Reconstructing the deglacial thinning history of Byrd Glacier, East Antarctica, using cosmogenic surface exposure dating

<p><strong>Past Antarctic ice sheet behaviour is complex and non-linear, necessitating understanding of interactions on deep timescales, especially considering future melt-induced sea level rise is the greatest uncertainty of our time. Antarctic outlet glaciers play a crucial role within this interconnected system, by modulating ice sheet discharge and global sea level contribution through their response to climate forcing. In our warming world, it is integral to examine the past response of the ice sheets to warming, in order to predict future ice sheet change. Glacier chronologies using deposits in the Transantarctic Mountains provide critical constraints on deglaciation of the paleo-ice sheet in the Ross Sea. Yet, neither the timing nor configuration of the grounded ice sheet at the Last Glacial Maximum (LGM) and subsequent grounding line retreat are fully understood. A glacier chronology exists upstream from the fjord of Byrd Glacier, a prominent fast-flowing outlet of East Antarctica, but fails to capture the entire deglacial history. Here, I present a new deglacial chronology from Mt. Tadpole in the Byrd Glacier fjord using in situ 10Be and 14C surface exposure dating of erratics.</strong></p><p>In the new exposure age record, a 14C-saturated sample unambiguously demonstrates that the ice surface did not overtop the summit of Mt. Tadpole (∼880 m above current ice surface) during the LGM. Below the LGM ice limit, unsaturated 10Be and 14C ages indicate exposure since the Early to Mid Holocene. The data indicate >600 m thinning of the ice surface profile occurred between ∼10–5 ka. The potentially rapid thinning rate (2 σ = 0.14–11.83 m/yr) is consistent with Byrd Glacier’s susceptibility to marine ice sheet instability, given the overdeepened bed topography and reverse bed slope of the Byrd Glacier system. The new chronology aligns with regional deglacial trends across the Ross Embayment, as it suggests debuttressing of the grounded ice sheet accelerated Byrd Glacier ice flow, resulting in thinning rates comparable to modern ice sheet thinning observations. This thesis provides new geochronological constraints that enhance understanding of likely ice sheet retreat mechanisms across the Ross Embayment since the LGM. Importantly, these findings should inform reassessment of current ice sheet model inputs to more accurately simulate past glacier dynamics and thus forecast the future contribution of ice mass loss to global sea level rise.</p><p>The second strand of this thesis draws on a possible connection between the nunatak adjacent to Mt. Tadpole, Mt. Tuatara, and a Māori voyaging narrative about Hui Te Rangiora, a mytho-historical figure who explored the Southern Ocean. Significant gaps in Antarctic research exist due to the exclusion of Indigenous knowledge systems such as mātauranga Māori. Analysis finds the legacy of colonialism underlies the barriers impeding Māori engagement with Antarctic research. This work uses the possible connection between Mt. Tuatara and Hui Te Rangiora to invite acknowledgement of iwi connections to Antarctica and the Southern Ocean as a foundation for collaboration. Disrupting the epistemological constraints of Western scientific frameworks, and centring mātauranga Māori and other Indigenous knowledges, is important for facing climate and glaciology challenges.</p>