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1
Schladow, S. Geoffrey, Ellen Thomas, and Jeffrey R. Koseff. "The dynamics of intrusions into a thermohaline stratification." Journal of Fluid Mechanics 236 (March 1992): 127–65. http://dx.doi.org/10.1017/s002211209200137x.
Повний текст джерелаАнотація:
Physical and numerical experiments were performed for a linearly stratified heat—salt system, uniformly heated at one endwall. The initial stratification was in the diffusive sense. Intrusions formed at the heated endwall and propagated out into the interior fluid. Three classes of flow were identified, based upon the gravitational stability ratio, Rp, and a lateral stability parameter, R1, For R1 > 1, a vertical lengthscale for the initial intrusion thickness was developed which agreed well with that observed in the physical experiments. In all cases, a region of salt fingering developed due to gradient reversal at the heated endwall. Two very distinct merging processes were observed depending on the specific flow class. The first process occurred under conditions of high gravitational and lateral stability, and appeared to be controlled by horizontal motions induced by the intrusions. The second process was observed under less stable conditions and was a result of vertical motions at the heated endwall within the intrusions themselves. In the least stable class of flow (low gravitational and lateral stability), the intrusions were found to be self-perpetuating in the sense that they continued to propagate following removal of the endwall heat flux.
2
Gordon, Arnold L., and Julie L. McClean. "Thermohaline Stratification of the Indonesian Seas: Model and Observations*." Journal of Physical Oceanography 29, no. 2 (February 1999): 198–216. http://dx.doi.org/10.1175/1520-0485(1999)029<0198:tsotis>2.0.co;2.
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3
Gong, Ye-Jun, Ying-Ying Luo, and Jie-Min Zhan. "Three-dimensional buoyancy-driven convection structures in thermohaline stratification." AIP Advances 6, no. 4 (April 2016): 045303. http://dx.doi.org/10.1063/1.4946783.
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4
Radko, Timour. "Thermohaline layering on the microscale." Journal of Fluid Mechanics 862 (January 14, 2019): 672–95. http://dx.doi.org/10.1017/jfm.2018.976.
Повний текст джерелаАнотація:
A theoretical model is developed which illustrates the dynamics of layering instability, frequently realized in ocean regions with active fingering convection. Thermohaline layering is driven by the interplay between large-scale stratification and primary double-diffusive instabilities operating at the microscale – temporal and spatial scales set by molecular dissipation. This interaction is described by a combination of direct numerical simulations and an asymptotic multiscale model. The multiscale theory is used to formulate explicit and dynamically consistent flux laws, which can be readily implemented in large-scale analytical and numerical models. Most previous theoretical investigations of thermohaline layering were based on the flux-gradient model, which assumes that the vertical transport of density components is uniquely determined by their local background gradients. The key deficiency of this approach is that layering instabilities predicted by the flux-gradient model have unbounded growth rates at high wavenumbers. The resulting ultraviolet catastrophe precludes the analysis of such basic properties of layering instability as its preferred wavelength or the maximal growth rate. The multiscale model, on the other hand, incorporates hyperdiffusion terms that stabilize short layering modes. Overall, the presented theory carries the triple advantage of (i) offering an explicit description of the interaction between microstructure and layering modes, (ii) taking into account the influence of non-uniform stratification on microstructure-driven mixing, and (iii) avoiding unphysical behaviour of the flux-gradient laws at small scales. While the multiscale approach to the parametrization of time-dependent small-scale processes is illustrated here on the example of fingering convection, we expect the proposed technique to be readily adaptable to a wide range of applications.
5
Stein, M. "Impacts of "Storis" on the Thermohaline Stratification off West Greenland." Journal of Northwest Atlantic Fishery Science 43 (March 17, 2010): 1–12. http://dx.doi.org/10.2960/j.v43.m655.
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6
Wright, J., and W. Shyy. "Numerical simulation of unsteady convective intrusions in a thermohaline stratification." International Journal of Heat and Mass Transfer 39, no. 6 (April 1996): 1183–201. http://dx.doi.org/10.1016/0017-9310(95)00214-6.
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7
Morin, P., P. Le Corre, and J. Le Févre. "Assimilation Aand Regeneration of Nutrients off the West Coast of Brittany." Journal of the Marine Biological Association of the United Kingdom 65, no. 3 (August 1985): 677–95. http://dx.doi.org/10.1017/s0025315400052528.
Повний текст джерелаАнотація:
A high degree of variation in hydrographic conditions is found in the so-called Iroise Sea, within less than 100 km of the west coast of Brittany. Tidal current maximal velocity, especially, ranges there from about 0·5 knot to more than 8 knots (locally, near the island of Ushant), i.e. practically as wide a range as found over the whole of north-west European shelf seas. Pelagic ecosystems accordingly exhibit a high degree of variety, related not only to classical inshore-offshore gradients, but also to the extent of vertical mixing or stratification. Areas where different physical and biological conditions prevail are generally separated by rather clearcut boundaries. The better-known of these is the Ushant thermal front, which runs in summer across the whole entrance to the English Channel, but also extends into the Iroise. In addition, freshwater runoff results in thermohaline stratification, or at least in the existence of thermohaline vertical gradients, in the two major bays of the west coast of Brittany. The relevant area is limited seawards by a thermohaline front, the Iroise inner front (Grail & Le Fèvre, 1967; Le Fèvre & Grall, 1970), beyond which are found the well-mixed waters inshore of the Ushant front. Fig. 1 sums up these hydrographic patterns in the area taken here into consideration.
8
Radko, Timour. "Thermohaline layering in dynamically and diffusively stable shear flows." Journal of Fluid Mechanics 805 (September 16, 2016): 147–70. http://dx.doi.org/10.1017/jfm.2016.547.
Повний текст джерелаАнотація:
In this study we examine two-component shear flows that are stable with respect to Kelvin–Helmholtz and to double-diffusive instabilities individually. Our focus is on diffusively stratified ocean regions, where relatively warm and salty water masses are located below cool fresh ones. It is shown that such systems may be destabilized by the interplay between shear and thermohaline effects, caused by unequal molecular diffusivities of density components. Linear stability analysis suggests that parallel two-component flows can be unstable for Richardson numbers exceeding the critical value for non-dissipative systems $(Ri=1/4)$ by up to four orders of magnitude. Direct numerical simulations indicate that these instabilities transform the initially linear density stratification into a series of well-defined horizontal layers. It is hypothesized that the combined thermohaline–shear instabilities could be ultimately responsible for the widespread occurrence of thermohaline staircases in diffusively stable regions of the World Ocean.
9
Arnon, A., J. S. Selker, and N. G. Lensky. "Thermohaline stratification and double diffusion diapycnal fluxes in the hypersaline Dead Sea." Limnology and Oceanography 61, no. 4 (April 23, 2016): 1214–31. http://dx.doi.org/10.1002/lno.10285.
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10
Liblik, T., and U. Lips. "Variability of synoptic-scale quasi-stationary thermohaline stratification patterns in the Gulf of Finland in summer 2009." Ocean Science 8, no. 4 (August 13, 2012): 603–14. http://dx.doi.org/10.5194/os-8-603-2012.
Повний текст джерелаАнотація:
Abstract. We present and analyze high-resolution observational data of thermohaline structure and currents acquired in the Gulf of Finland (Baltic Sea), using an autonomous buoy profiler and bottom-mounted acoustic Doppler current profiler during July–August 2009. Vertical profiles of temperature and salinity were measured in the upper 50-m layer with a 3 h time resolution, and vertical profiles of current velocity and direction were recorded with a 10 min time resolution. Although large temporal variations of vertical temperature and salinity distributions were revealed, it was possible to define several periods with quasi-stationary vertical thermohaline structure. These quasi-stationary stratification patterns persisted for 4–15 days and were dominated by certain physical processes: upwelling, relaxation of upwelling, estuarine circulation and its wind-induced reversal, and downwelling. Vertical profiles of current velocities supported the concept of synoptic-scale, quasi-stationary periods of hydrophysical fields, characterized by distinct layered flow structures and current oscillations. To estimate the contribution of different processes to the changes in stratification, a simple conceptual model was developed. The model accounts for heat flux through the sea surface, wind mixing, wind-induced transport (parallel to the horizontal salinity gradient) in the upper layer, and estuarine circulation. It reproduced observed changes in vertical stratification reasonably well. The largest discrepancies between observations and model results were found when water motions across the Gulf and associated vertical displacements of isopycnals (upwelling or downwelling) were dominant processes.
11
Sijp, Willem P., and Matthew H. England. "Southern Hemisphere Westerly Wind Control over the Ocean's Thermohaline Circulation." Journal of Climate 22, no. 5 (March 1, 2009): 1277–86. http://dx.doi.org/10.1175/2008jcli2310.1.
Повний текст джерелаАнотація:
Abstract The effect of the position of the Southern Hemisphere subpolar westerly winds (SWWs) on the thermohaline circulation (THC) of the World Ocean is examined. The latitudes of zero wind stress curl position exert a strong control on the distribution of overturning between basins in the Northern Hemisphere. A southward wind shift results in a stronger Atlantic THC and enhanced stratification in the North Pacific, whereas a northward wind shift leads to a significantly reduced Atlantic THC and the development of vigorous sinking (up to 1500-m depth) in the North Pacific. In other words, the Atlantic dominance of the meridional overturning circulation depends on the position of the zero wind stress curl over the Southern Ocean in the experiments. This position has a direct influence on the surface salinity contrast between the Pacific and the Atlantic, which is then further amplified by changes in the distribution of Northern Hemisphere sinking between these basins. The results show that the northward location of the SWW stress maximum inferred for the last glacial period may have contributed to significantly reduced North Atlantic Deep Water formation during this period, and perhaps an enhanced and deeper North Pacific THC. Also, a more poleward location of the SWW stress maximum in the current warming climate may entail stronger salinity stratification of the North Pacific.
12
Sayın, Erdem, and Canan Eronat. "The dynamics of İzmir Bay under the effects of wind and thermohaline forces." Ocean Science 14, no. 2 (April 13, 2018): 285–92. http://dx.doi.org/10.5194/os-14-285-2018.
Повний текст джерелаАнотація:
Abstract. The dominant circulation pattern of İzmir Bay on the Aegean Sea coast of Turkey is studied taking into consideration the influence of wind and thermohaline forces. İzmir Bay is discussed by subdividing the bay into outer, middle and inner areas. Wind is the most important driving force in the İzmir coastal area. There are also thermohaline forces due to the existence of water types of different physical properties in the bay. In contrast to the two-layer stratification during summer, a homogeneous water column exists in winter. The free surface version of the Princeton model (Killworth's 3-D general circulation model) is applied, with the input data obtained through the measurements made by the research vessel K. Piri Reis. As a result of the simulations with artificial wind, the strong consistent wind generates circulation patterns independent of the seasonal stratification in the bay. Wind-driven circulation causes cyclonic or anticyclonic movements in the middle bay where the distinct İzmir Bay Water (IBW) forms. Cyclonic movement takes place under the influence of southerly and westerly winds. On the other hand, northerly and easterly winds cause an anticyclonic movement in the middle bay. The outer and inner bay also have the wind-driven recirculation patterns expected.
13
Nilsson, Johan, Göran Broström, and Gösta Walin. "The Thermohaline Circulation and Vertical Mixing: Does Weaker Density Stratification Give Stronger Overturning?" Journal of Physical Oceanography 33, no. 12 (December 2003): 2781–95. http://dx.doi.org/10.1175/1520-0485(2003)033<2781:ttcavm>2.0.co;2.
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14
Bao, Ting, and Zhen (Leo) Liu. "Geothermal energy from flooded mines: Modeling of transient energy recovery with thermohaline stratification." Energy Conversion and Management 199 (November 2019): 111956. http://dx.doi.org/10.1016/j.enconman.2019.111956.
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15
Suárez, F., J. E. Aravena, M. B. Hausner, A. E. Childress, and S. W. Tyler. "Assessment of a vertical high-resolution distributed-temperature-sensing system in a shallow thermohaline environment." Hydrology and Earth System Sciences 15, no. 3 (March 30, 2011): 1081–93. http://dx.doi.org/10.5194/hess-15-1081-2011.
Повний текст джерелаАнотація:
Abstract. In shallow thermohaline-driven lakes it is important to measure temperature on fine spatial and temporal scales to detect stratification or different hydrodynamic regimes. Raman spectra distributed temperature sensing (DTS) is an approach available to provide high spatial and temporal temperature resolution. A vertical high-resolution DTS system was constructed to overcome the problems of typical methods used in the past, i.e., without disturbing the water column, and with resistance to corrosive environments. This paper describes a method to quantitatively assess accuracy, precision and other limitations of DTS systems to fully utilize the capacity of this technology, with a focus on vertical high-resolution to measure temperatures in shallow thermohaline environments. It also presents a new method to manually calibrate temperatures along the optical fiber achieving significant improved resolution. The vertical high-resolution DTS system is used to monitor the thermal behavior of a salt-gradient solar pond, which is an engineered shallow thermohaline system that allows collection and storage of solar energy for a long period of time. The vertical high-resolution DTS system monitors the temperature profile each 1.1 cm vertically and in time averages as small as 10 s. Temperature resolution as low as 0.035 °C is obtained when the data are collected at 5-min intervals.
16
Brown, Justin M., and Timour Radko. "Initiation of diffusive layering by time-dependent shear." Journal of Fluid Mechanics 858 (November 6, 2018): 588–608. http://dx.doi.org/10.1017/jfm.2018.790.
Повний текст джерелаАнотація:
The Arctic halocline is generally stable to the development of double-diffusive and dynamic instabilities – the two major sources of small-scale mixing in the mid-latitude oceans. Despite this, observations show the abundance of double-diffusive staircases in the Arctic Ocean, which suggests the presence of some destabilizing process facilitating the transition from smooth-gradient to layered stratification. Recent studies have shown that an instability can develop in such circumstances if weak static shear is present even when the flow is dynamically and diffusively stable. However, the impact of oscillating shear, associated with the presence of internal gravity waves, has not yet been addressed for the diffusive case. Through two-dimensional simulations of diffusive convection, we have investigated the impact of the magnitude and frequency of externally forced oscillatory shear on the thermohaline-shear instability. Simulations with stochastic shear – characterized by a continuous spectrum of frequencies from inertial to buoyancy – indicate that thermohaline layering does occur due to the presence of destabilizing modes (oscillations of near the buoyancy frequency). These simulations show that such layers appear as well-defined steps in the temperature and salinity profiles. Thus, the thermohaline-shear instability is a plausible mechanism for staircase formation in the Arctic and merits substantial future study.
17
Liblik, T., and U. Lips. "Short-term variations of thermohaline structure in the Gulf of Finland." Ocean Science Discussions 9, no. 2 (March 12, 2012): 877–908. http://dx.doi.org/10.5194/osd-9-877-2012.
Повний текст джерелаАнотація:
Abstract. We present and analyze high-frequency observational data of thermohaline structure and currents acquired in the Gulf of Finland (Baltic Sea) using an autonomous buoy profiler and a bottom mounted acoustic Doppler current profiler in July–August 2009. Vertical profiles of temperature and salinity were measured in the upper 50-m layer with a time resolution of 3 h and vertical profiles of current velocity and direction were recorded with a time resolution of 10 min. Although high temporal variations of the vertical temperature and salinity distributions were revealed, it was possible to define several periods with quasi-stationary vertical thermohaline structure. These quasi-stationary stratification patterns lasted from 4 to 15 days and were dominated by certain hydrophysical processes – upwelling, relaxation of the upwelling, wind induced reversal of the estuarine circulation, estuarine circulation, and downwelling. Vertical profiles of current velocities supported the concept of synoptic-scale quasi-stationary periods of hydrophysical fields. The periods with distinct layered flow structures and current oscillations with the prevailing period of 26 h were revealed. A simple model, where the heat flux through the sea surface, wind mixing, wind induced transport (parallel to the horizontal salinity gradient) in the upper layer and estuarine circulation were taken into account, simulated the observed changes in the vertical stratification reasonably well. The largest discrepancies between the observations and model results were found when water movement across the Gulf and associated vertical displacement of isopycnals (upwelling or downwelling) were dominant processes.
18
Johnston, T. M. Shaun, and Daniel L. Rudnick. "Observations of the Transition Layer." Journal of Physical Oceanography 39, no. 3 (March 1, 2009): 780–97. http://dx.doi.org/10.1175/2008jpo3824.1.
Повний текст джерелаАнотація:
Abstract The transition layer is the poorly understood interface between the stratified, weakly turbulent interior and the strongly turbulent surface mixed layer. The transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear, vertical stratification, and potential vorticity. A database of 91 916 km or 25 426 vertical profiles of temperature and salinity from SeaSoar, a towed vehicle, is used to define the transition layer thickness. Acoustic Doppler current measurements are also used, when available. Statistics of the transition layer thickness are compared for 232 straight SeaSoar sections, which range in length from 65 to 1129 km with typical horizontal resolution of ∼4 km and vertical resolution of 8 m. Transition layer thicknesses are calculated in three groups from 1) vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer; 2) the depths below the mixed layer depth of peaks in shear, stratification, and potential vorticity and their widths; and 3) the depths below or above the mixed layer depth of extrema in thermohaline variance, density ratio, and isopycnal slope. From each SeaSoar section, the authors compile either a single value or a median value for each of the above measures. Each definition yields a median transition layer thickness from 8 to 24 m below the mixed layer depth. The only exception is the median depth of the maximum isopycnal slope, which is 37 m above the mixed layer base, but its mode is 15–25 m above the mixed layer base. Although the depths of the stratification, shear, and potential vorticity peaks below the mixed layer are not correlated with the mixed layer depth, the widths of the shear and potential vorticity peaks are. Transition layer thicknesses from displacements and the full width at half maximum of the shear and potential vorticity peak give transition layer thicknesses from 0.11× to 0.22× the mean depth of the mixed layer. From individual profiles, the depth of the shear peak below the stratification peak has a median value of 6 m, which shows that momentum fluxes penetrate farther than buoyancy fluxes. A typical horizontal scale of 5–10 km for the transition layer comes from the product of the isopycnal slope and a transition layer thickness suggesting the importance of submesoscale processes in forming the transition layer. Two possible parameterizations for transition layer thickness are 1) a constant of 11–24 m below the mixed layer depth as found for the shear, stratification, potential vorticity, and thermohaline variance maxima and the density ratio extrema; and 2) a linear function of mixed layer depth as found for isopycnal displacements and the widths of the shear and potential vorticity peaks.
19
Gibson, John A. E. "The meromictic lakes and stratified marine basins of the Vestfold Hills, East Antarctica." Antarctic Science 11, no. 2 (June 1999): 175–92. http://dx.doi.org/10.1017/s0954102099000243.
Повний текст джерелаАнотація:
Thirty-four permanently stratified water bodies were identified in a survey of the Vestfold Hills. Of these, 21 were lakes, six were seasonally isolated marine basins (SIMBs), and seven were marine basins with year round connection to the open ocean. The basins varied markedly in salinity (4 g l−1 to 235 g l−1), temperature (−14°C to 24°C), depth (5 m to 110 m), area (3.6 ha to 146 ha) and surface level (−30 m to 29 m above sea level). The stratification in all the basins was maintained by increases in salinity. During winter, a thermohaline convection cell was present in all lakes and SIMBs directly beneath the ice cover. These cells were the result of brine exclusion from the forming ice, and increased in density throughout winter, penetrating progressively deeper into the lake. Minimum stability, and therefore the maximum likelihood of turnover, occurred at the time of maximum ice formation in spring. At the end of the period of ice formation, the convection cell broke down, and stratification of the surface water occurred. When the ice melted completely, lenses of relatively fresh water capped the lakes, which reduced the effect of wind mixing. Net meltwater input increased the stability of the meromictic basins, while periods of lower water level resulted in deeper penetration of the thermohaline convection cell, increasing the possibility of turnover and destratification.
20
Yang, Yantao, Wenyuan Chen, Roberto Verzicco, and Detlef Lohse. "Multiple states and transport properties of double-diffusive convection turbulence." Proceedings of the National Academy of Sciences 117, no. 26 (June 17, 2020): 14676–81. http://dx.doi.org/10.1073/pnas.2005669117.
Повний текст джерелаАнотація:
When fluid stratification is induced by the vertical gradients of two scalars with different diffusivities, double-diffusive convection (DDC) may occur and play a crucial role in mixing. Such a process exists in many natural and engineering environments. Especially in the ocean, DDC is omnipresent since the seawater density is affected by temperature and salinity. The most intriguing phenomenon caused by DDC is the thermohaline staircase, i.e., a stack of alternating well-mixed convection layers and sharp interfaces with very large gradients in both temperature and salinity. Here we investigate DDC and thermohaline staircases in the salt finger regime, which happens when warm saltier water lies above cold fresher water and is commonly observed in the (sub)tropic regions. By conducting direct numerical simulations over a large range of parameters, we reveal that multiple equilibrium states exist in fingering DDC and staircases even for the same control parameters. Different states can be established from different initial scalar distributions or different evolution histories of the flow parameters. Hysteresis appears during the transition from a staircase to a single salt finger interface. For the same local density ratio, salt finger interfaces in the single-layer state generate very different fluxes compared to those within staircases. However, the salinity flux for all salt finger interfaces follows the same dependence on the salinity Rayleigh number of the layer and can be described by an effective power law scaling. Our findings have direct applications to oceanic thermohaline staircases.
21
Bao, Ting, Han Cao, Yinghong Qin, Guosheng Jiang, and Zhen (Leo) Liu. "Critical insights into thermohaline stratification for geothermal energy recovery from flooded mines with mine water." Journal of Cleaner Production 273 (November 2020): 122989. http://dx.doi.org/10.1016/j.jclepro.2020.122989.
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22
Dyakonov, Gleb S., and Rashit A. Ibrayev. "Long-term evolution of Caspian Sea thermohaline properties reconstructed in an eddy-resolving ocean general circulation model." Ocean Science 15, no. 3 (May 16, 2019): 527–41. http://dx.doi.org/10.5194/os-15-527-2019.
Повний текст джерелаАнотація:
Abstract. Decadal variability in Caspian Sea thermohaline properties is investigated using a high-resolution ocean general circulation model including sea ice thermodynamics and air–sea interaction forced by prescribed realistic atmospheric conditions and riverine runoff. The model describes synoptic, seasonal and climatic variations of sea thermohaline structure, water balance, and sea level. A reconstruction experiment was conducted for the period of 1961–2001, covering a major regime shift in the global climate during 1976–1978, which allowed for an investigation of the Caspian Sea response to such significant episodes of climate variability. The model reproduced sea level evolution reasonably well despite the fact that many factors (such as possible seabed changes and insufficiently explored underground water infiltration) were not taken into account in the numerical reconstruction. This supports the hypothesis relating rapid Caspian Sea level rise in 1978–1995 with global climate change, which caused variation in local atmospheric conditions and riverine discharge reflected in the external forcing data used, as is shown in the paper. Other effects of the climatic shift are investigated, including a decrease in salinity in the active layer, strengthening of its stratification and corresponding diminishing of convection. It is also demonstrated that water exchange between the three Caspian basins (northern, middle and southern) plays a crucial role in the formation of their thermohaline regime. The reconstructed long-term trends in seawater salinity (general downtrend after 1978), temperature (overall increase) and density (general downtrend) are studied, including an assessment of the influence of main surface circulation patterns and model error accumulation.
23
Suárez, F., J. E. Aravena, M. B. Hausner, A. E. Childress, and S. W. Tyler. "Assessment of a vertical high-resolution distributed-temperature-sensing system in a shallow thermohaline environment." Hydrology and Earth System Sciences Discussions 8, no. 1 (January 5, 2011): 29–58. http://dx.doi.org/10.5194/hessd-8-29-2011.
Повний текст джерелаАнотація:
Abstract. In shallow thermohaline-driven lakes it is important to measure temperature on fine spatial and temporal scales to detect stratification or different hydrodynamic regimes. Raman spectra distributed temperature sensing (DTS) is an approach available to provide high spatial and temporal temperature resolution. A vertical high-resolution DTS system was constructed to overcome the problems of typical methods used in the past, i.e., without disturbing the water column, and with resistance to corrosive environments. This system monitors the temperature profile each 1.1 cm vertically and in time averages as small as 10 s. Temperature resolution as low as 0.035 °C is obtained when the data are collected at 5-min intervals. The vertical high-resolution DTS system is used to monitor the thermal behavior of a salt-gradient solar pond, which is an engineered shallow thermohaline system that allows collection and storage of solar energy for a long period of time. This paper describes a method to quantitatively assess accuracy, precision and other limitations of DTS systems to fully utilize the capacity of this technology. It also presents, for the first time, a method to manually calibrate temperatures along the optical fiber.
24
Silva, Brenno J., Felipe L. Gaspar, Pedro Tyaquiçã, Nathalie Lefèvre, and Manuel J. Flores Montes. "Carbon chemistry variability around a tropical archipelago." Marine and Freshwater Research 70, no. 6 (2019): 767. http://dx.doi.org/10.1071/mf18011.
Повний текст джерелаАнотація:
Oceanic islands affect the surrounding oceanic circulation by producing upwelling or vortices, resulting in the rising of a richer and colder subsurface water mass. This process increases primary production and can change some biogeochemical processes, such as carbon chemistry and the biological pump. The aim of this study was to describe the vertical variability of carbon chemistry around Fernando de Noronha Archipelago (FNA) and to verify how the island mass effect (IME) can affect carbon distribution. Two transects on opposite sides of the FNA were established according to the direction of the central South Equatorial Current, and samples were collected in July 2010, September 2012 and July 2014 from the surface down to a depth of 500m. The results showed strong stratification, with an uplift of the thermohaline structure, which resulted in an increase of chlorophyll-a concentration downstream of the island during the 2010 and 2014 cruises. Carbon chemistry parameters were strongly correlated with temperature, salinity and dissolved oxygen along the water column and did not change between sides of the island in the periods studied. We conclude that the IME did not significantly affect carbon chemistry, which was more correlated with thermohaline gradient.
25
Zhou, S. Q., L. Qu, Y. Z. Lu, and X. L. Song. "The instability of diffusive convection and its implication for the thermohaline staircases in the deep Arctic Ocean." Ocean Science 10, no. 1 (February 24, 2014): 127–34. http://dx.doi.org/10.5194/os-10-127-2014.
Повний текст джерелаАнотація:
Abstract. In the present study, the classical description of diffusive convection is updated to interpret the instability of diffusive interfaces and the dynamical evolution of the bottom layer in the deep Arctic Ocean. In the new consideration of convective instability, both the background salinity stratification and rotation are involved. The critical Rayleigh number of diffusive convection is found to vary from 103 to 1011 in the deep Arctic Ocean as well as in other oceans and lakes. In such a wide range of conditions, the interface-induced thermal Rayleigh number is shown to be consistent with the critical Rayleigh number of diffusive convection. In most regions, background salinity stratification is found to be the main hindrance to the occurrence of convecting layers. With the new parameterization, it is predicted that the maximum thickness of the bottom layer is 1051 m in the deep Arctic Ocean, which is close to the observed value of 929 m. The evolution time of the bottom layer is predicted to be ~ 100 yr, which is on the same order as that based on 14C isolation age estimation.
26
Zhou, S. Q., L. Qu, Y. Z. Lu, and X. L. Song. "The instability of diffusive convection and its implication for the thermohaline staircases in the deep Arctic Ocean." Ocean Science Discussions 10, no. 4 (August 13, 2013): 1343–66. http://dx.doi.org/10.5194/osd-10-1343-2013.
Повний текст джерелаАнотація:
Abstract. In the present study, the classical description of diffusive convection is updated to interpret the instability of diffusive interfaces and the dynamical evolution of the bottom layer in the deep Arctic Ocean. In the new consideration of convective instability, both the background salinity stratification and rotation are involved. The critical Rayleigh number of diffusive convection is found to vary from 103 to 1011 in the deep Arctic Ocean as well as in other oceans and lakes. In such a wide range of conditions, the interface-induced thermal Rayleigh number is indicated to be consistent with the critical Rayleigh number of diffusive convection. In most regions, background salinity stratification is found to be the main hindrance to the occurrence of convecting layers. With the new parameterization, it is predicted that the maximum thickness of the bottom layer is 1051 m, which is close to the observed value of 929 m. And the evolution time of the bottom layer is predicted to be of the same order as that based on 14C isolation age estimation.
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Smith, K. Shafer, and Raffaele Ferrari. "The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring." Journal of Physical Oceanography 39, no. 10 (October 1, 2009): 2477–501. http://dx.doi.org/10.1175/2009jpo4103.1.
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Abstract Temperature–salinity profiles from the region studied in the North Atlantic Tracer Release Experiment (NATRE) show large isopycnal excursions at depths just below the thermocline. It is proposed here that these thermohaline filaments result from the mesoscale stirring of large-scale temperature and salinity gradients by geostrophic turbulence, resulting in a direct cascade of thermohaline variance to small scales. This hypothesis is investigated as follows: Measurements from NATRE are used to generate mean temperature, salinity, and shear profiles. The mean stratification and shear are used as the background state in a high-resolution horizontally homogeneous quasigeostrophic model. The mean state is baroclinically unstable, and the model produces a vigorous eddy field. Temperature and salinity are stirred laterally in each density layer by the geostrophic velocity and vertical advection is by the ageostrophic velocity. The simulated temperature–salinity diagram exhibits fluctuations at depths just below the thermocline of similar magnitude to those found in the NATRE data. It is shown that vertical diffusion is sufficient to absorb the laterally driven cascade of tracer variance through an amplification of filamentary slopes by small-scale shear. These results suggest that there is a strong coupling between vertical mixing and horizontal stirring in the ocean at scales below the deformation radius.
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Erbacher, Jochen, Brian T. Huber, Richard D. Norris, and Molly Markey. "Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period." Nature 409, no. 6818 (January 2001): 325–27. http://dx.doi.org/10.1038/35053041.
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Miranda, Luiz Bruner de, Eugenio Dalle Olle, Alessandro Luvizon Bérgamo, Lourval dos Santos Silva, and Fernando Pinheiro Andutta. "Circulation and salt intrusion in the Piaçaguera Channel, Santos (SP)." Brazilian Journal of Oceanography 60, no. 1 (March 2012): 11–23. http://dx.doi.org/10.1590/s1679-87592012000100002.
Повний текст джерелаАнотація:
Analysis of thermohaline properties and currents sampled at an anchor station in the Piaçaguera Channel (Santos Estuary) in the austral winter was made in terms of tidal (neap and spring tidal cycles) and non-tidal conditions, with the objective to characterize the stratification, circulation and salt transport due to the fortnightly tidal modulation. Classical methods of observational data analysis of hourly and nearly synoptic observations and analytical simulations of nearly steady-state salinity and longitudinal velocity profiles were used. During the neap tidal cycle the flood (v<0) and ebb (v>0) velocities varied in the range of -0.20 m/s to 0.30 m/s associated with a small salinity variation from surface to bottom (26.4 psu to 30.7 psu). In the spring tidal cycle the velocities increased and varied in the range of -0.40 m/s to 0.45 m/s, but the salinity stratification remained almost unaltered. The steady-state salinity and velocity profiles simulated with an analytical model presented good agreement (Skill near 1.0), in comparison with the observational profiles. During the transitional fortnightly tidal modulation period there was no changes in the channel classification (type 2a - partially mixed and weakly stratified), because the potential energy rate was to low to enhance the halocline erosion. These results, associated with the high water column vertical stability (RiL >20) and the low estuarine Richardson number (RiE=1.6), lead to the conclusions: i) the driving mechanism for the estuary circulation and mixing was mainly balanced by the fresh water discharge and the tidal forcing associated with the baroclinic component of the gradient pressure force; ii) there was no changes in the thermohaline and circulation characteristics due to the forthnigtly tidal modulation; and iii) the nearly steady-state of the vertical salinity and velocity profiles were well simulated with a theoretical classical analytical model.
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Ballarotta, M., S. Falahat, L. Brodeau, and K. Döös. "On the glacial and inter-glacial thermohaline circulation and the associated transports of heat and freshwater." Ocean Science Discussions 11, no. 2 (March 20, 2014): 979–1022. http://dx.doi.org/10.5194/osd-11-979-2014.
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Abstract. The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, &approx; 21 kyr ago) and the present day climate are explored using an Ocean General Circulation Model and stream functions projected in various coordinates. Compared to the present day period, the LGM circulation is reorganised in the Atlantic Ocean, in the Southern Ocean and particularly in the abyssal ocean, mainly due to the different haline stratification. Due to stronger wind stress, the LGM tropical circulation is more vigorous than under modern conditions. Consequently, the maximum tropical transport of heat is slightly larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes and reorganising the freshwater transport. The LGM circulation is represented as a large intrusion of saline Antarctic Bottom Water into the Northern Hemisphere basins. As a result, the North Atlantic Deep Water is shallower in the LGM simulation. The stream functions in latitude-salinity coordinates and thermohaline coordinates point out the different haline regimes between the glacial and interglacial period, as well as a LGM Conveyor Belt circulation largely driven by enhanced salinity contrast between the Atlantic and the Pacific basin. The thermohaline structure in the LGM simulation is the result of an abyssal circulation that lifts and deviates the Conveyor Belt cell from the area of maximum volumetric distribution, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimation of the turnover times reveal a deep circulation almost sluggish during the LGM, and a Conveyor Belt cell more vigorous due to the combination of stronger wind stress and shortened circulation route.
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Radko, Timour. "Applicability and failure of the flux-gradient laws in double-diffusive convection." Journal of Fluid Mechanics 750 (May 30, 2014): 33–72. http://dx.doi.org/10.1017/jfm.2014.244.
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AbstractDouble-diffusive flux-gradient laws are commonly used to describe the development of large-scale structures driven by salt fingers – thermohaline staircases, collective instability waves and intrusions. The flux-gradient model assumes that the vertical transport is uniquely determined by the local background temperature and salinity gradients. While flux-gradient laws adequately capture mixing characteristics on scales that greatly exceed those of primary double-diffusive instabilities, their accuracy rapidly deteriorates when the scale separation between primary and secondary instabilities is reduced. This study examines conditions for the breakdown of the flux-gradient laws using a combination of analytical arguments and direct numerical simulations. The applicability (failure) of the flux-gradient laws at large (small) scales is illustrated through the example of layering instability, which results in the spontaneous formation of thermohaline staircases from uniform temperature and salinity gradients. Our inquiry is focused on the properties of the ‘point-of-failure’ scale ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}H_{pof}$) at which the vertical transport becomes significantly affected by the non-uniformity of the background stratification. It is hypothesized that$H_{pof} $can control some key characteristics of secondary double-diffusive phenomena, such as the thickness of high-gradient interfaces in thermohaline staircases. A more general parametrization of the vertical transport – the flux-gradient-aberrancy law – is proposed, which includes the selective damping of relatively short wavelengths that are inadequately represented by the flux-gradient models. The new formulation is free from the unphysical behaviour of the flux-gradient laws at small scales (e.g. the ultraviolet catastrophe) and can be readily implemented in theoretical and large-scale numerical models of double-diffusive convection.
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Kuzmina, Natalia, Bert Rudels, Tapani Stipa, and Victor Zhurbas. "The Structure and Driving Mechanisms of the Baltic Intrusions." Journal of Physical Oceanography 35, no. 6 (June 1, 2005): 1120–37. http://dx.doi.org/10.1175/jpo2749.1.
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Abstract Data from closely spaced CTD profiling performed in the eastern Gotland Basin after the 1993 inflow event are used to study thermohaline intrusions in the Baltic Sea. Two CTD cross sections display abundant intrusive layers in the permanent halocline. Despite the overwhelming dominance of the salinity stratification, diffusive convection is shown to work in the Baltic halocline enhancing diapycnical mixing. To understand the driving mechanisms of observed intrusions, these are divided into different types depending on their structural features. Only two types of observed intrusions are suggested to be strongly influenced by diffusive convection: 1) relatively thin (3–5 m) and long (up to 8 km) intrusions inherent to high-baroclinicity regions and 2) relatively thick (∼10 m) and short (2–5 km) intrusions inherent to low-baroclinicity regions. To verify this hypothesis the linear stability models of 3D and 2D double-diffusive interleaving in approximation of a finite-width front were used. It is shown that the horizontal and vertical scales of thick and short intrusions correspond well to the 3D rotational mode for a pure thermohaline front. Since mesoscale thermohaline fronts in the Baltic halocline are shown to be essentially baroclinic, the influence of baroclinicity on the rotational mode was studied, which resulted in more adequate estimates of the growth rate of the unstable modes. The thin and long intrusions are shown to be likely driven by 2D baroclinic instability triggered by diffusive convection. The model results demonstrated that diffusion convection can be considered as a possible driver for some intrusions observed in the Baltic halocline, while most of the intrusions have a non-double-diffusive origin. Nevertheless, diffusive convection can affect all types of observed intrusions, for example, by tilting them relative to isopycnals and thereby promoting diapycnal mixing and ventilation in the Baltic halocline.
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Ménesguen, A., and T. Hoch. "Modelling the biogeochemical cycles of elements limiting primary production in the English Channel:I. Role of thermohaline stratification." Marine Ecology Progress Series 146 (1997): 173–88. http://dx.doi.org/10.3354/meps146173.
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Luo, Yingying, and Yejun Gong. "Comparative study of buoyancy-driven instability for thermohaline stratification in a Hele-Shaw cell and extended geometry." Engineering Applications of Computational Fluid Mechanics 9, no. 1 (January 2015): 469–76. http://dx.doi.org/10.1080/19942060.2015.1066533.
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Bao, Ting, and Zhen (Leo) Liu. "Thermohaline stratification modeling in mine water via double-diffusive convection for geothermal energy recovery from flooded mines." Applied Energy 237 (March 2019): 566–80. http://dx.doi.org/10.1016/j.apenergy.2019.01.049.
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Trusenkova, O. O., A. G. Ostrovskii, A. Y. Lazaryuk, and V. B. Lobanov. "Evolution of the Thermohaline Stratification in the Northwestern Sea of Japan: Mesoscale Variability and Intra-annual Fluctuations." Oceanology 61, no. 3 (May 2021): 319–28. http://dx.doi.org/10.1134/s0001437021030152.
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Tarkhanova, Marina A., and Elena N. Golubeva. "NUMERICAL SIMULATION OF ARCTIC HALOCLINE FORMATION." Interexpo GEO-Siberia 4, no. 1 (July 8, 2020): 83–90. http://dx.doi.org/10.33764/2618-981x-2020-4-1-83-90.
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This paper discusses issues related to the analysis of the Arctic halocline state over the past decades. Observational data show that the layer of halocline in the Arctic Ocean significantly changed in the last 40 years, which may affect the Arctic ice cover. For the study we used a three-dimensional ocean and sea ice numerical model developed at the ICMMG SB RAS. The main attention was devoted to the analysis of the model distribution of water salinity in the upper 250-meter layer and its variability. Based on numerical experiments on the sensitivity of thermohaline stratification to variations in atmospheric effects and the intensity of river flow, we identified areas of the Arctic basin in which the variability of the Arctic halocline was the most pronounced.
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Luis, Alvarinho J. "Oceanographic features of the Indian Ocean sector of Coastal Antarctica (Short Communication)." Czech Polar Reports 10, no. 1 (August 7, 2020): 110–17. http://dx.doi.org/10.5817/cpr2020-1-10.
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A review is presented on physical oceanographic features based on expendable CTD data collected in the Indian Ocean sector of the Southern Ocean. The thermohaline structure is dominated by Circumpolar Deep Water. The temperature and salinity are affected by cyclonic circulation in the Weddell Sea and Prydz Bay. High chlorophyll-a blooms (2-4 mg m-3) evolve during austral summer due to stratification which is caused by freshwater generated from the sea ice melt and the glacial outflow which traps phytoplankton in a shallow mixed layer, where they are exposed to higher irradiances of photosynthetically active radiation. Attempts have been made to relate the physical characteristics to biomass inferred from data published from previous Indian Scientific expeditions. More in-situ observations related to biophysical and chemical are recommended in the near future projects.
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Schrum, Corinna. "Thermohaline stratification and instabilities at tidal mixing fronts: results of an eddy resolving model for the German Bight." Continental Shelf Research 17, no. 6 (May 1997): 689–716. http://dx.doi.org/10.1016/s0278-4343(96)00051-9.
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Tarkhanova, Marina A., and Elena N. Golubeva. "CHANGES IN THE HYDROLOGICAL CHARACTERISTICS OF THE ARCTIC OCEAN UNDER THE INFLUENCE OF INCREASING RIVER RUNOFF." Interexpo GEO-Siberia 4, no. 1 (May 21, 2021): 210–16. http://dx.doi.org/10.33764/2618-981x-2021-4-1-210-216.
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The paper considers issues related to the influence of increased Arctic river runoff on the formation of the thermohaline structure of waters outside the Arctic shelf and, in particular, on the variability of heat content of the deep Arctic Ocean. The study is carried out using the three-dimensional numerical model of the ocean and sea ice SibCIOM and atmospheric reanalysis data NCEP/NCAR. Numerical simulation results showed that increased flow of Arctic rivers contributes to the stability of water stratification outside the shelf areas, which reduces the depth of autumn-winter mixing and allows Atlantic waters spreading along the continental slope to retain their heat. This is evidenced by an increase in the heat content of the upper 200 m layer waters of the eastern Eurasian basin and the rise of the Atlantic water layer upper boundary in this region.
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Karagiorgos, John, Vassilios Vervatis, and Sarantis Sofianos. "The Impact of Tides on the Bay of Biscay Dynamics." Journal of Marine Science and Engineering 8, no. 8 (August 17, 2020): 617. http://dx.doi.org/10.3390/jmse8080617.
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The impact of tides on the Bay of Biscay dynamics is investigated by means of an ocean model twin-experiment, consisted of two simulations with and without tidal forcing. The study is based on a high-resolution (1/36∘) regional configuration of NEMO (Nucleus for European Modelling of the Ocean) performing one-year simulations. The results highlight the imprint of tides on the thermohaline properties and circulation patterns in three distinct dynamical areas in the model domain: the abyssal plain, the Armorican shelf and the English Channel. When tides are activated, the bottom stress is increased in the shelf areas by about two orders of magnitude with respect to the open ocean, subsequently enhancing vertical mixing and weakening stratification in the bottom boundary layer. The most prominent feature reproduced only when tides are modelled, is the Ushant front near the entrance of the English Channel. Tides appear also to constrain the freshwater transport of rivers from the continental shelf to the open ocean. The spectral analysis revealed that the tidal forcing contributes to the SSH variance at high frequencies near the semidiurnal band and to the open ocean mesoscale and small-scale features in the presence of summer stratification pattern.
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Yankovsky, Elizabeth, and Sonya Legg. "Symmetric and Baroclinic Instability in Dense Shelf Overflows." Journal of Physical Oceanography 49, no. 1 (January 2019): 39–61. http://dx.doi.org/10.1175/jpo-d-18-0072.1.
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AbstractIn this study, we revisit the problem of rotating dense overflow dynamics by performing nonhydrostatic numerical simulations, resolving submesoscale variability. Thermohaline stratification and buoyancy forcing are based on data from the Eurasian basin of the Arctic Ocean, where overflows are particularly crucial to the exchange of dense water between shelves and deep basins, yet have been studied relatively little. A nonlinear equation of state is used, allowing proper representation of thermohaline structure and mixing. We examine three increasingly complex scenarios: nonrotating 2D, rotating 2D, and rotating 3D. The nonrotating 2D case behaves according to known theory: the gravity current descends alongslope until reaching a relatively shallow neutral buoyancy level. However, in the rotating cases, we have identified novel dynamics: in both 2D and 3D, the submesoscale range is dominated by symmetric instability (SI). Rotation leads to geostrophic adjustment, causing dense water to be confined within the forcing region longer and attain a greater density anomaly. In the 2D case, Ekman drainage leads to descent of the geostrophic jet, forming a highly dense alongslope front. Beams of negative Ertel potential vorticity develop parallel to the slope, initiating SI and vigorous mixing in the overflow. In 3D, baroclinic eddies are responsible for cross-isobath dense water transport, but SI again develops along the slope and at eddy edges. Remarkably, through two different dynamics, the 2D SI-dominated case and 3D eddy-dominated case attain roughly the same final water mass distribution, highlighting the potential role of SI in driving mixing within certain regimes of dense overflows.
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Degtyareva, L. V., E. G. Lardygina, and D. V. Kashin. "The effect of thermohaline stratification of the Northern Caspian Sea waters on oxygen mode in the near-bottom layer." Environmental Protection in Oil and Gas Complex, no. 6 (2018): 23–28. http://dx.doi.org/10.30713/2411-7013-2018-6-23-28.
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Krasnodubets, L. A. "Multi-purpose information-measuring system for vertical profiling of the ocean environment." Monitoring systems of environment, no. 1 (March 25, 2021): 54–60. http://dx.doi.org/10.33075/2220-5861-2021-1-54-60.
Повний текст джерелаАнотація:
On the basis of a mathematical description of the processes of measuring the vertical profile of the density of the oceanic environment using a diving offshore autonomous probe – a profiler equipped with an onboard navigation system, a structure and a computer model of a multipurpose information-measuring system is proposed, which is intended for use in operational oceanology. The proposed system forms arrays of measurements of vertical profiles in situ of the density of seawater and its increment, as well as the speed of sound as functions of hydrostatic pressure, obtained during one sounding. At the same time, arrays of complete and thermohaline vertical stability of water layers, as well as the corresponding vertical distributions of the Väisälä-Brunt frequency of thermohaline oscillations in the stratified ocean environment, are formed almost in parallel. In the course of the simulation, an original model of the immersion of an autonomous marine probe in stratified sea water was used, as well as a dynamic model for measuring the trajectory parameters of its movement, taking into account the inertial properties of the acceleration and pressure sensors used. As an object of measurements, we used a simulation model of the ocean environment with vertical density stratification and the corresponding speed of sound in seawater, developed on the basis of real data of profile measurements obtained from specific hydrological stations. The verification of the models of the dynamic measurement processes was carried out by the method of computer simulation in the MATLAB & Simulink environment based on the comparison between the simulation results and available results from the hydrological stations. The illustrations of the results of computer simulation are presented.
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Campos, Edmo José Dias, Sueli Susana de Godói, Yoshimine Ikeda, Luis Vianna Nonato, and José E. Gonçalves. "Summertime thermohaline structure off the Brazil Current Region between Santos (SP) and Rio de Janeiro (RJ)." Boletim do Instituto Oceanográfico 42, no. 1-2 (1994): 01–18. http://dx.doi.org/10.1590/s0373-55241994000100001.
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Within the scope of the MAR-14 Project, part of the Brazil-Germany Bilateral Agreement in Marine Sciences, an oceanographic survey aboard the R/V Victor Hensen was carried out in Brazilian coastal waters between Santos (23º56'S) and Rio de Janeiro (22º54'S), from January 15 to January 22,1991. In this article we report results of preliminary analyses of the hydrographic data collected with CTD, STD, Nansen bottles and XBT's. These preliminary results show intense stratification in the first 200 m depth, and the penetration of the Brazil Current deep into the continental shelf region. Two eddy-like features were detected. The first one, anticyclonic, was located in the northern part of the domain and confined to the uppermost 200 m. The second, a cyclonic vortex, was found a little to the southwest below 200 m and extending downwards to about 800 m depth. Water mass analyses based on T-S diagrams suggest that the interface between the South Atlantic Central Water (SACW) and the Antarctic Intermediate Water (AIW) is located at about 500 m depth. One important aspect of this study is that this was the first time a high resolution survey with a CTD probe was realized along the eastern Brasilian Coast, south of Cabo Frio.
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Hosegood, P. J., M. C. Gregg, and M. H. Alford. "Restratification of the Surface Mixed Layer with Submesoscale Lateral Density Gradients: Diagnosing the Importance of the Horizontal Dimension." Journal of Physical Oceanography 38, no. 11 (November 1, 2008): 2438–60. http://dx.doi.org/10.1175/2008jpo3843.1.
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Abstract A depth-cycling towed conductivity–temperature–depth (CTD) and vessel-mounted acoustic Doppler current profiler (ADCP) were used to obtain four-dimensional measurements of the restratification of the surface mixed layer (SML) at a submesoscale lateral density gradient near the subtropical front. With the objective of studying the role of horizontal processes in restratification, the thermohaline and velocity fields were monitored for 33 h by 16 small-scale (≤15 km2) surveys centered on a drogued float. Daytime warming by insolation caused a unidirectional displacement of the initially vertical isopycnals toward increasing density. Across the entire SML (50-m vertical scale), solar insolation accounted for 60% of observed restratification, but over 10-m scales, the percentage decreased with depth from 80% at 25–35 m to ≤25% at 55–65 m. Below 35 m, stratification was enhanced by the vertically sheared horizontal advection of the lateral density gradient due to a near-inertial wave of ∼100-m vertical wavelength that rotated anticyclonically at the inertial frequency. The phase and similar period (25.4 h) of the local inertial period to the diurnal cycle ensured constructive interference with isopycnal displacements due to insolation. Restratification by sheared advection matched that predicted due to vertically sheared inertial oscillations generated during the geostrophic adjustment of a density front, but direct wind forcing may also have generated the wave that was subsequently modified by interaction with mesoscale vorticity associated with a nearby large-scale front. By further including the effects of lateral uncompensated thermohaline inhomogeneity, the authors can account for 100% ± 20% of the observed N 2 during daytime restratification. No detectable restratification due to the slumping of horizontal density gradients under gravity alone was found.
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Krasnodubets, L. A. "Concept of using and modeling of a marine autonomous smart profiler." Monitoring systems of environment, no. 3 (September 24, 2020): 106–13. http://dx.doi.org/10.33075/2220-5861-2020-3-106-113.
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The article focuses on the development of technical support in terms of expanding the measuring base and improving marine profilers for operational observation systems as part of a new and developing scientific and applied field – operational oceanography. The concept of using a marine autonomous intelligent profiler for operational measurements of the thermohaline profile parameters of a stratified ocean environment with a significant reduction in the time to conduct an experiment using smart profiling is presented. At the same time, time savings are achieved due to the flexible control of the high-speed modes of vertical movement of the marine autonomous profiler with adjustable buoyancy. Low profiling speeds avoid significant dynamic distortions in the measurements obtained from inertial sensors. However, in a homogeneous environment, after taking measurements, the speed of the profiler can be significantly increased. The purpose of the smart profiler as a mobile data collection platform is to analyze its own motion and the properties of the surrounding ocean environment and choose, on this basis, a high-speed profiling mode that provides an acceptable level of dynamic distortion in the sensor data installed on board the measuring equipment. The results of computer simulation of the proposed smart structure in the MATLAB & Simulink environment based on the original mathematical models that make up its subsystems are presented. We studied the process of “smart” profiling during the transition of the profiler from a cruising speed mode (fast) to a working speed mode (slow), as well as its return to cruising speed in a stratified ocean environment. In this case, the behavior strategy of the smart profiler (ensuring the specified accuracy of thermohaline measurements) was implemented by choosing a speed mode based on the analysis of dynamic measurements of its motion parameters and stratification of the profile by density.
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Cessi, Paola, and Maurizio Fantini. "The Eddy-Driven Thermocline." Journal of Physical Oceanography 34, no. 12 (December 1, 2004): 2642–58. http://dx.doi.org/10.1175/jpo2657.1.
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Abstract The role of baroclinic eddies in transferring thermal gradients laterally, and thus determining the stratification of the ocean, is examined. The hypothesis is that the density differences imposed at the surface by differential heating are a source of available potential energy that can be partially released by mesocale eddies with horizontal scales on the order of 100 km. Eddy fluxes balance the diapycnal mixing of heat and thus determine the vertical scale of penetration of horizontal thermal gradients (i.e., the depth of the thermocline). This conjecture is in contrast with the current thinking that the deep stratification is determined by a balance between diapycnal mixing and the large-scale thermohaline circulation. Eddy processes are analyzed in the context of a rapidly rotating primitive equation flow driven by specified surface temperature, with isotropic diffusion and viscosity. The barotropic component of the eddies is found to be responsible for most of the heat flux, and so the eddy transport is horizontal rather than isopycnal. This eddy transport takes place in the shallow surface layer where eddies, as well as the mean temperature, undergo diabatic, irreversible mixing. Scaling laws for the depth of the thermocline as a function of the external parameters are proposed. In the classical thermocline theory, the depth of the thermocline depends on the diffusivity, the rotation rate, and the imposed temperature gradient. In this study the authors find an additional dependence on the viscosity and on the domain width.
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Tett, P., R. Gowen, B. Grantham, K. Jones, and B. S. Miller. "The phytoplankton ecology of the Firth of Clyde sea-lochs Striven and Fyne." Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 90 (1986): 223–38. http://dx.doi.org/10.1017/s0269727000005005.
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SynopsisLochs Fyne and Striven are deep-silled fjords opening into the northern Firth of Clyde. They receive relatively little freshwater from local runoff, have a relatively low rate of tidal exchange, and undergo periods of deep water stagnation. Both contain fish farms which have lost stock because of phytoplankton blooms. Loch Striven was investigated in detail in 1980. Observations are also reported for 1979 and 1981, and for Loch Fyne from 1980–1982. Most stratification in Striven is due to salinity layering, but most of the freshwater in the loch probably originates in the Clyde Estuary and is associated with high concentrations of nitrate. Typical phytoplankton biomasses in Striven are the same as those in the western seaboard Loch Creran, but maxima exceed those in Creran. In addition to a red tide of Gyrodinium aureolum in September, 1980, three periods of high biomass seem to be a regular feature of the phytoplankton calendar in Striven. The spring increase takes place in March or early April, is dominated by the diatom Skeletonema costalum, and probably depends on the stabilizing effects of reduced near-surface salinities. A summer flourishing of Leptocylindrus danicus and dinoflagellates is also associated with near-surface salinity layering. A late spring bloom of diatoms, dinoflagellates and small flagellates, some ichthyotoxic, appears to be related to the occurrence of thermohaline stratification and near-surface nutrient depletion; on some occasions lochhead upwelling may also have been involved. Insofar as data are available, the ecology of phytoplankton in Loch Fyne appears similar to that in Loch Striven.
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Kerimoglu, Onur, Yoana G. Voynova, Fatemeh Chegini, Holger Brix, Ulrich Callies, Richard Hofmeister, Knut Klingbeil, Corinna Schrum, and Justus E. E. van Beusekom. "Interactive impacts of meteorological and hydrological conditions on the physical and biogeochemical structure of a coastal system." Biogeosciences 17, no. 20 (October 21, 2020): 5097–127. http://dx.doi.org/10.5194/bg-17-5097-2020.
Повний текст джерелаАнотація:
Abstract. The German Bight was exposed to record high riverine discharges in June 2013, as a result of flooding of the Elbe and Weser rivers. Several anomalous observations suggested that the hydrodynamical and biogeochemical states of the system were impacted by this event. In this study, we developed a biogeochemical model and coupled it with a previously introduced high-resolution hydrodynamical model of the southern North Sea in order to better characterize these impacts and gain insight into the underlying processes. Performance of the model was assessed using an extensive set of in situ measurements for the period 2011–2014. We first improved the realism of the hydrodynamic model with regard to the representation of cross-shore gradients, mainly through inclusion of flow-dependent horizontal mixing. Among other characteristic features of the system, the coupled model system can reproduce the low salinities, high nutrient concentrations and low oxygen concentrations in the bottom layers observed within the German Bight following the flood event. Through a scenario analysis, we examined the sensitivity of the patterns observed during July 2013 to the hydrological and meteorological forcing in isolation. Within the region of freshwater influence (ROFI) of the Elbe–Weser rivers, the flood event clearly dominated the changes in salinity and nutrient concentrations, as expected. However, our findings point to the relevance of the peculiarities in the meteorological conditions in 2013 as well: a combination of low wind speeds, warm air temperatures and cold bottom-water temperatures resulted in a strong thermal stratification in the outer regions and limited vertical nutrient transport to the surface layers. Within the central region, the thermal and haline dynamics interactively resulted in an intense density stratification. This intense stratification, in turn, led to enhanced primary production within the central region enriched by nutrients due to the flood but led to reduction within the nutrient-limited outer region, and it caused a widespread oxygen depletion in bottom waters. Our results further point to the enhancement of the current velocities at the surface as a result of haline stratification and to intensification of the thermohaline estuarine-like circulation in the Wadden Sea, both driven by the flood event.