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Abstract: In order to understand permafrost and paleoenvironmental conditions in the Mackenzie Delta Region, permafrost cores were collected in the winter of 2017, near the newly developed Inuvik-Tuktoyaktuk Highway (ITH), NWT, by the NWT Geological Survey, NWT Department of Infrastructure, the University of Alberta’s Permafrost Archives Science Laboratory (PACS Lab), and partners as part of the Sentinel Drilling program. This study analyzed five cores (BH-1, BH-2, BH-3, BH-4, and BH-8) located within hilltops, riparian, and peatland terrains, recording various depositional environments. Cores were analyzed for stratigraphy, density, cryostructures, water isotopes (18O and 2H) and radiocarbon dating to determine the origin of the sedimentary records and associated ground ice. This study highlights that the Mackenzie Delta region and its ground ice history have been extensively preconditioned by deglaciation, landscape evolution and climatic change, resulting in a landscape with reduced ground ice relative to the late Pleistocene surface. Collectively, these results indicate that deposits within low-relief areas (such as peatlands, lacustrine and riparian zones) are characterized by hosting ice-poor sediments with isotopic values, similar to modern-day, local isotopic composition. BH-1 and BH-3 are comprised of ice-poor diamicts with an isotopic composition between 18O -23‰ to -19‰, with a co-isotope slope lower than the local meteoric water line. These isotopic values indicate deep thaw following deglaciation, and subsequent talik formation, and likely enhanced by the Early Holocene thaw followed by stabilization and permafrost aggradation. Likewise, BH-4 and BH-8 are underlain by modest ice contents, in the form of Holocene-aged segregated ice within lacustrine and glaciolacustrine deposits. Radiocarbon dates and sedimentary structures indicate a changing landscape following deglaciation. Local lakes from ~11,500 to 9000 years ago, subsequently drained or lowered, developing epigenetic permafrost, and transitioning to syngenetic peat in the early Holocene. Lastly, deposits within high-relief areas, such as hummocky and ice-cored terrain, show little evidence of being affected by Holocene thaw. The ice within BH-2, located on a hilltop remnant of glaciofluvial outwash deposits, had depleted Pleistocene values ranging between 18O -30‰ to -27‰, at depths greater than 6-meters below the surface. This borehole included buried glacier ice and primary till below 11m depth, likely buried by glaciofluvial outwash in an ice-marginal landsystem. Overall, these results highlight the ground ice heterogeneity within the Mackenzie Delta region. This heterogeneity is primarily a function of landscape geologic history, including, first and foremost, the preservation or eradication of relict ice during deglaciation processes such as talik development within lakes and fluvial networks, and mass-wasting processes, and subsequent climatic warming during the early Holocene. The result of these landscape-wide processes over the Holocene suggests that the landscape today is less ice-rich than the late Pleistocene landscape. Since the distribution and abundance of ground ice are strongly related to the geologic history of permafrost regions, future work will focus on placing these observations into a Quaternary geologic context and allow future trajectories of thermokarst to be identified.

Abstract: Stable isotopic ratios of oxygen and hydrogen (δ18O and δD) from ground ice have been used to reconstruct paleoclimate temperatures spanning the Late Pleistocene and Holocene in subarctic and arctic regions. This is possible due to the strong relations between the isotopic composition of atmospheric moisture and air temperature. Pore and texture ice, common forms of ground ice in permafrost regions, have been used to qualitatively infer the timing of centennial- and millennial-scale climate fluctuations spanning the Holocene and late Pleistocene. However, these records can be difficult to interpret because their source waters may become isotopically altered by local hydrological and phase-change (water-ice) processes before undergoing long-term preservation into the underlying permafrost record. The manifestations and relative contributions of these “secondary” isotopic modifications, which occur within the active layer and underlying transition layer, are poorly understood. In this study, we investigate spatially-varying processes that drive isotopic development in pore and texture ice from a catena within the Southern Ogilvie Mountains, Yukon Territory. The objectives of this study are to (1) establish the history of local permafrost formation using geochemical and traditional cryostructure analyses; (2) examine the stable isotopic relations between the active layer, transition layer, and relict pore and texture ice; (3) assess the impacts of local processes on the stable isotope development of pore and texture ice; and (4) build upon existing evidence for 20th century warming captured by stable isotope records in pore and texture ice.

When NASA's Dawn mission arrived at Ceres on March 6, 2015 it made history by becoming the first spacecraft to enter orbit around a second extraterrestrial object after leaving the asteroid Vesta in September 2012. Dawn thoroughly investigated the surface and deep interior of the dwarf planet Ceres, the largest object in the main asteroid belt, through a series of successively lower mapping orbits until its end of mission on November 1, 2018. Prior to Dawn’s arrival Ceres was known to be the largest C-type asteroid, and was suspected of being rich in water ice and other hydrated materials. As a putative remnant of the earliest phases of rocky planet formation, Ceres was thought to contain clues as to how planetesimals accreted and how volatiles arranged themselves throughout the inner solar system during the tumultuous era of planet formation. The Dawn mission’s goals were to further elucidate the structure and composition of the early solar system, which would lead to an increased understanding of the conditions present during terrestrial planet formation, and to determine the chemical, geological, and structural nature of the largest surviving planetary embryos: Vesta and Ceres. At Ceres, this was accomplished by meticulously characterizing the surface geology, surface and near-surface geochemistry, and interior structure via a combination of photo geology; visible, infrared, and nuclear spectroscopy; and gravimetry. This dissertation contributes to the objectives of the Dawn mission by aiding in the global geologic mapping effort of Ceres, identifying and classifying geological features indicative of its compositional and physical properties, and then applying geophysical techniques to these features in order to estimate these properties, particularly the water ice content of the near-surface. Understanding the quantity and distribution of water ice in the upper layer of Ceres is paramount for understanding both its geochemical evolution and the nature of the early solar system. The investigations presented in this dissertation reveal that Ceres is ubiquitously covered in geologic features suggestive of significant quantities of near-surface ground ice, namely large constructional mountains and hills, and a broad spectrum of lobate flow and mass wasting deposits. The observed mass wasting features exhibits physical characteristics and runout efficiencies similar to many ground ice mediated flows on Earth, Mars, and Iapetus such as long run-out landslides and frozen debris flows. Additionally, many craters on Ceres were observed to emanate fluidized appearing ejecta similar to examples found on Mars, Ganymede, and other icy worlds. Analyzing the mobilities of these ejecta using a kinematic-dynamic sliding ejecta emplacement model indicated that the cerean crust is significantly weaker than competent silicate rock at impacting conditions, and that the frictional properties of its surface are consistent with a rock-ice mixture. Finally, a unique fractured terrain named Nar Sulcus was identified on Ceres’ southern hemisphere that displayed topography suggestive of elastic flexure. By applying a flexural-cantilever model to the observed topography, the flexural rigidity of the cerean crust was estimated to be similar to those of outer solar system moons such as Europa, Ganymede, and Enceladus, which are several orders of magnitude less rigid than the terrestrial planets. From the aforementioned observations and investigations, the ground ice content of the cerean crust is estimated to be ~30-70 vol %, although there is likely significant regional heterogeneity in its distribution. This result is significant as it independently supports the interpretation that Ceres is a water rich dwarf planet, and that large quantities of ice can be sequestered within massive C-type asteroids over geologically long time periods. This is particularly exciting as carbonaceous chondrites are the most spectrally similar meteorites to C-type asteroids, and their water is the most isotopically similar to the Earth’s oceans. In light of the results presented in this dissertation, and by a myriad of other authors, it increasingly appears that a significant portion of the Earth’s water was likely delivered by Ceres-like asteroids.

Abstract: A 50,000 year record of meteoric water isotopes (δ2H/δ18O) and paleoenvironmental conditions is presented from syngenetic ice-rich permafrost and macrofossils from eight sites in the Klondike area of central Yukon. Four sedimentary units are recognized based on cryostratigraphy, paleoecological indicators, and δ2H/δ18O of associated ground ice. Unit 1 (50,000-36,000 cal yrs BP) contains boreal indicators (large woody macrofossils indicating trees and shrubs) near the base of the unit and is bounded near the top by the appearance of arctic ground squirrel nests. The presence of arctic ground squirrel nests, a reliable indicator of steppe- tundra, coupled with the largely massive organic-rich silts and large syngenetic ice wedges, defines Unit 2 (36,000-27,000 cal yrs BP). Unit 3 (27,000-13,150 cal yrs BP) includes abundant arctic ground squirrel nests, while the silts are generally grey and less organic-rich, and ice wedges through the unit are rare. Unit 4 (13,150 cal yrs BP to present) lacks arctic ground squirrel nests and contains shrubs near the base of the unit and full-boreal indicators in the upper sections. δ2H/δ18O tracks large-scale climate trends with a shift from near-modern values near the base of Unit 1 to more depleted values, reaching a minima at the Last Glacial Maximum (LGM). Isotopic values increase abruptly at 15,000 cal yrs BP, marking a climate amelioration reaching maximum values during the early Holocene, followed by subsequent cooling after 9,000 cal yrs BP. Deuterium (d) excess shows no clear trends except a +9‰ anomaly from 29,000-22,000 cal yrs BP coinciding with the LGM. This period likely represents an enhanced seasonality of precipitation, either from increased winter or reduced summer precipitation. This multi-proxy permafrost record provides new insights on late Pleistocene-Holocene climate and environmental change in eastern Beringia, and highlights the potential to develop similar records in other unglaciated regions.