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IntroductionThe Arctic is home to about 21000 described species, many of which are specifically adapted to a cold climate (CAFF 2013). As this diversity is under pressure from several sources, [...], Chironomid flies (non-biting midges) are among the most abundant and diverse animals in Arctic regions, but detailed analyses of species distributions and biogeographical patterns are hampered by challenging taxonomy and reliance on morphology for species-level identification. Here we take advantage of available DNA barcode data of Arctic Chironomidae in BOLD to analyse similarities in species distributions across a northern Nearctic--West Palearctic gradient. Using more than 260 000 barcodes representing 4666 BINs (Barcode Index Numbers) and 826 named species (some with interim names) from a combination of public and novel data, we show that the Greenland chironomid fauna shows affinities to both the Nearctic and the West Palearctic regions. While raw taxon counts indicate a strong Greenland--North American affinity, comparisons using Chao's dissimilarity metric support a slightly higher similarity between Greenland and West Palearctic chironomid communities. Results were relatively consistent across different definitions of species taxonomic units, including morphologically determined species, BINs, and superBINs based on a ~4.5% threshold. While most taxa found in Greenland are shared with at least one other region, reflecting circum-Arctic dispersal, our results also reveal that Greenland harbours a small endemic biodiversity. Our exploratory study showcases how DNA barcoding efforts using standardized gene regions contribute to an understanding of broad-scale patterns in biogeography by enabling joint analysis of public DNA sequence data derived from diverse prior studies.Key words: Diptera, zoogeography, biogeography, Canada, Norway, Svalbard.Les chironomides (moucherons non-piqueurs) sont parmi les animaux les plus abondants et diversifies dans les regions arctiques, mais des analyses detaillees des distributions de ces especes et de leur repartition biogeographique sont entravees par une taxonomie difficile et une dependance a la morphologie pour l'identification des especes. Ici, les auteurs tirent profit des donnees disponibles en matiere de codes a barres de l'ADN pour les chironomides arctiques au sein de la base de donnees BOLD pour analyser les similarites pour ce qui est des distributions des especes au long d'un gradient nordique Nearctique-Palearctique occidental. Au moyen de plus de 260 000 codes a barres representant 4666 BIN (<< Barcode Index Numbers >>) et 826 especes nommees (dont certaines de maniere interimaire) a partir d'une combinaison de donnees publiques et inedites, les auteurs montrent que la faune des chironomides du Groenland montre des ressemblances a la fois avec celles des regions Nearctique et Palearctique occidentale. Bien que des decomptes bruts indiquent une grande affinite Groenland--Amerique du Nord, des comparaisons a l'aide de l'indice de dissimilarite de Chao suggerent une similarite legerement plus elevee entre les communautes du Groenland et du Palearctique occidental. Les resultats etaient relativement coherents en faisant appel a diverses definitions des unites taxonomiques specifiques, incluant les especes definies sur une base morphologique, des BIN et des superBIN a un seuil de 4,5%. Bien que la plupart des taxons du Groenland soient partages avec au moins une autre region, ce qui reflete une distribution circum-arctique, les resultats revelent aussi que le Groenland recele une petite biodiversite endemique. Cette etude exploratoire demontre comment les efforts en matiere de codage a barres au moyen de regions geniques standardisees contribuent a la comprehension de la biogeographie a grande echelle en rendant possible l'analyse conjointe de donnees moleculaires publiques derivees de diverses etudes anterieures. [Traduit par la Redaction]Mots-cles: Diptera, zoogeographie, biogeographie, Canada, Norvege, Svalbard.

a. Introduction--E. Osborne, J. Richter-Menge, and M. O. Jeffries Annual average Arctic air temperatures (above 60[degrees]N) in 2017 continued to increase at twice the rate of the rest of the [...]

Shifting weather patterns, particularly increasing extreme events, are observed in populous midlatitudes, and connections to climate change are becoming clearer. The specific roles of rapid Arctic warming and sea ice [...]

The Cretaceous to Paleogene High Arctic Large Igneous Province (HALIP) occurs in circum-Arctic regions, and the largest portion of the province occurs in Canada's Arctic Archipelago. This paper reviews and documents the geometry and distribution of the Canadian portion of the HALIP, focussing most notably on the architecture of its intrusive component. The extent of dyke swarms and sills of the Canadian HALIP is updated and is shown to be greater than previously acknowledged. Sills, in particular, occur throughout the Sverdrup Basin and crop out extensively on Axel Heiberg Island within Triassic to Cretaceous strata. The HALIP event is dominantly intrusive, with 3-5 times more intrusive rocks than extrusive rocks, by volume. There is local evidence of syn-emplacement fault activity, possibly involving the reactivation of older faults, controlling the emplacement of dykes. In the eastern Sverdrup Basin, exposures of components of the HALIP are controlled by tectonic elements of the Eocene Eurekan Orogeny, with plumbing systems (dykes, sills) exposed along regional-scale anticlines or the hanging walls of thrusts. Portions of the HALIP have been shown to be prospective for magmatic Ni-Cu--platinum group elements (PGEs) based on geochemistry, and although geochemical controls play a critical role in the genesis of such deposits, structural and magma dynamic controls are also important to consider at the scale of 1-10 km magmatic complexes. Underpinned by the architecture of the Canadian HALIP, we document the structural characteristics of three 1-10 km-scale volcanic-intrusive complexes of the province that show Ni-Cu-PGE prospectivity: the volcanic-intrusive complex of the Strand Fiord--Expedition Fiord area, the Surprise Fiord dykes, and the Wootton Intrusive Complex. All three represent physico-structural environments that would likely promote high magma flowthrough and sulphide transport, and could be targeted for Ni-Cu-PGE magmatic sulphide mineralization. La Grande Province Ignee de l'Extreme Arctique (High Arctic Large Igneous Province, HALIP), d'age Cretace a Paleogene, se trouve dans les regions Arctiques du globe, et la plus grande portion preservee de la province est exposee dans l'archipel Arctique Canadien. Dans cet article nous revisons et documentons la geometrie et la distribution de la portion canadienne du HALIP, nous concentrant notamment sur l'architecture de sa composante intrusive. L'etendue des essaims de dykes et de filons couches du HALIP canadien est mise a jour et est plus grande que reconnue anterieurement. Les filons couches, en particulier, existent a travers de la stratigraphie du bassin de Sverdrup et peuvent etre identifies sur l'ile Axel Heiberg parmi la stratigraphie Triasique a Cretacee. L'evenement du HALIP est surtout intrusif, avec 3 a 5 fois plus de roches intrusives qu'extrusives en volume. Il y a des evidences locales de mise-en-place de magmas le long de failles contemporaines ou reactivees. Dans la portion est du bassin de Sverdrup, l'affleurement de composantes du HALIP est controle par des elements tectoniques l'orogene Eurekenne d'age Eocene, avec les portions intrusives plus profondes du systeme localisees le longd'anticlinaux ou le long de toits de chevauchements. Des portions du HALIP canadien sont considerees geochimiquement prospectives pour des gisements Ni-Cu--elements du groupe du platine (EGP), et malgre le fait que la geochimie joue un role important dans la genese de tels gisements, les controles physiques et structuraux jouent aussi un role crucial dans leur genese a l'echelle de complexes magmatiques (1-10 km). Considerant l'architecture du HALIP canadien, nous documentons les caracteristiques geologiques et structurales de complexes magmatiques de la grande province ignee de l'Arctique pouvant demontrer une prospectivite en Ni-Cu-EGP, notamment le complexe expose aux fjords Strand et Expedition (ouest de l'ile Axel Heiberg), le complexe de l'essaim de dykes du fjord Surprise (sud-ouest de l'ile Axel Heiberg), et du complexe intrusif Wootton (nord-ouest de l'ile Ellesmere). Tous les trois pourraient etre cibles pour la mineralisation Ni-Cu-EGP magmatique puisqu'ils representent des environnements physico-structuraux propices a un flux important de magma, le transport de sulfure magmatique et la deposition de ces sulfures., Introduction The High Arctic Large Igneous Province (HALIP) consists of Cretaceous to Paleogene volcanic and intrusive rocks exposed in circum-Arctic regions (Fig. 1; e.g., Johnson and Rich 1986; Tarduno 1998; [...]

Author(s): R. Bintanja [sup.1] , F. M. Selten [sup.1] Author Affiliations: (1) Royal Netherlands Meteorological Institute (KNMI), Utrechtseweg 297, 3731GA, De Bilt, The Netherlands, Main Even though the moisture content [...], Precipitation is expected to increase far more over the twenty-first century in the Arctic than the global average; climate models show that this is driven mainly by increased local evaporation and sea-ice retreat, rather than by increased moisture transport from lower latitudes. Receding sea ice enhances surface evaporation Arctic precipitation is expected to increase by more than the global average during the twenty-first century. This trend has been attributed primarily to increased poleward moisture transport from lower latitudes. Now, Richard Bintanja and Frank Selten use climate models to suggest that in fact, the higher precipitation is driven by increased local evaporation, which is in turn linked to decreases in Arctic sea ice and general Arctic warming. Although tentative at this point, the results may have implications for the rate of sea-level rise and the strength of ocean circulation. Precipitation changes projected for the end of the twenty-first century show an increase of more than 50 per cent in the Arctic regions.sup.1,2. This marked increase, which is among the highest globally, has previously been attributed primarily to enhanced poleward moisture transport from lower latitudes.sup.3,4. Here we use state-of-the-art global climate models.sup.5 to show that the projected increases in Arctic precipitation over the twenty-first century, which peak in late autumn and winter, are instead due mainly to strongly intensified local surface evaporation (maximum in winter), and only to a lesser degree due to enhanced moisture inflow from lower latitudes (maximum in late summer and autumn). Moreover, we show that the enhanced surface evaporation results mainly from retreating winter sea ice, signalling an amplified Arctic hydrological cycle. This demonstrates that increases in Arctic precipitation are firmly linked to Arctic warming and sea-ice decline. As a result, the Arctic mean precipitation sensitivity (4.5 per cent increase per degree of temperature warming) is much larger than the global value (1.6 to 1.9 per cent per kelvin). The associated seasonally varying increase in Arctic precipitation is likely to increase river discharge.sup.6,7,8 and snowfall over ice sheets.sup.9 (thereby affecting global sea level), and could even affect global climate through freshening of the Arctic Ocean and subsequent modulations of the Atlantic meridional overturning circulation.sup.10,11.

Author Affiliations: An Arctic iceberg. Rising air temperatures are contributing to the growing incidence of marine heatwaves in the region. Credit: Felipe Dana/AP/Shutterstock A single Iceberg floats as the sun [...], Arctic waters have notched a growing number of extreme events called marine heatwaves, raising fears for the region&apos;s more heat-sensitive sea creatures. Arctic waters have notched a growing number of extreme events called marine heatwaves, raising fears for the region&apos;s more heat-sensitive sea creatures.

It can be argued that Arctic vegetation during the proximal Quaternary (the last circa 50 kyr) is less well understood than the ecology and population dynamics of the mammals that [...], Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25-15 kyr BP), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr BP, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

ABSTRACT. Glaucous gulls (Larus hyperboreus) are major predators in the Arctic and may benefit from human development. We studied use of garbage by glaucous gulls in Barrow, Alaska, in 2007, [...]

ABSTRACT. Hydrological and hydrochemical monitoring of paired watersheds in the High Arctic was conducted in 2003-04 to investigate the influence of seasonal runoff on lake water chemistry and productivity. Despite [...]

ABSTRACT. Surveys in six areas along the Gulf of Boothia produced large collections of radiocarbon samples from raised beaches that yield six new relative sea-level curves and information on Holocene [...]

ABSTRACT. The range of limnological conditions that support Atlantic cod populations in meromictic Arctic lakes is known to be relatively restricted. The degree to which differences in these features, particularly [...]

ARCTIC GIMMICKS The Arctic is widely presented as the object of a geopolitical race for natural resources, oil and gas in particular, with Russia as the main driver. Russia is [...]

Temperatures in the Arctic have increased by an astounding 1[degrees]C in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades. The Pliocene (2.6-5.3 Ma) is of particular interest as an analog for future warming because global temperatures were significantly warmer than today for a sustained period of time, with continental configurations similar to present. Here, we estimate mean annual temperature (MAT) based upon three independent proxies from an early Pliocene peat deposit in the Canadian High Arctic. Our proxies, including oxygen isotopes and annual ring widths (MAT = -0.5 [+ or -] 1.9[degrees]C), coexistence of paleovegetation (MAT = -0.4 [+ or -] 4.1[degrees]C), and bacterial tetraether composition in paleosols (MAT = -0.6 [+ or -] 5.0[degrees]C), yield estimates that are statistically indistinguishable. The consensus among these proxies suggests that Arctic temperatures were ~19[degrees]C warmer during the Pliocene than at present, while atmospheric C[O.sub.2] concentrations were ~390 ppmv. These elevated Arctic Pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo. These results indicate that Arctic temperatures may be exceedingly sensitive to anthropogenic C[O.sub.2] emissions. doi: 10.1130/G30815.1

Microorganisms have been repeatedly discovered in environments that do not support their metabolic activity. Identifying and quantifying these misplaced organisms can reveal dispersal mechanisms that shape natural microbial diversity. Using endospore germination experiments, we estimated a stable supply of thermophilic bacteria into permanently cold Arctic marine sediment at a rate exceeding [10.sup.8] spores per square meter per year. These metabolically and phylogenetically diverse Firmicutes show no detectable activity at cold in situ temperatures but rapidly mineralize organic matter by hydrolysis, fermentation, and sulfate reduction upon induction at 50[degrees]C. The closest relatives to these bacteria come from warm subsurface petroleum reservoir and ocean crust ecosystems, suggesting that seabed fluid flow from these environments is delivering thermophiles to the cold ocean. These transport pathways may broadly influence microbial community composition in the marine environment.

The rotation model for the opening of the Canada Basin of the Arctic Ocean predicts stratigraphic links between the Alaskan North Slope and the Canadian Arctic islands. The Katakturuk Dolomite is a 2080-m-thick Neoproterozoic carbonate succession exposed in the northeastern Brooks Range of Arctic Alaska. These strata have previously been correlated with the pre-723 Ma Shaler Supergroup of the Amundson Basin. Herein we report new composite [delta][sup.13]C profiles and detrital zircon ages that test this connection. We go further and use stratigraphic markers and a compilation of [delta][sup.13]C chemostratigraphy from around the world, tied to U-Pb ages, to derive an age model for deposition of the Katakturuk Dolomite. In particular, we report the identification of ca. 760 Ma detrital zircons in strata underlying the Katakturuk Dolomite. Moreover, a diamictite present at the base of the Katakturuk Dolomite is capped by a dark-colored limestone with peculiar roll-up structures. Chemostratigraphy and lithostratigraphy suggest this is an early-Cryogenian glacial diamictite-cap carbonate couplet and that deposition of the Katakturuk Dolomite spanned much of the late Neoproterozoic. Approximately 500 m above the diamictite, a micropeloidal dolomite, with idiosyncratic textures that are characteristic of basal Ediacaran cap carbonates, such as tubestone stromatolites, giant wave ripples, and decameters of pseudomorphosed former aragonite crystal fans, rests on a silicified surface. Chemostratigraphic correlations also indicate a large increase in sedimentation rate in the upper ~1 km of the Katakturuk Dolomite and in the overlying lower Nanook Limestone. We suggest that the accompanying increase in accommodation space, along with the presence of two low-angle unconformities within these strata, are the product of late Ediacaran rifting along the southern margin of the North Slope subterrane. There are no strata present in the Amundson Basin that are potentially correlative with the late Neoproterozoic Katakturuk Dolomite, as the Cambrian Saline River Formation rests on the ca. 723 Ma Natkusiak Formation. Detrital zircon geochronology, chemostratigraphic correlations, and the style of sedimentation are inconsistent with both a Canadian Arctic origin of the North Slope subterrane and a simple rotation model for the origin of the Arctic Ocean. If the rotation model is to be retained, the exotic North Slope subterrane must have accreted to northwest Laurentia in the Early to Middle Devonian. Keywords: Neoproterozoic, snowball Earth, cap carbonates, Arctic Alaska terrane, Katakturuk, Nanook, chemostratigraphy, detrital zircon geochronology, carbon isotope, oxygen isotope, glaciation.

High-latitude ecosystems store large amounts of carbon (C); however, the C storage of these ecosystems is under threat from both climate warming and increased levels of herbivory. In this study we examined the combined role of herbivores and climate warming as drivers of C[O.sub.2] fluxes in two typical high-latitude habitats (mesic heath and wet meadow). We hypothesized that both herbivory and climate warming would reduce the C sink strength of Arctic tundra through their combined effects on plant biomass and gross ecosystem photosynthesis and on decomposition rates and the abiotic environment. To test this hypothesis we employed experimental warming (via International Tundra Experiment [ITEX] chambers) and grazing (via captive Barnacle Geese) in a three-year factorial field experiment. Ecosystem C[O.sub.2] fluxes (net ecosystem exchange of C[O.sub.2], ecosystem respiration, and gross ecosystem photosynthesis) were measured in all treatments at varying intensity over the three growing seasons to capture the impact of the treatments on a range of temporal scales (diurnal, seasonal, and interannual). Grazing and warming treatments had markedly different effects on C[O.sub.2] fluxes in the two tundra habitats. Grazing caused a strong reduction in C[O.sub.2] assimilation in the wet meadow, while warming reduced C[O.sub.2] efflux from the mesic heath. Treatment effects on net ecosystem exchange largely derived from the modification of gross ecosystem photosynthesis rather than ecosystem respiration. In this study we have demonstrated that on the habitat scale, grazing by geese is a strong driver of net ecosystem exchange of C[O.sub.2], with the potential to reduce the C[O.sub.2] sink strength of Arctic ecosystems. Our results highlight that the large reduction in plant biomass due to goose grazing in the Arctic noted in several studies can alter the C balance of wet tundra ecosystems. We conclude that herbivory will modulate direct climate warming responses of Arctic tundra with implications for the ecosystem C balance; however, the magnitude and direction of the response will be habitat-specific. Key words: Arctic; Barnacle Goose; Branta leucopsis; carbon fluxes; climate change; herbivory; vegetation.

The spectacular preservation of middle Eocene (ca. 45 Ma) wood allows for intraseason sampling of stable carbon, oxygen, and hydrogen in order to reconstruct the paleoseasonal environment of this Arctic forest (paleolatitude 78.6[degrees] [+ or -] 1.6[degrees] N; present latitude 80[degrees] N). Carbon isotopes in bulk organics and cellulose reveal striking annual patterns interpreted as the seasonal switchover from stored to actively acquired carbon associated with deciduous growth in these unusual conifers. Oxygen and hydrogen stable isotopes of cellulose and cellulose nitrate allow for the calculation of changes in relative humidity and in the isotopic value of plant-available water. Clear annual patterns of increasing relative humidity resulting from tissue growth and concomitant transpiration are apparent, as is the systematic increase in the reconstructed oxygen isotope value of environmental water, reflecting progressively increasing temperatures during the growing season. Keywords: Eocene, Arctic, Metasequoia, relative humidity, deciduousness, tree ring.

Mixed-phase stratus clouds are ubiquitous in the Arctic and play an important role in climate in this region. However, climate and regional models have generally proven unsuccessful at simulating Arctic cloudiness, particularly during the colder months. Specifically, models tend to underpredict the amount of liquid water in mixed-phase clouds. The Mixed-Phase Arctic Cloud Experiments (M-PACE), conducted from late September through October 2004 in the vicinity of the Department of Energy's Atmospheric Radiation Measurement (ARM) North Slope of Alaska field site, focused on characterizing low-level Arctic stratus clouds. Ice nuclei (IN) measurements were made using a continuous-flow ice thermal diffusion chamber aboard the University of North Dakota's Citation II aircraft. These measurements indicated IN concentrations that were significantly lower than those used in many models. Using the Regional Atmospheric Modeling System (RAMS), we show that these low IN concentrations, as well as inadequate parameterizations of the depletion of IN through nucleation scavenging, may be partially responsible for the poor model predictions. Moreover, we show that this can lead to errors in the modeled surface radiative energy budget of 10-100 W [m.sup.-2]. Finally, using the measured IN concentrations as input to RAMS and comparing to a mixed-phase cloud observed during M-PACE, we show excellent agreement between modeled and observed liquid water content and net infrared surface flux. (Page 541)

The Arctic provides a test bed to understand and evaluate the consequences of threshold changes in regional system dynamics. Over the past several decades, the Arctic has warmed strongly in [...], A major challenge in predicting Earth's future climate state is to understand feedbacks that alter greenhouse-gas forcing. Here we synthesize field data from arctic Alaska, showing that terrestrial changes in summer albedo contribute substantially to recent high-latitude warming trends. Pronounced terrestrial summer warming in arctic Alaska correlates with a lengthening of the snow-free season that has increased atmospheric heating locally by about 3 watts per square meter per decade (similar in magnitude to the regional heating expected over multiple decades from a doubling of atmospheric C[O.sub.2]). The continuation of current trends in shrub and tree expansion could further amplify this atmospheric heating by two to seven times.

ABSTRACT. Historical relationships between people and a changing Arctic environment (which constitute a social-ecological system, or SES) can offer insights for management that promote both social and ecological resilience. The [...]

1 A field-experiment was used to determine how plant species might retain dominance in an arctic ecosystem receiving added nutrients. We both measured and modelled the above-ground and below-ground biomass allocation and root morphology of non-acidic tussock tundra near Toolik Lake, Alaska, after 4 years of fertilization with nitrogen and phosphorus. 2 Compared with control plots, the fertilized plots showed significant increases in overall root weight ratio, and root biomass, root length and root nitrogen concentration in the upper soil layers. There was a strong trend towards relatively more biomass below ground. 3 We constructed an individual teleonomic (i.e. optimality) plant allocation and growth model, and a competition model in which two plants grow and compete for the limiting resources. 4 The individual plant model predicted a strong decrease in root weight ratio with increased nutrient availability, contrary to the results obtained in the field. 5 The increased investment in roots in the fertilized plots found in the field could be explained in the competition model in terms of luxury consumption of nutrients (i.e. the absorbance of nutrients in excess of the immediate plant growth requirements). For slow-growing species with relatively low phenological and physiological plasticity it can be advantageous to increase relative investment into root growth and root activity. This increased investment can limit nutrient availability to other fast-growing species and, thereby, preclude the successful invasion of these species. 6 These results have implications for the transient response of communities and ecosystems to global change. Key-words: arctic, biomass allocation, competition, nutrients, tundra

1 Community assembly is described for two contrasting high Arctic chronosequences representing glacial regression of up to 2000 years on Svalbard. The chronosequences included a nutrient-poor glacier foreland (Midtre Lovenbre) and a series of nutrient-enriched islands (Loven Islands) progressively released from below a tidewater glacier. 2 Soil development and community assembly paralleled proglacial sequences elsewhere but time scales were extended and mature vegetation types comprised species-poor prostrate communities. 3 Initial colonization by Cyanobacteria stabilized soil surfaces and raised nutrient status. Cyanobacteria formed the dominant ground cover (up to 34%) for 60 years, after when they declined. 4 Vascular plants established slowly and represented minor components of ground cover for the first 100 years. Earliest colonizers were often species with ectomycorrhizal associations, followed by mid-successional species that tended to disappear as ground cover increased. Some species present in the mature vegetation at the oldest sites, established only after 60+ years. 5 Species richness of vascular plants increased for c. 100 years, beyond when only occasional species were added. Bryophytes became increasingly dominant with time. 6 Soil development on the Midtre Lovenbre and Loven Island chronosequences was similar after 100 years. Differences subsequently developed, with organic horizon depth, percentage organic matter and water content on the older Loven islands significantly greater than at equivalent Midtre Lovenbre sites. This was associated with increased bryophyte cover but lower vascular plant species richness. One explanation is a slightly more favourable microclimate, coupled with nutrient input from nesting birds. 7 Communities progressively recruit from a limited pool of effectively dispersed species, each with particular ecological requirements that determine their point of entry into the community. A measure of determinism by default is suggested in the way communities assembled. 8 Under climate warming, in the absence of nutrient enrichment, community development will accelerate but will be constrained by nutrient limitations and a restricted species pool. Where nutrients are less limiting, acceleration towards a moss-dominated community is expected, with a lower species richness of vascular plants. Key-words: Bryophyta, climate-change, Cyanobacteria, nutrients, succession

1 The uptake of free amino acids by the grass Puccinellia phryganodes was investigated in soils of an Arctic coastal salt marsh, where low temperatures and high salinity limit inorganic nitrogen (N) availability, and the availability of soluble organic N relative to inorganic N is often high. 2 Following the injection of [sup.13]C[sup.15]N-amino acid, [sup.15]N-ammonium and [sup.15]N-nitrate tracers into soils, rates of soluble nitrogen turnover and the incorporation of [sup.13]C and [sup.15]N into plant roots and shoots were assessed. Chloroform fumigation-extraction was used to estimate the partitioning of labelled substrates into microbial biomass. 3 Free amino acids turned over rapidly in the soil, with half-lives ranging from 8.2 to 22.8 h for glycine and 8.9 to 25.2 h for leucine, compared with 5.6 to 14.7 h and 5.6 to 15.6 h for ammonium and nitrate, respectively. 15N from both organic and inorganic substrates was incorporated rapidly into plant tissue and the ratio of [sup.13]C/[sup.15]N incorporation into plant tissue indicated that at least 5-11% of [sup.13]C[sup.15]N-glycine was absorbed intact. 4 Microbial C and N per unit soil volume were 1.7 and 5.4 times higher, respectively, than corresponding values for plant C and N. Plant incorporation of [sup.15]N tracer was 56%, 83% and 68% of the comparable incorporation by soil microorganisms of glycine, ammonium and nitrate ions, respectively. 5 These results indicate that P phryganodes can absorb amino acids intact from the soil despite competition from soil microorganisms, and that free amino acids may contribute substantially to N uptake in this important forage grass utilized by lesser snow geese in the coastal marsh. Key-words: ammonium, glycine, nitrate, organic nitrogen, Puccinellia phryganodes

1 LPBN is a parameterized simulation model of flows of nitrogen (N) in an ecosystem of cyanobacteria, grass and grazers, based on the N dynamics of a grazed Puccinellia lawn in an intertidal marsh on Hudson Bay. This system shows two alternate stable states: (a) lawns that either support a foraging population of lesser snow geese, or are not grazed by geese; and (b) exposed saline sediments that support little or no vegetation. The model represents the flow of N from cyanobacterial fixation, the major N input into the system, to the geese that migrate in autumn; those that do not return represent the major N output from the system. We have modelled N fixation, the transformations of N in the soil, plant growth, lawn regeneration, and goose grazing and grubbing. 2 The model simulates steady-state flows of N similar to those observed in the field at zero and at moderate goose density, and it also simulates the transition to the state of zero plant biomass, a consequence of increased grubbing at high goose density. The simulated steady-state flows are found to be more sensitive to changes in the parameters that describe N fixation and goose biology, than to similar changes in the parameters describing plant biology. 3 Because the model shows the alternate stable states and the transition between them, with values for the state variables that are consistent with field data, we conclude that N dynamics are crucial in determining the stability of the real salt marsh-goose system. The determining factor is the loss of the input of N from fixation when lawn area is reduced because the rate of goose grubbing exceeds that of plant re-establishment. Key-words: coastal ecosystem, grazing, grubbing, lesser snow goose, nitrogen cycle

Vascular plants are generally assumed to have no photosynthetic activity under the snow because of the severity of the subnivean environment. In the arctic tundra, snow cover persists into the spring after air temperatures and light increase to levels suitable for photosynthesis of vascular plants in the absence of snow cover. We found significant photosynthetic activity in four arctic evergreen species under springtime snow. This activity was facilitated by favorable conditions in the subnivean environment, where C[O.sub.2] concentrations are elevated, temperatures are often above freezing, and light levels are sufficient to drive photosynthesis. Diurnal changes in C[O.sub.2] concentration under the snow and light responses of snow-covered ecosystem C[O.sub.2] fluxes provide supporting evidence of carbon gain at the ecosystem level. This activity allows evergreens to rapidly increase photosynthesis upon snowmelt and reduces wintertime losses of carbon from arctic ecosystems. The loss of these species under predicted scenarios of climate change could have serious implications for tundra carbon balance, potentially increasing carbon losses. Key words: Brooks Mountain Range, Alaska; carbon cycling; chlorophyll fluorescence; climate change; subnivean; tussock tundra.

The high sensitivity of the Arctic implies that impact of climate change and related environmental changes on river discharge can be considerable. Sensitivity of discharge to changes in precipitation, temperature, permafrost and vegetation, was studied in the Usa basin, Northeast-European Russia. For this purpose, a distributed hydrological model (RHINEFLOW) was adapted. Furthermore, the effect of climate change simulated by a GCM (HADCM2S750 integration) on runoff was assessed, including indirect effects of permafrost thawing and changes in vegetation distribution. The study shows that discharge in the Usa basin is highly sensitive to changes in precipitation and temperature. The effect of precipitation change is present throughout the year, while temperature changes affect discharge only in seasons when temperature fluctuates around the freezing point (April and October). Discharge is rather sensitive to changes in vegetation. Sensitivity to permafrost occurrence is high in winter, because infiltration and consequently base flow increases if permafrost melts. The effect of climate change simulated by the scenario on discharge was significant. Peak flow can both decrease (by 22%) and increase (by 19%) compared with present-day, depending on the amount of winter precipitation. Also, runoff peaks earlier in the season. These results can have implications for the magnitude and timing of the runoff peak, break-up and water-levels.

The article examines research findings from sediment cores from the Bering Strait. Topics include sea level rise, glacial-interglacial cycles, thermohaline circulation, water salinity, lithosphere flexing, and storms data.

Robert E. Nelson (1) ABSTRACT. Some 56 species of Carabidae have been previously reported on the Arctic Slope of Alaska; of these, only nine have been found at coastal sites [...]

Hans Meltofte (1) ABSTRACT. There is increasing evidence that breeding wader censuses often have significantly underestimated densities in the Arctic and other areas. This evidence includes the recording of many [...]

(Received 7 April 1999; accepted in revised form 15 September 2000) ABSTRACT. In recent years, increasing scientific attention has been paid to sea mammals as biological indicators of Arctic environmental [...]

(Received 13 April 1999; accepted in revised form 25 April 2000) ABSTRACT. Changes according to elevation in frequencies of naturally stranded bowhead whale (Balaena mysticetus) remains on Holocene beaches in [...]