Warm Seawater Research Articles

Rapid tropicalization evidence of subtidal seaweed assemblages along a coastal transitional zone

Anthropogenic climate change, particularly seawater warming, is expected to drive quick shifts in marine species distribution transforming coastal communities. These shifts in distribution will be particularly noticeable in biogeographical transition zones. The continental Portuguese coast stretches from north to south along 900 km. Despite this short spatial scale, the strong physical gradient intensified by the Iberian upwelling creates a transition zone where seaweed species from boreal and Lusitanian-Mediterranean origin coexist. On the northern coast, kelp marine forests thrive in the cold, nutrient-rich oceanic waters. In the south, communities resemble Mediterranean-type seaweed assemblages and are dominated by turfs. Recent evidence suggests that in these coastal areas, marine intertidal species are shifting their distribution edges as a result of rising seawater temperatures. Taking advantage of previous abundance data collected in 2012 from subtidal seaweed communities, a new sampling program was carried out in the same regions in 2018 to assess recent changes. The results confirmed the latitudinal gradient in macroalgal assemblages. More importantly we found significant structural and functional changes in a short period of six years, with regional increases of abundance of warm-affinity species, small seaweeds like turfs. Species richness, diversity, and biomass increase, all accompanied by an increase of community temperature index (CTI). Our findings suggest that subtidal seaweed communities in this transitional area have undergone major changes within a few years. Evidence of “fast tropicalization” of the subtidal communities of the Portuguese coast are strong indication of the effects of anthropic climate change over coastal assemblages.

Sedimentary environment and reservoir characteristics of microbial carbonate rocks in Leikoupo Formation of Jiangyoutongkou Section

As an important part of carbonate rocks, microbial rock is a good reservoir rock type, and its type characteristics and reservoir formation mechanism are different in different environments. By selecting Jiangyou Tongkou section in western Sichuan, the development environment and reservoir physical characteristics of typical microbial rock are analyzed, and the formation conditions of high-quality microbial rock reservoir are discussed. The results show that: The types of microbial rocks in the Leikoupo Formation of Jiangyou Tongkou Section are mainly tubbers and stromatolites, among which the second and fourth members of Leikoupo Formation are typical. They are developed in relatively warm and high salinity seawater, and their sedimentary environment is anaerobic environment with strong reductive property. The reservoir space types of microbial rocks are mostly intra (intergrain) void and grainy pore. In terms of reservoir physical properties, microbiolites are superior to non-microbiolites, and the 4th member of Lei Formation is the dominant reservoir of microbiolites.

Hot and heavy: Responses of ragworms (Hediste diversicolor) to copper-spiked sediments and elevated temperature

Sediment contamination and seawater warming are two major stressors to macrobenthos in estuaries. However, little is known about their combined effects on infaunal organisms. Here we investigated the responses of an estuarine polychaete Hediste diversicolor to metal-contaminated sediment and increased temperature. Ragworms were exposed to sediments spiked with 10 and 20 mg kg−1 of copper at 12 and 20 °C for three weeks. No considerable changes were observed in the expression of genes related to copper homeostasis and in the accumulation of oxidative stress damage. Dicarbonyl stress was attenuated by warming exposure. Whole-body energy reserves in the form of carbohydrates, lipids and proteins were little affected, but the energy consumption rate increased with copper exposure and elevated temperature, indicating higher basal maintenance costs of ragworms. The combined effects of copper and warming exposures were mostly additive, with copper being a weak stressor and warming a more potent stressor. These results were replicable, as confirmed by two independent experiments of similar settings conducted at two different months of the year. This study suggests the higher sensitivity of energy-related biomarkers and the need to search for more conserved molecular markers of metal exposure in H. diversicolor.

Anthropogenic nitrogen pollution threats and challenges to the health of South Asian coral reefs

Nitrogen pollution is a widespread and growing problem in the coastal waters of South Asia yet the ecological impacts on the region’s coral ecosystems are currently poorly known and understood. South Asia hosts just under 7% of global coral reef coverage but has experienced significant and widespread coral loss in recent decades. The extent to which this coral ecosystem decline at the regional scale can be attributed to the multiple threats posed by nitrogen pollution has been largely overlooked in the literature. Here, we assess the evidence for nitrogen pollution impacts on corals in the central Indian Ocean waters of India, Sri Lanka and the Maldives. We find that there is currently limited evidence with which to clearly demonstrate widespread impacts on coral reefs from nitrogen pollution, including from its interactions with other stressors such as seawater warming. However, this does not prove there are no significant impacts, but rather it reflects the paucity of appropriate observations and related understanding of the range of potential impacts of nitrogen pollution at individual, species and ecosystem levels. This situation presents significant research, management and conservation challenges given the wide acceptance that such pollution is problematic. Following from this, we recommend more systematic collection and sharing of robust observations, modelling and experimentation to provide the baseline on which to base prescient pollution control action.

Approaches for reducing the iodine content of the brown seaweed Saccharina latissima—effects on sensory properties

AbstractThe effects of steam- or warm water treatments of the brown seaweed Saccharina latissima on iodine content and nutrient and sensory profiles were investigated. Warm freshwater or seawater treatments reduced the dry weight iodine content by 73% and 59%, respectively. Steam treatment was less efficient and only reduced the iodine content by 26%. Freshwater treatment resulted in a greater reduction in total solids and loss of water-soluble components, mainly reducing the content of ash and carbohydrates. Seawater treatment had a small effect on total solid content but altered the mineral profile leading to an increase in sodium and decrease in potassium content. The sensory profiles reflected the observed differences in composition as it revealed a significantly higher saltiness of the seawater-treated sample compared to other treatments, as well as a higher umami intensity compared to the freshwater-treated sample. The latter was characterized by low scores across all sensory attributes, indicating greater loss of flavour-active compounds. Further, including seawater-treated S. latissima at relatively low levels (0.5% and 1%) significantly altered the flavour of a commercial spinach soup compared to the same preparation without seaweed. Therefore, warm water treatment using seawater could be an alternative method for lowering the iodine content in brown seaweed while limiting nutrient loss and maintaining its flavour potential for applications in the food industry.

Long‐term monitoring of pikeperch (Sander lucioperca) populations under increasing temperatures and predator abundances in the Finnish coastal waters of the Baltic Sea

AbstractThe Baltic Sea has been under intense environmental changes in the recent decades, such as climate change, eutrophication and increasing abundance of top‐predators, which pose serious challenges to its aquatic life. For informed conservation measures and sustainable yields, we need to understand how the populations are being affected. Accordingly, we used long‐term data series (covering the period between 1980 and 2021) to assess how these changes have affected populations of an ecologically and economically important predatory fish, the pikeperch (Sander lucioperca), in the coastal waters of Finland in the northern Baltic Sea. We investigated the estimates of abundance and recruitment, commercial and recreational catch statistics and growth and mortality rates. We found a clear increase in the total catches in the northernmost part of the Finnish coast (Bothnian Bay) that were not explained by changes in fishing effort, indicating increased abundance, most likely due to higher water temperature. In the southern part of the study area (Archipelago Sea), density‐dependent factors prevented the development of particularly strong year classes, despite the beneficial conditions of warming seawater and consecutive warm summers. Individual growth has increased in younger age groups, contributing to an upward trend in the spawning population biomass. We also uncovered a declining trend in the total mortality in the southern area, despite increased abundances of cormorants and seals, explained by reduced total fishing mortality. These results show that the pikeperch is one of the species that has, thus far, benefited from the environmental change in the northern Baltic Sea, strengthening its role in the ecosystem.

Assessment of the stiffened panel performance in the OTEC seawater tank design: Parametric study and sensitivity analysis

Ocean thermal energy conversion (OTEC) is a process of generating electricity by exploiting the temperature difference between warm surface seawater and cold deep seawater. Due to the high static and dynamic pressures that are caused by seawater circulation, the stiffened panel that constitutes a seawater tank may undergo a reduction in ultimate strength. The current paper investigates the design of stiffening systems for OTEC seawater tanks by examining the effects of stiffening parameters such as stiffener sizes and span-over-bay ratio for the applied combined loadings of lateral and transverse pressure by fluid motion and axial compression due to global bending moment. The ultimate strength calculation was conducted by using the non-linear finite element method via the commercial software known as ABAQUS. The stress and deformation distribution due to pressure loads was computed in the first step and then brought to the second step, in which the axial compression was applied. The effects of pressure on the ultimate strength of the stiffener were investigated for representative stiffened panels, and the significance of the stiffener parameters was assessed by using the sensitivity analysis method. As a result, the ultimate strength was reduced by approximately 1.5% for the span-over-bay ratio of 3 and by 7% for the span-over-bay ratio of 6.

Record-breaking 2020 summer marine heatwaves in the western North Pacific

Record-breaking marine heatwaves (MHWs) occurred in the western North Pacific during the summer of 2020. These unprecedented MHWs were consistent with favorable large-scale conditions that are linked to an anomalous western North Pacific subtropical high (WNPSH), resulting mainly from sea surface temperature (SST) anomalies across the tropical oceans. In addition, a moderate La Niña-like pattern was also conducive to transporting warm seawater to the western North Pacific. Mixed-layer heat budgets suggest that surface heat flux contributed to the SST anomaly in the western subtropical Pacific. In contrast, oceanic heat advection dominanted in the South China Sea and the western equatorial Pacific. Numerical model experiments indicated that the tropical Indian Ocean SST anomalies were responsible for the enhanced WNPSH. The increased zonal SST gradient across the tropical Pacific also played an important role. Inter-ocean interactions can modulate climate variability through ocean-atmospheric coupling and deserve more attention when predicting MHWs within the context of global warming. In addition, it is critical to consider MHWs as a powerful tool in detecting acute, intense thermal stress events in the coral bleaching pre-warning system.

Long-lasting impact of winter North Atlantic Oscillation on Barents-Kara sea ice anomaly in recent decades

In this paper, the long-lasting impact of the winter North Atlantic Oscillation (NAO) on Arctic sea ice is investigated using reanalysis data, with focus on the Barents–Kara (BK) sea where the air-sea-ice response is closely associated with the interdecadal shift in the northern action center of the NAO. A significant negative correlation between the winter NAO and the late autumn BK sea ice has been dominant since the early 2000s, which is in sharp contrast to the extremely weak correlation before the late 20th century. When the northern center of the NAO retreats westward, a prevailing low-level southerly wind anomaly creates significant positive air temperature anomalies over the BK sea, and the induced ocean current strengthens the northward transport of warm sea water, resulting in a positive BK upper-layer ocean temperature anomaly and a negative sea ice anomaly until early spring. Entering summer, the preexisting less-than-normal sea ice causes the amount of solar shortwave radiation absorbed by the upper-layer sea water to significantly increase and thereby continues to warm up the upper layer of sea water and reduce the sea ice. The warmed sea water enables the negative sea ice anomaly to last until late autumn owing to its relatively large specific heat capacity. Thus, the NAO in the previous winter exerts a long-lasting impact on the BK sea ice.

Estimating global artisanal fishing fleet responses in an era of rapid climate and economic change

There is an urgent need to assess the extent to which the global fishing enterprise can be sustainable in the face of climate change. Artisanal fishing plays a crucial role in sustaining livelihoods and meeting food security demands in coastal countries. Yet, the ability of the artisanal sector to do so not only depends on the economic efficiency of the fleets, but also on the changing productivity and distribution of target species under rapid climate change in the oceans. These impacts are already leading to sudden declines, long-term collapses in production, or increases in the price of fish products, which can further exacerbate excess levels of fishing capacity. We examined historical changes (1950-2014) in technical efficiency within the global artisanal fishing fleets in relation to sea surface temperature anomalies, market prices by taxonomic group, and fuel costs. We show that temperature anomalies affected countries differently; while some have enhanced production from an increase in the resource distribution, which alter the structure of the ecosystem, others have had to adapt to the negative impacts of seawater warming. In addition, efficiency decreases are also related to rises in global marine fish price, whereby more labour and capital are attracted into the fishery, which in turn can lead to an excess in fleet capacity. Our results contribute to the understanding of how the effects of climate-induced change in the oceans could potentially affect the efficiency of artisanal fishing fleets.

Feasibility of ice sheet conservation using seabed anchored curtains.

Sea level rise is expected to be rapid and extremely damaging to coastal communities and infrastructure, with unavoidable losses and coastal protection costs in the tens of billions per year. Retreat of the Thwaites and Pine Island Glaciers is likely already in an unstable regime as their oceanic fronts are ablated by deep intruding layers of relatively warm seawater. Warm water can be blocked from reaching the grounding line by thin flexible buoyant curtains anchored to the seabed. The consequent reduction in ice shelf melting could result in increased ice sheet buttressing as the shelf makes contact with seabed highs. Flexible curtains are less costly than solid artificial barriers, more robust against iceberg collisions, and easier to repair or remove in the event of unforeseen side effects. We illustrate the technical viability of this approach by considering curtain design concepts that should withstand oceanographic forces, and feasible methods of installation. Suitable materials are commonly available. Installation of a seabed curtain in temperate ocean waters would be entirely within the capabilities of existing offshore and deep ocean construction techniques. Installing in polar waters presents severe challenges from icebergs, harsh weather, and brief working seasons, which can however, be overcome with present-day technology. An 80 km long curtain installed in 600 m deep waters on alluvial sediments could help stabilize Pine Island and Thwaites glaciers over the next few centuries at much lower cost ($40-80 billion + $1-2 billion/yr maintenance) than the global coastline protection (∼$40 billion/yr) needed due to their collapse.

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.

Structural and diagenetic signatures of a very shallow sub-volcanic intrusion into a carbonate platform (Albian, Basque-Cantabrian Basin, Northern Spain)

In several tectonic contexts and especially in hyper-extensive basins, magmatic rise may crosscut shallow marine carbonate series, forming either volcanic systems or only igneous intrusions at various depths. Impacts of these magmatic events on the surrounding carbonate sediments can be significant and are relatively well documented from a geometrical, sedimentological and hydrochemical point of view. Their diagenetic signature (e.g., early diagenetic phases in cases where magma reaches or approaches the surface) still remains poorly investigated. In this paper the authors use a multi-proxy approach combining morpho-structural, diagenetic (cement stratigraphy), geochemical (carbon and oxygen isotope, U–Pb dating) and sedimentological study to investigate the Larrano igneous body contemporaneous with the Urgonian limestones (Early Albian) of the Duranguesado platform, in the well-preserved and hyper-extended Basque-Cantabrian Basin. This investigative work produced several results: the first result, combining morpho-structural and sedimentological data, is the model of a basaltic magma rising along normal faults but stopping about 50 m below the paleo-seafloor; another is the detailed description the “Larrano eogenetic anomaly” that includes cataclastic fractures, dissolution, Fe oxy-hydroxides, ferroan saddle dolomite and magnesian calcite. Such phases form an early diagenetic overprint around the igneous body and testify to the thermal shock and warm seawater circulation occurring at the time of and just after the intrusion. Pre-intrusive and post-intrusive hydrothermally-influenced cements and facies are also recorded and are perfectly calibrated by a detailed cement stratigraphy associated with a layering model of the sedimentary units. The role of magmatic CO2 contribution is not quantified in the present study. Furthermore, the δ13C signature of various cements, micrites and bioclasts suggests no thermogenic methane contribution, unlike other Albian magmatic intrusions hosted by different lithologies and recorded at various depths below the paleo-seafloor.

Symbiodiniaceae in and ex hospite have differential physiological responses under different heat stress scenarios

ABSTRACT Extreme seawater temperatures are linked to increasingly frequent cnidarian bleaching, a breakdown of the symbiosis between host and endosymbiotic dinoflagellates. This can be driven by several anthropogenic stressors, of which seawater warming is a major and frequent one. It remains unclear whether this is caused by intrinsic properties of the host or exclusively by the symbiont. This study investigates the response to elevated temperatures of dinoflagellate symbionts in and ex hospite, particularly to find out whether thermal tolerance differs between endosymbionts and free-living micro-algae. Maximum quantum yield of photosystem II (Fv/Fm ) and symbiont cell density were measured in seven different cnidarian species and five cultures of isolated endosymbionts subjected to temperatures of 26°C (control), 30°C and 34°C for 21 days. Isolated dinoflagellate cells showed a susceptibility to elevated temperatures of 30°C, evidenced by a decrease in photochemical efficiency and cell density of the cultures, as well as a progressive disintegration of cellular structures and loss of pigmentation of all but two cultures during the first week of exposure. Bleaching of coral holobionts at 30°C could be explained by reduced density of algae cells in host tissue. This effect was particularly evident in soft corals. Exposure to 34°C resulted in drastic bleaching of stony coral species, anemones and jellyfish, and even the death of soft corals. Data from this study show different responses to elevated thermal conditions across several species and different genera of symbionts and emphasize the important role of dinoflagellate symbionts in the holobiont response to elevated seawater temperatures.

A performance study of R717 and R22 as the working fluid for OTEC plant

The purpose of this paper is to compare the thermal efficiency of an ocean thermal energy conversion (OTEC) cycle using R717 and R22 working fluids. An OTEC system typically operates at the temperature difference between the average warm surface seawater of 30 °C and the cold deep seawater of 8 °C. The temperature difference will then power a turbine to produce electricity. R22 and R717 are two potential working fluids to be used in the OTEC cycle to absorb heat due to their saturation temperature. However, R22 is associated with higher global warming potential and the global warming potential (GWP) of 1,760, compared to R717 with zero GWP. The study shows that the thermal efficiency of R22 is 0.211% higher than R717. Moreover, the thermal power required by the water circuit to cool/heat the OTEC circuit for R717 is 13% higher than R22. However, the required working fluid flow rate of the R717 system is 81.5% lower than R22, making the former significantly smaller in size.

Net Power Generation Control of OTEC Plant Using Rankine Cycle with Seawater Pumps by Warm Seawater Flow Rate Regulation*

In this research, net power generation control of an ocean thermal energy conversion (OTEC) plant using Rankine cycle is investigated. In the model construction, not only the seawater pumping powers described by static characteristics but also the net power output is taken into account. The dynamics of the heat exchangers are also considered, where they are represented as the first-order systems. For the plant model, proportional integral controller is designed so as to satisfy some specifications, where as the manipulated variable the warm seawater flow rate is adopted. The effectiveness of the proposed control system was confirmed by numerical simulations.

Zeolite-microfragmenting Media: A Potential Strategy to Accelerate Coral Growth

Coral reef is a critical underwater ecosystem that is rich in biodiversity. Coral growth has decreased drastically due to physical and chemical threats, such as the effect of warming seawater, fish bombing activities, and the effects of wastewater. The efficiency level of coral transplantation is determined by many factors, including the stability of the environment physical condition, the level of coral diversity, and the method of transplantation. The influence of the planting medium can also be a key factor in succeeding the coral transplantation process. The use of stable and natural growing media can be a solution to replace conventional growing media that have been used. Zeolite material is a medium that has many advantages such as amending the trace elemental contents of saltwater such as carbon absorbents, detoxifiers, ammonia remover, catalysts, promoting marine micro-algal growth, become a media for bacterial growth, etc. This review discusses the possibility of zeolites as the candidate media that can be used as a new medium in coral transplantation process to accelerate coral growth and maintain coral health by increasing the adaptation of corals to the effects of global climate change.

Rapid increase of pCO2 and seawater acidification along Kuroshio at the east edge of the East China Sea

Rates of seawater acidification and rise of partial pressure of CO2 (pCO2) at ocean margins are highly uncertain. In this study, nine years of time-series data sampled during 2010–2018 along Kuroshio Current near the East China Sea (ECS) were investigated. We found trends of surface seawater pCO2 at 3.70 ± 0.57 μatm year−1 and pH at −0.0033 ± 0.0009 unityear−1, both of which were significantly greater than those reported from other oceanic time series. Mechanistic analysis showed that seawater warming caused rapid rates of pCO2 increase and acidification under sustained DIC increase. The faster pCO2 growth relative to the atmosphere resulted in the CO2 uptake through the air-sea exchange declining by ~50 % (~−0.8 to −0.4 mol C m−2 year−1) over the study period. Our results imply that rapidly warming boundary currents could potentially present an elevated pCO2 trend, leading to a gradual reduction and eventual loss of oceanic CO2 uptake under climate change.

Relationship between Modern Deep-Sea Ostracods and Water Mass Structure in East Antarctica

This study investigated the relationship between the distribution of modern ostracod biofacies and environmental factors in Lützow–Holm Bay, off Cape Darnley, and off Totten Glacier in East Antarctica. We collected study samples from water depths of 219 to 987 m by the 61st Japanese Antarctic Research Expedition. Nineteen species belonging to 13 genera and 47 species belonging to 31 genera of ostracods were found in three samples from Lützow–Holm Bay and ten samples from off Totten Glacier, respectively. We found no ostracods in the samples off Cape Darnley. Q-mode cluster analysis reveals four ostracod biofacies (A to D). Antarctiloxoconcha frigida (Neale, 1967) and Australicythere polylyca (Müller, 1908) were common under the influence of cold water in the upper bathyal zone (biofacies A to C). The genus Krithe was the most abundant taxon in biofacies D with low dissolved oxygen and high-water temperature (0.38°C, 34.66, and 5.0 ml/L, respectively), indicating the presence of warm deep seawater, i.e., modified Circumpolar Deep Water. Thus, we have checked the relationships between the ostracod assemblages and the environmental parameters analyzed in Lützow–Holm Bay and off Totten Glacier, and so strengthened the previous ostracod and environmental data.

The investigation of optimum multi-component blends in organic Rankine cycle for ocean thermal energy conversion

This study investigates the effects of working fluids on the performance of an organic Rankine cycle (ORC) used in an Ocean Thermal Energy Conversion (OTEC) power plant. Working fluids of R1123, R161, R32 and their mixtures are employed. Parameters of pinch points, temperatures of deep cold and surface warm seawater, and efficiencies of pumps and expander are taken into consideration. The objective functions are either net power output or economic performance parameter, respectively. A numerical approach, gradient descent, is employed to solve the optimum mass fractions of mixture working fluids in the OTEC system. The results show that for pure working fluids, the net power output of the OTEC system using R1123 is 620.76 kW and is the highest, followed by R32 and R161, respectively. The economic performance parameter of the OTEC system using R32 is 6.28 m2/kW and is the best, followed by R1123 and R161, respectively. For net power output and economic performance, the two-component mixtures all outperform their pure working fluids of which they are composed. As for three-component mixture, the maximum Wnet and the minimum β and λ of R1123/R161/R32 mixture working fluid are obtained as 945.77 kW, 5.41 m2/kW, and 0.223 $/kW-h with the corresponding mass fractions of 0.72/0.18/0.1, 0.25/0.16/0.59, and 0.12/0.46/0.42, respectively. In addition, the three-component mixture, R1123/R161/ R32, performs best among all the working fluids, which is about 52.36% better than R1123 in net power output and is about 32% better than R717 in economic performance.