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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
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NASA NTRS1987

U-238-U-234-Th-230-Th-232 systematics and the precise measurement of time over the past 500,000 years

A method is presented for the high-precision measurement of the Th-230 abundance in corals by isotope-dilution mass spectrometry using techniques developed by Chen and Wasserburg (1980, 1981) and Chen et al. (1986). It is shown that 6 x 10 to the 8th atoms of Th-230 can be measured to + or - 30 percent (2 sigma) and 2 x 10 to the 10th atoms of Th-230 to + or - 2 percent. The time over which useful age data on corals can be obtained ranges from a few years to about 500 ky, with the uncertainty in age ranging from 5 y for a 180-y-old coral, to 44 y for a 8294-y-old coral, to 1.1 ky for a 123.1-ky-old coral. Ages were determined with high analytical precision for several corals that grew during high sea-level stands about 120 ky ago, supporting the view that the dominant cause of Pleistocene climate change was Milankovitch forcing.

Edwards, R. Lawrence↗
NASA NTRS1987

Azimuthal dependence in the gravity field induced by recent and past cryospheric forcings

Present-day glacial activities and the current variability of the Antarctic ice volume can cause variations in the long-wavelength gravity field as a consequence of transient viscoelastic responses in the mantle. The azimuthal dependence of the secular variations of the gravitational potential are studied and it is found that the nonaxisymmetric contributions are more important for recent glacial retreats than for Pleistocene deglaciation. Changes in land-based ice covering Antarctica can be detected by monitoring satellite orbits and their sensitivity to variations in gravitational harmonic for degree l greater than 3. Resonances in satellite orbits may be useful for detecting these azimuthally-dependent gravity signals.

Yuen, David A.↗
NASA NTRS1988

Diapirs of the Mediterranean ridge: The tectonic regime of an incipient accreted terrane

The occurrence of diapirs in the Mediterranean ridge stems mostly from the massive deposition of salt and gypsum in the Mediterranean basin during the late Miocean. The diapiric emplacement of the evaporitic sequence is not obvious, because the mobilization of the salt beds and the initiation of the diapiric upward flow are constrained by the relatively shallow thickness of the Plio-Pleistocene sedimentary overburden and by the low heat flow that prevails in the eastern Mediterranean. The diapirs consist also of early Cretaceous shales as well as other gravitationally metastable strata which are less mobile than salt. Studies of subduction trenches and their surroundings show that shallow ridges occur seaward of the trenches in many places. The collisional motion between the African and the Eurasian plates would further enhance accretion of sediments in the Mediterranean ridge, which would attain subaerial exposure, and eventually would become a mountain range accreted to southern Europe. The numerous diapirs of salt and shales that occur in the ridge would be common features in the future accreted terrane, indicating an intermediate extensional phase in the tectonic history of the development of crustal growth.

Mart, Y.↗
NASA NTRS1988

Abrupt climate change and extinction events

There is a growing body of theoretical and empirical support for the concept of instabilities in the climate system, and indications that abrupt climate change may in some cases contribute to abrupt extinctions. Theoretical indications of instabilities can be found in a broad spectrum of climate models (energy balance models, a thermohaline model of deep-water circulation, atmospheric general circulation models, and coupled ocean-atmosphere models). Abrupt transitions can be of several types and affect the environment in different ways. There is increasing evidence for abrupt climate change in the geologic record and involves both interglacial-glacial scale transitions and the longer-term evolution of climate over the last 100 million years. Records from the Cenozoic clearly show that the long-term trend is characterized by numerous abrupt steps where the system appears to be rapidly moving to a new equilibrium state. The long-term trend probably is due to changes associated with plate tectonic processes, but the abrupt steps most likely reflect instabilities in the climate system as the slowly changing boundary conditions caused the climate to reach some threshold critical point. A more detailed analysis of abrupt steps comes from high-resolution studies of glacial-interglacial fluctuations in the Pleistocene. Comparison of climate transitions with the extinction record indicates that many climate and biotic transitions coincide. The Cretaceous-Tertiary extinction is not a candidate for an extinction event due to instabilities in the climate system. It is quite possible that more detailed comparisons and analysis will indicate some flaws in the climate instability-extinction hypothesis, but at present it appears to be a viable candidate as an alternate mechanism for causing abrupt environmental changes and extinctions.

Crowley, Thomas J.↗
NASA NTRS1988

New approach to the origin of the tektite in China

The tektites in China are distributed on the north part of Australia - Southeastern Asia strewfield of tektite: Leizhou Peninsula of Guangdong Province and Hainan Island, and located exactly at the boundary between Zanjiang Formation and Beihai Formation. A new hypothesis is suggested: During the end of Lower Pleistocene, a comet of special components from the outer part of the Solar System approached the Earth, and then it was captured by the Earth, when it came approximately to the Roche's limet. It was crushed into countless fragments, detritus and dusts, which rotated around the Earth, probably far above the Earth's atmosphere, as a cloud ring. Under the action of crushing energy they could be in the situation of liquid-melt drop in the almost vacuum circumstances and the flow and bubble structure were formed. During their rotation the climate became anomalous and the violet Fe-Si concentration were formed on the surface of sediments. After a rather short time of rotation the unstable ring was broken and the fragments impacted on the hard ground instantaneously.

Qin-Wen, Zhang↗
NASA NTRS1989

Uranium-series dated authigenic carbonates and Acheulian sites in southern Egypt

Field investigations of aggraded paleovalleys, which were identified in southern Egypt using SIR, are discussed. Acheulian artifacts were found in authigenic carbonate deposites along the edges of the paleovalleys. Uranium series dating of 25 carbonate samples shows that widespread carbonate deposition in the area occurred about 45, 141, and 212 thousand years ago. Analysis of the carbonate suggests that the deposition may be related to late Pleistocene humid climates that facilitated human settlement in the region.

Szabo, B. J.↗
NASA NTRS1989

Fluctuation history of Great Salt Lake, Utah, during the last 13,000 years, part 2

Great Salt Lake level fluctuations from 13,000 yr B.P. to the present were interpreted by examination of shoreline geomorphic features, shoreline deposits, archeologic sites, isotopic data, and palynologic data. After the conclusion of the Bonneville paleolake cycle, between 13,000 and 12,000 yr B.P. the lake regressed to levels low enough to deposit a littoral oxidized red bed stratum and a pelagic Glauber's salt layer. A late Pleistocene lake cycle occurred between 12,000 and 10,000 yr B.P. depositing several beaches, the highest reaching an altitude of about 4250 ft (1295.3 m). The lake regressed after 10,000 yr B.P., only to rise to 4230 ft (1289.2 m) between 9700 and 9400 yr B.P. and then gradually lower at least 15 ft (4.5 m) or more. Lake levels fluctuated between 4212 and 4180 ft (1284 and 1274 m) for the next 4000 years. A late Holocene lake cycle, constrained by radiocarbon ages between 3440 and 1400 yr B.P., is reported at a highest static level of 4221 ft (1286.5 m). After a lake level drop to altitudes ranging between 4210 and 4205 ft (1283.2 and 1281.6 m), a 4217 ft (1285.7 m) level was reached after 400 yr B.P. This level lowered to 4214 ft (1284.4 m) in the mid to late 1700 s A.D. The lake levels have since stabilized aroung a 4200 ft (1280 m) mean.

Murchison, Stuart B.↗
NASA NTRS1989

Late quaternary geomorphology of the Great Salt Lake region, Utah, and other hydrographically closed basins in the western United States: A summary of observations

Attributes of Quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts are discussed. Basin-floor and basin-closure morphometry have set limits on paleolake sizes; lake morphometry and basin drainage patterns have influenced lacustrine processes; and water and sediment loads have influenced basin neotectonics. Information regarding inundated, runoff-producing, and extra-basin spatial domains is acquired directly from the paleolake record, including the littoral morphostratigraphic record, and indirectly by reconstruction. Increasingly detailed hypotheses regarding Lake Bonneville, the largest late Pleistocene paleolake in the Great Basin, are subjects for further testing and refinement. Oscillating transgression of Lake Bonneville began about 28,000 yr B.P.; the highest stage occurred about 15,000 yr B.P., and termination occurred abruptly about 13,000 yr B.P. A final resurgence of perennial lakes probably occurred in many subbasins of the Great Basin between 11,000 and 10,000 yr B.P., when the highest stage of Great Salt Lake (successor to Lake Bonneville) developed the Gilbert shoreline. The highest post-Gilbert stage of Great Salt Lake, which has been one of the few permanent lakes in the Great Basin during Holocene time, probably occurred between 3,000 and 2,000 yr B.P.

Currey, Donald R.↗
NASA NTRS1989

Calculating climate attractor dimension from delta O-18 records by the Grassberger-Procaccia algorithm

The Grassberger-Procaccia method of calculating dimension from a time series is applied to 14 late Pleistocene delta O-18 records. A step-by-step sequence leading from data to the Grassberger-Procaccia dimension is outlined, and the problems encountered when dealing with observed (as opposed to theoretical) data are discussed; for the climatic proxy data these problems include situations where the time series is not very long, is noisy and/or smoothed, and is not sampled at a constant time interval. The delta O-18 records to be used are described, and the results are presented and compared with previously published dimension calculations. New dimension interpretations are assessed, and an example using a synthetic time series that illustrates the possible error due to inconsistencies in the time scale is analyzed.

Maasch, Kirk A.↗
NASA NTRS1990

Sensitivity of the equilibrium surface temperature of a GCM to systematic changes in atmospheric carbon dioxide

The equilibrium response of surface temperature to atmospheric CO2 concentration, for six values between 100 and 1000 ppm, is calculated from a series of GCM experiments. This response is nonlinear, showing greater sensitivity for lower values of CO2 than for the higher values. It is suggested that changes in CO2 concentration of a given magnitude (e.g., 100 ppm) played a larger role in the Pleistocene ice-age-type temperature variations than in causing global temperature changes due to anthropogenic increases.

Oglesby, Robert J.↗
NASA NTRS1990

A Solar-luminosity Model and Climate

Although the mechanisms of climatic change are not completely understood, the potential causes include changes in the Sun's luminosity. Solar activity in the form of sunspots, flares, proton events, and radiation fluctuations has displayed periodic tendencies. Two types of proxy climatic data that can be related to periodic solar activity are varved geologic formations and freshwater diatom deposits. A model for solar luminosity was developed by using the geometric progression of harmonic cycles that is evident in solar and geophysical data. The model assumes that variation in global energy input is a result of many periods of individual solar-luminosity variations. The 0.1-percent variation of the solar constant measured during the last sunspot cycle provided the basis for determining the amplitude of each luminosity cycle. Model output is a summation of the amplitudes of each cycle of a geometric progression of harmonic sine waves that are referenced to the 11-year average solar cycle. When the last eight cycles in Emiliani's oxygen-18 variations from deep-sea cores were standardized to the average length of glaciations during the Pleistocene (88,000 years), correlation coefficients with the model output ranged from 0.48 to 0.76. In order to calibrate the model to real time, model output was graphically compared to indirect records of glacial advances and retreats during the last 24,000 years and with sea-level rises during the Holocene. Carbon-14 production during the last millenium and elevations of the Great Salt Lake for the last 140 years demonstrate significant correlations with modeled luminosity. Major solar flares during the last 90 years match well with the time-calibrated model.

Perry, Charles A.↗
NASA NTRS1990

Alteration of basaltic glasses from north-central British Columbia, Canada

The process of palagonitization in basaltic glasses from Pleistocene subglacial volcanics in the north-central British Columbia, Canada, is examined on the basis of results obtained from samples from three volcanoes located in the Tuya Range of Cassiar mountains: Ash Mountain, Southern Tuya, and Tuya Butte. The compositional changes from glass to palogonite, in particular with respect to Al content are described. Results of this study suggests that palagonitization is an isovolumetric replacement process in the British Coumbia hyaloclastites, in which glass is replaced by amorphous colloidal palagonite; the process is explained by the precipitation of insoluble material as critical nuclei under the conditions of supersaturation in the near-glass environment.

Jercinovic, M. J.↗
NASA NTRS1990

Cosmogenic Be-10, Al-26, and He-3 in olivine from Maui lavas

This paper reports the presence of cosmogenic Be-10 and Al-26 in olivines from the Maui Haleakala basalts in which cosmogenic He-3 and Ne-21 were discovered. Based on production-rate calibrations in quartz crystals from late Pleistocene granite exposures in the Sierra Nevada, the Haleakala crater erosion rates derived from Be-10 and Al-26 concentrations agree within 10 percent and give a mean rate of 12 m/Myr, about 40 percent greater than the rate of 8.5 m/Myr previously derived from He-3 measurements. These results establish the feasibility of the simultaneous use of radioactive and stable cosmogenic nuclides for studies of exposure-ages and erosion-rates in basaltic and andesitic terrains.

Nishiizumi, K.↗
NASA NTRS1991

Airborne SAR determination of relative ages of Walker Valley moraines, eastern Sierra Nevada

A regional study of the distribution and elevations of Pleistocene moraines in the Andes requires a method of determining relative age from space. One of our primary objectives is to establish the relative chronology of major climatic events responsible for glaciation in the Andes and other regions that are difficult to access on the ground and where suitable material for absolute age determination is lacking. The sensitivity of radar to surface roughness makes it possible to develop a remotely-based relative dating technique for landforms for which surface age and roughness can be correlated. We are developing such a technique with Airborne Synthetic Aperture Radar (AIRSAR) imagery of the eastern Sierra Nevada where independent evidence is available for the ages and physical characteristics of moraines. The Sierra Nevada moraines are similar in form and environmental setting to Andean moraines that we have targeted for study during the pending Shuttle Imaging Radar-C (SIR-C) mission. SAR imagery is used to differentiate the ages of five moraine sequences of Walker Valley in the eastern Sierra Nevada. Other aspects of this investigation are briefly discussed.

Fox, A.↗
NASA NTRS1992

Glacial geomorphic evidence for a late climatic change on Mars

In a series of preliminary reports, we documented evidence of former glacial epochs on Mars. Apparent glacial landforms seemed to be concentrated primarily at middle to high southern latitudes. We now have additional evidence supporting the view that Martian glaciation appears to have been more extensive than previously recognized. The growth and collapse of ice sheets on Mars seems closely analogous to the growth and decline of Earth's great Pleistocene ice sheets. This implies that climate change was probably somewhat comparable on the two planets, although in the case of Mars the entire planet seems to have changed rapidly to a cold, dry present-day environment after the collapse of the ice sheets.

Kargel, J. S.↗
NASA NTRS1992

Amazonis and Utopia Planitiae: Martian Lacustrine basins

Amazonis and Utopia Planitiae are two large (greater than 10(exp 6) sq. km) basins on Mars having morphological features commonly associated with former lakes. The investigation of these areas is an extension of our previous paleolake studies in the Elysium basin. Using Viking images, we are searching for familiar geologic forms commonly associated with standing bodies of water on Earth. Like Elysium, the two basins exhibit terraces and lineations resembling shorelines, etched and infilled floors with channel-like sinuous markings in places, inflow channels along their borders, and other geomorphic indicators believed to be related to the presence of water and ice. In some areas these features are better displayed than in others where they may be very tenuous; their value as indicators can be justified only by their association with related features. Even though these postulated paleolakes are very young in the Martian stratigraphic sequence, their shoreline features are poorly preserved and they are probably much older than large Pleistocene lakes on Earth.

Scott, David H.↗
NASA NTRS1992

New evidence of lacustrine basins on Mars - Amazonis and Utopia Planitiae

Amazonis and Utopia Planitiae are two large basins on Mars that have morphologic features commonly associated with former standing bodies of water. Like Elysium, the basins exhibit terraces and lineations resembling shorelines, etched and infilled floors marked by sinuous channels in places, inflow channels along their borders, and other geomorphic indicators believed to be related to the presence of water and ice. Moreover, most of the shoreline features have consistent elevations of about -1000 m, which suggests that the bodies of water thought to have occupied the basins may once have been connected. Although the concept of large paleolakes in the northern lowlands of Mars might be expanded to include inland seas, it is still premature to advance this hypothesis at the present stage of investigation. Even though these postulated paleolakes are very young in the Martian stratigraphic sequence, they are probably much older than large Pleistocene lakes on earth, and their shoreline features are less well preserved.

Scott, David H.↗
NASA NTRS1992

Ice ages and geomagnetic reversals

There have been speculations on the relationship between climatic cooling and polarity reversals of the earth's magnetic field during the Pleistocene. Two of the common criticisms on this relationship have been the reality of these short duration geomagnetic events and the accuracy of their dates. Champion et al. (1988) have reviewed recent progress in this area. They identified a total of 10 short-duration polarity events in the last 1 Ma and 6 of these events have been found in volcanic rocks, which also have K-Ar dates. Supposing that the speculated relationship between climatic cooling and geomagnetic reversals actually exist, two mechanisms that assume climatic cooling causes short period magnetic reversals will be investigated. These two methods are core-mantle boundary topography and transfer of the rotational energy to the core.

Wu, Patrick↗