Northeastern Canada Research Articles

Crustal-scale flexural slip folding during late tectonic amplification of an orogenic boundary perturbation in the Paleoproterozoic Torngat Orogen, northeastern Canada

Large variations in metamorphic grade over short distances, disparate orientations and diverse kinematics of contemporaneous structures, and a previously unexplained, 90° counterclockwise bend in the orogenic boundary of the amphibolite- to granulite-facies northern segment of the Paleoproterozoic Torngat Orogen are shown to be the result of multiple tectonic events acting upon an orogenic boundary perturbation. The perturbation was initiated when a promontory on the Nain Province margin, composed of a 1910–1885 Ma continental magmatic arc (Burwell domain), indented the Rae Province hinterland during the onset of collisional orogeny at ca. 1870 Ma (Dn+1). Sinistral transpression at ca. 1845–1822 Ma (Dn+2) caused formation of the orogen-parallel Abloviak shear zone and oblique burial of the Nain Province margin beneath a tilted section of the hot, buoyant magmatic arc. Reactivation of the orogen at ca. 1798–1770 Ma (Dn+3) involved crustal-scale flexural slip folding of the perturbation and simultaneous exhumation of the Burwell domain and the previously buried Nain crust across the Komaktorvik shear zone, which represents a sheared, tightened fold train localized along the western limit of thinned Nain crust affected by preorogenic rifting, but which does not represent a fundamental plate boundary. The along-strike heterogeneities in the Torngat Orogen document the influence of geometrical and competency heterogeneities in the colliding margins on subsequent deformation and the fact that heterogeneities in the deep crust persist through high-grade metamorphism.

RECONSTRUCTION OF MILLENNIAL FOREST DYNAMICS FROM TREE REMAINS IN A SUBARCTIC TREE LINE PEATLAND

Tree ring and growth form sequences of 319 black spruce (Picea mariana (Mill.) BSP.) stems buried in a treeless peatland at the arctic tree line of northern Quebec were used to reconstruct the development of a woodland in response to climate change and fires during the last 2500 years. A high frequency of diagnostic tree rings (light rings and narrow rings) allowed the cross-dating of 142 individuals and the construction of a master chronology spanning AD 690-1591. Three floating chronologies covering 964 ( 178 BC- AD 785), 349 (-587-239 BC) and 210 (-1274-1065 BC) years were also developed. The buried stems were classified as arborescent (75%), small fragments of unknown origin (13%), stumps (11%), and portions of stunted stems (1%). The high frequency of arborescent individuals indicates that the buried spruces were the remains of a former forest. The forest bordered the peatland between 600 BC and AD 1568, and successfully regenerated after two fires around 350 BC and 10 BC. Winter-damaged trees dominated during periods of suppressed growth at AD 760-860 and AD 1025-1400, whereas undamaged trees were more frequent during periods of rapid growth around AD 700-750, 860-1000, 1400-1450, and 1500-1570. Fast growth between AD 860-1000, along with the concurrent establish- ment of symmetrical trees, suggests well-defined boundaries for the Medieval Warm Period in northeastern Canada. The forest abruptly shifted to an open krummholz (stunted spruce) after the last fire in AD 1568, indicating that a climatic threshold inhibiting postfire re- generation was crossed between the second and the last fires. The maintenance of this old growth forest over 1500 yr, in the absence of external disturbances except climate change, was probably due to the buffering effect of aggregated trees on wind-drifted conditions at the snowpack line. With the exclusion of the forest influence on microclimate and local growth conditions, the AD 1568 fire caused the forest vegetation to shift to krummholz. The amplitude of these ecosystem changes at tree line does not mirror that of climate change. Hence, it is concluded that climate and vegetation reconstructions from proxy indicators cannot portray full ecological impact, because vegetation change at tree line is nonlinear relative to climate change.

Reconstruction of Millennial Forest Dynamics from Tree Remains in a Subarctic Tree Line Peatland

Tree ring and growth form sequences of 319 black spruce (Picea mariana [Mill.] BSP.) stems buried in a treeless peatland at the arctic tree line of northern Québec were used to reconstruct the development of a woodland in response to climate change and fires during the last 2500 years. A high frequency of diagnostic tree rings (light rings and narrow rings) allowed the cross-dating of 142 individuals and the construction of a master chronology spanning AD 690–1591. Three floating chronologies covering 964 (≈178 BC–AD 785), 349 (≈587–239 BC) and 210 (≈1274–1065 BC) years were also developed. The buried stems were classified as arborescent (75%), small fragments of unknown origin (13%), stumps (11%), and portions of stunted stems (1%). The high frequency of arborescent individuals indicates that the buried spruces were the remains of a former forest. The forest bordered the peatland between 600 BC and AD 1568, and successfully regenerated after two fires around 350 BC and 10 BC. Winter-damaged trees dominated during periods of suppressed growth at AD 760–860 and AD 1025–1400, whereas undamaged trees were more frequent during periods of rapid growth around AD 700–750, 860–1000, 1400–1450, and 1500–1570. Fast growth between AD 860–1000, along with the concurrent establishment of symmetrical trees, suggests well-defined boundaries for the Medieval Warm Period in northeastern Canada. The forest abruptly shifted to an open krummholz (stunted spruce) after the last fire in AD 1568, indicating that a climatic threshold inhibiting postfire regeneration was crossed between the second and the last fires. The maintenance of this old growth forest over 1500 yr, in the absence of external disturbances except climate change, was probably due to the buffering effect of aggregated trees on wind-drifted conditions at the snowpack line. With the exclusion of the forest influence on microclimate and local growth conditions, the AD 1568 fire caused the forest vegetation to shift to krummholz. The amplitude of these ecosystem changes at tree line does not mirror that of climate change. Hence, it is concluded that climate and vegetation reconstructions from proxy indicators cannot portray full ecological impact, because vegetation change at tree line is nonlinear relative to climate change.

An assessment of the regional distribution of the oxygen-isotope ratio in northeastern canada

A compilation of mean values of the oxygen-isotope ratio relative to standard mean ocean water (δ18O, in ‰) for 22 siIes representative of conditions in northeastern Canada is complemented with data on mean annual surface temperature, latitude, surface elevation, and mean annual shortest distance to open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analysis is used to develop a multivariate model suitable to inter the distribution of δ18O in an area of complex topography and possibly mixed sourcing of advected water vapor. The best model is produced by a run in the backward mode at the 95% confidence level in which only temperature, latitude and distance to the open ocean remain in the model (the correlation coefficient is 0.915, the adjusted coefficient of determination is 0.809, the root mean square residual is 1.62). This model is similar to the best δ18O predictive model derived elsewhere for Greenland, suggesting a common principal source of advected moisture.

An assessment of the regional distribution of the oxygen-isotope ratio in northeastern canada

A compilation of mean values of the oxygen-isotope ratio relative 10 Standard mean ocean waterfor 22 siIes representative of conditions in northeastern Canada is complemented with data on mean annual surface temperature, latitude, surface elevation, and mean annual shortest distance to open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analysis is used to develop a multivariate model suitable to inter the distribution ofin an area of complex topography and possibly mixed sourcing of advected water vapor. The best model is produced by a run in the backward mode at the 95% confidence level in which only temperature, latitude and distance to the open ocean remain in the model (the correlation coefficient is 0.915, the adjusted coefficient of determination is 0.809, the root mean square residual is 1.62). This model is similar to the bestpredictive model derived elsewhere for Greenland, suggesting a common principal source of advected moisture.

Tropospheric Water Vapor Climatology and Trends over North America: 1973–93

Abstract Here 21 years of radiosonde observations from stations in the Western Hemisphere north of the equator were analyzed for trends in tropospheric water vapor. Mean fields of precipitable water and relative humidity at several levels we shown. Annual trends of surface-500 mb precipitable water were generally increasing over this region except over northeastern Canada. When trends were expressed as a percentage of the climatological mean at each station, the trends south of ∼45°N represent a linear rate of increase of 3%–7% decade−1. Trends in the upper portion of this layer, 700–500 mb, were as large or larger than those of the middle (850–700 mb) or lower layer and were consistent in sign. Annual trends in dewpoint generally agree in sign with trends in temperature. However, the dewpoint trends tended to be larger than those of temperature. This was consistent with the annual increases found in relative humidity over this period. Relative humidity increased except in Canada, Alaska, and a few statio...

Tectonic evolution of the Paleoproterozoic Torngat Orogen: Evidence from pressure‐temperature‐time‐deformation paths in the North River map area, Labrador

The study of ancient, deeply eroded orogenic belts can provide information about tectonic processes in the deep crust that is unobtainable from upper crustal sections in younger belts. In this light, the Paleoproterozoic Torngat Orogen in northeastern Canada is ideal because it is well exposed and eroded to maximum depths of 28 km, revealing information about transpressional deformation mechanisms during continent‐continent collision between the Archean Nain and southeastern Rae provinces. Evidence from detailed structural mapping, metamorphic petrology, and geothermobarometry of a 115‐km transect of the orogen is combined with previously published geochronology to construct pressure‐temperature‐time‐deformation (P‐T‐t‐d) paths for rocks from the granulite‐facies core and amphibolite‐facies Foreland zone of the orogen. Results show that rocks followed a clockwise P‐T‐t path, but different parts of the orogen reached peak conditions at different times. The orogen evolved through three temporally and kinematically distinct events over ∼80 m.y., rather than continuous deformation. Events were separated by gaps of 15–30 m.y. and include (1) crustal thickening during continental collision at ca.1860 Ma under peak metamorphic conditions of 9.5 ± 0.5 kbar and 950° ± 50°C in the core of the orogen, and prethermal peak conditions of 4.5 kbar and 550°C in the Foreland zone; (2) sinistral transpressional shear at ca. 1845–1822 Ma under post‐peak conditions of 7.3 ± 0.5 kbar and 750° ± 50°C in the core of the orogen, but at thermal peak conditions of ∼5 kbar and 700°C in the Foreland zone; and (3) west‐directed exhumation of the orogen at 1794–1740 Ma, under lower‐grade conditions of up to ∼5 kbar and 600°C. The overall transpressional features of the orogen are shown to be a cumulative result of three distinct tectonic events which can be related to changes in plate/subduction configurations across the rest of NE Laurentia.

The role of hydrothermal processes in concentrating high-field strength elements in the Strange Lake peralkaline complex, northeastern Canada

The middle-Proterozoic peralkaline pluton at Strange Lake, Quebec/Labrador, comprises hypersolvus to subsolvus phases which are unusually enriched in Zr, Y, REEs, Nb, Be, and F, as exotic alkali and alkaline-earth silicate minerals. The highest concentrations of these elements are in subsolvus granite, which underwent intense low temperature (≤200°C) hydrothermal alteration involving hematization and the replacement of alkali high-field strength element (HFSE) minerals by calcic equivalents. This alteration is interpreted to have been caused by meteoric or formational waters. High temperature (≥ 350°C) alteration, attributed to orthomagmatic fluids, is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine. Comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected, except for depletion in Zr, Y, and HREEs. These elements were appreciably enriched in rocks that underwent low temperature alteration. Other elements affected by low temperature alteration include Ca and Mg, which were added and Na, which was removed. Available data on HFSE speciation in aqueous fluids and the chemistry of the pluton, suggest that the HFSEs were transported as fluoride complexes. If this was the case, the low temperature fluid could not have been responsible for HFSE transport, because the high concentration of Ca and low solubility of fluorite would have buffered F − activity to levels too low to permit significant complexation. We propose that HFSE mineralization and accompanying alteration were the result of mixing, in the apical parts of the pluton, of a F-rich, essentially Ca-free orthomagmatic fluid containing significant concentrations of HFSEs, with an externally derived meteoric-dominated fluid, enriched in Ca as a result of interaction with calc-silicate gneisses and gabbros. According to this interpretation, the latter fluid was responsible for the exchange of Ca for alkalis, mainly Na, in HFSE-rich minerals and, by sharply reducing F − activity in the mixed fluid through fluorite precipitation and/or increasing pH, destabilised the HFSE-fluoride complexes, causing deposition of HFSE-bearing minerals. An important implication of this study is that major HFSE enrichment may be restricted to those rare cases where F-rich, Ca-free, metal leaching environments and Ca-rich depositional environments are juxtaposed.

An analytical approximation of the distribution of total hydrocarbon discoveries as a function of discovery number

Recently, Manly's method has been successfully applied to hydrocarbon exploration modeling in order to approximate the expected value and the standard deviation of the total amount of hydrocarbons discovered. This method is much faster than running prolonged simulations normally required by the probabilistic model of the hydrocarbon discovery process, and the results are very accurate. This paper extends the usefulness of the approximation method by developing an approximate analytical model of the whole probability distribution of the total volume of hydrocarbons discovered. The mean and the standard deviation from Manly's approximation are used to help set the parameters of a family of beta distributions, to represent the distributions of the total amount of hydrocarbons discovered from the beginning to the end of the exploration process in an area. Three real datasets—the Nova Scotian Shelf from offshore northeastern Canada, the Bistcho Play, and the Zama Play from northwestern Canada—are chosen to verify the methodology developed. Confidence intervals of the forecast for each number of discovered fields are constructed from the analytical approximation and compared with confidence intervals generated by the simulation. Sensitivity analyses are performed to show that the idea of using a family of beta distributions is a robust approximation.

Burwell domain of the Palaeoproterozoic Torngat Orogen, northeastern Canada: tilted cross-section of a magmatic are caught between a rock and a hard place

Abstract The northern segment of the Palaeoproterozoic Torngat Orogen is unique relative to the southern segment in that it is underlain by a 1910–1885 Ma suite of diorite-tonalite-granite rocks (DTG suite) emplaced into the margin of the Archaean Nain Province. Field and geochemical data indicate that it represents a subduction-generated Andean-type magmatic arc. Slivers of MORB-type, tholeiitic amphibolites and metasedimentary rocks within the DTG suite are interpreted as remnants of a backarc basin. Arc rocks are preserved in a tilted section from homogeneous, foliated tonalites at mid-amphibolite facies in the east, through gneissic tonalites, to massive orthopyroxene-bearing granitoid rocks of the Killinek charnockitic suite in the west. This assemblage is separated from the Archaean Rae Province, with which Nain Province collided, by a wide belt of turbiditic sedimentary rocks, now at granulite facies, known as the Tasiuyak gneiss. A younger suite ( c. 1865 Ma) of mafic tonalites and megacrystic metagranites within the Nain arc suite represents either syn-collisional plutons or late additions to the continental magmatic arc. The southern segment of the orogen differs from the northern segment because it preserves no evidence of the DTG suite on Nain Province margin, but instead contains a widespread suite of calc-alkaline plutons across the Tasiuyak gneiss/Rae Province margin, dated as 1880 Ma. We develop two testable models to account for these along-strike variations and the presence of arc magmas on both sides of the suture. In Model A , a flip in subduction polarity from east-dipping at 1910–1885 Ma to west-dipping at c. 1885 Ma is invoked, in which the c. 1865 Ma suite of plutons in the northern segment are interpreted to represent syn-collisional magmas generated during accretion of the Burwell arc onto Nain Province. In Model B , the younger plutons in the northern segment may be interpreted as a late phase of the arc built on Nain Province, which we suggest may have been accomplished during a phase of double subduction immediately prior to collisional orogeny. The Nain-Rae collision at c. 1870–1860 Ma formed a doubly vergent thrust wedge, burying part of the arc in Burwell domain to depths of 35 km. During subsequent sinistral shear deformation at 1845–1822 Ma, Nain Province was buried obliquely beneath the still hot arc to depths of 40 km. At 1798–1780 Ma, crustal-scale disharmonic folding of the northern segment resulted in the simultaneous exhumation of the deeply-buried granulites of the arc and of the northwestern margin of the Nain Province across the Komaktorvik shear zone (KSZ). The KSZ was the site of significant translation between the Burwell domain and unreworked portions of the Nain Province, but it does not represent a fundamental plate boundary.

Proterozoic orogens of the northeastern Canadian Shield: new information from the Lithoprobe ECSOOT crustal reflection seismic survey

As part of the Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT), Lithoprobe acquired 1250 km of deep seismic reflection data along the coast of Labrador and across Ungava Bay, to image evidence of Proterozoic crustal accretion to the Archean nuclei of the Nain and Superior provinces of the Canadian Shield. The relatively pristine Archean crust of the Nain Province has low reflectivity and generally lacks systematic reflector orientations. Reworking of Archean crust on the margins of the Makkovik Province has little effect on this weak signature. In contrast, the Archean crust in the Eastern Churchill (Rae) Province appears to have been overprinted by a strongly developed, whole-crustal, easterly dipping reflection fabric, interpreted to result from Proterozoic collision of the Nain and Superior provinces in the paired New Quebec and Torngat orogens. Juvenile Proterozoic crust in the Makkovik and Grenville provinces also shows strong whole-crustal dipping reflection fabrics, interpretable as outwardly verging structures associated with collisional mobile belts. Crustal thickness varies from 35 to 45 km in Proterozoic provinces, except where thinner in areas probably affected by Mesozoic extension associated with rifting of the Labrador Sea. Dipping reflectors in the mantle are commonly associated with strong lower-crustal dipping reflections in a manner similar to that observed in some modern orogens. The ECSOOT data show that Proterozoic crust in this area has structural forms comparable with those of modern orogens and, inferentially, its tectonic development was controlled by very similar collisional processes.

Drainage and Water Quality in Northern United States and Eastern Canada

Drainage has been used in the northeastern United States and Canada since colonial times. It has only been since the 1970s that substantial quantities of subsurface drains have been installed annually in Quebec. Drainage in Ontario was first installed in the early 1900s. Today there is an increasing concern that drainage is harmful to the environment. It has only been in recent years that projects have been initiated to evaluate the environmental impacts of agricultural drainage. Both nitrates and pesticides have been detected in agricultural drainage waters, sometimes at concentrations exceeding drinking-water standards. Research has identified the need for integrated management of water quality and quantity. There is a need to quantify the role of preferential flow as a mechanism of pollutant transport in surface and subsurface drainage water and to develop a modeling approach that is applicable at the field and watershed scale.

Mercury concentration in tree rings of black spruce (Picea mariana Mill. B.S.P.) in boreal Quebec, Canada

Black spruce from boreal forests located in northeastern Canada (Quebec) were sampled during the summer of 1990, at two stations located at 6° latitude from one another. The objective of the study was to compare the temporal and spatial evolution of mercury in the tree rings of sites with differing degrees of mercury contamination in their soils. Mean mercury tree ring contents ranged from 13 to 37 ng/g, and were more concentrated in the southern than in the northern station. No evident relationship was found between annual growth and corresponding mercury concentrations. The difference in tree ring mercury content associated with geographic orientation of the disks indicates that daily exposure to sunlight as well as temperature may affect mercury uptake, and that the mercury observed in the tree rings must be deposited from the atmosphere onto the tree surface.

Mercury concentrations in black spruce (Picea mariana Mill. B.S.P.) and lichens in boreal Quebec, Canada

Mercury content was analysed in black spruce bark and needles and in the epiphytic lichens found growing on trees. The samples were collected in two distinct boreal forests of northeastern Canada (province of Quebec). The chosen sites were far from direct industrial mercurcy sources, and were located close to man made lakes of different ages. The objective of the study was to determine the role of atmospheric transport in the mercury contamination of trees growing in close proximity to reservoirs, both old and recently flooded. The lichen samples contained the highest mercury concentrations; 400–800 ng/g. They were several times higher than in the bark and one to two orders of magnitude greater than that found in the needles. The mercury concentrations measured in the lichens were significantly different between the two reservoir sites, whereas those of the needles and bark were not. The mercury concentrations in the black spruce bark sampled near the reservoirs were almost twice as high (∼130 ng/g) as those measured in the bark of black spruce trees growing near natural lakes (40–70 ng/g). However no differences were found between the mercury concentrations of young needles sampled close to reservoirs and those sampled near natural lakes, suggesting the existince of a relatively low but stable level of mercury in the local atmosphere.

Snow cover and sea ice sensitivity to generic changes in Earth orbital parameters

A low‐resolution general circulation model is used to examine the separate and combined effects on high‐latitude climate of large changes in Earth's obliquity (3° tilt angle increase) and precession (summer versus winter perihelion in conjunction with large eccentricity (0.04)). The orbital changes, encompassing the extremes for the past 150,000 years, produced significantly increased (decreased) northern summer (winter) radiation. Increased tilt caused a much greater reduction in sea ice than the precessional change. The decreases in annual mean sea ice thickness and fall sea ice coverage are respectively 50% and 41% (21% and 0%) for the tilt increase (precessional change). The larger obliquity effect is a consequence of enhanced annual mean radiation with tilt increase; the modest response of sea ice in the precessional experiments is attributed to a seasonal interaction between processes governing model sea ice growth and melt and heat transfer through the ice. The reduced winter insolation in the experiments with increased tilt and summer versus winter perihelion produced colder conditions and up to 15% greater areal coverage of snow over the northern continents from fall to early spring. The average depth of snow on the continents increased (by 20%) only with the change from winter to summer perihelion because of a greater length of the snow accumulation season. During late spring and summer, enhanced radiation (in the experiments with increased tilt and summer perihelion) rapidly melted the snowpack so that it did not persist as long into the summer season as in the experiments with reduced summer insolation (winter perihelion and decreased tilt). The experiments indicate that orbital reduction of spring‐summer radiation could be an important factor in initiating glaciation over northeastern Canada. The duration of the snow cover‐free season was found to decrease nonlinearly with decreased spring‐summer insolation. The change from modern to 115,000 year B.P. orbital conditions reduced the snow cover‐free season over northeastern Canada by 3–4 weeks. For a more exaggerated tilt (20°) and eccentricity (0.06), snowfields occasionally survived the summer season. Overall, the model results suggest that the orbital conditions at 115,000 years B.P. greatly enhanced the likelihood of perennial snowfields over northeastern Canada.

Initial phase of postfire forest regeneration in two lichen woodlands of northern Québec

:A five-year postfire monitoring of forest floor regeneration, black spruce (Picea mariana [Mill.] BSP) and jack pine (Pinus banksiana Lamb.) seed dispersal, germination and seedling establishment was performed in a black spruce and in a jack pine lichen woodland of the upper boreal forest in northern Québec. The plant species present before the fire and able to resprout vegetatively were the fastest to regenerate. The slower regeneration of the spruce stand forest floor probably resulted from deeper combustion of the organic layer which killed most potentially meristematic organs of species which otherwise might have regenerated. The total seed dispersal over the five-year postfire monitoring period in the spruce stand reached 1 700 886/ha and 270 830/ha for black spruce and jack pine, respectively. In the pine stand, these values were in the same order: 216 011/ha and 298 883/ha. The spatial pattern of seed dispersal was generally contagious. The number of seeds dispersed decreased during the last trapping periods, suggesting that seed banks were becoming exhausted. Likewise, seed viability dropped markedly over time. These temporal patterns of seed dispersal and viability fit the predictions of Wilton’s model. Despite a lower total seed input, jack pine established at a higher density than black spruce, particularly on charred organic seedbeds. Seedling establishment success observed in this study and elsewhere suggests that this parameter has been probably underestimated in simulation models of the dynamics of the northeastern Canadian lichen woodland.

The 1989 (MS 6.3) Ungava, Quebec, earthquake: a complex intraplate event

On 25 December 1989 the largest earthquake ( MS 6.3) in northern Quebec in at least 60 yr occurred in the Ungava Peninsula. This earthquake was unique in that it marked the first time surface faulting could be confirmed for a historical eastern North American earthquake. Field observations indicated a combination of thrust and strike-slip motion. Waveforms modeled in this study show that the earthquake consisted of two subevents—a thrust subevent on a NE-SW striking plane followed by a larger strike-slip subevent on a NNE-SSW striking plane. The surface waves give an equivalent double-couple moment of 1.3 × 1025 dyne cm. The sum of the subevent moments is greater than the simple source moment by almost a factor of 2. Both subevents occurred at a depth of 3 km. They were separated by 0.9 sec in time with the second subevent occurring 5.2 km southwest of the first. The source parameters determined by modeling and those inferred from the ground observations generally agree, but there are some differences with respect to the subevent offset. These may be reconciled if the strike-slip motion was distributed among the several small faults at the southwestern end of the rupture or if the complete surface rupture was not found. The stress orientation (NW compression) inferred from the fault plane solution is consistent with the focal mechanisms of many other recent northeastern Canadian events. The Ungava earthquake and many intraplate events from several continents share a number of characteristics, including shallow hypocenters, source complexity, and occurrence on faults that showed no evidence for previous ruptures.

Herd composition and behaviour of white whales (Delphinapterus leucas) in two Canadian arctic estuaries

White whales occupy the Nastapoka River and Cunningham Inlet estuaries in northeastern Canada each summer. They arrive at the Nastapoka in late June and at Cunningham in mid-July, where numbers build to maxima of 260 and 1750, respectively.
 Distribution of whales in both estuaries is influenced mainly by the state of the mixed semi-diurnal tides and, to a certain extent, by river outflow and date. Few adult males appear to be present in the estuaries, the herd being composed mainly of females with calves and weaned juveniles. Limited evidence suggests that the basic social units of herds are matrilines consisting of adult nursing females accompanied by older female offspring.
 The age structure of the herd changes seasonally with an increasing proportion of nursing pairs. Behaviour was grouped into four activity classes. These are descriptive and are not intended to imply functions, which remain somewhat obscure. Much of the nearshore behaviour appears to be related to the processes of shedding old skin and growing of new epidermis. Strong philopatry and physiological dependence of white whales on estuaries indicate that these are important habitats which must be managed and preserved in order to conserve the species.

Development of a simulation model of the forest–tundra transition zone of northeastern Canada

A forest succession model has been adapted to simulate the dynamics of subarctic spruce–lichen woodland of northeastern Canada. Most adaptations concern the simulation of seed regeneration of subarctic forest communities growing on moderately to well drained sites. The yearly seed production in Piceamariana (Mill.) B.S.R stands is controlled by temperature and stand structural characteristics. In addition to the seed input, the model considers the influence of seedbed properties on the establishment of seedlings. Overall, this model simulates the entire regeneration dynamics in a more realistic way than in most other gap models where successional processes are driven by resource constraints on tree growth. The model produces realistic predictions about the pattern of early post-fire age structure, and the biomas and density dynamics of black spruce populations. Simulations under a climate-warming scenario suggest that physiognomic change in subarctic spruce–lichen woodland would be more pronounced in areas subjected to moderately frequent forest fires than in those where the fire frequency is very low.

Analysis of tropospheric aerosol number density for aerosols of 0.2‐ to 3‐μm diameter: Central and northeastern Canada

NASA's Atmospheric Boundary Layer Experiment conducted during the summer of 1990 focused on the distribution of trace species in central and northeastern Canada (altitudes <6 km) and the importance of surface sources/sinks, local emissions, distant transport, tropospheric/stratospheric exchange. Aircraft flights were based from North Bay, Ontario, and Goose Bay, Labrador, Canada. As part of the aircraft measurements, aerosol number density (0.2‐ to 3‐μ diameter) was measured using an optical laser technique. Results show that summertime aerosol budgets of central and northeastern Canada can be significantly impacted by the transport of pollutants from distant source regions. Biomass burning in Alaska and western and central Canada exerts major influences on regional aerosol budgets. Urban emissions transported from the U.S./Canadian border regions are also important. Aerosol enhancements (mixed layer and free troposphere) were most prevalent in air with carbon monoxide mixing ratios >110 parts per billion by volume (ppbv). When data were grouped as to the source of the air (5‐day back trajectories) either north or south of the polar jet, aerosol number density in the mixed layer showed a tendency to be enhanced for air south of the jet relative to north of the jet. However, this difference was not observed for measurements at the higher altitudes (4 to 6 km). For some flights, mixed layer aerosol number densities were >100 higher than free‐tropospheric values (3‐ to 6‐km altitude). The majority of the observed mixed layer enhancement was associated with transport of effluent‐rich air into the Canadian regions. Aerosol emissions from natural Canadian ecosystems were relatively small when compared to transport.