The rapid rate of global warming currently underway highlights the need for a deeper understanding of abrupt climate change. The Younger Dryas is a Late-Glacial climate event of widespread and unusually rapid change whose study can help us address this need for increased understanding. Reconstructions from the glacial record offer important contributions to our understanding of the Younger Dryas due to (among other things) the direct physical response of glaciers to even minor perturbations in climate. Because the glacier equilibrium line altitude (ELA) provides a more explicit comparison of climate than properties such as glacier length or area, ELA methods lend themselves well to paleoclimate applications and allow for more direct comparisons in space and time. Here we present a physically based ELA model for alpine paleoglacier climate reconstructions that accounts for differences in glacier width, glacier shape, bed topography and ice thickness, and includes error estimates using Monte Carlo simulations. We validate the ELA model with published mass balance measurements from 4 modern glaciers in the Swiss Alps. We then use the ELA model, combined with a temperature index model, to estimate the changes in temperature and precipitation between the Younger Dryas (constrained by 10Be surface exposure ages) and the present day for three glacier systems in the Graubünden Alps. Our results indicate an ELA depression in this area of 320 m ±51 m during the Younger Dryas relative to today. This ELA depression represents annual mean temperatures 2.29 °C ±1.32 °C cooler relative to today in the region, which corresponds to a decrease in mean summer temperatures of 1.47 °C ±0.73 °C. Our results indicate relatively small changes in summer temperature dominate over other climate changes for the Younger Dryas paleoglaciers in the Alps. This ELA-based paleoclimate reconstruction offers a simple, fast, and cost-effective alternative to many other paleoclimate reconstruction methods. Continued application of the ELA model to more regions will lead to an improved understanding of the Younger Dryas in the Alps, and by extension, of rapid climate events generally.

Les latérites couvrent plus de 30% des surfaces émergées. Comprendre leur évolution future est essentiel pour prédire les changements qui affecteront le fonctionnement de la Zone Critique dans les siècles à venir. La littérature a pu montrer que les horizons indurés de ces sols comportaient plusieurs générations de minéraux secondaires qui pouvaient être reliées à différents événements paléoclimatiques. Des études isotopiques ont montré que les horizons non indurés de ces sols pouvaient aussi posséder des générations distinctes de minéraux secondaires. La datation par Résonance Paramagnétique Électronique, a été appliquée sur des kaolinites de latérites dans le but d’identifier si ce minéral possède bien plusieurs générations au sein d’un même profil et si ces dernières étaient corrélables avec des événements paléoclimatiques globaux ou régionaux. Au cours de cette thèse, deux régolithes du Plateau du Karnataka (Inde), quatre du bassin du Rio Négro (Brésil) et un de la région de Syerstone (Australie) ont été étudiés. Les résultats de ces datations ont permis de distinguer différentes générations de kaolinites au sein de chacun des profils étudiés. Ces dernières sont par ailleurs toutes corrélables avec des périodes de fortes précipitations liées aux évolutions climatiques régionales et/ou globales. Ces résultats confirment aussi l’existence du phénomène de rajeunissement profils latéritiques au cours des temps géologiques. Le travail de cette thèse corrobore l’hypothèse de l’évolution épisodique de ces sols tropicaux et souligne leur importante stabilité dans les temps géologiques. / Laterites are covering a third of the continental surfaces. Understanding their evolution through the ongoing climate change is critical to predict the future Critical Zone transformation. Laterite duricrusts can contain several generations of secondary minerals that can be correlated with distinct paleoclimatic events. Isotopic studies showed that loose laterites may also be formed by several generations of secondary minerals. The objective of this PhD was to confirm that loose laterites contain several generations of kaolinites and that they formed during regional and/or global paleoclimatic events. With this aim in view, a recent dating methodology, the Electron Paramagnetic Resonance dating of kaolinites, was used on tropical regolith profiles from three continents with distinct geodynamic histories: India (Karnataka plateau), South America (Rio Negro basin, Brazil) and Australia (Syerstone region, New South Wale). The data set of this PhD confirms that a regolith contains several generations of kaolinites. All the identified generations of the present study can be correlated with regional paleoclimatic events or with tropical weathering favourable periods initiated by global paleoclimatic trends. Kaolinite generations formed preferentially during high precipitations periods and result from the rejuvenation of laterite profiles. The results of this PhD confirm that laterites have an episodic evolution.

The Middle Ordovician Ancell Group, including the St. Peter Sandstone, Glenwood Shale and Starved Rock Formation, records intracontinental basin development during eustatic sea level changes in Iowa and Illinois. The St. Peter Sandstone overlies the Prairie du Chien Group across an erosional unconformity that marks a major sequence boundary, whereas upper contact of the St. Peter Sandstone with the Glenwood Shale also is a second sequence boundary. Data from 80 wells, selected well logs, and 20 cores were integrated to refine the high-resolution sequence stratigraphy of the Ancell Group. Two main sequences bounded by three sequence boundaries are interpreted to represent 3rd order sequences. Distinctive shallowing-upward parasequences bounded by flooding surfaces in many cores record higher frequency relative sea level fluctuations in the Ancell Group, but these cannot presently be correlated regionally. Facies variations define an aggradational transgressive systems tract TST), a prograding highstand systems tract (HST) and down stepping falling stage system tract (FSST) in both the St. Peter Sandstone and the Glenwood Shale-Starved Rock Formation units. The St. Peter Sandstone thickens towards the northeast and thins to the northwest and southwest in Iowa. In contrast, the St. Peter Sandstone in Illinois thickens to the south likely recording a prolonged FSST incised valley or channel fill. Detrital zircon geochronology of 13 samples from the St. Peter Sandstone and Starved Rock Formation define common peaks at 1100-1500 Ma and 2500-2700 Ma with minor components at 1670-1750 Ma and 3000-3600 Ma. The detrital zircon signature is dominated by Archean, and Grenville (1000-1300 Ma) ages. The detrital zircon geochronology indicates that the Ancell Group was sourced directly from the Archean Superior Province to the north and Grenville Province to the northeast, although recycling of Archean grains from the Paleoproterozoic Huron Basin cannot be ruled out. The near complete lack of 1800-1900 Ma ages argues against derivation of detritus from the Trans-Hudson or Penokean Orogens. The Transcontinental Arch northwest of the Iowa Basin acted as a barrier to sediment transport from the Trans-Hudson Orogen. Basement rocks of the Penokean Orogen are inferred to have been covered by water or younger sediments southeast of the Iowa Basin. CIA analyses of Ordovician shale samples from around the Transcontinental Arch indicate that the climate condition during Middle Ordovician time was warm and humid. This is consistent with a paleoclimate interpretation where mechanical erosion and chemical weathering yielded first cycle mature quartz arenites (Witzke, 1980).

Late Holocene climate variability includes the Little Ice Age (LIA, 450-150 BP) and the Medieval Warm Period (MWP, 1100-700 BP) that are characterized by contrasting hydrologic and thermal regimes. The degree of interaction between the North American continent and the ocean during these two abrupt climate events is not well known. Marine sedimentary records from basins proximal to major rivers integrate climate signals across large spatial scales and can provide a coherent, high-resolution assessment of the oceanic and continental responses to changing climate and hydrologic conditions. The Pigmy Basin in the northern Gulf of Mexico is ideally situated to record inputs from the Mississippi River and to relate these inputs to changing hydrologic conditions over North America during the LIA and MWP. Hydrologic variability recorded over the North America continent is directly dependent on the moisture balance (E/P) over the sub-tropical Gulf of Mexico (a major source of moisture to the North America continent). Warm, moist air masses from the south interact with cold/dry air masses from the north over the North American continent to produce storm fronts. Increased evaporation over the Gulf of Mexico leads to enhanced precipitation over the North American continent, due to the intensification of atmospheric circulation, which influences meridional moisture flux from the Gulf of Mexico to the North American continent. This study focuses on the sedimentary record spanning the last 1400 years and utilizes a multi-proxy approach incorporating organic and inorganic geochemical analyses to define intervals of varying continental inputs and to assess changes in the moisture balance (E-P) within the Gulf of Mexico.

Fluvial terraces contain information about incision, deformation, and climate change. In this study, a chronostratigraphic record of Colorado River terraces is constructed from optically stimulated luminescence (OSL) dating of Pleistocene alluvium and real-time kinematic (RTK) GPS surveys of terrace form. This record is analyzed to relate terrace formation to late Pleistocene climate fluctuations, and terrain analyses and longitudinal profile patterns reveal recent salt-related activity in the northern Paradox Basin as well as patterns in Colorado Plateau incision. A well-preserved, correlative suite of mainstem (M) fluvial deposits exists along the Colorado River upstream of Moab, Utah. Absolute dates indicate sedimentation >70 ka (M7, M6/M5), 70-50 ka (M4), 50-40 ka (M3), and 35-25 ka (M2). The M4 and M2 formed during the crescendo to glacial maxima, but the M7, M6/M5, and M3 were deposited during variable climate of marine isotope stages (MIS) 5 and 3. Deposits include thin (<7 m) strath terraces and thick (10-20 m) fill terraces. Our results suggest that terrace sedimentation is linked to enhanced sediment flux during glaciations in Rocky Mountain headwaters (M4 and M2), but major deposits also formed during dryland tributary sediment loading with markedly different timing (M6/M5 and M3). Conversely, incision may be driven by higher deglacial flows. Clast provenance data demonstrate greater percentages of locally-sourced sediment in M6/M5 and M3 deposits. Valley-bottom geometry and neotectonics control terrace form, with strath terraces found in bedrock-restricted reaches and fill terraces in wider valleys. Previously speculated salt deformation in this area is confirmed by localized collapse preserved in M4 stratigraphy in the Cache Valley graben and ~15 m of broader subsidence upstream. Concavity and knickzone distributions in tributary profiles are discordant and represent subtle expressions of salt-tectonic activity. Finally, a surprisingly rapid incision rate of ~900 m/Ma over the past ~70 ka suggests that the Colorado River may be responding to flexural rebound in the central plateau, but is faster than that predicted by the debated bull's-eye pattern of regional incision. This locally high rate may also reflect a transient wave of incision, as suggested by increased Pleistocene rates interpreted by studies in Glen and Grand canyons.

This thesis investigated marine isotope stage {MIS) 3-2 glacial sequences in the South Fork Hoh River Valley, Washington and the Lake Hawea Valley, New Zealand. Research objectives were to reconstruct the style and timing of ice advance in both areas and to assess the viability of luminescence dating of glacial sediments in various depositional facies and distances from the ice front. This thesis focused on the sedimentology and stratigraphy of surficial and older glacial sequences in the South Fork Hoh and Lake Hawea areas and used OSL and radiocarbon dating techniques to establish age control for the deposits. Specifically, this research identified, described, and dated the stratigraphy of glacial sequences in order to reconstruct ice dynamics. This work also presents updated geomorphic maps for both study areas as an additional way to show ice advance and retreat events recorded in deposited sediment and geomorphic surfaces. The glacial sequence expressed in the Lake Hawea moraine exposure shows four distinct depositional events that represent retreat from an ice position down -valley, re-advance to the Hawea moraine position, and subsequent retreat and deglaciation broadly spanning -32-18 ka. These results document the terminal glacial advance and subsequent retreat in the Lake Hawea Valley and contribute to the wider swath of research studying the last phase of glacial retreat and its connections to climate on the South Island of New Zealand. The Hawea chronology corresponds to other glacial records and paleoclimate reconstructions from the South Island that collectively suggest the commencement of deglaciation at -13 ka. Three late Pleistocene ice positions are preserved in the South Fork Hoh River Valley, here referred to as South Fork 1-3 (SF 1-3). One of these positions has not previously been recognized in this valley or in the mainstem Hoh River Valley. Optically stimulated luminescence (OSL) and radiocarbon (14C) ages are generally consistent throughout the valley. These finding s advocate for a detailed sedimentologic and stratigraphic approach to glacial depos its and questions whether a similar advance or still -stand occurred in other valleys in the region. If so, this may reveal information regarding climate influences on MIS 2 glaciers in the Olympic Mountains. This research also assesses the applicability of OSL dating to glacial deposits in both field areas. Quartz OSL dating was used in the South Fork Hoh study area; however, quartz produced unreliable results in the Hawea study area, so samples were therefore assessed using feldspar methods. The results advocate for a facies-based sampling approach in glacial settings, where better sorted sandy facies and more distal deposits produce better bleached and more reliable age results than other deposits.

The Sierra Nevada snowpack is vital to the water supply of California, the world’s sixth largest economy. Though tree ring and instrumental records show the dramatic influence of environmental change on California’s hydroclimate over the last millennium, few proxy archives assess winter precipitation variability farther back in time. Here, we use diatoms from a ~3,200 yr. old sediment core to reconstruct the paleolimnology of June Lake, a hydrologically closed glacial lake in the eastern Sierra Nevada. We test the hypothesis that limnologic and climatic changes control diatom assemblages at June Lake. Fossil diatom assemblages from June Lake sediments chiefly consist of the planktic genera Stephanodiscus and Lindavia; their relative abundances in sediments are controlled by lake response to changes in the length of the winter season. We establish a Lindavia:Stephanodiscus index to infer winter length; our results indicate three periods where winter seasons are longer than average: ~3.2-2.9 ka, ~2.2-1.7 ka, and ~0.6 ka-0.05 ka. Over the last ~100 yrs., June Lake has experienced stronger water column stratification and an expansion of the available benthic diatom habitat, indicating significantly warmer winters and lower lake levels. It is possible that this change is the result of anthropogenic climate warming.

Sediment accumulated in lakes stores valuable information about past environments and paleoclimatological conditions. Cores previously obtained from Saint Albans Bay, located in the Northeast Arm of Lake Champlain, VT record the transition from the Champlain Sea to Lake Champlain. Belrose (2015) documented the presence of a peat horizon separating the sediments of the Champlain Sea from those of Lake Champlain. Initially, this layer was thought to comprise the transition from the marine environment of the Champlain Sea to a freshwater wetland. However, based on the results from this study, the transition between marine and freshwater conditions is thought to be represented by an erosional unconformity, indicative of a lowstand at the end of the Champlain Sea period. For this study, five additional cores were collected from Saint Albans Bay along a transect following the long axis of the bay moving into progressively deeper water. These cores better constrain the spatial extent, thickness and age variability of the peat layer within the bay and allow us to better understand the environmental conditions that preceded the period of peat deposition. In each of the cores there is evidence of sediment reworking in the uppermost Champlain Sea sediments, indicated by the presence of coarse-grained sediment, which is suggestive of a lowstand at the end of the Champlain Sea period before the inception of Lake Champlain. This coarse-grained layer is immediately overlain by a thick peat horizon. The widespread occurrence of the peat layer points to a large wetland that occupied the entire inner portion of Saint Albans Bay, and lake level ~ 9 m lower than at present during the Early Holocene. Based on radiocarbon dating, this paleo-wetland existed in Saint Albans Bay from ~ 9,600-8,400 yr BP. The development of this wetland complex is time transgressive, reflecting rapidly increasing lake level during the Early Holocene. This hypothesis is supported by the basal peat radiocarbon dates, as well as by the composition of plant macrofossils recovered from the peat horizons. The shift from peat deposition to fine-grained, low organic content lacustrine sedimentation is believed to have occurred at ~8.6-8.4 ka and is likely the result of continued isostatically driven lake level rise coupled with a changing climate. Although it was not its primary focus, this study also seeks to address the variations in sediment composition in the Lake Champlain sections of the cores. Evidence from the Lake Champlain record in Saint Albans Bay indicates that there were notable fluctuations in sedimentation, which were likely linked to both climatic variations and a change in the morphology of the bay. The rebound in productivity from ~8-5 ka is likely the result of warmer conditions during the Hypsithermal period. An increase in terrigenous sedimentation during this same time suggests a change in the morphology of the bay in which the Mill River delta migrated towards the inner bay. Initially, the cooler conditions of the Neoglacial are reflected in Saint Albans Bay by a decrease in organic matter content from ~5-3 ka. During the latter part of the Neoglacial (~3-1 ka), increases in organic matter content and detrital input point to enhanced productivity in response to increased precipitation and runoff from the watershed. The most recently deposited sediments in Saint Albans Bay bear out the legacy of anthropogenic nutrient enrichment of the bay in the form of increased algal productivity.

Little is known about the paleo-precipitation of the Florida Peninsula. In order to better understand Floridas late Holocene climate variability (last 4,200 years), the isotopic composition was analyzed of four speleothems from two caves, in West-Central Florida. Two speleothems were collected from BRC Cave in Hernando County, and two others from Briar Cave in Marion County. This study represents the first speleothem-based paleoclimate records for Florida. Uranium-series disequilibrium analyses were determined by using thermal ionization mass spectrometry (TIMS) to provide accurate determination of chronology of the deposition of the speleothems. Stable isotopic analyses of oxygen and carbon were performed using stable isotope mass spectrometry, which provided information regarding changing amounts of precipitation (increase in precipitation, decrease in the δ18Oc) and types of vegetation above the cave (increased forest density, decrease in the δ13Cc). Variations in the speleothems δ18O composition reveal abrupt changes in precipitation amount, fluctuations that appear both regional and hemispheric in nature. Strong similarities between the speleothem δ18O, Lake TulaneδD record (Cross et al. 2003; 2004) and the SE US tree-ring record (surrogate for spring precipitation - Stahle and Cleaveland 1992) suggests a regional atmospheric influence on Floridas precipitation. The major causes of changes in precipitation are proposed to be Atlantic Multi-decadal Oscillation (AMO), El Nino and changes in the relative positions of the Intertropical Convergence Zone (ITCZ)-North Atlantic High (NAH). Comparison between the δ18Oc and surrogates of these influences, show all three have some effect. AMO and El Nino have short-term (decadal) influence and ITCZ-NAH has a long term (centennial) influence. The contributions of these climatic effects have implications for teleconnections involving Floridas climate; the AMO correlation shows higher latitude influence, while El Nino and the ITCZ show tropical influence on subtropical Florida.

Sclerochronology was conducted on the pedicle valves of four Sakmarian-age brachiopods (Squamaria moorei) to constrain climate model predictions of temperature seasonality along western equatorial Pangaea (WEP). The brachiopods are from a Lower Permian section within the Robledo Mountains, NM, and they reveal seasonal trends of δ18O and temperature for that interval that suggest global warming and moderation of seasonality. Elemental and SEM analyses verified the specimens were well preserved. δ18O profiles show a relatively rapid and consistent two-year growth rate corresponding to the organism's juvenile stage, followed by a slower, seasonal growth rate corresponding to the organism's sexually mature stage typical of most organismal growth. Their initial two-year cycles show consistent, high-amplitude profiles that captured virtually complete records of annual δ18O values, and these profiles were used for seasonality interpretations. The specimen from the stratigraphically lowest layer shows δ18O values varying from -4.26 to -2.17 minimum winter temperatures (MWT) and maximum summer temperatures (MST) of 25.2C and 35.7C, respectively; and a seasonal temperature variation ΔTs of 10.0C. The overlying horizon yielded two specimens showing δ18O values ranging from a minimum of -4.54 to a maximum of -2.79; MWT ranging from 28.2 to 29.6C; MST ranging from 34.9 to 37.2C; and ΔTs ranging from 6.7 to 7.6C. The uppermost layer yielded a specimen that shows δ18O values ranging from -4.49 to -3.03; MWT of 31.3C; MST of 37.0C; and ΔTs of 5.7C. The specimens show overall high seasonality for an equatorial regime, but the general trend shows increasing winter temperatures and a moderation of seasonality. The data supports climate-model predictions for the Permian of more equable temperatures, higher winter temperatures, and decreased seasonality. Three numerical climate models of Permian temperatures were evaluated against the brachiopod data, and their model predictions for ΔTs along WEP range from as high as 10C to as low as C. The models were supported somewhat by the independently derived temperature proxy data measured in this study.