Other formats

    Adobe Portable Document Format file (facsimile images)   TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

Victoria University Antarctic Research Expedition Science and Logistics Reports 1981-82: VUWAE 26

McMurdo Sound Sediment Sampling (K5) - A. Pyne/B. Ward

page 9

McMurdo Sound Sediment Sampling (K5) - A. Pyne/B. Ward.

Sphincter cores 20cm in diameter were recovered from 18 sites in depths ranging between 850 and 109m in McMurdo Sound and Granite Harbour (Fig. 6,7). Most cores were only a few centimetres long on account of the hard sandy bottom, and three were just mounds of disturbed sediment, but the remainder appeared quite undisturbed, with worms, sea spiders and sea-anemonies still alive on the sediment surface. Other common biogenic material in the sediment included sponge spicules and bryozoans. Four cores, three in Granite Harbour (14A, 15, 16) and one off Ferrar Glacier (18) were much longer (41 to 56cm), presumably because of the mud bottom.

Samples from the cores were treated with alcohol soon after recovery so that the living and dead foraminifera could be distinguished later in the laboratory (Ward, 1982). Splits were treated with rose bengal stain, and tests containing stained protoplasm extracted for further study. Non-stained tests were also separated for comparative purposes. Three areas of varying foraminiferal distribution have been identified in the McMurdo Sound area as follows: (1) below 560m there exists an assemblage of agglutinated foraminifera with Reophax spp. as the dominant taxa; (2) between 560 and about 210m there is a mixed assemblage, again with Reophax spp. as the dominant agglutinated taxa, and Trifarina earlandi, Globocassidulina cf. subglobosa and Cassidulinoides porrectus as the dominant calcareous taxa; this includes the Granite Harbour area; and (3) the New Harbour area supports an agglutinated population similar to that found below 560m in the open Sound.

Comparison of living (stained) and dead assemblages from the top 20m of five 22cm-diameter cores indicates that post-mortem alteration of assemblages, specifically, disappearance of calcareous tests, increases progressively with greater water depth until the CCD is reached, somewhere between 560 and 850 metres. The difference in proportions of calcareous and agglutinated foraminifera in live and dead assemblages increases the difficulty in the ecological interpretation of ancient (dead) assemblages.

Grain size analyses were carried out in all cores, and from these and samples from previous seasons several significant conclusions were drawn concerning marine sedimentation in the area (Barrett et al., 1982): The most important processes operating in the Sound today are ice-rafting of wind-blown sand by sea ice and sedimentation of fine terrigenous and biogenic material from suspension. Glacier and shelf ice locally make small contributions. Wind-blown sand is a major component, as much as 70 percent in places, of sea floor sediment on the western shelf and slope. However, the deep basins around Ross Island are floored with mud mostly containing less than 5 percent sand. Superglacial debris appears limited to the southern and western parts of the Sound. Coarse basal glacial debris was not found even close to the floating terminus of Mackay Glacier, where it appears to have already melted out.

References

Barrett, P.J., Pyne, A.R., ward, B.L. 1982. Modern sedimentation in McMurdo sound, Antarctica (abs.), Fourth International Symposium on Antarctic Earth science, Adelaide. August 16-22

Ward, B.L. 1982. Benthic foraminifera of McMurdo Sound (abs.), Fourth International Symposium on Antarctic Earth Science, Adelaide, August 16-22.