search for microfossils beneath the Greenland and west antarctic ice ...
(Nanophanerophytic Montane Tundra) up near the treeline in this zone, where the climate is cold, wet, and windy, and soils are thin. Vegetation is confined to protected areas and thus covers less than 30 percent of the surface; the rest is bare, giving a general aspect of mountain desert. Shrubs are stunted and ground-hugging, the dominant species being Escallonia serrata, Em pet rum rubrum and the shrubby forms of the tree species Nothofagus betuloides and N. antarctica. At lower elevations the conifer Pilgerodendron uvifera is abundant, both as trees and in shrub form, and the coniferous shrub Dacrydium fonckii. The western slopes of the southern Andes are very wet because they lie across the southern westerlies, in the path of frequent storms whose frontal precipitation is greatly increased by the orographic effect of the Cordillera. Comparable conditions are unlikely to have prevailed on the Ross Embayment slopes of the Transantarctic Mountains during the Neogene warm intervals. However, if the species of conifer or conifers that were present at Oliver Bluffs were closely related to the modern southernmost conifers Pilgerodendron uvifera and Dacrydium fonckii, rainfall is likely to have been at least moderate-perhaps 60-100 centimeters annually, as in Pisano's (1977, p. 219) Pilgerodendro-Sphagnetum magellanici sub-association, in the drier parts of the islands south of the Beagle Channel. Thus the environment of the Ross Embayment coasts at a time of Pliocene warmth may, as regards ice cover, have resembled the extremely wet fjord region of Patagonia and Tierra del Fuego, whereas the vegetation cover more closely resembled that of drier areas on the other side of the main divide. The figure shows a modern scene with some of the inferred environmental features at the head of the Beardmore fjord at the time the sedimentary sequence exposed at Oliver Bluffs was being deposited. The glacier at the head of Seno Eyre (49°S latitude), after advancing about 10 kilometers down the fjord after 1945, overriding trees and peat bogs, began a slow retreat in the early 1980's. The photograph of recently deglaciated terrain, taken in 1986, shows hummocky glacial sediments with abundant wood on the surface, chiefly Pilgerodendron uvifera, with some Nothofagus betuloides. The vegetation that was overrun also includes Dacrydium fonckii. In the Beardmore fjord at a time of Pliocene warmth, the glacier would have advanced into less luxuriant and more stunted vegetation than that shown here, where average midsummer temperature is about 12°C.
The search for microfossils beneath the Greenland and west antarctic ice sheets D.M. HARWOOD Institute of Polar Studies
and Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
This research was supported by National Science Foundation grant DPP 84-20622. References Almeyda, E., and F. Saez. 1958. RecopilaciOn de datos climáticos de Chile y mapas sinópticos respectivos. Santiago: Ministerio de Argricultura. (In Spanish) Askin, R.A., and V. Markgraf. 1986. Palynmorphs from the Sirius Formation, Dominion Range, Antarctica. Antarctic Journal of the U.S. 21(5). Carlquist, S. 1986. Fossil wood from the Sirius Formation. Antarctic Journal of the U.S., 21(5). Drewry, D.J. 1983. Isostatically adjusted bedrock surface of Antarctica. In D.J. Drewry (Ed.), Antarctica: Glaciological and geophysical folio (Sheet 6). Cambridge: Scott Polar Research Institute. Fitzgerald, P.G., and A.J.W. Gleadow. 1985. Uplift history of the Transantarctic Mountains, Victoria Land, Antarctica. In Abstracts, Sixth Gondwana Symposium. (Institute of Polar Studies, Ohio State University, Miscellaneous Publication 231.) Columbus: Ohio State University Press. Godley, E.J. 1959. The botany of southern Chile in relation to New Zealand and the Subantarctic. Proceedings of the Royal Society, (Series A), 152, 457-475. Greene, S.W. 1964. The vascular flora of South Georgia. (British Antarctic Survey, Science Report 45). Cambridge: British Antarctic Survey. Harwood, D.M. 1985. Late Neogene climatic fluctuations in the southern high-latitudes: Implications of a warm Pliocene and deglaciated antarctic continent. South African Journal of Science, 81, 239-241. Heusser, C.J. 1986. Personal communication. List, R.J. 1949. Smithsonian meteorological tables. (Sixth Edition). Washington, D.C.: Smithsonian Institution Press. Pisano, E. 1977. FitogeografIa de Fuego-Patagonia. I. Comunidades vegetales entre latitudes 52° y 56°S. Anales del instituto de la Patagonia, 8, 121-250. (In Spanish) Robin, G. de Q . , and R.J. Adie. 1964. The ice cover. In R. Priestley, R.J. Adie, and C. de Q . Robin (Eds.), Antarctic Research, London: Butterworths. Smith, AG., and D.J. Drewry. 1984. Delayed phase change due to hot asthenosphere causes Transantarctic uplift? Nature, 309, 536-538. Webb, P.-N., and D.M. Harwood. 1986. The terrestrial flora of the Sirius Formation: Its significance in interpreting late Cenozoic glacial history. Antarctic Journal of the U.S., 21. Webb, P.-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. Mercer. 1986. Late Cenozoic tectonic and glacial history of the Transantarctic Mountains. Antarctic Journal of the U.S., 21(5).
marine microfossils in the upper Pliocene/lower Pleistocene terrestrial Sirius Formation of the Transantarctjc Mountains (Harwood 1983, 1986a; Antarctic Journal, this issue; Webb et al. 1984, 1987). These fossils indicate a complex history of Cenozoic marine invasion and deglaciation of East Antarctica. Determining whether this history could be verified and improved from debris beneath the Greenland and west antarctic ice sheets was the goal of the present investigation. The results from my search for microfossils in subglacial debris from two ice cores, Camp Century in northwest Greenland and Byrd in central West Antarctica, and from glacial deposits associated with hyaloclastites in Ellsworth Land and Marie Byrd Land are reported below. West Antarctica
Interest in sediments beneath the Greenland and west antarctic ice sheets stems from the recent discovery of reworked 1986 REVIEW
Byrd ice core. The bottom of the west antarctic ice sheet contains, abundant stratified debris, including layers of clay, sand
105
and pebbles, and larger fragments of rock occasionally interspersed with bands of clear ice" (Cow, Epstein, and Sheehy 1979). Fourteen samples of basal debris from dirty-ice spanning the lower 4.83 meters of the Byrd ice core were examined for microfossils. Sediment material examined here includes debris melted out of the ice core and several soft mud-clots described in Cow et al. (979). Microfossils were not encountered during a thorough microscopic examination of this debris. Because sample size was exceptionally small (less than 1 cubic centimeter) for this type of study (Harwood, Grant and Karrer, Antarctic Journal, this issue), the absence of diatoms is not surprising. Due to the high potential scientific return, further examination of this material is warranted. Hyaloclastites. Volcanic deposits from Ellsworth Land (Rutford et al. 1972) and Marie Byrd Land (LeMasurier and Rex 1982) have been interpreted as subglacial hyaloclastites erupted beneath an ice mass in West Antarctica. Subglacial eruption is favored over marine eruption due to: (1) striated pavements beneath the deposits; (2) their thickness, elevation, and inland position; and (3) stratigraphic association with glacial deposits (LeMasurier and Rex 1982). A preliminary examination of six hyaloclastites and associated glacial sediments from Marie Byrd Land revealed the presence of marine siliceous microfossils in four samples from Mount Murphy, Shibuya Peak, Mount Takahe, and Mount Petras. Microfossils were not present in a sample from Jones Mountain in Ellsworth Land. In most samples microfossil occurrence was limited to less than 10 fragments of siliceous microfossils, most identifiable to genus. A rich siliceous microfossil assemblage of more than 150 specimens was recovered from tillite sample HC35F from Shibuya Peak. The assemblage includes marine diatoms and silicoflagellates of middle to late Miocene age. A subsequent preparation and examination of this sample yielded similar siliceous microfossils. Further paleontological study of these samples is in progress. The history of these microfossils is similar to that of recycled microfossils recovered in the Sirius Formation (Webb et al. 1984; Harwood 1986a; Antarctic Journal, this issue) in that they were initially deposited in a marine environment and later eroded and transported by ice. Original source area and transport distance is not known for the west antarctic material. Depositional processes, however, were markedly different as the hyaloclastite-associated tills were melted from the basal layers of an ice mass by subglacial vulcanism, whereas Sirius Formation deposits are largely ice-marginal or lodgement deposits. Greenland Camp Century ice core. Basal debris from the Greenland ice sheet was examined with the hope of recovering microfossils which could be used to determine and date changes in ice sheet size through time. Three samples of basal debris and debrisladen ice (Herron and Langway 1979) from the lower 18 meters of the Camp Century ice core revealed the presence of abundant nonmarine and few marine diatoms (Harwood 1986b).
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These diatoms may have lived in the vicinity of Camp Century in the Late Neogene prior to development of the Greenland ice sheet. More likely, they lived during a Pleistocene interglacial when the Camp Century site was ice-free and Greenland ice sheet was at least one-third smaller. The northwest corner of Greenland and probably much more of the continent, was exposed during an episode of ice-retreat. A warmer and/or longer interglacial than the present Holocene "interglacial" is suggested to explain the large decrease in ice-sheet volume. The following individuals are graciously acknowledged for supplying sample material used in this investigation: C. Craddock for the sample from the Jones Mountains; W. LeMasurier for the samples from Marie Byrd Land; and Tony Cow for material from the Byrd ice core. The Ice Core Storage Facility, State University of New York at Buffalo and the National Science Foundation provided sample material from the Camp Century ice core. This research was supported by' National Science Foundation grant DPP 83-15553 and DPP 84-20622 to Peter-N. Webb and 1985 Geological Society of America research grant to D. Harwood.
References Gow, A.J., S. Epstein, and W. Sheehy. 1979. on the origin of stratified debris in ice cores from the bottom of the Antarctic ice sheet. Journal of Glaciology, 23(89), 185-192. Harwood, D.M., 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. Harwood, D.M., 1986a. Diatom biostratigraphy and paleoecology with a Cenozoic history of Antarctic ice sheets. (Doctoral dissertation, Ohio State
University, Columbus, Ohio.) Harwood, D.M. 1986. Recycled siliceous microfossils from the Sirius Formation. Antarctic Journal of the U.S., 21(5). Harwood, D.M. 1986b. Diatoms beneath the Greenland Ice Sheet indicate interglacials warmer than present? Arctic. 39(4). Harwood, D.M., M.W. Grant, and M.H. Karrer. 1986. Techniques to improve diatom recovery from glacial sediments. Antarctic Journal of the U.S., 21(5). Herron, S., and C.C. Langway, Jr. 1979. The debris-laden ice at the bottom of the Greenland Ice Sheet. Journal of Glaciology, 23(89), 193-207. LeMasurier, WE., and D.C. Rex. 1982. Volcanic record of Cenozoic glacial history in Marie Byrd Land and western Ellsworth Land: Revised chronology and evaluation of tectonic factors. In C. Craddock (Ed.), Antarctic geoscience, Madison: University of Wisconsin Press. Rutford, RI-I., C. Craddock, C.M. White, and R.L. Armstrong. 1972. Tertiary glaciation in the Jones Mountains. In R.J. Adie, (Ed.), Antarctic Geology and Geophysics. Oslo: Universitetsforlaget. Webb, P.N., D. M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. Stott. 1984. Cenozoic marine sedime'tation and ice volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P.N., B.C. McKelvey, D.M. Harwood, M.C.G. Mabin, and J.H. Mercer. 1987. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S., 21(4).
ANTARCTIC JOURNAL
The search for microfossils beneath the Greenland and west antarctic ice sheets D.M. HARWOOD Institute of Polar Studies
and Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210
This research was supported by National Science Foundation grant DPP 84-20622. References Almeyda, E., and F. Saez. 1958. RecopilaciOn de datos climáticos de Chile y mapas sinópticos respectivos. Santiago: Ministerio de Argricultura. (In Spanish) Askin, R.A., and V. Markgraf. 1986. Palynmorphs from the Sirius Formation, Dominion Range, Antarctica. Antarctic Journal of the U.S. 21(5). Carlquist, S. 1986. Fossil wood from the Sirius Formation. Antarctic Journal of the U.S., 21(5). Drewry, D.J. 1983. Isostatically adjusted bedrock surface of Antarctica. In D.J. Drewry (Ed.), Antarctica: Glaciological and geophysical folio (Sheet 6). Cambridge: Scott Polar Research Institute. Fitzgerald, P.G., and A.J.W. Gleadow. 1985. Uplift history of the Transantarctic Mountains, Victoria Land, Antarctica. In Abstracts, Sixth Gondwana Symposium. (Institute of Polar Studies, Ohio State University, Miscellaneous Publication 231.) Columbus: Ohio State University Press. Godley, E.J. 1959. The botany of southern Chile in relation to New Zealand and the Subantarctic. Proceedings of the Royal Society, (Series A), 152, 457-475. Greene, S.W. 1964. The vascular flora of South Georgia. (British Antarctic Survey, Science Report 45). Cambridge: British Antarctic Survey. Harwood, D.M. 1985. Late Neogene climatic fluctuations in the southern high-latitudes: Implications of a warm Pliocene and deglaciated antarctic continent. South African Journal of Science, 81, 239-241. Heusser, C.J. 1986. Personal communication. List, R.J. 1949. Smithsonian meteorological tables. (Sixth Edition). Washington, D.C.: Smithsonian Institution Press. Pisano, E. 1977. FitogeografIa de Fuego-Patagonia. I. Comunidades vegetales entre latitudes 52° y 56°S. Anales del instituto de la Patagonia, 8, 121-250. (In Spanish) Robin, G. de Q . , and R.J. Adie. 1964. The ice cover. In R. Priestley, R.J. Adie, and C. de Q . Robin (Eds.), Antarctic Research, London: Butterworths. Smith, AG., and D.J. Drewry. 1984. Delayed phase change due to hot asthenosphere causes Transantarctic uplift? Nature, 309, 536-538. Webb, P.-N., and D.M. Harwood. 1986. The terrestrial flora of the Sirius Formation: Its significance in interpreting late Cenozoic glacial history. Antarctic Journal of the U.S., 21. Webb, P.-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. Mercer. 1986. Late Cenozoic tectonic and glacial history of the Transantarctic Mountains. Antarctic Journal of the U.S., 21(5).
marine microfossils in the upper Pliocene/lower Pleistocene terrestrial Sirius Formation of the Transantarctjc Mountains (Harwood 1983, 1986a; Antarctic Journal, this issue; Webb et al. 1984, 1987). These fossils indicate a complex history of Cenozoic marine invasion and deglaciation of East Antarctica. Determining whether this history could be verified and improved from debris beneath the Greenland and west antarctic ice sheets was the goal of the present investigation. The results from my search for microfossils in subglacial debris from two ice cores, Camp Century in northwest Greenland and Byrd in central West Antarctica, and from glacial deposits associated with hyaloclastites in Ellsworth Land and Marie Byrd Land are reported below. West Antarctica
Interest in sediments beneath the Greenland and west antarctic ice sheets stems from the recent discovery of reworked 1986 REVIEW
Byrd ice core. The bottom of the west antarctic ice sheet contains, abundant stratified debris, including layers of clay, sand
105
and pebbles, and larger fragments of rock occasionally interspersed with bands of clear ice" (Cow, Epstein, and Sheehy 1979). Fourteen samples of basal debris from dirty-ice spanning the lower 4.83 meters of the Byrd ice core were examined for microfossils. Sediment material examined here includes debris melted out of the ice core and several soft mud-clots described in Cow et al. (979). Microfossils were not encountered during a thorough microscopic examination of this debris. Because sample size was exceptionally small (less than 1 cubic centimeter) for this type of study (Harwood, Grant and Karrer, Antarctic Journal, this issue), the absence of diatoms is not surprising. Due to the high potential scientific return, further examination of this material is warranted. Hyaloclastites. Volcanic deposits from Ellsworth Land (Rutford et al. 1972) and Marie Byrd Land (LeMasurier and Rex 1982) have been interpreted as subglacial hyaloclastites erupted beneath an ice mass in West Antarctica. Subglacial eruption is favored over marine eruption due to: (1) striated pavements beneath the deposits; (2) their thickness, elevation, and inland position; and (3) stratigraphic association with glacial deposits (LeMasurier and Rex 1982). A preliminary examination of six hyaloclastites and associated glacial sediments from Marie Byrd Land revealed the presence of marine siliceous microfossils in four samples from Mount Murphy, Shibuya Peak, Mount Takahe, and Mount Petras. Microfossils were not present in a sample from Jones Mountain in Ellsworth Land. In most samples microfossil occurrence was limited to less than 10 fragments of siliceous microfossils, most identifiable to genus. A rich siliceous microfossil assemblage of more than 150 specimens was recovered from tillite sample HC35F from Shibuya Peak. The assemblage includes marine diatoms and silicoflagellates of middle to late Miocene age. A subsequent preparation and examination of this sample yielded similar siliceous microfossils. Further paleontological study of these samples is in progress. The history of these microfossils is similar to that of recycled microfossils recovered in the Sirius Formation (Webb et al. 1984; Harwood 1986a; Antarctic Journal, this issue) in that they were initially deposited in a marine environment and later eroded and transported by ice. Original source area and transport distance is not known for the west antarctic material. Depositional processes, however, were markedly different as the hyaloclastite-associated tills were melted from the basal layers of an ice mass by subglacial vulcanism, whereas Sirius Formation deposits are largely ice-marginal or lodgement deposits. Greenland Camp Century ice core. Basal debris from the Greenland ice sheet was examined with the hope of recovering microfossils which could be used to determine and date changes in ice sheet size through time. Three samples of basal debris and debrisladen ice (Herron and Langway 1979) from the lower 18 meters of the Camp Century ice core revealed the presence of abundant nonmarine and few marine diatoms (Harwood 1986b).
106
These diatoms may have lived in the vicinity of Camp Century in the Late Neogene prior to development of the Greenland ice sheet. More likely, they lived during a Pleistocene interglacial when the Camp Century site was ice-free and Greenland ice sheet was at least one-third smaller. The northwest corner of Greenland and probably much more of the continent, was exposed during an episode of ice-retreat. A warmer and/or longer interglacial than the present Holocene "interglacial" is suggested to explain the large decrease in ice-sheet volume. The following individuals are graciously acknowledged for supplying sample material used in this investigation: C. Craddock for the sample from the Jones Mountains; W. LeMasurier for the samples from Marie Byrd Land; and Tony Cow for material from the Byrd ice core. The Ice Core Storage Facility, State University of New York at Buffalo and the National Science Foundation provided sample material from the Camp Century ice core. This research was supported by' National Science Foundation grant DPP 83-15553 and DPP 84-20622 to Peter-N. Webb and 1985 Geological Society of America research grant to D. Harwood.
References Gow, A.J., S. Epstein, and W. Sheehy. 1979. on the origin of stratified debris in ice cores from the bottom of the Antarctic ice sheet. Journal of Glaciology, 23(89), 185-192. Harwood, D.M., 1983. Diatoms from the Sirius Formation, Transantarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. Harwood, D.M., 1986a. Diatom biostratigraphy and paleoecology with a Cenozoic history of Antarctic ice sheets. (Doctoral dissertation, Ohio State
University, Columbus, Ohio.) Harwood, D.M. 1986. Recycled siliceous microfossils from the Sirius Formation. Antarctic Journal of the U.S., 21(5). Harwood, D.M. 1986b. Diatoms beneath the Greenland Ice Sheet indicate interglacials warmer than present? Arctic. 39(4). Harwood, D.M., M.W. Grant, and M.H. Karrer. 1986. Techniques to improve diatom recovery from glacial sediments. Antarctic Journal of the U.S., 21(5). Herron, S., and C.C. Langway, Jr. 1979. The debris-laden ice at the bottom of the Greenland Ice Sheet. Journal of Glaciology, 23(89), 193-207. LeMasurier, WE., and D.C. Rex. 1982. Volcanic record of Cenozoic glacial history in Marie Byrd Land and western Ellsworth Land: Revised chronology and evaluation of tectonic factors. In C. Craddock (Ed.), Antarctic geoscience, Madison: University of Wisconsin Press. Rutford, RI-I., C. Craddock, C.M. White, and R.L. Armstrong. 1972. Tertiary glaciation in the Jones Mountains. In R.J. Adie, (Ed.), Antarctic Geology and Geophysics. Oslo: Universitetsforlaget. Webb, P.N., D. M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. Stott. 1984. Cenozoic marine sedime'tation and ice volume variation on the East Antarctic craton. Geology, 12, 287-291. Webb, P.N., B.C. McKelvey, D.M. Harwood, M.C.G. Mabin, and J.H. Mercer. 1987. Sirius Formation of the Beardmore Glacier region. Antarctic Journal of the U.S., 21(4).
ANTARCTIC JOURNAL
