The Antarctic Ice Sheets responded significantly to climatic conditions during the Last Glacial Maximum (LGM) and the subsequent warming that followed. Therefore, an understanding of how Antarctica reacted to past climates is necessary to predict the response of its ice sheets to current and future climate change. This thesis presents new evidence about the timing and magnitude of East and West Antarctic ice sheet (EAIS & WAIS) changes during the Quaternary Period, from the Darwin Hatherton glacial system (DHGS, 79.5S, 158E). The DHGS drains the EAIS through the Transantarctic Mountains into the Ross Ice Shelf and glacial deposits have been used to constrain ice sheet thicknesses in this sector of the Ross Sea Embayment. At four sites along the length of the system, glacial deposits were mapped and 73 erratic and bedrock samples collected for ¹⁰Be and ²⁶Al surface exposure dating (SED). The exposure ages range from 0.01 to 2.2 Ma and generally show a trend of oldest ages at the highest elevations, thus suggesting an overall decrease of ice volume within the DHGS over the Quaternary. The older ages suggest that during the Plio-Pleistocene, DHGS ice was at least 800-1000 metres thicker than present, while in the mid to late-Holocene thickening was less than 50-80 metres. Four glacial advance and retreat events were described and mapped previously from the DHGS by Bockheim et al (1989). The Isca and Danum drifts, are ~1-2 and 0.6 Ma respectively. The Britannia-II Drift, previously assumed to mark the maximum extent of the Last Glacial Maximum advance is more complex, with clusters of ages at ~6.5, ~36 and ~125 ka. The youngest drift, the Hatherton is mid to late-Holocene (<4.5 ka) and suggests that the DHGS has been near its equilibrium position during this period. Throughout the DHGS no unequivocal evidence of the LGM was observed and therefore poses questions about the past thickness of the Antarctic ice sheets during the LGM. Exposure ages from sites near the head of the Hatherton Glacier (Dubris Valley & Lake Wellman) suggest that at the LGM, the East Antarctic Ice Sheet may have been of similar size, or slightly smaller, than present. In stark contrast, at the confluence of the Darwin Glacier and the Ross Ice Shelf, a WAIS ~400-900 metres above the modern ice surface is tentatively suggested; A value in agreement with that proposed by modern glaciological models. Additionally, while the results from the Dubris and Bibra valleys show that the EAIS thins during glacial climates (i.e. the LGM), it also suggests thickening during interglacials. The Britannia-I and II drifts representing retreats at~6.5 and ~125 ka from glacial highstands. A number of key findings related to the application of SED in Antarctic settings are also presented. The use of dual-nuclides (¹⁰Be & ²⁶Al) show that within the DHGS, the proportion of samples displaying a prior burial history increases with distance from the catchment. The spread of exposure ages observed in the dataset also show the complexity of the depositional processes occurring at cold-based glacial margins and therefore judicious sample selection is required to obtain exposure ages that are representative of the true deglaciation age.

Research Doctorate - Doctor of Philosophy (PhD) / The northern Central Highlands region of Tasmania extending north from Cradle Mountain to the Middlesex Plains shows evidence of three glacial stages, with the final stage consisting of several ice advance phases. From oldest to youngest these have been named the Middlesex Glaciation, the Sunshine Glaciation and the Cradle Glaciation. Cosmogenic exposure-age dating of boulders and ice-abraded bedrock, radiocarbon dating of post-glacial organic deposits, and relative dating techniques have resulted in assignment of the following ages for the events: Middlesex Glaciation, MIS 10; Sunshine Glaciation, MIS 6 and the Cradle Glaciation having MIS 3 and MIS 2 phases. The Cradle Glaciation correlates with the global Last Glaciation. Exposure-age dating of three of the Cradle Glaciation ice advance phases indicates that the Pencil Pine Phase predates 38.9±4.0 ka, the Dove Phase occurred ca. 29.2±1.4 ka, and the Cradle Valley Phase occurred between >19.7±1.1 – 17.6±1.0 ka. At least two undated retreat/readvance phases followed the Cradle Valley Phase. Deglaciation of the area was probably complete considerably before 11.2 ka. The recognised glacial events decreased in areal extent in each successive advance. Using the 0°C summer mean isotherm as the base for the altitude of the equilibrium line altitude, the regional snowline, regional snowline depression and temperature depression for each of the events were: Middlesex Glaciation, 942 m/1616 m/10.5°C; Sunshine Glaciation, 984 m/1574 m/10.23°C; Pencil Pine Phase, 1010 m/1548 m/10.06°C; Dove Phase, 1050 m/1508 m/9.8°C; and the Cradle Valley Phase, 1060 m/1498 m/9.74°C. The geomorphic evidence and dating of several phases of the Cradle Glaciation indicates a complex history of ice advances for Tasmania during the Last Glaciation.

Dissertation (PhD)--University of Arizona, Tucson, Arizona, 2005.

The change of topography with time and the consequent structure of Earth's surface is dependent on the production and transport of weathered bedrock. I use measurements of in-situ cosmogenic 10Be to investigate erosion rates and exposure ages of boulders, streams, and hillslope sediments in central Pennsylvania, a landscape shaped by glacial/interglacial climate cycles and changes in base level. I measure rates of landscape change at three separate sites, Hickory Run boulder field, Young Womans Creek watershed, and Garner Run, a small upland catchment bounded by two ridgelines. Hickory Run Boulder field is the largest of its kind in the eastern United States. This enigmatic, 1-km-long field of boulders has been attributed to frost-induced processes during the last glacial maximum, when the Laurentide ice sheet margin was nearby. My isotopic data demonstrate that Hickory Run, and likely many other similar boulder fields in eastern North America are ancient, multigenerational features that have persisted over many glacial-interglacial cycles. These findings add nuance to the conventional view of periglaciation as a force that "wiped the slate clean" in the Appalachian Mountains -- in upland areas with resistant lithologies, I show that the landscape was reworked, but not reset by repeated periglaciation. Young Womans Creek is a 230 km2 drainage basin in the headwaters of the Appalachian Plateau physiographic province, where I investigate the role of non-equilibrium topography on the rates of erosion at a basin scale. Here, I use in-situ 10Be to understand the influence of fluvial incision into the landscape, contrasting erosion rates in undissected uplands with those in incised valleys. Erosion rates are positively correlated with slope, but correlate negatively with normalized channel steepness, ksn, and downstream distance. My results demonstrate the effects of lithology and base level on erosion rate are difficult to disentangle, and that when studied on a small scale, lithology exerts the strongest control over the spatial variability of erosion in a transient landscape. Resistant sandstone ridgelines such as those at Garner Run are common features in the Ridge and Valley province of central Pennsylvania. At this site, I strive to understand the influence of periglacial activity on the generation and movement of sediment downslope. My measurements demonstrate that sediment in small upland catchments such as Garner Run can have cosmogenic nuclide concentrations equal to and exceeding 100,000 years of surface exposure history. Despite perturbations by multiple glacial/interglacial cycles throughout the Pleistocene these sandstone-underlain environments are not young, and the exposure of surficial materials predates the last major advance of the Laurentide Ice Sheet at ˜26,000 years ago.

Thesis advisor: Jeremy D. Shakun / Glaciers in the tropics have retreated over recent decades, but whether the magnitude of this retreat has exceeded the bounds of past Holocene fluctuations is unclear. In this study, we measure cosmogenic 10Be and 14C concentrations from recently exposed bedrock at the margin of five glaciers in the tropical Andes, including four small glaciers and the Quelccaya Ice Cap, the world’s largest tropical ice mass. Concentrations at the Quelccaya Ice Cap margin suggest there was extended exposure during the first half of the Holocene, but that the site was covered by ice for the last 5 kyr. In contrast, nuclide concentrations are strikingly low in all samples at the margins of the four small glaciers, equivalent to ~200 years of 14C and 50 years of 10Be accumulation at surface production rates. These data suggest that the small tropical glaciers are now smaller than they have been at any point during the Holocene, whereas the Quelccaya Ice Cap has not yet retreated to its smallest extent of the Holocene, likely due to its larger size and slower response time. / Thesis (MS) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

No description available.

<p>  </p> <p>Reconstructing past glacier and ice-sheet extents is important to better understand how glacial systems have responded to past climate changes in hope of constraining predictions of their responses to ongoing anthropogenic climate warming. As such, the most recent period of climatic variations, from the Last Glacial Maximum (LGM, ca. 21 ka) through today, is of great interest as a prominent example of how ice has reacted to past climatic warming events. Surface exposure dating utilizing cosmogenic nuclides can directly constrain when past ice deglaciated in current and former glacial landscapes. Numerous studies have utilized long-lived cosmogenic radionuclides (i.e., 10Be, 26Al) in polar regions to reconstruct glacial systems. However, due to prevalent non-erosive cold-based ice, prior nuclides from pre-LGM can be preserved. </p> <p>The research described in this dissertation applies <em>in situ </em>cosmogenic 14C (<em>in situ</em> 14C), an emerging geochronometer, to polar glacial landscapes in Sweden and Antarctica to constrain the timing and rate of glacial ice retreat. <em>In situ </em>14C more closely reflects the post-LGM deglacial signal in polar regions because it is less likely to preserve prior nuclides (inheritance) under minimally erosive ice. Our cosmogenic 10Be–26Al–14C concentrations near the Riukojietna ice cap, the last remaining ice cap in Sweden, combined with a sedimentary record from a proximal proglacial lake, indicate the ice cap likely survived during a warm period in the Holocene, but was less extensive than today. The <em>in situ</em> 14C exposure data from nunataks in western Dronning Maud Land (DML), East Antarctica indicate significant coastal thickening (up to 850 m) not predicted by models to date. In addition, this work dates the timing of post-LGM ice surface lowering in two drainage basins in western DML. These results demonstrate the significant contribution of <em>in situ</em> 14C in polar regions.</p> <p>In addition to applications of <em>in situ</em> 14C in polar regions, this work also describes the development of a compositionally dependent <em>in situ</em> 14C production rate calculator. The ability to extract <em>in situ</em> 14C from samples which quartz cannot be separated (either quartz-poor or fine-grained) would allow new avenues of research. The computational framework will be a useful tool in efforts to broaden the utility of <em>in situ</em> 14C to quartz-poor and fine-grained rock types. </p>

Soil erosion undermines agricultural productivity, limiting the lifespan of civilizations. For agriculture to be sustainable, soil erosion rates must be low enough to maintain fertile soil, as was present in many agricultural landscapes prior to the initiation of farming. However, there have been few measurements of long-term pre-agricultural erosion rates in major agricultural landscapes. We quantified geological erosion rates in the Midwestern U.S., one of the world’s most productive agricultural areas. We sampled soil profiles from 14 native prairies and measured concentrations of the cosmogenic nuclide 10Be and chemically immobile elements to calculate physical erosion rates. We used the erosion rates and measurements of topographic curvature to estimate a pre- agricultural topographic diffusion coefficient. We find pre-agricultural erosion rates of 0.0001–0.1 mm yr-1 and a site-averaged diffusion coefficient of 0.005 m2 yr-1. The pre- agricultural erosion rates and diffusion coefficient we measured are both orders of magnitude lower than anthropogenic values previously measured in adjacent agricultural fields. The pre-agricultural erosion rates are one to four orders of magnitude lower than the 1 mm yr-1 soil loss tolerance value assigned to these locations by the U.S. Department of Agriculture. Hence, as currently defined, tolerable soil loss will lead to unsustainable erosion of Midwestern soils. However, quantifying natural erosion rates via cosmogenic nuclides provides a means for more robustly defining rates of tolerable soil loss and developing management guidelines that promote soil sustainability.

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No description available.