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1. Continuous Simulations over the Last 34 Million Years with a Coupled Antarctic Ice Sheet and Sediment Model

   Pollard, D. (December 2018, AGU Fall Meeting)

   Much of the knowledge of Antarctic Ice Sheet variations since its inception ~34 Ma derives from marine sediments on the continental shelf, deposited in glacimarine or sub-ice environments by advancing and retreating grounded ice, and observed today by seismic profiling and coring. If coupled ice-sheet and sediment models can simulate these deposits explicitly, direct comparisons with the sediment record would be valuable in linking it to Cenozoic ice and climate history. Here we apply an existing 3-D ice sheet and sediment model to the whole period of late Cenozoic Antarctic evolution. The ice-sheet model uses local parameterizations of grounding-line flux, ice-shelf hydrofracture and ice cliff failure. The sediment model includes quarrying of bedrock, sub-ice transport, and marine deposition. Atmospheric and oceanic forcing is determined by uniform shifts to modern climatology in proportion to records of atmospheric CO2, deep-sea-core d18O, and orbital insolation variations. Initial ice-free and sediment-free bedrock topography is prescribed from the 34 Ma reconstruction of Wilson et al., Palaeo3, 2011, and their estimated rate of tectonic subsidence is applied in West Antarctica. The model is run continuously from 34 Ma to the present, to capture the entire post-Eocene Antarctic landscape evolution and off-shore sediment packages in a single self-consistent simulation. In order to make these long simulations feasible, the model resolution is very coarse, 80 km. However the ice model's use of local parameterizations for fine-scale dynamical processes yields results that are not seriously degraded compared to finer resolutions in short tests. The primary goals are (1) to reproduce major recognized ice-sheet trends and fluctuations from the Eocene to today, and (2) to produce a 3-D model map of modern sediment deposits. "Strata" are tracked by recording times of deposition within the model sediment stacks. Unconformities in these strata occur in the model that can be compared with observed profiles. Initial results are presented, and preliminary overall comparisons are made with observed sediment packages, focusing on sensitivities to climate forcing, quarrying rates, and sediment parameters that stand in for alternate sediment rheologies. 

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2. Continuous simulations over the last 40 million years with a coupled Antarctic ice sheet-sediment model

   https://doi.org/10.1016/j.palaeo.2019.109374  

   Pollard, D.; DeConto, R. (January 2020, Palaeogeography palaeoclimatology palaeoecology)

   null (Ed.)

   Much of the knowledge of Antarctic Ice Sheet variations since its inception ~34 Ma derives from marine sediments on the continental shelf, deposited in glacimarine or sub-ice environments by advancing and retreating grounded ice, and observed today by seismic profiling and coring. Here we apply a 3-D coupled ice sheet and sediment model from 40 Ma to the present, with the goal of directly linking ice-sheet variations with the sediment record. The ice-sheet model uses vertically averaged ice dynamics and parameterized grounding-line flux. The sediment model includes quarrying of bedrock, sub-ice transport, and marine deposition. Atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric CO2, deep-sea-core δ18O, and orbital insolation variations. The model is run continuously over the last 40 Myr at coarse resolution (80 or 160 km), modeling post-Eocene ice, landscape evolution and off-shore sediment packages in a single self-consistent simulation. Strata and unconformities are tracked by recording times of deposition within the model sediment stacks, which can be compared directly with observed seismic profiles. The initial bedrock topography is initialized to 34 Ma geologic reconstructions, or an iterative procedure is used that yields independent estimates of paleo bedrock topography. Preliminary results are compared with recognized Cenozoic ice-sheet variations, modern sediment distributions and seismic profiles, and modern and paleo bedrock topographies. 

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3. Miocene ice sheet dynamics and sediment deposition in the central Ross Sea, Antarctica

   https://doi.org/10.1130/B37613.1  

   McKay, Robert; Cockrell, Jay; Shevenell, Amelia E; Laberg, Jan Sverre; Burns, Julianne; Patterson, Molly; Kim, Sunghan; Naish, Tim; Harwood, David; Levy, Richard; et al (October 2024, Geological Society of America Bulletin)

   Abstract Drill cores from the Antarctic continental shelf are essential for directly constraining changes in past Antarctic Ice Sheet extent. Here, we provide a sedimentary facies analysis of drill cores from International Ocean Discovery Program (IODP) Site U1521 in the Ross Sea, which reveals a unique, detailed snapshot of Antarctic Ice Sheet evolution between ca. 18 Ma and 13 Ma. We identify distinct depositional packages, each of which contains facies successions that are reflective of past baseline shifts in the presence or absence of marine-terminating ice sheets on the outermost Ross Sea continental shelf. The oldest depositional package (>18 Ma) contains massive diamictites stacked through aggradation and deposited in a deep, actively subsiding basin that restricted marine ice sheet expansion on the outer continental shelf. A slowdown in tectonic subsidence after 17.8 Ma led to the deposition of progradational massive diamictites with thin mudstone beds/laminae, as several large marine-based ice sheet advances expanded onto the mid- to outer continental shelf between 17.8 Ma and 17.4 Ma. Between 17.2 Ma and 15.95 Ma, packages of interbedded diamictite and diatom-rich mudstone were deposited during a phase of highly variable Antarctic Ice Sheet extent and volume. This included periods of Antarctic Ice Sheet advance near the outer shelf during the early Miocene Climate Optimum (MCO)—despite this being a well-known period of peak global warmth between ca. 17.0 Ma and 14.6 Ma. Conversely, there were periods of peak warmth within the MCO during which diatom-rich mudstones with little to no ice-rafted debris were deposited, which indicates that the Antarctic Ice Sheet was greatly reduced in extent and had retreated to a smaller terrestrial-terminating ice sheet, most notably between 16.3 Ma and 15.95 Ma. Post-14.2 Ma, diamictites and diatomites contain unambiguous evidence of subglacial shearing in the core and provide the first direct, well-dated evidence of highly erosive marine ice sheets on the outermost continental shelf during the onset of the Middle Miocene Climate Transition (MMCT; 14.2–13.6 Ma). Although global climate forcings and feedbacks influenced Antarctic Ice Sheet advances and retreats during the MCO and MMCT, we propose that this response was nonlinear and heavily influenced by regional feedbacks related to the shoaling of the continental shelf due to reduced subsidence, sediment infilling, and local sea-level changes that directly influenced oceanic influences on melting at the Antarctic Ice Sheet margin. Although intervals of diatom-rich muds and diatomite indicating open-marine interglacial conditions still occurred during (and following) the MMCT, repeated advances of marine-based ice sheets since that time have resulted in widespread erosion and overdeepening in the inner Ross Sea, which has greatly enhanced sensitivity to marine ice sheet instability since 14.2 Ma. 

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4. Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

   https://doi.org/10.1130/B35814.1  

   Pérez, Lara F.; Santis, Laura De; McKay, Robert M.; Larter, Robert D.; Ash, Jeanine; Bart, Phil J.; Böhm, Gualtiero; Brancatelli, Giuseppe; Browne, Imogen; Colleoni, Florence; et al (May 2021, GSA Bulletin)

   Abstract Oscillations in ice sheet extent during early and middle Miocene are intermittently preserved in the sedimentary record from the Antarctic continental shelf, with widespread erosion occurring during major ice sheet advances, and open marine deposition during times of ice sheet retreat. Data from seismic reflection surveys and drill sites from Deep Sea Drilling Project Leg 28 and International Ocean Discovery Program Expedition 374, located across the present-day middle continental shelf of the central Ross Sea (Antarctica), indicate the presence of expanded early to middle Miocene sedimentary sections. These include the Miocene climate optimum (MCO ca. 17–14.6 Ma) and the middle Miocene climate transition (MMCT ca. 14.6–13.9 Ma). Here, we correlate drill core records, wireline logs and reflection seismic data to elucidate the depositional architecture of the continental shelf and reconstruct the evolution and variability of dynamic ice sheets in the Ross Sea during the Miocene. Drill-site data are used to constrain seismic isopach maps that document the evolution of different ice sheets and ice caps which influenced sedimentary processes in the Ross Sea through the early to middle Miocene. In the early Miocene, periods of localized advance of the ice margin are revealed by the formation of thick sediment wedges prograding into the basins. At this time, morainal bank complexes are distinguished along the basin margins suggesting sediment supply derived from marine-terminating glaciers. During the MCO, biosiliceous-bearing sediments are regionally mapped within the depocenters of the major sedimentary basin across the Ross Sea, indicative of widespread open marine deposition with reduced glacimarine influence. At the MMCT, a distinct erosive surface is interpreted as representing large-scale marine-based ice sheet advance over most of the Ross Sea paleo-continental shelf. The regional mapping of the seismic stratigraphic architecture and its correlation to drilling data indicate a regional transition through the Miocene from growth of ice caps and inland ice sheets with marine-terminating margins, to widespread marine-based ice sheets extending across the outer continental shelf in the Ross Sea. 

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5. Investigating tectonic uplift and glacial incision in West Antarctica using detrital thermochronology and thermo-kinematic modeling

   Taylor, J; Siddoway, CS; Thomson, SN; Teyssier, C (December 2025, American Geophysical Union)

   Cenozoic exhumation in Marie Byrd Land (MBL), West Antarctica, has been dominated by uplift of the MBL dome, an ~800 by ~300 km topographic swell thought to be supported by a hot mantle anomaly, and West Antarctic ice sheet (WAIS) development resulting in deeply incised glacial troughs with up to 3 km of local relief. WAIS expansion is thought to potentially coincide with uplift of the MBL dome, which would have provided the elevated topography necessary to nucleate and grow a continental ice sheet beginning sometime between 34 – 20 Ma. Temporal and spatial relationships between these events remain unclear, however. This study investigates the timing, magnitude, and spatial relationships between tectonic uplift and glacial incision in MBL by leveraging thermo-kinematic modeling informed by detrital low-temperature thermochronology. We investigated Neogene detrital seafloor sediment samples from 14 dredge and core sites along the coast of MBL. Apatite He ages (closure temp ~60°C) of detrital samples range from 23.5 to >80 Ma. Most detrital ages are significantly younger than the ~80 Ma ages typical of exposed bedrock across the region, suggesting these originate from deeply incised bedrock of glacial troughs. The youngest ages obtained for samples retrieved from offshore central and eastern MBL are also significantly younger than the youngest ages obtained for samples from western MBL, suggesting spatial heterogeneity in the timing and/or magnitude of exhumation across the region. Thermo-kinematic modeling of western MBL suggests the regional exhumation rate has been low (10-3 km/myr) since 80 Ma, although focused erosion in glacial troughs produced local late Cenozoic exhumation rates as high as 0.15 km/myr. Preliminary models of the DeVicq glacial trough region of central MBL support these patterns of exhumation. Although model predictions generally agree with observed detrital age distributions, incorporation of detrital ages into these models is expected to provide new insight into the timing of WAIS inception, as well as rates and magnitudes of glacial incision across MBL. 

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