Filters: Tags: Paleo and Holocene (X)179 results (178ms)
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...
Evaluating GCM outputs for past climates in North America based on the distribution of Sphagnum peatlands
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...
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...
available at publisher's site.]
Quaternary glacial, lacustrine, and fluvial interactions in the western Noatak basin, northwest Alaska
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...
Holocene treeline dynamics in the mountains of northeastern British Columbia, Canada, inferred from fossil pollen and stomata
The early Holocene Milankovitch thermal maximum and humans :adverse conditions for the Denali complex of eastern Beringia
Late Quaternary glaciation and equilibrium line altitude variations of the McKinley River region, central Alaska Range
Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon
Tephras are often used in paleolimnology and other stratigraphic applications as a chronostratigraphic marker. Where analytical errors in radiocarbon or other dating methods make precise comparison between sites difficult, tephras provide an absolute stratigraphic reference that can be used to assess the relative ages of events across a region. Applications of tephrochronology typically make the assumption that a tephra is deposited at what was the top of the stratigraphic sequence at the time of deposition, and that the contact between the tephra and underlying sediments is an isochron. This paper presents evidence from two lakes in western Canada which suggest that tephras may be very mobile within the sedimentary...
Identification of last interglacial deposits in eastern Beringia; a cautionary note from the Palisades, interior Alaska
A 14,000 yr paleoenvironmental record from Windmill Lake, central Alaska; lateglacial and Holocene vegetation in the Alaska Range
The Nenana River valley, located in the northern foothills of the Alaska Range, contains a group of sites that collectively spans 11,300 to 7000 B.P., and provides critical information on the settlement of Alaska during this interval. Major localities include Dry Creek, Walker Road, Panguingue Creek, and Moose Creek, all of which contain cultural remains buried in a deep aeolian sedimentary context. Three of these sites yielded assemblages comprising small bifacial points, endscrapers, scraper planes, and other tools dating to between ca. 11,300 and 11,100 B.P. (Nenana complex). Three sites contain assemblages of microblades, lanceolate points, burins, and other lithic artifacts that stratigraphically overlie the...
Late Glacial and Holocene environmental change inferred from sedimentary archives of Kusawa Lake, Boundary Range Mountains, Yukon Territory, Canada
Vegetation buried under Dawson tephra (25,300 14C years BP) and locally diverse late Pleistocene paleoenvironments of Goldbottom Creek, Yukon, Canada
Paleoecological research at Goldbottom Creek in the Klondike region of Yukon Territory (NW Canada) documents an in situ riparian grassy meadow that was buried during the winter or early spring by Dawson tephra, near the onset of Marine Isotope Stage (MIS) 2, ca. 25,300 14C years BP. Analyses of vascular plant macrofossils, bryophytes, pollen, insects and paleosols from the riparian meadow contrast with evidence for well-drained, upland steppe–tundra habitats obtained from fossil arctic ground squirrel middens within the same valley. The mesic valley bottom vegetation consisted of grasses (Deschampsia caespitosa, Alopecurus), sedges (Carex), horsetail (Equisetum cf. palustre), diverse bryophytes and few forbs. Upland...