Antiphase dynamics between cold-based glaciers in the Dry Valleys region and ice extent in the Ross Sea, Antarctica during MIS 5

Mr Jacob Anderson1, Dr David Fink2, Dr Toshi Fujioka3, Professor Gary Wilson4, Dr Klaus Wilcken2, Dr Andrey Abramov5, Dr Nikita Demidov6

1University Of Otago, Dunedin, New Zealand, 2Australian Nuclear Science & Technology Organisation, Lucas Heights, Australia, 3Centro Nacional de Investigación sobre la Evolución Humana, Burgos, Spain, 4University of Otago & GNS Science, Wellington, New Zealand, 5Institute of Physicochemical and Biological Problems of Soil Science, Pushchino, Russia, 6Arctic and Antarctic Research Institute, St. Petersburg, Russia

During interglacial conditions in Marine Isotope Stage (MIS) 5, outlet and alpine glaciers in the Dry Valleys region, Antarctica, appear to have advanced in response to increased open ocean in the Ross Sea. However, the timing and extent of antiphase behaviour between these glaciers and ice in the Ross Sea is poorly resolved. Here, we report the antiphase behaviour through retreat of a peripheral lobe of Taylor Glacier in Pearse Valley, an area that was glaciated during MIS 5. First, we measured cosmogenic ¹⁰Be and ²⁶Al in 3 granite cobbles from thin, patchy drift (Taylor 2 Drift) in Pearse Valley to constrain the timing of retreat of Taylor Glacier. Assuming simple continuous exposure, our exposure ages suggest Taylor Glacier had partially retreated from Pearse Valley no later than 71 ka. Timing of retreat after 71 ka, until the Last Glacial Maximum (LGM), when Taylor Glacier was at a minimum position, remains unresolved. Second, we measured paired ¹⁰Be and ²⁶Al depth profiles to ~3 metres in permafrost in proximity to the cobble sampling sites at Pearse Valley and neighbouring Lower Wright Valley. The ¹⁰Be and ²⁶Al depth profiles from both sites show no clear exponential attenuation trend which suggest that both deposits are too young for the most recent exposure (≥71 ka for Pearse Valley and LGM – early Holocene for Lower Wright Valley) to alter the profile, and measured nuclide concentrations are essentially dominated by inheritance. Using ¹⁰Be depth profile data from Pearse Valley we calculate a maximum age of ~100 ka for surface layer permafrost formation. The cobble exposure-ages and depth profile constrain surface permafrost formation in Pearse Valley to between ~71 – 102 ka, following the retreat of the Taylor Glacier from Pearse Valley. These new data are consistent with geochronology from central Taylor Valley, and suggest changes in moisture delivery over Taylor Dome during MIS 5c and 5a appear to be associated with the extent of the Ross Ice Shelf and sea ice in the Ross Sea. Our ²⁶Al/¹⁰Be concentration ratios for all depth profile samples also exhibit relatively constant and suppressed ratios of 4.3 and 5.2 for Pearse and Wright valleys, respectively, indicating that prior to surface permafrost formation, these sediments experienced a significant complex prior exposure history. Assuming a simple burial scenario, the observed ²⁶Al/¹⁰Be ratios are equivalent to a total exposure-burial history of ~1.2 Ma, somewhat consistent with the Packard dune field in Victoria Valley. Our new data corroborate antiphase behaviour between outlet and alpine glaciers in the Dry Valleys region and ice extent in the Ross Sea, and imply a causal mechanism with cold-based glacier advance and retreat being controlled by moisture availability and drying, respectively due to ice retreat and expansion in the Ross Sea.


Biography:

Jacob is a PhD student in the Department of Marine Science at the University of Otago. Using cosmogenic-nuclide depth profiles and surface exposure dating his research focuses on reconstructing past changes of the Antarctic ice sheet and understanding geomorphic processes.

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Date

Nov 16 2021

Time

TUESDAY
9:45 am - 10:40 am