Physical Sciences and Mathematics Commons^™

Geologic And Tectonic Setting Of The Mark Area, R. S. Detrick, P. J. Fox, N. Schulz, R. Pockalny, L. Kong, Larry A. Mayer, W.B. F. Ryan

Affiliate Scholarship

No abstract provided.

Cenozoic Paleoceanography 1986: An Introduction, W. H. Berger, Larry A. Mayer

Affiliate Scholarship

New developments in Cenozoic paleoceanography include the application of climate models and atmospheric general circulation models to questions of climate reconstruction, the refinement of conceptual models for interpretation of the carbon isotope record in terms of carbon mass balance, paleocirculation, paleoproductivity, and the regional mapping of paleoceanographic events by acoustic stratigraphy. Sea level change emerges as a master variable to which changes in the ocean environment must be traced in many cases, and tests of the onlap-offlap paradigm therefore are of crucial importance.

Gamma-Ray Observations Of The Crab Region Using A Coded-Aperture Telescope, Mark L. Mcconnell, P. P. Dunphy, D J. Forrest, E. L. Chupp, A Owens

Physics & Astronomy

The region of the Galactic anticenter, including the Crab Nebula, was observed during a balloon flight of the University of New Hampshire Directional Gamma-Ray Telescope employing the coded-aperture imaging technique to image celestial gamma-radiation between 160 keV and 9.3 MeV. The background systematics are treated with a simple and relatively straightforward correction procedure. The results demonstrate that the coded-aperture procedure is a viable approach for imaging not only point sources of radiation, but also extended sources of emission. The results for the Crab's photon spectrum are consistent with a power-law spectrum. Upper limits on the flux levels of line emission …

On-Line Sea Beam Acoustic Imaging, Christian De Moustier, F V. Pavlicek

Center for Coastal and Ocean Mapping

This paper describes a system designed and built at the Marine Physical Laboratory of the Scripps Institution of Oceanography to produce acoustic images of the seafloor on-line with a Sea Beammultibeam echo-sounder. This system uses a stand alone interface between the Sea Beam system and a grey-scale line-scan recorder. The interface is built around a Motorola 68000 microprocessor and has digitizing capabilities. It digitizes the detected echo signals from each of the 16 preformed beams inside the Sea Beam echo processor as well as the roll information given by the ship's vertical reference. Theacoustic data are then roll compensated and …

Static Magnetic Field Models Consistent With Nearly Isotropic Plasma Pressure, Harlan E. Spence, Margaret G. Kivelson, Raymond J. Walker

Physics & Astronomy

Using the empirical magnetospheric magnetic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By “inverting” the magnetic field, we determine what distributions of an anisotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohydrostatic equilibrium condition, J × B = ∇ · P. The TU model, parameterized for different levels of geomagnetic activity by the Kp index, provided the magnetic field values from which J × B was numerically evaluated. A best fit solution was found that minimized the …

Phytoplankton Production In The Delaware Estuary: Temporal And Spatial Variation., Jonathan Pennock

School of Marine Science and Ocean Engineering

ABSTRACT:

Phytoplankton production in the Delaware Estuary (USA) was measured over several seasonal cycles (1980-1985). Seasonal variability in daily area1 production (JP; g C m-2 d-l) was dlrectly related to chlorophyll concentrations in the upper estuary, ranging from a maximum of 1.1 g C m-' d-' In summer to a minlmum of d-l) dunng summer in the presence of low phytoplankton biomass (2 to 10 kg Chl I-'), and in mid-estuary [2.6 g C d-l) during the spring diatom bloom (50 to 60 yg Chll-l). Desplte the occurrence of maximum nutnent concentrations in the freshwater region, highest JP and 90 …

The Average Magnetic Field Draping And Consistent Plasma Properties Of The Venus Magnetotail, David J. Mccomas, Harlan E. Spence, C. T. Russell, M. A. Saunders

Physics & Astronomy

A new technique has been developed to determine the average structure of the Venus magnetotail (in the range from −8 R_v to −12 R_v) from the Pioneer Venus magnetometer observations. The spacecraft position with respect to the cross-tail current sheet is determined from an observed relationship between the field-draping angle and the magnitude of the field referenced to its value in the nearby magnetosheath. This allows us statistically to remove the effects of tail flapping and variability of draping for the first time and thus to map the average field configuration in the Venus tail. From this …

Bathymetric Artifacts In Sea Beam Data: How To Recognize Them And What Causes Them, Christian De Moustier, Martin C. Kleinrock

Center for Coastal and Ocean Mapping

Sea Beam multibeam bathymetric data have greatly advanced understanding of the deep seafloor. However, several types of bathymetric artifacts have been identified in Sea Beam's contoured output. Surveys with many overlapping swaths and digital recording on magnetic tape of Sea Beam's 16 acoustic returns made it possible to evaluate actual system performance. The artifacts are not due to the contouring algorithm used. Rather, they result from errors in echo detection and processing. These errors are due to internal factors such as side lobe interference, bottom-tracking gate malfunctions, or external interference from other sound sources (e.g., 3.5 kHz echo sounders or …

Beyond Bathymetry: Mapping Acoustic Backscattering From The Deep Seafloor With Sea Beam, Christian De Moustier

Center for Coastal and Ocean Mapping

In its standard mode of operation, the multibeam echosounder Sea Beam produces high resolution bathymetric contour charts of the seafloor surveyed. However, additional information about the nature of the seafloor can be extracted from the structure of the echo signals received by the system. Such signals have been recorded digitally over a variety of seafloor environments for which independent observations from bottom photographs or sidescan sonars were available. An attempt is made to relate the statistical properties of the bottom‐backscattered sound field to the independently observed geologicalcharacteristics of the seafloor surveyed. Acoustic boundary mapping over flat areas is achieved by …

Seismic Modelling And Paleoceanography At Dsdp Site 574, Larry A. Mayer, Tom H. Shipley, Fritz Theyer, Roy H. Wilkens, Edward L. Winterer

Affiliate Scholarship

The analysis of high-resolution watergun seismic profiles collected in support of DSDP Leg 85 drilling reveals sev eral major, regionally traceable reflectors that can be correlated over more than 360,000 km2 in the central equatorial Pacific. Synthetic seismograms generated from shipboard physical property measurements (carefully corrected to in situ values) for DSDP Site 574 show excellent agreement with the field records; the agreement suggests that the traveltime to-depth conversion is accurate and permits the precise (± 5 m) location of reflectors in the cored section. The reflectors can be dated (±0.5 Ma) as follows: Orange, 21.5 to 22.5 Ma; Yellow, …

Initial Reports Of The Deep Sea Drilling Project, Vol. 85, Larry A. Mayer, Fritz Theyer, John A. Barron, Dean A. Dunn, Tim Handyside, Scott Hills, Ian Jarvis, Catherine A. Nagrini, Nicklas G. Pisias, Annick Pujos, Tsunemasa Saito, Paul Stout, Ellen Thomas, Norbert Weinreich, Roy H. Wilkens

Affiliate Scholarship

Covering Leg 85 of the cruises of the Drilling Vessel Glomar Challenger Los Angeles, California, to Honolulu, Hawaii March-April 1982.

Includes six chapters:

1. INTRODUCTION: BACKGROUND AND EXPLANATORY NOTES, DEEP SEA DRILLING PROJECT LEG 85, CENTRAL EQUATORIAL PACIFIC

2. SITE 571

3. SITE 572

4. SITE 573

5. SITE 574

6. SITE 575

The Equatorial Pacific High-Productivity Belt: Elements For A Synthesis Of Deep Sea Drilling Project Leg 85 Resultspaleoceanography, Fritz Theyer, Larry A. Mayer, John A. Barron, Ellen Thomas

Affiliate Scholarship

Leg 85 of the Deep Sea Drilling Project operated in the eastern central Pacific in the region of the equatorial highproductivity belt. We recovered uppermost Eocene to Quaternary reference sections amenable to fine-scale stratigraphic and paleoceanographic research, using primarily the hydraulic piston corer. Four sites (572 to 575) were drilled along an east-west (about 114 to 133°W) and north-south (about 0.5 to 6°N) transect across the equatorial belt. At Site 572 an apparently complete lower middle Miocene to Quaternary sequence was recovered: the sediment sections are dominantly siliceous-calcareous oozes and chalks, and sediment accumulation rates were high (30 to 60 …

Physical Properties Of Sediment Recovered On Deep Sea Drilling Project Leg 68 With The Hydraulic Piston Corer, Larry A. Mayer

Affiliate Scholarship

No abstract provided.

Erosion And Deposition In Interplain Channels Of The Maury Channel System, P. Lonsdale, C. D. Hollister, Larry A. Mayer

Affiliate Scholarship

Large turbidity currents originating on the insular margin of southern lceland have flowed clown a 2 500 km-long pathway comprising rise valleys, unchanneled plains and segments of erosional and depositional deep-sea channels that are collectively called the Maury Channel system. Two steep interplain reaches of the channel have been eut up to 100 m through volcanogenic turbidites of probable La te Pleistocene age. Near-bottom observations with side-scan sonars and profllers across the upper channels (at 59°24'N, 18°50'W, 2 750 m depth) and at the lower interplain channel (around 56°23'N, 24°25'W, 3 340 m depth) defmed their structure and morphology. The …

Near-Bottom Seismic Profiling: High Lateral Variability, Anomalous Amplitudes, And Estimates Of Attenuation, R. C. Tyce, Larry A. Mayer, F. N. Spiess

Affiliate Scholarship

For almost a decade the Marine Physical Laboratory of Scripps Institution of Oceanography has been conducting near‐bottom geophysical surveys involving quantitative seismic profiling. Operating initially at 4 kHz and more recently at 6 kHz, this system has provided a wealth of fine scale quantitative data on the acoustic properties of ocean sediments. Over lateral distances of a few meters, 7‐dB changes in overall reflected energy as well as 10‐dB changes from individual reflectors have been observed. Anomalously high amplitudes from deep reflectors have been commonly observed, suggesting that multilayer interference is prevalent in records from such pulsed cw profilers. This …

The Origin Of Fine Scale Acoustic Stratigraphy In Deep-Sea Carbonates, Larry A. Mayer

Affiliate Scholarship

In this paper we investigate the origin and geologic significance of the closely spaced high-frequency subbottom acoustic reflectors characteristic of pelagic carbonates. A detailed survey was conducted of a small area in the equatorial Pacific with the Marine Physical Laboratory's Deep-Tow instrument package, providing high-resolution 4-kHz profiles and precise positioning of core samples. The cores were sampled at closely spaced intervals for sound velocity and saturated bulk density. Acoustic impedances were calculated, and a reflection coefficient log determined for the upper 10 m of the sediment column. The reflection coefficient log revealed no interfaces with large reflection coefficients that correlated …

Distribution Of Carbonate In Surface Sediments Of The Pacific Ocean, W. H. Berger, Charles Adelseck, Larry A. Mayer

Affiliate Scholarship

The distribution of carbonate on the floor of the Pacific has been remapped on the basis of 1313 points from 80 references stored in the World Ocean Sediment Data Bank of Scripps Institution of Oceanography. Percent distribution maps and carbonate versus depth diagrams generally agree with previously published information and reflect the major controlling factors of carbonate sedimentation (depth, hydrography, fertility, and sedimentary processes). While carbonate distributions are of limited use in attempting to construct dissolution profiles, major trends are identifiable. In particular, the degree of lowering of the equatorial calcite compensation depth (CCD) together with an estimate of the …