Potential Energy Anomaly Research Articles

Shifts from surface density compensation to projected warming, freshening and stronger stratification in the subpolar North Atlantic

The hydrography and stratification of the subpolar North Atlantic is highly variable, with convection activating and deactivating across parts of the Labrador and Irminger seas. Likely consequential for the Atlantic Meridional Overturning Circulation (AMOC), this variability is examined in an eddy-rich ocean model hindcast spanning 1958–2021 and in 1950–2050 simulations with four climate models, spanning differences in ocean resolution (eddy-rich or eddy-permitting), code and implementation. Stratification of the Labrador and Irminger seas is quantified with the Potential Energy Anomaly (PEA) in the upper 1000 m of the water column. Monthly PEA anomalies are evaluated alongside corresponding anomalies of sea surface temperature, salinity, and density. For 30-year windows, moving correlations between PEA and surface properties are obtained over the 100-year simulations to characterize the evolving relationships. As climate change progresses, stratification in three of the four models is increasingly associated with variable surface salinity, in both regions. Lagrangian analyses of surface flow pathways in the decades preceding 1990 and 2040 are undertaken for one of the models in which surface salinity grows in influence. The subpolar presence of low-salinity Arctic waters and high-salinity subtropical Atlantic waters are found to increase and decrease respectively by 2040. Furthermore, in three of the four models, surface density compensation associated with correlation of surface temperature and salinity anomalies is progressively replaced by combined surface warming and freshening, lowering surface density, and strengthening stratification. The extent of these model-dependent changes and processes are of consequence for the projected fate of the AMOC by the mid twenty-first century.

Prediction of long-term changes of weak diurnal stratification in shallow lakes using artificial neural networks

ABSTRACT Thermal stratification plays a key role in lakes' ecosystems. In contrast to deep lakes, the thermal structure of shallow polymictic lakes is characterized by a weak stratification with an apparent diurnal cycle. Long-term changes in stratification are governed by climate change and anthropogenic effects such as water level regulation. We developed a simple and robust model system consisting of an energy balance model to estimate depth-averaged water temperatures and an artificial neural network (ANN) model to predict stratification with high temporal resolution. One novelty of our approach is that instead of directly estimating water temperatures at different depths, we simulated the potential energy anomaly index, the indicator of stratification's strength. The ANN-based model's performance was assessed against a physical-based one-dimensional model (General Ocean Turbulence Model) by modeling a 40-year-long period from 1981 to 2020. The new model accurately predicts a shallow lake's weak stratification and its diurnal cycle. Besides, the model proved reliable on longer time scales, capturing the effect of climate change, anthropogenic water level regulation, and their synergistic interaction on the change of stratification's intensity and duration.

Influence of Fluvial Discharges and Tides on the Salt Wedge Position of a Microtidal Estuary: Magdalena River

The linkage between the salt wedge, tidal patterns, and the Magdalena River discharge is established by assessing the ensuing parameters: stratification (ϵ), buoyancy frequency (β), potential energy anomaly (φ), Richardson number by layers (RL), and bottom turbulent energy production (P). The salinity, temperature, density, and water velocity data utilized were derived from MOHID 3D, a previously tailored and validated model for the Magdalena River estuary. To grasp the dynamics of the river, a flow regime analysis was conducted during both the wet and dry climatic seasons of the Colombian Caribbean. The utilization of this model aimed to delineate the estuary’s spatial reach, considering flow rates spanning from 2000 to 6500 m3/s across two tidal cycles. This approach facilitates the prediction of the position, stability, and stratification degree of the salt front. Among the conclusions drawn, it is highlighted that: 1. The river flow serves as the principal conditioning agent for the system, inducing a strong estuary response to weather stations; 2. The extent of wedge intrusion and the river discharge exhibit a non-linear, inversely correlation; 3. Tidal waves cause differences of up to 1000 m in the horizontal extent of the wedge; 4. Widespread channel erosion occurs during the rainy season when the salt intrusion does not exceed 2 km; 5. Flocculation processes intensify during the transition between the dry and wet seasons; 6. The stability of the salt layering and the consolidation of the FSI–TMZ are contingent upon the geometric attributes of the channel.

Transitions between different estuarine states in a low-inflow estuary of arid coasts (Mond Estuary, Persian Gulf) with a focus on freshwater lenses

This study shows that the Mond Estuary, Persian Gulf experiences notable time-dependent longitudinal salinity variations. Monthly-seasonal variability in salinity changes from a positive estuarine system in wintertime to inverse and salt-plug estuaries during summertime. A highly unsteady state (time scale of hours-days) occurs in the wintertime named the freshwater lens estuary (FLE), in which a low-salinity water mass (lens) is confined by both marine and riverine saltwater sources. Here, FLE dynamics is investigated using realistic and idealized numerical models and two 25-hour data sets collected immediately before a hypersaline runoff (weak FLE condition) and during another one (strong FLE condition). The Péclet Number (Pe) reveals a much stronger advective transports than diffusive one (Pe>5.7) throughout the estuary. An exception from this behavior (stronger mixing with Pe=0.8) is observed at the estuary downstream, where a significant amount of freshwater mixes with seawater during the weak FLE conditions. Also, the minimum hypersaline runoff of ∼400 m3/s estimated by the numerical model can dampen tidal waves at the head of the estuary. In an idealized basin, the model shows that FLE longitudinal flows form two cells of positive estuarine circulation separated by a maximum mixing zone (the potential energy anomaly <0.75 J/m3). In the Mond Estuary, a sea-level rise of 20 cm increases salinity in the FLE state and the positive estuary during winter. Conversely, it decreases salinity in the inverse and salt-plug estuaries in summer.

Fast Enhancement of the Stratification in the Indian Ocean over the Past 20 Years

Abstract Indian Ocean (IO) stratification has important effects on the air–sea interaction, ocean dynamics, and ecology. It is, therefore, of significance to investigate the changes in IO stratification. In this study, we use ensemble empirical mode decomposition (EEMD) to extract the nonlinear long-term trend in the upper IO stratification quantified by potential energy anomalies. The results show that the strengthening of the stratification is spatially and temporally nonuniform. Specifically, the trend of stratification intensified gradually before 1996, but accelerated rapidly after 1996. Temperature and salinity changes play a crucial role in the fast enhancement of stratification and its regional differences. Temperature variations dominate the stratification trend in ∼90% of the IO area, while the contributions of salinity changes are mainly in the southeast Indian Ocean (SEIO). Vertically, the rapid enhancement of stratification is caused by the trend of temperature and salt in the upper 400 m. We further perform temperature budget analysis and find that the warming trend in the upper 400 m south of the IO is mainly modulated by vertical advection and meridional advection, while the warming in the north of the IO is mainly induced by air–sea heat fluxes. Salinity budget analysis shows that ocean advection has played a primary role in modulating SEIO salinity over the past 20 years.

Effect of Benthic Flux on the Nutrient Dynamics of Bottom Water during Stratification in an Artificial Brackish Lake

In semi-closed coastal brackish systems, the stratification of the water column due to the interaction between freshwater and seawater can lead to a reduction in the dissolved oxygen (DO) levels in the bottom layers, consequently affecting the benthic nutrient flux and causing the degradation in water quality. We performed in situ investigations using a benthic lander to examine changes in the sediment oxygen demand (SOD) and benthic nutrient flux during the development of stratification in the downstream area of an artificially constructed brackish lake. During each measurement period, the temperature and salinity of the water column showed vertically stable stratification. The potential energy anomaly was 88.1–125.7 J/m3, with the stratification intensity strengthening gradually over the measurement period. The concentration of DO in bottom waters gradually decreased as the stratification of the water intensified and the temperature increased, establishing hypoxic conditions. As the stratification intensified, the SOD decreased with the DO concentration in bottom waters, while the benthic fluxes of NH4-N and PO4-P exhibited an opposite effect. When the effect of offshore water (introduced through a sluice gate) was insignificant, the SOD contributed 33% of the net loss of DO below the pycnocline. During this period, the benthic NH4-N and PO4-P fluxes were estimated to contribute 55% and 87% to the net fluxes in NH4-N and PO4-P, respectively, in the water column below the pycnocline. The benthic NH4-N and PO4-P fluxes resulted in excess phosphorus in the bottom water. When the inflow of seawater through the sluice gate was sufficient, the flow in the upstream direction of the bottom layer moved phosphorus-rich bottom water downstream, which is important for algal growth in the middle-upstream region.

Intermittent migration of mixing front driven by typhoon events on the inner shelf of the East China Sea: A FVCOM modeling study

Mixing fronts on the inner shelf of the East China Sea (ECS) are common under normal summer conditions, yet its migration during extreme weather events, such as typhoons, has been poorly understood due to limited availability of observational data. In this study, we used a well-validated Finite-Volume Community Ocean Model (FVCOM) to investigate the intermittent migration of mixing fronts on the inner shelf of the ECS during the passage of Typhoon Chan-hom in July 2015. The sedimentary and ecological effects of the front migration were also revealed. Results suggested that the potential energy anomaly (PEA) of 10 J/m3 could be a critical value to determine the location of the mixing front, which was consistent with that derived from the Simpson-Hunter (SH) parameter. Accordingly, the mixing front showed a rapid seaward migration from 15-m isobaths to 60-m isobaths under the drastic ocean turbulence during the typhoon and recovered shortly after its passage. This intermittent migration of the mixing front had the potential to facilitate cross-shelf material transport during the typhoon. On the one hand, the front migration could not only open the access for the seaward transport of nearshore resuspended sediments but also trap them within a certain area, causing an offshore deposition between 20 and 60 m isobaths south of the typhoon track. The mixing fronts had a boundary effect constraining the typhoon-induced sedimentation. On the other hand, unlike sediments that would settle down with weakened ocean dynamics, the offshore movement of coastal diluted water triggered by the typhoon remained after the front recovery. These nutrient-rich waters could be transported to the middle or even outer shelf of the ECS by the subsequent southwest summer monsoon, enhancing local primary production and potentially trigering significant algal blooms.

A Dynamic Estuarine Classification of the Vertical Structure Based on the Water Column Density Slope and the Potential Energy Anomaly

The aim of this work is to develop a new estuarine classification attending to their vertical structure by examining the advantages and disadvantages of the existing classifications. For this purpose, we reviewed the main classifications, finding that most of them analyze the entire estuary as a unique water body without considering the spatiotemporal variability of the mixing zone in estuaries. Furthermore, the proposed classifications require the calculation of parameters that are not easily measurable, such as tidal current amplitude. Thus, we developed a new classification based on density profile slopes of the water column, which has been correlated to the potential energy anomaly. To test this classification, the proposed method was applied to the Suances estuary (Spain) during the year 2020 and to analyze the potential estuarine modifications under four climate change projections (RCP 4.5 and 8.5 for the years 2050 and 2100). To carry out this study, a calibrated and validated high-resolution horizontal and vertical 3D model was used. The application showed a high variability in the vertical structure of the estuary due to the tide and river. According to the proposed classification, the well mixed category was predominant in the estuary in 2020 and tended to grow in the projections of climate change. As a result, the fully mixed and weakly stratified mixing classes were reduced in the projected scenarios due to a decrease of external forcing, such as river flow and sea level rise. Furthermore, areas classified as stratified tended to move upstream of the estuary.

A numerical study of the mixing and stratification alterations in estuaries due to climate change using the potential energy anomaly

The competition between mixing and stratification in estuaries determines the quality of their waters, living conditions, and uses. These processes occur due to the interaction between tidal and fluvial contributions, which significantly vary depending on the estuarine characteristics. For the study of mixing and stratification alterations in estuaries due to climate change, a new methodology is proposed based on high-resolution 3D hydrodynamic modeling to compute the Potential Energy Anomaly (PEA). Regarding the model scenarios, first, a base case is analyzed with the realistic forcings of the year 2020. Subsequently, the forecasts of anomalies due to climate change for sea conditions (level, temperature, and salinity), atmosphere conditions (precipitation, air temperature, relative humidity, and solar irradiance), and river conditions (flow and temperature) are projected for the year 2020. The selected scenarios to analyze hydrodynamic changes are RCP 4.5 and 8.5 for the years 2050 and 2100. The proposed methodology has been applied to the Suances estuary. Independently of the climate change scenario, the stratification intensity increases and decreases upstream and downstream of the estuary, respectively. These results indicate that unlike the 2020 base scenario, in which the stratification zone has been mainly centered between km 4 and 8, for the new climate change scenarios, the stratification zone will be displaced between km 2 and 8, attenuating its intensity from km 4 onwards. The Suances estuary presents and will present under the considered scenarios a high spatiotemporal variability of the mixing and stratification processes. On the one hand, sea level rise will pull the stratification zones back inland from the estuary. On the other hand, climate change will generate lower precipitations and higher temperatures, decreasing runoff events. This phenomenon will decrease the freshwater input to the estuary and increase the tidal excursion along the estuary, producing a displacement of the river/estuarine front upstream of the areas.

The Impact of Tidal Straining and Advection on the Stratification in a Partially Mixed Estuary

Stratification and mixing of the water column is an important dynamic process in the estuary, which plays a significant role in the estuarine circulation, mass transport and energy exchange. Based on the multi-station synchronous observation data from 26 February to 6 March in 2011 during dry season in the North Channel of the Changjiang Estuary, the Richardson number, the Simpson number and the potential energy anomaly of water were calculated to analyze the tidal variation of the mixing and stratification processes. The roles of the depth-mean straining, longitudinal advection, non-mean straining and tidal stirring in the processes of mixing and stratification of the water column were analyzed by calculating the contribution terms of the time-derivative of potential energy anomaly. The results show that the mixing and stratification of the water column in the North Channel have significant spatiotemporal variation. Stability of the stratification gradually decreases from neap tide to spring tide. In the reaches of salt wedge migration, permanent stratification develops during neap and mean tide, with stability increasing on the flood and decreasing on the ebb, which is dominated by longitudinal advection. During spring tide, periodic stratification develops, with development of stratification on the flood and its breakdown on the ebb, which is dominated by longitudinal advection and tidal stirring. In the main reaches of saltwater intrusion, permanent stratification develops during neap tide, with stability increasing on the ebb and decreasing on the flood, which is dominated by depth-mean tidal straining. During mean and spring tide, periodic stratification occurs, with development of stratification on the ebb and its breakdown on the flood, which is controlled by depth-mean tidal straining and assisted by tidal stirring. In the North Channel, tidal advection is the main stratifying agent in the salt wedge migration reaches, and tidal straining is the main stratifying agent in the main reaches of saltwater intrusion.

Seabird abundances projected to decline in response to climate change in Britain and Ireland

Estimating species’ vulnerability to climate change is a key challenge in conservation. Many seabird species are particularly sensitive to the negative effects of warming and are thus threatened by climate change. We projected seabird abundance in 2050 in Britain and Ireland, an internationally important region for seabirds, under climate change scenario RCP8.5. Our projections were based on fitted relationships between abundance and both climatic (air temperature, precipitation) and oceanographic (sea surface temperature, potential energy anomaly) variables, estimated using a Bayesian hurdle model with spatial random effects. The most consistent responses to environmental variables were negative relationships between species presence or abundance and breeding season maximum terrestrial air temperature. Although data and modelling issues meant that future projections could be made for only 15 of the 25 species and with low predictive power for spatial abundance, predictive power was high for spatial presence and moderate for temporal abundance change. Projections suggest that seabirds will generally fare poorly under climate change in Britain and Ireland, with 10 species projected to decline in abundance by 2050. Variable model fit and projection uncertainty limited confidence, which was generally greater for declines than for increases. Fulmar, puffin and Arctic tern were each projected to decline by over 70% with higher confidence. For a few species, colonisation of new areas may reduce projected losses, but this is potentially limited by low availability of suitable habitat. Projected abundance change was more negative for marine specialists than for generalists. Our findings highlight the vulnerability and conservation needs of seabirds in a changing climate.

Influence of sluice gate operation on salinity stratification and hypoxia development in a brackish estuary dam

The water quality in the artificially made Saemangeum Lake, located in an estuary, is poor; here, we explored the causes of hypoxia development. The field survey for spatial and vertical distribution of salinity and dissolved oxygen (DO) was conducted three times at 6 sites in the Mankyung Basin during the period when the salinity stratification was developed, and continuous observations for temporal and vertical distribution of water temperature, salinity, DO, and flow direction and velocity were performed at a site in the downstream of the lake for about 40 days. Hypoxia was detected at the bottom layer of the survey sites, which were directly affected by seawater inflow. At these sites, the salinity stratification, one of the causes of hypoxia, was clearly observed. The Richardson number and potential energy anomaly (PEA) calculated from the continuous observation measurement results indicated that the water column was very stable and strongly stratified during the investigation period. The vertical salinity structure due to the stabilization of the water column and the bottom temperature above 20 °C caused hypoxia of the bottom layer when insufficient seawater inflow or non-operation of sluice gate. Due to the horizontal salinity gradient by the seawater flowing in through the sluice gate operation, a baroclinic force acts from the sluice gate to the upstream direction at the bottom layer. In contrast, a barotropic force acts from the upstream inlet toward the sluice gate at the surface layer. The directional flow of each water layer changes in opposite directions to form a repeated reversing current which prevents the supply of DO through the inflow of fresh seawater. Therefore, to improve the water quality of Saemangeum Lake, it is necessary to control the short/ long-term reversing current that obstructs DO supplementation from seawater flowing through the sluice gate.

Observation of Abrupt Changes in the Sea Surface Layer of the Adriatic Sea

We observed interannual changes in the temperature and salinity of the surface layer of the Adriatic Sea when measured during the period 2005–2020. We observed non-stationarity and a positive linear trend in the series of mixed layer depth, heat storage, and potential energy anomalies. This non-stationarity was related to the climate regime that prevailed between 2011 and 2017. We observed significant changes in the interannual variability of salinity above and below the mixed layer depth and a positive difference in the surface barrier layer. In an effort to reconstruct the cause of this phenomenon, a multi-stage investigation was conducted. The first suspected culprit was the change in wind regime over the Mediterranean and Northeast Atlantic regions in September. Using the growing neural gas algorithm, September wind fields over the past 40 years were classified into nine distinct patterns. Further analysis of the CTD data indicated an increase in heat storage, a physical property of the Adriatic Sea known to be strongly influenced by the inflow of warm water masses controlled by the bimodal oscillating system (BiOS). The observed increase in salinity confirmed the assumption that BiOS activity affects heat storage. Unexpectedly, this analysis showed that an inverse vertical salinity profile was present during the summer months of 2015, 2017, and 2020, which can only be explained by salinity changes being a dominant factor. In addition, the aforementioned wind regime caused an increase in energy loss through latent energy dissipation, contributing to an even larger increase in salinity. While changes in the depth of the mixed layer in the Adriatic are usually due to temperature changes, this phenomenon was primarily caused by abrupt changes in salinity due to a combination of BiOS and local factors. This is the first record of such an event.

The role of heat wave events in the occurrence and persistence of thermal stratification in the southern North Sea

Abstract. Temperature extremes not only directly affect the marine environment and ecosystems but also indirectly influence hydrodynamics and marine life. In this study, the role of heat wave events in the occurrence and persistence of thermal stratification was analysed by simulating the water temperature of the North Sea from 2011 to 2018 using a fully coupled hydrodynamic and wave model within the framework of the Geesthacht Coupled cOAstal model SysTem (GCOAST). The model results were assessed against reprocessed satellite data and in situ observations from field campaigns and fixed Marine Environmental Monitoring Network (MARNET) stations. To quantify the degree of stratification, the potential energy anomaly throughout the water column was calculated. The air temperatures and potential energy anomalies in the North Sea (excluding the Norwegian Trench and the area south of 54∘ N) were linearly correlated. Different from the northern North Sea, where the water column is stratified in the warm season each year, the southern North Sea is seasonally stratified in years when a heat wave occurs. The influences of heat waves on the occurrence of summer stratification in the southern North Sea are mainly in the form of two aspects, i.e. a rapid rise in sea surface temperature at the early stage of the heat wave period and a higher water temperature during summer than the multiyear mean. Another factor that enhances the thermal stratification in summer is the memory of the water column to cold spells earlier in the year. Differences between the seasonally stratified northern North Sea and the heat wave-induced stratified southern North Sea were ultimately attributed to changes in water depth.

Generation of Data-Driven Expected Energy Models for Photovoltaic Systems

Although unique expected energy models can be generated for a given photovoltaic (PV) site, a standardized model is also needed to facilitate performance comparisons across fleets. Current standardized expected energy models for PV work well with sparse data, but they have demonstrated significant over-estimations, which impacts accurate diagnoses of field operations and maintenance issues. This research addresses this issue by using machine learning to develop a data-driven expected energy model that can more accurately generate inferences for energy production of PV systems. Irradiance and system capacity information was used from 172 sites across the United States to train a series of models using Lasso linear regression. The trained models generally perform better than the commonly used expected energy model from international standard (IEC 61724-1), with the two highest performing models ranging in model complexity from a third-order polynomial with 10 parameters (Radj2 = 0.994) to a simpler, second-order polynomial with 4 parameters (Radj2=0.993), the latter of which is subject to further evaluation. Subsequently, the trained models provide a more robust basis for identifying potential energy anomalies for operations and maintenance activities as well as informing planning-related financial assessments. We conclude with directions for future research, such as using splines to improve model continuity and better capture systems with low (≤1000 kW DC) capacity.

Interannual and seasonal variability of stratification and mixing in a high-discharge micro-tidal delta: Magdalena River

The spatio-temporal variability of stratification and mixing at the mouth of the Magdalena River Delta (MMRD) was studied for the warm (El Niño), cold (La Niña), and neutral phases of El Niño–Southern Oscillation (ENSO), using the Richardson number (RL), potential energy anomaly (φ), buoyancy frequency (β), turbulent kinetic energy production (P), and bottom shear stress (τxz). These parameters were obtained from the MOHID numerical model outputs, which were implemented and calibrated for the MMRD. Analysis of the spatio-temporal variability of φ and β indicated stratification at different mouth zones, and the spatio-temporal variability of RL and P indicated a mixing process. Results show that during the dry season, the mixing zone of the MMRD presents its maximum intra-annual variability, and during El Niño conditions, it has its highest interannual variability. Further, the maximum penetration of the salt wedge occurs during El Niño - dry season conditions. On the other hand, during the wet season, the salt wedge is located at the mouth entrance, independent of the ENSO phase. During La Niña conditions, the mixing zone restricts its intra-annual variability to around 0 km of the MMRD.

Characteristics and Driving Mechanisms of Mixing and Stratification in the North Passage of the Changjiang Estuary, China

Wang, Y.; Jiang, C.; Cheng, H.; Li, W., and Teng, L., 2022. Characteristics and driving mechanisms of mixing and stratification in the North Passage of the Changjiang estuary, China. Journal of Coastal Research, 38(1), 140–153. Coconut Creek (Florida), ISSN 0749-0208. Based on the measured hydrological and sediment data of spring and neap tides in the dry and flood seasons of 2016 in the North Passage of the Changjiang Estuary, the gradient Richardson number, Simpson number, and potential energy anomalies were calculated to analyze the tidal cycle, spring-neap variation, and seasonal variation of mixing and stratification. Taking into account the vertical difference of horizontal density gradient, the contribution terms of time derivative of potential energy anomalies was derived, including depth-mean straining, advection, nonmean straining, and tidal stirring. The driving mechanisms of mixing and stratification was investigated by calculating and comparing these four contribution terms. The results show that the seasonal variation of freshwater discharge mainly affected the distance of saltwater intrusion, the saline wedge moved upstream in dry season, while the tidal dynamics had a significant impact on mixing and stratification. In the reaches with saline wedge tip migration, the water column was periodically stratified, and the process was dominated by advection term. In the main reaches of saltwater intrusion, during spring tide the water column was periodically stratified, which was stratified during flood tidal current; it was well mixed during ebb tidal current, and the stratification during flood tidal current was promoted by advection and depth-mean straining. The mixing during ebb tidal current was promoted by tidal stirring and advection; during neap tide, the water column was permanently stratified. The stratification was enhanced during flood tidal current and weakened during ebb tidal current, and the stratification was mainly maintained by depth-mean straining.

Effects of Long-Term Increases in Water Temperature and Stratification on Large Artificial Water-Source Lakes in South Korea

Long-term changes in air and water temperatures and the resulted stratification phenomena were observed for Soyang Lake (SY), Paldang Lake (PD), Chungju Lake (CJ), and Daecheong Lake (DC) in South Korea. Non-parametric seasonal Kendall and Mann-Kendall tests, Sen slope estimator, and potential energy anomaly (PEA) were applied. The lake surface water temperatures (LSWTs) of SY and DC increased at the same rate (0.125 °C/y), followed by those of CJ (0.071 °C/y) and PD (0.06 °C/y). Seasonally, the LSWT increase rates for all lakes, except PD, were 2–3 times higher than the air temperature increase rates. The lake stratification intensity order was similar to those of the LSWT increases and correlations. SY and DC displayed significant correlations between LSWT (0.99) and PEA (0.91). Thus, the LSWT significantly affected stratification when the water temperature increased. PD demonstrated the lowest correlation between LSWT and PEA. Inflow, outflow, rainfall, wind speed, and retention time were significantly correlated, which varied within and between lakes depending on lake topographical, hydraulic, and hydrological factors. Thus, hydraulic problems and nutrients should be managed to minimize their effects on lake water quality and aquatic ecosystems because lake cyanobacteria can increase as localized water temperatures increase.

Bayesian network modelling provides spatial and temporal understanding of ecosystem dynamics within shallow shelf seas

Understanding ecosystem dynamics within shallow shelf seas is of great importance to support marine spatial management of natural populations and activities such as fishing and offshore renewable energy production to combat climate change. Given the possibility of future changes, a baseline is needed to predict ecosystems responses to such changes. This study uses Bayesian techniques to find the data-driven estimates of interactions among a set of physical and biological variables and a human pressure within the last 30 years in a well-studied shallow sea (North Sea, UK) with four contrasting regions and their associated ecosystems. A hidden variable is incorporated to model functional ecosystem change, where the underlying interactions dramatically change, following natural or anthropogenic disturbance. Data-driven estimates of interactions were identified, highlighting physical (e.g. bottom temperature, potential energy anomaly) and biological variables (e.g. sandeel larvae, net primary production) to be strong indicators of ecosystem change. There was consistency in the physical and biological variables, identified as good indicators in three of the regions, however the shallower region (with depths < 50 m, that is targeted for static offshore wind developments) was the most dissimilar. The use of contrasting regions provided useful insights on responses linked to ecosystem disturbances and identified the top predators as better indicators for each region, with the harbour porpoise being a particularly valuable indicator of ecosystem change across most regions. Another important finding was the dramatic changes in the strength of many interactions over time. This suggests that physical and biological indicators should only be used with additional temporal information, as changes in strength led to the identification of two potentially significant periods of ecosystem change (after 2005 and after 2010), linked to physical pressures (e.g. cold-water anomalies, seen in bottom temperatures; salinity changes, seen in the potential energy anomaly) and primary production changes. The hidden variable also modelled a change in the early 2000s for all the regions and identified maximum chlorophyll-a and sea surface temperature as some of the better indicators of these ecosystem changes.

Stratification and mixing in the Chilean Inland Sea using an operational model

The Chilean Inland Sea (CIS) is an extensive estuary system with a complex topography and many fjords and channels. The degrees of stratification and mixing in the CIS are strongly affected by river discharges, high levels of rainfall, wind, and tidal forces. Field and satellite observations have suggested that stratification and mixing fluctuate on different timescales and spatial scales, but the length and resolution of this record are insufficient to resolve these trends across the entire water column. We used an operational oceanographic forecasting model (MOSA) based on the Regional Ocean Modeling System (ROMS) to study the yearly and seasonal patterns of stratification and mixing in the CIS. The evaluation of the model showed a satisfactory response to the seasonal variability of temperature, salinity, and currents. The representation of the monthly stratification degrees of the system obtained with the buoyancy frequency and the potential energy anomaly reveals a highly dynamic estuary system with heterogeneous patterns on distinct spatial and temporal scales in the CIS. We conclude that the CIS can be classified into three zones: seasonal stratification regions, permanent stratification regions, and permanent mixing regions. Our results reveal a highly dynamic system that can be studied on different timescales with an operational model such as MOSA. This information may be relevant for studies of decade-scale fluctuations linked to climate change.