Warm Seawater Temperatures Research Articles

Experimental study of an absorption-based refrigeration driven by ocean thermal energy

Establishing an island-based cold chain is essential for ensuring food storage, vaccine preservation, and fish freezing on islands, which is indispensable for the sustainable development of island communities. The compression-absorption refrigeration system that uses ocean-thermal-energy is ideal for cold storage on islands as it efficiently utilizes local renewable energy sources and can meet refrigeration needs below 0 °C. Therefore, a refrigeration prototype has been constructed and thoroughly experimentally investigated to obtain refrigeration characterization under variations of refrigeration demand and environmental conditions. The system's energy-saving potential is evaluated by conducting comparisons with conventional refrigeration techniques. The results indicate that refrigeration temperature plays a crucial role in determining refrigeration capacity, with an increase of approximately 8.2 % observed for every 1 °C rise in refrigeration temperature. Lower cold-seawater temperatures or higher warm-seawater temperatures do not have a significant effect on the refrigeration capacity, but contribute to a reduction in compressor power due to increased thermally-driven compression force. Consequently, for every 1 °C change, the refrigeration capacity per unit compressor power increases by approximately 4 %. Additionally, the refrigeration capacity of the system is three times greater than that of a vapor-compression-refrigeration-system. The findings provide theoretical and experimental guidelines for the design and operation of refrigeration using ocean-thermal-energy.

Were Late Jurassic climatic fluctuations responses to Pangea breakup? Evidence from isotopic analyses of belemnite rostra from the eastern Tethyan Ocean

Late Jurassic paleogeographic patterns were influenced by the growth of the Pacific plate and the breakup of Pangea, impacting the global paleoclimate during this warm and equable greenhouse period. However, the use of different proxies may introduce bias in seawater temperature reconstructions. In this study, we reconstructed midlatitude Tethyan seawater paleotemperatures in the Northern Hemisphere using carbonate clumped isotopes (Δ47) in well-preserved parts of belemnite rostra from the Upper Jurassic Hongqilafu Formation in the Taxkorgan Basin, southwest Xinjiang, China. Throughout the entire studied section, an increase in the 87Sr/86Sr ratio was observed. Comparison of this ratio with the published global seawater 87Sr/86Sr curve suggests a good correlation with the biostratigraphic and U-Pb age assignments of the Oxfordian−Tithonian interval. The Δ47-derived paleotemperature estimates indicate a long-term, relatively stable, and warm seawater temperature of ∼27 °C within the epipelagic zone of the eastern Tethyan Ocean during the Late Jurassic. Cooler seawater temperatures were recorded at the Oxfordian−Kimmeridgian boundary and in the late Tithonian, likely reflecting changes in paleogeography and paleoceanography resulting from the breakup of Pangea and/or variations in belemnite habitat depth. When compared with global seawater temperature data from different proxies, the results suggest that elevated atmospheric pCO2 levels during the Late Jurassic may have caused warmer conditions in midlatitude and polar regions. The reconstructed δ18Osea values exhibit a remarkably modern midlatitude seawater character and are more positive than values traditionally assumed for the Jurassic ice-free world. Given that the Taxkorgan Basin was located in a semi-enclosed basin and was dominated by evaporation in the Late Jurassic, the reconstructed δ18Osea values may represent regional seawater signals. Consequently, they cannot be used to support the existence of ice sheets in both polar regions. Our results suggest that climatic changes in the Jurassic greenhouse world may have been overprinted by local factors, potentially masking broader climatic trends.

Compound marine cold spells and hypoxic events in a nearshore upwelling system

Prolonged periods of extreme warm and cold seawater temperature anomalies, known as marine heatwaves (MHWs) and marine cold spells (MCSs), respectively, can have significant impacts on coastal marine ecosystems. Prior research has examined the co-occurrence of multiple extremes [low dissolved oxygen (DO) and/or low pH] during MHWs, with the impact of these compound events potentially exceeding that of a single stressor due to synergistic effects. However, we are not aware of any studies that have examined compound extreme events during MCSs, despite the ecosystem implications. Along Eastern Boundary Current Upwelling Systems (EBUS), strong-wind driven upwelling has led to reduced warming trends and persistence of MCSs, as well as an increased seasonal risk for coastal hypoxia via the cross-shelf advection of cold, low DO subthermocline waters. In this short communication, we investigated for the first time compound MCS-hypoxic events at a nearshore site in central California using several decades of nearshore water temperature data, short-term nearshore DO data, and several decades of DO data from the California Cooperative Oceanic Fisheries Investigations program. From 1988 to 2020, we identified 55 MCS events, with 50 events (∼90.9%) initiated during anomalously strong upwelling. Using long-term temperature-DO relationships, we identified 20 of the 55 MCS events (∼34.6%) as potential compound MCS-hypoxic events, with an average duration of 11.7 days. These compound events occurred almost exclusively during the major upwelling season (March to June) when there is a high propensity for the advection of cold, low DO subthermocline waters from the adjacent shelf into the nearshore. This work provides the first known investigation into the co-occurrence of MCS and hypoxic events in a nearshore upwelling system and provides a baseline for assessing future changes to these compound events in a changing climate, with important implications for ecosystem health in EBUS globally.

Theoretical, numerical and experimental research on an innovative ocean thermal energy conversion coupled VMD desalination system

This paper proposes an OTEC-VMD desalination system that fully exploits tropical ocean thermal energy to alleviate freshwater shortages on remote islands, with no need of coupling with other heat sources. Based on an in-depth analysis of the mass and heat transfer theory of the OTEC-VMD desalination, a CFD model is established by embedding a UDF program in commercial software and an experimental prototype with a water production capacity of 1 kg/h is designed and manufactured. The CFD simulation and experimental test results show good agreement, with relative errors around 5 %. The proposed system can stably produce water, demonstrating the feasibility of OTEC-VMD seawater desalination experimentally for the first time. At a warm seawater temperature of 30 °C, the water production reaches 1.07 kg/h, achieving the design target. The system's water recovery ratio and specific electrical energy consumption are 0.254 % and 2.62 kWh/m3, respectively, and the TDS is lower than 5 mg/L. Compared to low-pressure flashing, the equipment achieves an average volume reduction rate of 94.71 %, making it more suitable for installation and transportation in remote marine locations, with great potential in replacing the low-pressure flashing device in the open-cycle of OTEC power plant to promote the large-scale application of OTEC technology.

Performance Analysis of a 10 MW Ocean Thermal Energy Conversion Plant Using Rankine Cycle in Malaysia

Ocean thermal energy conversion (OTEC) is a solution for environmental and climate change issues in the tropics. The OTEC potential in Malaysia using ocean conditions and bathymetry data has been previously studied and demonstrated. Following this, it is vital to perform a basic performance analysis of a 10 MW Rankine Cycle OTEC plant using the Malaysian ocean conditions. In this paper, the results of heat and mass balance will be reported for a 10 MW Rankine cycle OTEC plant which uses heat exchangers of plate-type and anhydrous ammonia as its working fluid. The value of a minimum objective function (γ) is derived by total heat surface area (AT) divided by the net power (PN). γ decreases when the inlet temperature difference (inlet temperature of warm seawater (TWSWI)—inlet temperature of cold seawater (TCSWI)) increases. PN is clarified to be approximately 70–80% of the PG (gross power) using Malaysian ocean conditions.

Marine Heatwaves and their Impacts: Research Perspectives in the Philippines

Marine heatwaves are discrete and prolonged periods of anomalously warm seawater temperature which have devastating ecological and socioeconomic impacts. Being part of the center of marine biodiversity and a fisheries-dependent country, the Philippines is vulnerable to the threats of marine heatwaves, but these extreme events remain understudied in the country. It is, therefore, crucial to investigate the development of marine heatwaves and to assess and predict the impacts of these events in the Philippine seas. In this perspective paper, we aim to put forward the research direction for advancing our understanding of marine heatwaves and their impacts in the Philippines. The limited studies on marine heatwaves in the Philippines highlight the need for progress in understanding the spatiotemporal patterns, physical processes, and impacts of marine heatwaves in the country. Advancing our knowledge of marine heatwaves will help us formulate mitigating strategies for ocean warming in fisheries management and marine biodiversity conservation in the Philippines.

Climate refugia on the Great Barrier Reef fail when global warming exceeds 3°C.

Increases in the magnitude, frequency, and duration of warm seawater temperatures are causing mass coral mortality events across the globe. Although, even during the most extensive bleaching events, some reefs escape exposure to severe stress, constituting potential refugia. Here, we identify present‐day climate refugia on the Great Barrier Reef (GBR) and project their persistence into the future. To do this, we apply semi‐dynamic downscaling to an ensemble of climate projections released for the IPCC's recent sixth Assessment Report. We find that GBR locations experiencing the least thermal stress over the past 20 years have done so because of their oceanographic circumstance, which implies that longer‐term persistence of climate refugia is feasible. Specifically, tidal and wind mixing of warm water away from the sea surface appears to provide relief from warming. However, on average this relative advantage only persists until global warming exceeds ~3°C.

Investigation of a low-pressure flash evaporation desalination system powered by ocean thermal energy

To alleviate the consequences of the freshwater crisis and fully utilize marine resources in tropical coastal areas, this study presents a low-pressure flash evaporation desalination system driven by ocean thermal energy (OTE). Through gravity and atmospheric pressure, a natural vacuum can be formed in the evaporator, which achieves flash evaporation for warm surface seawater. Then, the vapour is condensed into freshwater via an inner coil condenser with flowing cold deep seawater. Using a water pump to fill the evaporator intermittently, the non-condensable gas accumulated in the desalination process can be thoroughly discharged. Based on the process of mass and heat transfer inside the system, a thermodynamic model was developed. Several performance evaluation indices, including water productivity, specific electrical energy consumption (SEEC) and recovery ratio (RR), were experimentally investigated under different parameters. The results indicate that productivity and SEEC are higher with increasing seawater flow rate and decreasing deep seawater temperature. Under a warm seawater temperature of 30 °C and a deep cold seawater temperature of 8 °C, the system obtained a maximum water productivity of 5.3 kg/h, and the corresponding SEEC and RR were 0.126 kWh/kg and 1.5%, respectively. Finally, compared with solar-driven desalination systems, the proposed OTE desalination system requires less energy consumption, which shows an attractive application prospect.

Study of surface and vertical sea temperatures during the process of tropical cyclone formation in the territory of Indonesia (case study 2019-2021)

A tropical cyclone is an atmospheric phenomenon that has a system of low air pressure that forms over the oceans in the warm tropics. Tropical cyclones can form in oceans with sea surface temperatures above 26.5°C. In addition to the sea surface temperature which must be more than 26.5°C, the depth of warm sea water temperature strongly supports the formation of tropical cyclones in the territory of Indonesia. In this study, research was conducted on the surface and vertical temperatures of the sea during the formation of tropical cyclones or when cyclone seeds occurred in the case of tropical cyclones that occurred in 2019-2021 in the territory of Indonesia. The data used is processed using Ocean Data View 4.1 to determine the distribution of surface and vertical sea temperatures. Based on the results on this study, the vertical distribution of sea surface temperatures during the formation of tropical cyclones in Indonesia has an average sea temperature higher than 26.5°C which reaches a depth of 64 meters to 70 meters. Then the sea surface temperature during the tropical cyclone formation process averaged 28 °C to 29 °C.

Compression-assisted absorption refrigeration using ocean thermal energy

Renewable ocean energy is regarded as an attractive candidate resource for the development of maritime cold chain systems. To meet the refrigeration requirement of seafood freezing and preservation storage, this study proposes two-type compression-assisted ammonia-water absorption refrigeration cycles using ocean thermal energy. The effects of intermediate pressure on the exergy efficiency and primary energy rate ratio are analyzed and discussed. Moreover, the role of the heat source and sink temperatures on the primary energy rate ratio was examined. The results indicated that the absorption refrigeration system with a compressor in the low-pressure stage has a higher exergy efficiency and a higher primary energy rate ratio than the corresponding compressor in the high-pressure stage. For a warm seawater temperature of 29 °C and cold seawater temperature of 8 °C, the low-pressure compression-assisted refrigeration cycle is the best solution with an exergy efficiency up to 0.284, and the optimal primary energy rate ratio equals 1.392. Furthermore, a higher primary energy rate ratio can be realized by increasing warm seawater temperature or reducing cold seawater temperature.

Marine Heatwaves in the Chesapeake Bay

Prolonged events of anomalously warm sea water temperature, or marine heatwaves (MHWs), have major detrimental effects to marine ecosystems and the world's economy. While frequency, duration and intensity of MHWs have been observed to increase in the global oceans, little is known about their potential occurrence and variability in estuarine systems due to limited data in these environments. In the present study we analyzed a novel data set with over three decades of continuous in situ temperature records to investigate MHWs in the largest and most productive estuary in the US: the Chesapeake Bay. MHWs occurred on average twice per year and lasted 11 days, resulting in 22 MHW days per year in the bay. Average intensities of MHWs were 3°C, with maximum peaks varying between 6 and 8°C, and yearly cumulative intensities of 72°C × days on average. Large co-occurrence of MHW events was observed between different regions of the bay (50–65%), and also between Chesapeake Bay and the Mid-Atlantic Bight (40–50%). These large co-occurrences, with relatively short lags (2–5 days), suggest that coherent large-scale air-sea heat flux is the dominant driver of MHWs in this region. MHWs were also linked to large-scale climate modes of variability: enhancement of MHW days in the Upper Bay were associated with the positive phase of Niño 1+2, while enhancement and suppression of MHW days in both the Mid and Lower Bay were associated with positive and negative phases of North Atlantic Oscillation, respectively. Finally, as a result of long-term warming of the Chesapeake Bay, significant trends were detected for MHW frequency, MHW days and yearly cumulative intensity. If these trends persist, by the end of the century the Chesapeake Bay will reach a semi-permanent MHW state, when extreme temperatures will be present over half of the year, and thus could have devastating impacts to the bay ecosystem, exacerbating eutrophication, increasing the severity of hypoxic events, killing benthic communities, causing shifts in species composition and decline in important commercial fishery species. Improving our basic understanding of MHWs in estuarine regions is necessary for their future predictability and to guide management decisions in these valuable environments.

Theoretical and experimental study on the performance of a high-efficiency thermodynamic cycle for ocean thermal energy conversion

A new high-efficiency ocean thermal energy conversion (OTEC) system using non-azeotropic mixed working fluids with two regenerative cycles is proposed. Based on the first law of thermodynamics, a numerical calculation model for the proposed cycle was established to study the effects of the mass fraction of mixed working fluids, turbine inlet pressure and seawater temperature on the performance of the cycle system. An experimental plant of the proposed OTEC system was established to study the effects of seawater temperature and turbine inlet pressure on the cycle thermal efficiency. The results show that the cycle thermal efficiency and net output power of the system both increase with a decrease in cold seawater temperature or an increase in warm seawater temperature. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the working fluid mass fraction. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the turbine inlet pressure under a certain working fluid mass fraction. The experimental results of cycle thermal efficiency with various performance parameters were basically consistent with the theoretical analysis results; however, the experimental values were lower than the theoretical analysis results.

Warming resistant corals from the Gulf of Aqaba live close to their cold-water bleaching threshold

Global climate change is causing increasing variability and extremes in weather worldwide, a trend set to continue. In recent decades both anomalously warm and cold seawater temperatures have resulted in mass coral bleaching events. Whilst corals’ response to elevated temperature has justifiably attracted substantial research interest, coral physiology under cold water stress is relatively unfamiliar. The response to below typical winter water temperature was tested for two common reef building species from the Gulf of Aqaba in an ex situ experiment. Stylophora pistillata and Acropora eurystoma were exposed to 1 or 3 °C below average winter temperature and a suite of physiological parameters were assessed. At 3 °C below winter minima (ca. 18.6 °C), both species had significant declines in photosynthetic indices (maximum quantum yield, electron transport rate, saturation irradiance, and photochemical efficiency) and chlorophyll concentration compared to corals at ambient winter temperatures. It was previously unknown that corals at this site live close to their cold-water bleaching threshold and may be vulnerable as climate variability increases in magnitude. In order to determine if a cold winter reduces the known heat resistance of this population, the corals were subsequently exposed to an acute warm period at 30 °C the following summer. Exposed to above typical summer temperatures, both species showed fewer physiological deviations compared to the cold-water stress. Therefore, the cold winter experience did not increase corals’ susceptibility to above ambient summer temperatures. This study provides further support for the selection of heat tolerant genotypes colonising the Red Sea basin and thereby support the mechanism behind the Reef Refuge Hypothesis.

Off-design performance of closed OTEC cycles for power generation

The present study illustrates the development of a detailed model to estimate the part-load performance of an ammonia closed OTEC system for on-shore installations. A previously published Matlab® suite is extended by accounting for off-design conditions in terms of variable seawater temperature and mass flow on the cycle performance. The off-design behavior of each component is thoroughly discussed, with particular attention devoted to the single-stage axial-flow turbine, whose performance maps are obtained by means of three-dimensional CFD simulations. Assuming a representative plant sized for warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), the model predicts an annual electricity yield of 15.963 GWhe and LCOE of 316 €/MWhe when including seawater measured data of a simile-Hawaiian site. Moreover, a sensitivity analysis is assessed in order to identify the best design parameters (i.e. warm seawater temperature and cold seawater mass flow rate) that minimize the LCOE for the given location. The new design guarantees a reduction of approximately 11% of the LCOE (284 €/MWhe). The simulation capabilities of the developed model prove it as valuable tool to estimate the OTEC competitiveness in different scenarios.

Conodont biostratigraphy of Upper Devonian–Lower Carboniferous deposits in eastern Alborz (Mighan section), North Iran

The Devonian/Carboniferous (D/C) transition is characterized by a major transgressive/regressive cycle which led to a widespread ocean anoxia known as the Hangenberg Black Shale Event (HBSE), as well to a major sea-level fall (Hangenberg Sandstone Event, HSSE), recognized around the world. Both events are known as the Hangenberg Crisis. In order to examine the D/C transition in shallow water environment, the Mighan section in eastern Alborz was studied in terms of conodont biostratigraphy and stable isotope geochemistry. Twenty-five conodont species belonging to seven genera were identified and 5 conodont zones discriminated; namely, the Bispathodus aculeatus aculeatus Zone, Bispathodus costatus Zone, Bispathodus ultimus Zone, Siphonodella praesulcata Zone, costatus-kockeli Interregnum, and the sulcata Zone. Below the Devonian–Carboniferous boundary (DCB), the Hangenberg Black Shale and Hangenberg Sandstone equivalents were recognized, representing the Hangenberg Crisis that highly affected trilobite, ammonoid, brachiopod and conodont faunas at Mighan and worldwide. The kockeli Zone of the latest Famennian is missing at Mighan due to the lack of conodonts, probably related with the major environmental changes linked with the Hangenberg Crisis recognizable worldwide. Carbon isotopes measured of micrites from Mighan indicate a proximal depositional environment of a shallow shelf with terrestrial input and the oxygen isotope values from conodont apatite suggest warm seawater temperatures of tropical and subtropical setting in the study area.

Untreated sewage outfalls do not promote Trichodesmium blooms in the coasts of the Canary Islands

During the summer of 2017, recurrent extensive blooms of the diazotrophic cyanobacterium Trichodesmium invaded the beaches and coastal waters of the Canary Islands, causing great social alarm. Some local media and public sectors ascribed, without any strong scientific evidence, the origin and reactivation of these blooms to untreated sewage outfalls distributed along the coasts. In order to test whether sewage outfalls could have any influence on the metabolic activity of Trichodesmium, we performed 13C and 15N2 uptake experiments with colonies experiencing three different bloom development stages, incubated both with clear seawater and sewage water from an outfall south of Gran Canaria island. Our results showed that sewage outfalls did not promote any increase in dinitrogen (N2) fixation in Trichodesmium, supporting the hypothesis that decaying blooms were generated offshore and transported shoreward by local currents and winds, accumulating mostly leeward of the islands. The combination of unusually warm seawater temperatures, enhanced and sustained stratification of the upper water column and recurrent dust deposition events would have favored the development of the Trichodesmium blooms, which lasted for at least four months.

Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula

Pteropods (pelagic snails) are abundant zooplankton in the Southern Ocean where they are important grazers of phytoplankton, prey for higher trophic levels, and sensitive to environmental change. The Western Antarctic Peninsula (WAP) is a highly dynamic and productive region that has undergone rapid warming, but little is known about how environmental changes there will affect pteropod physiology. In this study, the effects of warming seawater temperatures and shifting food availability on Limacina helicina antarctica metabolism (respiration and excretion) were determined by conducting shipboard experiments that exposed pteropods to a range of temperatures and phytoplankton (food) concentrations. Highest respiration (up to 69 μmol O2 gDW−1 h−1) and usually highest excretion rates occurred under higher temperature with more limited metabolic response to food concentration, indicating these factors do not always have an additive effect on pteropod metabolism. The proportion of dissolved organic matter (DOM) to total organic and inorganic dissolved constituents was high and was also significantly affected by shifts in temperature and food. Dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP) were on average 27, 51, and 11.5% of the total C, N, and P metabolized, respectively. The proportion of total N excreted as DON and the proportion of total P excreted as DOP were significantly affected by a combination of shifting temperature and food concentrations. There were no effects of temperature or food on DOC excretion (mean 8.79 μmol C gDW−1 h−1; range 0.44 to 44) as a proportion of total C metabolized. Metabolic O2:N ratio ranged from 2 to 9 and decreased significantly with increasing temperature and food, indicating a shift toward increased protein catabolism. Metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which has implications for phytoplankton nutrient uptake and bacterial production. Respiration rates at ambient conditions of other WAP pteropods, and excretion rates for Clio pyramidata, were also measured, with respiration rates ranging from 24.39 (Spongiobranchaea australis) to 28.86 (L. h. antarctica) μmol O2 gDW−1 h−1. Finally, a CO2 perturbation experiment measuring L. h. antarctica metabolism under pre-industrial and elevated dissolved pCO2 conditions showed no significant change in mean L. h. antarctica respiration or excretion rates with higher pCO2. These insights into the metabolic response of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.

Detecting Marine Heatwaves With Sub-Optimal Data

Marine heatwaves (MHWs), or prolonged periods of anomalously warm sea water temperature, have been increasing in duration and intensity globally for decades. However, there are many coastal, oceanic, polar, and sub-surface regions where our ability to detect MHWs is uncertain due to limited high quality data. Here we investigate the effect that short time series length, missing data, or linear long-term temperature trends may have on the detection of MHWs. We show that MHWs detected in time series as short as 10 years did not have durations or intensities appreciably different from events detected in a standard 30 year long time series. We also show that the output of our MHW algorithm for time series missing less than 25% data did not differ appreciably from a complete time series, and that the level of allowable missing data could cautiously be increased to 50% when gaps were filled by linear interpolation. Finally, linear long-term trends of 0.10°C/decade or greater added to a time series caused larger changes (increases) to the count and duration of detected MHWs than shortening a time series to 10 years or missing more than 25% of the data. The long-term trend in a time series has the largest effect on the detection of MHWs and has the largest range in added uncertainty in the results. Time series length has less of an effect on MHW detection than missing data, but adds a larger range of uncertainty to the results. We provide suggestions for best practices to improve the accuracy of MHW detection with sub-optimal time series and show how the accuracy of these corrections may change regionally.

Warm seawater temperature promotes substrate colonization by the blue coral, Heliopora coerulea.

BackgroundHeliopora coerulea, the blue coral, is a reef building octocoral that is reported to have a higher optimum temperature for growth compared to most scleractinian corals. This octocoral has been observed to grow over both live and dead scleractinians and to dominate certain reefs in the Indo-Pacific region. The molecular mechanisms underlying the ability of H. coerulea to tolerate warmer seawater temperatures and to effectively compete for space on the substrate remain to be elucidated.MethodsIn this study, we subjected H. coerulea colonies to various temperatures for up to 3 weeks. The growth and photosynthetic efficiency rates of the coral colonies were measured. We then conducted pairwise comparisons of gene expression among the different coral tissue regions to identify genes and pathways that are expressed under different temperature conditions.ResultsA horizontal growth rate of 1.13 ± 0.25 mm per week was observed for corals subjected to 28 or 31 °C. This growth rate was significantly higher compared to corals exposed at 26 °C. This new growth was characterized by the extension of whitish tissue at the edges of the colony and was enriched for a matrix metallopeptidase, a calcium and integrin binding protein, and other transcripts with unknown function. Tissues at the growth margin and the adjacent calcified encrusting region were enriched for transcripts related to proline and riboflavin metabolism, nitrogen utilization, and organic cation transport. The calcified digitate regions, on the other hand, were enriched for transcripts encoding proteins involved in cell-matrix adhesion, translation, receptor-mediated endocytosis, photosynthesis, and ion transport. Functions related to lipid biosynthesis, extracellular matrix formation, cell migration, and oxidation-reduction processes were enriched at the growth margin in corals subjected for 3 weeks to 28 or 31 °C relative to corals at 26 °C. In the digitate region of the coral, transcripts encoding proteins that protect against oxidative stress, modify cell membrane composition, and mediate intercellular signaling pathways were enriched after just 24 h of exposure to 31 °C compared to corals at 28 °C. The overall downregulation of gene expression observed after 3 weeks of sustained exposure to 31 °C is likely compensated by symbiont metabolism.DiscussionThese findings reveal that the different regions of H. coerulea have variable gene expression profiles and responses to temperature variation. Under warmer conditions, the blue coral invests cellular resources toward extracellular matrix formation and cellular migration at the colony margins, which may promote rapid tissue growth and extension. This mechanism enables the coral to colonize adjacent reef substrates and successfully overgrow slower growing scleractinian corals that may already be more vulnerable to warming ocean waters.

Thermodynamic and economic analysis of a hybrid ocean thermal energy conversion/photovoltaic system with hydrogen-based energy storage system

The purpose of this study is to define and assess a new, renewable and sustainable energy supply system for islands and remote area where ocean thermal energy conversion (OTEC)/photovoltaic with hydrogen storage system is proposed. Components of this system are a turbine, generator, evaporator, condenser, pumps, photovoltaic panels, electrolyzer, hydrogen tanks, fuel cell and converter. To evaluate the proposed hybrid system, energy, exergy and economic analysis are employed. For OTEC, an optimization algorithm is applied to find the optimum working fluid (R134A, R407C, R410A, R717, R404A, and R423A), evaporation and condensation temperatures, and cold and warm seawater temperature differences between the inlet and outlet of evaporator/condenser. The results demonstrate that the maximum specific power of OTEC was achieved to be 0.3622 kW/m2 for R717 and 0.3294 kW/m2 for R423A working fluids. The overall energy efficiency for the hybrid renewable energy system was obtained 3.318%. The maximum energy loss was occurred by the turbine. The exergy efficiency of the hybrid system was obtained 18.35% and the payback period of the proposed system was obtained around 8 years. The unit electricity cost for the system was achieved as 0.168 $/kWh which is valuable compared to 0.28 $/kWh of the previous system.