Naval Oceanography Office

Research Article| March 01, 1986 Are oceanic fracture zones locked and strong or weak?: New evidence for volcanic activity and weakness Allen Lowrie; Allen Lowrie 1Ocean Projects Division, NAVOCEANO, NASA Space Technology Laboratory Station, Mississippi 39529 Search for other works by this author on: GSW Google Scholar Christian Smoot; Christian Smoot 2Bathymetry Division, NAVOCEANO, NASA Space Technology Laboratory Station, Mississippi 39529 Search for other works by this author on: GSW Google Scholar Rodey Batiza Rodey Batiza 3Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130 Search for other works by this author on: GSW Google Scholar Author and Article Information Allen Lowrie 1Ocean Projects Division, NAVOCEANO, NASA Space Technology Laboratory Station, Mississippi 39529 Christian Smoot 2Bathymetry Division, NAVOCEANO, NASA Space Technology Laboratory Station, Mississippi 39529 Rodey Batiza 3Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (3): 242–245. https://doi.org/10.1130/0091-7613(1986)14<242:AOFZLA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Allen Lowrie, Christian Smoot, Rodey Batiza; Are oceanic fracture zones locked and strong or weak?: New evidence for volcanic activity and weakness. Geology 1986;; 14 (3): 242–245. doi: https://doi.org/10.1130/0091-7613(1986)14<242:AOFZLA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Traditionally, oceanic fracture zones and other lithospheric and crustal faults have been viewed as zones of weakness that are vulnerable to seismic and volcanic activity. This notion has recently been questioned on the basis of evidence showing that initial depth offsets (scarp height) across some Pacific fracture zones are preserved even after ∼100 m.y. of differential subsidence. This evidence suggests that some parts of oceanic fracture zones are locked shortly) after they drift away from ridge-transform intersections. Because the fracture zones seem to be strong welds, differential cooling stresses cause flexure in the lithosphere on both sides of the fracture. In this paper we briefly review the seemingly contradictory evidence for the thermomechanical characteristics of oceanic fracture zones (locked and strong vs. slipped and weak) and present new evidence indicating that parts of some fracture zones are volcanically active. Volcanism is an indication of relative weakness because strain and failure are required to open volcanic conduits. This and other evidence for the inherent weakness of fracture zones can be reconciled with evidence for strength if different segments of fracture zones exhibit contrasting thermomechanical behavior. More data are needed to determine whether this is so and whether there are systematic patterns of distribution for weak and strong parts of individual fracture zones. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Numerical solutions for the impulsively started spin-up of a thermally stratified fluid in a cylinder with an insulating side wall are presented. Previous experimental and numerical work on stratified spin-up had not provided a comprehensive and accurate set of flow-field data. Further, comparisons of this work with theory showed, in general, a substantial discrepancy. The theory was scaled using the homogeneous meridional-flow spin-up time scale and thus viscous-diffusion effects were excluded from the interior. It was anticipated that these effects could only be significant on the larger viscous-diffusion time scale. However, the comparisons with theory showed a faster rate of decay for the measurements even over the shorter meridional-flow spin-up time scale. Previous workers had suggested a number of explanations but the cause of the discrepancy was still unresolved. To provide data to extend the previous work, a numerical model was used. The model was first checked against accurate experimental measurements of stratified spin-up made using a laser-Doppler velocimeter. New accurate results which cover ranges of Ekman number (5·92 × 10 −4 ≤ E ≤ 7·24 × 10 −4 ), Rossby number (0·019 ≤ ε ≤ 0·220), stratification parameter (0·0 ≤ Sa −1 ≤ 1·03), and Prandtl number (5·68 ≤ σ ≤ 7·10) are presented. These results show the radial and vertical structure of the decaying azimuthal and meridional flows. The inertial–internal gravity oscillations excited by the impulsive spin-up are clearly seen. By making use of conclusions from the previous work and the results presented in this paper, it is established that viscous diffusion in the interior is the cause of the discrepancy with theory. Stratification causes the meridional spin-up flow to be confined closer to the boundary disks. This results in non-uniform spin-up of the interior and hence flow gradients in the interior. These gradients introduce viscous diffusion into the interior sooner than anticipated by the theory. A previous suggestion that the faster decay rate is due to angular momentum being injected into the interior from an oscillation of the meridional corner-jet flow is shown to be untenable.

Harmful algae blooms (HAB) in coastal marine environments are increasing in number and duration, pressuring local resource managers to implement mitigation solutions to protect human and ecosystem health. However, insufficient spatial and temporal observations create uninformed management decisions. In order to better detect and map blooms, as well as the environmental conditions responsible for their formation, long-term, unattended observation platforms are desired. In this article, we describe a new cost-efficient, autonomous, mobile platform capable of accepting several sensors that can be used to monitor harmful algae blooms in near real-time. The Navocean autonomous sail-powered surface vehicle is deployable by a single person from shore, capable of waypoint navigation in shallow and deep waters, and powered completely by renewable energy. We present results from three surveys of the Florida Red Tide harmful algae bloom (Karenia brevis) of 2017-2018. The vessel made significant progress towards waypoints regardless of wind conditions while underway measurements revealed patches of elevated chl. a likely attributable to the K. brevis blooms as based on ancillary measurements. Measurements of colored dissolved organic matter (CDOM) and turbidity provided an environmental context for the blooms. While the autonomous sailboat directly adds to our phytoplankton/HAB monitoring capabilities, the package may also help to ground-truth satellite measurements of HABs if careful validation measurements are performed. Finally, several other pending and future use cases for coastal and inland monitoring are discussed. To our knowledge, this is the first demonstration of a sail-driven vessel used for coastal HAB monitoring.

Both breakwater distance from the shoreline and the gap between successive breakwaters are shown in a model study to be important factors in determining the amount of sand that can be entrapped by an offshore breakwater. Using an experimentalist's approach, this model study examines the effect of different gap spacings between successive breakwater for several cases that vary breakwater distance from the original shoreline. The purpose of the experiment was to quantify the effect of different spacings on the sand volume entrapped in the sheltered area of a breakwater. Experimental data are compared with available field and model studies in dimensionless form, and a relationship between the amount of sand accumulated in the sheltered area and the distance of the breakwater from the shoreline is given.

The Naval Oceanographic Office (NAVOCEANO) High Performance Computing (HPC) Major Shared Resource Center (MSRC) recently reengineered the existing mass storage system serving its high-performance compute platforms. The purpose was to provide significantly improved file system availability, to refresh the technology and the architectural design, and to position the MSRC to incorporate emerging technologies such as Storage Area Networks (SANs). The resultant configuration utilizes two SUN Enterprise 10000s (E10K) with 3 TB of switched Fibre Channel Disk Arrays and the latest generation of tape devices. The theoretical peak system capacity is in excess of 2 Terabytes (TB) per day, with management of up to 1 PetaBytes (PB) of storage and an aggregate external network throughput of 220 Megabytes (MB) per second. This paper discusses the technologies and considerations used in the design of the MSRC Resilient Mass Storage Server (RMSS), its architecture, implementation and integration, deployment and transition from the existing CRAY Data Migration Facility (DMF).

In September 2007 the Littoral Acoustic Demonstration Center (LADC) collected acoustic and related data from three moored arrays and ship-deployed hydrophones spanning the full water column to measure the three-dimensional acoustic field of a seismic airgun array. The seismic source vessel shot a series of lines to give a detailed angle and range information concerning the field. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, and one-third octave band analyses are measures used to characterize the field. Three dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Both the direct and indirect fields are characterized. Moveout analysis is done to delineate arrivals and to detect ducted and interface waves. [Research supported by the International Association of Oil and Gas Producers.]

The Challenger tragedy has temporarily halted the U.S. space shuttle program. When the program resumes in early 1988, the opportunity to use the shuttle for ocean research will be renewed. In the U.S. Navy, we are using this hiatus to develop a long‐range program for an oceanographer in space. This program will become part of a fully integrated Office of the Chief of Naval Research (OCNR) science and technology plan to guide future programs in space oceanography.

This dataset was generated during an entire year of operations (2020-12-31 to 2021-01-01) of the Nav2 Sail and Solar ASV (Navocean, Inc.) Vela, to survey Lake Okeechobee as part of the HALO program. Vela was equipped with the following sensors: C/T (Aanderaa), ADCP (Nortek), BB3 backscatter (Wetlabs), dissolved O₂ (Aanderaa), and Fluorometric sensors (Turner Cyclops Integrator). The dataset includes variables from all sensors as well as navigation parameters. The individual logger files have been combined under one register per TIMESTAMP, and a 1st level of quality control has been applied. This dataset is used in the publication in preparation: Ruiz Xomchuk, V., Duncan, S. McFarland M and Beckler, J. [2023] Elucidating Lake Okeechobee Harmful Algal Bloom population tracking through long-duration monitoring with an Autonomous Surface Vehicle, to be submitted to <em>Environmental Monitoring and Assessment.</em> Within the HALO program, the following public outreach bulletins were prepared during Vela's deployment time as data became available: HALO Bulletin 06/04/2021. Issue No 1. <strong>DOI</strong>: <strong>10.13140/RG.2.2.27803.44323</strong> HALO Bulletin 06/18/2021 Issue No. 2. <strong>DOI</strong>: <strong>10.13140/RG.2.2.21092.55688</strong> HALO Bulletin 07/02/2021. Issue No. 3. <strong>DOI</strong>: <strong>10.13140/RG.2.2.12703.94884</strong> HALO Bulletin 07/15/2021. Issue No. 4. <strong>DOI</strong>: <strong>10.13140/RG.2.2.34514.32969</strong> HALO Bulletin 08/14/2021. Issue No. 5.<strong> DOI: 10.13140/RG.2.2.16059.39201</strong> HALO Bulletin 08/27/2021. Issue No. 6. <strong>DOI</strong>: <strong>10.13140/RG.2.2.26125.72164</strong> HALO Bulletin 09/24/2021. Issue No. 7: <strong>DOI</strong>: <strong>10.13140/RG.2.2.19414.83529</strong>

Abstract This article describes the main findings of a full year of continuous operation of a 2-meter Autonomous Sail and Solar Surface Drone, the Nav2 (Navocean Inc.), as part of a Harmful Algal Bloom (HAB) monitoring program in Lake Okeechobee. The Nav2 was equipped with a set of water quality and atmospheric sensors, that recorded high frequency measurements (¡ 1 min) and transmitted near real-time information to allow reporting through a web portal for assessment and operation responses. Major findings include detection of HABs early in the year through chlorophyll (chl-a) and phycocyanin (phyco) fluorometric measurements, as well as different spatial scales of variability in the algal patches. The 24/7 high resolution monitoring allowed detection of patch motion and discrimination between growth and motion along a transect. Furthermore, the platform can potentially fingerprint specific HAB species based on the relatively fine-scale spatial expression of the phyco to chl-a ratio, which essentially captures the bloom macrostructure (e.g. surface scums versus more uniform sub-surface waves over 0.1 - 1 km scale). Sensor outputs, when converted to concentrations based on calibrated with pure laboratory standards, did not accurately yield true chl-a or phyco values when compared to validation samples, likely due to the high turbidity of the lake. However, routine solid-state validations of fluorometric measurements proved useful for assessing consistency in optical sensors to check for sensor drift (e.g. to due biofouling), which was not significant. Overall this demonstration shows that the Nav2 can uniquely and reliably provide in situ HAB and environmental monitoring capabilities in a large, turbid, shallow lake. We envision that platform as an innovative technology for water resource managers by providing turn-key long-duration baseline environmental data (hands-off waypoint navigation), early warnings of HABs for protecting human health, and for HAB mitigation monitoring.

Abstract This article describes the main findings of a full year of continuous operation of a 2-meter Autonomous Sail and Solar Surface Drone, the Nav2 (Navocean Inc.), as part of a Harmful Algal Bloom (HAB) monitoring program in Lake Okeechobee. The Nav2 was equipped with a set of water quality and atmospheric sensors, that recorded high frequency measurements (\textless 1 min) and transmitted near real-time information to allow reporting through a web portal for assessment and operation responses. Major findings include detection of HABs early in the year through chlorophyll (chl-a) and phycocyanin (phyco) fluorometric measurements, as well as different spatial scales of variability in the algal patches. The 24/7 high resolution monitoring allowed detection of patch motion and discrimination between growth and motion along a transect. Furthermore, the platform can potentially fingerprint specific HAB species based on the relatively fine-scale spatial expression of the phyco to chl-a ratio, which essentially captures the bloom macrostructure (e.g. surface scums versus more uniform sub-surface waves over 0.1 - 1 km scale). Sensor outputs, when converted to concentrations based on calibrated with pure laboratory standards, did not accurately yield true chl-a or phyco values when compared to validation samples, likely due to the high turbidity of the lake. However, routine solid-state validations of fluorometric measurements proved useful for assessing consistency in optical sensors to check for sensor drift (e.g. to due biofouling), which was not significant. Overall this demonstration shows that the Nav2 can uniquely and reliably provide in situ HAB and environmental monitoring capabilities in a large, turbid, shallow lake. We envision that platform as an innovative technology for water resource managers by providing turn-key long-duration baseline environmental data (hands-off waypoint navigation), early warnings of HABs for protecting human health, and for HAB mitigation monitoring.

We discuss three factors: short range sediment variability, bio-attenuation, and seafloor roughness. In a previous presentation (ASA 2013), we have shown that statistical distributions of bottom loss values derived from measured transmission loss (TL) are nearly invariant to measured sediment properties such as sound speed, density, and porosity. To test if this surprising result was caused by under-sampling of sediment cores, three TL runs were done in 2014 when cores were collected at 1 km intervals. The results of these showing short range variations will be discussed. Among the stations in our HFBL database we have found possible evidence for bio-attenuation due to fish (anchovies) swim bladder resonance (Diachok-Wales, JASA 2005). Finite element modeling of a TL station has shown that seafloor roughness can explain the observed frequency dependence of HFBL values (Isakson, report to NAVO). All these will be discussed.

Statistical characteristics of acoustic fields scattered in the forward direction from simulated three-dimensional wind-driven sea surfaces are studied for frequencies from 0.1–10 kHz, high grazing angles, and ranges in the Fresnel region. The simulated surfaces have the Pierson-Moskowitz directional spectrum for a 5-m/s wind speed. Complex pressures are calculated using Helmholtz-Kirchhoff theory with a minimum number of approximations. Statistics of the acoustic fields are calculated as ensemble averages of the complex pressures and their moments. Comparisons are presented for differences in the ensemble of surfaces, spectral forms, surface illumination patterns, and implementation of the scattering theory. The technique allows for the accurate representation of first- and higher-order moments of the acoustic field scattered from a three-dimensional surface. Such quantities are usually difficult to obtain by other techniques. [This work has been supported by NAVOCEANO and NORDA.]

We report the results of a study correlating mid-frequency transmission loss (TL) measurements with properties of nearby sediment core samples. A large number of measurements were made in shallow water areas with water depths ranging from 50 to 160 m. The statistical distributions of the derived bottom-loss values are found to be nearly invariant to various sediment properties derived from the corresponding core samples. These properties include seafloor sound speed, density, and porosity as well as a number of others. It is shown from Parabolic Equation model calculations that use Hamilton’s values for the different sediment types [J. Acoust. Soc. Am. 68, 1313 (1980)] that the TL can vary by 15 dB or more at a range of 20 km. Therefore the absence of substantial bias in the data with respect to sediment types is somewhat surprising and worth investigation. The possible explanations, such as high spatial variability of seafloor processes including presence of ripples, gas, and other causes are being investigated and will be discussed. [Approved for public release].

This dataset was generated during an entire year of operations (2020-12-31 to 2021-01-01) of the Nav2 Sail and Solar ASV (Navocean, Inc.) Vela, to survey Lake Okeechobee as part of the HALO program. Vela was equipped with the following sensors: C/T (Aanderaa), ADCP (Nortek), BB3 backscatter (Wetlabs), dissolved O₂ (Aanderaa), and Fluorometric sensors (Turner Cyclops Integrator). The dataset includes variables from all sensors as well as navigation parameters. The individual logger files have been combined under one register per TIMESTAMP, and a 1st level of quality control has been applied. This dataset is used in the publication in preparation: Ruiz Xomchuk, V., Duncan, S. McFarland M and Beckler, J. [2023] Elucidating Lake Okeechobee Harmful Algal Bloom population tracking through long-duration monitoring with an Autonomous Surface Vehicle, to be submitted to <em>Environmental Monitoring and Assessment.</em> Within the HALO program, the following public outreach bulletins were prepared during Vela's deployment time as data became available: HALO Bulletin 06/04/2021. Issue No 1. <strong>DOI</strong>: <strong>10.13140/RG.2.2.27803.44323</strong> HALO Bulletin 06/18/2021 Issue No. 2. <strong>DOI</strong>: <strong>10.13140/RG.2.2.21092.55688</strong> HALO Bulletin 07/02/2021. Issue No. 3. <strong>DOI</strong>: <strong>10.13140/RG.2.2.12703.94884</strong> HALO Bulletin 07/15/2021. Issue No. 4. <strong>DOI</strong>: <strong>10.13140/RG.2.2.34514.32969</strong> HALO Bulletin 08/14/2021. Issue No. 5.<strong> DOI: 10.13140/RG.2.2.16059.39201</strong> HALO Bulletin 08/27/2021. Issue No. 6. <strong>DOI</strong>: <strong>10.13140/RG.2.2.26125.72164</strong> HALO Bulletin 09/24/2021. Issue No. 7: <strong>DOI</strong>: <strong>10.13140/RG.2.2.19414.83529</strong>

The effect of a finite fetch on the acoustic field scattered by the ocean wind-driven surface for various wind speeds is analyzed through numerical simulation. The JONSWAP spectrum is adopted to describe the surface statistics of growing seas and the Pierson-Moskowitz spectrum for fully developed seas. Ensembles of three-dimensional surfaces having the desired directional spectra are numerically generated. For each surface realization, the complex pressure of the forward scattered field is calculated within the framework of the Helmholtz-Kirchhoff theory for kr &amp;gt; 1. Statistical moments of the scattered field are then calculated as ensemble averages. The fields scattered in the windward and cross-wind directions are evaluted for frequencies up to 1.5 kHz and for angles away from grazing incidence. Results indicate that the scattered field is sensitive to the difference between the JONSWAP and the Pierson-Moskowitz spectra. In particular, the total intensity and the coherence of the scattered field are significantly affected by the wind fetch. [Work supported by NAVOCEANO and NORDA.]

In an earlier paper [Novarini et al., J. Acoust. Soc. Am. Suppl. 1 83, S48 (1988)], the scattered acoustic fields resulting from fully developed (generated from the Pierson-Moskowitz spectrum) and fetch-limited (generated from the JONSWAP spectrum) 3-D wind-driven sea surfaces were compared. Within the context of the Helmholtz-Kirchhoff theory, it was demonstrated that there are significant acoustic differences between these two descriptions of the sea surface. In this meeting, the scattered acoustic field resulting from 3-D sea surfaces generated from nonstationary, nonuniform wind fields are considered. These sea surfaces are generated from a spectral representation which, given the wind field specified over an extended area, is provided by the Global/Regional Deep Water Wave Model (D. Ressio, “Program Wave,” Offshore &amp; Costal Technologies Inc., Vicksburg, MS). This model has the ability to describe very realistic sea surfaces that include swell from distant storms and growing wind-driven seas. The scattered field resulting from such surfaces will be compared with results from sea surfaces generated by simple spectral descriptions which are functions of wind speed or wind speed and fetch. Preliminary results show strong differences in the coherence as well as the scattering strength over the entire frequency range under consideration (100–2000 Hz).