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Victoria University Antarctic Research Expedition Science and Logistics Reports 1978-79: VUWAE 23

Discussion

Discussion

The age of young marine sediments in the shallow parts of the Ross Sea is as yet difficult to determine paleontologically. Of the seventeen Brunhes and Gauss age diagnostic taxa described by Fillon (1972) twelve are restricted to depths greater than 450 metres. The remaining five taxa occur at shallower depths. Two of these, page 13 Globocassidulina crassa rossensis Kennett and Cassidulina porrechis Heron-Allen & Earland, are found at New Harbour and Butter Point respectively. Both species indicate a Brunhes age (Fillon 1972, 1974). The presence at Butter Point of the diatom taxon Eucampia balustrum McCollum found in Gilbert to Brunhes sediments, but more commonly restricted to the Brunhes, also supports a Brunhes age for the Butter Point assemblage. Radiolarian species found have extended age ranges and precise age determinations cannot be made. Present day (Recent) Ross Sea taxa are typically endemic and similar to Gauss assemblages (Fillon 1973).

The difference in foraminiferal test composition between the New Harbour and Butter Point Sites, dominantly arenaceous and dominally calcareous species respectively has been described in other regions of McMurdo Sound and the Ross Sea (McKnight, 1962; Kennett, 1966; Fillon, 1972, 1974). Kennett (1966) suggested that a calcium carbonate solution boundary (CCD) occurred at 500-550 metres, separating arenaceous faunas below from calcareous faunas above. Fillon (1972) described 'relic Gauss' and Brunhes sediments which contain dominantly calcareous and arenaceous taxa respectively. He explained the latter as due to an increased undersaturation of calcium carbonate associated with a late Gauss - early Matuyama expansion of the Ross Ice Shelf.(Fillon, 1974. The four samples studied are well above the present day CCD.

Butter Point foraminiferal assemblages lack both the characteristic Brunhes taxon Globocassidulina crassa rossensis Kennett and its Gauss ancestor G. biora (Crespin). A possible intermediate form, Globocassidulina sp., which has a typical G. crassa rossensis shape but lacking the distinctive L-shaped aperture, is common.

High salinities, low temperature and possibly low photosynthetic activity related to the presence of semi-permanent sea ice cover may explain a calcium carbonate depletion of waters at New Harbour, though none of these parameters have been measured yet at the New Harbour Site. Arenaceous taxa may be better adapted than calcareous taxa to oligotrophic areas such as New Harbour where there is no current activity.

Neogloboquadina pachyderma (Ehrenberg) is absent from New Harbour, although photosynthetic planktonic diatoms are common. This suggests that photosynthetic activity is present at New Harbour, but not high enough to support higher trophic groups.

we thank Dr M.A. Harper for identifying the diatoms and Mr S.H. Eager for the ostracods. Mr P.H. Robinson reviewed the manuscript.