Filters: Tags: Paleo and Holocene (X)
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The global climate is dynamic and has undergone many significant changes throughout Earth's history. Since the industrial revolution, anthropogenic activities have released significant amounts of CO2 and other greenhouse gasses (GHG) into the atmosphere, which is believed to be impacting global climate. A change to a warmer climate as is predicted by many scientists will have a profound effect on various ecosystems, such as those in northern regions. To better understand the impacts of climate change and disturbances such as forest fires on vegetation, this study examined proxy data to determine how these factors have interacted during the Holocene. The objectives of the thesis were to determine if fire frequency...
Categories: Publication;
Types: Citation;
Tags: Paleo and Holocene,
R2b-Effects of Fire on Ecosystems
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...
Categories: Publication;
Types: Citation;
Tags: B4-Ecological Land Classification Scheme,
Paleo and Holocene
In glaciated British Columbia, Canada, Quaternary climate changes are responsible for profound spatial reorganization of earth surface processes. These changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs. The evolution of formerly glaciated landscapes is examined by considering a set of scaling relations and assessing their departures from known unglaciated trends. Ultimately, the magnitude of these departures should provide a measure of the state of landscape recovery (transience) from glacial disturbance. The set of scaling dependences studied includes slope-area relations, for assessing geomorphic process domains; landslide magnitude-frequency (LMF)...
Plant and insect macrofossil assemblages dating to the full-glacial (late Wisconsinan) are rare from eastern Beringia. Here we present an assemblage of fossil pollen, insect and plant macrofossils recovered from alluvium at the Bluefish Exposure, northern Yukon Territory. Nine AMS radiocarbon ages place these data between ca. 18,880–16,440 14C yr BP (22,313–19,597 cal. yr BP). These data indicate that xeric steppe, rich in bunchgrasses Poa and Elymus, Artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types, including mid-rich fens, mesic graminoid meadows, steppe-tundra and herb-tundra. Macrofossils and minor pollen of tundra forbs suggest steppe-tundra plant associations within...
Glacier mass-balance reconstructions provide a means of placing relatively short observational records into a longer-term context. In western North America, mass-balance records span four to five decades and capture a relatively narrow window of glacial behavior over an interval that was dominated by warming and ablation. We use temperature- and moisture-sensitive tree-ring series to reconstruct annual mass balance for six glaciers in the Pacific Northwest and Alaska. Mass-balance models rely on the climatic sensitivity of tree-ring chronologies and teleconnection patterns in the North Pacific. The reconstructions extend through the mid to latter portions of the Little Ice Age (LIA) and explore the role of climate...
A multiple-proxy investigation was undertaken on two short cores (85 cm and 101 cm long) from Kepler Lake, an evaporation-insensitive, groundwater-fed marl lake in South-Central Alaska, with the goal of reconstructing climate and environmental changes in recent centuries. The proxies employed in this study include: calcite Carbon-Oxygen isotopes, organic matter (OM) Carbon-Nitrogen isotopes, and loss on ignition (LOI) analysis. An 800-year chronology for two cores was established based on four calibrated AMS 14 C dates on terrestrial macrofossils, 210 Pb analysis and core-to-core correlations using LOI results. δ18 O VPDB values of inorganic calcite range from -17.0[per thousand] to -15.7[per thousand], with the...
In this dissertation, tephrostratigraphy is used as the central method to address issues of chronology in the late Quaternary sedimentary record of eastern Beringia (non-glaciated Yukon and Alaska) at a variety of spatial and temporal scales. The Palisades, central Alaska, preserves paleoenvironmental records thought to span, with major unconformities, the Holocene to early Pleistocene (~2 Ma). Two paleomagnetic transects of normal polarity and tephrostratigraphic data show the Palisades are Middle to Late Pleistocene in age, with no major unconformities. Of 19 tephra beds identified, nine are Middle Pleistocene beds known from other sites. The Variegated (VT) tephra has a known distribution second only to the Old...
Categories: Publication;
Types: Citation;
Tags: Adaptation planning 1-Best management practices,
Paleo and Holocene,
landscape scale conservation: Climate Change
Upland soils formed in three different parent materials in the Lewes Plateau of the Central Yukon were studied: till from the McConnell (MIS 2) and penultimate (MIS 4 or 6) glaciations, and weathered bedrock beyond the penultimate limit Soils at penultimate and McConnell sites have solum thicknesses of 50-75 cm and <50 cm respectively but other field and chemical observations did not identify differences in weathering patterns between age groups. The two groups have distinctive clay mineral assemblages, with smectite present in the youngest deposits. These results contrast with reconnaissance studies conducted in the 1970s and 1980s on low-elevation soils in the Klondike Plateau. My study shows that field criteria...
Categories: Publication;
Types: Citation;
Tags: M3-Improve Permafrost Mapping,
Modeling,
Paleo and Holocene,
and Monitoring
Creating a global perspective on past treeline changes is problematic due to the varying methods and definitions used. A general lack of a detailed description of the modern treeline position and vegetation complicates any comparative analysis of the magnitude of the most important changes. However, one seemingly common factor in most regions was an extremely rapid dispersal of trees when climate warmed drastically from full glacial conditions. Most Arctic treelines reached their northernmost positions in the early Holocene and receded to present positions starting at about 5.8 ka. The early occupation of the northernmost sites in ice-free and early deglaciated areas was possible because of the close proximity of...
Categories: Publication;
Types: Citation;
Tags: P2-Changes in Plant and Animal Species Due to Climate Change,
Paleo and Holocene
Studies the implication of the modeling gravity and magnetism of ophiolites on Cordilleran terranes in Brooks Range, Australia. Geophysical characteristics of mafic and ultramafic rocks; Effect of low-density Cenozoic cover rocks on isostatic residual gravity values of the Noatak region; Causes of spatial separation strains.
General Circulation Models (GCMs) used to distinguish anthropogenic forcing of the Earth's past climate from its natural variability need to be validated by observations. The GCM ECHO-g was used to produce three millennial simulations of the Earth's climate. Two simulations include changes in anthropogenic and natural external forcing factors through the last millennium, differing only in their initial conditions, and a control run with constant external forcing representing internal variability. Since the ground contains a record of long-term trends in SAT, we use borehole temperatures in Canada, grouped into regions, as a record of past climate. The regional average SATs from ECHO-g were used to solve the forward...
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...
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