Distribution of modern benthic foraminifera of McMurdo Sound, Antarctica - B.L. Ward (PhD).

Abstract:

This thesis presents the results of a study of benthic foraminifera from McMurdo Sound, Antarctica. The sound is 50 km across and more than 900 m deep, and is ice-covered for at least 9 months of the year. However, salinity and temperature of the bottom waters are constant (35%. and −1.8°c). Sea floor sediment is mainly fine sand and mud with a little ice-rafted gravel.

The composition of the assemblages is controlled largely by the calcium carbonate compensation depth (CCD). Calcareous species are abundant and varied (84 calcareous species) in the SWA above 620 m, but are virtually absent from the DWA, which is found in deeper water. The dominance of agglutinated foraminifera in the HA indicates an even shallower CCD (about 230 m) in restricted coastal settings.

Death assemblages have a similar species diversity to corresponding life assemblages and are reasonably respresentative of them, except for the 200 m zone above the offshore CCD, where death assemblages are depleted in calcareous taxa. The diversity of the agglutinated component of each assemblage remains nearly constant in all habitats and at all water depths, even though shallow water samples include a range of calcareous species. Thus competition from calcareous species appears not to be a stress factor for agglutinated species, which are considered to have reached the limit of their evolutionary potential in these waters.

The structure and origin of the Strand Moraines, Antarctica P.J. Currie (BSc Hons).

Abstract:

The Strand Moraines is a stagnant ice-cored moraine. It is a glacial remnant of the last Glaciation (20-5 kyr ago) and is grounded against the Bowers Piedmont Glacier on the west coast of McMurdo Sound, Antarctica.

The surface topography of the Strand Moraines is controlled and related to the structure of the underlying ice. The structure indicates that the Strand Moraines is a homogeneous ice body that has undergone two periods of folding deformation. The mechanism of fold development can be equated with cylindrical folding mechanisms and formed during glacial movement processes.

Oxygen isotope analysis determined that the Strand Moraines ice core is a mixture of alpine glacier ice and seawater derived ice. The seawater is considered to have been incorporated into the original ice body by glacial processes associated with a grounded and thickening ice sheet. The presence of a mirabilite salt bed supports this. Mirabilite is precipitated from freezing seawater.

Englacial and surficial debris present at the Strand Moraines are genetically related. The surficial debris is derived from the englacial page 66 debris by surface ablation. It has a coarser texture because the fine sediments are removed by wind deflation and meltwater winnowing. The debris originated in a subglacial environment and moved to an englacial position by glacial processes.

The debris has a mixed provenance and indicates a continental source for the Strand Moraines.

Evidence from this study suggests that the Strand Moraines was formed 6.8 kyr ago at a time when the grounded ice sheet present in the McMurdo Sound during the last Glaciation was in recession. Ice flow models for the ice sheet have been postulated. It is considered that the ice sheet is as likely to have flowed into the McMurdo Sound from the south in a northward direction as flowed around the northern end of Ross Island and in a southern direction as proposed by earlier authors.