Showing papers by "Arjen P. Stroeven published in 1996"

On marine microfossil transport and pathways in Antarctica during the late Neogene: Evidence from the Sirius Group at Mount Fleming

Abstract: There are two extreme views of the evolution of the Pliocene Antarctic Ice Sheet. Dynamicists argue for ice-sheet reduction and reexpansion on the basis of Pliocene marine diatoms in a glacial deposit, the Sirius Group, that is widespread in the Transantarctic Mountains. Stabilists argue from other evidence that the Antarctic cryosphere remained essentially constant in area and volume; they propose marine diatom transport by eolian processes and emplacement into terrestrial glacial strata. Hence, the inferred source area and transport mechanism of marine diatoms are of critical importance. We tested the reduction hypothesis on an important outcrop of the Sirius Group at Mount Fleming, South Victoria Land. We observed very few, unidentifiable, marine diatom fragments in Sirius Group strata. In contrast, marine diatoms enclosed in a surface diamicton covering the Sirius Group were more abundant and identifiable. Our study further indicates that the Sirius Group at Mount Fleming was not deposited by the East Antarctic Ice Sheet but rather by alpine ice originating on the Transantarctic Mountains. On the basis of both data sets, we infer that marine diatoms postdate Sirius Group deposition at Mount Fleming and that transport was by wind, and we advance alternative scenarios for their source and transport pathways.

The Robustness of One-Dimensional, Time-Dependent, Ice-Flow Models: A Case Study from Storglaciären, Northern Sweden

Abstract: The robustness of a simple flow-line model has been tested against new data from Storglaciaren. The model appears robust for given subglacial geometry. A realistic longitudinal profile and acceptab...

Field Evidence for Wet-based Ice Sheet Erosion from the South-central Queen Elizabeth Islands, Northwest Territories, Canada

Abstract: Glacial erosional features were studied in detail at three locations in the southcentral Queen Elizabeth Islands, Canada. Numerous striated bedrock outcrops, indicating ice flowing from the sea onto the coast, were discovered on BaillieHamilton Island, off the west coast of northern Devon Island. The consistency of obtained ice-flow directions indicates that thick, wet-based ice overrode the >200m-high island from northwest, west-northwest, and northeast, without topographic deflection. We conclude that this ice also flowed across the >300 m deep Queens and Wellington channels bordering Baillie-Hamilton Island. A similar conclusion was derived from striated bedrock outcrops on the northeast coast of North Kent Island, positioned between Devon and Ellesmere islands. Ice flowing from the northwest obliquely across Baillie-Hamilton and North Kent Islands, and from the northeast across Baillie-Hamilton Island, could not have emanated from local ice domes. Instead, these results are consistent with a large ice sheet covering the central and southern Queen Elizabeth Islands with an ice spreading center in the Norwegian Bay region. The timing of these events remains uncertain, but the degree of weathering of the striated outcrops indicates that both northwest and northeast ice-flow directions could be of late Wisconsinan age.

Deficiencies in the diatom evidence for a Pliocene reduction of the East Antarctic Ice Sheet

Abstract: Evidence for Pliocene reduction of the East Antarctic Ice Sheet (EAIS) has been inferred from the presence of Pliocene planktic marine diatoms in tills of the Sirius Group now exposed along the slopes of the Transantarctic Mountains. We highlight deficiencies in this diatom evidence for a Pliocene reduction of the EAIS. First, we examine what diatom habitats are left behind by a retreating ice sheet, in this case the Fennoscandian Ice Sheet (FIS), and find that diatoms should occur in planktic and benthic marine, brackish water, freshwater, and terrestrial habitats. We expect that during former reexpansions, these diverse diatom assemblages were picked up by the advancing FIS and deposited in tills. This is shown to be the case, and diatoms found in tills from Sweden and Finland reflect the many habitats over which the FIS passed. If there was a reduction of the EAIS during the Pliocene followed by renewed glaciation, diatoms from many different habitats should be found in the resulting tills of the Sirius Group. This is not the case. Only marine planktic diatoms and a few freshwater forms are reported. Similarly, vertical (downsection) distribution of diatoms in Sirius Group and Fennoscandian tills differ. While in the Sirius Group, diatoms appear restricted to surface and near-surface sediments, in Fennoscandia they are found throughout the tills. Such data do not support a Pliocene reduction model for the EAIS.

Late Tertiary glaciations and climate dynamics in Antarctica : evidence from the Sirius Group, Mount Fleming, Dry Valleys

Abstract: Late Tertiary glaciations and climate dynamics in Antarctica : evidence from the Sirius Group, Mount Fleming, Dry Valleys