Where tectonics meets ice-sheet dynamics: roots of West Antarctica’s next ice-sheet collapse

• Main Author: Gohl, Karsten
• Format: Conference Object
• Language: unknown
• Published: 2018
• Subjects: Antarctic; Ross Sea; West Antarctica; Amundsen Sea; West Antarctic Ice Sheet; Bellingshausen Sea; New Zealand; Byrd; Marie Byrd Land; Antarc*; Antarctica; Ice Sheet; Ice Shelves
• Online Access: https://epic.awi.de/id/eprint/47721/; https://hdl.handle.net/10013/epic.a70076ad-7e5e-49b9-af1a-d1c379ea6b45

West Antarctica is one of the most fascinating and challenging regions for studying the relationship and interplay of geodynamic, tectonic, and sedimentation processes as well as past and present ice-sheet dynamics. Its mostly rift-related tectonic evolution, driven by yet largely enigmatic mantle-dynamic processes, led to a topographic and morphological setting for a dominantly submarine-based ice sheet that is highly sensitive to climate change and ocean warming. Originally an assemblage of various Palaeozoic and Mesozoic crustal blocks and mobile belts, West Antarctica’s transformation into the worldwide second largest continental rift system began when subduction at the East Gondwana margin partially stalled and the New Zealand micro-continent separated from Antarctica in the mid-Cretaceous. Crustal extension continued in West Antarctica in various phases creating major rift basins of thin crust, but partial uplift also occurred with the Marie Byrd Land dome event by an intercepting mantle plume. Cretaceous rifting and continental breakup as well as later stages of West Antarctic Rift System activities formed the basement architecture of the major embayments of the Ross Sea, Amundsen Sea and Bellingshausen Sea, which have acted as prominent outlet regions for the West Antarctic Ice Sheet. The onset of early ice caps and glaciers likely occurred in highly elevated ranges already in the early Cenozoic, but seismic and sediment core records indicate that first glaciers and ice-streams reached the costs and inner shelves not before the Oligocene. A palaeotopographic model of Antarctica, derived from a study on offshore/onshore sedimentary erosion-transport-deposition mass balance, indicates that an early continuous West Antarctic Ice Sheet may have formed on a land-surface higher than today and above sea level in the early Oligocene. Seismic and sediment records from the continental shelves and rises of the West Antarctic margin demonstrate that most of the terrigenous sedimentary volume deposited has been glacially transported with a minor fraction in a transitional phase between the Oligocene and early Miocene, and the majority in a full glacial phase since the mid-Miocene. Massive glacially driven prograding sequences are responsible for the build-up of shelf extensions towards the deep ocean. Sediment drifts characterize the continental rise and indicate that strong ocean-bottom currents have been active already since the Oligocene. Warm circum-polar deep water, that follows a path along the deeply incised glacial troughs on the shelf, has been identified as the prominent mechanism for melt processes at the glacier’s grounding zones and beneath ice-shelves. This seems to be a process in particular characteristically for the Amundsen Sea Embayment where grounded ice retreated relatively fast from is maximum extent on the outer shelf during the last glacial maximum at about 20 thousand years ago to the innermost shelf until the early Holocene. The remarkable present rapid retreat of glaciers in the Amundsen Sea sector, which may lead to a future collapse of the West Antarctic Ice Sheet, is a consequence of recurring warm bottom-water incursions exploiting incised pathways formed mainly by tectonic processes.