Subglacial Landform Analysis and Reconstruction of Miocene Paleotopography of Marie Byrd Land Perry Spector 1,2, Christine Siddoway 1, and Paul Morin 2 1 Dept Geology, Colorado College, Colorado Springs, CO 2 Antarctic Geospatial Information Center, University of Minnesota, Minneapolis, MN

ANTscape International group of Antarctic researchers and climate scientists ACE subcommittee on Antarctic Paleotopographic Maps 3 yr mission: Create a series of series of paleotopographic maps from Cretaceous to Present which: Show change in bedrock elevations, landforms, and geotectonic configuration of Antarctica over the past ~100 Ma. Visualizations of past landscapes Provide a geographical base for diverse paleo-environmental data: Cretaceous through Recent climate variations Biological evolution and biodiversity Glacial cycles and growth of continental ice sheets. ANT scape

Time intervals for paleotopographic reconstruction First Priority: 1.~34 Ma Landscape that supported first continental ice sheet when global temperatures dropped from ~8 to ~4°C above present 2.~4 Ma Pliocene warm period when global temperatures were ~3°C warmer 3.~50 Ma Eocene warm peak (as distinct from the PETM at 55 Ma) Warmest part of Greenhouse Earth (10-15°C warmer than present) Will help address the question of formation of ABW in a Greenhouse world

Time intervals for paleotopographic reconstruction Second Priority: 4.14 Ma Mid Miocene climate transition 5.~70 Ma Antarctic margins were established once Gondwana breakup was complete The Late Cretaceous was a time of cool climate 6.~92 Ma Continental separation had occurred on all but the West Antarctic margin Intracontinental extension underway in the WARS Early Cretaceous was a time of warm climate (Miller et al, 2005) ~20 m sea level drop observed in the oceanographic record is attributed to glaciation

34 Ma restoration (Wilson and Luyendyk, GRL, 2009) Image from Studinger and Barrett, 2009, Nature Geoscience Factors accounted for: 1.Loading from growth of ice sheets 2.Subsidence from thermal contraction as a result of prior tectonic extension 3.Erosion and sediment deposition 4.Horizontal tectonic motion since 34 Ma

BEDMAP1_plus

WAIS initiation models / high topog Pollard and DeConto, 2003

MBL Subaerial Volcano Ages High summits and alpine areas absent at 34 Ma onset of continental Glaciation 17 Ma or younger (Mt Petras and Reynolds excepted) LeMasurier and Rocchi, 2005

Glacial Incision Jamieson and Sugden, 2008: -Following mid-Miocene climate transition, Antarctica entered an arid period when extensive areas of the ice sheets became cold-based. Warm-based glacial erosion became focused within preexisting drainages at low elevation, leading to development of deeply incised outlet glacier troughs.

Red line --lithospheric boundary, inferred. Origin: intracontinental transform active in Cretaceous time. Takahe, 3460m Sidley, 4181 m Hampton 13.7 – 8.5 Ma Perkins, 1178m c. 1.4 Ma Siple, 3110 m Petras Ma Berlin, 3478m 2.5 Ma – 0 yr Crary Mtns Siddoway et al., 2005; Siddoway 2008; McFadden et al in revision Miocene Volcanoes and glacier streams

BEDMAP1_plus WARS Mt Takahe Ford Ranges

~21 Ma Reconstruction WARS

BEDMAP1_plus Analyzed cross-sectional profiles of bedrock topography (BEDMAP1_plus) on a 40 km grid

BEDMAP1_plus Analyzed cross-sectional profiles of bedrock topography (BEDMAP1_plus) on a 40 km grid

Assumptions Volcanism - Interpret the majority of eastern MBL subglacial vertical relief to be a result of volcanism Close proximity to subaerial volcanoes Topographically concentric morphology Comparison with findings of numerous subglacial volcanoes from CWA geophysical surveys. Glacial Incision – Certain deep, structurally-controlled troughs have been further deepened by glacial incision Sedimentation - Deep, structural basins have been locations of deposition

Methods, assumptions, and reasoning - Volcanoes

Methods, Assumptions, and Reasoning - Incised glacial valleys

Methods, Assumptions, and Reasoning - Sediment volumes For more in-depth treatment, see Wilson and Luyendyk, GRL, September 2009

Alpine glacier troughs in Executive Committee Range

Flexural Moat around Executive Committee Range

Conclusions ANTscape’s effort to create a series of paleotopographic maps of Antarctica over the past ~100 Ma MBL volcanoes are 17 Ma to present (Petras and Reynolds excepted) and thus were not present to serve as high elevation sites for ice cap nucleation during early history of WAIS. Alpine glacier troughs on 14 Ma and younger volcanoes of Executive Committee Range Wet-based erosive features formed at high elevations after the mid- Miocene climate transition (change to hyper arid climate and onset of cold-based mode of Antarctic glaciation (Jamieson and Sugden, 2008)) is a possible indication of elevated basal thermal conditions in the vicinity of the volcanoes. Volcanic moat on north and south margins of Executive Committee Range Potentially show the need of accounting for volcanic rock in addition to ice in isostatic corrections of WANT

Methods, Assumptions, and Reasoning

BEDMAP1_plus Mt Takahe WARS Ford Ranges

~21 Ma Reconstruction WARS