Seawater Heat Research Articles

An evaluation and innovative coupling of seawater heat pumps in district heating networks

Seawater heat pumps present promising solutions for the decarbonization of the heating sector by utilising seawater as a renewable heat source. This study explores their integration into district heating networks in cold climate regions, focusing on case studies in Estonia, and Norway. A main challenge lies in the freezing threat of seawater during winter, prompting investigations into innovative solutions. This research evaluates two proposed strategies: coupling seawater heat pumps with an additional heat source and locating them far off the shore where water temperatures are more stable. The study employs a multifaceted approach, considering technical, economic, and environmental factors. The research assesses and models seawater heat pumps in two case studies, exploring 10 MW heat supply scenarios. Performance indicators include Coefficient of Performance (COP), Electricity consumption, CO2 emissions, and Levelized Cost of Heat (LCOH). Results highlight the feasibility and advantages of coupling free heat sources with seawater heat pumps in district heating networks. In the Norwegian case, coupling waste heat and seawater heat pumps significantly reduces electricity consumption, CO2 emissions, and LCOH by 88 %, 65 %, and 76 %, respectively. In Tallinn, where seawater freezing is a concern, installing far-off the shore seawater heat pumps maintain year-round operation with a seasonal COP of 3.5 and a 34 % reduction in CO2 emissions compared to electric boiler coupling. Economic assessments suggest the feasibility of integrating far-off the shore seawater heat pumps in low-power price scenarios.

Oceanographic preconditions for planning seawater heat pumps in the Baltic Sea – an example from the Tallinn Bay, Gulf of Finland

Abstract. The use of low-temperature seawater heat for renewable energy installations is demonstrated with an example from the Tallinn Bay, Baltic Sea, based on Copernicus Marine Service reanalysis data. Tallinn and its surrounding seaside counties are home to about half a million people and produce about half of Estonia's gross domestic product (GDP). The Tallinn Bay with an area of 223 km2 extends to the north and has an open connection to the Gulf of Finland. Depths more than 50 m that cover the halocline already appear at a distance of 3–4 km from the coast. Surface layers get too cold during winter to be used in heat pumps for district heating; therefore, a feasible option is to pump slightly warmer seawater from the deeper halocline layers. The lowest monthly mean halocline temperature – down to 2.6 °C at 50 m depth and 3.3 °C at 70 m – is found in March and April based on reanalysis data from 1993–2019. The seawater seasonally cools below 3 °C on average on 1 January at 20 m depth and on 12 February at 50 m depth. At the 70 m depth, the average start of T<3 °C was calculated on 28 February, although only 14 winters out of 26 had such water present; in 12 winters the condition T>3 °C was always fulfilled. The median number of cold days is 11, with a maximum of 128 d in the winter 1993/1994 when stratification became rather weak due to the prolonged absence of Major Baltic Inflows of saltier and warmer North Sea waters. During the recent warmer period of 2009–2019, the start of the cold seawater period was delayed on average by 5–10 d. Tallinn has, among other Baltic Sea cities and industrial sites, a favorable location for seawater heat extraction because of the short distance to the unfreezing sub-halocline layers. Still, episodically there are colder-water events with T<3 °C, when seawater heat extraction has to be complemented by other sources of heating energy.

Innovative integration of sustainable technologies in educational programs: Fostering freshwater production and environmental preservation awareness

This study highlights the integration of sustainable desalination technologies into educational programs to raise awareness of freshwater production and environmental preservation. Through a comprehensive curriculum, students explore innovative methods such as pressure-retarded osmosis, multi-effect desalination, and seawater source heat pumps, all powered by renewable seawater thermal energy. The curriculum emphasizes the importance of reducing greenhouse gas emissions, lowering reliance on fossil fuels, and protecting aquatic ecosystems. Students engage in practical evaluations of energy efficiency, economic viability, and environmental impact. Sensitivity analyses are incorporated to help students identify critical factors affecting system performance and optimize operational conditions for various modes. Through hands-on experiments, students learn that components like the heat pump condenser contribute the most to energy loss (29 %), followed by the expansion valve (12 %), compressor (11 %), and seawater heat exchanger (8 %). Economic analyses reveal that while the heat pump condenser and seawater heat exchanger have the lowest financial impact (0.33 % and 2.48 %, respectively), the pressure-retarded osmosis and compressor units have the highest (100 % and 60.3 %, respectively). The findings demonstrate that an optimally designed desalination system can produce freshwater at 80 % lower costs compared to traditional plants, while also reducing carbon emissions by 15 %. Educational experiments also show that integrating pressure-retarded osmosis downstream of multi-effect desalination significantly reduces brine salinity and temperature, highlighting the system's potential for environmental sustainability. This approach not only fosters a deeper understanding of desalination technologies but also equips students with the tools to address future global water challenges.

Numerical study on efficiency and robustness of wave energy converter-power take-off system for compressed air energy storage

The unpredictable fluctuations of wave lead to an imbalance between energy supply and demand. This article proposes a wave-driven compressed air energy storage system, which uses wave mechanical energy instead of electrical energy as the direct driving force for the compressors. Compressed air energy storage solves the problem of stability of wave energy output by accumulating and storing wave energy and then releasing it in a centralized manner. Due to the significant change in load damping compared to the generator, the damping force of the power take-off with compressed air energy storage load is analyzed. And a robust strategy with adjustable buoy draft and load compressor number is proposed, and the highest capture width ratio of 26.71 % and wave energy to compressed air energy conversion efficiency of 13.00 % are achieved under regular wave conditions. Surface seawater is used for heat supplementation in the expansion phase, and a closed-loop system is designed to avoid the damage of low-temperature condensation, the round-trip efficiency of the system is 11.26 %. This research provides a potential power generation path for wave energy and surface seawater heat. And it may beneficial to provide stable and relatively cheap power supply for coastal and offshore users.

TOWARDS CARBON-NEUTRAL FISH COLD STORAGE: A SUSTAINABLE APPROACH THROUGH RENEWABLE ENERGY

Preserving perishable foods, particularly fish, demands meticulous attention throughout the entire supply chain, from capture to consumption. The critical role of cold storage facilities in maintaining optimal conditions, encompassing temperature and humidity regulation, is indispensable. Nevertheless, these facilities pose a considerable challenge due to their substantial electrical energy consumption, which significantly contributes to operational costs. In addressing this challenge, the implementation of energy-efficient strategies, including the utilization of advanced equipment and real-time monitoring facilitated by automation technologies, becomes imperative. This research investigates an innovative integrated cold storage system situated in Tarrafal, Santiago, Cape Verde, which harmoniously incorporates wind, solar, and tidal energy sources. The primary objectives are to evaluate the energy efficiency, financial viability, and environmental impact across four distinct hypothesis. Hypothesis 1 entails the deployment of two R134a refrigeration units powered by the conventional public grid, while Hypothesis 2 adopts a transcritical CO2 system reliant on grid electricity, Hypothesis 3 integrates CO2 technology with autonomous renewable energy sources and Hypothesis 4 leverages CO2 for refrigeration coupled with seawater heat exchange and autonomous renewable energy generation. The research findings strongly favor Hypothesis 4, demonstrating emissions of 15880 kg CO2eq with an impressive 5-year return on investment. The autonomous electricity production associated with this hypothesis markedly reduces emissions by more than 90%. Despite an initial higher investment, Hypothesis 3 showcases financial viability, contributing significantly to long-term energy sustainability. The autonomous energy production in this scenario results in a noteworthy reduction of more than 600000 kgCO2 compared to conventional systems, underscoring the positive impact of integrating local renewable energy sources.

Model of a 100 % renewable energy system of self-sufficient wider urban area based on a short-term scale and the integration of the transport and thermal sector

The mutual integration of different energy sectors and their conversion to electricity could promote the integration of renewable energy sources. This paper analyses 100 % renewable electrical power system of the Dubrovnik wider urban area. The Calliope energy system model was developed and compared based on 10-min and hourly data. The energy scenario is modelled up to the year 2050. It includes the replacement of all conventional passenger vehicles with electric vehicles. The vehicle-to-grid model was developed using the Calliope modelling tool. All fossil fuels used in the heating sector are replaced by seawater heat pump systems. Additional storage is added to the system and the system is connected to the adjacent electricity market. The 10-min model led to a reduction in cross-border transmission capacity of around 60 % and a 7-fold reduction in the difference between import and export compared to the hourly model. This led to a more stable system operation, as the import and export capacities were equalised. The vehicle-to-grid technology in the regulated system led to a reduction in import and export transmission capacities of up to 17 % and 42 % respectively compared to the unregulated system, including extremely fast charging and discharging in a short-term step model.

Sustainable CO2 Refrigeration System for Fish Cold Storage Facility Using a Renewable Integrated System with Solar, Wind and Tidal Energy for Cape Verde—Analyzing Scenarios

This study compares four feasible alternative solutions for an integrated cold storage system in the city of Tarrafal, Santiago, Cape Verde. Integrated systems using grid electricity are compared with autonomous systems generating electrical energy from renewable sources, alongside various types of refrigeration facility systems. Its objective is to assess the energy efficiency, financial feasibility, and environmental impact across four scenarios. Scenario 1 utilizes two R134a refrigeration units powered by the public grid. Scenario 2 employs a transcritical R744 (CO2) system using grid electricity. Scenario 3 incorporates R744 and autonomous renewable energy. Scenario 4 employs R744 for refrigeration with seawater heat exchange and autonomous renewable energy sources. The findings favor Scenario 4, emitting 15,882 kg CO2 eq with a 5-year return on investment. Autonomous electricity production in this scenario reduces emissions by 95%. Despite an initial cost of EUR 769,172.00, Scenario 3 demonstrates financial viability, contributing to energy sustainability. This autonomous production reduces emissions by 360,697 kg CO2 compared to conventional systems, highlighting the positive impact of local renewable energy integration.

Thermal circuit model of DC submarine cable considering the influence of seawater property variations

The IEC 60287 standard, when calculating the steady-state current-carrying of DC submarine cables, does not take into account the influence of seawater property variations on changing the heat transfer efficiency of seawater, thereby affecting the current-carrying capacity of the cable. resulting in deviations in the calculated ampacity results. This paper considers the influence of seawater heat transfer characteristics on cable heat dissipation efficiency based on heat transfer theory, and Proposes an improved thermal circuit model for submarine DC cables that takes into account variations in seawater properties. Taking the example of a 160 kV submarine XLPE cable, the current-carrying capacity results of the improved model have an error of no more than 1.9 % compared to finite element simulation results. Under identical environmental conditions, the maximum deviation between the improved model and the IEC thermal circuit model is 123A, confirming the necessity of considering variations in seawater properties in the improved thermal circuit model. The seawater property variations studied in this paper include changes in seawater temperature, salinity, and pressure. If the impact of seawater property variations on submarine cable current-carrying capacity is not considered, the obtained current-carrying capacity results are higher, with a maximum error of 5.5 %. Among these variations, temperature has the most significant impact, with an error reaching 3.3 %, while salinity and pressure have relatively smaller impacts, with errors of 1.1 % each.

An innovative ocean thermal energy conversion system with zeotropic Rankine cycle and direct contact membrane distillation for enhanced efficiency and sustainability

This research introduces an integrated ocean thermal energy conversion water and power cogeneration system (OTEC-WPCS), combining a Zeotropic Rankine Cycle (ZRC) with Direct Contact Membrane Distillation (DCMD) for efficient power and water production. The hydrofluoroolefins (HFOs), chosen for their zero ozone depletion potential (ODP) and extremely low global warming potential (GWP), are used as working fluid components in the ZRC. Additionally, DCMD is implemented for freshwater generation. A mathematical model is established, incorporating both thermodynamic and CFD simulations. The goal is to identify optimal operating conditions that maximize the output of the system. By coupling DCMD and ZRC in series, the system's efficiency reaches 8.92 %, an improvement of 5.71 % compared to a standalone ZRC system. This configuration allows for more efficient use of surface seawater heat compared to an ammonia-based Organic Rankine Cycle (ORC)-DCMD system. The enhancements include an increase in power and water production per unit mass flow of surface seawater by 0.55 kW/(kg·s) and 30 %, respectively. Over 60 % of the system's exergy destruction occurs in the DCMD modules and evaporator, while nearly 80 % of the capital cost is associated with the evaporator, condenser, and DCMD heat exchanger. Enhancing the DCMD module structure and heat exchanger can improve both energy and exergy efficiency, and economic feasibility.

Photovoltaic panel and wind turbine as an electric energy source for water evaporation and desalination

The purpose of the article is to study the process of heating and desalination of seawater due to electricity from wind turbines and solar panels. This electric current is collected and transmitted through wires to be used to power electrical devices. The advantages of using solar panels as an alternative energy source include environmental cleanliness, long service life, no noise, low cost of operation and no emissions of harmful substances. Boiling water using wind turbine energy is a great way to use renewable wind energy to support daily activities. By placing a wind turbine in an area with a steady wind, the turbine can collect kinetic energy from the air and convert it into mechanical energy that can be used to rotate the generator. This generator can then convert mechanical energy into electrical energy, which can be used to power an electric boiler. The boiler can then use electrical energy to heat the water, producing steam to boil the water.

Carbon Reduction Path and Economic Analysis of Seawater Desalination in China under the “Dual Carbon” Goal

Carbon Reduction Path and Economic Analysis of Seawater Desalination in China under the “Dual Carbon” Goal

Study on the seawater cooled PRHRS of a nuclear propulsion ship with the upper heat exchanger for driving force and the seawater heat exchanger as an ultimate heat sink

As international maritime trade among countries increases, great efforts are being made to reduce the amount of greenhouse gases emitted from ships using conventional fossil fuels. A variety of environment-friendly power sources for ships are being considered, and nuclear energy is one of them. The research described in this paper focuses on elemental technologies related to nuclear-powered ships rather than the nuclear reactor technology itself. Among those technologies, the Passive Residual Heat Removal System (PRHRS) of a nuclear-powered ship is studied to remove residual heat by using seawater as an alternative heat sink. New concept of PRHRS is proposed and it is named as SWC-PRHRS. SWC-PRHRS has two heat exchangers: one is for driving force and another is for dumping the most of residual heat to the sea. Numerical analysis and experimental studies are conducted to improve the performance of SWC-PRHRS. The numerical results show that most of the residual heat comes from a reactor core is eliminated by sea water cooling proving the concept of SWC-PRHRS is working properly without any operator intervention and additional water supply. Experimental studies are conducted based on the numerical analysis results. From the experimental results, it is found that the mass flow rate of SWC-PRHRS is very sensitive to the filling ratio of SWC-PRHRS and there are three distinctive filling ratio ranges. Through the experiment, it is confirmed that SWC-PRHRS is working efficiently with the lower mass flow rate and the smaller upper heat exchanger without any operator intervention. SWC-PRHRS could remove a large amount of residual decay heat from the ship's reactor and release it to the sea. Considering the size, weight, and exceptional heat removal capability of SWC-PRHRS, it is clear that SWC-PRHRS is well suited for marine application usage.

Performance analysis and techno-economic assessment of a developed cooling/preheating small PVT-RO desalination plant

Middle East and North Africa (MENA) countries are experiencing rapid population growth, so water and electricity consumption plays a crucial role in the sustainable development of these countries. To overcome the water scarcity and electricity problems facing the MENA region, the developed cooling/preheating small PVT-RO desalination plants have been proposed as a practical solution. To achieve sustainable water and energy development in the MENA region, this study presents a commendable and highly efficient renewable energy project for freshwater production and electricity generation to solve the energy crisis and water scarcity in the MENA countries. Therefore, this study aims to develop a cooling/preheating small PVT-RO desalination plant to facilitate freshwater supply to remote regions and produce electricity. This was done by connecting photovoltaic/thermal (PVT) collectors with reverse osmosis (RO) desalination systems, where seawater is used as a medium to cool photovoltaic cells to increase electric power generation and at the same time recover thermal energy and use it in the initial heating of feed seawater before it is fed into the RO plants, thus increasing its productivity. The results indicate that using the photovoltaic thermal panels as preheating units will lead to a 0.135 kWh/m3 reduction in the rate of specific electricity consumption for the RO desalination plant, as well as increase the electricity generation from PVT panels by a rate of 8%. The economic feasibility presented that the proposed developed cooling/preheating small PVT-RO desalination plant represents an effective technology that reduced the freshwater cost by a rate of 49.5%.

Assessment of the OTEC cold water pipe design under bending loading: A benchmarking and parametric study using finite element approach

Abstract Ocean thermal energy conversion (OTEC) is a floating platform that generates electricity from seawater heat. The cold water pipe (CWP) used in OTEC has a length of 1,000 m and a diameter of 10 m, making it susceptible to bending loads from ocean currents. To find suitable geometry and material for the CWP, the finite element method was used to model the real-world geometry. In the D/t variation, lower ratios (increased thickness) result in higher critical moments, maximum stress, strain, and displacement. D/t 50 was chosen for the CWP. In the L/D variation, the critical moment’s impact on L/D ratio was minimal, while reducing L/D (shorter pipe) increased strain, and larger L/D geometries had higher displacements. L/D 10 was selected as it balanced critical moments and reduced the number of stiffeners needed. For diameter size variation, larger diameters increased critical moment and strain, but smaller diameters (larger L/D ratios) also showed high strain due to necking at two points. A diameter of 12 m was chosen for its exceptionally high critical moment. Steel was selected as the suitable material due to its higher critical moment and maximum stress, despite its higher weight and lower maximum strain than composites. Capital shape imperfections had a minimal effect on the CWP’s structure as they were localized.

Study on refined mathematical model of solar chimney power plant integrated with seawater desalination and the influence of dewing

In order to more accurately evaluate the operation and output characteristics of the solar chimney power plant integrated seawater desalination, a refined mathematical model for unsteady heat and mass transfer was built under consideration of the convection heat transfer mechanism of the collector, dewing phenomenon, and the disturbance to the hot airflow caused by the oblique-toothed flow channel boundary. The influence of nighttime dewing and humid environments on system performance was discussed. The results show that it is feasible and more appropriate to use the forced convection heat transfer coefficient of bellows to consider the influence of the oblique-toothed flow channel boundary; the refined mathematical model is also more accurate and reliable. Due to the effect of seawater heat storage, dewing has little effect on system performance, and the integrated system has a better anti-dewing negative impact characteristic. However, when the ambient humidity reached a higher level, dewing had a greater negative impact on freshwater production. The critical value of relative humidity for dewing to occur is 51 %. When the relative humidity increases from 45 % to 60 %, the daily utilization efficiency of solar energy decreases from 27.4 % to 22.5 %.

Preliminary Results of a Closed-Loop Sea Water Heat Pump: Application in Large-Scale Elderly Home Center for Heating and Cooling Load Coverage

Preliminary Results of a Closed-Loop Sea Water Heat Pump: Application in Large-Scale Elderly Home Center for Heating and Cooling Load Coverage

ПРОСТРАНСТВЕННО-ВРЕМЕННАЯ ИЗМЕНЧИВОСТЬ ГИДРОФИЗИЧЕСКИХ И ЭНЕРГЕТИЧЕСКИХ ХАРАКТЕРИСТИК ЦИРКУЛЯЦИИ ЧЕРНОГО МОРЯ ПРИ ДОМИНИРОВАНИИ ДВИЖЕНИЙ РАЗНЫХ МАСШТАБОВ

Simulation results of the Black Sea dynamics for two periods when the annual mean circulation corresponded to the basin-scale and eddy regimes (2011 and 2016) are considered in the paper. Numerical experiments are carried out using the MHI model and considering the realistic atmospheric forcing from SKIRON. The seasonal variability of dynamic and thermohaline fields, as well as the kinetic and available potential energy, and their conversion rates are estimated. According to the model data on the seasonal mean distribution of currents velocity, it is found that in 2011 the RIM Current is detected in all seasons, and the most intense mesoscale eddies developed on its periphery over the continental slope in the warm period of the year; in 2016, separate cyclonic jets in the area of the continental slope are observed in the northern and southwestern parts of the basin during cold seasons, and mesoscale eddies are propagated in the central part of the sea throughout the year. The change in the mean current kinetic energy is determined by the circulation regime: energy maxima are revealed in the spring of 2011 and in the winter of 2016, when the mean current was the most intense. The distribution of the mean available potential energy is predominantly seasonal, the time variability is qualitatively similar for both modes and is provided by an increase in the density anomaly due to seawater heating. The eddy kinetic energy characterizing the mesoscale variability depends both on the circulation regime and on the season. In the spring 2011, the mean current and eddy kinetic energies are comparable; in 2016, the maximum eddy energy exceeded the mean current kinetic energy. In autumn and winter, for both calculations, the increase in eddy energy occurs due to the energy transfer from the wind and the mean current through the barotropic instability mechanism. In summer when wind activity weakens, in the basin-scale circulation mode, mesoscale variability is supported by commensurate contributions from barotropic and baroclinic instability; in the eddy circulation mode – mainly due to the conversion of available potential energy through baroclinic instability.

Comprehensive parametric analysis, sizing, and performance evaluation of a tubular direct contact membrane desalination system driven by heat pipe-based solar collectors

Feed seawater heating is one of the crucial bottlenecks in membrane desalination (MD) systems. The interest of usage solar energy techniques for feed seawater preheating in MD systems is recently regarded as an improvement pathfor sustainable distillate production. This study presents a conceptual design, theoretical modeling, and comprehensive parametric analysis of a tubular direct contact membrane desalination system (TDCMDS) driven by heat pipe-based solar collectors (HPSCs). An improved theoretical model performed in MATLAB software was conducted to simulate the hybrid solar TDCMDS operation in order to analyse its performance in the climate conditions of Tanta, Egypt. The effects of the number of utilized solar collectors, feed seawater flowrate, cooling water flowrate, and utilization of additional electric heaters on the energy performance of the solar TDCMDS are parametrically investigated. The findings show that the number of the utilized solar collectors, feed seawater flowrate, and cooling water flowrate, were the most sensitive to the performance of the solar TDCMDS, which should be desired to be 5.0 ≥n≥ 2.0, 20.0 lpm, and 5.0 lpm, respectively, in the design of the TDCMDS to maximize the freshwater production. Moreover, the maximum permeates flux are 0.45, 0.39, 0.32, and 0.25 kg/h per m2 of solar collecting area with total daily freshwater production of 35.0, 24.60, 15.48, and 7.95 kg/day by integrating five, four, three, and two HPSCs connected in series, respectively, compared to only 0.08 kg/h.m2 and 1.44 kg/day when coupling one solar collector at feed seawater and cooling water flowrates of 20 and 5.0 lpm, respectively. Conclusively, it can be recommended that this investigation provides an emerging strategy for designing solar-based MD systems.

Effects of temperature shock on the survival of different life stages of large yellow croaker (Larimichthys crocea) by simulated power plant cooling water

Seawater temperatures have increased with global climate change. Coolant water discharged from coastal nuclear power-generating and coal-powered plants, coupled with already increasing seawater temperatures, can adversely affect local fish communities. A sudden drop in temperature caused by the winter shutdown of power plants can also affect fish health and behavior. To assess the effects of temperature change on fish populations, we subjected early life stages of the once commercially important large yellow croaker (Larimichthys crocea) to various water temperature experiments. Fertilized eggs showed the highest hatching rate at 23.4°C and the lowest rate of deformity in hatched larvae at 23.0°C. We determined the incipient lethal temperature for each life stages using derivation models. Ranges between the upper and lower incipient lethal temperatures increased during development from yolk-sac larvae to juveniles, especially in response to cold shock, indicating that later developmental stages in this species are more tolerant of temperature fluctuations. However, thermal tolerance is not solely determined by life stage. Our results suggest that rapid changes in seawater temperature caused by power plant coolant water discharges may significantly affect early developmental stages of fish. Critical thermal maximum tests indicate that the seawater heating rate is significantly negatively correlated with survival time and affects the critical thermal maximum value of L. crocea. On the basis of our determination of incipient lethal temperatures, emergency measures could be taken to avoid adverse economic and ecological impacts due to changes in seawater temperature caused by coolant water discharges.

Sources of Mg Enrichments in Vent Fluids From the Kermadec Arc Recorded by Li, B, and Mg Isotopes

AbstractMagnesium concentrations in acid‐sulfate fluids from Brothers and Macauley volcano, Kermadec arc, Western Pacific, exceed those of seawater and differ from previously known acid‐sulfate fluids with seawater‐like Mg concentrations. Earlier studies explained these Mg enrichments as due to phase separation, caminite (Mg1.25SO4(OH)0.5 × 0.5H2O) dissolution, water‐rock interaction and/or “mining” of deep seated magmatic brines. Since these different and partly contradictory explanations could neither be confirmed nor refuted, we investigated B, Li, and Mg isotope compositions in acid‐sulfate and black smoker fluids from both Brothers and Macauley to understand the origin of the high Mg concentrations and investigate a possible connection with the alteration of basement rocks. In addition, we performed seawater heating experiments to investigate Mg isotope fractionation during caminite precipitation. Lithium and B isotope signatures in all studied acid‐sulfate fluids indicate water‐rock interaction. Magnesium isotopes in fluids from Macauley correspond to seawater, implying Mg enrichment through phase separation in the fluids. In contrast, Mg‐enriched acid‐sulfate fluids from Brothers volcano have higher δ26Mg values (up to −0.62‰) than seawater. Considering that our seawater heating experiment shows a preferential incorporation of 24Mg into caminite, caminite dissolution would lead to lower δ26Mg values and thus cannot solely account for the enriched Mg concentrations seen at Brothers. Additionally, we thus suppose leaching of Mg from the basement during the interaction of acidic fluids with a relatively unaltered basement.