Filters: Tags: Paleo and Holocene (X)179 results (42ms)
Resedimentation of the late Holocene White River ash, Yukon Territory, Canada and Alaska, United States
The White River ash is one of the most distinct and widely dispersed pyroclastic deposits in Yukon-Alaska. It was produced from volcanic eruptions ca. 1887 (north lobe; Lerbekmo et al. 1975) and 1147 years B.P. (east lobe; Clague et al. 1995). The source of the deposit, Mount Churchill, is an ice-covered stratovolcano located 25 km west of the Yukon-Alaska border (61°25'N, 141°70'W). Distal deposits of ash occur as primary airfall over much of Alaska, Yukon, and Northwest Territories. Locally resedimented deposits of ash are common closer to the volcanic source and occur in highly glaciated regions. Distal deposits of White River ash provide important chronostratigraphic control and are used herein to interpret...
Holocene treeline dynamics in the mountains of northeastern British Columbia, Canada, inferred from fossil pollen and stomata
Aim? Using a new approach to analyse fossil pollen data, we investigate temporal and spatial patterns in Populus (poplar, cottonwood, aspen) from the Late Glacial to the present at regional to continental scales. Location? North America. Methods? We extracted data on the timing and magnitude of the maximum value of Populus pollen from each pollen diagram in the North American Pollen Database (NAPD). The information was plotted in histograms of 150-year bins to identify times when Populus was abundant on the landscape. We also mapped the maximum values to identify spatial patterns and their causes. Results? Our analyses show that there have been several periods since the Late Glacial when Populus was abundant on...
Quaternary glacial, lacustrine, and fluvial interactions in the western Noatak basin, northwest Alaska
Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon
Late Quaternary glaciation and equilibrium line altitude variations of the McKinley River region, central Alaska Range
The early Holocene Milankovitch thermal maximum and humans :adverse conditions for the Denali complex of eastern Beringia
Evaluating GCM outputs for past climates in North America based on the distribution of Sphagnum peatlands
Lake sediment cores collected from four lakes (Upper Fly Lake 61.04°N, 138.09°W, 1326 m a.s.l.; Jenny Lake 61.04°N, 138.36°W, 817 m. a.s.l.; Donjek Kettle 61.69°N, 139.76°W, 732 m a.s.l.; Lake WP02 61.48°N, 139.97°W, 1463 m a.s.l.) in the southwest Yukon provide records of postglacial climatic variability in the region. A 13,000 year pollen record from Upper Fly Lake indicated that herbaceous tundra existed on the landscape from 13.6 to 11 ka, followed by birch shrub tundra until 10 ka, when Picea forests were established in the region. Pollen-, chironomid-, and ostracode-inferred paleoclimate reconstructions showed a long-term cooling with increasing moisture from the late glacial through the Holocene. The early...
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Timing and cause of water level fluctuations in Kluane Lake, Yukon Territory, over the past 5000 years
We reconstructed late Holocene fluctuations of Kluane Lake in Yukon Territory from variations in bulk physical properties and carbon and nitrogen elemental and isotopic abundances in nine sediment cores. Fluctuations of Kluane Lake in the past were controlled by changes in climate and glaciers, which affected inflow of Slims and Duke rivers, the two largest sources of water flowing into the lake. Kluane Lake fluctuated within a narrow range, at levels about 25 m below the present datum, from about 5000 to 1300 cal yr BP. Low lake levels during this interval are probably due to southerly drainage of Kluane Lake to the Pacific Ocean, opposite the present northerly drainage to Bering Sea. Slims River, which today is...
The objective biomization method developed by Prentice et al. (1996) for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 14C yr bp. The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and north-western Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under-representation of Larix in pollen spectra. The biome distribution across Beringia at 6000...
Combining proxy methods in paleoecology studies has the potential to bring new insight into changes in vegetation over time. Keyhole Pond, a small lake in southwest Yukon Territory, is surrounded by small grasslands but located within the boreal forest. This lake was chosen to explore local grassland and forest changes over the Holocene, as well as the impact of fire on these communities. A 3-metre lake sediment core was retrieved from the deepest part of the lake using a modified Livingston piston-corer. The lake sediment core has a basal date of ∼11,000 before present (BP). Samples were extracted at 3-centimetre intervals (∼100 years between samples) and processed for both pollen and charcoal analysis. Only charcoal...
A 14,000 yr paleoenvironmental record from Windmill Lake, central Alaska; lateglacial and Holocene vegetation in the Alaska Range
Identification of last interglacial deposits in eastern Beringia; a cautionary note from the Palisades, interior Alaska