Lack of calibrated instruments and written records prior to European contact in North America has forced palaeoclimatic researchers to develop various proxies capable of reconstructing ancient environments. Stable isotope analysis of tooth enamel of large terrestrial herbivores has increasingly become a creditable method of determining the ancient environments which these large mammals occupied during life. Archaeological evidence indicates human inhabitants of the northern Great Plains relied heavily on bison procurement throughout much of the Holocene. Because of this correlation, stable isotope analysis of bison tooth enamel has the capability of informing on palaeoenvironmental conditions which these ancient cultural groups occupied for the last 10,000 years on the northern Great Plains. Decades of research has provided evidence that stable isotope analysis of tooth enamel of large bodied herbivores (e.g. bovids) has the potential to be used as a proxy for reconstructing palaeoclimate, palaeoecology, foraging strategies and herd behaviour. Oxygen (δ 18O) isotope ratios are used as a proxy to track the meteoric hydraulic cycle (i.e. precipitation), which in turn is driven by local surface temperatures. Carbon (δ13C) isotope ratios have the ability to indicate photosynthetic pathways used by plant species, thus indicating local terrestrial plant cover. Dietary intake of water (δ 18O) and food (δ13C) are associated with isotopic signals which are recorded in the tooth enamel of a bison during amelogenesis (tooth enamel formation). Once tooth enamel is formed it never remodels; therefore, isotopic ratios recovered from fossil enamel become an archive of dietary consumption. In general, δ 18O isotope ratios are used to determine surface water and surface temperature conditions, whereas δ13C isotope values are used to indicate the abundance of C3 to C4 grasses consumed during an animal’s life. This study analyzes stable isotope (δ 18O and δ13C) ratios obtained from fossil bison enamel associated with archaeological sites in the northern Great Plains (Saskatchewan) region. The purpose of this study is to create a comparative model used to indicate ancient seasonality and palaeoenvironmental conditions over a 9,000 year period in the Holocene. A total of eight archaeological sites were examined, with each site representing a distinct time period and an affiliated human culture. In addition, isotope (δ 18O and δ13C) ratios recovered from tooth enamel was compared to isotope (δD and δ13C) values previously (Leyden 2004) examined from bone collagen of bison remains from the same archaeological sites. Results of this study demonstrates that original isotopic values from consumed water (δ 18O) and food (δ13C) from archaeological bison tooth enamel reflects seasonal changes for an approximate 18 month period. Further, results from this study also indicate that several climate and plant ecology changes occurred in the Saskatoon, Saskatchewan region over the last 9,000 years. Episodes of climate warming and cooling have been inferred by changes in δ 18O ratios at different time periods of the Holocene. Similarly, significant differences are also detected in δ13C values from different archaeological sites, inferring that bison populations consumed various abundances of C4 grasses at different time periods. In addition, evidence from this study has indicated that stable isotope ratios from enamel (δ 18O) and collagen (δD) from the same archaeological site, for the purpose of inferring climate conditions, demonstrate differing data for several time periods and close correlations for others. On the contrary, δ13C from both tooth enamel and bone collagen from each archaeological site produce comparable data which were used to measure the abundance of C4 grasses consumed by bison population during particular time periods.

The Red Tail site is one of 19 archaeological sites that lie within central Saskatchewan’s Wanuskewin Heritage Park. Since the creation of a long-term research program in 1984, many of these sites have been excavated making this the longest running archaeological project in Canada. This has provided an extensive body of archaeological evidence of human activity dating as early as the Early Precontact Period. Despite the extensive archaeological excavation and research that has occurred, relatively few geomorphic and paleoenvironmental studies have been conducted within the area. Paleoenvironmental data provide important context in building archaeological interpretations of past lifeways. The Red Tail site was originally excavated in 1988 and 1989 to a depth of approximately 2.7 m. In 2007, the site was revisited in order to conduct subsurface coring to a depth of over 6 m using a Geoprobe coring rig. This method allowed recovery of culturally sterile soils/sediments beyond the depth of the original excavation. This project includes analysis of these cores in order to investigate geomorphic processes active at the site and proxy indicators of paleoenvironment and paleoclimate. Analysis of two of the cores included detailed description of the recovered soils and sediments, as well as stable isotope and phytolith analysis of selected units in one of the cores. This suite of methods provides a robust, multi-proxy interpretation of geomorphic change and paleoenvironmental conditions at the site. The site was geomorphically active during the Late Pleistocene and Early Holocene, reflective of a dynamic and fluctuating climate following the glacial retreat. As the environment became more stable during the Middle to Late Holocene, periods of landscape stability are reflected in a sequence of buried soils. The paleoenvironmental and paleoclimatic record recovered from these buried soils shows a fairly consistent history of C3-plant dominated communities, reflective of moist, cool climate conditions. The relatively stable environmental and climatic conditions reflected at the site contribute to the understanding of the Wanuskewin area as an oasis on the prairies.

Two drilled cores were collected from the Jhuoshuei River delta for this study, which is focused on the analyses of sedimentological, statistical analysis, AMS C14 dating and paleoenvironment interpretation based on the benthic foraminiferal fossils. Foraminiferal shell do not exist between 30000 and 12000 yr B.P., indicating the environment of this sections might be terrestrial. Between 12000 and 8000 yr B.P., the southern core do not have traces of foraminifera, suggesting the deposition site was terrestrial. The northern core contains the benthic foraminiferal shell between 12000 and 9000 yr B.P. The foraminiferal assemblage indicates the sedimentation might be a inner shelf like enviroment. An estuarine like environment was suggested between 9000 and 8000 yr B.P.. Between 8000 and 6000 yr B.P., foraminiferal cluster analysis indicates a middle to inner shelf environment at the southern core site; a inner shelf at the northern core. From 6000 to 3000 yr B.P., foraminiferal cluster analysis indicates a inner shelf at the south core while northern core foraminifera became fewer and the environment gradually changing to terrestrial facies. From 3000 yr B.P. upwards, foraminiferal cluster analysis indicates a shallower inner shelf at the southern core. From 2000 yr B.P. to today, the southern core changed to terrestrial.

Two deeply buried, well-stratified, and well-dated components dating to the Early Holocene period were excavated at the Richard Beene site (41BX831) in Bexar County, Texas. This thesis utilizes both qualitative (interpretation of maps) and quantitative (unconstrained clustering) spatial analysis techniques to identify site structure and assess post-depositional disturbance by analyzing patterns among artifact categories, selected artifacts, and features from these components. Results of spatial analysis are compared to expectations of the archaeological record based on previous research. Each component revealed a distinct pattern. The Lower Medina component (ca. 6900 B.P.) is well preserved and spatial analysis showed clear distinctions between domestic and peripheral zones. The Upper Perez component (8800 B.P.) is a fluvial lag deposit of displaced artifacts and fire-cracked rock features. Results of spatial analysis confirmed that most, if not all, of this component is disturbed, revealing no site structure.

Understanding the paleoclimate of a region is important, especially when trying to determine the extent of natural climate variability within the context of anthropogenic impacts. Recent anomalous periods of climate change in the Late Holocene, including the Little Ice Age and Medieval Warm Period, could possibly repeat in the future, having significant worldwide consequences. This holds especially true for tropical and subtropical karst environments, where limited paleoclimate proxies provide minimal data regarding past climate change. An investigation into past climate change in Belize using fulvic acids from cave sediments shows periods of drought during the collapse of the Maya society around 1400 years ago. Comparison of changes in the carbon isotope data from the fulvic acids agree with speleothem records, but more closely reflect changes in the vegetation above the cave, showing Maya population decline through waning agriculture. Further investigation of using fulvic and other organics acids are examined from cave sediments in Florida. The data show fulvic acid carbon isotopes are the most robust recorders of climate change, agreeing with several nearby speleothem d¹8O and d¹³C records from west-central Florida. A more detailed record of climate change in Florida through a calibration study of precipitation and cave dripwater oxygen and hydrogen isotopes revealed that the amount effect dominates rainfall in west-central Florida. Homogenization of epikarst dripwater gives average d¹8O values representative of the annual amount-weighted average of precipitation d¹8O for the area, suggesting speleothem isotope records reflect changes in rainfall amount. Examination of two speleothems from west-central Florida show complex teleconnection and solar forcing mechanisms responsible for past climate changes. A high-resolution stable isotope, trace element, and time series analysis study for the last 1500 years shows variability during the LIA and MWP, pointing to a combined influence of Pacific and Atlantic teleconnection mechanisms, especially the ITCZ, NAO and PDO, being responsible for precipitation variability. Long-term reconstruction of the mid-Holocene and Late Pleistocene from another speleothem reveals differences in temperature and precipitation between glacial and interglacial conditions in Florida. Climate proxies from the tropics and subtropics provide additional clues to global climate change crucial to understanding future water availability.

Stratigraphic records in Middle Park in north-central Colorado provide evidence for the late Quaternary geomorphic and environmental history of a non-glaciated Southern Rocky Mountain basin. Episodes of geomorphic instability apparent in the stratigraphic record coincide with changes in paleoenvironmental records from above 2750 m in north-central Colorado, suggesting that the western Middle Park landscape was sensitive to environmental changes affecting the region over the last ~14,000 years. Tributaries were incised prior to 14.0 ka, but deposits older than 12.0 ka are rare. Upland erosion and incision followed by rapid aggradation in alluvial settings between 12.0 and 11.0 ka coincide with evidence for regional temperatures at or above present, and is interpreted to signal the onset of Holocene summer-wet precipitation. A widespread soil-stratigraphic marker represents a long period of landscape stability between <11.0 and 6.0 ka in upland and alluvial settings. Pedologic evidence from upland settings indicates the expansion of grass and forest cover to lower elevations that today are characterized by sagebrush steppe, probably during a period of increased summer precipitation relative to present. During the late Holocene, episodes of aggradation in alluvial valleys at 6.0-1.0 ka and 0.6-0.2 ka and soil formation in uplands at 5.0-3.5 ka and 2.5-1.0 ka overlap with evidence for cooling at higher elevations. Incision of valley floors documented at 1.0-0.6 ka and during the last few centuries and episodes of erosion in uplands at 3.5-2.5 ka, after 1.0 ka, and within the last few centuries, are roughly synchronous with evidence for warming. Upland and alluvial stratigraphic records are interpreted to indicate that during cool intervals summer precipitation was diminished, resulting in relative hillslope stability and gradual valley bottom aggradation, while pulses in summer precipitation accompanying warmer episodes caused basin-wide geomorphic instability. The recent increasing frequency of geomorphic instability appears to correspond with an increase in sagebrush steppe at the expense of forest and grass cover, interpreted to represent progressive drying during the late Holocene. It stands to reason that future warming, if accompanied by similar patterns in precipitation, will result in continued erosion on a landscape already at a threshold of geomorphic instability.

Les tourbières nordiques, sont des écosystèmes humides ayant la particularité de produire plus de matière organique qu'elles n'en décomposent. Elles ont ainsi accumulé de formidables quantités de carbone depuis le début de la dernière déglaciation. C'est pour cette raison qu'elles représentent un intérêt particulier pour la modélisation du climat global. En effet, contenant environ un tiers du carbone des sols tout en ne couvrant qu'environ 3% de la surface terrestre, les tourbières émettent également de grandes quantités de méthane, qui a un pouvoir de réchauffement climatique 23 fois plus important que le dioxyde de carbone. Afin de pouvoir intégrer ces différents facteurs dans les modèles globaux du climat et d'estimer leur incidence sur le cycle global du carbone, il est nécessaire de mieux connaitre la dynamique du carbone dans les tourbières elles-mêmes. Les tourbières nordiques ont la capacité d'archiver des informations rapportant les différents changements qu'elles ont subis depuis leur développement. Ces changements incluent les changements climatiques régionaux, qui ont affecté leur végétation et la dynamique du carbone, mais aussi des changements autogènes, c'est-à-dire propres à leur dynamique interne. Il est donc nécessaire de prendre en compte ces différents facteurs en vue de reproduire leur dynamique. Cette thèse a pour objectif d'évaluer la connaissance de la dynamique du carbone dans les tourbières par le biais de l'évaluation du Holocene Peat Model (Frolking et al. 2010). Ce modèle comprend une description des processus d'accumulation, de décomposition, du bilan hydrique et une représentation de la végétation par 12 groupes fonctionnels de plantes ainsi que les boucles de rétroaction entre ces différents processus. Son évaluation a été effectuée en deux étapes. Dans un premier temps, une analyse de sensibilité a permis de déceler les paramètres du modèle ayant une influence sur la quantité totale de carbone dans les simulations, puis les interactions entre les paramètres ont également été analysées. Les résultats montrent que certains paramètres représentent des sources d'incertitude importantes et devraient être l'objet de plus amples recherches (tels que la conductivité hydraulique, le gradient d'anoxie, certains paramètres contrôlant le bilan hydrique et la densité sèche). De plus, parmi les milliers de simulations effectuées, on observe que plusieurs types de développements des tourbières sont possibles, bien que la méthodologie mette l'emphase sur les processus autogènes et contraigne les processus allogènes à un régime de précipitation et une productivité primaire nette (PPN, servant d'indicateur climatique) constants. Par ailleurs, il apparaît que les sphaignes ont une influence sur le type de développement de la tourbière, ce qui affecte par conséquent l'accumulation du carbone. Dans un second temps, le modèle est calibré pour deux sites de la région de la Baie James au Québec. Il s'agit de deux tourbières ombrotrophes ouvertes ayant des caractéristiques écohydrologiques et des taux d'accumulation de carbone différents. Pour chacun de ces sites, deux simulations sont réalisées : la première est basée sur une reconstruction des précipitations et la seconde sur une reconstruction des niveaux de nappe phréatique. Il est notable que les résultats des simulations révèlent des périodes durant lesquelles les tourbières présentent des pertes nettes de carbone. En comparant les résultats des simulations avec les taux d'accumulation de carbone et les résultats des analyses de macrorestes végétaux, on constate que le modèle reproduit, de façon générale, les variations observées dans ces séries de données. De plus, il est conclu que ce modèle peut être utilisé comme outil d'identification des causes de variations de l'assemblage végétal. Bien que de certains processus doivent être étudiés plus avant afin de limiter les incertitudes du modèle, cette thèse a permis d'établir la validité des concepts de dynamique du carbone dans les tourbières en intégrant l'évaluation des dynamiques d'échelle globale et locale. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Tourbière, modélisation, évaluation, analyse de sensibilité, forçage, fonction de transfert.

Paleoclimatic research in the Canadian Arctic has increased in recent decades; however, there is still much to learn about the nature and extent of past climate change in this vast, environmentally sensitive region. This thesis uses diatom assemblages in dated lake sediment cores as proxy indicators to infer how climate has changed over the Holocene in two very different lakes in the central Canadian Arctic: one located in a poorly-studied geographical region, and another possessing limnological characteristics that are unusual in an Arctic context. Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies. In addition, diatom shifts occurring ~7000 and ~3500 cal yr BP are indicative of mid-Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which agree with those from other studies farther south. Finally, shifts in the diatom assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are consistent with reduced ice cover, related to recent warming. Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the High Arctic on Ellesmere Island, is characterized by unusually high ionic concentrations for an inland Arctic pond. As in TK-2, Stygge’s diatom assemblages changed substantially throughout the Holocene, but especially in the most recent sediments. Diatom shifts near ~10,500 cal yr BP suggest an early onset for the Holocene Thermal Maximum (and for the successive Neoglacial cooling trend) in this region, consistent with previous studies from the High Arctic. Marked diatom assemblage changes occurred in the most recent sediments, and are indicative of climate warming and reduced ice cover, as well as increased ionic concentration due to enhanced evaporative concentration. The dynamic nature of the diatom assemblage changes at the Stygge site suggests that sediments from these rare athalassic ponds represent an especially sensitive archive of Arctic climatic and environmental change. / Thesis (Master, Biology) -- Queen's University, 2008-11-12 16:46:47.174

No description available.

Holocene climate variability in the British Columbia Coast Mountains has resulted in repeated intervals of glacier expansion and retreat. Since reaching their late Holocene maximum positions in the late 20th century, glaciers in the region have experienced significant volumetric loss. The subsequent downwasting and frontal retreat has revealed forests buried by glacier advances throughout the Holocene, enabling description of significant intervals of ice expansion using dendroglaciology. This thesis characterizes dendroglaciological evidence as it relates to climate at two scales: (1) at Franklin Glacier in the Mt. Waddington area, and; (2) throughout the Coast Mountains. Dendroglaciological evidence from glacier forefields and lateral moraines in the Coast Mountains provides evidence for at least 11 intervals of glacier activity during the Holocene. The earliest record glacier activity is documented in the Pacific Ranges from 8.5 to 7.8 ka, after which glaciers in this region retreated during the early Holocene warm and dry interval. Following this a glacial advance from 6.7 to 5.6 ka was followed by a subsequent expansion episode from 5.1 to 4.6 ka in response to attendant cool and moist conditions in the Pacific Ranges. After 4.6 ka, glaciers in the Pacific and Boundary ranges advanced at 4.4 to 4.0 and 3.8 to 3.4 ka during intervals characterized wet conditions resulting from an intense, eastwardly positioned Aleutian Low pressure centre. Following 3.4 ka most glaciers retreated before expanded between 3.2 and 2.8 ka, retreated, and then advanced from 2.6 to 2.4 ka. Glacier advances from 1.8 to 1.1 ka occurred in response to a regional cooling event, and proceeded Little Ice Age advances from 0.6 to 0.4 ka. Franklin Glacier is an 18-km long valley glacier that originates below the west face of Mt. Waddington. Radiocarbon-dated wood samples from the proximal faces of lateral moraines flanking the glacier show that it expanded at least nine times since 13 ka. A probable Younger Dryas advance of Franklin Glacier at 12.8 ka followed the late glacial retreat and downwasting of the Cordilleran Ice Sheet from ca. 16.0 to 12.9 ka. During the succeeding early Holocene warm period, Franklin Glacier appears to have retreated significantly, leaving no record of glacial expansion until the mid-Holocene when it repeatedly advanced at 6.3, 5.4, and 4.6 ka in response to cool summer temperatures and generally moist conditions. Downwasting of the glacier surface after 4.6 ka was followed by intervals of expansion at 4.1, 3.1, and 2.4 ka contemporaneous with a period of increased precipitation. Following ice expansion at 2.4 ka into trees over 224 years in age, there is no record of the glacier activity until 1.5 ka when Franklin Glacier thickened and advanced into young subalpine fir trees, reflecting attendant cool and wet environmental conditions. During the Little Ice Age, advances at 0.8 and 0.6 ka preceded a mid-19th to early-20th century advance that saw Franklin Glacier attain its maximum Holocene extent in response to an extended interval of cold temperatures. The dendroglaciological record at Franklin Glacier is among the most comprehensive recovered from the British Columbia Coast Mountains and showcases the complexity of latest Pleistocene and Holocene glacier behaviour in the region. / Graduate / 0368 / bjmood@uvic.ca