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A mass coral bleaching event occurred in the summer of 2022 in subtropical Hong Kong, driven by two marine heatwaves (MHWs) with high intensities of 1.56 and 0.86 °C above a mean climate condition, both MHWs 7 days with a short gap of 4 days during the strong La Niña year. A transect survey was conducted at nine study sites in three regions, which revealed widespread coral bleaching with bleached coral cover ranging from 2.4 to 70.3%. In situ environmental data revealed the presence of a thermocline and halocline. Local conditions, including depth and wave exposure, significantly influenced the bleaching response. Shallow-water (2–4 m) corals were primarily affected, particularly in sheltered and moderately sheltered sites that exhibited higher levels of bleached coral cover (42.97 ± 15.4% and 44.93 ± 29.4%, respectively) compared to the exposed sites (31.8 ± 5.2%). Bleaching in deep waters (4–6 m) was minimal, with only a few colonies of Goniopora at two of the three sheltered sites exhibiting bleaching (1.7 ± 1.5%). Heat stress resistance differed between coral genera. Recovery rate for four common coral genera is low for Acropora tumida. Additionally, a minor hypoxia event was found to cause mortality of non-coral benthos at a sheltered site (Sharp Island). These findings highlight the alarming impact of extreme heatwaves on subtropical coral communities and underscore the importance of monitoring coral bleaching. [ABSTRACT FROM AUTHOR]

Solar energy is one of the major sources of renewable energy and is being extensively harnessed. However, the intermittent nature limits solar energy to act as a stand-alone energy source. Therefore, it becomes imperative that effective and economical methods of storing solar energy on a large scale are developed. Both sensible and latent heat storage methods are available. The use of a thermal energy storage (TES) system is an attractive choice for high-temperature applications such as power generation plants. The present study investigates the development of a small-scale TES system using a concentrated solar collector. For this purpose, a small cylindrical thermocline tank with suspended copper pipes in the storage medium was developed, with vegetable oil working as the heat transfer fluid (HTF) and being circulated through the pipes to transfer heat to used engine oil as the storage medium. A pump continuously circulates the HTF through the charging loop. TES was designed and developed based on the results of numerical simulations before the physical development of the experimental setup. Numerical calculations were performed for determining heat transfer and charging characteristics using different heat storage materials. The numerical results showed that a maximum temperature of 67 °C was achieved in the 100-min simulation while in the experimental results, a maximum temperature of 64 °C was achieved. The experimental results were found in close conformance with the simulation results. The experiments showed that the flow rate of 0.088 L s−1 was optimal and provided the highest temperature in the thermocline tank. The discharging experiment showed that the apparatus is viable to be used for 5.5 h for heating purposes. The salient feature of the study is an inexpensive TES system development and can act as a benchmark for the future development of renewable technology. [ABSTRACT FROM AUTHOR]

NOAA generates a suite of Ocean Heat Content (OHC) products for the North Atlantic and the North and South Pacific basins on a daily basis. Knowledge of the upper Ocean Heat Content is a critical aid in assessing the ocean's impact on Tropical Cyclones (TCs) and weather events. In-situ and satellite measurements of Sea Surface Temperature (SST) and Sea Surface Height Anomaly (SSHA) are used to generate the OHC product suite. The evaluated suite includes the 20°C (D20) and 26°C (D26) isotherm depths, the mixed layer depth (MLD) and mapping errors. Two cases are presented within the context of situational awareness showing the underling oceanic variability during the lifecycles of TC's Irma and Dorian. [ABSTRACT FROM AUTHOR]

Reconstructing the spatial patterns in thermocline depth is critical for understanding ocean‐atmosphere interactions. Previous foraminiferal proxies of thermocline depth focus on gradients between planktonic foraminifera living in the surface and subsurface ocean. However, both thermocline depth changes and stratification changes will impact this measure. In this study, we outline a method for reconstructing the tropical upper ocean vertical water column profile, enabling the separate assessment of thermocline depth and stratification changes. This method uses oxygen isotope data from surface and sub‐surface calcifying planktonic foraminifera (Globigerinoides ruber albus, Globorotalia tumida, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata) as well as data from benthic foraminifera from a core site below the thermocline. Using newly generated and compiled oxygen isotope data from Holocene‐aged marine sediments, we construct vertical profiles at 20 core sites in the Tropical Pacific Ocean. Quantitative estimates of thermocline depth along with error ranges from Monte Carlo simulations are extracted from the reconstructed profiles. There is a strong correlation between reconstructed Holocene and climatological thermocline depth, but the East‐West contrast in the depth of the thermocline is underestimated by 30%. Incorporating benthic information in thermocline estimates results in a dramatic improvement in the reconstruction of spatial gradients in thermocline depth compared to a simpler proxy, the difference in oxygen isotope ratio between a deeper calcifying planktonic species and the surface species, G. ruber. Plain Language Summary: The thermocline is a layer of the ocean where temperature changes rapidly, and the depth of this layer is related to many climatic phenomena. Understanding where and when this layer was deeper and shallower in the past is important to our overall understanding of the climate system. We outline a novel method to reconstruct the thermocline with microscopic shells collected from the sea floor. Our method can reconstruct the changes we see across the Pacific today and also recreate the changes found between the last ice age and today. Key Points: We show a novel method for reconstructing the upper water column using oxygen isotope measurements on multiple species of foraminiferaThis method can be used to quantitatively reconstruct spatial and temporal changes in thermocline depthIf a simple differencing method is preferred, thermocline depth can be most accurately reconstructed using subsurface species only [ABSTRACT FROM AUTHOR]

In the Sea of Japan, field studies have found snow crab and red snow crab larvae occur between the surface and depths of up to 550 m and 1100 m, respectively. In this region, snow crab larvae hatch at depths of 240–260 m and red snow crab larvae hatch at 1000–1500 m. To understand their vertical distribution during the larval period, we investigated the upward swimming speed of newly hatched larvae (first-stage zoea) and the behaviour of all larval stages (first and second zoeal and megalopal stages) in a temperature gradient under laboratory conditions. Our results showed that the larvae have the potential to reach the surface within a few days of hatching. As the larvae developed, they preferred greater depth and lower temperatures; although they temporarily rose to higher levels immediately after each moult. The zoeae and megalopae of both species did not occur beyond the 16 and 6°C temperature layers, respectively. The preferred position of the larvae in the gradient temperature did not differ between the two species. The present study suggests that Chionoecetes larvae transported to unsuitable temperatures may not die, but could escape from low temperatures by upward swimming and from high temperatures by sinking. [ABSTRACT FROM AUTHOR]

Mixing processes in lakes are important in determining sedimentation zones and in setting the so‐called "wash zone", the area of lake bottom in contact with an oscillating thermocline during wind‐driven internal seiche events. The wash zone also aligns with a sharp change in sediment roughness and hardness. Taken together, these rapid changes in temperature and sediment indicate that the wash zone is a distinctive ecotone in stratified lakes. Depth stratified randomised netting was used to develop count‐based habitat use models for three common benthic fish species as a function of depth or temperature covariates. Using data from two lakes with quite different wash zone depths, we show the wash zone to describe fish habitat for two of three benthic fish species by utilising the top 50% of estimated fish abundance as an indicator of habitat use. White sucker (Catostomus commersoni) habitat use was within the boundaries of the wash zone. Lake whitefish (Coregonus clupeaformis) habitat was adjacent and within the wash zone. Longnose sucker (C. catostomus) habitat use was in the deep areas of lakes dominated by sediment focusing and did not overlap white sucker. Lake whitefish habitat use overlapped both catostomids, but peak abundance of both lake whitefish and white sucker overlapped pointing to potential interactions between these species. Smaller lakes have less vigorous mixing processes and a narrower wash zone, so with a decline in lake size the likely area of the wash zone as habitat for benthic feeding fish would become smaller. [ABSTRACT FROM AUTHOR]

To achieve sustainable development goals and meet the demand for clean and efficient energy utilization, it is imperative to advance the penetration of renewable energy in various sectors. Energy storage systems can mitigate the intermittent issues of renewable energy and enhance the efficiency and economic viability of existing energy facilities. Among various energy storage technologies, thermocline heat storage (THS) has garnered widespread attention from researchers due to its stability and economic advantages. Currently, there are only a few review articles focusing on THS, and there is a gap in the literature regarding the optimization design of THS systems. Therefore, this paper provides a comprehensive review of the recent research progress in THS, elucidating its principles, thermal storage materials, applications, and optimization designs. The novelty of this work lies in the detailed classification and analysis of various optimization designs for THS, including tank shape, aspect ratio, inlet/outlet configuration, thermal energy storage materials arrangement, operating strategies, and numerical model optimization approaches. The limitations of existing research are also identified, and future perspectives are proposed, aiming to provide recommendations for THS research and contribute to the development and promotion of THS technology. [ABSTRACT FROM AUTHOR]

Rapid warming in the High Arctic has induced changes in terrestrial environments that have included major recent shifts in lakes and ponds. Numerous studies exist of spatial trends in water chemistry, bioindicator groups, and paleoenvironmental change from High Arctic lakes; however, little is known about lake thermal stratification regimes at high latitudes beyond assumptions based on generalized classification schemes. Here, we report on the presence in late July 2022 of positive thermal stratification during open-water conditions in two freshwater lakes near Clements Markham Inlet, on northern Ellesmere Island. These lakes are situated in the polar desert at 82.6°N, >1000 km north of the generally accepted northern limit of summer thermal stratification. Given their location approaching the northernmost land on Earth, the thermal profiles of these lakes suggest that the occurrence of summer stratification may no longer be discounted anywhere in the Northern Hemisphere.

The vertical distribution of microplastics in Lake Ladoga was studied under conditions of density stratification with the presence of a thermocline and under homothermal conditions. Using a pump filtration device, water samples were taken at different water layers (0–70 m) under different hydrological conditions and a comparative analysis of the concentrations of microplastic particles with a size of 60–5000 μm was carried out. Microplastic particles were analyzed using both optical microscopy and Raman spectroscopy methods. Based on the obtained data, it was concluded that under conditions of density stratification, the concentrations of microplastic particles in the thermocline and above it are increased in comparison with the underlying layers (50 ± 40.2 and 15.9 ± 13 particles/m3, respectively). Under homothermal conditions, the vertical distribution of microplastics in the surface layer and in water column is more uniform (17.3 ± 17.8 and 12.7 ± 15.6 particles/m3, respectively). [ABSTRACT FROM AUTHOR]

Thermal stratification has become more extensive and prolonged because of global warming, and this change has had a significant impact on the distribution patterns of the phytoplankton communities. However, the response of phytoplankton community structures and assembly processes to thermal stratification is not fully understood. We predicted that the structure and assembly processes of phytoplankton communities would be affected by thermal stratification among water layers associated with environmental condition changes, reflecting certain patterns in temporal and spatial scales. Phytoplankton from Danjiangkou Reservoir were collected from October 2021 to July 2022 to verify this prediction. During the sampling period, Danjiangkou Reservoir remained thermally stratified with stability. The composition of the phytoplankton community in the surface layer significantly differed from that in both the thermocline and bottom layer. The phenomenon of thermal stratification affected the pattern of nitrogen and phosphorus distribution and, thus, the processes of the phytoplankton community structures. Deterministic processes had a greater influence on the assembly of the phytoplankton communities in the surface and bottom layers. In contrast, stochastic processes were more prevalent in the assembly of the thermocline phytoplankton community. The phytoplankton community within the thermocline layer exhibited a broader niche range than that in the surface and bottom layers, showing notable dissimilarity from that of the bottom layer. Canonical correspondence analysis (CCA) revealed that the vertical distributions of the phytoplankton communities were significantly correlated with NH4+-N, pH, and water temperature (WT). In summary, this study explained the distribution patterns of phytoplankton community structures and assembly processes in deep-water reservoirs during the stratification period. Additionally, the study explored the potential of using the distribution patterns of phytoplankton in stratified-state deep-water reservoirs under a subtropical–warm temperate climate as climate indicators in the context of global warming. [ABSTRACT FROM AUTHOR]

The hydrological processes of cascading hydroelectric reservoirs differ from those of lakes, due to the importance of the inflows and outflows that vary with energy demand. These heat and water advection terms are rarely considered in water body energy balance analyses even though reservoirs are common man-made structures, especially in North America, and thus may affect the regional climate. This study provides a comprehensive assessment of the water and energy balance of the 85-km2 Romaine-2 northern reservoir (50.69°N, 63.24°W), mean depth of 44 m, highlighting the significant contribution of the advection heat fluxes. The water balance input was primarily controlled by upstream (turbine) inflows (77.6%), while lateral (natural) inflows and direct precipitation represented 21.2% and 1.2%, respectively. As for the reservoir's heat budget, the net advection of heat accounted on average for 25.0% of the input, of which net radiation was the largest component (73.3%). After accounting for the absence of energy balance closure, latent heat and sensible heat fluxes represented 73.2% and 25.1% of total energy output from the reservoir, respectively. The thermal regime was influenced by the hydrological flow conditions, which were regulated by reservoir management. This played a major role in the evolution of the thermocline and the temperature of the epilimnion, and ultimately, in the dynamics of the turbulent heat fluxes. This study suggests that the heat advection term represents a large fraction of the heat budget of northern reservoirs and should be properly considered. [ABSTRACT FROM AUTHOR]

The development of intelligent oceans requires exploration and an understanding of the various characteristics of the oceans. The emerging Internet of Underwater Things (IoUT) is an extension of the Internet of Things (IoT) to underwater environments, and the ability of IoUT to be combined with deep learning technologies is a powerful technology for realizing intelligent oceans. The underwater acoustic (UWA) communication network is essential to IoUT. The thermocline with drastic temperature and density variations can significantly limit the connectivity and communication performance between IoUT nodes. To more accurately capture the complexity and variability of ocean remote sensing data, we first sample and analyze ocean remote sensing datasets and provide sufficient evidence to validate the temporal redundancy properties of the data. We propose an innovative deep learning approach called Ocean-Mixer. This approach consists of three modules: an embedding module, a mixer module, and a prediction module. The embedding module first processes the location and attribute information of the ocean water and then passes it to the subsequent modules. In the mixing module, we apply a temporal decomposition strategy to eliminate redundant information and capture temporal and channel features through a self-attention mechanism and a multilayer perceptron (MLP). The prediction module ultimately discerns and integrates the temporal and channel relationships and interactions among various ocean features, ensuring precise forecasting. Numerous experiments on ocean temperature and salinity datasets show that Mixer-Ocean performs well in improving the accuracy of time series prediction. Mixer-Ocean is designed to support multi-step prediction and capture the changes in the ocean environment over a long period, thus facilitating efficient management and timely decision-making for innovative ocean-oriented applications, which has far-reaching significance for developing and conserving marine resources. [ABSTRACT FROM AUTHOR]

The application of an old open-pit lignite mine as an auxiliary reservoir for the supply of the city of La Coruña has involved a detailed analysis of the chemical quality of the vertical profile. The study has shown that a stratified lake is formed where the shape of the filling (first with groundwater and later surface waters from the nearby rivers were added) has influenced the formation of the lake profile. The Meirama mine is an open-pit brown lignite mine located in NW Spain. Exploitation ended in March 2008, leaving a pit of approximately 146 hm3 with a maximum depth of 205 m. The rehabilitation of the pit consisted of the creation of a lake that will serve as an auxiliary water reservoir for the city of La Coruña. The filling process lasted approximately 8 years (March 2008–May 2016) with subterranean and surface contributions from the environment. The formation of an invariant chemocline and a seasonal thermocline was observed. Therefore, in this work, (the first of a series of two articles), an analysis of the evolution of various physicochemical parameters, elements, and compounds at certain heights (the surface, the first 2 m (2 mbs), at 59 masl, and at the bottom (2 masl)). In this first article, the physicochemical parameters of pH, dissolved oxygen, temperature, and some metallic elements (iron and manganese) are analysed. From the analyzed parameters it can be seen the creation of a surface thermocline and a chemocline at a depth of 59 masl with the beginning of the formation of anoxic conditions of the bottom of the pit through the consumption of oxygen. [ABSTRACT FROM AUTHOR]

Solar thermal technologies can be an attractive option for the decarbonization of process heat applications; in particular, thermal energy storage is a high value proposition for continuous processes that may operate at a range of thermal conditions. A thermal-fluid model is developed to investigate the buoyant flow in a horizontal thermocline storage tank for a sludge-drying application. The process conditions and tank geometry considered are unique compared to the domestic water heating application typically considered in the literature and well suited for parabolic trough collectors. It was found that good separation of hot and cold fluids can be achieved with the long horizontal tank geometry depending on the inlet configuration. Uniform flow distribution along the length of the tank is required to establish a thermocline. Assuming desirable inlet conditions can be achieved, the tank outlet temperature predicted by the thermal-fluid model shows good agreement with the system-level performance model.

The water temperature of many lakes has recently risen as a result of climate change. We evaluated trends in the cloudiness, solar radiation, wind, air and water temperatures, ice cover, thermocline depth, transparency, and composition of two Bohemian Forest lakes (Czech Republic) from 1998 to 2022. Lake water temperatures increased by 0.32–0.47 °C decade−1, and the ice cover periods decreased by 11.7–14.8 days decade−1. These changes were mostly associated with increasing air temperatures during most months and increasing solar radiation (due to decreasing cloudiness) especially in March and November (the months preceding ice-on/off). Decreasing snow cover in winter (by 3.8 cm decade−1) further accelerated the earlier ice melt. The number of days with water temperature ≥4 °C increased similarly in both lakes by 12–13 days decade−1. However, the number of days with water temperature ≥20 °C increased and the depth of the summer thermocline decreased more in the lake with tree dieback in its catchment. Tree dieback accelerated the leaching of organic carbon and phosphorus, increasing water brownification, algal production, and decreasing water transparency. Solar radiation was absorbed in shallower water layers. Changes in catchment forest thus contributed to the variability in the response of lake water temperatures to climate change. HIGHLIGHTS The water temperature of two Bohemian Forest lakes rose from 1998 to 2022.; Ice-on was delayed, ice-off was earlier, and the ice-free period increased by 30 days.; The number of days with daily mean temperatures ≥4 and ≥20 °C increased.; Steeper water warming occurred in the lake with more decreasing transparency.; The transparency decreased due to elevated dissolved organic carbon and phosphorous leaching after tree dieback.;

This manuscript proposes an optimization method for power production and fresh-water using renewable sources with thermal energy storage (TES). The proposed method is the fire hawk optimization (FHO) method. The objective of the proposed method is to find better thermal efficiency. The waste heat in the steam power plant is converted to fresh water using the multi-effect desalination method. The cost of freshwater strongly depends on solar-electricity cost and displays a significant variation because of the variable solar availability state. The integrated structure using thermodynamics is examined by Exergy analysis. Heat exchangers and collectors are related to the energy efficiency of the total integrated structure and the equipment's highest share of energy destruction. The FHO method is implemented in MATLAB and its execution is calculated with existing approaches. The thermal efficiency in solar collectors is 80% and it is better than existing methods. [ABSTRACT FROM AUTHOR]

The latitudinal distribution of the ctenophores Mnemiopsis leidyi A. Agassiz, 1865, and Beroe ovata Bruguière, 1789, in the Russian sector of the Caspian Sea has different boundaries for their ranges. Studies on the occurrence of ctenophores in the water column have demonstrated that each species has a characteristic temperature limit of its vertical distribution. Studies of interactions between ctenophores showed considerable suppression of the abundance of M. leidyi (particularly of smaller individuals) by B. ovata. [ABSTRACT FROM AUTHOR]

Submesoscale turbulence in the upper ocean consists of fronts, filaments, and vortices that have horizontal scales on the order of 100 m to 10 km. High-resolution numerical simulations have suggested that submesoscale turbulence is associated with strong vertical motion that could substantially enhance the vertical exchange between the thermocline and mixed layer, which may have an impact on marine ecosystems and climate. Theoretical, numerical, and observational work indicates that submesoscale turbulence is energized primarily by baroclinic instability in the mixed layer, which is most vigorous in winter. This study demonstrates how such mixed layer baroclinic instabilities induce vertical exchange by drawing filaments of thermocline water into the mixed layer. A scaling law is proposed for the dependence of the exchange on environmental parameters. Linear stability analysis and nonlinear simulations indicate that the exchange, quantified by how much thermocline water is entrained into the mixed layer, is proportional to the mixed layer depth, is inversely proportional to the Richardson number of the thermocline, and increases with increasing Richardson number of the mixed layer. The results imply that the tracer exchange between the thermocline and mixed layer is more efficient when the mixed layer is thicker, when the mixed layer stratification is stronger, when the lateral buoyancy gradient is stronger, and when the thermocline stratification is weaker. The scaling suggests vigorous exchange between the permanent thermocline and deep mixed layers in winter, especially in mode water formation regions. Significance Statement: This study examines how instabilities in the surface layer of the ocean bring interior water up from below. This interior–surface exchange can be important for dissolved gases such as carbon dioxide and oxygen as well as nutrients fueling biological growth in the surface ocean. A scaling law is proposed for the dependence of the exchange on environmental parameters. The results of this study imply that the exchange is particularly strong if the well-mixed surface layer is thick, lateral density gradients are strong (such as at fronts), and the stratification below the surface layer is weak. These theoretical findings can be implemented in boundary layer parameterization schemes in global ocean models and improve our understanding of the marine ecosystem and how the ocean mediates climate change. [ABSTRACT FROM AUTHOR]

The application of thermal energy storage (TES) has been proved effective to improve the energy utilization efficiency of renewable energy and industrial waste heat energy. In this paper, a modified one-dimensional dimensionless model for the thermocline thermal energy storage tank is derived to simulate the system more accurately. An adaptive strategy for solving region compartmentalization is proposed for reducing computing time. Based on the proposed model, the effects of three different parameters on the performance of the thermocline tank are studied. The results show that increasing the inlet velocity can reduce the thickness of the thermocline and improve the system efficiency. Increasing the temperature difference between hot and cold water leads to a thicker thermocline, but the thermal energy stored in the tank increases. Increasing the tank height has no effect on the motion characteristic of thermocline, but the system efficiency can be increased. [ABSTRACT FROM AUTHOR]

Simple Summary: This paper provides a novel approach to integrating available environmental information into fishery data using gradient-dependent optimal interpolation. Comparative verifications of observations show that the constructed subsurface temperature and salinity profiles were very consistent with the in situ observations. The data assimilation method, named gradient-dependent optimal interpolation, gave refined matching results applied to represent the relationship between squid and environmental information. Our new method represents a useful tool in the deep research of fishery oceanography. A key issue in fishery forecasting is the collection of high-precision subsurface environmental data. A data assimilation method, named gradient-dependent optimal interpolation, was used to construct the near-real-time vertical temperature and salinity structure of a squid fishery ground based on Argo observations. The results were verified by truth-finding comparisons and applied to analyze the relationship between neon flying squid and the subsurface environment in the Kuroshio–Oyashio Confluence Region. The temperature and salinity differences between the constructed results and survey data were less than ±0.5 °C and ±0.02, respectively. Most of the relative analysis errors were less than the observational errors. Statistical analysis revealed that the most suitable temperature for squid was 18–24 °C at the near-surface (<5 m), although the squid can endure a temperature range from 11 to 12 °C at a depth of 300 m. There was an obvious thermocline in the fishery ground, with a thermocline depth of 65 m and a mean strength of approximately 0.10 °C/m. The regressive relationship between vertical temperature (thermocline parameters) and squid catch per unit effort (CPUE) followed the exponential (Gaussian) function. The most suitable salinity was 33.0–34.2 at depths shallower than 300 m. [ABSTRACT FROM AUTHOR]

Aerators are necessary for the conservation of water quality in dams, as they increase water circulation and oxygenate the water. To estimate aerator performance characteristics in the field, the optimal spatial range, resolution, and sampling time interval need to be determined for the targeted water mass. In this study, we conducted precise field experiments at Hiyoshi Dam in Kyoto, Japan, by employing a new type of aerator in the summer of 2012. Initially, the water temperature distribution near one aerator was observed using an automatic temperature profiler capable of horizontal movement on the water surface over a distance of 90 m at a speed of 0.1 m/s during a sampling cycle of 15 minutes. The vertical temperature distribution was determined by a series of thermocouples suspended in steps of 0.1 to 1 m on a 10-m-long cable beneath the surface. Subsequently, the water temperature distribution between two identical aerators located 275 m apart was observed using 6 pairs of vertically suspended thermocouples connected horizontally with a cable at 25-m intervals. Finally, the water flow distribution near one aerator was observed with an electromagnetic flowmeter. Analysis of the results clearly showed how an entrained water mass intruded into a thermocline that formed at a depth of 2.5 m. In addition, details regarding the speed and flow rate of the intrusion, the mixing efficiency, and the estimated number of days required for shallow layer circulation were estimated.

To achieve sustainable development goals and meet the demand for clean and efficient energy utilization, it is imperative to advance the penetration of renewable energy in various sectors. Energy storage systems can mitigate the intermittent issues of renewable energy and enhance the efficiency and economic viability of existing energy facilities. Among various energy storage technologies, thermocline heat storage (THS) has garnered widespread attention from researchers due to its stability and economic advantages. Currently, there are only a few review articles focusing on THS, and there is a gap in the literature regarding the optimization design of THS systems. Therefore, this paper provides a comprehensive review of the recent research progress in THS, elucidating its principles, thermal storage materials, applications, and optimization designs. The novelty of this work lies in the detailed classification and analysis of various optimization designs for THS, including tank shape, aspect ratio, inlet/outlet configuration, thermal energy storage materials arrangement, operating strategies, and numerical model optimization approaches. The limitations of existing research are also identified, and future perspectives are proposed, aiming to provide recommendations for THS research and contribute to the development and promotion of THS technology.

An anomalous anticyclone (AAC) recurs over the Indo-Northwest Pacific during post-El Niño summers, regulating climate anomalies in the densely populated South, Southeast, and East Aisa. However, AACs simulated in phase 5/6 of the Coupled Model Intercomparison Project (CMIP5/6) multi-model ensemble mean fail to persist through post-El Niño summers. The present study suggests that this weak persistence bias likely stems from the weakly persistent sea surface temperature (SST) anomalies' gradient between the North Indian Ocean and tropical Western Pacific. On one hand, the simulated North Indian Ocean warming decays faster compared with its observational counterpart due to the weakened cross-equatorial antisymmetric wind patterns and wind–evaporation–SST feedback, which may arise from the deep thermocline bias in the Southwest Indian Ocean in CMIP models. On the other hand, the long-lasting Western Pacific warming bias may be led by the intensified upper-ocean zonal advection feedback and wind–downwelling–SST feedback, which can be further traced back to the Pacific cold tongue bias in CMIP models. Compared with CMIP5 models, CMIP6 models simulate a more realistic Southwest Indian Ocean thermocline dome and equatorial Pacific cold tongue. Therefore, the overall simulation skill in the summertime AAC persistence is improved in CMIP6 than in CMIP5 models. The persistence of AAC is further investigated during post-Eastern Pacific (EP) and Central Pacific (CP) El Niño summers in CMIP models. The simulated AAC displays a remarkable stronger persistence during post-EP El Niño summer compared to its post-CP counterpart. The present study highlights that reducing mean-state biases in climate models may elevate the simulation skills of summertime AAC persistence, thereby enhancing seasonal prediction and future projection skills of Asian summer monsoon. [ABSTRACT FROM AUTHOR]

The sinkholes along the Dead Sea (DS) shores form by dissolution of an 11–10 kyr old subsurface salt layer (hereafter named the 'Sinkholes Salt') that precipitated on the lake's floor during periods of negative water balance, water level decline and salinity increase. We analyze the variations in absolute elevation and thickness of this layer in 40 boreholes along the western shores of the DS, reconstruct water-body stratification, past lake levels, and paleo-bathymetry during salt deposition, and comment on the role of the salt-layer elevation in future sinkhole formation. In the northern basin of the DS, maximum thickness of salt (~ 23 m) is found where salt top and bottom elevations are below ~ 440 meters below sea level (mbsl) and ~ 465 mbsl, respectively. Above these elevations the salt layer gradually thins out until 416 mbsl, above which it is no longer found. These relationships suggest that thermohaline stratification, with a thermocline at 25–30 m depth, similar to the present day dynamics of the DS, developed annually during the salt-precipitation period, giving rise to uniform salt accumulation below the thermocline and partial to full dissolution above it. Salt accumulation was controlled by the bathymetry of the lake and its configuration relative to the thermocline, and locally hampered by discharge of subaqueous under-saturated groundwater. The truncation of the salt layer at elevation of 416 mbsl is attributed to salt dissolution down to this elevation by a relatively diluted upper water layer that developed following inflow of fresh surface water at the end of the salt period. This event also marks the change to a positive water balance and lake level rise from its lowest stand of ~ 405 mbsl, as determined from limnological considerations. [ABSTRACT FROM AUTHOR]

A primary objective of contemporary district heating (DH) networks is to minimize the use of primary energy, especially fossil fuels, for meeting the heating demands of grid customers. In this context, thermal energy storages (TESs) serve as crucial devices, facilitating the decoupling of grid demand from heat generation. This study presents an experimental comparison of three large-scale TESs, each employing distinct injection and extraction systems. The performance of these were examined based on data collected over a consistent two-month operational period, enabling a quantitative comparison. The TESs under scrutiny, located in the DH networks of Milan and Brescia in Northern Italy, each have a capacity of a few thousand cubic meters of water and differ in their injection system and shape ratio. Notably, the evolution and thickness of the thermocline and the percentage of energy waste were examined to discern the impact of the injection system, specifically the presence of a flow-straightening device, and the shape ratio on the performance of the TES systems. These characteristics were found to significantly influence energy waste in heat storage, which ranged from 1.56% to 6.50% of the total stored energy, depending on the specific TES tank under consideration. [ABSTRACT FROM AUTHOR]

Decadal variability of the North Pacific subtropical mode water (STMW) and its influence on the upper thermocline and mixed layer are examined in a four-dimensional variational ocean re-analysis for the Western North Pacific over 30 years (FORA–WNP30). The STMW that forms south of the Kuroshio Extension becomes thick/cold and thin/warm on decadal timescales. These variations are subducted and advected to the south, where thick (thin) STMW causes the upper thermocline to heave up (down) above the STMW, producing cold (warm) temperature anomalies at subsurface depths, with especially large anomalies at the depths of the seasonal thermocline. Temperature anomalies also appear in the mixed layer from March to November, except in September. These anomalies have the same sign as the temperature anomalies of the STMW, although they are due not to the reemergence of the STMW at the surface but to the heaving of the upper thermocline. In the FORA–WNP30, because the formation of the mixed layer temperature anomalies owes much to the increment introduced by data assimilation, the mechanism remains unclear. A heat budget analysis of the mixed layer, however, suggests the importance of entrainment and/or vertical diffusion at the base of the mixed layer for conveying temperature anomalies from the upper thermocline to the mixed layer. The STMW also affects the mixed layer depth. A thick (thin) STMW shoals (deepens) the seasonal thermocline, enhancing (weakening) stratification at depths below the mixed layer and thus hindering (favoring) mixed layer development from July to September. [ABSTRACT FROM AUTHOR]

The development of intelligent oceans requires exploration and an understanding of the various characteristics of the oceans. The emerging Internet of Underwater Things (IoUT) is an extension of the Internet of Things (IoT) to underwater environments, and the ability of IoUT to be combined with deep learning technologies is a powerful technology for realizing intelligent oceans. The underwater acoustic (UWA) communication network is essential to IoUT. The thermocline with drastic temperature and density variations can significantly limit the connectivity and communication performance between IoUT nodes. To more accurately capture the complexity and variability of ocean remote sensing data, we first sample and analyze ocean remote sensing datasets and provide sufficient evidence to validate the temporal redundancy properties of the data. We propose an innovative deep learning approach called Ocean-Mixer. This approach consists of three modules: an embedding module, a mixer module, and a prediction module. The embedding module first processes the location and attribute information of the ocean water and then passes it to the subsequent modules. In the mixing module, we apply a temporal decomposition strategy to eliminate redundant information and capture temporal and channel features through a self-attention mechanism and a multilayer perceptron (MLP). The prediction module ultimately discerns and integrates the temporal and channel relationships and interactions among various ocean features, ensuring precise forecasting. Numerous experiments on ocean temperature and salinity datasets show that Mixer-Ocean performs well in improving the accuracy of time series prediction. Mixer-Ocean is designed to support multi-step prediction and capture the changes in the ocean environment over a long period, thus facilitating efficient management and timely decision-making for innovative ocean-oriented applications, which has far-reaching significance for developing and conserving marine resources.

This study evaluates and compares the effects of five actual solid filling materials (SFMs) on the operation and mechanical characteristics of liquid sodium thermoclinic heat storage (THS) tank, including the quartzite, high-temperature concrete, copper foam, silicon carbide and alumina ceramics. By utilizing the computational fluid dynamics method, the charging, discharging and mechanical performances of the THS tank using different SFMs as well as with no SFM are compared. The results demonstrate that the introduction of SFM can enhance the charging and discharging performances of the THS tank. The high-temperature concrete can lead to the maximum average discharging power of 4.93×105 J/s and the second maximum total discharging quantity of 7.55×109 J, and the alumina ceramics could bring the maximum total discharging quantity of 8.59×109 J and the second maximum average discharging power of 4.77×105 J/s. The THS tank using high-temperature concrete has the largest discharging efficiency of 90.14% as well as the smallest peak maximum mechanical stress of the THS tank wall (42.4 MPa). The THS tank with no SFM has the smallest total charging quantity and lowest discharging efficiency, which are 4.62×109 J and 77.84%. In general, the THS tanks using alumina ceramics and high-temperature concrete both have better operation performances, and the high-temperature concrete can bring the best mechanical performance of the THS tank.

• Innovative thermocline TES prototype with internal heat exchangers tested by ENEA. • A vertical internal channel assists the movement of the molten salt in the tank. • A dynamic 2D axis-symmetric CFD model of the prototype has been developed. • The model is validated against the experimental data under justified assumptions. • The model is exploited to assess how the channel diameter affects the performance. Thermocline thermal energy storage is a (potentially) cost-effective alternative to the more widespread two-tank solution, as both the hot and the cold medium are stored in a single tank. An innovative single-medium indirect thermocline technology was recently developed by ENEA and a prototype was experimentally tested at the Casaccia laboratories. The storage tank is equipped with two flat-coil heat exchangers (HXs) located at the bottom and at the top of the tank, for the charge and discharge phases, respectively. The storage medium is a mixture of molten salt (Hitec XL) and the heat transfer fluid is a mineral oil (Delcoterm Solar E15). An internal vertical channel, which assists the motion of the storage medium during the charge and discharge transients, connects the two HXs. In this paper, a detailed, transient 2D axisymmetric Computational Fluid Dynamics (CFD) model of the prototype has been developed. The model simulates the charge and discharge transients, determining the heat losses and the temperature distribution of the molten salt in the tank. The computational domain includes the storage medium, the tank insulated walls and the main components immersed in the molten salt, i.e., the heat exchangers and the vertical channel. The model has been first calibrated by best-fitting the data measured during a test conducted without any thermal load, then validated against another independent set of experimental data. A first comparison against a charge transient showed some discrepancies between the computed and the measured temperatures of the salt, which could be explained by assuming the presence of a bypass at the location of the HXs. This assumption is discussed and justified in the paper. The CFD domain has then been modified to include the bypass, and this allowed to successfully validate the model against experimental data in both charge and discharge phases. The validated model is finally exploited to assess how a variation in the diameter of the internal vertical channel could affect the thermal performance of the storage system in a charge transient. The results indicate that decreasing the channel diameter leads to an increase of the salt temperature at the very top of the tank at the cost of a longer time to fully charge the storage. [ABSTRACT FROM AUTHOR]

Parabolic trough concentrated solar power (CSP) plants are particularly promising renewable sources of energy, whose easy integration with thermal energy storage (TES) systems allows to mitigate the intermittency of electricity generation. Currently, molten nitrates, with two tanks arrangement, are mainly used for sensible heat accumulation. To reduce costs and make the CSP storage systems more manageable, single tank configurations have been proposed, where the cold and hot fluids are stored in the same container and separated because of their density difference. The aim of the present work is to study the storage performances presented by two novel ternary and quaternary mixtures, proposed within the European project IN POWER. An experimental campaign was preliminarily performed to investigate the fluids thermo-physical properties, and the obtained values were utilized as input data to model the discharge phase in a thermocline tank. The simulation results were compared with the ones acquired considering two commercial materials, namely, solar salt and Hitec XL®. Overall, considering same temperature ranges, higher discharging times are obtained for the quaternary and ternary mixtures, with the ternary presenting a smaller thermocline thickness than the solar salt while this parameter is the same considering the quaternary and Hitec XL®. [ABSTRACT FROM AUTHOR]

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system. [ABSTRACT FROM AUTHOR]

The addition of storage capacity to district heating systems increases flexibility and expands the range of usable heat sources. Despite their apparently simple nature, thermal energy storage (TES) tanks display a wide range of performances due to different construction and operation choices, as proven by numerous literature studies. However, most of the investigations focus on domestic-size tanks of few cubic metres or, on the other hand, very large seasonal storages of hundreds of thousands of cubic metres. In this work, the performances of a 5000 m3 TES recently introduced in a district heating network in Brescia, Italy, are experimentally analysed using temperature and flow rate measurements acquired over two months in the heating season. First-law efficiencies, exergy, and stratification parameters are calculated and discussed. Energy and exergy efficiencies computed for all examined cycles are above 90%, in line with literature values for smaller and larger TESs. The thermocline profile is generally stable through the cycle unless anomalous events occur, and its average thickness is below 4% of the water height. The combined analysis of single-point indicators, thermocline profiles, and qualitative temperature heatmaps shows that short partial charge/discharge events followed by long stand-by periods negatively affect performances. Stratification efficiency and stratification number give further time-dependent information on the vertical distribution of temperatures in the TES. Heat losses towards the outside are also estimated and discussed in the light of integrative measurements performed on other TESs with similar characteristics, showing that particular care must be paid to the top, where dissipation could be increased by evaporation phenomena if the water surface is not protected.

In this paper, a new thermal energy storage (TES) scheme of basalt fiber bundles is proposed. This basalt fiber bundle TES tank adopts two-stage runner arrangement to increase the specific surface area and improve the heat exchange effect. Based on this, a variable flow rate and preheating control scheme is proposed to enhance the discharging stability. The results when the air initial flow rate is 1m/sshow that the two methods of automatically controlling the flow rate change and using two tanks in series to make full use of the waste heat can significantly increase the stable discharging time of the TES tank. The increase in the stable discharging time reached 115% with variable flow rate scheme. And the simultaneous use of variable flow and preheating control schemes can extend the stable discharging time to 166% of the constant flow scheme. This TES tank can provide a wide heating power range and the maximum discharging power per unit area reaches 1.005MW±1% when the initial flow rate is 1m/s. However, it is difficult for honeycomb and packed bed to achieve such output under the same flow rate. In short, this new scheme can realize the coexistence of high thermal energy storage density, strong stable discharging, small volume and high discharging power, and can be used in mobile thermal energy storage system to meet user groups with significant differences in heating demand.

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems. [ABSTRACT FROM AUTHOR]

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10−10 to 4.18 × 10−7 W·kg−1. In the surface mixed layer, high values of ε (10−9∼10−8 W·kg−1) were observed toward the water surface. In the thermocline, ε was 10−9.5∼10−9 W·kg−1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations. [ABSTRACT FROM AUTHOR]

The South China Sea has huge reserves of thermal energy resources and suitable water depth and seabed topography. It is an ideal place for exploring ocean thermal energy. To analyze the impact of cooling water discharge on the environment of the sea near Ganquan Island where an ocean thermal power station is planned in Xisha Archipelago, the South China Sea, a three-dimensional hydrodynamic model was established by using a numerical simulation method and the reliability of the model was verified against the measurement date of tide level at the Yongxing Island tide survey station. The diffusion process of cooling water around the power plant and its influence on water temperature structure in nearby waters were simulated and analyzed. Results show that the cooling water from the power station generates a sharp drop in temperature around the outfall, and then a thermocline is formed locally. However, the temperature drop is mainly concentrated near the outfall and spreads with the tidal flow. The temperature gradient at the outfall is the largest, and the temperature gradient tends to be smaller away from the outfall. The envelope area of the thermocline decreases with the increase of the drainage temperature and increases with the increase of the drainage flow. There is a thermocline above the cold water mass and an inverse one below, and the upper boundary depth of the thermocline increases with the increase of drainage depth. This research assesses the environmental issues involved in the construction of the ocean thermal power stations and provides a scientific basis for the management of the ecological environment. [ABSTRACT FROM AUTHOR]

A validated three-dimensional unsteady computational fluid dynamics analysis is performed in this study to investigate the effects of the inlet flow conditions on the thermal performance of solar storage tanks. First, effects of different mass flow rates on the thermal performance of a simple tank (Model 1, single inlet and single outlet) are investigated. The results show that higher mass flow rates deteriorate thermocline and thermal stratification which is desirable. To reduce the unfavorable effects of inlet jet mixing with stagnant fluid, the mass flow rates are divided equally between two inlet ports in the next model (Model 2). The results show that this model acts better than previous model form heat transfer point of view. In the next model (Model 3), the simple inlet port is replaced by a circular truncated cone shaped diffuser to reduce the momentum of the jet and impede unwanted mixing in the tank. The effects of the diffuser aspect ratio are analysed at fixed mass flow rates. The results reveal that small aspect ratios improve the performance of the tank while higher aspect ratios deteriorate the performance because of strongly adverse pressure gradient occurred inside the diffuser, which consequently results in a high-speed core flow, that contradicts with the idea of employing a diffuser. The outcomes indicate that only the aspect ratios between 1.0 and 1.5 have positive effects. In the final section, the study continues by modifying Model 3 through examining different orientations of the inlet port with respect to horizon (Model 4). Different angels including −30°, −15°, 15°, 30° are considered and the results show that changing inlet orientation is not as effective as the previous modifications.

A key issue in fishery forecasting is the collection of high-precision subsurface environmental data. A data assimilation method, named gradient-dependent optimal interpolation, was used to construct the near-real-time vertical temperature and salinity structure of a squid fishery ground based on Argo observations. The results were verified by truth-finding comparisons and applied to analyze the relationship between neon flying squid and the subsurface environment in the Kuroshio–Oyashio Confluence Region. The temperature and salinity differences between the constructed results and survey data were less than ±0.5 °C and ±0.02, respectively. Most of the relative analysis errors were less than the observational errors. Statistical analysis revealed that the most suitable temperature for squid was 18–24 °C at the near-surface (

The application of thermal energy storage (TES) has been proved effective to improve the energy utilization efficiency of renewable energy and industrial waste heat energy. In this paper, a modified one-dimensional dimensionless model for the thermocline thermal energy storage tank is derived to simulate the system more accurately. An adaptive strategy for solving region compartmentalization is proposed for reducing computing time. Based on the proposed model, the effects of three different parameters on the performance of the thermocline tank are studied. The results show that increasing the inlet velocity can reduce the thickness of the thermocline and improve the system efficiency. Increasing the temperature difference between hot and cold water leads to a thicker thermocline, but the thermal energy stored in the tank increases. Increasing the tank height has no effect on the motion characteristic of thermocline, but the system efficiency can be increased.

To explore the effects of eutrophic deep waters offshore on red-tide outbreaks, waters were collected from 0, 20, and 40 m depths at an offshore station in the South Sea of Korea, and the growth rate of each major red-tide dinoflagellate Prorocentrum donghaiense, Tripos furca, Alexandrium fraterculus, and Margalefidinium polykrikoides in the waters was measured. No species grew at dissolved inorganic nitrogen concentrations (DIN) of < 7.0–8.4 µM, but the growth rates of all four species rapidly increased and became saturated at 12–15 µM DIN. On July 31, 2020, the DIN was 4.1–4.6 µM in 0–10 m depth waters but 8.9–18.4 µM in 20–50 m depth waters. Under these circumstances, considering that calculated reachable depths of P. donghaiense, T. furca, A. fraterculus, and M. polykrikoides were 10, 15, 24, and 52 m, respectively, A. fraterculus and M. polykrikoides can reach the deep waters and grow, but P. donghaiense and T. furca cannot. However, if the deep waters intrude and ascend by 10–20 m relative to that on July 31, four species can reach deep waters and grow, whereas if the deep waters retreat and descend by 10–20 m, only M. polykrikoides can reach the deep waters and grow. Red-tide outbreaks by M. polykrikoides in the South Sea in 2014 occurred after the deep water retreat. Thus, the position of the eutrophic deep waters, affected by their intrusion and retreat and solar insolation, can affect outbreaks of harmful M. polykrikoides red tides. [ABSTRACT FROM AUTHOR]

Earth's climate underwent secular structural evolution and cooling since the Pliocene Warmth, punctuated by increasing thermal gradients between the Western Pacific Warm Pool (WPWP) and the surrounding cooler regions of Eastern Pacific Cold Tongue and extra-tropics. One key mechanism for deciphering the climate evolution since Pliocene is the shoaling of the ocean thermocline, but much remains unknown about the upper-water structure of the western Pacific Warm Pool, the heat engine of the climate system, and its linkage to global ocean circulations. Here, by a newly made series of millennial-resolved δ18O and δ13C records of paired mixed-layer and thermocline dwelling planktonic foraminifera from IODP Site U1489 drilled in the center of WPWP, the trends of cooling and respired carbon content decreasing in the WPWP thermocline since ∼4 Ma are revisited and diagnosed. Our data allows us to propose that, the tropical Pacific upper-water circulation cell had shoaled and shrunk and the vertical mixing from deeper waters may have increased, since the Pliocene. Development towards a modern-style Warm Pool was initially onset at ∼3.1 and finalized at ∼0.7 Ma, respectively. • The Western Equatorial Pacific thermocline shoaled and cooled since the Pliocene Warmth. • Key shifts of the Western Equatorial Pacific thermocline structure at ∼3.1 and ∼0.7 Ma. • The Pacific Shallow meridional overturning circulation shrunk and shifted equatorward since Pliocene. [ABSTRACT FROM AUTHOR]

Marine organisms can change their habitat depth based on feeding strategies and physiological requirements. Here, we investigated habitat depth selections of juvenile sardines in the western and eastern North Pacific, Sea of Japan, and East China Sea from summer to autumn, which have been poorly documented. Habitat depth was estimated by comparing stable oxygen isotope values at the edges of otoliths formed several weeks before capture with in situ temperature and salinity observations near the sampling sites. The estimated depths at the three stations in the Sea of Japan for which acoustic data were available were consistent with the maximum acoustic scattering layer. Habitat depths in the eastern North Pacific, Sea of Japan, and the East China Sea varied considerably between regions in the upper 70 m. Still, they were mostly ± 10 m from the seasonal thermocline. Average temperatures at the thermocline in the regions were 16.8−24.5°C, which included temperatures significantly higher than the presumed optimal temperatures. However, the habitat depths in the subarctic North Pacific, where the mean temperature at the thermocline was 8.4°C, were consistently in the surface mixed layer above the thermocline. These results suggested that juvenile sardines tend to reside in the thermocline to feed efficiently on aggregated plankton, provided the temperature is physiologically tolerable. Our results may be useful for increasing sampling efficiency, validating assumptions in behavioural models, and providing insight into how atmospheric forcing affects sardine growth and survival. • Microvolume isotope analysis of otolith allows prediction of fish habitat depth. • The habitat depth of sardine juveniles varied significantly around the Pacific. • The juveniles mostly resided in the thermocline when the temperature is tolerable. • The food availability is likely the primary factor in their habitat depth selection. [ABSTRACT FROM AUTHOR]

A data-driven approach to assess the occurrence of thermal stratification and the depth of the thermocline in water masses has been developed and tested in the Spanish reservoir of El Val. The novelty of this approach is that it relies only on readily available data that can be collected for almost any reservoir, providing water managers with a transferable tool that can be easily adapted for any other reservoirs or lakes. The input variables were meteorological data, the water level and the output flow. A non-supervised clustering technique, k-means , was used to identify the stratification period with unlabelled data, that is to say inferring patterns when data from the target variable is not available. As a supervised method, Artificial Neural Networks were used to classify a given day as having or not having stratification and, in the positive case, to infer the depth of the thermocline. The classification showed a very high accuracy (96%) and the estimation of the thermocline depth showed a mean absolute error (MAE) of 1.94 m and 1.99 m in the training and test fractions, respectively. Shapley Additive Explanations (SHAP) values were used to improve the explainability and they revealed that the most important features to infer the depth of the thermocline were the water level, the daily average solar irradiance and the air temperature. [Display omitted] • Open data relating water quality continuous monitoring in a reservoir are used. • Clustering technique allows identifying stratification periods. • Meteorological, storage state and flow data allow inferring the thermal behaviour. • Up to 3 days-lagged variables are useful to infer the thermocline depth. • The level in the reservoir and solar irradiance are the most relevant variables. [ABSTRACT FROM AUTHOR]

A schematic of reversible solid oxide cell with thermocline thermal energy storage. [Display omitted] • A reversible solid oxide cell system with thermocline-type energy storage was proposed. • System simulations were conducted to analyze the system characteristics. • The performances of the system were analyzed and compared with previous systems. • Techno-economic analysis validates the viability of the proposed system. • The proposed system outperforms in terms of efficiency, water use, emissions, and cost. In this study, a novel system − a reversible solid oxide cell system with a thermocline-type thermal energy storage is proposed to address the limits of green hydrogen. This system utilizes a solid oxide cell, operating selectively in both fuel cell and electrolysis modes. In the fuel cell mode, the system produces electricity and an enormous amount of heat that can be stored in thermal energy storage. Conversely, heat stored in the thermal energy storage during electrolysis produces steam and facilitates the electrolysis reaction to produce hydrogen. We conducted a numerical analysis and determined a design of thermocline-type thermal energy storage at representative driving load. Three alternative setups that operated under the same conditions were compared in this study: the reversible solid oxide cell system integrated with thermal energy storage, a stand-alone reversible solid oxide cell system, and a stand-alone solid oxide electrolysis system. The results indicate that the reversible solid oxide cell system with thermal energy storage outperforms the other two setups in terms of system efficiency, water consumption reduction, and greenhouse gas emissions. The proposed system achieves a 27.5 % improvement in efficiency over the solid oxide electrolysis stand-alone system. The study indicated that the proposed system could achieve 0 kg-CO 2 -eq/kg-H 2 of greenhouse gas emission, by replacing the natural gas burner with a thermocline-type thermal energy storage. Furthermore, a techno-economic analysis was conducted for all three systems, confirming that the proposed system can reduce a hydrogen production cost from $5.15/kg-H 2 to $3.03/kg-H 2. [ABSTRACT FROM AUTHOR]