Large Temperature Changes Research Articles

Exploring the heat capacity and magnetocaloric behaviors of rare-earth based multicomponent (Ce0.71Pr0.07Nd0.22)2Fe17‐xSix alloys

The rare–earth based multicomponent (Ce0.71Pr0.07Nd0.22)2Fe17−xSix (x = 0–0.6) alloys were fabricated by conventional arc melting following the standard annealing and quenching processes. The prepared alloys were characterized by X-ray diffraction (XRD), backscattered scanning electron (BSE) microscope, energy dispersive X-ray (EDX) spectroscopy, magnetization, and heat capacity measurements. Combination of Rietveld refinement of XRD patterns, EDX/BSE analyses confirm the formation of stable rhombohedral Th2Zn17 type crystal structure with R-3 m space group in all studied samples. The investigated samples experience second-order phase transition as confirmed through phenomenological universal scaling analysis. The magnetic entropy change (−ΔSM) and associated relative cooling power (RCP) values for all compositions were found in the range of 1.1–1.4 Jkg−1K−1 and 55–66 Jkg−1 under magnetic field change (ΔH) of 0–1 T. The ΔSM curves as a function of temperature exhibit a wide working temperature range (δTFWHM) over 40 K for all studied compositions. The performance-cost ratio − ΔSM/cost and RCP/cost values are estimated to be 0.1 JK−1$−1 and 5.0 J$−1, respectively. In particular, a large adiabatic temperature change of 7.36 K and 8.09 K was achieved for x = 0.2 and x = 0.4, respectively, at low ΔH= 0–1 T. The better performance-cost ratio and good magnetocaloric properties with near-zero magnetic hysteresis loss may make these alloys promising candidates for magnetic refrigeration.

Observation of superior magnetocaloric performance in multicomponent (Ce0.71Pr0.07Nd0.22)2Fe17-xAlx (x = 0.6, 0.8) compounds

Magnetocaloric effect (MCE) in multicomponent (Ce0.71Pr0.07Nd0.22)2Fe17-xAlx (x = 0.6, 0.8) alloys was studied using the heat capacity and magnetization data. Both the samples crystallize in a rhombohedral Th2Zn17-type structure. The maximum values of magnetic entropy change (-ΔSM) without hysteresis loss are found to be 1.19 Jkg−1K−1 and 1.23 Jkg−1K−1 with relative cooling power (RCP) values of 52.3 Jkg−1 and 66.4 Jkg−1 under an applied field change of 0–1 T for x = 0.6 and 0.8, respectively. Meanwhile, a wide working temperature range (44/54 K) and a large adiabatic temperature change (ΔTad) of 5.6/5.8 K were also achieved for the present compounds.

Enhanced elastocaloric effect and mechanical properties of Gd-doped Ni-Co-Mn-Ti-Gd metamagnetic shape memory alloys

Improving elastocaloric effect (eCE) and mechanical properties is the key to developing high-performance eCE cooling materials. In this paper, the metamagnetic shape memory alloys Ni35.5Co13.5Mn35Ti15-xGdx (x = 0–0.9) were successfully prepared by arc melting method, and the effects of Gd substitution for Ti on the martensitic transformation (MT) temperature, phase composition, microstructure, eCE and mechanical properties of the alloys were systematically investigated. With the introduction of Gd elements, the transformation temperature shifts to a low temperature, and the mechanical properties of the alloy are also enhanced. The fracture strength increased from 980 MPa (x = 0) to 1142 MPa (x = 0.9). At room temperature (RT), a large adiabatic temperature change of + 13.5 K/− 12.7 K is obtained after loading/unloading, and a constant temperature change of + 5.6 K/− 5.5 K is obtained without apparent degradation under the compressive stress of 400 MPa during 61 cycles for all-d metal Heusler Ni36.5Co13.5Mn35Ti14.9Gd0.1 alloy. The adiabatic temperature change of 13.5 K exceeds the elastocaloric temperature change of most NiMn-based alloys available at present, and the mechanical properties of Ni-Co-Mn-Ti-Gd alloy are at a high level among the NiMn-based alloys. The precipitation of the Gd-rich second phase along the grain boundaries is intrinsically responsible for the improved mechanical properties.

Zooplankton community size structure across lakes within a semi-arid landscape: the effect of temperature and salinity

AbstractBody size is a master trait controlling biological communities and ecosystem functioning. Mean population size not only depends on the size of individuals, but also on the size distribution of individuals within the population. Mean community size is additionally influenced by the composition of species (larger- or smaller-sized species). Shallow lakes within semi-arid landscapes are prone to experience large changes in temperature and salinity, which affect the zooplankton size structure. Higher temperatures are expected to result in smaller average body size, while the effect of salinity appears to depend on the range under study. Here we analyze zooplankton body size patterns across shallow lakes from the semi-arid central region of Argentina. All community size descriptors point to decreasing size and a narrow size range at higher temperatures. On the other hand, the maximum average community body size occurred at intermediate (~30 gL−1) salinity levels. The combined effect of both variables resulted in a bell-shaped pattern, with maximum community body size toward lower temperatures and intermediate salinities. Based on future temperature scenarios, one may anticipate an overall decrease in community body size. But such prediction is strongly conditioned by regional and local trends in salinity.

Effect of Hydrophilic Polyurethane on Interfacial Shear Strength of Pisha Sandstone Consolidation under Freeze-Thaw Cycles.

The W-OH type polyurethane (W-OH) has been proven to be an economical and environmentally friendly slope protection solution for slope maintenance in Pisha sandstone areas. However, the Pisha area belongs to a typical temperate continental climate with large diurnal temperature changes in winter, spring, and autumn and freezing and thawing occurring alternately between days and nights. Under freeze-thaw cycle conditions, the effect of slope treatment largely depends on the interface shear strength between W-OH-treated Pisha sandstone and pristine sandstone. Therefore, this paper studies the interfacial shear strength and long-term durability of Bisha sandstone consolidation (W-OH-treated Pisha sandstone) and Pisha sandstone under freeze-thaw cycles. First, the effects of different W-OH concentrations and different water contents on the freeze-thaw cycle interface were studied using a direct shear test. Based on the experimental results, the W-OH material was further modified with ethylene vinyl acetate (EVA). Finally, the damaged surface of the sample was observed through an ultra-depth-of-field microscope, and the damage mechanism of the interface caused by the freeze-thaw cycles was further discussed. The experimental results show that the peak shear strength at the interface increases with the increase in W-OH concentration and decreases with the increase in freeze-thaw cycles. The cohesion at the interface generally increases with the increase in W-OH concentration and reaches a maximum value of 43.6 kPa when the W-OH concentration is 10%. At the same time, under the condition of high water content, the curing of the W-OH material has no significant effect on the bonding performance of the interface. Using EVA to modify the W-OH material can improve the freeze-thaw durability of the interface. After modification, the interfacial cohesion of the sample increases with the increase in the EVA concentration and can reach 162% of the original. Using an ultra-depth-of-field microscope, it was found that the repeated solidification-melting action of water between the interfaces makes the consolidated body on the damaged surface fall off, resulting in cracks. As the water content between the interfaces increases, the damage to the material is greater. However, the addition of EVA can fill the uncovered pores of W-OH cement, thereby improving the cohesion at the interface and effectively alleviating the freeze-thaw damage caused by the high water content at the interface. The results of this study can provide some theoretical references for slope treatment in the Pisha sandstone area using W-OH materials.

Multicaloric effect in metamagnetoelectric linarite spin chain PbCuSO4(OH)2

The cross response of magnetic and electric fields on the ribbon CuO2 spin chain is used to investigate the multicaloric properties of linarite PbCuSO4(OH)2. The theory is built on a frustrated Heisenberg scheme. Following the magnetoelectric properties, the thermodynamic and caloric coefficients report multiple field–dependent criticalities attributed to the metamagnetoelectric effect. The isentropes of PbCuSO4(OH)2 particularly exhibit about five and six major sharper dips in magnetic and electric field sweeps respectively. This corresponds to the metamagnetoelectric transitions which in turn come along with a large temperature change in the entropy and heat capacity analyses and then increasing the cooling ability of linarite. Further analysis of the magnetocaloric as well as the electrocaloric effects shows a significant growth during the metamagnetoelectric transitions. A clear relationship is established between the magnetoelectric coupling constant, the magnetocaloric and the pyroelectric coefficients, witnessing the metamagnetoelectric transitions-driven multicaloric effect in PbCuSO4(OH)2. Obviously, the resulting total adiabatic temperature change expressed through the magnetocaloric or the pyroelectric coefficient depends on the sign of the magnetoelectric coupling constant. Therefore, the occurrence of the metamagnetoelectric effect with several magnetic and electric field-dependent transitions characterized by a set of positive and negative increases in the magnetoelectric coupling provides a great advantage by increasing the possibilities of a significant multicaloric effect in the linarite PbCuSO4(OH)2 cuprate spin chain.

Earth-air thermal siphon as a passive air-conditioning system for an arid climate

A passive air-conditioning system for an arid climate with large temperature changes is proposed using a thick wall with pipes in its interior, and the siphon effect caused by natural convection. The thick wall acts as a capacitance term, absorbing heat from hot air at daytime, and releasing it to cold air at night. The system is modeled through a semi-analytic model that combines the use of scale analysis, a harmonic treatment, and the enhanced multipole method. This model is validated by means of a finite difference numerical scheme, that includes the terms neglected by the semi-analytic model, with favorable results. Furthermore, a parametric analysis is made considering the variation of the pipe’s radius and length, and the wall’s thermal parameters and thickness. It is shown that pipe’s radius and length have a larger influence on the system’s performance than the rest of parameters. The design seems to perform as expected, with promising outcomes. Further studies to improve this work are mentioned.

Global beta-diversity of angiosperm trees is shaped by Quaternary climate change.

As Earth's climate has varied strongly through geological time, studying the impacts of past climate change on biodiversity helps to understand the risks from future climate change. However, it remains unclear how paleoclimate shapes spatial variation in biodiversity. Here, we assessed the influence of Quaternary climate change on spatial dissimilarity in taxonomic, phylogenetic, and functional composition among neighboring 200-kilometer cells (beta-diversity) for angiosperm trees worldwide. We found that larger glacial-interglacial temperature change was strongly associated with lower spatial turnover (species replacements) and higher nestedness (richness changes) components of beta-diversity across all three biodiversity facets. Moreover, phylogenetic and functional turnover was lower and nestedness higher than random expectations based on taxonomic beta-diversity in regions that experienced large temperature change, reflecting phylogenetically and functionally selective processes in species replacement, extinction, and colonization during glacial-interglacial oscillations. Our results suggest that future human-driven climate change could cause local homogenization and reduction in taxonomic, phylogenetic, and functional diversity of angiosperm trees worldwide.

Investigation on ferroelectric, dielectric and pressure sensing properties of samarium substituted lead magnesium niobate-lead titanate oxide

In the last several decades, researchers have been developing hydraulic pressure sensors suitable in harsh oil mediums with high figures of merit. A well-known columbite method is used to prepare a series of phase pure electroceramics Pb(1-1.5y)Smy[(Mg1/3Nb2/3)1-xTix]O3 (Sm(y)-PMN(x)PT) with x = 0.20, 0.30; and y = 0.010, 0.025 for possible applications as hydraulic pressure sensors. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to study the crystal structure, microstructure, and morphology of the sintered ceramics. The frequency and temperature-dependent dielectric and ac conductivity analyses were performed over a temperature range of 300–480 K to understand the phase stability and phase transition temperatures. Room temperature (297 K) polarization-electric field and PUND analysis confirmed the large polarization (∼30–40 μC/cm2) in the investigated compositions. The hydrostatic pressure-dependent relative capacitance change was examined using a lab-made setup for different compositions for the pressure varying from 0 to 50 MPa. The percentage sensitivity varies with samarium and titanium compositions that range from 0.078 MPa−1 to 0.197 MPa−1. The highest relative change in capacitance was obtained for Pb0.963Sm0.025[(Mg1/3Nb2/3)0.80Ti0.20]O3 (Sm0.025-PMN0.20PT) ceramic with percentage sensitivity 0.197 MPa−1, nearly double to our earlier report on Pb[(Mg1/3Nb2/3)0.7Ti0.3]O3 composition. The improvement in sensitivity may be due to inherent properties, such as slim hysteresis, low tangent loss (∼0.002–0.1), large change in phase transition temperature (∼25 K) due to dielectric dispersion and relaxor-like nature compared to other investigated systems.

Research on MPPT control strategy based on the Perturbation observation method

About traditional disturbance observation of larger changes in the external environment, the need for successive change step length, thus slow convergence speed of the shortcomings, based on traditional disturbance observation method, will be the main factors influencing the photovoltaic battery power curve (temperature, light intensity) is introduced into the control strategy of, when external conditions change dramatically, the method can directly reach the optimal duty ratio near, in this way, the slow convergence speed of the traditional perturbation observation method is effectively improved, and the dynamic tracking performance is optimized. In Matlab/Simulink, the improved control strategy model is built to verify that the improved control strategy can significantly improve the convergence speed and efficiency of the photovoltaic power generation system under the working condition of large changes in temperature and external illumination intensity.

Electrocaloric effect in BaTiO3 multilayer capacitors with first-order phase transitions

Electrocaloric (EC) materials, presenting large adiabatic temperature change or isothermal entropy change under the application (or removal) of electric fields, offer an efficient alternative to caloric heat pumps for replacing hazardous gases used in traditional vapor-compression systems. Recently, a large EC temperature change of 5.5 K have been reported in Pb(Sc0.5Ta0.5)O3 multilayer ceramic capacitors (Nair et al 2019 Nature 575 468) thanks to its strong first-order phase transition and a temperature span of 13 K has been reported in a prototype based on these capacitors (Torelló et al 2020 Science 370 125). However, the toxicity of lead forces researchers to find eco-friendly materials exhibiting competitive EC performances. Here, we study the EC effect in lead-free BaTiO3 multilayer capacitors using an infrared camera. Unlike commercial BaTiO3 capacitors, we prepared our samples without sacrifying the first-order phase transition in BaTiO3 while a low amount of 0.2 mol% Mn was added as an acceptor dopant to improve electrical resistivity. Their EC adiabatic temperature variations show two peaks versus temperature, which match BaTiO3 two first-order phase transitions, as observed by differential scanning calorimetry. We measured a temperature drop of ∼0.9 K over a temperature range of 70 K under 170 kV cm−1, starting at 30 °C near the tetragonal-to-orthorhombic phase transition. Under the same electric field, a maximum temperature change of 2.4 K was recorded at 126 °C, at BaTiO3’s Curie temperature. Our findings suggest that further optimized BaTiO3 capacitors could offer a path for designing lead-free caloric cooling prototypes.

Large adiabatic temperature change in Bi0·5Na0·5TiO3 ferroelectric ceramics in the vicinity of depolarization temperature

Large adiabatic temperature change in Bi0·5Na0·5TiO3 ferroelectric ceramics in the vicinity of depolarization temperature

Indian Ocean variability changes in the Paleoclimate Modelling Intercomparison Project

Abstract. The Indian Ocean exhibits multiple modes of interannual climate variability, whose future behaviour is uncertain. Recent analysis of glacial climates has uncovered an additional El Niño-like equatorial mode in the Indian Ocean, which could also emerge in future warm states. Here we explore changes in the tropical Indian Ocean simulated by the Paleoclimate Model Intercomparison Project (PMIP4). These simulations are performed by an ensemble of models contributing to the Coupled Model Intercomparison Project 6 and over four coordinated experiments: three past periods – the mid-Holocene (6000 years ago), the Last Glacial Maximum (21 000 years ago), the last interglacial (127 000 years ago) – and an idealized forcing scenario to examine the impact of greenhouse forcing. The two interglacial experiments are used to characterize the role of orbital variations in the seasonal cycle, whilst the other pair focus on responses to large changes in global temperature. The Indian Ocean Basin Mode (IOBM) is damped in both the mid-Holocene and last interglacial, with the amount related to the damping of the El Niño–Southern Oscillation in the Pacific. No coherent changes in the strength of the IOBM are seen with global temperature changes; neither are changes in the Indian Ocean Dipole (IOD) nor the Niño-like mode. Under orbital forcing, the IOD robustly weakens during the mid-Holocene experiment, with only minor reductions in amplitude during the last interglacial. Orbital changes do impact the SST pattern of the Indian Ocean Dipole, with the cold pole reaching up to the Equator and extending along it. Induced changes in the regional seasonality are hypothesized to be an important control on changes in the Indian Ocean variability.

An Active Pixel-Matrix Electrocaloric Device for Targeted and Differential Thermal Management.

More than 55% of electronic failures are caused by damage from localized overheating. Up to now, there is still no efficient method for targeted temperature control against localized overheating. Although some existing thermal management devices handle this issue by full coverage cooling, it generates a lot of useless energy consumption. Here, a highly efficient pixel-matrix electrocaloric (EC) cooling device is reported, which can realize a targeted and differential thermal management. The modified poly(vinylidene fluoride-tertrifluoroethylene-chlorofluoroethylene) reaches a large adiabatic temperature change of 7.8 K and is more suitable for thermal transfer and electrostatic actuation at high frequencies. All active pixels in the EC cooling device exhibit a stable temperature span of 4.6 K and a heat flux of 62mWcm-2 , which is more than twice that of the one-layer EC device. Each refrigeration pixel can be independently controlled and effectively cooled down the localized overheating site(s) in situ. The surface temperature of the simulated central processing unit decreases by 33.2 K at 120 s after applying this EC device. Such a compact, embeddable, low cost, and active solid-state pixel-matrix cooling device has great potential for localized overheating protection in microelectronics.

Large negative electrocaloric response induced by nanoscale phase transition in (Bi, Na)TiO3-based thin films

Electrocaloric effect (ECE) offers an efficient and environmentally friendly route for solid-state cooling. Either positive or negative ECE could exhibit a large adiabatic temperature change (ΔT). Compared to the positive electrocaloric response, the investigation of negative ECE is lagging behind, largely due to the fact that its origin is still elusive. In this work, the negative ECE behavior of conventional ferroelectric thin films, namely 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNBT), was studied. A remarkable ΔT of −26.1 K was acquired near 160 °C under a moderate electric field of 875 kV/cm, attributing to the ferroelectric phase transition in the polar nanoregions from rhombohedral (R3c) to tetragonal (P4bm), as confirmed by temperature-dependent dielectric permittivity, Raman spectra, and x-ray reciprocal space mapping. The BNBT thin film presents a high electrocaloric coefficient (ΔT/ΔE) of 0.0298 K cm kV−1, transcending that of the most reported negative electrocaloric response of thin films.

Geothermal Anomalies and Coupling with the Ionosphere before the 2020 Jiashi Ms6.4 Earthquake

Rock temperature reflects the adjustment in crustal stress, and the fluctuation of ionospheric electron concentration is closely related to short-term disturbances of the stress field. Their coupling may reveal short-term effects before strong earthquakes. This study explores the rock temperature changes and mechanical-electrical coupling in the lithosphere–ionosphere before the Jiashi Ms6.4 earthquake on 19 January 2020. The observed data were detrended by general polynomial piecewise fitting; three observation points within 150 km of the epicenter were found to show significant temperature fluctuations in the 15 days before the earthquake. The peak occurred synchronously five days before the earthquake, and the variation range was approximately 10−3 orders of magnitude. Five days before the earthquake, the electromagnetic satellite Zhangheng-1 synchronously observed an anomalous electron concentration in orbit near the epicenter, with a maximum value of 2.01 × 1010 m−3. The loading/unloading response ratio (LURR) was calculated using small earthquakes within 100 km of the epicenter; it showed that the large changes in rock temperature and the ionosphere occurred at high LURR, indicating high-stress accumulation in the region. Various anomalies appeared simultaneously and may indicate fault rupture, which may be caused by an acoustic-gravity wave, indicating a synchronous coupling between the lithosphere atmosphere and the ionosphere.

Evaluation of Mechanical Properties of Different Casing Drilling Steels

An investigation into the mechanical properties of K55, N80, and P110 steels commonly used for casing drilling was carried out together with microstructural and fractographic analysis. The results show that P110 steel consisted of almost fully tempered martensite and exhibited a synergy combination of static tensile, dynamic impact, and fatigue crack propagation properties among the three steels, possessing a higher fatigue limit and deeper crack tolerance before failure occurred. The K55 steel consisted of the pearlite and network structure of ferrite and possessed a high strain hardening exponent and low impact property, which led to the more suitable application under incidental large overload and temperature change, but it was unsuitable under the condition of higher impact force. The properties of N80 steel were moderate, and its fatigue property was higher than that of K55 and lower than that of P110; its incidental overload resistance was also higher than that of P110. The casing drilling steel can be selected according to the environment.

Nature and origin of variations in pelagic carbonate production in the tropical ocean since the mid-Miocene (ODP Site 927)

Abstract. Marine plankton is an important component of the global carbon cycle. Whereas the production and seafloor export of organic carbon produced by the plankton, the biological pump, has received much attention, the long-term variability in plankton calcification, controlling the carbonate counter pump, remains less well understood. However, it has been shown that changes in pelagic calcification (biological compensation) could affect the ocean's buffering capacity and thus regulate global carbon budget on geological timescales. Here we use Neogene pelagic sediments deposited on the Ceara Rise in the tropical Atlantic to characterize the variability in pelagic carbonate production with a focus on warm climates. A re-evaluation of published records of carbonate accumulation at the Ceara Rise reveals a systematic increase in sedimentation rates since the late Miocene, but the carbonate accumulation rate does not show a clear trend. Instead, we observe substantial orbital timescale variability in carbonate accumulation, combined with a trend towards less carbonate on average at sites located below 4 km, likely due to the effect of carbonate dissolution. To evaluate long-term changes against possible orbital-scale variability, we generated new high-resolution records of carbonate accumulation rate at Ocean Drilling Program (ODP) Site 927 across two Quaternary interglacials (MIS 5 and MIS 9), the Pliocene warm period (MIS KM5) and the Miocene Climatic Optimum (MCO). We observe that the highest carbonate accumulation rates occurred during the Pliocene but that each of the studied intervals was characterized by large-magnitude orbital variability. Prominent variations in carbonate accumulation prior to the Quaternary preservation cycles appear to follow Earth obliquity and eccentricity. These results imply that pelagic carbonate accumulation in the tropical ocean, buffered from large temperature changes, varied on orbital timescales. The magnitude of the orbital-scale variability was similar or even higher than the long-term mean differences among the studied intervals. Since preservation can be excluded as a driver of these changes prior to the Quaternary, the observed variations must reflect changes in the export flux of pelagic biogenic carbonate. We conclude that the overall carbonate production by pelagic calcifiers responded to local changes in light, temperature, and nutrients delivered by upwelling, which followed long orbital cycles, as well as to long-term shifts in climate and/or ocean chemistry. The inferred changes on both timescales were sufficiently large such that when extrapolated on a global scale, they could have played a role in the regulation of the carbon cycle and global climate evolution during the transition from the Miocene warm climates into the Quaternary icehouse.

Evolution of high-temperature extremes over the main Euro-Mediterranean airports

The increasing intensity and frequency of high-temperature events in response to climate change can potentially impact the aviation industry, since aircraft takeoff and landing performances depend on near-surface air temperature. Previous studies have combined climate data with aircraft technical data to estimate the future impact of rising high temperatures on aircraft takeoff. They found a decrease of maximum takeoff weights and the lengthening of takeoff distances. The Mediterranean region is a climate change “hot spot” area, specially concerned by extreme high-temperatures increase. In this study, the magnitude and trends of the daily maximum near-surface temperature extremes in summer were analysed over major airports in Southwestern Europe. Trends in the period 1961–2014 were analysed from observations and reanalysis. Future changes by 2021–2050 and 2071–2100, with respect to 1961–2005, were analysed from simulations performed with Regional and Global Climate Models (RCMs and GCMs). Before assessing future climate projections, climate models were evaluated in present climate, and the RCM and GCM ensembles were compared to each other. No clear added value was found for RCMs over GCMs in present climate at the airport scale in these terms. GCMs project larger temperature changes than RCMs over the same locations. Multi-model ensemble mean projected changes under the RCP8.5 scenario range between + 1.7 and + 3.2 ^{circ }C by the near term, and between + 4.9 and + 8.5 ^{circ }C by the long term, across the airports and the RCM and GCM ensembles. This increase of high-temperature extremes would impact airport operations. Adaptation or mitigation policies would become necessary.

The effect of temperature on haemoglobin-oxygen binding affinity in regionally endothermic and ectothermic sharks.

Haemoglobin (Hb)-O2 binding affinity typically decreases with increasing temperature, but several species of ectothermic and regionally endothermic fishes exhibit reduced Hb thermal-sensitivity. Regionally endothermic sharks, including the common thresher shark (Alopias vulpinus) and lamnid sharks such as the shortfin mako shark (Isurus oxyrinchus), can maintain select tissues and organs warmer than ambient temperature by retaining metabolic heat with vascular heat exchangers. In the ectothermic bigeye thresher shark (Alopias superciliosus), diurnal movements above and below the thermocline subject the tissues, including the blood, to a wide range of operating temperatures. Therefore, blood-O2 transport must occur across internal temperature gradients in regionally endothermic species, and over the range of environmental temperatures encountered by the ectothermic bigeye thresher shark. While previous studies have shown temperature-independent Hb-O2 affinity in lamnid sharks, including shortfin mako, the Hb-O2 affinity of the common and bigeye thresher sharks is unknown. Therefore, we examined the effect of temperature on whole blood Hb-O2 affinity in common thresher shark and bigeye thresher shark. For comparison, analyses were also conducted on the shortfin mako shark and two ectothermic species, blue shark (Prionace glauca) and spiny dogfish (Squalus acanthias). Blood-O2 binding affinity was temperature-independent for common thresher shark and shortfin mako shark, which should prevent internal temperature gradients from negatively affecting blood-O2 transport. Blue shark and spiny dogfish blood-O2 affinity decreased with increasing temperature, as expected, but bigeye thresher shark blood exhibited both a reduced temperature-dependence and a high Hb-O2 affinity, which likely prevents large changes in environment temperature and low environmental oxygen from affecting O2 uptake.