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

Global vegetation variability and its response to elevated CO2, global warming, and climate variability – a study using the offline SSiB4/TRIFFID model and satellite data

Abstract. The climate regime shift during the 1980s had a substantial impact on the terrestrial ecosystems and vegetation at different scales. However, the mechanisms driving vegetation changes, before and after the shift, remain unclear. In this study, we used a biophysical-dynamic vegetation model to estimate large-scale trends in terms of carbon fixation, vegetation growth, and expansion during the period 1958–2007, and to attribute these changes to environmental drivers including elevated atmospheric CO2 concentration (hereafter eCO2), global warming, and climate variability (hereafter CV). Simulated Leaf Area Index (LAI) and Gross Primary Product (GPP) were evaluated against observation-based data. Significant spatial correlations are found (correlations > 0.87), along with regionally varying temporal correlations of 0.34–0.80 for LAI and 0.45–0.83 for GPP. More than 40 % of the global land area shows significant trends in LAI and GPP since the 1950s: 11.7 % and 19.3 % of land has consistently positive LAI and GPP trends, respectively; while 17.1 % and 20.1 % of land, saw LAI and GPP trends respectively, reverse during the 1980s. Vegetation fraction cover (FRAC) trends, representing vegetation expansion/shrinking, are found at the edges of semi-arid areas and polar areas. Overall, eCO2 consistently contributes to positive LAI and GPP trends in the tropics. Global warming is shown to mostly affected LAI, with positive effects in high latitudes and negative effects in subtropical semi-arid areas. CV is found to dominate the variability of FRAC, LAI, and GPP in the semi-humid and semi-arid areas. The eCO2 and global warming effects increased after the 1980s, while the CV effect reversed during the 1980s. In addition, plant competition is shown to have played an important role in determining which driver dominated the regional trends. This paper presents a new insight into ecosystem variability and changes in the varying climate since the 1950s

Technology development: A partnership that makes sense

Discussed here is an approach to how academic institutions, government entities, and industrial organizations can work effectively to utilize their relative strengths to more effectively meet common goals. The discussion relates to the University of Houston-Clear Lake (UHCL) Research Institute for Computing and Information Systems (RICIS) Program to bring about this type of triad in the Clear Lake area. It is concluded that the interfaces among these groups must remain independent to maintain a healthy counterbalance to their respective entities. However, each entity can and must understand the entire mechanism to exploit each interface to the fullest. Only through such cooperation can the continued technical success of the NASA/Clear Lake area be assured

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

Electromechanical Coupling between Skeletal and Cardiac Muscle: Implications for Infarct Repair

Skeletal myoblasts form grafts of mature muscle in injured hearts, and these grafts contract when exogenously stimulated. It is not known, however, whether cardiac muscle can form electromechanical junctions with skeletal muscle and induce its synchronous contraction. Here, we report that undifferentiated rat skeletal myoblasts expressed N-cadherin and connexin43, major adhesion and gap junction proteins of the intercalated disk, yet both proteins were markedly downregulated after differentiation into myo-tubes. Similarly, differentiated skeletal muscle grafts in injured hearts had no detectable N-cadherin or connexin43; hence, electromechanical coupling did not occur after in vivo grafting. In contrast, when neonatal or adult cardiomyocytes were cocultured with skeletal muscle, ∼10% of the skeletal myotubes contracted in synchrony with adjacent cardiomyocytes. Isoproterenol increased myotube contraction rates by 25% in coculture without affecting myotubes in monoculture, indicating the cardiomyocytes were the pacemakers. The gap junction inhibitor heptanol aborted myotube contractions but left spontaneous contractions of individual cardiomyocytes intact, suggesting myotubes were activated via gap junctions. Confocal microscopy revealed the expression of cadherin and connexin43 at junctions between myotubes and neonatal or adult cardiomyocytes in vitro. After microinjection, myotubes transferred dye to neonatal cardiomyocytes via gap junctions. Calcium imaging revealed synchronous calcium transients in cardiomyocytes and myotubes. Thus, cardiomyocytes can form electromechanical junctions with some skeletal myotubes in coculture and induce their synchronous contraction via gap junctions. Although the mechanism remains to be determined, if similar junctions could be induced in vivo, they might be sufficient to make skeletal muscle grafts beat synchronously with host myocardium

Assessment of the performance of a turbulence closure model: along the tidally-influenced Kaipara River to the estuary, NZ

The success of many coastal management projects hinges on the ability to predict the dispersal and settling of sediment particles. Hydrodynamic models have enabled the efficient simulation of sediment transport scenarios at large spatial scales and long time scales. However, these models have limited predictive capacity owing to an incomplete understanding of the processes involved. Turbulence has been shown to have a substantial influence on sediment transport by influencing flocculation (i.e. aggregation of particles), hence driving the behaviour of particles (e.g. deposition, erosion, mixing). Turbulence tends to promote aggregation at low shear stresses and cause floc breakups at high shear stresses. However, despite the key role of turbulence in coastal modelling, there is not a unique approach but several methods to describe turbulence, each based on a different combination of assumptions. We present modelling results exploring the performance of one closure scheme implemented in a hydrodynamic and sediment transport model, Delft3D. The assessment of the performance of the model is based on comparisons with measured data collected in the heavily sediment-laden Kaipara river, New Zealand. Data was collected in October 2013 using Lagrangian “flocdrifter” platforms released at multiple locations to capture both hydrodynamic and sediment data. In general the model was found to be able to reproduce the right order of magnitude of dissipation rates. However, turbulence characteristics in some sections of the river, usually in the vicinity of abrupt bends, are relatively poorly reproduced. Future work will aim to use the present model to improve the conceptual understanding of fundamental physical processes, in particular the effect of turbulence on flocculation, and floc formation and breakup in estuarine and riverine systems