• Arctic landscape dynamics: modern processes and pleistocene legacies

      Farquharson, Louise M.; Mann, Daniel; Romanovsky, Vladimir; Grosse, Guido; Jones, Benjamin M.; Swanson, David (2017-12)
      The Arctic Cryosphere (AC) is sensitive to rapid climate changes. The response of glaciers, sea ice, and permafrost-influenced landscapes to warming is complicated by polar amplification of global climate change which is caused by the presence of thresholds in the physics of energy exchange occurring around the freezing point of water. To better understand how the AC has and will respond to warming climate, we need to understand landscape processes that are operating and interacting across a wide range of spatial and temporal scales. This dissertation presents three studies from Arctic Alaska that use a combination of field surveys, sedimentology, geochronology and remote sensing to explore various AC responses to climate change in the distant and recent past. The following questions are addressed in this dissertation: 1) How does the AC respond to large scale fluctuations in climate on Pleistocene glacial-interglacial time scales? 2) How do legacy effects relating to Pleistocene landscape dynamics inform us about the vulnerability of modern land systems to current climate warming? and 3) How are coastal systems influenced by permafrost and buffered from wave energy by seasonal sea ice currently responding to ongoing climate change? Chapter 2 uses sedimentology and geochronology to document the extent and timing of ice-sheet glaciation in the Arctic Basin during the penultimate interglacial period. Chapter 3 uses a combination of surficial geology mapping and remote sensing to explore the distribution and vulnerability of modern day landscapes on the North Slope of Alaska to thermokarst caused by rapid warming. Chapter 4 uses high spatial and temporal resolution remote sensing data and field surveys to show how sea ice decline is causing AC coastlines to become more geomorphologically dynamic. Together the results of this research show that the AC is a highly dynamic system that can respond to climate warming in complex and non-linear ways. Chapter 2 provides terrestrial evidence that ice-sheet glaciation occurred offshore in the Arctic Ocean in the later stages of the last interglacial period at a time when lower latitude sections of the Laurentide and Cordilleran were in retreat. These findings have important implications for how Arctic ice sheets respond to increased moisture availability caused by sea ice decline and atmospheric warming. This study also provides a new approach to reconstructing and establishing an absolute chronology for periods of Arctic Ocean glaciation during the mid- to late-Pleistocene. Chapter 3 illustrates how Pleistocene-legacy effects exert important influences over the vulnerability of Arctic lowlands to climate warming. Striking differences are revealed in Holocene thermokarst activity between different surficial geology units. During the Holocene, regions of marine silts have been the most susceptible to thermokarst, while regions of ice-poor aeolian sand have seen the least thermokarst activity. In future decades, areas of ice-rich aeolian silt will be most vulnerable to rapid warming because these areas contain large amounts of ground ice that have so far undergone little thermokarst development during the Holocene. Findings from this study have important implications for understanding future landscape evolution and carbon cycling in the Arctic. Chapter 4 shows that permafrost coastlines in the Kotzebue Sound region are already responding to ongoing climate change. Remote sensing data demonstrates that declines in the extent and timing of sea ice are causing an increasingly dynamic coastal system. Rates of change along the coast are more dynamic now than at any time during the past 64 years, and these geomorphic responses to sea ice decline are non-linear. Furthermore, future coastal change will not necessarily be characterized by higher erosion rates, because accretion rates are simultaneously rising. In general, the research described in this dissertation illustrates that the future response of AC components to ongoing climate change will be complex and nonlinear. These results serve to emphasize the value of using past responses of the AC to better understand its possible future trajectories. They also highlight the importance of taking into account a wide variety of processes operating across a wide range of spatial and temporal scales to refine future projected changes.
    • Sedimentology of thermokarst lakes forming within yedoma on the Northern Seward Peninsula

      Farquharson, Louise M. (2012-05)
      Thermokarst lakes forming in yedoma (organic-rich permafrost containing massive syngenetic Pleistocene ice wedges) play an important role in periglacial landscape evolution. These lakes alter landscape elevation and topography, as well as redistribute upland sediment into lower basins. However, sediment deposition within yedoma thermokarst lakes is not well understood. Sedimentological, biogeochemical and macrofossil analyses enabled identification of five prominent fades in yedoma thermokarst lakes in my study region on the northern Seward Peninsula, Alaska. These include a Yedoma Taberal Silt facies situated below a sub-lacustrine unconformity, three types of basal facies and a Lacustrine Silt facies. A preliminary geomorphological model based on sediment cores from mature yedoma thermokarst lakes illustrates how fades distribution changes through the different stages of lake development. First-generation lakes (those forming in undisturbed upland) and later-generation lakes (those forming in thermokarst-affected lowland) were present on the northern Seward Peninsula. A comparison between these two lake types indicates that the depositional environments of later-generation lakes are much more variable than first-generation lakes. Understanding the depositional history and development of yedoma thermokarst lakes is critical to understanding their role in landscape evolution and the carbon cycle.