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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
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 NTRS1989

Geological and geochemical record of 3400-million-year-old terrestrial meteorite impacts

Beds of sand-sized spherules in the 3400-million-year-old Fig Tree Group, Barberton Greenstone belt, South Africa, formed by the fall of quenched liquid silicate droplets into a range of shallow- to deep-water depositional environments. The regional extent of the layers, their compositional complexity, and lack of included volcanic debris suggest that they are not products of volcanic activity. The layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions. Geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt, komatiite, and CI carbonaceous chondrite. The spherules are thought to be the products of large meteorite impacts on the Archean earth.

Lowe, Donald R.↗
NASA NTRS1988

Late Pleistocene variations in Antarctica sea ice. I - Effect of orbital isolation changes. II - Effect of interhemispheric deep-ocean heat exchange

A dynamic-thermodynamic sea-ice model is presently used to ascertain the effects of orbitally-induced insolation changes on Antarctic sea-ice cover; the results thus obtained are compared with modified CLIMAP reconstructions of sea-ice 18,000 years ago. The minor influence exerted by insolation on Pleistocene sea-ice distributions is attributable to a number of factors. In the second part of this investigation, variations in the production of warm North Atlantic Deep Water are proposed as a mechanism constituting the linkage between climate fluctuations in the Northern and Southern hemispheres during the Pleistocene; this hypothesis is tested by examining the sensitivity of the dynamic-thermodynamic model for Antarctic sea-ice changes in vertical ocean heat flux, and comparing the simulations with modified CLIMAP sea-ice maps for 18,000 years ago.

Crowley, Thomas J.↗
NASA NTRS1991

Biological control of surface temperature in the Arabian Sea

In the Arabian Sea, the southwest monsoon promotes seasonal upwelling of deep water, which supplies nutrients to the surface layer and leads to a marked increase in phytoplankton growth. Remotely sensed data on ocean color are used here to show that the resulting distribution of phytoplankton exerts a controlling influence on the seasonal evolution of sea surface temperature. This results in a corresponding modification of ocean-atmosphere heat exchange on regional and seasonal scales. It is shown that this biological mechanism may provide an important regulating influence on ocean-atmosphere interactions.

Sathyendranath, Shubha↗
NASA NTRS1991

The fossil record of evolution: Data on diversification and extinction

Understanding of the evolution of complex life, and of the roles that changing terrestrial and extraterrestrial environments played in life's history, is dependent upon synthetic knowledge of the fossil record. Paleontologists have been describing fossils for more that two centuries. However, much of this information is dispersed in monographs and journal articles published throughout the world. Over the past several years, this literature was surveyed, and a data base on times of origination and extinction of fossil genera was compiled. The data base, which now holds approximately 32,000 genera, covers all taxonomic groups of marine animals, incorporates the most recent taxonomic assignments, and uses a detailed global time framework that can resolve originations and extinctions to intervals averaging three million years in duration. These data can be used to compile patterns of global biodiversity, measure rates of taxic evolution, and test hypotheses concerning adaptive radiations, mass extinctions, etc. Thus far, considerable effort was devoted to using the data to test the hypothesis of periodicity of mass extinction. Rates of extinction measured from the data base have also been used to calibrate models of evolutionary radiations in marine environments. It was observed that new groups, or clades of animals (i.e., orders and classes) tend to reach appreciable diversity first in nearshore environments and then to radiate in more offshore environments; during decline, these clades may disappear from the nearshore while persisting in offshore, deep water habitats. These observations have led to suggestions that there is something special about stressful or perturbed environments that promotes the evolution of novel kinds of animals that can rapidly replace their predecessors. The numerical model that is being investigated to study this phenomenon treats environments along onshore-offshore gradients as if they were discrete habitats. Other aspects of this investigation are presented.

Sepkoski, J. J., Jr.↗
NASA NTRS1991

The dependence of wind stress on wave height and wind speed

Three near-neutral boundary layer data sets were investigated with the aim of finding a dependence of wind stress on both wind speed and significant wave height. The data set most representative of open-ocean wave height, wind speed, and momentum flux conditions, was selected and analyzed by means of the least-squares method to produce a new parameterization for the wind stress as a function of both wind speed and significant wave height. This study shows that the wind stress, and consequently the drag coefficient, decreases with increasing wave height for a fixed wind speed. The study also shows that the curvature of the wind profile decreases with increasing wave height and that the C(DN) = A + BU-bar(10) form for the drag coefficient parameterization is inadequate. A drag coefficient that applies to both smooth and rough flows is proposed. These results are more applicable for open-ocean deep-water conditions and less applicable for sheltered, closed, shallow water sites.

Blake, Reginald A.↗
NASA NTRS1993

Elemental abundance anomalies in the late Cenomanian extinction interval - A search for the source(s)

Measurements of elemental abundances by neutron activation methods across the Cenomanian-Turonian extinction interval in samples collected from 16 sites in the Western Interior Basin of North America from 12 widely separated locations around the globe, including six ODP/DSDP sites, are reported. In most Western Interior Basin sites, in Colombia, and in Western Europe, two closely spaced elemental abundance peaks occur in the upper Cenomanian (about 92 m.y.), spanning the ammonite zones of Sciponoceras gracile through Neocardioceras juddii. Elements with anomalously high concentrations include Sc, Ti, V, Cr, Mn, Co, Ni, Ir, Pt, and Au. The lower peak coincides with the disappearance (extinction) of the foraminifer Rotalipora cushmani. In North American sections R. greenhornensis also disappears at or just below this horizon, but in Europe it disappears considerably earlier than R. cushmani. Although the weak geochemical signal from comet impact(s) could be masked by the strong terrestrial-like overprint, these anomalies more likely resulted in the large late Cenomanian through early Turonian eustatic rise and deep-water opening of the South Atlantic.

Orth, Charles J.↗
NASA NTRS1993

Underwater hydrophone location survey

The Atlantic Undersea Test and Evaluation Center (AUTEC) is a U.S. Navy test range located on Andros Island, Bahamas, and a Division of the Naval Undersea Warfare Center (NUWC), Newport, RI. The Headquarters of AUTEC is located at a facility in West Palm Beach, FL. AUTEC's primary mission is to provide the U.S. Navy with a deep-water test and evaluation facility for making underwater acoustic measurements, testing and calibrating sonars, and providing accurate underwater, surface, and in-air tracking data on surface ships, submarines, aircraft, and weapon systems. Many of these programs are in support of Antisubmarine Warfare (ASW), undersea research and development programs, and Fleet assessment and operational readiness trials. Most tests conducted at AUTEC require precise underwater tracking (plus or minus 3 yards) of multiple acoustic signals emitted with the correct waveshape and repetition criteria from either a surface craft or underwater vehicle.

Cecil, Jack B.↗
NASA NTRS1994

Graphical programming: A systems approach for telerobotic servicing of space assets

Satellite servicing is in many ways analogous to subsea robotic servicing in the late 1970's. A cost effective, reliable, telerobotic capability had to be demonstrated before the oil companies invested money in deep water robot serviceable production facilities. In the same sense, aeronautic engineers will not design satellites for telerobotic servicing until such a quantifiable capability has been demonstrated. New space servicing systems will be markedly different than existing space robot systems. Past space manipulator systems, including the Space Shuttle's robot arm, have used master/slave technologies with poor fidelity, slow operating speeds and most importantly, in-orbit human operators. In contrast, new systems will be capable of precision operations, conducted at higher rates of speed, and be commanded via ground-control communication links. Challenge presented by this environment include achieving a mandated level of robustness and dependability, radiation hardening, minimum weight and power consumption, and a system which accommodates the inherent communication delay between the ground station and the satellite. There is also a need for a user interface which is easy to use, ensures collision free motions, and is capable of adjusting to an unknown workcell (for repair operations the condition of the satellite may not be known in advance). This paper describes the novel technologies required to deliver such a capability.

Pinkerton, James T.↗
NASA NTRS1994

Ocean response to surface heat anomalies

An ocean general circulation model (OGCM) is used to study the response of ocean heat and mass transport to positive and negative heat flux anomalies at the ocean surface. As expected, tropical and low-latitude mixed layers respond rapidly (e-folding time about 50-70 years) to external forcing, while the response of the high-latitude mixed layer, especially the Southern Ocean and northern North Atlantic, is very slow (e-folding time greater than 300 yr). The overall response is faster for negative than positive heat flux anomaly at the surface. The meridional heat transport changes by 15% in the first 50 yr in the southern high latitudes. Surprisingly, for the next 400-500 yr the change is very small. The analysis shows that the meridional mass transport intensifies in response to a negative surface heat flux anomaly but weakens in response to a positive heat flux anomaly. For example, at model year 100 the North Atlantic Deep Water (NADW) is reduced from about 18 Sv to about 10 Sv for the positive heat flux experiment but increased to about 26 Sv for the negative heat flux experiment.

Jiang, Xingjian↗
NASA NTRS1999

A Global Ocean Tide Model From TOPEX/POSEIDON Altimetry: GOT99.2

Goddard Ocean Tide model GOT99.2 is a new solution for the amplitudes and phases of the global oceanic tides, based on over six years of sea-surface height measurements by the TOPEX/POSEIDON satellite altimeter. Comparison with deep-ocean tide-gauge measurements show that this new tidal solution is an improvement over previous global models, with accuracies for the main semidiurnal lunar constituent M2 now below 1.5 cm (deep water only). The new solution benefits from use of prior hydrodynamic models, several in shallow and inland seas as well as the global finite-element model FES94.1. This report describes some of the data processing details involved in handling the altimetry, and it provides a comprehensive set of global cotidal charts of the resulting solutions. Various derived tidal charts are also provided, including tidal loading deformation charts, tidal gravimetric charts, and tidal current velocity (or transport) charts. Finally, low-degree spherical harmonic coefficients are computed by numerical quadrature and are tabulated for the major short-period tides; these are useful for a variety of geodetic and geophysical purposes, especially in combination with similar estimates from satellite laser ranging.

Ray, Richard D.↗
NASA NTRS1997

Climate Variability in the Amundsen and Bellingshausen Seas

Satellite data reveal a 20% decline in sea ice extent in the Amundsen and Bellingshausen Seas in the two decades following 1973. This change is negatively correlated with surface air temperatures on the west side of the Antarctic Peninsula, which have increased -0.5 C / decade- since the mid-1940s, The recession was strongest during summer, when monthly average minima in 1991-92 removed much of the incipient multiyear ice over the continental shelf. This would have lowered the regional-mean ice thickness, impacting snow ice formation, brine production, and vertical heat flux. The northern ice edge contracted by 1 deg of latitude in all seasons from 1973-79 to 1987-93, returning toward mean conditions in 1993-95. The decline included multiyear cycles of several years in length, superimposed on high interannual variability. A review of atmospheric forcing shows winds consistent with mean and extreme ice extents, and suggests links to larger-scale circulation changes in the South Pacific. Historical ocean measurements are sparse in this sector, but mixed-layer depths and upper pycnoclines beneath the sea ice resemble those in the Weddell Sea. Weaker surface currents or changes in the upwelling of Circumpolar Deep Water on the continental shelf could have contributed to the anomaly persistence.

Jacobs, Stanley S.↗
NASA NTRS2000

Life in Extreme Environments Research #2

The goal of this project was to collect suspended particles and microbes for spectral analysis from deep water around hydrothermal vent study sites on the Juan de Fuca Ridge. To accomplish this, the McLane WTS 6-24-47 Sampler (McLane Research Laboratories, Falmouth, MA) was used. The WTS sampler is a programmable unit which is able to collect individual samples across twenty-four 47mm diameter filters at predetermined intervals and duration. Although only one successful deployment was needed, a maximum of three 3 deployments were possible (deployment opportunities were limited by the number of battery packs available). The initial behavior of the WTS and the ship's schedule both indicated that three deployments would be possible. However, it was revealed upon recovery after the first deployment that the WTS failed as it was preparing to collect its first sample.

Fisher, Charles R.↗
NASA NTRS2000

Southern Ocean Response to NADW Changes

The possibility of North Atlantic Deep Water (NADW) changes in both past and future climates has raised the issue of how the Southern Ocean would respond. Recent experiments with the GISS coupled atmosphere-ocean model have shown that a "bipolar see-saw" between NADW production and Antarctic Bottom Water (AABW) production in the Weddell Sea can occur in conjunction with freshening of the North Atlantic. However, this effect operates not through a slow ocean response but via a rapid atmospheric mechanism. As NADW reduces, colder temperatures in the North Atlantic, and Northern Hemisphere in general, are associated with higher surface pressure (increased atmospheric mass). Reduced mass in the Southern Hemisphere occurs in response, with lower pressure over the South Pole (an EOF #1 effect, the "high phase" of the Antarctic Oscillation).The lower pressure is associated with stronger west winds that generate an intensified Antarctic Circumpolar Current (ACC), which leads to longitudinal heat divergence in the South Atlantic (and heat convergence in the Southern Indian Ocean). Colder temperatures in the Weddell Sea region lead to sea ice growth, increased salinity and surface water density, and greater Weddell Sea Bottom Water production. Increased poleward transport of heat occurs in the South Atlantic in conjunction with increased bottom water production, but its convergence at high latitudes is not sufficient to offset the longitudinal heat divergence due to the intensified ACC. The colder temperatures at high latitudes in the South Atlantic increase the latitudinal temperature gradient, baroclinic instability, eddy energy and eddy poleward transport of momentum, helping to maintain the lower pressure over the pole in an interactive manner. The heat flux convergence in the Indian Ocean provides a warming tendency in that region, and overall global production of AABW remains unchanged. These results have implications for the interpretation of the ice core records of the last deglaciation, but may also be relevant for changes during the Holocene and perhaps even in response to increased CO2 forcing,

Rind, David↗
NASA NTRS2002

Carbonate Platform Development and Stromatolite Morphogenesis: Constraints on Environmental and Biological Evolution

Work this past year has focused on the globally significant events of faunal turnover, tectonic reorganization, and biogeochemical change that closely coincided with the Precambrian-Cambrian boundary in the Sultanate oilman. Higher temporal and chronostratigraphic resolution are required in order to answer this question. Stratigraphic sections must contain fossils, volcanic rocks, and abundant carbonates with little or no diagenetic overprint. The Ara Group of the South Oman Salt Basin presents such a succession - with carbonate rocks tightly enclosed in a protective envelope of impermeable halite, these rocks have likely never exchanged with younger fluids. Our work has had two thrusts. The first pertains to the geochemistry of the Athel Formation, a deep water deposit formed at the Precambrian-Cambrian boundary which contains unique records of ocean anoxia for that time interval. This unit is important because it will enable tighter focus on the links which existed between global biogeochemical events and episodes of faunal extinction and radiation. The second direction involves a comparison of terminal Proterozoic thrombolites between Oman (subsurface) and Namibia (outcrop). These thrombolites are important not only as significant deposits of ancient microbial communities, but because they formed the key substrate for growth of the oldest calcified metazoans - Cloudina and Namacalathus.

Grotzinger, John P.↗
NASA NTRS1999

Ocean View

Analytical Spectral Devices was able to commercialize the "engine" of SeaSpec. The Dual CCD developed for SeaSpec is used in our FieldSpecO Dual UV/VNIR/CCD. This product is very popular for coastal research. It allows for a small suitcase sized spectrometer to be placed in a boat and the attached fiber optic cable can be lowered 30 feet below the surface allowing researchers to perform the same studies as SeaSpec just not at the deep-water depths. Most of the people who inquire about SeaSpec end up purchasing a FieldSpec Dual CCD.SeaSpec was designed to withstand harsh marine environments and depths up to 200 m. While it meets these requirements it is the only instrument of its kind and we consider it a prototype. The first version was released in April 1997. It was tested, we made modification and returned the product in March 1998.

Source record↗
NASA NTRS2002

Tides and Modern Geodesy

In modem high-precision geodesy, and especially in modem space geodesy, every measurement that one makes contains tidal signals. Generally these signals are considered noise and must somehow be eliminated. The stringent requirements of the latest space geodetic missions place severe demands on tidal models. On the other hand, these missions provide the strongest data for improving tidal models. In particular, TOPEX/POSEIDON altimetry and LAGEOS laser ranging have improved models to such an extent that new geophysical information about the ocean and the solid Earth are coming to light. Presumably GRACE intersatellite ranging data will also add to this information. This paper discusses several of these new geophysical results, with special emphasis given to the dissipation of tidal energy. Strong constraints have recently been placed on the partitioning of energy dissipation among the ocean, atmosphere, and solid earth and between the deep and shallow ocean. The dissipation in deep water is associated with internal tides and has potentially important implications for understanding the ocean's thermohaline circulation.

Ray, Richard D.↗