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Between May 1995 and June 1999, we studied denning ecology of 81 barren-ground grizzly bears (Ursus arctos) equipped with satellite radio-collars within a study area of 235,000 k[m.sup.2], centered 400 km northeast of Yellowknife, Northwest Territories, Canada. All dens were located on well-drained slopes ([bar]X = 25.3 [degrees], SE = 1.20, n = 55). Choice of den aspect was nonrandom ([chi square] = 12.4, d.f. = 3, P < 0.01, n = 56); the majority of dens faced south (25), followed by west (13), east (10), and north (8). Most dens were constructed under cover of tall (> 0.5 m) shrubs (Betula glandulosa and Salix), the root structures of which supported ceilings of dens. Selection of denning habitat by bears was significantly different from random (G = 127.67, d.f. = 6, P < 0.0001). Bonferroni confidence intervals indicated that esker habitat was selected more than expected by chance (P < 0.10). Den entrance occurred primarily in last 2 weeks of October. The majority of bears emerged from dens in the 1st week of May. Key words: Arctic, den ecology, grizzly bear, habitat use, Northwest Territories, Nunavut, radio telemetry, resource development, Tundra

Rates of neckband loss are calculated for Chen caerulescens caerulescens, or lesser snow geese, banded between 1993 to 1996 in the Russian and Canadian western Arctic. Females were found to have higher neckband retention than males; overall neckband retention rates decreased with time. Since neckbanding is an important population monitoring technique, improved retention is crucial to future research.

This article discusses the successful restoration of the muskoxen in Nunivak Island, Alaska. A description of the animal's history, behavior, and physiology are included.

Research presented concerns the habitat and biology of the narwhal whale, distinguished by its long, singular tusk. Topics addressed include the major populations of narwhals in Canada, the purpose of the tusk within the narwhals' social hierarchy, and how hunting has impacted the survival of the narwhal.

Carbon-14 dating of stratigraphic samples permits the first reconstruction of the glacial history of the southeastern Barents Sea. The Last Glacial Maximum ice movement in this area was from the northeast before retreating approximately 13,000 years ago.

This paper outlines the fundamental roles sea ice plays during the spring Arctic climate, and it demonstrates the use of passive microwave remote sensing in measuring climatically important sea ice variables during the spring transitional period. It discusses the theoretical concepts underlying passive microwave remote sensing of sea ice, and it summarizes the historical use of satellite microwave radiometry in the Arctic region. In addition, this paper discusses the derivation of climatically important sea ice variables, including sea ice extent, concentration, multiyear ice fraction, and snow melt onset, with additional comments on the precision and accuracy of the remote sensing estimates. It also discusses interannual trends in sea ice extent and presents interannual trends in snow melt onset dates. Finally, this paper provides a brief discussion on the future directions in passive microwave remote sensing of climatically important sea ice variables during the spring transitional period. Key Words: climate, microwave remote sensing, sea ice.

Research concerning the evaluation of the temperature of eggs of Arctic nesting Greater Snow Geese during laying and incubation is presented. Female presence at the nest and egg cooling rates were also studied.

Data is presented on the physiology of the Arctic freshwater pearl shell mollusk in relation to its longevity, which can reach 200 years. Contributing factors include the cold climate, which lowers metabolic rates, coupled with the species' ability to speed up the metabolic rate to repair damaged tissue or shell.

We examined the annual exchange of CO(sub 2) between the atmosphere and moist tussock and dry heath tundra ecosystems (which together account for over one-third of the low arctic land area) under ambient field conditions and under increased winter snow deposition, increased summer temperatures, or both. Our results indicate that these two arctic tundra ecosystems were net annual sources of CO(sub 2) to the atmosphere from September 1994 to September 1996 under ambient weather conditions and under our three climate change scenarios. Carbon was lost from these ecosystems in both winter and summer, although the majority of CO(sub 2) evolution took place during the short summer. Our results indicate that (1) warmer summer temperatures will increase annual CO(sub 2) effiux from both moist and dry tundra ecosystems by 45-55% compared to current ambient temperatures; (2) deeper winter snow cover will increase winter CO(sub 2) effiux in both moist and dry tundra ecosystems, but will decrease net summer CO(sub 2) effiux; and (3) deeper winter snow cover coupled with warmer summer temperatures will nearly double the annual amount of CO(sub 2) emitted from moist tundra and will result in a 24% increase in the annual CO(sub 2) effiux of dry tundra. If, as predicted, climate change alters both winter snow deposition and summer temperatures, then shifts in CO(sub 2) exchange between the biosphere and atmosphere will likely not be uniform across the Arctic tundra landscape. Increased snow deposition in dry tundra is likely to have a larger effect on annual CO(sub 2) flux than warmer summer temperatures alone or warmer temperatures coupled with increased winter snow depth. The combined effects of increased summer temperatures and winter snow deposition on annual CO(sub 2) flux in moist tundra will be much larger than the effects of either climate change scenario alone.

Research was conducted to examine sulfate reduction rates (SRRs) in cold and temperate sediments by quantifying sulfate reducers in two polar sediments and by comparing specific SRRs of new psychrophilic isolates to those of known mesophilic sulfate-reducing bacteria. Results suggest that psychrophilic sulfate reducers have considerably higher specific metabolic rates than their mesophilic counterparts at similarly low temperatures.

Synchronous changes in high-resolution loss on ignition profiles from widely separated shallow Arctic lakes in West Greenland suggest that sedimentary records of lake productivity provide a sensitive century-scale time series of variability in surface-air temperatures throughout the Holocene. Ice cover greatly reduces biological activity in arctic lakes, and the common productivity response among lakes is attributed to air-temperature-controlled variations in the length of the ice-cover period. Comparison with the Greenland oxygen isotope records from Summit ice cores demonstrates that the inferred temperature fluctuations in the lakes closely follow the century-scale fluctuations in the Greenland Ice Core Project [[Delta].sup.18]O record but correlate less well with the Greenland Ice Sheet Project 2 record. Low-altitude continental lake records thus not only confirm features of Holocene atmospheric temperature variability otherwise seen only in high-altitude ice cores from central Greenland, but also highlight discrepancies between the ice-core time series. The combined lake and ice-core data provide corroborative evidence for an intrinsically unstable Holocene climate in Greenland, including the 8200 yr B.P. event that is currently recognized as the most pronounced Holocene climatic cooling with possible global significance. Our finding of a link between paleoproductivity and surface-air temperature has important implications for reconstructing natural climate variability in areas where such information is still rare. The results illustrate the large potential of paleolimnologicai studies in the Arctic.

Two mixed-phase cloudy boundary layer events observed over the Arctic ice pack in autumn are extensively analyzed. The local dynamic and thermodynamic structure of the boundary layers is determined from aircraft measurements including analysis of turbulence, longwave radiative transfer, and cloud microphysics. The large-scale forcing is determined from the National Centers for Environmental Prediction reanalysis fields while mesoscale forcing is estimated from 40-km aircraft box patterns. The two cases differed somewhat in their local static stability, surface characteristics, and large-scale forcing. One case was characterized by a stably stratified cloudy boundary layer over a heterogeneous surface containing numerous open leads. The other case occurred over a fairly homogenous surface of multiyear ice and consisted of a surface-based stable layer surmounted by a low-level jet and a cloud-topped mixed layer. An important large-scale factor in the development of low clouds appears to have been water vapor advection. Low clouds formed irrespective of the sign of the large-scale vertical velocity. Observed flux profiles indicate that both cloudy boundary layers are cooled through turbulent eddies except at cloud top where entrainment of warm moist air aloft occurs. Maximum turbulent kinetic energy occurs near cloud top where turbulent motions are driven by strong radiative cooling (>-70 K [day.sub.-1]) and in the vicinity of the low-level jet where turbulence is shear induced. The presence of both liquid and ice in the cloud layers appears to be a nearly steady-state feature at temperatures between -13 [degrees] and -20 [degrees] C. Results of a simple condensed water budget indicate that these colloidally unstable mixed-phase clouds may be maintained through strong cloud-top radiative cooling. The isobaric cooling rate required to maintain the presence of both liquid and ice in a stratiform cloud is quite sensitive to variations in the highly uncertain concentration of ice-forming nuclei.

1 Five treeline species had low seed germination rates and low survivorship and growth of seedlings when transplanted into Alaskan tundra. Seed germination of all species increased with experimental warming, suggesting that the present treeline may in part result from unsuccessful recruitment under cold conditions. 2 Growth, biomass and survivorship of seedlings of treeline species transplanted into tundra were largely unaffected by experimental warming. However, transplanted seedlings of three species (Betula papyrifera, Picea glauca and Populus tremuloides) grew more when below-ground competition with the extant community was reduced. All three measures of transplant performance were greater in shrub tundra than in the less productive tussock or heath tundra. Establishment of trees in tundra may thus be prevented by low resource availability and competition. 3 Two species (Alnus crispa and Populus balsamifera) had low seed germination and survivorship of germinated seeds; transplants of these species did not respond to the manipulations and lost biomass following transplanting into tundra. Isolated populations of these two species north of the present treeline in arctic Alaska probably became established during mid-Holocene warming rather than in recent times. 4 Of all the species studied here, Picea glauca was the most likely to invade intact upland tundra. Its seeds had the highest germination rates and it was the only species whose seedlings survived subsequently. Furthermore, transplanted seedlings of Picea glauca had relatively high survivorship and positive growth in tundra, especially in treatments that increased air temperature or nutrient availability, two factors likely to increase with climate warming. Keywords: Alaskan treeline, climate change, Picea glauca, tree establishment, tundra

Eriophorum vaginatum and E. angustifolium are dominant arctic sedges of the well-drained tussock tundra and the permanently flooded wet-sedge tundra, respectively. We determined diurnal courses of gas exchange and water relations of the two species in their natural habitat and compared their responses to changes in light, air temperature, and humidity. Mean photosynthetic response to light was similar between E. angustifolium and E. vaginatum and carbon gain in both species was light limited during most of the growing season. On sunny and dry days, both species closed stomata in response to high leaf-to-air vapor pressure deficits. Even though E. angustifolium was growing in standing water, it exhibited a tighter control of transpirational water loss and had lower hydraulic conductivity in the soil-root-shoot pathway than E. vaginatum. The different response pattern between the two species is discussed in the context of differences in habitat conditions. Key words: Arctic tundra; Cyperaceae; Eriophorum; gas exchange; water relations.

Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant.

In the period between Jan 1996 and Mar 1996, 120 Dobson units (DU) to 160 DU of ozone were chemically destroyed in the Arctic. This was the result of the simultaneous occurrence of very low Arctic stratospheric temperatures and large stratospheric chlorine loadings. It is likely that stratospheric chlorine concentrations will continue to rise, even though chlorofluorocarbon production is being phased out in the developed world. There is significant interannual variability in Arctic winter temperatures, but there are signs of a cooling of the stratosphere, prompted by rises in radiatively active trace gases.

A high-resolution multiparameter stratigraphy allows the identification of late Quaternary glacial and interglacial cycles in a central Arctic Ocean sediment core. Distinct sandy layers in the upper part of the otherwise fine-grained sediment core from the Lomonosov Ridge (lat 87.5 [degrees] N) correlate to four major glacials since ca. 0.7 Ma. The composition of these ice-rafted terrigenous sediments points to a glaciated northern Siberia as the main source. In contrast, lithic carbonates derived from North America are also present in older sediments and indicate a northern North American glaciation since at least 2.8 Ma. We conclude that large-scale northern Siberian glaciation began much later than other Northern Hemisphere ice sheets.

The arctic atmosphere is the repository for surprisingly high concentrations of pollutants throughout the winter months. The polluted air mass in question includes virtually all the atmosphere above the Arctic Circle and also two great lobes that extend down over Eurasia and North America. In extent, this generally polluted airmass system is about as large as the African continent. The rather severe pollution throughout this airmass system in winter is, to a large extent, a result of the lowered rates of particle and gas removal in this cold, dark, and rather stable system. The arctic haze possibly has important climatic and ecological and global change implications that are coming under investigation in a number of planned studies.

The southern Yermak Plateau (northwest of Spitsbergen) was investigated with 11-12 kHz sidescan sonar and 3.5 kHz profiler to test whether thick Pleistocene ice streams ever calved into the Arctic Ocean and/or whether a continuous Arctic ice sheet existed. In either case, the ice would have grounded on the plateau crest on its way out of the Arctic. Several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m, perhaps recording the deepest iceberg keels known. The plateau crest (510-530 m) is nearly bare of plowmarks, perhaps because of beveling by an ice rise formed of grounding shelf ice. This implies continuous, 400-600-m-thick grounded ice, consistent with but not proving the postulated existence of an Arctic ice sheet. Most plowmarks are probably late Pleistocene products of the calving of Barents-Kara ice sheets into the Arctic Ocean. Plowmarks in 450-850-m-deep water require unusually deep ice-sheet grounding lines (e.g., Svyataya Anna Trough) and/or draft-increasing capsizing events, even if sea levels were 100-150 m lower than today. At water depths of 800 to 1800 m, the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau.

To investigate whether shorebirds breeding in the High Arctic have relatively high rates of energy expenditure due to the harsh climatic conditions that prevail even in summer, we measured daily energy expenditure (DEE) and water turnover of Ruddy Turnstones (Arenaria interpres) during the incubation phase on Rowley Island in Foxe Basin, N.W.T., Canada, at 69 degrees N, using the doubly-labeled-water technique. Simultaneously, we conducted detailed measurements of ambient climatic conditions, including in situ measurements with heated taxidermic mounts. A series of 11 doubly-labeled-water measurements with eight individual Ruddy Turnstones, of which at least seven successfully hatched eggs, yielded a mean DEE of 4.08 W. This is a relatively high value for a 108-g bird, equalling four times their basal metabolic rate (BMR). Most variation in DEE was attributable to standard operative temperature, which combines the effects of air temperature, wind and radiation on heat loss from the turnstone's point of view. On average, 25% of DEE was attributable to BMR, 31% to the cost of thermoregulation, and 44% to the cost of activity. The average value for water turnover of 96.6 g/day is high compared to published values for other birds and confirms the large requirement for food (which is water-rich) of incubating Ruddy Turnstones. An analysis of the climatic conditions prevalent in Foxe Basin during the breeding seasons of Ruddy Turnstones, based on the 33-year period 1958-1990, indicated that they faced thermostatic hardships, defined as energy expenditure exceeding the maximum sustained working level (estimated at 4.5 times BMR), on 15% of the days. Climatic conditions were most severe in the early 1960s, but have improved since.

Acoustic backscatter imagery in the Fram strait (between Greenland and Spitzbergen) reveals a 1-3-km-wide, 50-km-long belt of approximately 50 pointlike backscatter objects decorating the approximately 1300-m-deep crest of Vestnesa Ridge, a 1->2 km thick sediment drift possibly underlain by a transform-parallel oceanic basement ridge (crustal ages approximately 3-14 Ma). A 3.5 kHz seismic-reflection profile indicates that at least some objects are pockmarks approximately 100-200 m in diameter and 10-20 m deep. The pockmarks (possibly also mud diapirs) may have been formed by evolution of methane generated by the decomposition of marine organic matter in the Vestnesa ridge sediment drift. The ridge may be underlain by an anticlinal carapace of methane-hydrate calculated to be 200-300 m thick, comparable to the hydrate thickness measured just to the south. The rising methane would collect in the ridge-crest trap, intermittently escaping to the sea floor. This hypothesis is supported by multichannel evidence for bright spots and bottom-simulating reflectors in the area. The pockmark belt may also be located above a transcurrent fault. Sediment slumps on the flanks of Vestnesa ridge and northeast of Molloy ridge may have been triggered by plate-boundary earthquakes and facilitated by methane hydrates.

Alaska's Denali National Park and Preserve has become the most accessible and famous subarctic sanctuary in the world. Around 300,000 people visit the area annually, helping the state's tourist industry become Alaska's fastest growing source of income. Environmentalists are calling for more restrictions on the number of visitors allowed to see the park, hoping that limited access will allow the park to remain pristine. Many of the so-called ecotourist agencies in the state, however, are not practising environmentally sound business.

The temporal and spatial distribution of polar bear (Ursus maritimus) maternal denning in the Beaufort Sea region of Alaska and Canada was studied to improve the understanding of the effects of hunting and industrial development on polar bears. The study protocol involved capturing and attaching radio-collars on bears from 1981-91. The results showed that of 90 dens found, 48 were on pack ice, 38 were on land and four were on land-fast ice. Predictable denning chronology and lack of denning site fidelity may mitigate the effects of human activities on polar bear reprodduction.

Foraging behavior and physiological adaptations for diving were studied in Thick-billed Murres, Uria lomvia, in the field and laboratory. Electronic, light-emitting diode, and capillary recording devices were used to measure foraging behavior. Individual dives were a flattened U shape in profile, and occurred in bouts lasting [is nearly equal] 15 min. Dive patterns were nocturnal; most dives occurred between 2000 and 0400. Murres probably concentrate their foraging effort at times when prey is most available as it migrates closer to the surface in the evening as part of the deep scattering layer. Although dives averaged 18 m in depth and 55 s in duration, most time-at-depth was spent between 21 and 40 m. Thus, murres made a large number of shallow, short-duration dives. Maximum dive depth was 210 m, while maximum dive duration was 224 s. Descent and ascent rates averaged 0.94 and 0.85 m/s, respectively. Hematocrit, hemoglobin, blood volume, and pectoralis myoglobin levels were measured in the laboratory as 52.8%, 18.0 g/100 mL, 12.3% body mass, and 1.9 g/100 g, respectively. Total useable oxygen store was calculated as 44.8 mL/kg, giving an estimated aerobic dive limit (ADL) of 47 s. Murres exceeded the calculated ADL in 48% of their dives. Long-duration diving is probably a more efficient foraging strategy for murres given their relatively small size and limited oxygen storage capabilities. The observed dive depths raised questions of potential problems with decompression sickness (bends) and lung collapse. Key words: alcid; Arctic; diving; feeding; foraging; physiology; seabird; Thick-billed Murre; Uria lomvia.

Primary production, plant biomass, plant element content, and various measures of turnover and element cycling were compared among four contrasting tundra vegetation types near Toolik Lake, Alaska. The study sites were selected to represent extreme examples of the wide variation in plant growth form composition that is typical of northern ecosystems. The aim of the research was to determine whether vegetation types that differ in their dominant plant growth form also differ in their production: biomass relationships and overall patterns of element use. The four sites included tussock tundra, a deciduous shrub-dominated reparian tundra, an evergreen heath tundra, and wet sedge tundra. Biomass and elements content (N, P, K, Ca, and Mg) were determined for both vascular and nonvascular plants, and production estimates were obtained for vascular plants. Production and biomas of mass tissues were determined by quadrat harvest methods, with additional, separate determinations of stem secondary growth and belowground rhizome growth as components of net primary production (NPP). Production, biomass, and element content of roots were not determined. Vascular plant biomass (excluding roots) varied by nearly 19 X among sites, from 217 to 1877 [g/m.sup.2]. At least 50% of the vascular biomass at all four sites was belowground stems, but the relative allocation to leaves vs. aboveground stems varied greatly. When mosses and lichens were included, total biomass varied by only 5 x among sites, and lichens were in fact the most abundant plant form at the evergreen heath site. The element content in vascular biomass of these communities varied by 8-21 x, depending upon the element; including mosses and lichens, element content varied by 6-12 x. Primary productivity of vascular plants also varied sharply among sites, from 32 to 305 [g.m.sup.-2..yr.sup.-1] (not including root production). Leaves were the largest single component of NPP at all sites, but the relative importance of above- and belowground stem growth varied considerably. The element requirements of vascular NPP varied by 9-17 x, depending pppn the element. Despite these order-of-magnitude differences among sites in biomass, production, and element requirements, and the dramatic variation in allocation patterns, there was remarkably little difference among sites in the overall production: biomass relationships and element turnover. These overall similarities were due to the dominant effect of stems and rhizomes in the whole-plant and whole-vegetation biomass and element budgets. The wide range of leaf turnover rates and leaf production efficiencies was compensated at the wholeplant level by stem processes, especially element storage. Thus, we conclude that plant growth form composition is not a good indicator of whole-vegetation biomass turnover rates and patterns of element use, although growth form composition is related to total production and biomass.

Surface temperatures over the Arctic Ocean recorded between 1950 and 1990 failed to confirm the atmospheric greenhouse model that predicted a general warming trend for the Arctic. In fact, the Arctic during this time became cooler rather than warmer. Biases that may exist in these temperature records are insufficient to overturn this result. Revised greenhouse models should be based on better knowledge of polar climatic phenomena.

A parameterization is described for low-level clouds that are characteristic of the Arctic during winter. This parameterization simulates the activation of aerosols, the aggregation/coalescence, and the gravitational deposition of ice crystals/water droplets and the deposition/condensation of water vapor onto ice crystals/water droplets. The microphysics scheme uses four prognostic variables to characterize clouds: ice water content, liquid water content, and the mean diameter for ice crystals and for water droplets, and includes prognostic supersaturation. The parameterization simulates stable clouds where turbulence add entrainment are weak, like ice fogs, thin stratus, and diamond dust. The parameterization is tested into the Local Climate Model (LCM), which is the single column version of the Northern Aerosol Regional Climate Model (NARCM). NARCM is a regional model with an explicit representation of the aerosol physics and with the physics package of the Canadian Climate Center General Circulation Model version two. Since most climate models do not have prognostic size-segregated aerosol representation, an alternate method is proposed to implement the microphysical parameterization into these models. The model results are compared to observations of diamond dust and ice fog at Alert (Canada) for the period 1991-94. Two aerosol scenarios are compared in the simulation: a natural background aerosol scenario and an acidic aerosol scenario. Results show that the LCM reproduces approximately the time variation of the observed weekly frequency of the total ice crystal precipitation with a correlation coefficient of 0.4. Although it overestimates diamond dust frequency and underestimates ice fog frequency, the LCM predicts quite well the total precipitation frequency (ice fog and diamond dust added). The acidic aerosol scenario is in good agreement with the observations, showing a mean frequency of total precipitation over the 4 yr of 39% compared to the observed value of 37%. The natural aerosol scenario overestimates this frequency with a value of 47%. These results were expected since recent aerosol observations have shown the predominance of sulfuric acid-coated aerosols in the Arctic during winter.

High-latitude faunal migrations have been documented during a rapid warming event near the Paleocene-Eocene boundary (the latest Paleocene thermal maximum, LPTM). The migrations are difficult to explain from a climate perspective. Climate along these routes is at present too harsh to support the migrations, and no mechanism has yet proved adequate to explain the past high-latitude warmth required by such migrations. A large negative excursion in the [Delta] [sup.13]C record at the LPTM suggests that a large quantity of [CH.sub.4] was released into the atmosphere at this time. High concentrations of atmospheric [CH.sub.4] have been linked to the formation of polar stratospheric clouds. We used an atmospheric general circulation model to explore early Cenozoic climate response to the combined effects of high atmospheric [CH.sub.4] levels and polar stratospheric clouds, a unique combination of forcing factors in paleoclimate modeling studies. Our interests are in understanding if the climate response to this forcing may explain the high-latitude faunal migrations. Model results indicate that high-latitude winter warming with high methane levels and polar stratospheric clouds is sufficient to facilitate the high-latitude migrations. Temperatures along high-latitude migration routes remained above freezing year-round and thus permitted exchanges of fauna between Asia, North America, and Europe. On the basis of our results, we suggest that other Paleogene migrations may be correlated with LPTM-Iike events with high concentrations of greenhouse gases and polar stratospheric clouds. Keywords: paleoclimatology, Paleogene, Arctic region, methane, mammals, migration.

The impact of solar heating and infrared cooling on the growth of a population of drops is studied with two numerical modeling frameworks. An eddy-resolving model (ERM) simulation of Arctic stratus clouds is used to generate a dataset of 500 parcel trajectories that follow the mean dynamic motions of the simulated cloud. The 500-parcel dataset is used to drive a trajectory ensemble model (TEM) coupled to an explicit microphysical model that includes the radiative term in the vapor growth equation. The second framework is that of the ERM itself. Results from the TEM show that the production of drizzle-sized drops is strongly dependent upon parcel cloud-top residence time for both radiative- and nonradiative-influenced growth. Drizzle-sized drops can be produced between 20 and 50 min earlier through the inclusion of the radiative term, which corroborates earlier results. The radiative effect may also cause drops with r [is less than] 10 [micro]m to evaporate, producing a bimodal size spectrum. Parcel cloud-top residence times as short as 12 min can initiate this bimodal spectrum. TEM results show that the radiative effect increases drizzle drop mass predominately in parcels that tend to contribute to drizzle even in the absence of the radiative term. Activation of large cloud condensation nuclei appears to have a larger effect on drizzle production than does the radiative term. ERM simulations show a weak overall influence of the radiative term. Drizzle onset occurs earlier when the radiative term is included (about 20 min), but there is no strong change in the overall structure or evolution of the cloud.

Research presented concerns the habitats and food sources of the migratory shore bird, the red knot. Researchers are studying the relationship between horseshoe crab harvesting by fishermen and a decline in red knot populations.

The Tertiary Eurekan orogen of northernmost North America differs from a standard fold-and-thrust belt in several respects. It lacks a metamorphic-plutonic hinterland and wedge-shaped profile; instead, 2-km-high mountains of southeast Ellesmere Island face the frontal trust, whereas halotectonic polygons, gentle warps, and subdued topography extend form Axel Heiberg Island in the center of the system back to the Sverdurp Rim at its rear. Clastic deposits are not located in a single flexural foredeep but are distributed in topographic lows amid several thrust sheets. The age of the stratigraphy, amount of displacement, and intensity of strain all increase cratonward, and the system's width-to-length ratio is anomalously high. The orogen is attributed to Greenland's pivotal movement relative to North America, which formed a braided Cenozoic plate boundary in Ellesmere and Axel Heiberg Islands, not a single transform in Nares Strait as previously proposed. The three major strands of this braided system are the Parrish Glacier, Vesle Fiord, and Stolz thrusts. They die out toward a structural pole of rotation in the south, whereas to the north, movement is accommodated by a dextral transpression zone extending from Lake Hazen to northern Greenland. Field studies on Ellesmere Island combined with a regional synthesis of previous work show that Eurekan deformation style is indicative of pivotal tectonism, that the contraction necessary to accommodate Greenland's displacement is similar in magnitude to that documented by Eurekan structures, and that the ages of continental structures are compatible with the paleomagnetic record of seafloor spreading in Labrador Sea and Baffin Bay. Previously proposed sinistral strike-slip displacement is not confirmed; rather, eastvergent thrusts and dextral wrench faults typify the system. We propose that the Eurekan orogeny marked a change from tip propagation to pivotal tectonism as the North Atlantic rift system penetrated the entire width of the Laurasian continent.