Elena Serra

Paleoglaciological study of the Ahlmannryggen, Borgmassivet and Kirwanveggen nunatak ranges, Dronning Maud Land, East Antarctica, using WorldView imagery

Datum, tid och plats: Måndag den 4/9, kl. 10.30 i Högbomsalen
Handledare: Arjen Stroeven och Robin Blomdin
Examinator: Krister Jansson
Masterprogram i glaciologi och polarmiljöer
Examensarbete i naturgeografi och kvartärgeologi, 30 hp

Presentationen är på engelska

Abstract

Paleoglaciological reconstructions based on glacial geological and geomorphological evidence are used to constrain and test numerical models of ice sheet extent and dynamics. The MAGIC-DML research project (“Mapping, Measuring and Modelling Antarctic Geomorphology and Ice Change, in Dronning Maud Land”) is trying to reconstruct the timing and pattern of ice surface elevation changes since the mid-Pliocene across western Dronning Maud Land, East Antarctica. This reconstruction will work as the basis for testing and constraining ice sheet numerical models to improve climate understanding in Antarctica.

This master thesis project contributes to MAGIC-DML by adopting a high-resolution remote sensing-based mapping of glacial geomorphology and ice sheet surface structures, for a coast-inland transect including the Ahlmannryggen, Borgmassivet, and Kirwanveggen nunatak ranges. The primary aim of this study is to investigate the glaciology and paleoglaciology of the study area, in order to map evidence for a former thicker ice sheet on nunatak slopes and plateaus, and patterns of ice flow of the current ice sheet surface. Meso-scale glacial landforms and ice flow features were identified and mapped using different remote sensing data sets: the LANDSAT Image Mosaic of Antarctica (LIMA), DigitalGlobe Worldview-2 (WV02) and Worldview-3 (WV03) panchromatic and multispectral images, the Radarsat Antarctica Mapping Project (RAMP) Ice Surface Digital Elevation Model (DEM) version 2, and the Bedmap2 datasets. The satellite imagery was analysed in a multi-step procedure using ArcGIS, including image processing and mosaicking, visual feature recognition, and mapping. The identification of some key landforms required the adoption of assumptions, for example in order to distinguish till cover from regolith or boulders derived from rock fall from glacial erratics. Present-day ice flow directions were traced according to the distribution of ice surface features such as blue ice areas, crevasse fields, longitudinal surface structures, and supraglacial moraines. The occurrence of till cover and erratics above the present-day ice surface on some nunataks slopes and plateaus was considered indicative of a thicker ice sheet in the past. Paleo-ice flow directions were inferred from the proximity of locations to the closest ice streams, since that latter have been active since the Oligocene.

Geomorphological and ice flow direction maps were obtained and used to infer the paleoglaciology of the three nunatak ranges. Ice sheet thinning reconstructions reveal a minimum ice surface lowering of ~400–500 m in the Ahlmannryggen and Borgmassivet nunatak ranges, of ~300 m north of the Kirwanveggen escarpment and of ~100 m on the edge of Amundsenisen polar plateau. The paleo-ice sheet flow pattern probably differed from today, because ice flow has locally been influenced by an increased topographical complexity, due to the thinning of the ice sheet and the emerging of nunatak outcrops. According to dating studies conducted elsewhere in DML, the inferred ice surface decrease was probably initiated in the Late Pliocene/Early Pleistocene, and continued after the Last Glacial Maximum interruption across the coastal sector of the ice sheet. The reliability of derived paleo-ice sheet reconstructions, based on the mapping and interpretation of landforms, needs to be verified in future field studies. This master thesis project has identified 34 well-suited locations for the sampling of erratic boulders and bedrock surfaces for cosmogenic nuclide (CN) surface exposure dating during the MAGIC-DML 2017/18 field season. The chronology derived from CN dating and field verification of the presented mapping will permit the delineation of ice sheet surface elevations as targets for ice sheet modelling.

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