Vegetation of the Continental Northwest Territories at 6 ka BP

Pollen records are used to reconstruct vegetation in the continental Northwest Territories at 6 ka (6000 14C yr BP). Picea glauca, P mariana, Larix laricina, Populus tremuloides, P. balsamifera, Alnus crispa and A. incana were present throughout their modern ranges in the Boreal and Subarctic Forest Zones by 6000 BP. Pinus banksiana, however, had not yet reached its present northern limits. Population densities of the dominant trees, Picea glauca and Picea mariana, were close to, or as high as, present. In the Mackenzie Delta region the range limit of Picea glauca was approximately 25 km north of its modern location just prior to 6000 BP. In contrast, the northern limits of the forest in central Canada were similar to present. The tundra vegetation close to the edge of the forest was similar to modern Low Arctic Tundra. Development of extensive Sphagnum peatlands had begun in the forested areas and the adjacent Low Arctic Tundra. Palaeoecological information regarding vegetation at 6000 BP remains lacking for the northeastern half of the study area. Therefore, the nature of the vegetation in much of the area now occupied by Low Arctic and Middle Arctic Tundra remains unknown. Important vegetation changes that occurred following 6 ka include : (1) the advance of Pinus banksiana to its present northern range limits, (2) the retreat of the northern range limits of Picea glauca in the Mackenzie Delta region between 6000 and 3500 BP and (3) the rapid and marked increase in the population density of Picea mariana in the treeline zone of the central Northwest Territories at 5000 BP followed by a decline at 4000 BP.La reconstitution de la végétation de la partie continentale des Territoires du Nord-Ouest à 6 ka a été faite à partir des données polliniques. Picea glauca, P. mariana, Larix laricina, Populus tremuloides, P. balsamifera, Alnus crispa et A. incana avaient déjà atteint leur répartition moderne dans les zones des forêts boréales et subarctiques à 6 ka. Pinus banksiana, toutefois, n'avait pas encore atteint sa limite nordique. Les densités de population des arbres dominants, Picea glauca et P. mariana, étaient aussi fortes ou presque que maintenant. Dans la région du delta du Mackenzie, Ia limite de Picea glauca était à environ 25 km au nord de sa limite actuelle juste avant 6 ka. Par contre, la limite septentrionale de la forêt dans la partie centrale du Canada était semblable à l'actuelle. La végétation de la toundra située à proximité de la marge forestière était semblable à celle de la toundra du bas Arctique moderne. Le développement de vastes tourbières à sphaigne était déjà commencé dans les zones forestières et dans la toundra du bas Arctique adjacente. Les données paléoécologiques sur la végétation à ~6 ka sont déficientes pour la partie nord-est de la région à l'étude. Dès lors, la nature de la végétation dans la plus grande partie du territoire maintenant occupée par la toundra du bas Arctique et du moyen Arctique est encore inconnue. Les grands changements apportées à la végétation après ~6 ka comprennent : 1) la remontée de Pinus banksiana jusqu'à sa limite septentrionale actuelle, 2) le recul de la limite septentrionale de Picea glauca dans la région du delta du Mackenzie entre 6000 et 3500 BP et 3) l'augmentation rapide et prononcée de la densité de la population de Picea mariana dans la zone de la limite des arbres du centre des Territoires du Nord-Ouest à 5000 BP suivie d'un déclin à 4000 BP.Man benutzte Pollen-Belege, um die Vegetation in den kontinentalen Nordwest-Territorien um 6 ka ( 6000 14C Jahre v.u.Z.) zu rekonstruieren. Picea glauca, P. mariana, Larix laricina, Populus tremoluides, P. balsamifera, Alnus crispa und A. incana hatten um 6000 v.u.Z. schon ihre moderne Verteilung in den nôrdlichen und subarktischen Waldgùrtelzonen erreicht. Jedoch hatte Pinus banksiana noch nicht seine gegenwârtigen nôrdlichen Grenzen erreicht. Die Populations-Dichte der vorherrschenden Baume, Picea glauca und Picea mariana war fast so hoch oder so hoch wie gegenwârtig. In der Gegend des Mackenzie-Deltas war die Grenze von Picea glauca kurz vor 6 ka etwa 25 km nôrdlich von ihrer modernen Position. Im Gegensatz dazu war die nôrdliche Grenze des Waldes in Zentralkanada der gegenwârtigen àhnlich. Die Tundra-Vegetation nah an der WaId-grenze war der modernen Tundra der niederen Arktis àhnlich. Die Entwicklung ausgedehnter Sphagnum-Torfmoore hatte in den bewaldeten Gebieten und der angrenzenden Tundra der niederen Arktis begonnen. Fur die nordôstliche Hàlfte des erforschten Gebiets gibt es keine palâoôkologische Information in Bezug auf die Vegetation um 6000 v.u.Z. Deshalb bleibt die Art der Vegetation in einem groBen Teil des heute von der niederen arktischen und mittleren arktischen Tundra eingenom-menen Gebiets unbekannt. Zu wichtigen Vegetationswechseln, die auf 6 ka folgten, gehôren: (1) das Vordringen von Pinus banksiana zu seiner heutigen nôrdlichen Grenze, (2) der Rùckzug der nôrdlichen Grenze von Picea glauca im Gebiet des Mackenzie-Deltas zwischen 6000 und 3500 v.u.Z. und (3) die schnelle und deutliche Zunahme in der Populationsdichte von Picea mariana in der Zone der Baumgrenze der zentralen Nordwest-Territorien um 5000 v.u.Z., gefolgt von einer Abnahme um 4000 v.u.Z

Rising minimum daily flows in northern Eurasian rivers: A growing influence of groundwater in the high‐latitude hydrologic cycle

A first analysis of new daily discharge data for 111 northern rivers from 1936–1999 and 1958–1989 finds an overall pattern of increasing minimum daily flows (or “low flows”) throughout Russia. These increases are generally more abundant than are increases in mean flow and appear to drive much of the overall rise in mean flow observed here and in previous studies. Minimum flow decreases have also occurred but are less abundant. The minimum flow increases are found in summer as well as winter and in nonpermafrost as well as permafrost terrain. No robust spatial contrasts are found between the European Russia, Ob\u27, Yenisey, and Lena/eastern Siberia sectors. A subset of 12 unusually long discharge records from 1935–2002, concentrated in south central Russia, suggests that recent minimum flow increases since ∼1985 are largely unprecedented in the instrumental record, at least for this small group of stations. If minimum flows are presumed sensitive to groundwater and unsaturated zone inputs to river discharge, then the data suggest a broad‐scale mobilization of such water sources in the late 20th century. We speculate that reduced intensity of seasonal ground freezing, together with precipitation increases, might drive much of the well documented but poorly understood increases in river discharge to the Arctic Ocean

Movement of an Ice-Cored Rock Glacier, Tungsten, N.W.T., Canada, 1963-1980

In August 1963 Dr. H. Gabrielse, of the Geological Survey of Canada, established five lines of marked boulders on what is now believed to be a large ice-cored rock glacier near Tungsten, Northwest Territories. The boulders were aligned with survey targets located on the rock walls of the valley in which the rock glacier is located. The distances from the snout of the rock glacier to eight forest trees along its perimeter were measured and blazed into the trees. In July 1980, we visited the rock glacier and resurveyed the marked boulders and the rock glacier's snout in order to establish the rate and nature of movement of the rock glacier over the past 17 years

Investigation of North American vegetation variability under recent climate: a study using the SSiB4/TRIFFID biophysical/dynamic vegetation model

PublishedJournal ArticleThis is the final version of the article. Available from AGU via the DOI in this record.Recent studies have shown that current dynamic vegetation models have serious weaknesses in reproducing the observed vegetation dynamics and contribute to bias in climate simulations. This study intends to identify the major factors that underlie the connections between vegetation dynamics and climate variability and investigates vegetation spatial distribution and temporal variability at seasonal to decadal scales over North America (NA) to assess a 2-D biophysical model/dynamic vegetation model's (Simplified Simple Biosphere Model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID)) ability to simulate these characteristics for the past 60-years (1948 through 2008). Satellite data are employed as constraints for the study and to compare the relationships between vegetation and climate from the observational and the simulation data sets. Trends in NA vegetation over this period are examined. The optimum temperature for photosynthesis, leaf drop threshold temperatures, and competition coefficients in the Lotka-Volterra equation, which describes the population dynamics of species competing for some common resource, have been identified as having major impacts on vegetation spatial distribution and obtaining proper initial vegetation conditions in SSiB4/TRIFFID. The finding that vegetation competition coefficients significantly affect vegetation distribution suggests the importance of including biotic effects in dynamical vegetation modeling. The improved SSiB4/TRIFFID can reproduce the main features of the NA distributions of dominant vegetation types, the vegetation fraction, and leaf area index (LAI), including its seasonal, interannual, and decadal variabilities. The simulated NA LAI also shows a general increasing trend after the 1970s in responding to warming. Both simulation and satellite observations reveal that LAI increased substantially in the southeastern U.S. starting from the 1980s. The effects of the severe drought during 1987-1992 and the last decade in the southwestern U.S. on vegetation are also evident from decreases in the simulated and satellite-derived LAIs. Both simulated and satellite-derived LAIs have the strongest correlations with air temperature at northern middle to high latitudes in spring reflecting the effect of these climatic variables on photosynthesis and phenological processes. Meanwhile, in southwestern dry lands, negative correlations appear due to the heat and moisture stress there during the summer. Furthermore, there are also positive correlations between soil wetness and LAI, which increases from spring to summer. The present study shows both the current improvements and remaining weaknesses in dynamical vegetation models. It also highlights large continental-scale variations that have occurred in NA vegetation over the past six decades and their potential relations to climate. With more observational data availability, more studies with different models and focusing on different regions will be possible and are necessary to achieve comprehensive understanding of the vegetation dynamics and climate interactions. Key Points Climate forcing and spatial and temporal variability of North American ecosystem Evaluate a 2-D biophysical model/dynamic vegetation using satellite data Mechanisms affecting vegetation/climate interactio