Bottom Temperature Variations Research Articles

Large-Amplitude Internal Wave Transformation into Shallow Water

Abstract Large-amplitude internal solitary wave (ISW) shoaling, breaking, and run-up was tracked continuously by a dense and rapidly sampling array spanning depths from 500 m to shore near Dongsha Atoll in the South China Sea. Incident ISW amplitudes ranged between 78 and 146 m with propagation speeds between 1.40 and 2.38 m s−1. The ratio between wave amplitude and a critical amplitude A0 controlled breaking type and was related to wave speed cp and depth. Fissioning ISWs generated larger trailing elevation waves when the thermocline was deep and evolved into onshore propagating bores in depths near 100 m. Collapsing ISWs contained significant mixing and little upslope bore propagation. Bores contained significant onshore near-bottom kinetic and potential energy flux and significant offshore rundown and relaxation phases before and after the bore front passage, respectively. Bores on the shallow forereef drove bottom temperature variation in excess of 10°C and near-bottom cross-shore currents in excess of 0.4 m s−1. Bores decelerated upslope, consistent with upslope two-layer gravity current theory, though run-up extent Xr was offshore of the predicted gravity current location. Background stratification affected the bore run-up, with Xr farther offshore when the Korteweg–de Vries nonlinearity coefficient α was negative. Fronts associated with the shoaling local internal tide, but equal in magnitude to the soliton-generated bores, were observed onshore of 20-m depth.

Numerical investigations on boiling of moderator during PT/CT contact in 220 MWe IPHWR under postulated accidental scenario

For an Indian pressurised heavy water reactor, a numerical investigation was performed to study the boiling of moderator in a fully voided single nuclear channel during Pressure tube- calandria tube contact condition by applying variable heat flux. The setup included calandria tube, moderator, pressure tube, fuel bundle and an enclosure. It was observed that because of the contact between calandria tube and pressure tube, a notable variation in the circumferential temperature distribution of calandria tube and pressure tube were observed pointing out that contact condition drastically affects the temperatures of top and bottom portion of the tubes. It was also observed that upon increasing the heat flux, the top to bottom temperature variation decreases for pressure tube but increases for calandria tube. The phenomenon of boiling of moderator started when 1650 W/m2 heat flux was given to the system as input and the rate of boiling increased as the heat flux was increased which resulted in increasing moderator vapour fraction in the enclosure and decrease in average moderator density. The film thickness of the moderator vapour on the outer circumference of the calandria tube varied with time, following a cycle of increasing and decreasing thickness. The result showed that upto 4950 W/m2 heat flux, the moderator acted as an efficient heat sink. If the heat flux is increased further, the moderator can fail to act as a good heat sink and eventually lead to fuel channel failure.

Observed variability in physical and biogeochemical parameters in the central Arabian Gulf

In situ measurements of physical and biogeochemical variables were conducted along a transect in the Exclusive Economic Zone (EEZ) of Qatar during late summer (September 2014) and winter (January 2015) to investigate their vertical, spatial and temporal variability. The study reveals that the water column is characterized by strong stratification during late summer in the deepest station, where the water depth is around 65 m and the surface to bottom temperature variation is around 9.1°C. The water column is vertically homogeneous during winter due to surface cooling and wind mixing. The surface to 23 m water column is characterized by ample dissolved oxygen (DO) during late summer and winter in the offshore regions, however, relatively low DO is found during late summer due to weak mixing and advection under weak winds and currents. Dissolved oxygen drops to hypoxic levels below the summer thermocline, and the winter high DO layer extends up to the bottom. Chlorophyll-a (Chl-a) is relatively high during late summer in the offshore region, while that in the nearshore regions is very low, which is linked to the anthropogenic stresses from the central east coast of Qatar. The results identified in this study fill an essential gap in the knowledge of regional primary production dynamics.

Modeling the bottom temperature variation patterns on a coastal marine ecosystem of the Southwestern Atlantic Ocean (El Rincón), with special emphasis on thermal changes affecting fish populations

Abstract The detailed knowledge of temperature variation patterns in marine ecosystems is important to understand marine communities' dynamics. The present study modeled the historical (1980–2016) daily bottom temperatures on a shallow marine ecosystem of the Southwestern Atlantic Ocean (El Rincon), which is a reproductive ground for several commercially important fish. A detailed description of bottom temperature variation patterns was performed mainly focusing on those changes influencing fish populations. The model used in the present study is a modification from previous models applied to lakes and tidal inlets, and predicts daily water temperatures from air temperatures and radiation, considering in turn the change of thermal inertia with depth. Bottom temperature data for model calibration, and also salinity, were recorded on 666 oceanographic stations between July 1993 and December 2012. More than 95% of daily bottom temperature variation was explained by the fitted model, and predictability decreased from 98 to 82% in relation to the increase in thermal inertia with depth. High model deviations (>1.5 °C) were associated with a particular salinity range (33.6–33.9) and evidenced eventual occurrence of cold water advections more evident during the warm season. In response to the changes in thermal inertia with depth, the seasonal occurrence of two opposite horizontal thermal gradients was evident each year. These gradients involved a shoreward warming during the warm season, which promotes fish reproductive aggregations, and a shoreward cooling (warming toward deeper zones) during the cold season, which is related with adult fish dispersion or even migration. Up to more than one month of difference in the onset-end pattern of these thermal gradients was observed depending on the year. Long-term linear variation trends in temperature changed seasonally, with higher cooling rates during spring months, which was particularly evident during October. Also, irregular 3 to 7 year thermal oscillations appeared to occur, indicating the influence of one or more climate variability phenomena. These results depict the general dynamics of bottom temperature patterns in a shallow temperate marine ecosystem, with particular emphasis on their implications for understanding different aspects of fish populations. Particularly, the model and specific data provided in this study will help to further advance our knowledge of this marine ecosystem, in which fishes play an important economical role.

Responses of Yellow Sea Cold Water Mass to Typhoon Bolaven

A two-month seabed-mounted observation (YSG1 area) was carried out in the western Yellow Sea Cold Water Mass (YSCWM) using an RDI-300K acoustic Doppler current profiler (ADCP) placed at a water depth of 38 m in late summer, 2012. On August 2012, Typhoon Bolaven passed east of YSG1 with a maximum wind speed of 20 m s−1. The water depth, bottom temperature, and profile current velocities (including u, v and w components) were measured, and the results showed that the typhoon could induce horizontal current with speed greater than 70 cm s−1 in the water column, which is especially rare at below 20 meters above bottom (mab). The deepening velocity shear layer had an intense shear velocity of around 10 cm s−1 m−1, which indicated the deepening of the upper mixed layer. In the upper water column (above 20 mab), westward de-tide current with velocity greater than 30 cm s−1 was generated with the typhoon’s onshore surge, and the direction of current movement shifted to become southward. In the lower water column, a possible pattern of eastward compensation current and delayed typhoon-driven current was demonstrated. During the typhoon, bottom temperature variation was changed into diurnal pattern because of the combined influence of typhoon and tidal current. The passage of Bolaven greatly intensified local sediment resuspension in the bottom layer. In addition, low-density particles constituted the suspended particulate matter (SPM) around 10 mab, which may be transported from the central South Yellow Sea by the typhoon. Overall, the intensive external force of the Typhoon Bolaven did not completely destroy the local thermocline, and most re-suspended sediments during the typhoon were restricted within the YSCWM.

Numerical analysis and experimental visualization of phase change material melting process for thermal management of cylindrical power battery

Organic phase change materials (PCMs) have been of increasing interest in battery thermal management due to their high latent heat and excellent cycling stability. This paper reports both numerical analysis and visualization experiments for the melting process of paraffin PCM surrounding a cylindrical power battery. Specifically, two different housing materials are considered, one made of metal and the other made of acrylics. For the metal housing case, the PCM exhibits a melting front isolated both from the battery and housing wall with accelerated melting in the B∼C stage, accounting for the isothermal temperature plateau observed in both the numerical modeling and experimental measurements. For the acrylic housing case, the unmelted PCM instead adheres to the inner wall of housing all the way, melting at the rate slower than the metal housing case. In both housing cases, the numerically predicted liquid fractions are found to agree with our experimentally visualized results. The battery top to bottom temperature variation is also examined with regard to the melting process. Moreover, the instantaneous Nusselt number is obtained to identify the different heat transfer characteristics in the different melting stages.

Experimental investigation on the thermal behavior of cylindrical battery with composite paraffin and fin structure

The thermal behavior of the cylindrical battery was examined with composite paraffin and fin structure through experimental measurements and benchmarking with other thermal management techniques. The mock-up cylindrical battery, made of aluminum, had vertical straight fins as enlarged heat transfer area to submerge in the paraffin wax as phase change material (PCM) with a maximum melting temperature of 44°C. For the pure PCM case, the melting process could be divided into AB segment with battery temperature ramp-up, BC segment with a clear-cut temperature plateau, and CE segment to reach complete melting, which is also basically represented in the evolutionary trend for the battery top to bottom temperature variation. The instantaneous Nusselt number would increase around the CE segment with a small portion of unmelted PCM as visualized by the numerical analysis, but the battery temperature would ramp up from the plateau in spite of the incomplete melt. Thermal enhancement with the PCM-fin cases was examined experimentally and the logarithmic dependence of the time-averaged Nusselt number is correlated with the heat transfer area ratio. In addition, the effective thermal control point C is found to relate to the melting front intersecting the bottom of the metal housing, and the corresponding thermal resistance is used to benchmark the thermal performance of PCM based thermal management systems. Independent of heating power, such a parameter can be correlated with the melting temperature to the ambient temperature difference for existing thermal management systems. It is found that the present composite PCM-fin system had the advantages of good thermal performance with prolonged work time.

A probe heat flow value of the East China Sea shelf

Bottom temperature variation (BTV) is a serious problem in determining the thermal gradient and heart flow of the sediments in shallow seas. The water depth of the East China Sea shelf is mostly below 150m, and the heat flow measurement is strongly affected by BTV. Following a statistical algorithm, we rechecked the temperature and thermal conductivity data of the cruises KX90-1 and KX91-1, carried out by a cooperation program of China and Japan, and calculate the heat flow in a site without long-term temperature record. The calculated heat flow in the site was 58.6±3.6 mW/m2, being just within the range of the drill heat flow value of East China Sea shelf. The inversed amplitude spectrum of BTV has a peak in frequency of 1/10 per year, and the annual component is also an important part. Comparison with two lakes of Lake Greifensee and Lac Leman (i.e. Lake Geneva), which are in different water depth, revealed that with increasing water depth, the peak of amplitude spectrum moved towards low frequency components. The heat flow values calculated in this paper and from petroleum bore hole in East China Sea shelf are much more close to that in southeast China than in Okinawa Trough.

Seasonal variations in Arctic sediment dynamics—evidence from 1-year records in the Laptev Sea (Siberian Arctic)

Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a 1-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June–early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf. SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June–July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport.

Dynamics of gas hydrate: case of the Congo continental slope

A numerical model is developed to study the temperature effect on stability and phase transformation of gas-hydrate. The model uses a mathematical formulation based on the enthalpy form of the conservation law of energy. The use of the enthalpy form instead of the temperature form as often done in the literature has made the problem numerically simpler. The model is then applied to describe the effect of sea bottom temperature variations on the stability of gas hydrate occurrences and on the seafloor reflectivity in sediments of the Congo continental slope. Indeed, a migrating seafloor reflectivity front is observed on 3D seimic images from two surveys performed 6 months apart and interpreted as a migrating gas hydrate stability zone. Seawater temperature variations were recorded over a 230-day period. At the seafloor, the amplitude of these variations could explain a 75-m shift in water depth of the upper limit of the gas hydrate stability zone. However, the response of the sediment to a perturbation applied at the seafloor is not immediate because of the effects of thermal diffusion and of latent heat of hydrate dissociation. Thermal modelling shows that the depth of penetration of these perturbations is around 2 m for the saturated sediment and around 6 m for hydrate-bearing sediments (hydrate fraction of 0.1). The switch between gas and gas hydrate generated by these temperature fluctuations concern only the first meter of sediment. These appear too small to explain the migration of the seafloor reflectivity, considering that the wavelength of the seismic signal is significantly larger (around 10 m). However, for temperature fluctuations with larger wavelength the switch between gas and gas hydrate will be more important and consequently could explain the reflectivity contrast as a possible migrating gas or gas hydrate front.

Anomalous temperatures in central Scotia Sea sediments – Bottom water variation or pore water circulation in old ocean crust

We report low temperature gradients (from 60% to 12% of geothermal), and extrapolated temperatures offset from modern bottom water temperatures, in sediments from the central Scotia Sea. We examine possible causes, bearing in mind similar anomalous measurements 18 years previously, attributed at the time to instrumental error. Small temperature offsets (±0.1°C) may reflect short‐term bottom temperature variation within eddies of the Antarctic Circumpolar Current. Low sediment temperature gradients may be caused by horizontal advection of cold water within the upper oceanic basaltic layer (documented in younger ocean floor elsewhere), or by northward encroachment of colder bottom waters (from the Antarctic Peninsula shelf or Weddell Sea) for several years prior to measurement.

Inversion of temperature measurements in lake sediment

SUMMARY The problem of determining heat flow density (HFD) from temperature data obtained in lake sediments is formulated using an iterated linear inverse theory with numerical results presented in the forms of probability density function and sensitivity coefficient. The Galerkin finite element method and a weighted finite difference scheme are used in the spatial and temporal domains respectively to allow for layered structure in the sediments and for transient disturbances arising from lake bottom temperature variation (BTV) with time. When a record of BTV is lacking, inversion of temperature data from a single probe penetration gives an unreliable estimate of HFD. This difficulty is alleviated by using multiple probe measurements which, if taken at intervals of several months, prove adequate for a reliable estimation of the HFD and the most recent part of BTV. Thermal properties of the sediments, however, must be accurately known a priori because a simultaneous estimation of HFD, BTV, and the thermal properties remains unattainable. In a practical case, HFD is usually resolved to the same extent that thermal conductivity is known a priori.

Heat flow measurement in lacustrine or oceanic sediments without recording bottom temperature variations

Water bottom temperature variations (BTV) introduce many uncertainties into heat flow density (HFD) values determined from the temperature‐depth (T‐z) plot from a one‐time probe insertion into the top few meters of sediments. The BTV have to be carefully monitored for a number of years up to the date of the probe measurements; this makes the method time consuming and economically unattractive. In this paper we present the theory for a promising new technique. The method does not require monitoring of the BTV but does require at least two T‐z profiles separated in time by only a few months. A generalized inversion of the BTV history using the separated T‐z data, and any other a priori information that is available, is then performed in the frequency domain to give the most probable Bayesian estimates of various parameters and their error bounds. Numerical examples show that the inversion can resolve not only the HFD but also the mean sediment surface temperature and gives information on the longer‐term trend as well as details of the BTV over the previous year; these, together with thermal properties structure, are the factors that contribute most to the shape of the time‐dependent T‐z profiles used. In a typical situation where a uniform half‐space with a background HFD = 60 mW m−2 has been perturbed by complex BTV with a maximum variation of ±1.8 K, using a misguessed HFD of 90 ± 100 mW m−2 in the inversion of two T‐z profiles taken 3 months apart over a 2‐ to 5‐m section results in a posteriori HFD of 58 ± 11 m W m−2. Although the technique gives an optimally determined mean HFD, its principal value lies in the ability to place reliable error bounds on the mean.

On the effects of thermal properties structure and water bottom temperature variation on temperature gradients in lake sediments

In heat flow determinations, it is customary to treat the surface temperature variation as a finite sum of Fourier components. The medium is assumed to be homogeneous or horizontally stratified with each layer having a constant conductivity and diffusivity. This allows the effect of each periodic component to be calculated analytically. We extend this formulation to include cases where thermal conductivities in some layers of a stratified medium may vary linearly with depth as have been found in the sediments of some continental lakes. The application of this formalism to temperature measurements in Lake Greifensee and Lac Leman shows that even with excellent records of bottom temperature variations over several years, failure to take into account the conductivity variation leads to errors as high as 20% in heat flow density values, depending on the depth interval used. The combined effects of lack of detailed knowledge of conductivity structure and the use of too short and (or) inaccurate records of bottom temperature variations, leading to very significant errors, are also discussed, with particular reference to the problems arising from a lack of recognition of the existence of nonannual terms in the bottom temperature variation and the use of probes that do not penetrate the sediments deeply enough.