(Nanophanerophytic Montane Tundra) up near the treeline in This research was supported by National Science Foundation this zone, where the climate is cold, wet, and windy, and soils grant DPP 84-20622. are thin. Vegetation is confined to protected areas and thus covers less than 30 percent of the surface; the rest is bare, giving References a general aspect of mountain desert. Shrubs are stunted and ground-hugging, the dominant species being Escallonia serrata, Almeyda, E., and F. Saez. 1958. RecopilaciOn de datos climáticos de Chile y Em pet rum rubrum and the shrubby forms of the tree species mapas sinópticos respectivos. Santiago: Ministerio de Argricultura. (In Spanish) Nothofagus betuloides and N. antarctica. At lower elevations the Askin, R.A., and V. Markgraf. 1986. Palynmorphs from the Sirius conifer Pilgerodendron uvifera is abundant, both as trees and in Formation, Dominion Range, Antarctica. Antarctic Journal of the U.S. shrub form, and the coniferous shrub Dacrydium fonckii. 21(5). The western slopes of the southern Andes are very wet be- Carlquist, S. 1986. Fossil wood from the Sirius Formation. Antarctic cause they lie across the southern westerlies, in the path of Journal of the U.S., 21(5). frequent storms whose frontal precipitation is greatly increased Drewry, D.J. 1983. Isostatically adjusted bedrock surface of Antarctica. by the orographic effect of the Cordillera. Comparable condi- In D.J. Drewry (Ed.), Antarctica: Glaciological and geophysical folio (Sheet tions are unlikely to have prevailed on the Ross Embayment 6). Cambridge: Scott Polar Research Institute. slopes of the Transantarctic Mountains during the Neogene Fitzgerald, P.G., and A.J.W. Gleadow. 1985. Uplift history of the Trans- warm intervals. However, if the species of conifer or conifers antarctic Mountains, Victoria Land, Antarctica. In Abstracts, Sixth that were present at Oliver Bluffs were closely related to the Gondwana Symposium. (Institute of Polar Studies, Ohio State Univer- modern southernmost conifers Pilgerodendron uvifera sity, Miscellaneous Publication 231.) Columbus: Ohio State Univer- and sity Press. Dacrydium fonckii, rainfall is likely to have been at least moder- Godley, E.J. 1959. The botany of southern Chile in relation to New ate-perhaps 60-100 centimeters annually, as in Pisanos (1977, Zealand and the Subantarctic. Proceedings of the Royal Society, (Series p. 219) Pilgerodendro-Sphagnetum magellanici sub-association, in A), 152, 457-475. the drier parts of the islands south of the Beagle Channel. Thus Greene, S.W. 1964. The vascular flora of South Georgia. (British Antarctic the environment of the Ross Embayment coasts at a time of Survey, Science Report 45). Cambridge: British Antarctic Survey. Pliocene warmth may, as regards ice cover, have resembled the Harwood, D.M. 1985. Late Neogene climatic fluctuations in the south- extremely wet fjord region of Patagonia and Tierra del Fuego, ern high-latitudes: Implications of a warm Pliocene and deglaciated whereas the vegetation cover more closely resembled that of antarctic continent. South African Journal of Science, 81, 239-241. drier areas on the other side of the main divide. Heusser, C.J. 1986. Personal communication. List, R.J. 1949. The figure shows a modern scene with some of the inferred Smithsonian meteorological tables. (Sixth Edition). Wash- ington, D.C.: Smithsonian Institution Press. environmental features at the head of the Beardmore fjord at the Pisano, E. 1977. FitogeografIa de Fuego-Patagonia. I. Comunidades time the sedimentary sequence exposed at Oliver Bluffs was vegetales entre latitudes 52° y 56°S. Anales del instituto de la Patagonia, being deposited. The glacier at the head of Seno Eyre (49°S 8, 121-250. (In Spanish) latitude), after advancing about 10 kilometers down the fjord Robin, G. de Q . , and R.J. Adie. 1964. The ice cover. In R. Priestley, R.J. after 1945, overriding trees and peat bogs, began a slow retreat Adie, and C. de Q . Robin (Eds.), Antarctic Research, London: in the early 1980s. The photograph of recently deglaciated Butterworths. terrain, taken in 1986, shows hummocky glacial sediments with Smith, AG., and D.J. Drewry. 1984. Delayed phase change due to hot abundant wood on the surface, chiefly Pilgerodendron uvifera, asthenosphere causes Transantarctic uplift? Nature, 309, 536-538. with some Nothofagus betuloides. The vegetation that was over- Webb, P.-N., and D.M. Harwood. 1986. The terrestrial flora of the Sirius Formation: Its significance in interpreting late Cenozoic glacial histo- run also includes Dacrydium fonckii. In the Beardmore fjord at a ry. Antarctic Journal of the U.S., 21. time of Pliocene warmth, the glacier would have advanced into Webb, P.-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. less luxuriant and more stunted vegetation than that shown Mercer. 1986. Late Cenozoic tectonic and glacial history of the Trans- here, where average midsummer temperature is about 12°C. antarctic Mountains. Antarctic Journal of the U.S., 21(5).

The search for microfossils marine microfossils in the upper Pliocene/lower Pleistocene terrestrial Sirius Formation of the Transantarctjc Mountains beneath the Greenland and west (Harwood 1983, 1986a; Antarctic Journal, this issue; Webb et al. antarctic ice sheets 1984, 1987). These fossils indicate a complex history of Cenozoic marine invasion and deglaciation of East Antarctica. Determin- ing whether this history could be verified and improved from D.M. HARWOOD debris beneath the Greenland and west antarctic ice sheets was the goal of the present investigation. The results from my search Institute of Polar Studies for microfossils in subglacial debris from two ice cores, Camp and Century in northwest Greenland and Byrd in central West Ant- Department of Geology and Mineralogy arctica, and from glacial deposits associated with hyaloclastites Ohio State University in Ellsworth Land and Marie Byrd Land are reported below. Columbus, Ohio 43210 West Antarctica Interest in sediments beneath the Greenland and west ant- Byrd ice core. The bottom of the west antarctic ice sheet con- arctic ice sheets stems from the recent discovery of reworked tains, abundant stratified debris, including layers of clay, sand

1986 REVIEW 105 and pebbles, and larger fragments of rock occasionally inter- These diatoms may have lived in the vicinity of Camp Century spersed with bands of clear ice" (Cow, Epstein, and Sheehy in the Late Neogene prior to development of the Greenland ice 1979). Fourteen samples of basal debris from dirty-ice spanning sheet. More likely, they lived during a Pleistocene interglacial the lower 4.83 meters of the Byrd ice core were examined for when the Camp Century site was ice-free and Greenland ice microfossils. Sediment material examined here includes debris sheet was at least one-third smaller. The northwest corner of melted out of the ice core and several soft mud-clots described Greenland and probably much more of the continent, was ex- in Cow et al. (979). Microfossils were not encountered during a posed during an episode of ice-retreat. A warmer and/or longer thorough microscopic examination of this debris. Because sam- interglacial than the present Holocene "interglacial" is sug- ple size was exceptionally small (less than 1 cubic centimeter) gested to explain the large decrease in ice-sheet volume. for this type of study (Harwood, Grant and Karrer, Antarctic The following individuals are graciously acknowledged for Journal, this issue), the absence of diatoms is not surprising. Due supplying sample material used in this investigation: C. Crad- to the high potential scientific return, further examination of dock for the sample from the Jones Mountains; W. LeMasurier this material is warranted. for the samples from Marie Byrd Land; and Tony Cow for Hyaloclastites. Volcanic deposits from Ellsworth Land (Rut- material from the Byrd ice core. The Ice Core Storage Facility, ford et al. 1972) and Marie Byrd Land (LeMasurier and Rex 1982) State University of New York at Buffalo and the National Science have been interpreted as subglacial hyaloclastites erupted be- Foundation provided sample material from the Camp Century neath an ice mass in West Antarctica. Subglacial eruption is ice core. favored over marine eruption due to: (1) striated pavements This research was supported by National Science Foundation beneath the deposits; (2) their thickness, elevation, and inland grant DPP 83-15553 and DPP 84-20622 to Peter-N. Webb and 1985 position; and (3) stratigraphic association with glacial deposits Geological Society of America research grant to D. Harwood. (LeMasurier and Rex 1982). A preliminary examination of six hyaloclastites and associ- ated glacial sediments from Marie Byrd Land revealed the pres- ence of marine siliceous microfossils in four samples from References Mount Murphy, Shibuya Peak, Mount Takahe, and Mount Pe- Gow, A.J., S. Epstein, and W. Sheehy. 1979. on the origin of stratified tras. Microfossils were not present in a sample from Jones debris in ice cores from the bottom of the Antarctic ice sheet. Journal of Mountain in Ellsworth Land. In most samples microfossil oc- Glaciology, 23(89), 185-192. currence was limited to less than 10 fragments of siliceous Harwood, D.M., 1983. Diatoms from the Sirius Formation, Transan- microfossils, most identifiable to genus. A rich siliceous micro- tarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. fossil assemblage of more than 150 specimens was recovered Harwood, D.M., 1986a. Diatom biostratigraphy and paleoecology with a from tillite sample HC35F from Shibuya Peak. The assemblage Cenozoic history of Antarctic ice sheets. (Doctoral dissertation, Ohio State includes marine diatoms and silicoflagellates of middle to late University, Columbus, Ohio.) Miocene age. A subsequent preparation and examination of this Harwood, D.M. 1986. Recycled siliceous microfossils from the Sirius sample yielded similar siliceous microfossils. Further paleon- Formation. Antarctic Journal of the U.S., 21(5). tological study of these samples is in progress. Harwood, D.M. 1986b. Diatoms beneath the Greenland Ice Sheet indi- The history of these microfossils is similar to that of recycled cate interglacials warmer than present? Arctic. 39(4). Harwood, D.M., M.W. Grant, and M.H. Karrer. 1986. Techniques to microfossils recovered in the Sirius Formation (Webb et al. 1984; improve diatom recovery from glacial sediments. Antarctic Journal of this issue) in that they were Harwood 1986a; Antarctic Journal, the U.S., 21(5). initially deposited in a marine environment and later eroded Herron, S., and C.C. Langway, Jr. 1979. The debris-laden ice at the and transported by ice. Original source area and transport bottom of the Greenland Ice Sheet. Journal of Glaciology, 23(89), distance is not known for the west antarctic material. Deposi- 193-207. tional processes, however, were markedly different as the LeMasurier, WE., and D.C. Rex. 1982. Volcanic record of Cenozoic hyaloclastite-associated tills were melted from the basal layers glacial history in Marie Byrd Land and western Ellsworth Land: of an ice mass by subglacial vulcanism, whereas Sirius Forma- Revised chronology and evaluation of tectonic factors. In C. Crad- tion deposits are largely ice-marginal or lodgement deposits. dock (Ed.), Antarctic geoscience, Madison: University of Wisconsin Press. Greenland Rutford, RI-I., C. Craddock, C.M. White, and R.L. Armstrong. 1972. Adie, (Ed.), Ant- Basal debris from the Greenland ice Tertiary glaciation in the Jones Mountains. In R.J. Camp Century ice core. arctic Geology and Geophysics. Oslo: Universitetsforlaget. sheet was examined with the hope of recovering microfossils Webb, P.N., D. M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. which could be used to determine and date changes in ice sheet Stott. 1984. Cenozoic marine sedimetation and ice volume variation size through time. Three samples of basal debris and debris- on the East Antarctic craton. Geology, 12, 287-291. laden ice (Herron and Langway 1979) from the lower 18 meters Webb, P.N., B.C. McKelvey, D.M. Harwood, M.C.G. Mabin, and J.H. of the Camp Century ice core revealed the presence of abun- Mercer. 1987. Sirius Formation of the Beardmore Glacier region. Ant- dant nonmarine and few marine diatoms (Harwood 1986b). arctic Journal of the U.S., 21(4).

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