Central Ellesmere Island Research Articles

WOOD JAMS OR BEAVER DAMS? PLIOCENE LIFE, SEDIMENT AND LANDSCAPE INTERACTIONS IN THE CANADIAN HIGH ARCTIC

ABSTRACT During the mid-Pliocene (Zanclean, ca. ∼ 3.9 Ma), parts of the Canadian High Arctic experienced mean annual temperatures that were 14–22°C warmer than today and supported diverse boreal-type forests. The landscapes of this vegetated polar region left behind a fragmented sedimentary record that crops out across several islands in the Canadian Arctic Archipelago as the Beaufort Formation and correlative strata. Paleoecological information from these strata provides a high-fidelity window onto Pliocene environments, and prominent fossil sites yield unparalleled insights into Cenozoic mammal evolution. Significantly, many of the strata reveal evidence for life-sediment interactions in a warm-climate Arctic, most notably in the form of extensive woody debris and phytoclast deposits. This paper presents original field data that refines the sedimentological context of plant debris accumulations from the anactualistic High Arctic forests, most notably at the ‘Fyles Leaf Beds' and ‘Beaver Pond' fossil-bearing sites in the ‘high terrace deposits' of central Ellesmere Island. The former is a remarkably well-preserved, leaf-rich deposit that is part of a complex of facies associations representing lacustrine, fluvio-deltaic and mire deposition above a paleotopographic unconformity. The latter yields tooth-marked woody debris within a peat layer that also contains a rich assemblage of vertebrate and plant fossils including abundant remains from the extinct beaver-group Dipoides. Here we present sedimentological data that provide circumstantial evidence that the woody debris deposit at Beaver Pond could record dam-building in the genus, by comparing the facies motif with new data from known Holocene beaver dam facies in England. Across the Pliocene of the High Arctic region, woody debris accumulations are shown to represent an array of biosedimentary deposits and landforms including mires, driftcretions, woody bedforms, and possible beaver dams, which help to contextualize mammal fossil sites, provide facies models for high-latitude forests, and reveal interactions between life and sedimentation in a vanished world that may be an analogue to that of the near-future.

Evidence for fire in the Pliocene Arctic in response to amplified temperature

Abstract. The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO2 concentrations because atmospheric CO2 concentrations are thought to have been comparable to the current day and yet the climate and distribution of ecosystems were quite different. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified Arctic temperature response and its impact on Arctic ecosystems. Only the most recent models appear to correctly estimate the degree of warming in the Pliocene Arctic and validation of the currently proposed feedbacks is limited by scarce terrestrial records of climate and environment. Here we reconstruct the summer temperature and fire regime from a subfossil fen-peat deposit on west–central Ellesmere Island, Canada, that has been chronologically constrained using cosmogenic nuclide burial dating to 3.9+1.5/-0.5 Ma. The estimate for average mean summer temperature is 15.4±0.8 ∘C using specific bacterial membrane lipids, i.e., branched glycerol dialkyl glycerol tetraethers. This is above the proposed threshold that predicts a substantial increase in wildfire in the modern high latitudes. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that included an increase in abundance of fire-promoting Pinus and Picea. Paleo-vegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire-adapted boreal forests of North America and central Siberia. To our knowledge, this site provides the northernmost evidence of fire during the Pliocene. It suggests that ecosystem productivity was greater than in the present day, providing fuel for wildfires, and that the climate was conducive to the ignition of fire during this period. The results reveal that interactions between paleo-vegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO2 concentrations were similar to modern values.

Seismic tomography of the Arctic region: inferences for the thermal structure and evolution of the lithosphere

Abstract Waveform tomography with very large datasets reveals the upper-mantle structure of the Arctic in unprecedented detail. Using tomography jointly with computational petrology, we estimate temperature in the lithosphere–asthenosphere depth range and infer lithospheric structure and evolution. Most of the boundaries of the mantle roots of cratons in the Arctic are coincident with their geological boundaries at the surface. The thick lithospheres of the Greenland and North American cratons are separated by a corridor of thin lithosphere beneath Baffin Bay and through the middle of the Canadian Arctic Archipelago; the southern archipelago is part of the North American Craton. The mantle root of the cratonic block beneath northern Greenland may extend westwards as far as central Ellesmere Island. The Barents and Kara seas show high velocities indicative of thick lithosphere, similar to cratons. The locations of intraplate basaltic volcanism attributed to the High Arctic Large Igneous Province are all on thin, non-cratonic lithosphere. The lithosphere beneath the central part of the Siberian Traps is warmer than elsewhere beneath the Siberian Craton. This observation is consistent with lithospheric erosion associated with the large igneous province volcanism. A corridor of relatively low seismic velocities cuts east–west across central Greenland. This indicates lithospheric thinning, which appears to delineate the track of the Iceland hotspot.

Regional crustal architecture of Ellesmere Island, Arctic Canada

Abstract New deep seismological data from Ellesmere Island and the adjacent Arctic continental margin provide new information about the crustal structure of the region. These data were not available for previous regional crustal models. This paper combines and redisplays previously published results – a gravity-derived Moho map and seismological results –to produce new maps of the Moho depth, the depth to basement and the crystalline crustal thickness of Ellesmere Island and contiguous parts of the Arctic Ocean, Greenland and Axel Heiberg Island. Northern Ellesmere Island is underlain by a thick crustal block (Moho at 41 km, c. 35 km crust). This block is separated from the Canada–Greenland craton in the south by a WSW–ENE-trending channel of thinned crystalline crust (Moho at 30–35 km, <20 km thick crust), which is overlain by a thick succession of metasedimentary and younger sedimentary rocks (15–20 km). The Sverdrup Basin in the west and the Lincoln Sea in the east interrupt the crustal architecture of central Ellesmere Island, which is interpreted to be more representative of its initial post-Ellesmerian Orogen structure, but with a later Sverdrup Basin and Eurekan overprint.

Tectonic map of the Ellesmerian and Eurekan deformation belts on Svalbard, North Greenland, and the Queen Elizabeth Islands (Canadian Arctic)

The tectonic map presented here shows the distribution of the major post-Ellesmerian and pre-Eurekan sedimentary basins, parts of the Caledonian orogen, the Ellesmerian fold-and-thrust belt, structures of the Cenozoic Eurekan deformation, and areas affected by the Eurekan overprint. The present continental margin of North America towards the Arctic Ocean between the Queen Elizabeth Islands and Northeast Greenland and the present west margin of the Barents Shelf are characterized by the Palaeozoic Ellesmerian fold-and-thrust belt, the Cenozoic Eurekan deformation, and, in parts, the Caledonian orogen. In many areas, the structural trends of the Ellesmerian and Eurekan deformations are more or less parallel, and often, structures of the Ellesmerian orogeny are affected or reactivated by the Eurekan deformation. While the Ellesmerian fold-and-thrust belt is dominated by orthogonal compression and the formation of wide fold-and-thrust zones on Ellesmere Island, North Greenland, and Spitsbergen, the Eurekan deformation is characterized by a complex network of regional fold-and-thrust belts (Spitsbergen, central Ellesmere Island), large distinct thrust zones (Ellesmere Island, North Greenland), and a great number of strike-slip faults (Spitsbergen, Ellesmere Island). The Ellesmerian fold-and-thrust belt was most probably related to the approach and docking of the Pearya Terrane (northernmost part of Ellesmere Island) and Spitsbergen against the north margin of Laurasia (Ellesmere Island/North Greenland) in the earliest Carboniferous. The Eurekan deformation was related to plate tectonic movements during the final break-up of Laurasia and the opening of Labrador Sea/Baffin Bay west, the Eurasian Basin north, and the Norwegian/Greenland seas east of Greenland.

Additions to the Eocene Perissodactyla of the Margaret Formation, Eureka Sound Group, Ellesmere Island, Arctic Canada

We describe early Eocene (Wasatchian) occurrences of the isectolophid Homogalax, tapiroids Heptodon posticus, Heptodon cf. H. posticus, and Heptodon sp., as well as early middle Eocene (Bridgerian) fossils of the brontothere Palaeosyops from localities in the Margaret Formation of the Eureka Sound Group on Ellesmere Island, Nunavut, Arctic Canada. Their occurrence on Ellesmere Island considerably extends the geographic range of these taxa, previously known from mid-latitude localities in British Columbia (only Heptodon), the Western Interior of the United States, and Asia (Homogalax, Heptodon, and Palaeosyops). We also place the fossil localities near Bay Fiord on central Ellesmere Island into a refined lithostratigraphic framework based upon data from three measured stratigraphic sections. Our stratigraphic data confirm the presence of two, stratigraphically distinct fossil assemblages — a late Wasatchian-aged lower assemblage and a Bridgerian-aged upper assemblage that were previously hypothesized by others based on faunal differences — that are separated by a 478 m thick stratigraphic gap that appears to lack fossil vertebrates. From a paleoenvironmental perspective, occurrence of the tapiroid Heptodon in the Eocene Arctic corroborates an hypothesis put forward by others that tapiroids are proxies for densely forested habitats, although they were adapted to a range of temperatures including near (or at) freezing temperatures of Eocene Arctic winters. Further, Arctic occurrences of tapiroids and brontotheres imply that these typical mid-latitude ungulate mammals were adapted to Arctic environments, thereby increasing the probability of Trans-Beringian dispersal during early and middle Eocene time.

Reassessment ofIschnacanthus?scheiiSpjeldnaes (Acanthodii, Ischnacanthiformes) from the latest Silurian or earliest Devonian of Ellesmere Island, arctic Canada

Articulated specimens of jawed fishes, and assemblages of disarticulated elements that can be assigned to a single biological species, are extremely rare from pre-Devonian deposits. The acanthodian species Ischnacanthus? scheii Spjeldnaes is based on a monospecific assemblage, comprising fin spines, dentigerous jaw bone fragments and scales, from the ?Siluro-Devonian boundary beds of the Devon Island Formation in central west Ellesmere Island, Canadian Arctic Archipelago, Nunavut. A new examination of the type material, in particular by scanning electron microscopy and thin sectioning of scales, shows that the species is a porosiform poracanthodid that is now assigned to Radioporacanthodes scheii comb. nov. Scales of the same species are also recognized from the upper Pridoli of Cornwallis Island and the ?Pridoli or Lochkovian of north Greenland.

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550-1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems.

Seasonal variability in Arctic temperatures during early Eocene time

As a deep time analog for today's rapidly warming Arctic region, early Eocene (52–53 Ma) rock on Ellesmere Island in Canada's High Arctic (∼ 79°N.) preserves evidence of lush swamp forests inhabited by turtles, alligators, primates, tapirs, and hippo-like Coryphodon. Although the rich flora and fauna of the early Eocene Arctic imply warmer, wetter conditions than at present, the quantification of Eocene Arctic climate has been more elusive. By analyzing oxygen isotope ratios of biogenic phosphate from mammal, fish, and turtle fossils from a single locality on central Ellesmere Island, we infer early Eocene Arctic temperatures, including mean annual temperature (MAT) of ∼ 8 °C, mean annual range in temperature of ∼ 16.5–19 °C, warm month mean temperature of 19–20 °C, and cold month mean temperature of 0–3.5 °C. Our seasonal range in temperature is similar to the range in estimated MAT obtained using different proxies. In particular, relatively high estimates of early Eocene Arctic MAT and SST by others that are based upon the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in terrestrial soil bacteria and isoprenoid tetraether lipids in marine Crenarchaeota fall close to our warm month temperature, suggesting a bias towards summer values. From a paleontologic perspective, our temperature estimates verify that alligators and tortoises, by way of nearest living relative-based climatic inference, are viable paleoclimate proxies for mild, above-freezing year-round temperatures. Although for both of these reptilian groups, past temperature tolerances probably were greater than in living descendants.

Stratigraphic analysis of an ice core from the Prince of Wales Icefield, Ellesmere Island, Arctic Canada, using digital image analysis: High‐resolution density, past summer warmth reconstruction, and melt effect on ice core solid conductivity

High‐resolution (1 mm) stratigraphic information was derived from digital image analysis of an ice core from the Prince of Wales (POW) Icefield, Central Ellesmere Island, Canada. Following careful image processing, a profile of ice core transmitted light was derived from the greyscale images and used to reconstruct high‐resolution density variations for the unfractured sections of the core. Images were further classified into infiltration and glacier ice using an automatic thresholding procedure, and were converted to a high‐resolution melt percentage index. The mean annual melt percentage over the last 580 years was 9%, and melting occurred in 8 years out of 10. Melting obliterated most of the original depositional sequence, and seasonal density cycles were mostly unrecognizable. The ice core solid conductivity was greater and more variable in melt features than in glacier ice, owing to washout of strong acids by meltwater (elution) and chemical enrichment upon refreezing. This hindered the identification of acid volcanic layers and further compromised dating by annual layer counting. Comparison of the melt record with those from other Arctic ice caps shows that the melt‐temperature relationship on POW Icefield is site‐specific. We speculate that this is due to the peculiar position of the icefield, which rests on the periphery of the Baffin Bay maritime climate zone, and to the proximity of the North Open Water polynya, which controls snow accumulation variability on the icefield and affects the melt percentage index.

Early Eocene Brontotheriidae (Perissodactyla) from the Eureka Sound Group, Ellesmere Island, Canadian High Arctic—implications for brontothere origins and high-latitude dispersal

ABSTRACT The northernmost records of early Eocene brontotheres, fossils of cf. Eotitanops and Brontotheriidae gen. et sp. indet., are described here from late Wasatchian-aged strata of upper parts of the Eureka Sound Group on central Ellesmere Island (~79°N). Although the fossils were initially tentatively identified on faunal lists as Lambdotherium, their larger size and dental morphology ally them more closely to mid-latitude Eotitanops and Palaeosyops. The Ellesmere Island specimens are dentally most similar to mid-latitude Eotitanops, but can be distinguished from the latter by derived characters on their premolars that are shared with the younger (i.e., Bridgerian) Palaeosyops. The presence of brontotheres in early Eocene strata on Ellesmere Island implies that the group's evolution was well underway early in its history at northern high latitudes, and is consistent with either an Asian or North American origin and trans-Beringian dispersal. While cf. Eotitanops from Ellesmere Island appears dentally too advanced to be ancestral to mid-latitude co-eval Eotitanops, it may be a suitable ancestor to Palaeosyops. The presence of cf. Eotitanops on Ellesmere Island may reflect a high-latitude lineage that subsequently dispersed to mid-latitudes during early middle Eocene (Bridgerian) time.

The thermal history of the Nares Strait, Kane Basin, and Smith Sound region in Canada and Greenland: constraints from apatite fission-track and (U–Th–Sm)/He dating

Apatite fission-track and (U–Th–Sm)/He data for samples with Proterozoic–Neogene lithologic ages from eastern Ellesmere, Devon, and Baffin islands in the Canadian Arctic Archipelago and northwest Greenland provide insights into the complex thermal history of this region. Most data reflect exhumational cooling of the region as a sediment source area for the developing Sverdrup Basin to the west during late Paleozoic – Mesozoic time. Samples proximal to the basin margin record late Paleozoic cooling consistent with erosion of uplifted rift flanks and widespread clastic sedimentation during early rifting and thermal subsidence. Data from distal samples are consistent with early Mesozoic epeirogenic denudational cooling during periods of high sediment supply from well-developed river systems. Around northern Baffin Bay, the data record erosional cooling of uplifted rift flanks in response to Late Cretaceous rifting. Rapid denudation rates are indicated for southeastern Devon Island, compatible with thick Upper Cretaceous strata offshore in Lancaster Sound. Slower denudation rates are indicated for northwest Greenland. Along Nares Strait, data reflect mafic volcanism or erosional exhumation associated with strike-slip and (or) thrust displacements during the Paleogene Eurekan orogeny and offer limited support for the existence of a Wegener fault. Fission-track ages older than those obtained in central Ellesmere Island, however, suggest that active tectonics occurred earlier near the strait, and strike-slip tectonism and deformation were likely partitioned across a relatively wide belt. Apatites obtained from Archean gneisses and Franklinian dykes have up to 500 ppm Sm, and up to 15% of the radiogenic He is Sm derived.

Arcticanodon dawsonae, a primitive new palaeanodont from the lower Eocene of Ellesmere Island, Canadian High Arctic

A new genus and species of palaeanodont, Arcticanodon dawsonae, is based on a single lower jaw fragment from lower Eocene (Wasatchian) strata of the Margaret Formation, Eureka Sound Group, on central Ellesmere Island, Nunavut. The new taxon is more derived than early Paleocene Escavadodontidae, but lacks derived traits of Metacheiromyidae. It is therefore most similar to primitive epoicotheriids, although the similarities are essentially in plesiomorphic features. Consequently, Arcticanodon dawsonae is classified as Palaeanodonta, incertae sedis, pending discovery of more complete specimens.

Rapid Lacustrine Response to Recent High Arctic Warming: A Diatom Record from Sawtooth Lake, Ellesmere Island, Nunavut

Diatoms from Sawtooth Lake (79°20′N, 81°51′W) on the Fosheim Peninsula in Central Ellesmere Island, Canada were analyzed to assess the temporal extent and magnitude of climatic change in the High Arctic during the late Holocene. Diatom results from the sediment cores show an absence of diatoms throughout the last ∼2.5 ka (4.6 m) until the 1920s. However, ca. 1926 (5.3-cm depth), a rapid colonization of diatoms in the lake occurred. Within the uppermost section of the core (∼1920 to ∼1997), the diatom flora shift from a small Fragilaria-dominated assemblage to a more diverse assemblage that is dominated by large planktonic taxa (e.g., Cyclotella bodanica) and large raphid benthic species. The postglacial nature of this assemblage suggests a decrease in ice cover and a concomitant increase in light and nutrient availability for diatom growth over the last ∼75 yr. Of particular significance is this absence of diatoms prior to the ∼1920s, which indicates that environmental conditions of the last ∼75 yr are unlike any of the previous ∼2500 yr.

Early Eocene Leptictida, Pantolesta, Creodonta, Carnivora, and Mesonychidae (Mammalia) from the Eureka Sound Group, Ellesmere Island, Nunavut

We describe the leptictid Prodiacodon; the pantolestids Palaeosinopa sp.nov., cf. Palaeosinopa, and Pantolestidae, gen. et sp. indet.; the creodonts Palaeonictis and Prolimnocyon; the carnivorans Viverravus, cf. Vulpavus, and Miacis; and the mesonychid Pachyaena from early Eocene (i.e., Wasatchian) strata of the Eureka Sound Group on central Ellesmere Island, Nunavut. Palaeosinopa and Palaeonictis may have originated in mid-latitude North America and subsequently migrated to Europe via a north Atlantic land bridge, while Prolimnocyon and Pachyaena probably originated in Asia. Additionally, the occurrence of Pachyaena in the Early Eocene of Europe probably is best explained by dispersal from high-latitude North America to Europe via a north Atlantic land bridge. We update the Eureka Sound Group mammalian faunal list.

Demography of three dominant sedges under contrasting grazing regimes in the High Arctic

Abstract. Tiller demography of Carex aquatilis ssp. stans, Carex membranacea, and Eriophorum angustifolium ssp. triste was investigated in ungrazed and grazed high arctic vegetation on central Ellesmere Island, Canada. Tiller birth, growth, flowering and death were studied from excavated clonal fragments, and tiller density and biomass were studied from excavated turfs. Five life‐cycle stages were determined: dormant buds, juvenile, mature, flowering and dead tillers. A stage‐based transition matrix model was developed to estimate the long‐term dynamics of the sedge populations and to compare life‐history strategies between ungrazed and grazed populations. Short‐term and retrospective models, based on the growth during the sampling year and during the lifetime of the clonal fragments, respectively, were compared to see how well the short‐term model can describe demography of long‐lived plants. According to the short‐term model, tiller populations were decreasing (λ < 1 except for C. membranacea), whereas the retrospective model indicated that the tiller populations were increasing. Tiller population growth rates did not differ between ungrazed and grazed habitats. Nevertheless, the similar growth rates may be obtained by balanced differences in the vital rates between plants of the two habitats. The plants in the ungrazed habitat tended to remain in their current life‐cycle stage, whereas plants in the grazed habitat moved quickly to the next stage and died earlier. C. aquatilis ssp. stans appears to gain a competitive advantage over the other species under intensive grazing, as indicated by the higher tiller density and greater below‐ground biomass in grazed vegetation. The greater amount of below‐ground biomass apparently buffers C. aquatilis ssp. stans against grazing better than the other species.

Small scale plant distribution within a polar desert plateau, central Ellesmere Island, Canada

In order to quantify the availability of vacant favourable or “safe” microsites, the spatial distribution of plants on a sparsely vegetated dolomitic plateau was studied in central Ellesmere Island (Canada). Vegetation (vascular plants and bryophytes), boulders and polygon margins were mapped to the closest centimetre in a 10 m ¥ 5 m plot and the microtopography of 8.5 m ¥ 5 m of that plot was surveyed at a 10 cm ¥ 10 cm scale. Vascular plant density was low (6.9 plants m-2). Individuals of the most frequent species found in the plot totalled 300 for Draba subcapitata Simm., 8 for Saxifraga oppositifolia L. and 27 for Papaver radicatum Rottb.. Many plants grew in flat microsites in proximity to boulders and larger plants of the same species indicating successful, though infrequent, reproduction on the site. Still, the total uncolonized area including microsites around boulders and plants was much larger than the area occupied by plants (total plant cover = 0.16%). Clearly, vacant microsites were abundant on this polar desert plateau. However, the rare occurrence of established plants, in spite of the presence of viable seeds, implies that for an available microsite to become a favourable one, additional conditions must be met, such as moisture availability and higher temperatures. Adequate conditions may be met only infrequently, during favourable years.

High Grazing Impact, Selectivity, and Local Density of Muskoxen in Central Ellesmere Island, Canadian High Arctic

Grazing activities and densities of muskoxen in Sverdrup Pass, Central Ellesmere Island, were investigated by use of an automatic camera monitoring system from May to August, 1987 and by direct observation from March to May 1988. Average seasonal density of muskoxen was 6.4 ± 1.9 (S.E.M.) animals × km−2 resulting in an average of 48.3 ± 5.1 (S.E.M.) % of available shoots grazed in meadow stands. These figures far surpass previous estimates of density or impact of muskoxen in the High Arctic. It shows that in some high arctic plant communities herbivores can reach high densities and have a high impact, even though aerial survey counts of large areas indicate low average animal densities. Muskoxen selected wet and mesic meadow communities between April and August, except in late June and late July of 1987, when willow herb fields were chosen. In March and early April of 1988 muskoxen grazed valley slopes with little snow cover and little vegetation. In total, 82.8% of the grazing time between 18 May and 18 August 1987, was spent in meadows, despite the fact that these communities covered only 31% of the study area. Muskoxen were therefore highly selective grazers.

High Grazing Impact, Selectivity, and Local Density of Muskoxen in Central Ellesmere Island, Canadian High Arctic

Grazing activities and densities of muskoxen in Sverdrup Pass, Central Ellesmere Island, were investigated by use of an automatic camera monitoring system from May to August, 1987 and by direct observation from March to May 1988. Average seasonal density of muskoxen was 6.4 ? 1.9 (S.E.M.) animals X km-2 resulting in an average of 48.3 ? 5.1 (S.E.M.) % of available shoots grazed in meadow stands. These figures far surpass previous estimates of density or impact of muskoxen in the High Arctic. It shows that in some high arctic plant com

Spatial pattern of Lesquerella arctica: Effects of seed bank and desiccation cracks

High Arctic plant communities are often sparsely vegetated, but the opportunities for seedling establishment, provided by the unvegetated ground, are seldom exploited. In order to identify the processes controlling the micro-scale distribution of Lesquerella arctica, a typical High Arctic perennial herb, I related the distribution of seeds, seedlings, and adult plants of L. arctica to the distribution of conspecific individuals and to desiccation cracks. All individuals of L. arctica were mapped within an area of 10 m ¥ 16 m at a polar semi-desert in central Ellesmere Island, Canada, and seed bank samples were collected close to L. arctica plants both along desiccation cracks and randomly. Greenhouse seedling emergence from the seed bank samples gave an estimated minimum seed bank of 187 germinable seeds/m2 for the upper 1 cm of soil, which is within the range of observed seed bank sizes in similar High Arctic communities. Densities of both seeds and seedlings of L. arctica decreased with distance from adult plants, creating an overall clumped distribution of adult plants. Desiccation cracks contained more L. arctica seeds, seedlings, and adults than would be expected from a random distribution, probably because desiccation cracks acted as seed traps. Consequently, the micro-scale distribution of L. arctica is primarily a result of a varied spatial incorporation of seeds into the seed bank, and the distribution of adult plants directly reflects the distribution of germinable seeds in the seed bank.