Variations in Mid-Pleistocene glacial-interglacial cycles: insights from osmium isotopes (Goss and Rooney, 2023)
The reconstruction of Pleistocene glacial cycles from oxygen isotope records identifies dramatic changes in both global climate and ice sheet size. The Mid-Pleistocene Transition (MPT) is an interval during which ice sheets underwent a major transition from temporally symmetrical 41 thousand-year (kyr) cycles in the Early-Middle Pleistocene to broadly asymmetrical 100-kyr cycles in the Middle-Late Pleistocene. Both the timing of this transition and the proposed triggers responsible for the transition remain contentious. Herein, we use variations in seawater osmium isotope values over an 800 kyr interval to evaluate the impact of changes in the basal substrate beneath the Laurentide Ice Sheet in driving this transition. Our data identify a lithological shift across the Mid-Pleistocene Transition beneath the Laurentide Ice Sheet that resulted in a marked change in chemical weathering flux and composition to the ocean. We also identify a distinctive pulse of glacially weathered material reaching the central North Atlantic, likely during the first Heinrich event in response to the MPT.
Quantifying Geomorphological Response to Climate-Change Induced River Piracy, Yukon, Canada
Understanding landscape response to current climate-driven change is a vital component for assessing the future state of the environment. As sensitive regions around the world undergo variations in streamflow, precipitation, and, air temperature, adjustments are being made. What are these changes, what rate of change is occurring, and most importantly, are these changes permanent? Glacial and fluvial systems are at high risk of these drastic and potentially permanent changes. To assess landscape response, we have analyzed a nearly instantaneous event resulting in river capture due to glacier retreat. In May 2016, river capture occurred in southwest Yukon due to the retreat of Kaskawulsh Glacier in Kluane National Park, Yukon, redirecting flow from Ä’äy Chù to Kaskawulsh River. To evaluate the planform geomorphic response of these two rivers, we quantified changes in channel complexity and alluvial fans pre and post river capture. Through satellite remote sensing, we mapped the braiding intensity of each river approximately biweekly from May – September (2013-2020) and measured the areas of 9 alluvial fans within Ä’äy Chù and 6 in Kaskawulsh River from 2013-2020, and normalized them to 2015 extents. River capture resulted in an increase in discharge to Kaskawulsh River causing braiding intensity to rapidly increase and alluvial fan area to reduce. Discharge rapidly decreased to Ä’äy Chù causing braiding intensity to decrease and marginally affected alluvial fans. This event has allowed us to identify how a sensitive landscape has responded to a climate-driven change and the extent of its effects.
Fluvial response to the formation of proglacial lakes, a 70-year perspective
The second portion of my master's thesis. I have selected nine study sites throughout North America where there has been the formation of a proglacial lake due to glacial retreat. Over the past 50-70 years, as these proglacial lakes are forming, fluvial systems are undergoing major changes in discharge and sediment transport.
How have these proglacial rivers evolved over the past 5-7 decades as glaciers rapidly retreat?
Ground-Penetrating Radar Ice Thickness Survey of Mathis, Llewellyn, and Tulsequah Glaciers on the Juneau Icefield, Alaska and Canada
In this study, we investigated the bed topography and ice thickness of Mathis, Llewellyn, and Tulsequah Glaciers. Mathis is a major tributary to one of Southeast Alaska’s largest and deepest temperate glaciers, Taku Glacier. Taku Glacier recently ceased a long term advance likely due to a decreasing accumulation area ratio, making it an object of concern for a potential future retreat. Measurements of ice thickness and estimated volume, with mass balance and ice flow velocity records collected annually across the Juneau Icefield by the Juneau Icefield Research Program, will provide crucial data for modeling current and future advance or retreat. However, measuring deep temperate valley glacier ice is notoriously difficult due to high attenuation rates and valley wall clutter. We used a 1.5 MHz ground-penetrating-radar (GPR) dipole antenna set with a 2.5 kV Kentech transmitter towed by a snow machine to measure ice thickness over 80km of glacier terrain. Data included a centerline profile of Llewellyn and Mathis Glacier and a 4 km by 4 km grid collected at the triple ice divide between Mathis, Tulsequah, and Llewellyn Glaciers between July 20-28th, 2018. GPR survey revealed smooth valley wall reflections on glacier cross-sections and ice thicknesses over 900 meters depth near the center of the Mathis Glacier. Continued monitoring of the Taku Glacier is crucial to understand how Mathis, Llewellyn, and Tulsequah glaciers will react to further climate change impacts. Our results, in conjunction with other available mass balance and velocity datasets, provide information for the robust modeling of this system.
In collaboration with Marisa Borreggine, Gryphen Goss, Isabelle Henzmann, Cody Barnett, Roberta Miller, Seth Campbell