Paleoclimatological indices in the southern ocean based ...
Initial Reports of the Deep Sea Drilling Project, Vol. 71. Washington,
D.C.: U.S. Government Printing Office. Ciesielski, P.F., M.T. Ledbetter, and B.B. Ellwood. 1982. The development of Antarctic glaciation and the Neogene paleoenvironment of the Maurice Ewing Bank. Marine Geology, 46, 1-51. Ciesielski, RE, and S.W. Wise. 1977. Geologic history of the Maurice Ewing Bank of the Falkland Plateau based on piston and drill cores. Marine Geology, 25, 175-207.
Plafker, G., S. Bartsch-Winkler, and A.T. Ovenshine. 1977. Paleoglacial
Paleoclimatological indices in the southern ocean based on morphological parameters in the radiolarian genus Antarctissa A. GRANLUND Department of Geology Stockholm University S-106 91 Stockholm, Sweden
Relationships between radiolarian assemblages and climatic parameters have been noted by many workers (Hays 1965; Keany 1973; Lozano and Hays 1976). Such relationships have been used for establishing paleoclimatologic equations (transfer functions) (Williams and Keany 1977). In this study, the morphology of the radiolarian genus Antarctissa (A. denticulata—A. strelkovi complex) is analyzed in relation to physical parameters. The Antarctissa complex is very abundant in the southern ocean; it is one of the most common representatives of the Antarctic radiolarian fauna (Hays 1965; Nigrini 1967; Petrushevskaya 1967; Keany 1973; Lozano and Hays 1976; Williams and Keany 1977). This group is, therefore, suitable for a morphometric study.
implications of coarse detritus in DSDP Leg 36 cores. In P.F. Barker, I.W.D. Daiziel etal., Initial Reports of the Deep Sea Drilling Project, Vol. 36. Washington, D.C.: U.S. Government Printing Office. Rabinowitz, P.D., M. Delach, M. Truchan, and A. Lonardi. 1978. Bathymetry Chart Argentine Continental Margin. AAPG Argentine Map Series. Singer, J.K., and J.B. Anderson. 1984. Use of total grain size distribu-
tions to define bed erosion and transport for poorly sorted sediment undergoing simulated bioturbation. Marine Geology, 57, 335-359.
The study area is a latitudinal transect from the southern Indian Ocean sector of the southern ocean (45°S to 65°S). A pilot study of five core-top samples from each of the South Atlantic Ocean, South Pacific Ocean, and southern Indian Ocean showed that morphologic gradients do not differ among these oceans. Since more core-top material is available from the southern Indian Ocean, this ocean was chosen to represent the southern ocean. Initially, 50 core-top samples were selected for this study. Only those 21 samples that contained more than 100 specimens of Antarctissa per gram sediment were included. These samples are from an area between 45°S and 65°S. The remaining 29 samples mainly came from the north of 45°S. To determine whether the core-tops are Recent, counts were made of the relative abundances of Cycladophora davisiania. In none of the samples, C. davisiana exceeded 5 percent. Thus, they reflect Recent conditions (Lozano and Hays 1976). The absence of Stylatractus universus in all samples indicated that they are not older than 400,000 years (Hays and Shackleton 1976). The greater than 60-micrometer fraction was used for the morphologic study. The samples were prepared using an improved version of Moore's (1973) settling technique (Granlund 1983), which provides 32 slides with equally distributed radiolarian faunas from each sample. For the measurements, 10 slides, containing about 100 specimens, were randomly selected from each sample. Seven morphological characters were measured on each specimen (cephalis width, contour width, thorax width, length
Correlation coefficients for two morphological parameters versus some physical parameters for the South Indian Ocean transect In the southern ocean Physical parameters Morphological Silica Phosphate . Oxygen parameters Temperature Temperature Temperature (micromoles (micromole (microliters Bb Cc A° per liter) per liter) per liter) Width of cephalis (in micrometers) (Vi)
_0.662d
_0.631e _0.685d
—0.200
0.223 _0.695d 0.6430
Width of thorax (in micrometers) (V2)
0.715'
0.696' _0.723d
—0.153
0.309 - 0.532 0.487
a Annual average temperature, °C b Winter temperature, °C
Summer temperature, °C d Denotes significance at the 0.1 percent level. Denotes significance at the 1.0 percent level. Denotes significance at the 5.0 percent level.
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Width of cephalis and width of thorax compared to annual average surface-water temperature.
to maximum width of cephalis, length of cephalis, length to maximum width of thorax, and total length). The measurements were carried out using a microcomputer-based measuring device. This system permits very rapid acquisition of morphologic data. In total more than 7,000 measurements were made. Several physical parameters (silica, phosphate, dissolved oxygen, salinity, summer surface-water temperature, winter surface-water temperature, annual average surface-water temperature, water-depth, average number of Antarctissa per gram sediment, and latitude) (Reid 1981) were compared with these morphological dimensions to determine possible relationships. Analyses revealed close correlations between surface-water temperature and the morphological parameters. The width of the cephalis and the width of the thorax showed the highest correlation with annual average surface-water temperature (table) and are used to illustrate morphological gradients (figure). The width of the thorax ranges between 90 micrometers at temperatures of about 0°C and 60 micrometers at 8°C. Similarly, the width of the cephalis ranges between 55 urn at temperatures of about 0°C and 40 micrometers at 8°C. The correlationship between temperature and morphological parameters thus determined is potentially useful for paleoclimatological studies in the southern ocean. This may be especially so in antarctic waters, where calcareous organisms (planktonic foraminifera and coccoliths), which are widely used for palecimatic analyses, are rare. I thank Dennis Cassidy (Florida State University) who generously provided the core-top samples used in this study; Björn Malmgren (Stockholm University) who gave valuable comments and suggestions on the manuscript; and Otto Hermelin (Stockholm University) who helped me with the figures.
1984 REVIEW
References Granlund, A. 1983. An approach to a statistically random settling technique for micropaleontology. Stockholm Contributions in Geology. Hays, J.D. 1965. Radiolaria and late Tertiary and Quaternary history of antarctic seas. Biology of the antarctic sea, II: Antarctic Research Series.
Washington, D.C.: American Geophysical Union. Hays, J.D., J.A. Lozano, N.J. Shackleton, and G. Irving. 1976. An 18,000 B.P. reconstruction of the Atlantic and Western Indian Ocean sectors of the antarctic ocean. In R.M. Cline and J.D. Hays (Eds.), Investigations of Late Quaternary paleoceanography and paleoclimatology. Geological Society of America Memoir, 145. Hays, J. D., and N.J. Shackleton. 1976. Globally synchronous extinctions of the radiolarian Stylatractus universus. Geology, 4, 649-652. Keany, J . 1973. New radiolarian paleoclimatic index in the PlioPleistocene of the southern ocean. Nature, 246, 139-141. Lozano, J.A., and J.D. Hays. 1976. Relationship of radiolarian assemblages to sediment types and physical oceanography in Atlantic and Western Indian Ocean sectors of the antarctic ocean. In R.M. Cline, and J. D. Hays, Investigations of Late Quaternary paleoceanography and paleoclimatology. Geological Society of America Memoir, 145.
Moore, T. C., Jr. 1973. Method of randomly distributing grains for microscopic examination. Journal Sedimentary Petrology, 43, 904-906. Nigrini, C. 1967. Radiolana in pelagic sediments from the Indian and Atlantic Oceans. Scripps Institution of Oceanography Bulletin, 11, 1-125. Petrushevskaya, M. C. 1967. Radiolyarii otryadov Spumellariai Nasselaria antarkticheskoi ovlasti (po materiallam Sovietskoi antarkticheskoi ekspeditsii). [Antarctic spummeline and nasseline radiolarians (in collections of the Soviet Antarctic Expedition)]. In E.N. Pavlovskii (Ed.) Issl. Fauny Morei, Nau Ka Lenningrad, 3, 3-186. Reid, J. L. 1981. On the mid-depth circulation of the world ocean. In B.A. Warren and C. Wunsch (Eds.) Evolution of Physical Oceanography.
London: MIT Press. Williams, DR and J. Keany. 1977. Comparison of radiolarian/planktonic foraminiferal paleoceanography of the subantarctic Indian Ocean. Quaternary Research.
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