Ice dynamics and glacial history from remote sensing of the Seno Skyring-Seno Otway-Strait of Magellan region, southernmost Patagonia

Abstract

The glacial geomorphology of southernmost Patagonia records the advance and retreat of the Patagonian ice sheet over a number of glacial cycles. The well-preserved landform assemblages and sediments that have been left behind comprise one of the longest and most complete records of Quaternary glaciations in the world. Despite this, little is known about the pre-Last Glacial Maximum (LGM) ice sheet dynamics in a number of areas, particularly around the Strait of Magellan. This study has mapped in detail the glacial geomorphology of the Seno Skyring-Seno Otway-Strait of Magellan region from a combination of Landsat and ASTER satellite imagery and oblique and aerial photographs for the purposes of reconstructing the ice sheet dynamics.
A wide variety of glacial landforms have been mapped, including glacial lineations, moraine ridges, meltwater channels, outwash plains and palaeo-shorelines. The most distinct features within the study area are highly elongate streamlined glacial lineations on the western side of the Strait of Magellan. A landsystems approach has been employed in order to decipher this group of lineations and three potentially plausible landsystems are evaluated: a palaeo-ice stream, a surging glacier, and an ice-marginal terrestrial landsystem. Based on the characteristic shape, dimensions and abrupt lateral margin of the flow-set, the lateral variation in lineation length and elongation ratios, and the presence of a potentially-deformable bed, these lineations are interpreted as being diagnostic of a terrestrial palaeo-ice stream. It is suggested that the initiation of ice streaming was caused by calving into one of two ice-dammed proglacial lakes. The lakes were located within the former Seno Skyring and Seno Otway ice lobes, which are well-defined by arcuate sequences of moraine ridges. The westernmost of the lakes, proglacial Lake Skyring, is delimited by a series of palaeo-shorelines surrounding the present-day lake Laguna Blanca. The size and orientation of meltwater channels and an outwash plain suggests that proglacial Lake Skyring drained eastwards towards the Strait of Magellan in an abrupt event.
The ice sheet has been reconstructed at 10 time-steps, documenting stages of both advance and retreat. An attempt has been made to place this reconstruction within the framework of the wider glacial chronology of the region. From this, it is suggested that ice stream activity contributed to the rapid deglaciation of this sector of the ice sheet during the penultimate glaciation. Future work should focus on applying fieldwork to help validate the interpretations of this study. This should include dating of the landforms and sediments that have been mapped in order to improve the pre-LGM glacial chronology of this region, which is currently poorly-constrained.