Thermocline Layer Research Articles

Modeling of the Black Sea circulation using equations of heat and salt advection–diffusion having discrete nonlinear invariants

In this work the accuracy of reconstructing the Black Sea circulation by using new approximations of nonlinear terms in the transport equations, ensuring the conservation of temperature and salinity to a power greater than two, is analyzed based on the results of forecast calculations. Three numerical experiments with differences in the schemes for calculating temperature and salinity are carried out. In the first experiment – traditional schemes are used to conserve of temperature and salinity in the first and second degrees; in the second one – the temperature is conserved in the first and fifth degrees, salinity in the first and third; in the third one – the temperature in the first and third, salinity in the first and fifth degrees. Calculations are performed on the basis of the MHI model with a resolution of 1.6 km and taking into account realistic atmospheric forcing for 2016. Validation of the results is carried out based on comparison of model fields with in-situ and satellite measurements of temperature and salinity in 2016. Analysis of mean and root mean square errors showed that new schemes for the advection-diffusion equations of heat and salt, ensuring the conservation of predictive parameters to a power greater than two, improve the accuracy of reconstructing the salinity in the Black Sea upper 100m layer throughout the year compared with traditional approximation. The root mean square errors in the salinity field are reduced by 15–20%, the thickness of the upper mixed layer in winter and the depth of the upper boundary of the thermocline layer in summer in the central part of the sea are modeled approximately 10% more accurately. Based on the results of three experiments, the smallest deviations from observational data are obtained when using approximations that ensure the conservation of temperature to the third power and salinity to the fifth power.

Marine plankton community and net primary production responding to island-trapped waves in a stratified oligotrophic ecosystem

The oligotrophic Adriatic Sea is characterized during a typical summer by low productivity caused by strong water column stratification, which inhibits vertical mixing and nutrient supply to the euphotic zone. These conditions can be disrupted by transient physical forcing, which enhances nutrient fluxes and creates localized hotspots of relatively high net primary production. In this study, plankton abundance and diversity were investigated in relation to the physical forcing and nutrient concentrations in an area affected by island-trapped waves (ITWs) near Lastovo Island (Adriatic Sea). The episodic ITW events resulted in enhanced uplift and vertical excursion of the thermocline, marked by anomalously higher nutrient concentrations and a corresponding increase in net primary production in the thermocline layer. Physicochemical properties explained 11.7 % (p = 0.002) of the variability in micro- and nanophytoplankton and 88.9 % (p = 0.001) in the picoplankton community. A significant response to the ITW phenomenon in the plankton community composition (p = 0.001) was observed for bacterioplankton. Among the identified amplicon sequence variances, primary producers were scarce and mainly represented cyanobacteria (Synechococcus strain CC9902), stramenopiles (Pelagomonas), and chlorophytes (Ostreococcus). The remaining amplicon sequence variances were assigned to the classes Copepoda, parasitic fungi (Meyerozyma spp.), mixotrophic dinoflagellates (family Peridiniales, mostly the genus Blastodinium), and parasitic Ciliophora (Scuticociliata). Bacterial ecological functions corresponded to chemoheterotrophic, degradation, and fermentation processes, whereas samples collected after the most intense ITW episode also showed abundant bacteria linked to microplastic degradation and parasitosis. These results highlight the ecological role of localized physical phenomena in enhancing nearshore primary productivity and fine shifts in plankton taxa in oligotrophic systems.

The Seasonal Variations of the Thermocline in the Banda Sea and its Water Mass Characteristics

This research was conducted to examine the seasonal variations in the Banda Sea's thermocline layer and its water mass characteristics. The research was conducted by analyzing Argo Float data. The data consists of six observation stations in West Season and Transitional Season II, and four stations in Transition Season I and East Season The thermocline layer thickness was identified based on the depth where the temperature decreased ≥ 0.05oC/m. The thermocline layer's distribution of depth and thickness and the distribution of temperature and salinity seasonally in the thermocline layer were analyzed with Microsoft Excel 2010. The analysis results showed that East Season and Transition Season II have a shallower upper boundary depth of the thermocline layer, a deeper lower boundary of the thermocline layer, and the thermocline layer is thicker when compared to the West Season and Transition Season I. The average temperature distribution is higher and the average salinity is lower in the West Season and Transition Season I. The mean rate of change in salinity and temperature in the thermocline layer seasonally ranged from 0.002-0.004 PSU/m and 0.06-0.08oC/m. The thermocline layer's stratification is stronger in the West Season and Transition Season I.

Quantifying the functional genes of C, N, P, and S cycling in a deep lake: Depth patterns and drivers

Microbial functional composition is important for biogeochemical cycles, and is usually constrained by taxonomic species pool and natural environmental gradients. However, the distribution of functional genes in deep lakes and the driving factors remains elusive. Here, we quantified the abundance of 71 functional genes relevant to carbon degradation, carbon fixation, methane metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling in 38 sediments along the water depth ranging from 0 to 90 m in Lugu Lake, China, using Quantitative Microbial Ecology Chip (QMEC) and then explored their water-depth diversity pattern and abiotic and biotic drivers. Functional gene diversity showed a hump-shaped pattern along the depth and peaked at around 50 m which is the low boundary of thermocline layer. There were specific environmental preferences among functional gene subgroups such as nitrogen and sulfur cycling genes preferring to deeper and shallow waters, respectively. The dissimilarity of total functional genes increased with water depth distance indicating a distance-decay relationship. There was a congruence between functional and taxonomic composition by showing the positive correlations between the compositions of functional genes and bacteria or archaea. This phenomenon is consistently observed for the six functional gene subgroups, and the congruence strength was highest for nitrogen cycling while lowest for sulfur cycling. Compared to abiotic factors, biotic factors were more relevant to the functional gene diversity and composition. Biotic factors explained 28.5 % of the variance of functional gene diversity, while water depth and other environmental factors such as water total phosphorus and sediment carbon explained 4.2 % and 3.8 %, respectively. For functional gene composition, biotic factors accounted for 25.2 % of the variance, whereas water depth and other environmental factors contributed to 0.7 % and 4.4 %, respectively. Among all explanatory variables for function genes, bacterial composition had the highest contribution, which was further supported by showing its direct effects of 1.45 and 0.86 on functional diversity and composition, respectively. This study for the first time quantified the microbial functional genes along water depth in deep lakes and provided a more comprehensive understanding of the functional dynamics in microbial communities within aquatic ecosystems.

Analysis of nitrogen migration and transformation in the typical deep and large reservoir of the Lancang River — Evidence from nitrogen and oxygen isotopes

The environmental effect resulting from dam construction and the formation of large reservoirs has long been a topic of significant concern. While current research at a macro scale provides a well understanding regarding the evolution of nitrogen nutrient status in river-reservoir ecosystems, the vertical migration and transformation characteristics of nitrogen in reservoirs under changing runoff remain less defined. This study centers on a typical deep reservoir along the Lancang River-Nuozhadu (NZD) Reservoir in April and December. The monitoring reveals a distinct vertical stratification phenomenon in the NZD Reservoir in the vertical profile in April, which can be categorized into a mixed layer (ML) (0–5 m), a thermocline layer (TL) (5–40 m), and an isothermal layer (IL) (>40 m) based on the water temperature. However, little stratification in the profile is occurred in December. The results of nitrogen and oxygen isotopes in April indicate that the biochemical process of nitrogen in the NZD Reservoir is predominantly driven by nitrification. However, different nitrogen biochemical processes are coupled in various stratified regions in the vertical direction. In the ML, simultaneous assimilation of ammonia nitrogen by phytoplankton occurs. In the TL, there is a process of oxidation and decomposition of particulate organic nitrogen due to a significant stratification effect and an extended hydraulic retention time. In the region of minimal dissolved oxygen (30–40 m), simultaneous denitrification may take place. In December, the main process is nitrogen assimilation in reservoir surface (ML). Statistical analysis of environmental factors highlights water temperature (T) and dissolved oxygen (DO) as crucial environmental factors influencing nitrogen migration and transformation within the reservoir. This study suggests that in deep reservoirs experiencing vertical thermal stratification, the characteristics of DO and nitrogen migration and transformation exhibit significant vertical spatial heterogeneity. This phenomenon may lead to diverse ecological environmental effects. Future efforts should focus on enhancing the fine monitoring of stratified water bodies in deep and large reservoirs and analyzing the ecological environmental effects of material cycling in greater detail.

Vertical Characteristic of Water Mass in The Flores Sea: The Effect of The ITF on The Transitional Season

Abstract Indonesian Through Flow (ITF) forms unique water mass characteristics in Indonesian Marine Waters. This water mass enters through the Makassar Strait into the Banda Sea by crossing the Flores Sea. This study aims to analyse the characteristics of water masses in the Flores Sea during the transition season. In situ data was obtained using conductivity temperature depth (CTD) at four stations in the Flores Sea from April to May 2023. Next, the data was processed and analysed for layer thickness through vertical stratification and water mass characteristics using T-S diagrams. The analysis results show that the thickness of the homogeneous layer in the Flores Sea in the first transition season is between a depth of 0-40 m, the thermocline layer is at a depth of 40-300 m, and the depth layer is from a depth of 400-900 m. Apart from that, the characteristics of the water mass identified through the T-S diagram are: North Pacific Subtropical Water (NPSW) is found at a depth of 100-150 m with a temperature between 20-26° C and a salinity between 34.9-35.4 psu. Another water mass is South Pacific Intermediate Water (SPIW) at a depth of 500-800 m with a temperature of 6-8° C and a salinity of 34.55-34.65 psu. In contrast, the Antarctic Intermediate Water (AAIW) was found at a depth of >750 m with a temperature of 5-6° C and a salinity of 34.5-34.6 psu.

Ocean Circulation and Variability in the Seram and Northern Banda Seas

Abstract The Seram and Banda Seas (SBS) convey the eastern pathway of Indonesian Throughflow (ITF) from Maluku and Halmahera inflow portals. This study aims to investigate circulation and variability at near-surface and thermocline layers in the SBS region using validated INDESO model output datasets (2008-2015). It is shown that much warmer and saltier thermocline ITF water (24,36°C and 34,65 psu) from Halmahera is predominant, flowing southward and impinging on the northern coast of Seram near 128.5°E. The flows then bifurcate eastward into the Banda outer ring arc and westward into Banda via the Manipa Strait and western Seram Seas. In Banda, two clockwise eddies are found related to these inflows. Secondary southward inflow via Lifamatola is associated with cooler and less salty water (23,3°C and 34,45 psu), which merges with ITF Halmahera. The variability of oceanographic parameters is dominated by the annual period. However, on an interannual scale, the response of seawater temperature to ENSO is evident, and its amplitude, as shown by the principal component time series EOF, is much stronger in Banda than in Seram at -2.7. A decreasing trend of seawater temperature was also found in 2015.

Pockmarks and associated fresh submarine groundwater discharge in the seafloor of Puck Bay, southern Baltic Sea

This is the first well-documented report on the occurrence of pockmarks in Puck Bay. Pockmarks in the seafloor of Puck Bay were discovered during a hydroacoustic survey carried out in 2020. They are located at a depth of 25–27 m in the southwestern part of the bay. Significant depletion of chloride (Cl−) concentrations in sediment pore water was found within the depressions. Most likely, the formation of pockmarks was due to groundwater flow through the Miocene–Pleistocene system of aquifers, which extends from land to the bay area. One-dimensional modeling of vertical Cl− concentration profiles in pore water revealed the upward flow of freshened groundwater within the pockmarks. The magnitude of submarine groundwater discharge (SGD) was estimated to vary from 1.53·10−2 to 18·10−2 L·m−2·h−1. The effect of groundwater seepage was also observed at 3 cm above the seafloor within the pockmarks, which was identified as a decrease in salinity of approximately 0.12 PSU compared to reference sites.Furthermore, due to the effect of water advection, SGD can be detected even several meters above the seafloor as a decrease in salinity values within the thermocline layer.

Multidecadal Phase Changes in the Thermodynamic State of the System: Ocean–Atmosphere–Continent

The present-day climate (the recent 100–150 years) obviously constitutes the structure of a global intra-system rhythmic process with an individual rhythm of about 60 years. In turn, each of the rhythms is presented by the two climate phases of about 25–35 years characterized by qualitative differences: one phase is relatively continental, while the other is humid. Globality and quasi-synchronism of environmental changes are accompanied by planetary structures: the Global Atmospheric Oscillation (GAO) in the atmosphere and the Multidecadal Oscillation of the Heat content in the Ocean (MOHO) discovered relatively recently. Unexpected and rapid qualitative phase changes in the climate, which first focused attention in the mid-1970s of the last century, were titled “climate shifts”. The revealed features of the present-day climate are of exceptional scientific and practical interest and deserve the development of methods for predicting the timing of the forthcoming climate shift. Arising unexpectedly and accompanied by rapid significant changes, these shifts identified the problem of understanding the nature and establishing the processes and mechanisms causing them. First of all, of interest are phase changes in the thermodynamic state of the climate system components: the ocean, atmosphere, and continents. As a result of the World Ocean (WO) thermohydrodynamics numerical modelling, it is shown that MOHO is localized in the layer of the main thermocline, where the most important elements of the WO circulation are located. The performed study based on observational data allows us to conclude that, during the phase of the WO thermal discharge (1975–1999), the two key systems of currents, the Kuroshio and the Gulf Stream, were under similar thermodynamic conditions.

Phytoplankton Communities’ Response to Thermal Stratification and Changing Environmental Conditions in a Deep-Water Reservoir: Stochastic and Deterministic Processes

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.

Spatial-temporal characteristics of temperature in Indonesian Sea based on a high-resolution reanalysis data

Influenced by both the Pacific and Indian Oceans, the temperature field in the Indonesian Sea are complicated. In order to reveal the spatial-temporal variability, the surface, thermocline and intermediate layers of the temperature field are studied based on the global ocean reanalysis data of Copernicus Marine Environment Monitoring Service (CMEMS) from 1993 to 2019 and the Empirical Orthogonal Function (EOF) analysis method. The results show that there is a warming trend of 1.36×10−2 °C /year in the surface layer. The first two modes both show reverse changes close to the Pacific and Indian Oceans. The correlation coefficients between the first and second modal time coefficients and the Niño 3.4 index are 0.62 and 0.48, respectively. And the correlation coefficient between the second modal time coefficient and the ITF inflow is -0.45. In the thermocline, there is a warmer trend, which is 4.78×10−2 °C /year. The correlation index of the first and second modal time coefficient with the Niño 3.4 and DMI indices are 0.87 and 0.43, respectively. The correlation index between the first and second modal time coefficient and the ITF inflow are -0.60 and 0.38, respectively. In the intermediate layer, the warming trend is 2.18×10−2 °C /year. From 1993 to 1999, from 2000 to 2016 and from 2017 to 2019, the Sulu Sea and northern Halmahera Sea experienced three periods of warming, cooling and warming, respectively. The study is helpful for further understanding the variation of the temperature field in the Indonesian Sea.

Organic Matter Enrichment Mechanisms in the Lower Cambrian Shale: A Case Study from Xiangandi #1 Well

In order to investigate the effect of primary productivity, organic matter dilution, and preservation on the accumulation of organic matter, geochemical data, and proxies of primary productivity, clastic influx, and redox conditions were obtained for organic-rich shales in the Cambrian Niutitang Formation. The primary productivity (total organic carbon [TOC], Mo, P, Ba, and Babio) and redox (Ni/Co, V/Cr, U/Al, and Th/U) proxies suggest the organic-rich shales were deposited in anoxic-euxinic conditions during periods of high primary productivity. Pyrite in the Niutitang Formation comprises spherical framboids, which also indicate that anoxic bottom waters were present during organic matter deposition. High primary productivity enhanced the organic C flux into the thermocline layer and bottom waters, which lead to the development of anoxic bottom waters owing to O2 consumption by microorganisms and organic matter degradation. The anoxic bottom waters were beneficial for the preservation of organic matter. In addition, Ti/Al ratios correlate well with TOC contents throughout the Niutitang Formation, indicating that clastic input increased the burial rate and prevented organic matter degradation during deposition. Therefore, the accumulation of organic matter in the Niutitang Formation was controlled mainly by primary productivity rather than bottom-water redox conditions.

Flow measurement in the southern coast of the Caspian Sea

Oceanographic monitoring was conducted in the southern basin of the Caspian Sea to evaluate the physical structure of seawater and sea currents. This monitoring aimed to gather data and analyze the characteristics of the seawater, including temperature, salinity, density, and other relevant parameters. Additionally, the monitoring also focused on studying the patterns and dynamics of sea currents in the region. The collected data and analysis from this monitoring period provided valuable insights into the oceanographic conditions of the southern basin of the Caspian Sea. During storm events, a high level of correlation between the current and wind data was observed in the southern basin of the Caspian Sea during the 2017-2018 monitoring period. The measured current data indicated that the predominant directions were north (N) and northwest (NW). It was observed that strong gusts predominantly originated from the north (N) and northwest (NW) directions. Additionally, a smaller portion of the strong gusts was observed to come from the South-Southeast (S-SE) direction. These findings indicate that the prevailing wind patterns during the monitoring period were primarily from the north and northwest, with a lesser contribution from the South-Southeast direction. The current profiles observed during the monitoring period in the southern basin of the Caspian Sea were primarily influenced by the general circulation pattern of the region. This circulation pattern played a significant role in shaping the current profiles observed during the measurements. In terms of the surface current speed, the maximum recorded value was approximately 200 cm/s, which occurred in January. This indicates that there were instances of relatively high-speed currents in the southern basin of the Caspian Sea during that time. The evaluation of inter-annual variability in vertical structure and seawater temperature profiles during the monitoring period confirmed the presence of seasonal stratification in the water column of the southern basin of the Caspian Sea. This stratification was observed to consist of different layers, including the surface mixed layer, thermocline, and deep-water layers. The formation of these layers is indicative of the seasonal variations in temperature and density within the water column. The vertical changes in the water’s physical parameters during the monitoring period revealed the formation of stratification in the southern basin of the Caspian Sea. In March, it was observed that the water temperature decreased from 11.5°C at the surface to 8.5°C at a depth of 100 m, indicating the presence of a temperature gradient. As the monitoring progressed into May, the stratification became stronger, with the surface water temperature reaching around 23°C. By August, the surface layer of the sea water experienced a significant increase in temperature, reaching 29°C. These observations highlight the development of stratification and the seasonal variations in water temperature during the monitoring period in spring and summer seasons. The water temperature beneath the thermocline layer, specifically at a depth of 100 meters, was recorded to be around 8-8.5 oC. Additionally, the water salinity in the water column exhibited fluctuations between 12-12.5 (psu). Monitoring and understanding physical properties variations are crucial for assessing the oceanographic conditions and their potential impact on marine ecosystems in the southern basin of the Caspian Sea.

Simulated ocean circulation and its variability in the Northern Banda Sea from CROCO model

A simulation of 1/24º resolution 3-dimension regional ocean circulation of CROCO was successfully performed from 2015 to 2022 (8 years), covering the ENSO year in El Niño 2015 and La Niña 2022 in the northern Banda Sea (NBS). The model and data comparison of sea surface temperature/height reproduced the observed satellite datasets well, with correlation coefficients above 0.9. It is shown that the mean circulation in the NBS is fed by two inflows from western Buru and the Manipa Strait, resulting in a meandering eastward mean circulation with warmer water accumulated in the eastern NBS, associated with high current variance south of Buru and along the Manipa Strait. Seasonal variations in the oceanographic parameters were dominant in the study area. For example, during the southeast (northwest) monsoon period, the seawater temperature is minimum (maximum) and the salinity is maximum (minimum). Furthermore, the interannual timescale ENSO and IOD significantly modulated seawater temperature and salinity variation, particularly at the thermocline layer (110 m). Much cooler and saltier water is associated with El Niño 2015 and a positive IOD, in contrast to warmer and fresher water during La Niña 2022 and a negative IOD.

Stratification of Indonesian Throughflow Water and Its Circulation along 125E in the Banggai - Maluku Sea

secondary pathway of Indonesian Throughflow (ITF) that enters from its inflow portal of the northern Maluku Sea is assumed to recirculate in the Banggai - Maluku Sea, where its upper-layer circulation returns into the Pacific and deeper flows continue southward into Seram/Banda Sea via Lifamatola Strait. However, direct observation in this key region is still limited. Here, using direct CTD (Conductivity Temperature Depth) casts and shipboard ADCP (Acoustic Doppler Curent Profiler) measurement datasets from BUDEE (Banggai Upwelling Dynamics and Ecosystem Experiment) cruise in September 2023, we study stratification and structure of ITF water and its circulation in a meridional section along 125E. The results show the water mass stratification of the mixed layer having a depth of 0-75m with a temperature range of 26-29°C, while the thermocline layer has a depth of 28-407m with a temperature range of 23-26°C, and the deep layer has a depth of 407-1000m with a temperature value of 4-12°C. The current pattern of the Banggai Sea Maluku Sea at a depth of 52-400m is more dominantly influenced by non-tidal currents, the influence of tidal currents only covers a depth of 52m less than non-tidal currents.

Observed Anomaly of Temperature and Mixed Layer Depth Associated with the Madden Julian Oscillation (MJO) Active Phase in the Banda Sea, Indonesia

The eastward propagation of atmospheric waves along the equatorial band from the central equatorial Indian Ocean to the western Pacific Ocean passing through the Indonesian Maritime Continent (IMC), known as the intraseasonal Madden Julian Oscillation (MJO) event, plays an important role on modulating both atmospheric and upper ocean dynamics along its path. This study aims to investigate the MJO active phase dynamics and its impact on changes in near-surface seawater temperature and mixed layer depth (MLD) anomaly in the Banda Sea Indonesia, using multi-datasets of atmospheric reanalysis, satellites derived sea surface temperature (SST), and Argo float between 2017 - 2018. This study revealed that the MJO waves propagate eastward along the southern equator-line over the IMC and pass through the Banda Sea, associated with significant decreased on Outgoing Longwave Radiation (OLR) and increased in zonal wind speed at 850hPa. The study result shows anomalous increased on surface wind speed and SST cooling during of MJO active phase. The amplitude peaks of filtered ocean-atmosphere variables range between 30 – 60 days. Argo float datasets in the Banda Sea for the first time captured upper ocean responses to the arrival of the MJO active phase, as characterized by a negative temperature anomaly of ~0.3°C in the surface mixed layer, large temperature anomaly of ~0.8°C in the thermocline layer and the deepening of the MLD of ~25 m. Hence, the MJO active phase impacts significantly on surface and vertical temperature cooling and regulate upper ocean mixing intensity in the Banda Sea.

Vertical Exchange Induced by Mixed Layer Instabilities

Abstract 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.

Seasonal Evolution of Stable Thermal Stratification in Central Area of Lake Ladoga

The complete climatic courses of the parameters of stable thermal stratification for the central part of Lake Ladoga, the largest European lake, are presented on the basis of empirical relationships, taking into account the physical processes governing water temperature variations. For the first time, the seasonal cycle of the surface water temperature, the temperature and the depth of the thermocline, and the hypolimnion temperature are calculated using the vertical profiles of the temperature obtained from the central area of Lake Ladoga. Temperature data are used for the period of in situ observations from 1897 to the present. The proposed functional forms of the temporal temperature cycle and the course of thermocline’s boundaries deepening are useful for examination and simulation of the heat vertical transport from air to water. Approximation curves for the parameters of heating and cooling periods were developed with high significant determination coefficients. Time dependencies of the climatic rates of change in water temperature and the depth of the thermocline boundaries were determined from the onset of stable stratification to its dissipation. The highest rate of water temperature change in the heating stage takes place in late June–early July, which at the water surface, is 0.32 °C/day, while in the thermocline layer, it is 0.18 °C/day. The peak velocity during the cooling stage at the surface occurs in late August–early September and is 0.14 °C/day, whereas in the thermocline, it is 0.08 °C/day and takes place between September and early October. During the period of heating, the deepening parameters of the thermocline layer do not fluctuate very much, only within the range of 0.1–0.3 m/day. During the cooling period, under the influence of free convection, rates increase drastically. The maximum rates of deepening during the period of full autumn mixing reach 1.8 m/day. When the autumn overturn occurs, the epilimnion thickness equals the bottom depth, and the bottom temperature reaches its maximum during the annual cycle. Climatic norms of the stratification parameters against which it is necessary to assess climate change are calculated.

Environmental impacts of shallow water mining in the Baltic Sea

The discovery of rare metal resources in international waters has raised seabed mining claims for large areas of the bottom. There is abundant scientific evidence of major negative consequences for the maritime environment, such as the destruction of natural landforms and the fauna that depend on them, as well as the production of enormous silt plumes that disrupt aquatic life. This study investigated the environmental risks of seabed mining for metal resources in the Baltic Sea using a combination of hydrodynamic, particle-tracking, and sediment-transport models. The models were applied for ten years i.e., 2000-2009 under prevailing conditions to simulate seabed mining operations. The focus was on sediment concentration near the seabed and its spread. The mean background concentrations were low with small seasonal bed-level variations throughout the Baltic Sea Basin. Late summer and early autumn periods were the most active. Seabed mining significantly alters the dynamics of sediment suspensions and bed level variations. The concentrations increase unsustainably to high levels, posing a serious threat to the ecological health of the Baltic Sea. The Gotland basins in the Baltic Sea are the most susceptible to mining. The bed level variations will be ten-fold, exposing the highly contaminated sediments at the seabed to the flow. In less than a year, 30-60% of the total particles released in each basin reached the thermocline layers. This study suggests that seabed mining in the Baltic Sea is not sustainable.

Experimental analyses of solidification phenomena in an ice-based thermal energy storage system

Latent thermal energy storage devices can efficiently store surplus thermal energy during off-peak hours. The system's phase change material (PCM) improves energy storage capacity and isothermal properties. Most PCMs have weak thermal conductivity, which hampers heat transfer. Thus, the present analysis involves an insight into the heat transfer characteristics and thermal performance of a vertical tube-in-tank cold storage system. The objective of this investigation is to gain a better understanding of the significance of buoyancy-driven convection within the side bulk region during the discharging of water as PCM in the heat exchanger. A series of experiments are conducted to investigate the effect of varying the initial bulk temperature on the rate of PCM solidification. The effects of three distinct initial bulk temperatures which are 20 °C, 15 °C, and 5 °C on the solidified mass fraction, thermal performance, and heat transfer rate at various radial and axial locations in PCM are examined. It is seen that PCM experienced a varying cooling rate with varying axial height and is found to be the highest in the bottom region. PCM temperature decreases from top to bottom under the cases of 20 °C and 15 °C, respectively. In contrast, a narrow-ranged thermocline layer is observed under 5 °C bulk temperature, making uniform temperature distribution within the bulk. The influence of bulk natural convection prevails in the later stages of the discharging process under 5 °C bulk, whereas it predominantly exists during the initial stages of solidification under bulk temperatures of 20 °C and 15 °C.