Submarine glacial landforms and interactions with volcanism around Sub-Antarctic Heard and McDonald Islands

Unravelling the glacial history of Sub-Antarctic islands can provide clues to past climate and Antarctic ice sheet stability. The glacial history of many sub-Antarctic islands is poorly understood, including the Heard and McDonald Islands (HIMI) located on the Kerguelen Plateau in the southern India...

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Bibliographic Details
Main Authors: Watson, S, Fox, JM, Post, A, Whittaker, J, Lucieer, VL, Carey, RJ, Coffin, MF, Hodgson, D, Hogan, K, Graham, AGC, Picard, K
Format: Conference Object
Language:English
Published: . 2017
Subjects:
Earth Sciences
Geology
Marine Geoscience
Antarctic
Heard
Heard Island
Indian
Kerguelen
McDonald Islands
Antarc*
Ice Sheet
Iceberg*
Online Access:https://agu.confex.com/agu/fm17/meetingapp.cgi/Paper/265395
http://ecite.utas.edu.au/124924
Description
Summary:Unravelling the glacial history of Sub-Antarctic islands can provide clues to past climate and Antarctic ice sheet stability. The glacial history of many sub-Antarctic islands is poorly understood, including the Heard and McDonald Islands (HIMI) located on the Kerguelen Plateau in the southern Indian Ocean. The geomorphologic development of HIMI has involved a combination of construction via hotspot volcanism and mechanical erosion caused by waves, weather, and glaciers. Today, the ~2.5 km 2 McDonald Islands are not glacierised; in contrast, the ~368 km 2 Heard Island has 12 major glaciers, some extending from the summit of 2813 m to sea level. Historical accounts from Heard Island suggest that the glaciers were more extensive in the 1850s to 1870s, and have retreated at least 12% (33.89 km 2 ) since 1997. However, surrounding bathymetry suggests a much more extensive previous glaciation of the HIMI region that encompassed ~9,585 km 2 , likely dating back at least to the Last Glacial Maximum (LGM) ca. ~26.5 -19 ka. We present analyses of multibeam bathymetry and backscatter data, acquired aboard RV Investigator in early 2016, that support the previous existence of an extensive icecap. These data reveal widespread ice-marginal and subglacial features including moraines, over-deepened troughs, drumlins and crag-and-tails. Glacial landforms suggest paleo-ice flow directions and a glacial extent that are consistent with previously documented broad scale morphological features. We identify >660 iceberg keel scours in water depths ranging from ~150 - 530 m. The orientations of the iceberg keel scours reflect the predominantly east-flowing Antarctic Circumpolar Current and westerly winds in the region. 40 Ar/ 39 Ar dating of volcanic rocks from submarine volcanoes around McDonald Islands suggests that volcanism and glaciation coincided. The flat-topped morphology of these volcanoes may result from lava-ice interaction or erosion by glaciers post eruption during a time of extensive ice-sheet cover and/or wave base erosion during sea level low stands. The prevalence and range of glacial landforms around HIMI suggest extensive past glaciation, and that glaciers have exerted a major influence on submarine geomorphology.

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