leading to an increase in the organic carbon in the Arctic Ocean. We evaluated the effects of ice melt on bacterioplankton at 21 stations in the Greenland Sea and Arctic Ocean in the summer of 2007, when a historical minimum of Arctic ice coverage was measured. Polar Surface Waters, which have a low temperature and low salinity and originate mainly from melted ice, contained a very low abundance of bacteria (7.01 × 10⁵ ± 2.20 × 10⁵ cells ml⁻¹); however, these bacteria had high specific bacterial production (2.40 ± 1.61 fmol C bac⁻¹ d⁻¹) compared to those in Atlantic Waters. Specifically, bacterioplankton in Polar Surface Waters showed a preference for utilizing carbohydrates and had significantly higher specific activities of the glycosidases assayed, i.e. β-glucosidase, xylosidase, arabinosidase and cellobiosidase. Furthermore, bacterioplankton in Polar Sea Waters showed preferential growth on some of the carbohydrates in the Biolog Ecoplate, such as d-cellobiose and N-acetyl-d-glucosamine. Our results suggest that climate change and the associated melting of Arctic ice might induce changes in bacterioplankton functional diversity by enhancing the turnover of carbohydrates. Since organic aggregates are largely composed of polysaccharides, higher solubilization of aggregates might modify the carbon cycle, weaken the biological pump and have biogeochemical and ecological implications for the future Arctic Ocean.     

Reproduction of Calanus glacialis in the Laptev Sea, Arctic Ocean

Abundance and reproductive biology (gonad maturation and egg production) of the Arctic copepod Calanus glacialis were studied in the Laptev Sea and adjacent Arctic Ocean in September 1993 and from July to September 1995. Both abundance and reproductive activity were subject to strong spatial and seasonal variability, which was related to the ice cover, feeding conditions and circulation pattern. Maximum abundance of the C. glacialis population was generally confined to the outer shelf and slope with depths between 50 and 1000 m. During both cruises, highest egg production rates and largest number of young copepodite stages were observed in the eastern Laptev Sea, where the development of the C. glacialis population seems to follow the opening of the “Siberian Polynya”. In the western part, which is usually covered by pack ice, females were all immature, and no young stages were found. However, females responded quickly to a temporary opening of the ice there in 1995 and spawned. Starvation experiments showed that food-independent reproduction fuelled by internal energy resources was at least partly responsible for relatively high egg production rates at low ambient food concentrations. Egg production rates in starved females were considerably higher than those previously reported. Accepted: 14 June 2000     

Winter Temperature Affects the Prevalence of Ticks in an Arctic Seabird

The Arctic is rapidly warming and host-parasite relationships may be modified by such environmental changes. Here, I showed that the average winter temperature in Svalbard, Arctic Norway, explained almost 90% of the average prevalence of ticks in an Arctic seabird, the Brünnich’s guillemot Uria lomvia. An increase of 1°C in the average winter temperature at the nesting colony site was associated with a 5% increase in the number of birds infected by these ectoparasites in the subsequent breeding season. Guillemots were generally infested by only a few ticks (≤5) and I found no direct effect of tick presence on their body condition and breeding success. However, the strong effect of average winter temperature described here clearly indicates that tick-seabird relationships in the Arctic may be strongly affected by ongoing climate warming.