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This paper presents data on and discusses the degree of postglacial stability of the northern Canadian tree limit. Holocene climatic changes have been both directional and synchronous for this region, though deteriorations/ameliorations either (1) lagged from west to east, (2) were buffered by local geographic factors, or (3) were not registered in the fossil record owing to the inherent persistence of the vegetation at some sites. The present northern tree limit in eastern Canada is in equilibrium with the prevailing climate, with the tree populations successfully regenerating both sexually and vegetatively. These tree stands are still occupying their maximum Hypsithermal positions. In contrast, the tree limit, tree line, and intervening forest-tundra ecotone in central and western Canada are out of equilibrium with today's climate. These populations are not sexually regenerative and apparently became established during warmer climates where the tree line was north of its present position. As such, they are susceptible to destruction by further climatic deterioration or anthropogenic disruption. [ABSTRACT FROM AUTHOR]

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 - 02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (10³ - 104 year) ice-core r ecords of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this region. Comparison of these records has allowed for variations in climate and atmospheric composition to be linked with changes in the vertical structure and dynamics of the North Pacific atmosphere, providing a unique perspective on these changes over the Holocene. Owing to their privileged location, cores from the St. Elias Icefields also contain a remarkably detailed record of aerosols from various sources around or across the North Pacific. In this paper we review major scientific findings from the study of St. Elias Mountain ice cores, focusing on five main themes: (1) The record of stable water isotopes (δ18O, δD), which has unique characteristics that differ from those of Greenland, other Arctic ice cores, and even among sites in the St. Elias; (2) the snow accumulation history; (3) the record of pollen, biomass burning aerosol, and desert dust deposition; (4) the record of long-range air pollutant deposition (sulphate and lead); and (5) the record of paleo-volcanism. Our discussion draws on studies published since 2000, but based on older ice cores from the St. Elias Mountains obtained in 1980 and 1996. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the activity of a small meandering stream and the development of its floodplain during the last 4600 years (calendar years BP) in the northern boreal zone of Québec. Three trenches were excavated across the floodplain''s full width and permitted the interpretation of morphosedimentary units in relation to modern analogs. Chronological controls within trenches was provided by the dendrochronological and radiocarbon dating of buried tree trunks. From 4600 to 2900 cal. BP and from 1000 to 120 cal. BP, the channel migrated and constructed its floodplain at very slow rates, mostly because of low flow velocities, vegetated streambanks and the cohesive texture of marine sediments reworked by the channel. Vertical accretion rates were extremely variable on the floodplain, with high rates proximal to the modern channel and low rates over distal (also older) portions of the floodplain. Following a major channel shift (meander cut-off or avulsion) around 2900 cal. BP, channel migration appears to have been constrained to a narrow zone adjacent to the modern channel. Within this constrained zone, the migrating channel has reworked its own sediments leading to a marked unconformity between 2900–1000 cal. BP. It is thought that underlying marine sediments protrusions, and perhaps the forested banks, protected older alluvial sediments from being eroded during the last three millenniums. Our study shows that small boreal floodplains may contain, in a very small area, abundant and diversified archives of their evolution. [Copyright &y& Elsevier]

This study presents the long-term (over the last 8000 years) natural variability of a portion of the Picea mariana-moss bioclimatic domain belonging to Québec's Clay Belt. The landscapes are dominated by mesic-subhydric clay and early successional forests composed of Populus tremuloides, Pinus banksiana and Picea mariana. The natural variability (fires and vegetation) of one of these landscapes was reconstructed by means of pollen and macroscopic charcoal analysis of sedimentary archives from two peatlands in order to assess when and how such landscapes were formed. Following an initial afforestation period dominated by Picea (8000-6800 cal. Years BP), small and low-severity fires favored the development and maintenance of landscapes dominated by Picea and Abies balsamea during a long period (6800-1000 BP). Over the last 1000 years, fires have become more severe and covered a larger area. These fires initiated a recurrence dynamic of early successional stands maintained until today. A decline of Abies balsamea has occurred over the last centuries, while the pollen representation of Pinus banksiana has recently reached its highest abundance. We hypothesize that the fire regime of the last millennium could characterize Québec's Clay Belt belonging to the western Picea mariana-moss and Abies balsamea-Betula papyrifera domains. [ABSTRACT FROM AUTHOR]

Zoological remains were examined from the sediments of the Pingualuit Crater Lake, Nunavik, Canada. Our objective was to describe past climate events in the area of delayed deglaciation in northernmost Ungava Peninsula. Our record covers 3 separate sections of deglacial and postglacial invertebrate dynamics interrupted by laminated proglacial sediments and a basin-scale erosive slumping event. The abundance of animal remains in the ultra-oligotrophic and extremely deep arctic lake was low, but distinct faunal assemblages were found among the intervals, results implying that they were environmentally heterogeneous. The lowermost fine-grained interval (before 6850 calibrated years before present [cal BP]), revealed that Cladocera Chydorus sphaericus-type and Bosmina (Eubosmina) longispina-type were common in the lake, whereas Chironomidae were relatively rare. The dominance of B. longispina-type showed that planktonic communities were successful at the time, probably indicating more favorable climatic conditions than today soon after the last deglaciation (~7000 cal BP). In the middle interval (between~6850 and 5750 cal BP), chironomids became more common and were dominated by Heterotrissocladius subpilosus-type and Protanypus, taxa that are characteristic of oligotrophic lakes. The extirpation of B. longispina-type suggests that planktonic invertebrate communities were not successful, probably because of predation by Arctic char. The presence of the chironomid Oliveridia tricornis-type during the late Holocene (between ~4200 and 600 cal BP) suggested general climate cooling. Our paleoclimatic conclusions on the regional environmental history suggest a stationary ice front in the initial stages of the Holocene, favorable climatic conditions in the mid- Holocene and a general late-Holocene cooling. Our records also indicate a subtle increase in nutrient availability throughout the Holocene. The paleoecological record from Pingualuit Crater Lake is valuable in describing the faunal history and biotic resilience in this environmentally extreme lake, which presently contains one of the world's softest and most transparent waters. [ABSTRACT FROM AUTHOR]

Crawford Lake, Ontario, Canada (43°28.1' N, 79°56.9' W, 278 masl) has varved and AMS dated sediments containing fossil pollen that record native Iroquoian farming ca. AD 1268 to 1520. From before AD 1000 to 1268, bioturbating organisms caused poor varve preservation but since then, well-preserved varves and dung pellets reflect anoxic bottom water due to meromixis. The onset of varve preservation coincides with the occurrences of pollen grains of Zea (maize), Helianthus (sunflower), Phaseolus (bean), Cucurbita (squash) and Portulaca (purslane), and spores of Ustilago cf. maydis (maize smut). These pollen grains and spores are more abundant in pellets between varve laminae than in the surrounding sediment matrix. Analyses of DNA from five pellets demonstrate that they are dung from wild Canada geese (Branta canadensis). In the autumn, as geese foraged in Iroquoian fields, they inadvertently ingested pollen and spores before flying to the lake. There they roosted and cast the pollen-rich dung pellets, which became part of the sediment. This study demonstrates that birds, wild geese and perhaps ducks, can be important vectors of pollen to lake sediments located near agricultural settlements. [ABSTRACT FROM AUTHOR]