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1
Guo, Hu Sheng, Bin Yan, and Zhi Dong Wu. "The Design of New Low Cost Ocean Bottom Seismometers." Applied Mechanics and Materials 226-228 (November 2012): 2107–10. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.2107.
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The performance of the Ocean Bottom Seismometers (OBS) in seismic wave field measurement is vital to seismic exploration. In order to improve the performance of OBS, we have been developed a new Ocean Bottom Seismometer based 3-component MEMS accelerometer sensors. In order to sample seismic data synchronously, we have been designed multichannel A/D unit under the control of MSP430.We also are involved in a handle and sophisticated equipment allows to storage sampling data in the SD card module. The system based MEMS sensor are compared with conventional analog moving coil geophones, the result shows that the new measurement system with the advantage of high dynamic range, low noise and anti-jamming that suit for the high resolution seismicity information. The paper show that the new digital OBS using MEMS accelerometer will replace the tradition OBS in oil exploration, scientific research and seabed surveys.
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Flexas, Mar M., Martina I. Troesch, Steve Chien, Andrew F. Thompson, Selina Chu, Andrew Branch, John D. Farrara, and Yi Chao. "Autonomous Sampling of Ocean Submesoscale Fronts with Ocean Gliders and Numerical Model Forecasting." Journal of Atmospheric and Oceanic Technology 35, no. 3 (March 2018): 503–21. http://dx.doi.org/10.1175/jtech-d-17-0037.1.
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ABSTRACTSubmesoscale fronts arising from mesoscale stirring are ubiquitous in the ocean and have a strong impact on upper-ocean dynamics. This work presents a method for optimizing the sampling of ocean fronts with autonomous vehicles at meso- and submesoscales, based on a combination of numerical forecast and autonomous planning. This method uses a 48-h forecast from a real-time high-resolution data-assimilative primitive equation ocean model, feature detection techniques, and a planner that controls the observing platform. The method is tested in Monterey Bay, off the coast of California, during a 9-day experiment focused on sampling subsurface thermohaline-compensated structures using a Seaglider as the ocean observing platform. Based on model estimations, the sampling “gain,” defined as the magnitude of isopycnal tracer variability sampled, is 50% larger in the feature-chasing case with respect to a non-feature-tracking scenario. The ability of the model to reproduce, in space and time, thermohaline submesoscale features is evaluated by quantitatively comparing the model and glider results. The model reproduces the vertical (~50–200 m thick) and lateral (~5–20 km) scales of subsurface subducting fronts and near-bottom features observed in the glider data. The differences between model and glider data are, in part, attributed to the selected glider optimal interpolation parameters and to uncertainties in the forecasting of the location of the structures. This method can be exported to any place in the ocean where high-resolution data-assimilative model output is available, and it allows for the incorporation of multiple observing platforms.
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Matsumoto, Hiroyuki, Mikhail A. Nosov, Sergey V. Kolesov, and Yoshiyuki Kaneda. "Analysis of Pressure and Acceleration Signals from the 2011 Tohoku Earthquake Observed by the DONET Seafloor Network." Journal of Disaster Research 12, no. 1 (February 1, 2017): 163–75. http://dx.doi.org/10.20965/jdr.2017.p0163.
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Ocean-bottom pressure and acceleration data simultaneously recorded by the DONET seafloor network during the 2011 Tohoku earthquake approximately 800 km from the earthquake epicenter are processed and analyzed. The close location of pressure and acceleration sensors together with the high data-sampling rate enable us to quantitatively examine and interpret pressure variations together with ocean-bottom acceleration for the first time to our knowledge. To interpret observed data, we introduce a set of characteristic frequencies that enable us to identify physical processes responsible for water layer behaviour dependent on the frequency of ocean-bottom oscillations. Explicit formulas are given for calculating all of the characteristic frequencies, which are the basis for introducing nonoverlapping frequency bands, i.e., hydroacoustic waves, forced oscillations, and gravity waves. The physical correctness of such a subdivision is confirmed by the high coherence and nearly zero phase difference between in-situ measured pressure and acceleration variations observed in the forced oscillation frequency band – a band neither hydroacoustic nor gravity waves are generated by ocean-bottom oscillation because the water layer simply follows the ocean bottom, generating forced oscillations. The dominant, long-lasting pressure fluctuations recorded by DONET during the 2011 earthquake are associated with the forced oscillation, or, more precisely, with water and sedimentary layer coupling oscillation. DONET clearly observed the 2011 Tohoku tsunami signal during more than 24 hours following the earthquake. In contrast to DART records, phase dispersion was not manifested in the tsunami signals registered by DONET.
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Nash, Jonathan D., Matthew H. Alford, and Eric Kunze. "Estimating Internal Wave Energy Fluxes in the Ocean." Journal of Atmospheric and Oceanic Technology 22, no. 10 (October 1, 2005): 1551–70. http://dx.doi.org/10.1175/jtech1784.1.
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Abstract Energy flux is a fundamental quantity for understanding internal wave generation, propagation, and dissipation. In this paper, the estimation of internal wave energy fluxes 〈u′p′〉 from ocean observations that may be sparse in either time or depth are considered. Sampling must be sufficient in depth to allow for the estimation of the internal wave–induced pressure anomaly p′ using the hydrostatic balance, and sufficient in time to allow for phase averaging. Data limitations that are considered include profile time series with coarse temporal or vertical sampling, profiles missing near-surface or near-bottom information, moorings with sparse vertical sampling, and horizontal surveys with no coherent resampling in time. Methodologies, interpretation, and errors are described. For the specific case of the semidiurnal energy flux radiating from the Hawaiian ridge, errors of ∼10% are typical for estimates from six full-depth profiles spanning 15 h.
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Yu, Pengfei, and Jianhua Geng. "Acoustic-elastic coupled equations in vertical transverse isotropic media for pseudoacoustic-wave reverse time migration of ocean-bottom 4C seismic data." GEOPHYSICS 84, no. 4 (July 1, 2019): S317—S327. http://dx.doi.org/10.1190/geo2018-0295.1.
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Quasi-P (qP)-wave separation and receiver-side records back extrapolation are two key technologies commonly applied in vertical transverse isotropic (VTI) media for ocean-bottom 4C seismic data pseudoacoustic-wave reverse time migration (RTM). However, it remains problematic to quickly and accurately separate the qP-wave in VTI media. The qP-wave can be fast separated by synthesizing pressure in weakly anisotropic media. Like the derivation of acoustic-elastic coupled equations (AECEs) in an isotropic medium, novel AECEs can also be obtained in VTI media. Based on these novel coupled equations, we have developed a method for pseudoacoustic-wave RTM of ocean-bottom 4C seismic data. Three synthetic examples are provided to illustrate the validity and effectiveness of our method. The results indicate that our method possesses three advantages for ocean-bottom 4C data compared with the conventional method when conducting pseudoacoustic-wave RTM in VTI media. First, these new coupled equations are able to obtain a qP-wave during wavefield propagation. Second, ocean-bottom 4C records can be implemented strictly for receiver-side tensorial extrapolation with undulating topography of the seafloor, which brings benefits for suppressing artifacts in pseudoacoustic-wave RTM and improving imaging quality. Finally, our method is fairly robust to coarse sampling.
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Cornils, Astrid, Rainer Sieger, Elke Mizdalski, Stefanie Schumacher, Hannes Grobe, and Sigrid B. Schnack-Schiel. "Copepod species abundance from the Southern Ocean and other regions (1980–2005) – a legacy." Earth System Science Data 10, no. 3 (August 16, 2018): 1457–71. http://dx.doi.org/10.5194/essd-10-1457-2018.
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Abstract. This data collection originates from the efforts of Sigrid Schnack-Schiel (1946–2016), a zooplankton ecologist with great expertise in life cycle strategies of Antarctic calanoid copepods, who also investigated zooplankton communities in tropical and subtropical marine environments. Here, we present 33 data sets with abundances of planktonic copepods from 20 expeditions to the Southern Ocean (Weddell Sea, Scotia Sea, Amundsen Sea, Bellingshausen Sea, Antarctic Peninsula), one expedition to the Magellan region, one latitudinal transect in the eastern Atlantic Ocean, one expedition to the Great Meteor Bank, and one expedition to the northern Red Sea and Gulf of Aqaba as part of her scientific legacy. A total of 349 stations from 1980 to 2005 were archived. During most expeditions depth-stratified samples were taken with a Hydrobios multinet with five or nine nets, thus allowing inter-comparability between the different expeditions. A Nansen or a Bongo net was deployed only during four cruises. Maximum sampling depth varied greatly among stations due to different bottom depths. However, during 11 cruises to the Southern Ocean the maximum sampling depth was restricted to 1000 m, even at locations with greater bottom depths. In the eastern Atlantic Ocean (PS63) sampling depth was restricted to the upper 300 m. All data are now freely available at PANGAEA via the persistent identifier https://doi.org/10.1594/PANGAEA.884619.Abundance and distribution data for 284 calanoid copepod species and 28 taxa of other copepod orders are provided. For selected species the abundance distribution at all stations was explored, revealing for example that species within a genus may have contrasting distribution patterns (Ctenocalanus, Stephos). In combination with the corresponding metadata (sampling data and time, latitude, longitude, bottom depth, sampling depth interval) the analysis of the data sets may add to a better understanding how the environment (currents, temperature, depths, season) interacts with copepod abundance, distribution and diversity. For each calanoid copepod species, females, males and copepodites were counted separately, providing a unique resource for biodiversity and modelling studies. For selected species the five copepodite stages were also counted separately, thus also allowing the data to be used to study life cycle strategies of abundant or key species.
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Harrison, C. G. A., J. C. Belshé, A. S. Dunlap, J. D. Mudie, and A. I. Rees. "A Photographic Compass Inclinometer for the Orientation of Deep Sea Sediment Samples." Marine Technology Society Journal 40, no. 2 (May 1, 2006): 13–15. http://dx.doi.org/10.4031/002533206787353484.
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An inexpensive instrument is briefly described which has been designed to provide a method of recording the orientation of deep-sea sampling devices. A compass and bull's-eye spirit level are photographed by a single shot camera shortly after the sampling device hits the bottom. The azimuth of a line on the device may be measured to within 2 degrees, and the inclination of the device to within 1/2 degree.
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Wei, Guo, Zhang Pengyu, Yang Xiang, Lei Jiang, Sun Youhong, Jia Rui, and Wang Yuan. "Development and application of hole-bottom freezing drilling tool for gas-hydrate-bearing sediment sampling." Ocean Engineering 203 (May 2020): 107195. http://dx.doi.org/10.1016/j.oceaneng.2020.107195.
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Brenke, Nils. "An Epibenthic Sledge for Operations on Marine Soft Bottom and Bedrock." Marine Technology Society Journal 39, no. 2 (June 1, 2005): 10–21. http://dx.doi.org/10.4031/002533205787444015.
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A multi-purpose epibenthic sledge, designed for sampling of small benthic macrofauna in marine habitats and at any navigable depth, is presented. The new epibenthic sledge operates reliably on soft sediments in shallow and in open oceanic deep water, as well as on steep slopes, between rocks and glacier moraines as frequently found in Antarctic waters, and on primary hard substrate. The construction is of high mechanical stability with fully protected nets. In case of damage, parts of the sledge can be replaced or repaired easily on board. A description of the gear with a detailed construction plan, as well as parameters for handling in diverse marine habitats, is given. Calculation of the towing distance and first results with possible sources of errors are discussed.
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Saito, Tatsuhiko, Takanori Matsuzawa, Kazushige Obara, and Toshitaka Baba. "Dispersive tsunami of the 2010 Chile earthquake recorded by the high-sampling-rate ocean-bottom pressure gauges." Geophysical Research Letters 37, no. 23 (December 2010): n/a. http://dx.doi.org/10.1029/2010gl045290.
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Schilling, J., T. C. E. Van Weering, and D. Eisma. "Advantages of light-weight kevlar rope for ocean bottom sampling with the piston corer and box corer." Marine Geology 79, no. 1-2 (February 1988): 149–52. http://dx.doi.org/10.1016/0025-3227(88)90164-8.
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Xiao, Jing, Jiawang Chen, Zhenwei Tian, Hai Zhu, Chunsheng Wang, Junyi Yang, Qinghua Sheng, Dahai Zhang, and Jiasong Fang. "Visible Fidelity Collector of a Zooplankton Sample from the Near-Bottom of the Deep Sea." Journal of Marine Science and Engineering 9, no. 3 (March 17, 2021): 332. http://dx.doi.org/10.3390/jmse9030332.
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The multi-net visible fidelity zooplankton collector is designed to obtain near-bottom fidelity zooplankton. The collector is sent to the designated sampling location based on the information provided by the camera and altimeter. The host computer sends instructions to control the opening of the net port for sample collection and closing of the sampling cylinder cover after sampling. The collector contains three trawls so that three samples can be collected for each test, and environmental parameters can be collected simultaneously. After sampling, The sample maintains its fidelity, that is, maintaining the temperature and pressure of the seabed sample after sampling. Two experiments were carried out in the Western Pacific, and six bottles of zooplankton samples were successfully obtained. The development of a multi-net visible zooplankton collector is of great significance for the collection of near-bottom zooplankton.
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Wasilewska-Błaszczyk, Monika, and Jacek Mucha. "Application of General Linear Models (GLM) to Assess Nodule Abundance Based on a Photographic Survey (Case Study from IOM Area, Pacific Ocean)." Minerals 11, no. 4 (April 17, 2021): 427. http://dx.doi.org/10.3390/min11040427.
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The success of the future exploitation of the Pacific polymetallic nodule deposits depends on an accurate estimation of their resources, especially in small batches, scheduled for extraction in the short term. The estimation based only on the results of direct seafloor sampling using box corers is burdened with a large error due to the long sampling interval and high variability of the nodule abundance. Therefore, estimations should take into account the results of bottom photograph analyses performed systematically and in large numbers along the course of a research vessel. For photographs taken at the direct sampling sites, the relationship linking the nodule abundance with the independent variables (the percentage of seafloor nodule coverage, the genetic types of nodules in the context of their fraction distribution, and the degree of sediment coverage of nodules) was determined using the general linear model (GLM). Compared to the estimates obtained with a simple linear model linking this parameter only with the seafloor nodule coverage, a significant decrease in the standard prediction error, from 4.2 to 2.5 kg/m2, was found. The use of the GLM for the assessment of nodule abundance in individual sites covered by bottom photographs, outside of direct sampling sites, should contribute to a significant increase in the accuracy of the estimation of nodule resources.
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Wu, Shi-Jun, Shuo Wang, and Can-Jun Yang. "Collection of Gas-Tight Water Samples from the Bottom of the Challenger Deep." Journal of Atmospheric and Oceanic Technology 35, no. 4 (April 2018): 837–44. http://dx.doi.org/10.1175/jtech-d-17-0170.1.
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AbstractA new gas-tight pair sampler was designed for the collection of gas-tight fluid samples from the hadal zone. The sampler uses two titanium bottles and one sampling valve to collect two samples at once. The sampler can be deployed in the deepest trenches in the ocean as a result of its ability to resist ultrahigh pressure and its good bidirectional sealing performance. It can be used on manned submersibles, remotely operated vehicles, and deep-sea landers. Three sets of this new sampler were constructed and field tested in the Mariana Trench during the cruise TS-03 from 15 January to 23 March 2017, during which 3 L of water samples were successfully obtained from the bottom of the Challenger Deep.
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Smith, W. A. M. Nimmo, J. Katz, and T. R. Osborn. "On the Structure of Turbulence in the Bottom Boundary Layer of the Coastal Ocean." Journal of Physical Oceanography 35, no. 1 (January 1, 2005): 72–93. http://dx.doi.org/10.1175/jpo-2673.1.
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Abstract Six sets of particle image velocimetry (PIV) data from the bottom boundary layer of the coastal ocean are examined. The data represent periods when the mean currents are higher, of the same order, and much weaker than the wave-induced motions. The Reynolds numbers based on the Taylor microscale (Reλ) are 300–440 for the high, 68–83 for the moderate, and 14–37 for the weak mean currents. The moderate–weak turbulence levels are typical of the calm weather conditions at the LEO-15 site because of the low velocities and limited range of length scales. The energy spectra display substantial anisotropy at moderate to high wavenumbers and have large bumps at the transition from the inertial to the dissipation range. These bumps have been observed in previous laboratory and atmospheric studies and have been attributed to a bottleneck effect. Spatial bandpass-filtered vorticity distributions demonstrate that this anisotropy is associated with formation of small-scale, horizontal vortical layers. Methods for estimating the dissipation rates are compared, including direct estimates based on all of the gradients available from 2D data, estimates based on gradients of one velocity component, and those obtained from curve fitting to the energy spectrum. The estimates based on vertical gradients of horizontal velocity are higher and show better agreement with the direct results than do those based on horizontal gradients of vertical velocity. Because of the anisotropy and low turbulence levels, a −5/3 line-fit to the energy spectrum leads to mixed results and is especially inadequate at moderate to weak turbulence levels. The 2D velocity and vorticity distributions reveal that the flow in the boundary layer at moderate speeds consists of periods of “gusts” dominated by large vortical structures separated by periods of more quiescent flows. The frequency of these gusts increases with Reλ, and they disappear when the currents are weak. Conditional sampling of the data based on vorticity magnitude shows that the anisotropy at small scales persists regardless of vorticity and that most of the variability associated with the gusts occurs at the low-wave-number ends of the spectra. The dissipation rates, being associated with small-scale structures, do not vary substantially with vorticity magnitude. In stark contrast, almost all the contributions to the Reynolds shear stresses, estimated using structure functions, are made by the high- and intermediate-vorticity-magnitude events. During low vorticity periods the shear stresses are essentially zero. Thus, in times with weak mean flow but with wave orbital motion, the Reynolds stresses are very low. Conditional sampling based on phase in the wave orbital cycle does not show any significant trends.
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Shimada, Keishi, Shigeru Aoki, and Kay I. Ohshima. "Creation of a Gridded Dataset for the Southern Ocean with a Topographic Constraint Scheme." Journal of Atmospheric and Oceanic Technology 34, no. 3 (March 2017): 511–32. http://dx.doi.org/10.1175/jtech-d-16-0075.1.
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AbstractThis study investigated a method for creating a climatological dataset with improved reproducibility and reliability for the Southern Ocean. Despite sparse observational sampling, the Southern Ocean has a dominant physical characteristic of a strong topographic constraint formed under weak stratification and strong Coriolis effect. To increase the fidelity of gridded data, the topographic constraint is incorporated into the interpolation method, the weighting function of which includes a contribution from bottom depth differences and horizontal distances. Spatial variability of physical properties was also analyzed to estimate a realistic decorrelation scale for horizontal distance and bottom depth differences using hydrographic datasets. A new gridded dataset, the topographic constraint incorporated (TCI), was then developed for temperature, salinity, and dissolved oxygen, using the newly derived weighting function and decorrelation scales. The root-mean-square (RMS) of the difference between the interpolated values and the neighboring observed values (RMS difference) was compared among available gridded datasets. That the RMS differences are smaller for the TCI than for the previous datasets by 12%–21% and 8%–20% for potential temperature and salinity, respectively, demonstrates the effectiveness of incorporating the topographic constraint and realistic decorrelation scales. Furthermore, a comparison of decorrelation scales and an analysis of interpolation error suggests that the decorrelation scales adopted in previous gridded datasets are 2 times or more larger than realistic scales and that the overestimation would increase the interpolation error. The interpolation method proposed in this study can be applied to other high-latitude oceans, which are weakly stratified but undersampled.
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Codiga, Daniel L., Joseph A. Rice, Paul A. Baxley, and David Hebert. "Networked Acoustic Modems for Real-Time Data Telemetry from Distributed Subsurface Instruments in the Coastal Ocean: Application to Array of Bottom-Mounted ADCPs." Journal of Atmospheric and Oceanic Technology 22, no. 6 (June 1, 2005): 704–20. http://dx.doi.org/10.1175/jtech1739.1.
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Abstract Through the winter and spring of 2002, networked acoustic modems demonstrated real-time wireless data telemetry from an array of bottom-mounted acoustic Doppler current profilers (ADCPs) on the inner continental shelf 20–60 m deep off of Montauk Point, New York. To achieve typical temporal and spatial sampling needs for data assimilative numerical modeling, the array spanned 10 km × 10 km and transmitted data each ∼2 h. Network nodes included five sensors, each an ADCP with acoustic modem housed in a trawl-resistant bottom frame; five repeaters that are individual acoustic modems on near-bottom taut-wire moorings; and two gateways, each a buoy with a subsurface acoustic modem and topside cellular modem allowing for two-way communication with the shore. Deliveries from an ADCP adjacent to the gateway buoy were more than 97% successful through both winter and spring. Deliveries from ADCPs 5 km from the gateway averaged 25% (86%) reliability in winter (spring). Winter performance degrades because of upward-refracting sound speed profiles that limit direct acoustic paths, and strong winds that disrupt sea surface reflectivity and increase ambient noise. Reliability improved up to 36% due to the receive-all gateway mode, and more than doubled for certain node pairs due to a handshake protocol incorporating an automatic repeat request. Shore-based network control demonstrated adaptive sampling by changing ADCP vertical and temporal resolution, and network data path rerouting in response to unplanned events, such as trawling impacts. Networked acoustic modems are well suited for coastal ocean-observing systems, particularly at sites such as this where seafloor cables and surface buoys are vulnerable to fishing and shipping activities.
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Lamarque, Bastien, Bruno Deflandre, Adriana Galindo Dalto, Sabine Schmidt, Alicia Romero-Ramirez, Frédéric Garabetian, Nicolas Dubosq, et al. "Spatial Distributions of Surface Sedimentary Organics and Sediment Profile Image Characteristics in a High-Energy Temperate Marine RiOMar: The West Gironde Mud Patch." Journal of Marine Science and Engineering 9, no. 3 (February 24, 2021): 242. http://dx.doi.org/10.3390/jmse9030242.
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The spatial distributions of (1) surface sediment characteristics (D0.5, Sediment Surface Area (SSA), Particulate Organic Carbon (POC), Chlorophyll-a (Chl-a), Phaeophytin-a (Phaeo-a), Total and Enzymatically Hydrolyzable Amino Acids (THAA, EHAA), δ13C) and (2) sediment profile image (apparent Redox Potential Discontinuity (aRPD), numbers and depths of biological traces) characteristics were quantified based on the sampling of 32 stations located within the West Gironde Mud Patch (Bay of Biscay, NE Atlantic) in view of (1) assessing the spatial structuration of a temperate river-dominated ocean margin located in a high-energy area, (2) disentangling the impacts of hydrodynamics and bottom trawling on this structuration, and (3) comparing the West Gironde Mud Patch with the Rhône River Prodelta (located in a low-energy area). Results support the subdivision of the West Gironde Mud Patch in a proximal and a distal part and show (1) the existence of depth gradients in surface sedimentary organics characteristics and bioturbation within the distal part; (2) no evidence for a significant effect of bottom trawling, as opposed to Bottom Shear Stress, on the West Gironde Mud Patch spatial structuration; and (3) major discrepancies between spatial structuration in the West Gironde Mud Patch and the Rhône River Prodelta, which were attributed to differences in tidal regimes, sedimentation processes, and local hydrodynamics, which is in agreement with current river-dominated ocean margin typologies.
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Desbruyères, Damien, Elaine L. McDonagh, Brian A. King, and Virginie Thierry. "Global and Full-Depth Ocean Temperature Trends during the Early Twenty-First Century from Argo and Repeat Hydrography." Journal of Climate 30, no. 6 (March 2017): 1985–97. http://dx.doi.org/10.1175/jcli-d-16-0396.1.
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The early twenty-first century’s warming trend of the full-depth global ocean is calculated by combining the analysis of Argo (top 2000 m) and repeat hydrography into a blended full-depth observing system. The surface-to-bottom temperature change over the last decade of sustained observation is equivalent to a heat uptake of 0.71 ± 0.09 W m−2 applied over the surface of Earth, 90% of it being found above 2000-m depth. The authors decompose the temperature trend pointwise into changes in isopycnal depth (heave) and temperature changes along an isopycnal (spiciness) to describe the mechanisms controlling the variability. The heave component dominates the global heat content increase, with the largest trends found in the Southern Hemisphere’s extratropics (0–2000 m) highlighting a volumetric increase of subtropical mode waters. Significant heave-related warming is also found in the deep North Atlantic and Southern Oceans (2000–4000 m), reflecting a potential decrease in deep water mass renewal rates. The spiciness component shows its strongest contribution at intermediate levels (700–2000 m), with striking localized warming signals in regions of intense vertical mixing (North Atlantic and Southern Oceans). Finally, the agreement between the independent Argo and repeat hydrography temperature changes at 2000 m provides an overall good confidence in the blended heat content evaluation on global and ocean scales but also highlights basin-scale discrepancies between the two independent estimates. Those mismatches are largest in those basins with the largest heave signature (Southern Ocean) and reflect both the temporal and spatial sparseness of the hydrography sampling.
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Dommisse, Michaela, Dan Urban, Bruce Finney, and Susan Hills. "Potential Depth Biasing Using the Biosonics VBT Seabed Classification Software." Marine Technology Society Journal 39, no. 2 (June 1, 2005): 90–93. http://dx.doi.org/10.4031/002533205787443926.
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The use of digital echosounders with post-processing commercial seabed classification software is becoming increasingly popular to create high-resolution resource maps of marine habitats over large scales. Here, we examine the Biosonics Visual Bottom Typing (VBT) seabed classification software (version 1.91). Although the VBT software uses potentially robust seabed classification parameters and has many useful features, a major drawback of the software is that it does not normalize echoes to a reference depth (typically the average survey depth). Depth normalizing adjusts for a change in echo length with depth. Without it, the VBT classification parameters that are calculated from the energy integral of the returned echo envelope over a fixed sampling window can be depth biased. The degree of misclassification from depth biasing will depend on the particular echosounder specifications (beamwidth (at −3dB) and pulse length) and characteristics of the survey area (depth variation and bottom acoustic diversity). Depth normalization applied before classification parameters are calculated is a very simple solution to potential depth-related misclassification and should be incorporated into the VBT software as a matter of priority to ensure its reliability and broad user application.
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Fletcher, Barbara, Andrew Bowen, Dana R. Yoerger, and Louis L. Whitcomb. "Journey to the Challenger Deep: 50 Years Later With the Nereus Hybrid Remotely Operated Vehicle." Marine Technology Society Journal 43, no. 5 (December 1, 2009): 65–76. http://dx.doi.org/10.4031/mtsj.43.5.26.
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AbstractThe hybrid remotely operated vehicle Nereus, developed by the Woods Hole Oceanographic Institution in collaboration with the Space and Naval Warfare Systems Center Pacific and Johns Hopkins University, is designed to provide a new level of access to a maximum depth of 11,000 m. Nereus operates in two different modes. The vehicle can operate untethered as an autonomous underwater vehicle for broad area survey, capable of exploring and mapping the seafloor with sonars, cameras, and other onboard sensors. Nereus can be converted at sea to become a remotely operated vehicle (ROV) to enable close-up imaging and sampling. The ROV configuration incorporates a lightweight fiber-optic tether to the surface for high-bandwidth real-time video and data telemetry to the surface to enable high-quality teleoperation, additional cameras and lights, manipulator arm, and sampling gear. Nereus underwent sea trials in May and June of 2009 during which it completed eight dives, including two dives to more than 10,900 m in the Challenger Deep of the Mariana Trench with a total bottom time in excess of 12 h.
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Bao, Roberto, Henko De Stigter, and Tjeerd C. E. Van Weering. "Diatom fluxes in surface sediments of the Goban Spur continental margin, NE Atlantic Ocean." Journal of Micropalaeontology 19, no. 2 (December 1, 2000): 123–31. http://dx.doi.org/10.1144/jm.19.2.123.
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Abstract. Continental slopes are presumed key areas for deposition of organic carbon exported from the shelf. Analysis of across-slope differences in diatom and silicoflagellate fluxes recorded in bottom sediments of the Goban Spur margin, a typical North Atlantic slope environment, was carried out to test if they can provide information on the magnitude of advection of material from the shelf into deeper waters. Total diatom and silicoflagellate accumulation rates showed strong across-slope differences. Minimum values are recorded at the shelf break where maximum surface productivity conditions occur while the deeper sampling stations record fluxes as high as 183×106 valves cm–2 ka–1. While high diatom fluxes show a clear correspondence with the activity of a permanent bottom nepheloid layer operating in the region, they do not correlate with productivity patterns observed in the water column. Diatom assemblages are mainly composed of Chaetoceros resting spores and Thalassionema nitzschioides (Grunow) Grunow ex Hustedt, typical indicators of spring bloom conditions in the area. The absence of clear across-slope trends in the diatom assemblages is interpreted as the effect of random mixing driven by the strong hydrodynamic regime provoked by the activity of the bottom nepheloid layer. The dominance of Chaetoceros resting spores across the slope is related to important exportation of shelf-derived production. However, due to the broad ecological tolerances of the main taxa composing the diatom assemblages, they do not allow precise estimations on the magnitude of the primary vertical flux vs. the secondary lateral flux in this slope environment. Use of the tychoplanktonic and benthic diatoms, which are restricted to the neritic realm, allows only the estimation of the minimum amount of shelf-derived diatoms reaching the slope sediments (at least 13% of the total diatom assemblage for the upper slope area of the Goban Spur). This study shows that major limitations exist for the use of diatoms preserved in surface sediments of this area as tracers of shelf-derived production transported to the continental slope.
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Terry, Darrell A., and Camelia C. Knapp. "Identification of gas hydrates and bottom-simulating reflectors in far-offset seismic images." Interpretation 9, no. 2 (April 21, 2021): SD53—SD69. http://dx.doi.org/10.1190/int-2020-0168.1.
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The presence of marine gas hydrates is routinely inferred based on the identification of bottom simulating reflectors (BSRs) in common-depth-point (CDP) seismic images. Additional seismic studies such as amplitude variation with offset (AVO) analysis can be applied for corroboration. Although confirmation is needed by drilling and sampling, seismic analysis has proven to be a cost-effective approach to identify the presence of marine gas hydrates. Single-channel far-offset seismic images are investigated for what appears to be a more reliable and cost-effective indicator for the presence of BSRs than traditional CDP processing or AVO analysis. A nontraditional approach for processing seismic data is taken to be more relevant to imaging the gas/gas hydrate contact. Instead of applying the traditional CDP seismic processing workflows from the oil industry, we more carefully review the significant amount of information existing in the data to explore how the character of the data changes as offset angle increases. Three cases from different environments are selected for detailed analysis. These include (1) stratigraphy running parallel with the ocean bottom, (2) a potential BSR, running parallel to the ocean bottom, and cross-cutting dipping reflections, and (3) a suspected thermal intrusion without a recognizable BSR. This investigation considers recently collected multichannel seismic data from the deep waters of the central Aleutian Basin beneath the Bering Sea, the preprocessing of the data sets, and the methodology for processing and display to generate single-channel seismic images. Descriptions are provided for the single-channel near- and far-offset seismic images for the example cases. Results indicate that BSRs related to marine gas hydrates, and originating due to the presence of free gas, are more easily and uniquely identifiable from single-channel displays of far-offset seismic images than from traditional CDP displays.
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Aoyama, Michio, and Katsumi Hirose. "Artificial Radionuclides Database in the Pacific Ocean: HAM Database." Scientific World JOURNAL 4 (2004): 200–215. http://dx.doi.org/10.1100/tsw.2004.15.
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The database “Historical Artificial Radionuclides in the Pacific Ocean and its Marginal Seas”, or HAM database, has been created. The database includes90Sr,137Cs, and239,240Pu concentration data from the seawater of the Pacific Ocean and its marginal seas with some measurements from the sea surface to the bottom. The data in the HAM database were collected from about 90 literature citations, which include published papers; annual reports by the Hydrographic Department, Maritime Safety Agency, Japan; and unpublished data provided by individuals. The data of concentrations of90Sr,137Cs, and239,240Pu have been accumulating since 19571998. The present HAM database includes 7737 records for137Cs concentration data, 3972 records for90Sr concentration data, and 2666 records for239,240Pu concentration data. The spatial variation of sampling stations in the HAM database is heterogeneous, namely, more than 80% of the data for each radionuclide is from the Pacific Ocean and the Sea of Japan, while a relatively small portion of data is from the South Pacific. This HAM database will allow us to use these radionuclides as significant chemical tracers for oceanographic study as well as the assessment of environmental affects of anthropogenic radionuclides for these 5 decades. Furthermore, these radionuclides can be used to verify the oceanic general circulation models in the time scale of several decades.
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Mosher, S. G., Z. Eilon, H. Janiszewski, and P. Audet. "Probabilistic inversion of seafloor compliance for oceanic crustal shear velocity structure using mixture density neural networks." Geophysical Journal International 227, no. 3 (August 9, 2021): 1879–92. http://dx.doi.org/10.1093/gji/ggab315.
Full textAbstract:
SUMMARY Measurements of various physical properties of oceanic sediment and crustal structures provide insight into a number of geological and geophysical processes. In particular, knowledge of the shear wave velocity (VS) structure of marine sediments and oceanic crust has wide ranging implications from geotechnical engineering projects to seismic mantle tomography studies. In this study, we propose a novel approach to nonlinearly invert compliance signals recorded by colocated ocean-bottom seismometers and high-sample-rate pressure gauges for shallow oceanic shear wave velocity structure. The inversion method is based on a type of machine learning neural network known as a mixture density neural network (MDN). We demonstrate the effectiveness of the MDN method on synthetic models with a fixed deployment depth of 2015 m and show that among 30 000 test models, the inverted shear wave velocity profiles achieve an average error of 0.025 km s−1. We then apply the method to observed data recorded by a broad-band ocean-bottom station in the Lau basin, for which a VS profile was estimated using Monte Carlo sampling methods. Using the mixture density network approach, we validate the method by showing that our VS profile is in excellent agreement with the previous result. Finally, we argue that the mixture density network approach to compliance inversion is advantageous over other compliance inversion methods because it is faster and allows for standardized measurements.
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Tian, Jinyu, Jian Lin, Fan Zhang, Min Xu, Yayun Zhang, Laiyin Guo, and Xin Zeng. "Time Correction of Ocean-Bottom Seismometers Using Improved Ambient Noise Cross Correlation of Multicomponents and Dual-Frequency Bands." Seismological Research Letters 92, no. 3 (January 13, 2021): 2004–14. http://dx.doi.org/10.1785/0220200358.
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Abstract An effective approach was developed for identifying and correcting ocean-bottom seismometer (OBS) time errors through improving ambient noise cross-correlation function (NCCF) analysis and combination with other methods. Significant improvements were illustrated through analyzing data from a passive-source seismic experiment in the southwestern sub-basin of the South China Sea. A novel method was first developed that can effectively identify errors in the sampling frequency of the OBS instruments. The traditional NCCF method was then expanded by increasing the analyzed data spectrum from a single-frequency band to dual-frequency band pairs, thus doubling the number of available data points and substantially improving the time correction quality. For data with relatively low signal-to-noise ratios, the average time errors were reduced from the original average values of 60–80 ms by the conventional methods to <40 ms using the improved approaches. The new multistep procedure developed in this study has general applicability to analysis of other OBS experiments. The demonstrated significant improvements in the data quality are critical for advancing seismic tomography and other modern marine geophysical studies that require high accuracy in the OBS data.
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Erdem, Zeynep, Joachim Schönfeld, Anthony E. Rathburn, Maria-Elena Pérez, Jorge Cardich, and Nicolaas Glock. "Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera." Biogeosciences 17, no. 12 (June 24, 2020): 3165–82. http://dx.doi.org/10.5194/bg-17-3165-2020.
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Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p<0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.
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Wysession, Michael E. "How well do we utilize global seismicity?" Bulletin of the Seismological Society of America 86, no. 5 (October 1, 1996): 1207–19. http://dx.doi.org/10.1785/bssa0860051207.
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Abstract This article describes a method for quantifying the ability to record teleseismic phases at particular epicentral distance ranges, given the geographical history of global seismicity. With the use of geographical sampling maps, we identify the regions of the Earth that are best suited to record the greatest numbers of earthquakes at particular distances. Since seismic studies of the Earth's interior use teleseismic phases that have unique ranges, this information can be useful in the planning of future permanent and temporary deployments of seismometers. Deployment of ocean-bottom seismometers would be required for recording large numbers of earthquakes in the 40° to 80° range, corresponding to phases like ScS and PcP, and in the 140° to 170° range, important for investigations of the PKP branches. An examination of existing analog and digital networks shows that they do either better or worse than a hypothetical grid of evenly spaced seismometers, depending upon the distance range examined. The use of temporary deployments of seismometers, perhaps even in the oceans, may be the best way to significantly sample poorly examined regions of the Earth's interior.
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Ollitrault, Michel, and Jean-Philippe Rannou. "ANDRO: An Argo-Based Deep Displacement Dataset." Journal of Atmospheric and Oceanic Technology 30, no. 4 (April 1, 2013): 759–88. http://dx.doi.org/10.1175/jtech-d-12-00073.1.
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Abstract During the first decade of the twenty-first century, more than 6000 Argo floats have been launched over the World Ocean, gathering temperature and salinity data from the upper 2000 m, at a 10-day or so sampling period. Meanwhile their deep displacements can be used to map the ocean circulation at their drifting depth (mostly around 1000 m). A comprehensive processing of the whole Argo dataset collected prior to 1 January 2010 has been performed to produce a world-wide dataset of deep displacements. This numerical atlas, named ANDRO, after a traditional dance of Brittany meaning a swirl, comprises some 600 000 deep displacements. These displacements, based on Argo or GPS surface locations only, have been fully checked and corrected for possible errors found in the public Argo data files (due to incorrect decoding or instrumental failure). Park pressures measured by the floats while drifting at depth are preserved in ANDRO (less than 2% of the park pressures are unknown): 63% of the float displacements are in the layer (900, 1100) dbar with a good (more or less uniform) degree of coverage of all the oceans, except around Antarctica (south of 60°S). Two deeper layers—(1400, 1600) and (1900, 2100) dbar—are also sampled (11% and 8% of the float displacements, respectively) but with poorer geographical coverage. Grounded cycles (i.e., if the float hits the sea bottom) are excluded. ANDRO is available online as an ASCII file.
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Junying, Sun, Ren Jiawen, and Qin Dahe. "60 years record of biogenic sulfur from Lambert Glacier basin firn core, East Antarctica." Annals of Glaciology 35 (2002): 362–67. http://dx.doi.org/10.3189/172756402781817077.
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AbstractA 15.2 m deep firn core and a 2.7 m snow pit were drilled in the western side of Lambert Glacier basin, East Antarctica, in January 1993. the sampling site LGB16 (72.8˚ S, 57.3˚ E) is located about 650 km from the coast, at approximately 2690ma.s.l. the concentration of methanesulfonate (MSA) was determined in the firn core and snow pit. the continuous MSA record from LGB16, spanning about 60 years from 1933 to 1992, displays a decreasing trend in general, and sharp differences between the upper 10.2 m (corresponding to AD 1952) and the bottom part from 10.2 to 15.2 m. the mean MSA concentration for the whole core is 11.3±14.5 ng g–1; for the upper 10.2 m it is 9.3 ±6.3 ng g–1, compared to 15.4±23.0 ng g–1 for the bottom part. the bottom part has a greater number of high MSA peaks, which is consistent with the Cl– and, to a lesser extent, Na+ records for this core. A negative correlation was observed between sea-ice area for the South Indian Ocean sector (40–90˚E) and MSA concentration in LGB16. No significant link was observed between the high MSA concentration and El Niño events at this location.
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D’Asaro, Eric. "Surface Wave Measurements from Subsurface Floats." Journal of Atmospheric and Oceanic Technology 32, no. 4 (April 2015): 816–27. http://dx.doi.org/10.1175/jtech-d-14-00180.1.
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AbstractPressure gradient measurements on a subsurface Lagrangian float are used to measure the spectrum of surface waves for 100 days of measurements at Ocean Weather Station Papa. Along Lagrangian trajectories of surface waves, the pressure is constant and the vertical pressure gradient fluctuations equal the Eulerian fluctuations at the mean float depth to second order in wave height. Measurement of the pressure difference between the top and the bottom of the float can thus be used to measure the waves. Corrections for the wave decay with depth, for the vertical motion of the float, for the finite sampling interval, and for the sampling noise (among others) are necessary to obtain accurate results. With these corrections, scalar spectra accurately match those from a nearby Waverider buoy for significant wave heights greater than about 3 m. For smaller wave heights, noise in the pressure measurements biases the float spectral measurements. Significant wave height is measured with an rms error of 0.37 m over the measured range of 1–9 m. This demonstrates that Lagrangian floats accurately follow the Lagrangian trajectories of surface waves. More detailed and quieter measurements of float motion could likely measure directional wave spectra from below the surface. Similar methods could be used to infer surface wave properties from other subsurface vehicles.
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Widya, Devita Aristya Sri, Djoko Suprapto, and Churun Ain. "PROFIL BAKTERI TOTAL BERDASARKAN KEDALAMAN WADUK JATIBARANG SEMARANG Profile of Total Bacteria Base On Depth in the Jatibarang Reservoir, Semarang." Management of Aquatic Resources Journal (MAQUARES) 8, no. 4 (January 28, 2020): 321–26. http://dx.doi.org/10.14710/marj.v8i4.26551.
Full textAbstract:
Perairan waduk memiliki karakteristik secara vertikal yang dipengaruhi oleh masuknya sinar matahari ke perairan. Karateristik ini memberikan pengaruh terhadap kualitas air. Salah satu yang mendapatkan pengaruh adalah keberadaan bakteri di perairan. Bakteri adalah mikroorganisme air yang berperan dalam proses dekomposisi di perairan. Tujuan penelitian ini adalah untuk mengetahui total dan profil bakteri di Waduk Jatibarang berdasarkan kedalaman. Penelitian dilakukan pada 27 Maret 2019. Metode penelitian yang digunakan adalah metode deskriptif dengan pendekatan studi kasus. Teknik pengambilan sampel menggunakan metode purposive sampling, yang dilakukan di tujuh stasiun dengan tiga titik kedalaman (permukaan, tengah dan dasar). Perhitungan bakteri total dilakukan berdasarkan SNI Nomor 2332.3.2015 tentang Uji Mikrobiologi-bagian 3: Penentuan Angka Lempeng Total (ALT). Pengelolaan data menggunakan aplikasi SPSS 20 dan analisis sebaran menggunakan Ocean Data View 4. Berdasarkan perhitungan bakteri total di Waduk Jatibarang, total bakteri di permukaan waduk berkisar antara 1,9 × 103 – 1,5 × 105 CFU/ml, pada tengah yaitu 1,3 × 102 – 1,5 × 104 CFU/ml dan pada dasar 1,5 × 103 – 2,7 × 104 CFU/ml. Analisa sebaran bakteri total di Waduk Jatibarang menunjukkan bahwa terdapat kecondongan perbedaan stratifikasi secara vertikal.Reservoir have vertical characteristic be affected by entering sunlight in to waters. This characteristic effected to water quality, such as total bacteria. Bacteria is water microorganism that being a decomposer in the decomposition process. The purpose of this research is to know the consentration and profile of total bacteria base on depth in the Jatibarang Reservoir. The research was conducted on March 27th 2019. The research methods use descriptive methods with case study, and technical sampling methods using purposive sampling in seven stations with three points of depth water (surface, middle, and bottom). Accounting of total bacteria is base on the Standard National of Indonesia Number 2332.3.2015 about Microbiology Analisis-Chapter 3: Plate Number Determintion. Data processing use software SPSS 20 and distribution analysis with Ocean Data View 4. Base on the results, total bacteria in the surface level is 1,9 × 103 – 1,5 × 105 CFU/ml, in the middle is 1,3 × 102 – 1,5 × 104 CFU/ml. Total bcteria in the bottom level is 1,5 × 103 – 2,7 × 104 CFU/ml. Distribution analisis total bacteria in the Jatibarang reservoir show that there is different stratification of total bacteria in tendency vertically.
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Bali, Enikő, László E. Aradi, Robert Zierenberg, Larryn W. Diamond, Thomas Pettke, Ábel Szabó, Guðmundur H. Guðfinnsson, Guðmundur Ó. Friðleifsson, and Csaba Szabó. "Geothermal energy and ore-forming potential of 600 °C mid-ocean-ridge hydrothermal fluids." Geology 48, no. 12 (August 19, 2020): 1221–25. http://dx.doi.org/10.1130/g47791.1.
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Abstract The ∼4500-m-deep Iceland Deep Drilling Project (IDDP) borehole IDDP-2 in Iceland penetrated the root of an active seawater-recharged hydrothermal system below the Mid-Atlantic Ridge. As direct sampling of pristine free fluid was impossible, we used fluid inclusions to constrain the in situ conditions and fluid composition at the bottom of the hydrothermal convection cell. The fluid temperature is ∼600 °C, and its pressure is near-hydrostatic (∼45 MPa). The fluid exists as two separate phases: an H2O-rich vapor (with an enthalpy of ∼59.4 kJ/mol) and an Fe-K–rich brine containing 2000 µg/g Cu, 3.5 µg/g Ag, 1.4 µg/g U, and 0.14 µg/g Au. Occasionally, the fluid inclusions coexist with rhyolite melt inclusions. These findings indicate that the borehole intersected high-energy steam, which is valuable for energy production, and discovered a potentially ore-forming brine. We suggest that similar fluids circulate deep beneath mid-ocean ridges worldwide and form volcanogenic massive sulfide Cu-Zn-Au-Ag ore deposits.
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Feng, Junxi, Niu Li, Min Luo, Jinqiang Liang, Shengxiong Yang, Hongbin Wang, and Duofu Chen. "A Quantitative Assessment of Methane-Derived Carbon Cycling at the Cold Seeps in the Northwestern South China Sea." Minerals 10, no. 3 (March 12, 2020): 256. http://dx.doi.org/10.3390/min10030256.
Full textAbstract:
Widespread cold seeps along continental margins are significant sources of dissolved carbon to the ocean water. However, little is known about the methane turnovers and possible impact of seepage on the bottom seawater at the cold seeps in the South China Sea (SCS). We present seafloor observation and porewater data of six push cores, one piston core and three boreholes as well as fifteen bottom-water samples collected from four cold seep areas in the northwestern SCS. The depths of the sulfate–methane transition zone (SMTZ) are generally shallow, ranging from ~7 to <0.5 mbsf (meters below seafloor). Reaction-transport modelling results show that methane dynamics were highly variable due to the transport and dissolution of ascending gas. Dissolved methane is predominantly consumed by anaerobic oxidation of methane (AOM) at the SMTZ and trapped by gas hydrate formation below it, with depth-integrated AOM rates ranging from 59.0 and 591 mmol m−2 yr−1. The δ13C and Δ14C values of bottom-water dissolved inorganic carbon (DIC) suggest discharge of 13C- and 14C-depleted fossil carbon to the bottom water at the cold seep areas. Based on a two-endmember estimate, cold seeps fluids likely contribute 16–26% of the bottom seawater DIC and may have an impact on the long-term deep-sea carbon cycle. Our results reveal the methane-related carbon inventories are highly heterogeneous in the cold seep systems, which are probably dependent on the distances of the sampling sites to the seepage center. To our knowledge, this is the first quantitative study on the contribution of cold seep fluids to the bottom-water carbon reservoir of the SCS, and might help to understand the dynamics and the environmental impact of hydrocarbon seep in the SCS.
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Hofmann, Andreas F., Peter M. Walz, Hans Thomas, Edward T. Peltzer, and Peter G. Brewer. "High-Resolution Topography-Following Chemical Mapping of Ocean Hypoxia by Use of an Autonomous Underwater Vehicle: The Santa Monica Basin Example." Journal of Atmospheric and Oceanic Technology 30, no. 11 (November 1, 2013): 2630–46. http://dx.doi.org/10.1175/jtech-d-12-00249.1.
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Abstract This paper reports on the execution of a combined chemical sensing/high-resolution terrain-following autonomous underwater vehicle (AUV) survey to explore the fine structure and functional boundaries of the Santa Monica Basin suboxic zone and its relationship to topography. An AUV mapping vehicle is used in a novel configuration—combining the mapping vehicle tail section, with precision inertial navigation and acoustic communications systems, with CTD/O2, NO3 sensing, and Gulper water sampling systems. The challenge was to perform a long-distance near-bottom physical/chemical survey in deep water without any intermediate surfacing to disrupt the survey or require the vehicle to surface in areas of heavy ship traffic. Some 210 km of AUV cruise track at ≈10 m above bottom were accomplished during a 3-day survey. The dissolved oxygen concentration [O2] data are combined with temperature T, salinity S, and hydrostatic pressure P to produce maps of oxygen partial pressure pO2 that help define the limits at which the oceanic supply of O2 can match the O2 demands required to sustain various forms of marine life. The chemical NO3 sensing was included to define the critical pO2 boundary at which NO3 reduction occurs. The combination of a high-resolution terrain-following AUV with chemical sensors is important for a diverse array of investigations, including the study of vent sites, and for locating the source of chemical signals originating from the seafloor. The hypoxic basin example here permits better discrimination between general climate/circulation controls on hypoxia and more specific point-source-driven processes.
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Sandanbata, Osamu, Shingo Watada, Tung-Cheng Ho, and Kenji Satake. "Phase delay of short-period tsunamis in the density-stratified compressible ocean over the elastic Earth." Geophysical Journal International 226, no. 3 (May 17, 2021): 1975–85. http://dx.doi.org/10.1093/gji/ggab192.
Full textAbstract:
SUMMARY Tsunamis are often modelled as surface gravity waves of incompressible homogenous water propagating over a rigid seafloor. Previous studies have noted that when computing long-period tsunamis travelling at trans-oceanic distances with dominant periods of thousands of seconds, we need to consider four factors that are not included in the surface gravity wave theory: compressibility of seawater, density stratification of oceans, elasticity of the Earth and gravitational potential change associated with the tsunami motion. However, their effects on short-period tsunamis with dominant periods below 1000 s have not been examined. Here, we investigate how the four factors influence short-period tsunamis. Theoretical analyses and 1-D simulations using phase speeds of different tsunami models indicate that the resultant phase delay of short-period tsunamis becomes apparent after ∼1000 km propagation, mainly because of the first three factors. We then introduce a new phase correction method for dispersive short-period tsunamis with consideration of period-dependent ray paths and apply it to a 2-D simulation of a short-period tsunami from a submarine volcanic earthquake near Japan in 2015. The correction of the traveltime of a synthetic waveform by including the four factors amounts to ∼40 s at a distant station 1430 km away from the source, whereas the effects of the four factors on the waveforms are negligibly small at stations < ∼500km from the source. The observed traveltime at the ocean bottom pressure (OBP) gauge with a sampling interval at 15 s of the distant station can be explained only when these factors are incorporated into synthetic waveforms, indicating the effects due to the four factors are detectable by high-sampling OBP gauges that are deployed over broad oceanic regions.
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Joye, S. B., I. R. MacDonald, J. P. Montoya, and M. Peccini. "Geophysical and geochemical signatures of Gulf of Mexico seafloor brines." Biogeosciences 2, no. 3 (October 28, 2005): 295–309. http://dx.doi.org/10.5194/bg-2-295-2005.
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Abstract. Geophysical, temperature, and discrete depth-stratified geochemical data illustrate differences between an actively venting mud volcano and a relatively quiescent brine pool in the Gulf of Mexico along the continental slope. Geophysical data, including laser-line scan mosaics and sub-bottom profiles, document the dynamic nature of both environments. Temperature profiles, obtained by lowering a CTD into the brine fluid, show that the venting brine was at least 10°C warmer than the bottom water. At the brine pool, thermal stratification was observed and only small differences in stratification were documented between three sampling times (1991, 1997 and 1998). In contrast, at the mud volcano, substantial temperature variability was observed, with the core brine temperature being slightly higher than bottom water (by 2°C) in 1997 but substantially higher than bottom water (by 19°C) in 1998. Detailed geochemical samples were obtained in 2002 using a device called the "brine trapper" and concentrations of dissolved gases, major ions and nutrients were determined. Both brines contained about four times as much salt as seawater and steep concentration gradients of dissolved ions and nutrients versus brine depth were apparent. Differences in the concentrations of calcium, magnesium and potassium between the two brine fluids suggest that the fluids are derived from different sources, have different dilution/mixing histories, or that brine-sediment reactions are more important at the mud volcano. Substantial concentrations of methane, ammonium, and silicate were observed in both brines, suggesting that fluids expelled from deep ocean brines are important sources of these constituents to the surrounding environment.
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Burd, Brenda J., and Richard E. Thomson. "Seasonal patterns in deep acoustic backscatter layers near vent plumes in the northeastern Pacific Ocean." FACETS 4, no. 1 (June 1, 2019): 183–209. http://dx.doi.org/10.1139/facets-2018-0027.
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We used moored 75 kHz acoustic Doppler current profilers (ADCPs) to examine seasonal cycles in zooplankton deep scattering layers (DSLs) observed below 1300 m depth at Endeavour Ridge hydrothermal vents. DSLs are present year-round in the lower water column near vent plumes. Temporal variations suggest passive, flow-induced displacements superimposed on migratory movements. Although the strongest DSLs are shallower than the neutrally buoyant plumes (1900–2100 m), anomalies also occur at and below plume depth. Upward movement from plume depth in the main DSL is evident in late summer/fall, resulting in shallower DSLs in winter, consistent with the timing of adult diapause/reproduction in upper-ocean migratory copepods. Movement from the upper ocean to plume depth coincides with pre-adult migration to greater depths in spring. Synchronous 20–40 d cycles in DSLs may account for patchiness in space and time of above-plume zooplankton layers observed in summer during previous net-sampling surveys, and suggests lateral and vertical migratory movements to counter current drift away from plume-derived food sources. Persistent near-bottom DSLs move vertically between the spreading plume and seafloor. Historical net data suggests that these are deep, resident fauna. Unlike upper ocean fauna, they seem to be advected considerable distances from the ridge axis, where they are evident as remnant scattering layers.
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Donohue, Kathleen A., Maureen A. Kennelly, and Amy Cutting. "Sea Surface Height Variability in Drake Passage." Journal of Atmospheric and Oceanic Technology 33, no. 4 (April 2016): 669–83. http://dx.doi.org/10.1175/jtech-d-15-0249.1.
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AbstractIntercomparisons between altimeter sea surface height (SSH) and open-ocean in situ observations have been limited owing to sparse available datasets. Here, SSH anomaly (SSHA) determined from current and pressure recording inverted echo sounders (CPIES) from the cDrake experiment were compared with an up-to-date AVISO-mapped product. Meandering Antarctic Circumpolar Current (ACC) fronts in the passage interior elevated SSHA variance; south of the Shackleton Fracture Zone and along the northern continental slope, the variance decreased by factors between 6 and 10. In situ analysis focused on the two constituents of SSHA, SSHAref determined from bottom pressure and SSHAbcb calculated from geopotential height referenced to the bottom. The peak variance of both SSHAbcb and SSHAref occurred in the energetic region between the Subantarctic Front and the Polar Front. The contribution of SSHAbcb to total SSHA variance was greater than 40% at all sites and averaged over all sites it was 73%. For most sites, high-frequency (>1/20 cpd) SSHAbcb signals dominated total high-frequency variance. Aliasing of high-frequency signals resulting from 10-day altimeter sampling was assessed. The fraction of aliased energy at frequencies longer than 1/50 cpd for sites at and north of the Shackleton Fracture Zone approached 0.25 and approached 0.50 for southern sites. CPIES and mapped altimeter SSHA agreed well. The mean correlation coefficient was 0.82 and the mean RMS difference was 0.075 m. Correlations between CPIES and AVISO were notably poorer at the northern and southern boundaries. RMS differences increased as a function of CPIES high-frequency SSHA variance because the mapped altimetry product does not resolve these frequencies.
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Baumstein, Anatoly, and Ramesh Neelamani. "Accurate data reconstruction through simultaneous application of statistical and physics-based constraints to multiple geophysical data sets." GEOPHYSICS 75, no. 6 (November 2010): WB165—WB172. http://dx.doi.org/10.1190/1.3481653.
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Insufficient sampling is a key problem that affects seismic data-processing techniques. Although existing interpolation methods can fill in large gaps in the data under certain assumptions, their performance degrades as shot and receiver sampling becomes coarser. Most existing data-interpolation techniques overcome insufficient sampling by making assumptions regarding either the statistical properties of the data or the physics that explain the data. Recognizing that statistical and physics-based constraints can be expressed as convex sets, we propose overcoming some of the deficiencies of existing methods by incorporating multiple types of prior information and equations describing the mapping between different types of data into a mathematically consistent framework based on the projection onto convex sets (POCS) methodology. The proposed method is easy to implement in practice because it relies only upon the iterative application of projection operators (e.g., soft thresholding). At the same time, full advantage of various forms of prior information can be taken. Using a synthetic example of combining conventional streamer and ocean-bottom–cable (OBC) data, we show that our method provides substantial improvement compared to using statistical assumptions alone. Other potential applications include data reconstruction in the case of over-under streamer acquisition, dual-sensor streamer acquisition, multi-azimuth surveys, and vertical seismic profiling.
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Urn, Tze W., and John R. Potter. "Pop-up Ambient Noise Data Acquisition (PANDA) System." Marine Technology Society Journal 33, no. 1 (January 1, 1999): 45–54. http://dx.doi.org/10.4031/mtsj.33.1.6.
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The Pop-up Ambient Noise Data Acquisition (PANDA) system described in this paper is a compact, cost-effective and self-contained submerged data acquisition system for collecting acoustic data. PANDA can be bottom-mounted, collecting data without surface eocpression, making it ideal for collecting data in high shipping and/or fishing activity locations. Assembled largely from “commercial off-the-shelf (COTS) components, the design time and unit cost have been minimised without compromising reliability. The electronic design is based on a PC motherboard computer system. The system as currently configured has a maximum sampling rate of 330 kHz and a maximum storage capacity of 1.2 GB. These values can be changed simply by exchanging COTS plug-in components. This flexibility of design, permitting the configuration to be changed quickly and cheaply to suit different deployment requirements, is an important feature of the system. The system can also be configured to record from multiple transducers of all types. PANDA was designed and built in 7 months, and is currently being used to collect long-term samples of ambient noise for ship noise analysis. Some example data are presented to illustrate the system’s capability.
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White, Brittny A., James McClintock, Charles D. Amsler, Christopher L. Mah, Margaret O. Amsler, Stephanie White, Langdon B. Quetin, and Robin M. Ross. "The abundance and distribution of echinoderms in nearshore hard-bottom habitats near Anvers Island, western Antarctic Peninsula." Antarctic Science 24, no. 6 (July 26, 2012): 554–60. http://dx.doi.org/10.1017/s0954102012000569.
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AbstractEchinoderms are well represented in nearshore hard-bottom (< 100 m depth) habitats along the Antarctic Peninsula where they are presumably important contributors to benthic production, carbon flow, and determinants of community structure. The present study assesses the densities of echinoderms at shallow depths (2–15 m) at five sampling sites within three kilometres of Anvers Island on the central western Antarctic Peninsula. The asteroids Odontaster validus, Granaster nutrix, Lysasterias perrieri and Adelasterias papillosa, two ophiuroids in the Amphiuridae, the holothuroids Psolicrux coatsi and Psolus carolineae and one representative of the Cucumaridae, and the regular echinoid Sterechinus neumayeri were enumerated. Mean total echinoderm densities were high (34.9 individuals m-2) and ranged from 21.9 individuals m-2 for asteroids to 2.7 individuals m-2 for holothuroids. With the exception of a positive relationship between the abundance of the regular echinoid Sterechinus neumayeri and the biomass of the brown alga Himanthothallus grandifolius, no significant relationships were found between the abundance of asteroids, ophiuroids, or holothuroids and two species of brown algae or three algal ecotypes. The present study indicates nearshore hard-bottom echinoderms are important in the carbon cycle and their inherent vulnerability to ocean acidification may have community-level impacts.
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Braga, Elisabete de Santis, Vitor Gonsalez Chiozzini, and Chiara Machado Vieira. "Seasonal variation of nutrients and hydrological conditions in the State Marine Park of Laje de Santos (SMPLS) and adjacent continental shelf areas (South Atlantic Ocean - Brazil)." Brazilian Journal of Oceanography 65, no. 4 (December 2017): 628–43. http://dx.doi.org/10.1590/s1679-87592017136806504.
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Abstract Marine parks constitute important areas for the conservation of marine life and the genetic heritage around the world. The creation of such marine parks must be accompanied by careful measures to guarantee the coexistence of natural biota and human activities in these systems. The State Marine Park of Laje de Santos (SMPLS) is so close to an industrial pole and urban area that its creation and maintenance is an example for humanity. However, no program has yet been installed for the monitoring of its biotic and abiotic water parameters. Thus, the objective of this study is to provide hydrological and hydrochemical parameters with emphasis on dissolved nutrients to establish a starting point for the monitoring of these waters. The presence of the South Atlantic Central Water (SACW) in the marine park during the spring and summer sampling periods was evidenced by the observation of low temperatures (< 17ºC) associated with salinity around 35 at the bottom of the water column, indicating a thermohaline feature. The dissolved oxygen presented high values, with few data below 4 mL L-1 occurring at the bottom of the water column. The pH was always in accordance with marine values (~8). Dissolved silicate and phosphate presented high values associated with inputs from the SACW intrusion, continental runoff and bottom resuspension processes, reaching maximum values of 15.86 and 1.23 µmol L-1, respectively. Nitrogen compounds were also associated with a natural fertilization process by the presence of the SACW at the bottom of the water column, as evidenced by the high nitrate concentrations (> 7.00 µmol L-1), while the concentration of N-ammonium (maximum 9.86 µmol L-1) demonstrated a rapid regeneration of the organic matter, mainly in the euphotic zone. Analysis of the data from summer periods revealed an annual difference, showing January 2014 to be drier than January 2015, which influenced the availability of some nutrients and the standard distribution of hydrochemical parameters in this region. The results of the distribution of hydrochemical parameters in the marine park confirms the preserved conditions of the seawater around the Laje de Santos, demonstrated by the excellent water quality, concluding the need to implant monitoring actions based on these reference data to preserve this important reserve of marine life.
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Vihtakari, Mikko, Robinson Hordoir, Margaret Treble, Meaghan D. Bryan, Bjarki Elvarsson, Adriana Nogueira, Elvar H. Hallfredsson, Jørgen Schou Christiansen, and Ole Thomas Albert. "Pan-Arctic suitable habitat model for Greenland halibut." ICES Journal of Marine Science 78, no. 4 (March 8, 2021): 1340–56. http://dx.doi.org/10.1093/icesjms/fsab007.
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Abstract Deep-sea marine fishes support important fisheries but estimates of their distributions are often incomplete as the data behind them may reflect fishing practices, access rights, or political boundaries, rather than actual geographic distributions. We use a simple suitable habitat model based on bottom depth, temperature, and salinity to estimate the potential distribution of Greenland halibut (Reinhardtius hippoglossoides). A large presence-only dataset is examined using multivariate kernel densities to define environmental envelopes, which we link to spatial distribution using a pan-Arctic oceanographic model. Occurrences generally fit the model well, although there were gaps in the predicted circum-Arctic distribution likely due to limited survey activity in many of the ice-covered seas around the Arctic Ocean. Bottom temperature and depth were major factors defining model fit to observations, but other factors, such as ecosystem interactions and larval drift could also influence distribution. Model predictions can be tested by increasing sampling effort in poorly explored regions and by studying the connectivity of putative populations. While abundances of Greenland halibut in the High Arctic are currently low, some areas are predicted to be suitable habitat for this species, suggesting that on-going sea-ice melt may lead to fisheries expansion into new areas.
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Svendsen, GM, M. Ocampo Reinaldo, MA Romero, G. Williams, A. Magurran, S. Luque, and RA González. "Drivers of diversity gradients of a highly mobile marine assemblage in a mesoscale seascape." Marine Ecology Progress Series 638 (March 19, 2020): 149–64. http://dx.doi.org/10.3354/meps13264.
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With the unprecedented rate of biodiversity change in the world today, understanding how diversity gradients are maintained at mesoscales is a key challenge. Drawing on information provided by 3 comprehensive fishery surveys (conducted in different years but in the same season and with the same sampling design), we used boosted regression tree (BRT) models in order to relate spatial patterns of α-diversity in a demersal fish assemblage to environmental variables in the San Matias Gulf (Patagonia, Argentina). We found that, over a 4 yr period, persistent diversity gradients of species richness and probability of an interspecific encounter (PIE) were shaped by 3 main environmental gradients: bottom depth, connectivity with the open ocean, and proximity to a thermal front. The 2 main patterns we observed were: a monotonic increase in PIE with proximity to fronts, which had a stronger effect at greater depths; and an increase in PIE when closer to the open ocean (a ‘bay effect’ pattern). The originality of this work resides on the identification of high-resolution gradients in local, demersal assemblages driven by static and dynamic environmental gradients in a mesoscale seascape. The maintenance of environmental gradients, specifically those associated with shared resources and connectivity with an open system, may be key to understanding community stability.
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O’Hern, T. J., L. d’Agostino, and A. J. Acosta. "Comparison of Holographic and Coulter Counter Measurements of Cavitation Nuclei in the Ocean." Journal of Fluids Engineering 110, no. 2 (June 1, 1988): 200–207. http://dx.doi.org/10.1115/1.3243535.
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Holographic and Coulter Counter detection techniques were jointly used to measure the concentration density distribution of cavitation nuclei in the ocean. Comparison of the two techniques indicates that Coulter Counter analysis measures particulate contents up to an order of magnitude smaller than indicated by the holographic method and may also produce a distorted concentration density distribution. Several possible explanations of the observed discrepancies are proposed and discussed, including fundamental differences between the in situ holographic samples and the collected samples examined with the Coulter Counter, differences between the unknown electrical conductivity of the measured particles in the sea water samples and the non-conductive polystyrene spheres used to calibrate the Coulter Counter, the rupture of aggregate particles in the flow through the Coulter Counter orifice, the effect of electronic noise on the Coulter Counter signal, and the influence of statistical sampling error. The particle number concentration density distributions decrease approximately with the fourth power of the particle radius in the observed size range of 10 to 50 μm radius. Both sets of data indicate an increase in particle concentration near the bottom of the thermocline, and the holographic bubble concentrations also indicate a similar behavior. Much higher concentrations of particles were detected in the ocean, according to the holographic analysis, than in typical cavitation test facilities. Consideration of the static mechanical equilibrium of individual air bubbles suggests that the average tensile strength of the ocean waters examined in this study is not larger than about 2000 Pa and occasionally as low as about 100 Pa.
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Carluccio, Angela, Francesca Capezzuto, Porzia Maiorano, Letizia Sion, and Gianfranco D’Onghia. "Deep-Water Cartilaginous Fishes in the Central Mediterranean Sea: Comparison between Geographic Areas with Two Low Impact Tools for Sampling." Journal of Marine Science and Engineering 9, no. 7 (June 22, 2021): 686. http://dx.doi.org/10.3390/jmse9070686.
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Baited lander represents a low impact technique, an alternative to the traditional trawl sampling for collecting data on fish diversity and abundance, especially for threatened species such as Chondrichthyes living in sensitive habitats. In this study, distribution and abundance of cartilaginous fish were compared between two geographic areas, the southern Adriatic Sea and the north-western Ionian Sea, with two low impact sampling gears, an experimental bottom longline and a baited lander. Species diversity was evaluated by applying ecological indices and difference in mean abundances were tested using multivariate analysis. A total of 13 species of cartilaginous fish were collected. Significant differences in the assemblage recorded in the same area using different sampling tools were detected and no significant differences were detected among different areas explored with the same method. Using longline, the most abundant species collected in both areas was Galeus melastomus, while using lander, the most observed species were Dalatias licha in the southern Adriatic Sea and Hexanchus griseus in the north-western Ionian Sea. According to IUCN classification, of the 13 species collected, 2 are near threatened and 5 are threatened. A better governance of sensitive habitats coinciding with the essential fish habitat for these species would ensure them a better conservation status.
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SMITH, W. A. M. NIMMO, J. KATZ, and T. R. OSBORN. "The effect of waves on subgrid-scale stresses, dissipation and model coefficients in the coastal ocean bottom boundary layer." Journal of Fluid Mechanics 583 (July 4, 2007): 133–60. http://dx.doi.org/10.1017/s0022112007006118.
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Six sets of particle image velocimetry (PIV) data from the bottom boundary layer of the coastal ocean are examined. The data represent periods of high, moderate and weak mean flow relative to the amplitude of wave-induced motion, which correspond to high, moderate and low Reynolds numbers based on the Taylor microscale (Re). The two-dimensional PIV velocity distributions enable spatial filtering to calculate some of the subgrid-scale (SGS) stresses, from which we can estimate the SGS dissipation, and evaluate the performance of typically used SGS stress models. The previously reported mismatch between the SGS and viscous dissipation at moderate and low Reynolds numbers appears to be related to the sparsity of large vortical structures that dominate energy fluxes.Conditional sampling of SGS stresses and dissipation based on wave phase using Hilbert transforms demonstrate persistent and repeatable direct effects of large-scale but weak straining by the waves on the SGS energy flux at small scales. The SGS energy flux is phase-dependent, peaking when the streamwise-wave-induced velocity is accelerating, and lower when this velocity is decelerating. Combined with strain rate generated by the mean flow, the streamwise wave strain causes negative energy flux (backscatter), whereas the vertical wave strain causes a positive flux. The phase-dependent variations and differences between horizontal and vertical contributions to the cascading process extend to strains that are substantially higher than the wave-induced motion. These trends may explain the measured difference between spatial energy spectra of streamwise velocity fluctuations and spectra of the wall-normal component, i.e. the formation of spectral bumps in the spectra of the streamwise component at the wavenumbers for the transition between inertial and dissipation scales.All the model coefficients of typical SGS stress models measured here are phase dependent and show similar trends. Thus, the variations of measured SGS dissipation with phase are larger than those predicted by the model variables. In addition, the measured coefficients of the static Smagorinsky SGS stress model decrease with decreasing turbulence levels, and increase with filter size. The dynamic model provides higher correlation coefficients than the Smagorinsky model, but the substantial fluctuations in their values indicate that ensemble averaging is required. The ‘global’ dynamic model coefficients indicate that the use of a scale-dependent dynamic model may be appropriate. The structure function model yields poor correlation coefficients and is found to be over-dissipative under all but the highest turbulence levels. The nonlinear model has higher correlations with measured stresses, as expected, but it also does not reproduce the trends with wave phase.
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Grevemeyer, Ingo. "Upper Mantle Structure beneath the Mid-Atlantic Ridge from Regional Waveform Modeling." Bulletin of the Seismological Society of America 110, no. 1 (January 14, 2020): 18–25. http://dx.doi.org/10.1785/0120190080.
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ABSTRACT The lithosphere is the outermost rigid layer of the Earth and includes the crust and brittle uppermost mantle. Because the poor seismic coverage of the ocean basins is the mantle structure of young lithosphere below midocean spreading centers poorly constrained, especially along slow spreading ridges. Surface waves radiated by midocean ridge earthquakes are excellent agents to study young lithosphere when being recorded in the vicinity of the ridge crest. Here, we use body and Rayleigh waves from six central Atlantic transform fault earthquakes with magnitude Mw>6 to constrain upper mantle structure away from ocean islands. Earthquakes were recorded by a network of broadband ocean-bottom seismometers deployed at the Mid-Atlantic Ridge (MAR) near 14°45′ N. Waveform modeling of vertical-component data at periods of 10–60 s yielded the velocity structure of the uppermost ∼100 km of the mantle and hence of the depth interval where lithospheric cooling is most evident. The data support that both S-wave velocity of the lithospheric lid and its thickness increases with age; velocities increase from 4.35 to 4.75 km/s and thickness from 30–50 to 70 km, sampling mantle with an average path age of ∼7 and 18 My, respectively. With respect to constraints found previously in the Pacific, lid velocities beneath the MAR are faster than beneath fast-spreading ridges, whereas asthenospheric velocities are similar to the Pacific. The fast velocity of the lid and slow velocity of the inversion zone may indicate effective hydrothermal cooling of the lithosphere.
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Guðmundsson, Kristinn, Mike R. Heath, and Elizabeth D. Clarke. "Average seasonal changes in chlorophyll a in Icelandic waters." ICES Journal of Marine Science 66, no. 10 (August 13, 2009): 2133–40. http://dx.doi.org/10.1093/icesjms/fsp208.
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Abstract Guðmundsson, K., Heath, M. R., and Clarke, E. D. 2009. Average seasonal changes in chlorophyll a in Icelandic waters. – ICES Journal of Marine Science, 66: 2133–2140. The standard algorithms used to derive sea surface chlorophyll a concentration from remotely sensed ocean colour data are based almost entirely on the measurements of surface water samples collected in open sea (case 1) waters which cover ∼60% of the worlds oceans, where strong correlations between reflectance and chlorophyll concentration have been found. However, satellite chlorophyll data for waters outside the defined case 1 areas, but derived using standard calibrations, are frequently used without reference to local in situ measurements and despite well-known factors likely to lead to inaccuracy. In Icelandic waters, multiannual averages of 8-d composites of SeaWiFS chlorophyll concentration accounted for just 20% of the variance in a multiannual dataset of in situ chlorophyll a measurements. Nevertheless, applying penalized regression spline methodology to model the spatial and temporal patterns of in situ measurements, using satellite chlorophyll as one of the predictor variables, improved the correlation considerably. Day number, representing seasonal variation, accounted for substantial deviation between SeaWiFS and in situ estimates of surface chlorophyll. The final model, using bottom depth and bearing to the sampling location as well as the two variables mentioned above, explained 49% of the variance in the fitting dataset.