Showing papers on "Foraminifera published in 1981"

Miocene Stable Isotope Record: A Detailed Deep Pacific Ocean Study and Its Paleoclimatic Implications

Abstract: Deep Sea Drilling Project site 289 in the western equatorial Pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the Miocene deep ocean. The isotopic record reflects major changes in paleoclimate and paleoceanography, probably dominated by a major phase of Antarctic ice-cap growth. The transition from a relatively unglaciated world to one similar to today occurred between 16.5 x 10(6) and 13 x 10(6) years before the present, with the greatest change occurring between approximately 14.8 x 10(6) and 14.0 x 10(6) years before the present.

Phyletic gradualism in a Late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific

Abstract: Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage (Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically.

Oxygen-18 enrichment of planktonic foraminifera due to gametogenic calcification below the euphotic zone.

Abstract: Empty shells of spinose planktonic foraminifera on the seabed are significantly enriched in oxygen-18 as compared with the shells of their living counterparts in surface waters. This enrichment is due to gametogenic calcification, which extracts calcium carbonate from deeper and colder waters as the shell sinks below the euphotic zone. JEAN-CLAUDE DUPLESSY

Production of Carbonate Sediments by Selected Large Benthic Foraminifera on Two Pacific Coral Reefs

Abstract: Carbonate production, deposition, and turnover rates by selected members of the rotaliine foraminiferal families Asterigerinidae, Calcarinidae, and Nummulitidae were calculated using growth and standing crop data. In Palau, Western Caroline Islands, carbonate production rates on seaward reef flats were up to 2.8 kg CaCO3 m-2 yr-1, which is equivalent to carbonate deposition of almost 1 mm yr-1. Productivity on lagoonal reef slopes was about 0.6 kg CaCO3 m-2 yr-1 or deposition of about 0.2 mm yr-1. Carbonate turnover rates in the living populations were 11-16 times per year. In Hawaii, production rates were much lower because of slower growth rates and the absence of the family Calcarinidae. Product on rates were up to 0.15 kg CaCO3 m-2yr-1 on seaward reef slopes, which is a depositional rate of about 0.05 mm yr-1. Carbonate turnover rates were 7-11 times per year. These production rates are comparable to many values reported in the literature for coral, coralline algae, and macrobenthos.

Stable isotope composition of benthic foraminifera from the equatorial Pacific

Abstract: When ranked according to deviation from isotopic equilibrium, deep-sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon. Both rank sequences are stable from east to west in the equatorial Pacific (fertility-independent) and from Glacial to post-Glacial (time-independent). Records for the past 15,000 yr suggest marked changes in deep-sea circulation during this time interval.

Fourier analysis of test shape of planktonic foraminifera

Abstract: The exact characterization of test shape is important in morphological studies of foraminifera and other marine micro-fossils Most biometrie studies of microfossils, however, have only measured test diameter or other linear components1. The tests of planktonic foraminifera exhibit a wide range of morphological traits, some of which are related to environmental conditions and others to the phylogenetic history of the taxon1,2. Mean test size or linear measurements of chambers and/or whole tests of fossil foraminifera can be used for palaeoecological interpretations from the morphological variations3–10. We report here that Fourier series analysis could be an objective and unambiguous biometric method for determining the components which comprise the shape of foraminifera. Fourier shape analysis has been successfully applied to fossil ostracods11,12 , fossil bryozoans13,14 and miospores15. In the present study, Fourier series shape analysis was performed on the planktonic foraminifera, Globorotalia truncatulinoides, from the southern Indian Ocean, to differentiate palaeo-environmentally significant trends in the test shape of this species. Kennett16 and Takayanagi et al.17 have used linear test measurements to describe latitudinal gradients in the test morphology of G. truncatulinoides. Highly conical forms dominate in tropical waters, whereas more compressed, biconvex forms dominate in cool water.

Direct use of dissolved organic carbon by agglutinated benthic foraminifera

Abstract: Foraminifera are known to obtain nutrients in a variety of ways: they are omnivores, carnivores or herbivores1–3 and some species are known to use the extracellular metabolites of their photosynthetic endosymbionts1,2,4. None, however, has previously been proven to utilize exogenous dissolved organic carbon directly, although this is well known in other marine species5,6. Knowledge of foraminiferal trophic positions is important because foraminifera are common in most marine communities1 and may be the most abundant eukaryotic organism in the extensive deep-sea benthos7–9. Our studies of benthic foraminifera from an unusual Antarctic shallow water embayment now show that certain species utilize both particulate and dissolved organic material in their nutrition.

Late Quaternary tephrochronology and paleo-oceanography of the sediments of the Japan Sea

Abstract: The purpose of this paper is twofold: to establish a tephrochronological framework for the sediments of the Japan Sea on the basis of the identification of the abyssal tephra layers and to examine the paleo-oceanographic conditions of the Japan Sea during the last 60, 000 years, based on the foraminiferal biostratigraphy and 18O record in two piston cores.Accurate determinations of the refractive indices of volcanic glass shards and minerals, together with other data, have enabled successful characterization of several tephra layers and permitted correlation to be made between cores.Of the five marker-tephras described in this paper, three can be correlated with the dated widespread tephras which originated from eruptions of gigantic caldera volcanoes in Kyushu. They are: the Akahoya ash, the Aira-Tn ash and the Aso-4 ash. The Akahoya ash (Kikai caldera, 6, 300Y.B.P.) occurs in cores from the southern part of the Japan Sea. The Aira-Tn ash (Aira caldera, 21, 000-22, 000Y.B.P.) is the most prominent marker, found in cores from the whole area of the sea. The Aso-4 ash (Aso caldera, approximately 50, 000Y.B.P.) is found in cores from the central and southeastern part of the sea.The other two marker-tephras, the Oki ash and the Yamato ash, are the products of major eruptions of Holocene and Late Pleistocene age, and have probably originated from the Ulreung-do Island in South Korea. This estimate is based on their peculiar petrographic nature and distribution. The Oki ash is found in a stratigraphic horizon between the Akahoya ash and the Aira-Tn ash in cores from a tract extending from the area adjacent to the Ulreung-do to the Kinki district of central Honshu, where three radiocarbon ages of around 9, 300Y.B.P. were obtained for the eruption. The Yamato ash occurs in cores from areas to the east of the Ulreung-do. A reliable age for this tephra has not yet been determined, although its stratigraphic relationship to the overlying Aira-Tn ash and the underlying Aso-4 ash, suggests that it must occur within a range of between 25, 000 and 35, 000Y.B.P.Vertical changes in the lithological, foraminiferal and oxygen isotope characteristics of the two tephrochronoiogically dated cores from the Oki bank in the Japan Sea occur at about 6, 500-9, 500Y.B.P., 13, 000 and 23, 000Y.B.P. The paleo-oceanographic conditions of the Japan Sea between these ages are reconstructed from the data of paleosalinity and paleo-temperature, which were calculated on the basis of the 18O values of the benthonic and planktonic foraminiferal tests in the cores.The water of the Japan Sea seems to have been of relatively constant salinity (33-34‰) and low temperature (8-10°C) in the period between 60, 000Y.B.P. and 23, 000Y.B.P. Relatively minor amounts of Pacific sea water flowed into the Japan Sea during this period. A conspicuous, continuous decrease in the salinity of the sea water took place in the period from 23, 000Y.B.P. to 13, 000Y.B.P., as inferred from the decrease of the 18O values of the planktonic foraminiferal tests. It seems probable that the inflow of water from the open sea was checked by some paleogeographic changes at the straits, caused by lowering of sea level during this glacial stage. The 18O values of the planktonic foraminifera tests increased suddenly at about 13, 000Y.B.P. Subsequently, the benthonic foraminiferal fauna which live today in the shallow water of the Northwest Pacific coast appeared in the cores of the Japan Sea. These facts suggest that a remarkable inflow of the Oyashio current through the Tsugaru Straits into the Japan Sea began about 13, 000Y.B.P. The coiling direction of Globigerina pachyderma changed from sinistral to dextral approximately 8, 000Y.B.P. Then warm water planktonic foraminifera appeared in the cores, and the temperature of the surface water of the sea increased abruptly by 7-8°C.