Seawater Velocities Research Articles

Seismological Constraints on the Causes of Intraplate Earthquakes in Yangjiang Region, South China

AbstractLarge earthquakes that occur away from plate boundaries (i.e., large intraplate earthquakes), though rare, could cause heavy damage. Understanding their causes could help with seismic hazard assessment. In this study, we image the seismogenic structure under the 1969 Ms6.4 Yangjiang intraplate earthquake within the stable South China Block with a high‐resolution three‐dimensional shear‐wave velocity model constructed from ambient noise tomography based on a dense nodal seismic array. The model images relatively low velocities at a fault intersection region from the surface to at least 13 km depth in the Yangjiang seismogenic zone. Given spatial links among the intersection zone of faults, surface seawater, and low velocities, we interpret the low velocities to reflect the presence of seawater‐filled, highly fractured rocks created by the intersection of faults. We infer that the seawater infiltration through densely‐fractures could have elevated pore pressure in the long term, as evidenced by low earthquake b values at 8–13 km depths. We hypothesize that this long‐term seawater infiltration could have lowered the stress threshold of earthquake occurrence and contributed to the generation of the 1969 Ms6.4 Yangjiang earthquake. We propose that the large intraplate earthquakes within stable plates tend to occur in regional weakening regions (e.g., fault intersections) favorable to stress buildup. Given sufficient tectonic stress accumulation, the long‐term hydrologically driven crustal stress variations could play an essential role in triggering large intraplate earthquakes. This study could potentially contribute to improving seismic hazard assessment in the Guangdong‐Hong Kong‐Macao‐Greater‐Bay‐Area, China.

Grounding Event of Iceberg D28 and Its Interactions with Seabed Topography

Iceberg D28, a giant tabular iceberg that calved from Amery Ice Shelf in September 2019, grounded off Kemp Coast, East Antarctica, from August to September of 2020. The motion of the iceberg is characterized herein by time-series images captured by synthetic aperture radar (SAR) on Sentinel-1 and the moderate resolution imaging spectroradiometer (MODIS) boarded on Terra from 6 August to 15 September 2020. The thickness of iceberg D28 was estimated by utilizing data from altimeters on Cryosat-2, Sentinel-3, and ICESat-2. By using the iceberg draft and grounding point locations inferred from its motion, the maximum water depths at grounding points were determined, varying from 221.72 ± 21.77 m to 269.42 ± 25.66 m. The largest disagreements in seabed elevation inferred from the grounded iceberg and terrain models from the Bedmap2 and BedMachine datasets were over 570 m and 350 m, respectively, indicating a more complicated submarine topography in the study area than that presented by the existing seabed terrain models. Wind and sea water velocities from reanalysis products imply that the driving force from sea water is a more dominant factor than the wind in propelling iceberg D28 during its grounding, which is consistent with previous findings on iceberg dynamics.

Experimental evaluation of the effect of water velocity on the development of string-attached kelp seedlings (Laminariales) with implications for hatchery and nursery production

Kelp sea farming is performed using seedlings (early stage of sporophyte development) attached to string, known as seedling string, which are produced from an indoor culture under controlled environmental conditions. However, very little is known about the influence of water movement and the optimal growth level of early kelp sporophytes on string. Thus, the present study evaluated the development of string-attached kelp seedlings (Undaria pinnatifida) simultaneously exposed to simulated seawater velocities in an indoor tank. The experiment was conducted using string that had seedlings approximately 2mm in length, whose growth was measured after 28 and 56 days of culture. Seawater velocity level was found to significantly influence both the rates of increase in total biomass (dry weight) and in length of kelp seedlings on string. Seedling growth rates increased up to a water velocity range of 15.8–17.1cm s−1 beyond which it declined. This pattern is similar for the two time periods explored during the experiment, although both growth rates were significantly higher during the first 28 days of culture than after 56 days of culture. This difference is related to the increase in kelp seedling size throughout the experiment, and this increase could affect the requirements and/or optimal environmental conditions for their growth. In addition, comparatively, the rate of total biomass increase for seedlings was significantly higher than the rate of length increase for seedlings, indicating seawater velocity favours greater biomass productivity over length increase. Based on these results, suitable seawater velocities are recommended that would be the most productive for kelp seedling growth on strings in hatchery and nursery phases.

Building a Maxey–Riley framework for surface ocean inertial particle dynamics

A framework for the study of surface ocean inertial particle motion is built from the Maxey–Riley set. A new set is obtained by vertically averaging each term of the original set, adapted to account for Earth’s rotation effects, across the extent of a sufficiently small spherical particle that floats at an assumed unperturbed air–sea interface with unsteady nonuniform winds and ocean currents above and below, respectively. The inertial particle velocity is shown to exponentially decay in time to a velocity that lies close to an average of seawater and air velocities, weighted by a function of the seawater-to-particle density ratio. Such a weighted average velocity turns out to fortuitously be of the type commonly discussed in the search-and-rescue literature, which alone cannot explain the observed role of anticyclonic mesoscale eddies as traps for marine debris or the formation of great garbage patches in the subtropical gyres, phenomena dominated by finite-size effects. A heuristic extension of the theory is proposed to describe the motion of nonspherical particles by means of a simple shape factor correction, and recommendations are made for incorporating wave-induced Stokes drift and allowing for inhomogeneities of the carrying fluid density. The new Maxey–Riley set outperforms an ocean adaptation that ignored wind drag effects and the first reported adaption that attempted to incorporate them.

Dealuminification of heat exchanger tubes

This paper presents a failure analysis of heat exchanger tubes manufactured from aluminum bronze. The equipment operates as an intercooler after the first stage compression. The cooling medium was seawater that passed inside the tubes. The investigation involved visual inspection, chemical analysis, metallography, hardness test, scanning electron microscope analysis, and thermal-hydraulic evaluation.The aluminum content of the analyzed tube was higher than the maximum value defined by the design specification ASTM B111 C61400. The high aluminum content promoted γ2 phase formation that was preferentially attacked from the tube inner surface. The tubes failed due to dealloying (dealuminification) associated with under-deposit corrosion in regions of higher temperatures and lower seawater velocities.

Attachment capacity of the sea urchin Paracentrotus lividus in a range of seawater velocities in relation to test morphology and tube foot mechanical properties

Intertidal rocky shores are stressful environments where benthic invertebrates experience large wave-induced hydrodynamic forces that can detach them from the substratum. The tube feet of echinoids counteract these forces and help them remain securely affixed. Sea urchins display a high degree of phenotypic plasticity which may help them cope with hydrodynamic stress. We evaluated whether habitats presenting different seawater velocities induce plastic responses in the attachment capacity of the sea urchin Paracentrotus lividus by quantifying their morphology and the adhesive and mechanical properties of their tube feet. Intertidal adult sea urchins from three subpopulations were collected around the Crozon peninsula (France). Localities differed according to measured water velocities. Size was significantly lower in the two most exposed sites where sea urchins also presented a higher density of tube feet. Tube foot adhesive properties were not significantly different between sites, but their extensibility and toughness were significantly higher in individuals from the most exposed site. Using this information, we calculated a safety factor to predict the flow velocity that would cause detachment from the substratum. It showed individuals from the most exposed habitat would resist higher flow velocities (up to 7.59 ± 0.90 m s−1). Both morphometry and tube foot mechanical properties vary among subpopulations and show an intraspecific plasticity in P. lividus. Although, differences in sea water velocity may be one cause of this intraspecific variation, it likely results from a combination of biotic and abiotic factors.

Numerical investigation of the Arctic ice–ocean boundary layer and implications for air–sea gas fluxes

Abstract. In ice-covered regions it is challenging to determine constituent budgets – for heat and momentum, but also for biologically and climatically active gases like carbon dioxide and methane. The harsh environment and relative data scarcity make it difficult to characterize even the physical properties of the ocean surface. Here, we sought to evaluate if numerical model output helps us to better estimate the physical forcing that drives the air–sea gas exchange rate (k) in sea ice zones. We used the budget of radioactive 222Rn in the mixed layer to illustrate the effect that sea ice forcing has on gas budgets and air–sea gas exchange. Appropriate constraint of the 222Rn budget requires estimates of sea ice velocity, concentration, mixed-layer depth, and water velocities, as well as their evolution in time and space along the Lagrangian drift track of a mixed-layer water parcel. We used 36, 9 and 2 km horizontal resolution of regional Massachusetts Institute of Technology general circulation model (MITgcm) configuration with fine vertical spacing to evaluate the capability of the model to reproduce these parameters. We then compared the model results to existing field data including satellite, moorings and ice-tethered profilers. We found that mode sea ice coverage agrees with satellite-derived observation 88 to 98 % of the time when averaged over the Beaufort Gyre, and model sea ice speeds have 82 % correlation with observations. The model demonstrated the capacity to capture the broad trends in the mixed layer, although with a significant bias. Model water velocities showed only 29 % correlation with point-wise in situ data. This correlation remained low in all three model resolution simulations and we argued that is largely due to the quality of the input atmospheric forcing. Overall, we found that even the coarse-resolution model can make a modest contribution to gas exchange parameterization, by resolving the time variation of parameters that drive the 222Rn budget, including rate of mixed-layer change and sea ice forcings.

Canopy macroalgae influence understorey corallines’ metabolic control of near-surface pH and oxygen concentration

Understorey macroalgae can alter pH at their surface via metabolic activity within the concentration boundary layer (CBL), but it is unknown to what degree the presence of larger macroalgal canopies can modify the pH micro-environment of understorey species. We examined whether flow reduction by a canopy-forming macroalga could alter the thickness of the CBL at the surface of understorey crustose coralline macroalgae (CCA). This could lead to a greater metabolic influence of macroalgae on the pH and oxygen environment at the coralline’s surface. Three experimental treatments were examined in a re-circulating flume: (1) a full canopy (consisting of Carpophyllum maschalocarpum ) and understorey ( Corallina officinalis and CCA), (2) a mimic (plastic/silk) canopy plus understorey, and (3) an understorey only. Profiles of seawater velocity and pH/O 2 concentration gradients were measured at 3 bulk seawater velocities (2, 4 and 8 cm s -1 ) above the CCA in both the light and dark. Canopy macroalgae altered the pH and O 2 environment encountered by understorey coralline algae via their physical presence rather than by directly altering bulk seawater chemistry through their metabolism. Reduced seawater velocities beneath Carpophyllum and mimic canopies resulted in increased CBL thicknesses, higher pH (up to 8.9) and O 2 concentrations in the light, and lower pH (down to 7.74) and O 2 concentrations in the dark. The ability of canopies to facilitate greater metabolic changes in pH at the surface of understorey species highlights a previously unrecorded species interaction that could play an important role in influencing the physiology and ecology of understorey assemblages.

Trait-mediated ecosystem impacts: how morphology and size affect pumping rates of the Caribbean giant barrel sponge

Sponges are a dominant component of Caribbean coral reef suspension-feeding communi- ties. Understanding how pumping rates are affected by sponge size and morphology, as well as the en - vironment, is fundamental to understanding the ecological interactions that are mediated by sponge filtration. In a comprehensive in situ investigation of sponge pumping, the excurrent seawater velocities of 274 specimens of the largest Caribbean species, the giant barrel sponge Xestospongia muta, were measured at sites in the Bahamas and Florida Keys to investigate (1) the relationship between excurrent velocity distributions and sponge morphology, (2) the scaling relationship between pumping and sponge size, and (3) temporal variation of pumping and sensitivity to environmental changes. Excurrent velocity distributions across the osculum showed peak velocities at the center and diminishing veloci- ties near the edges of the osculum. The degree of center-weighting was explained by the distribution of sponge biomass relative to the spongocoel. Volu- metric pumping rates scaled isometrically with sponge size and averaged 0.06 ± 0.04 l s −1 l −1 sponge tissue, but were reduced for extremely large sponges. Pumping activity was relatively constant over short temporal scales, but varied over longer scales; how- ever, variations in pumping rates, in cluding periods of cessation, were asynchronous across the pop - ulation and uncorrelated with changes in environ- mental conditions. We estimate that populations of X. muta in the Florida Keys and Bahamas process a volume of water equivalent to a layer 1.7 to 12.9 m thick each day and overturn the water column every 2.3 to 18.0 d.

Effect of biofouling on corrosion behaviour of grade 2 titanium in Mandapam seawaters

Titanium has the ability to withstand extremely high seawater velocities with negligible corrosion. The inherent passive nature of the metal favours the attachment of bio-organisms more. In this paper the biofouling characteristics and the influence of macrofouling on grade 2 titanium have been investigated in the Palk Bay waters of Mandapam (India) over a period of a year.This work comprises both field exposure as well as laboratory studies. The deposits on titanium were analyzed with the XRD technique. Green algae such as Cladophorapsis zoolengeri, Cheatomorpha area, Chlorodesmis hillibrandii, Enteromorpha intestinalis, Cladophora species and red algae species of Hypnea valentiae, and animals such as bryozoans and barnacles 4 mm in size were identified on the titanium metal surface. The effect of macrofouling on corrosion of titanium was investigated by both impedance and polarization techniques. Titanium experienced negligible corrosion in seawater exposure with an appreciable fouling load of 0.4527 kg.m −2y −1.

Variation in sessile microflora as function of flow velocity on coupons exposed to seawater

The variability of several groups of microorganisms on AISI 1020 carbon steel coupons as a function of seawater velocity in a water circulation loop was investigated. The metal probes as well as electrodes were fixed onto ducts connected to a 35l capacity tank, in order to study both biofilm formation and some electrochemical parameters. The experiments were carried out at different seawater velocities. The technique of the most probable number was used to enumerate bacterial aerobes and anaerobes as well as sulphate-reducing bacteria and iron-reducing bacteria. Fungi were quantified by counting the number of colony forming units. At velocities of 3.6 cm/s, which correspond to a laminar flow, the numbers of aerobic and anaerobic bacteria attached to the metal surfaces reached a maximum. Such values were markedly reduced at velocities of 17.4–26.0 and 34.8 cm/s. The corrosion rate at the start of the process was 1.4 mm/year, decaying to levels of about 0.4–0.6 mm/year over the experimental period. Analysis of loss of carbon steel coupons mass after 35 days of the process indicated a mean corrosion rate of approximately 2 mm/year.

Effect of Velocity on Current Density for Cathodically Polarized Steel in Seawater

A series of cathodic polarization experiments was performed in which sections of UNS G10230 steel pipe were galvanically coupled through an external resistor to an aluminum anode ring. These cells were incorporated into a seawater flow loop such that the hydrodynamic conditions were defined quantitatively. Seawater velocities for the experiments were 0.03, 0.09, and 0.30 m/s. From the results, the trend of steady-state potential vs current density at a given velocity was characterized in terms of the recently proposed slope parameter approach to cathodic protection (CP) design. Also, an expression for the velocity dependence of the maintenance current density was developed. Anomalous behavior was encountered for some specimens tested at velocities of 0.09 m/s and 0.30 m/s in that these exhibited a period of depolarization followed, in some cases, by repolarization. This behavior was reviewed in terms of transitory calcareous deposit protectiveness, possibly reflecting the relative amounts of calcium and magnesium in the deposits at a particular time.

Visualization of seawater flow around morphologically distinct forms of the giant kelp Macrocystis integrifolia from wave‐sheltered and exposed sites

Our objective was to determine whether blades of Macrocystis integrifolia from a wave‐sheltered site possess morphological features that “trip” velocity boundary layers (VBL) from laminar to turbulent in conditions of low water motion, compared to blades from a wave‐exposed site. The movement of seawater around morphologically distinct blades of M. integrifolia from wave‐sheltered and exposed sites was visualized in a recirculating flow tank in which seawater flow was initially laminar at velocities up to 8 cm s−1. Turbulent VBLs were observed for both blade morphologies at free‐stream seawater velocities of 2 cm s−1, and at a Reynolds numbers of between 102 and 104, which is lower than that predicted from boundary layer theory. Flow around blades from a wave‐sheltered site was dominated by separation induced by large edge undulations. For the wave‐exposed morphology, the flow pattern was similar to that along a smooth, flat plate, but the observed thickness of the VBL was up to a factor of 2 greater than that predicted from laminar or turbulent boundary layer theory. There were no obvious differences in how structural features such as marginal spines and bulbs affected seawater flow around the different blade morphologies.

Effect of seawater velocity on inorganic nitrogen uptake by morphologically distinct forms of Macrocystis integrifolia from wave-sheltered and exposed sites

In conditions of low water motion (<0.06 ms−1), the availability of essential nutrients to macroalgae, and thus their potential productivity, may be limited by thick diffusion boundary-layers at the thallus surface. The ability of macroalgae to take up nutrients in slow moving water may be related to how their blade morphology affects diffusion boundarylayer thickness. For the giant kelp, Macrocystis integrifolia Bory, morphological measurements indicate that blades of plants from a site exposed to wave action are thick, narrow and have a heavily corrugated surface. In contrast, blades from a site with a low degree of water motion are relatively thin, with few surface corrugations and large undulations along their edges. The aim of our work was to test the hypothesis that morphological features of M. integrifolia blades from a sheltered site allow enhanced inorganic nitrogen uptake at low seawater velocities compared to blades with a wave-exposed morphology. The rate of nitrate and ammonium uptake by morphologically distinct blades of M. integrifolia, from sites that were sheltered from and exposed to wave action, were measured in the laboratory at a range of seawater velocities (0.01 to 0.16 ms−1), between March and May 1993. For both sheltered and exposed blade morphologies, nitrate and ammonium uptake rates increased with increasing seawater velocity, reaching a maximum rate at 0.04 to 0.06 ms−1. Uptake parameters Vmax (maximum uptake rate) and U0.37 (the velocity at which the uptake rate is 37% of the maximum rate) were estimated using an exponential decay formula. These parameters were similar for both blade morphologies, at all seawater velocities tested. Additional measurements suggest that the nitrogen status of M. integrifolia blades from wavesheltered and exposed sites were similar throughout the experimental period, and thus nitrogen status did not affect the rate of nitrogen uptake in these experiments. on the basis of these results, we conclude that blade morphology does not enhance nitrogen uptake by M. integrifolia in conditions of low water motion. Potential effects of diffusion boundary-layers on kelp productivity are discussed.

Effect of Flow on Corrosion of Copper-Nickel Alloys in Aerated Sea Water and in Sulfide-Polluted Sea Water

Abstract The corrosion of 90:10 Cu:Ni and 70:30 Cu:Ni alloys in aerated sea water and deaerated sea water containing ∼ 0.2 g/m3 sulfide has been studied using a recirculating flow loop. Tubular specimens of each alloy were tested under well characterized hydrodynamic and mass transfer conditions. At sea water velocities up to 5 m/s (Reynolds numbers up to 74,000), the corrosion rates in the sulfide polluted sea water were lower than in the aerated sea water. Thus, even under comparatively adverse flow conditions, the mere presence of sulfide does not cause accelerated attack of copper-nickel alloys. These results can be compared with those of other workers who found that when both sulfide and oxygen were present in flowing sea water, the rates of corrosion of copper-nickel alloys were higher than those obtained in unpolluted aerated sea water. Under most of the experimental conditions examined, corrosion occurred fairly uniformly across the exposed surfaces of the specimens. However, in aerated sea water,...

Impressed-Current Cathodic Protection of Aluminum-Hulled Craft

Overprotection is a major problem accompanying cathodic protection of aluminumhulled craft. Investigations were conducted concerning the protection and overprotection of aluminum under various conditions of galvanic coupling, seawater velocities and dilutions, dielectric shield materials, lengths of exposure and influence of seawater location. Overprotection was found to occur above 1500 mv, the exact value depending on seawater velocity and other conditions. The corrosion resulting from overprotection was severe, making imperative a protection system design which eliminates the possibility of accidental overprotection. Data is presented which can aid in the design of a reliable protection system.

Use of ultrasonics in laboratory development tests of cupro-nickel alloys for desalination

Ultrasonic agitation of the salt water bath is suggested as a simple laboratory corrosion test method for evaluating the relative performance of alloys intended for use at moderate or high sea water velocities.

Condenser Tube Materials for Seawater Service

The results of a series of investigations to assess the performance of a variety of alloys in small experimental condenser configurations at seawater velocities of 10 to 20 fps are summarized. They demonstrate that the addition of 1 percent aluminum increases the maximum velocity limits of copper-nickel alloys to 12–15 fps. Stainless steels, nickel alloys, and titanium are satisfactory for use at velocities of 20 fps, but many of these would be susceptible to pitting and/or crevice corrosion under stagnant conditions.

Corrosion of Steel Pipe By Chlorinated Seawater at Various Velocities

Corrosion rates of steel pipe in sea-water were obtained for six residual chlorine concentrations ranging from 0 to 4.0 ppm at five seawater velocities from 0.1 to 6.4 feet per second. Pitting rate...

The measurement of sea-water velocities by electromagnetic induction

A description is given of a method of measuring the velocity of sea-water, using the fundamental law of electrodynamics, regarding the water as a conductor and measuring the e.m.f. generated when it moves relative to a magnetic field. Descriptions are given of an underwater unit for producing the magnetic field, apparatus for measuring the motive e.m.f. and experiments made with the unit in a flume in order to calibrate it. It is shown that the method is very convenient for comparing velocities and can be used for the measurement of water velocities due to swell, tidal current, etc.