Decrease In Temperature Gradient Research Articles

Investigation of Air Turbulence Intensity Effect on the Flame Structure in Different Flame Holder Geometry

In this paper, the effect of air turbulence intensity on the flame structure in various radii and lengths of a flame holder numerically studied. Finite volume method is used to solve the governing equations. The obtained numerical results using realizable k-e and β-PDF models show a good agreement with the experimental data. The results show that flame holder with greater lengths yield shorter flame lengths and higher flame temperature. Also, it is observed that by increasing flame holder radius, flame length slightly decreases at first and then it increases. When holder radius increases, flame temperature increases at first and thereafter decreases. The obtained results indicate that increasing air turbulence intensity results in considerable decrease in flame length, flame temperature, NO formation and temperature gradient in the flame zone.

Pilot-Scale Gas Double-Dynamic Solid-State Fermentation for the Production of Industrial Enzymes

Presently, the modern solid-state fermentation (SSF) industry remains traditional; there are few designs available for bioreactors operating in SSF on a large scale, which is mainly caused by the problems in engineering that appear when scaling up this technique. Gas double-dynamic solid-state fermentation (GDD-SSF) technology has been proven available in industrial production of biopesticide. However, there are few other examples using the GDD-SSF technology in other fermentation industries. To test its applicability in other fermentation industries, the self-made pilot-scale bioreactor for GDD-SSF of 800 L was used for the production of various typical enzymes. The comparing effects of liquid-solid ratio and air pressure on enzyme production in different fermentation modes were investigated. Results showed that GDD-SSF offered greater advantages to the static SSF in industrial enzyme preparation, such as pectinase, glucoamylase, protease, and cellulase. It could not only improve enzyme activities with a largest increase reached 2.84 times but also shorten the fermentation period. Furthermore, decreased temperature gradient was found in GDD-SSF, which is crucial for online controlling in industry production. Thus, the necessary and successful pilot-scale fermentation of various enzymes was a rational indication of applicability to large-scale SSF by GDD-SSF.

A precise search for drastic temperature shifts of the past 40,000 years in southeastern Europe

Climatic models simulate abrupt oscillations that are associated, in the North Atlantic, with Dansgaard‐Oeschger and Heinrich events. However, the geographic extension of temperature anomalies is largely uncontrolled due to the scarcity of quantitative records of sufficient time resolution on the European continent. Here, we propose, based on a recently developed temperature proxy (TEX86), a reconstruction of millennial‐scale temperature variations in a Black Sea sediment archive for the last 40,000 years. Prior to any paleoclimatological interpretations the effects of potential bias, such as seasonality and depth of maximum export production on temperature reconstructions, are considered for the Black Sea. Based on previous work, a tentative method for temperature corrections, taking into account varying terrigenous inputs, is further proposed. Reconstructed temperatures for Black Sea core MD042790 were remarkably stable during the last glacial. However, significant shifts toward lower temperatures of 2°C occurred during Heinrich events 2 and 3. The deglaciation displayed a temperature increase of 10°C consistent with neighboring European reconstructions. A Younger Dryas cooling of approximately 5–6°C was clearly expressed in the reconstruction. In notable contrast to observations from nearby archives, Heinrich events imprinted our glacial temperature record consistent with a strong reorganization of oceanic circulation and a large spreading of the temperature anomaly from the North Atlantic toward the southeast. Furthermore, in contrast to high‐latitude records, our Black Sea record lacks the signatures of Dansgaard‐Oeschger interstadials, suggesting a decreasing temperature gradient away from the North Atlantic.

Decreasing Asian summer monsoon intensity after 1860 AD in the global warming epoch

The trend of the Indian summer monsoon (ISM) intensity and its nature during the past 100 and 200 years still remain unclear. In this study we reconstructed the ISM intensity during the past 270 years from tree ring δ18O at Hongyuan, eastern edge of the Tibet Plateau. The monsoon failures inferred from δ18Otree ring correlate well with those recorded in ice cores, speleothem, and historical literature sources. 22.6, 59.0, and 110.9-years frequency components in the Hongyuan δ18Otree ring series, which may be the responses to solar activities, synchronize well with those recorded in other ISM indices. A notable feature of the reconstructed ISM intensity is the gradually decreasing trend from about 1860 to the present, which is inversely related to the increasing temperature trend contemporaneously. Such “decreasing ISM intensity–increasing temperature” tendency can also be supported by ice core records and meteorological records over a wide geographic extension. The decrease in sea surface temperature gradient between tropical and north Indian Ocean, and the decrease in land-sea thermal contrast between tropical Indian Ocean and “Indian sub-continent–western Himalaya” are possibly responsible for the observed decreasing ISM trend.

In-Plane Elastic Buckling of Shallow Parabolic Arches under an External Load and Temperature Changes

This paper studies the in-plane stability of rotationally restrained shallow arches subjected to a vertical uniform load and temperature changes below 100°C. The virtual work principle method was used to establish the nonlinear equilibrium and buckling equations. Analytical solutions for the nonlinear in-plane symmetric snap-through and asymmetric bifurcation critical loads are obtained. Then the effects of the uniform temperature field and temperature gradients on the in-plane stability for arches are studied. The influence of temperature variations on the critical loads for both the symmetric snap-through and asymmetric bifurcation modes was significant. The critical loads increase with an increase of the uniform temperature field and a decrease of temperature gradients. Furthermore, the effect of temperature changes on the critical load increases with the span-rise ratio m of arches. Increasing the stiffness of the rotational springs will increase the effect of the uniform temperature field but reduce the effect of the temperature gradients.

A finite element thermal analysis of various dowel and core materials

Thermal analysis of the temperature and stress distribution of parallel sided, threaded and non-threaded dowels and core materials under thermal loading within a maxillary central incisor using a three dimensional finite element study. 3D models of endodontically treated maxillary central incisor with parallel sided, threaded and non- threaded post and core materials were simulated using the ANSYS software. Materials simulated were parallel sided cast gold post and core, parallel sided fibre reinforced composite (FRC) post and core, and parallel sided, threaded, prefabricated stainless steel post and amalgam core. Thermal loads simulating hot (60 degree C/ 333K) and cold (15 degree C/288K) liquid were applied for 15 seconds at the incisal edge. The temperature changes at the selected nodes were obtained on the various post and core materials, interface between post and dentin, interface between core and dentin, within the dentin and within the cement layer. Temperature and stress distribution pattern were represented in numerical and color coding and results interpreted. Thermal stresses arises as a result of temperature changes. A decreased temperature gradient of the metallic dowels and core (T1 hot - 0.002K, T3 hot - 1.071K, T1 cold -0.99K, T3 cold - 0K) were obtained than that of the FRC dowel and core of 1.982K(hot) and1.55K(cold) respectively due to the higher thermal conductivity of the metals. Higher thermal stress values of 3.567 Mpa(hot) and 3.092 Mpa(cold) respectively were obtained for the FRC dowels and higher stress values of 39.679 Mpa(hot) and 57.855 Mpa(cold) respectively were also obtained for the FRC cores. These values indicated that thermal stresses of the FRC dowel and core were greater than that of cast gold dowel and core and prefabricated stainless steel dowel and amalgam core due to its high coefficient of thermal expansion. Maximum stress values of the FRC dowel and core of 1.87 Mpa(hot) and 2.57 Mpa(cold) respectively were also generated in the cement layer, core and metal ceramic crown. The junction of the metal ceramic crown and dentin demonstrated the maximum stress. Higher thermal stress values of 59.162 ± 10 Mpa were obtained in the restoration and the coronal portion of the dentin than the stress levels of .0039 ± 10 Mpa in the supporting bone due to an increased thermal expansion. Non-metallic dowel and core materials such as fibre reinforced composite dowels (FRC) generate greater stress than metallic dowel and core materials. This emphasized the preferable use of the metallic dowel and core materials in the oral environment.

A spatio-temporal reconstruction of Holocene temperature change in southern Scandinavia

Holocene mean July ( TJul) and mean January ( TJan) temperatures were reconstructed at Lake Trehörningen in southwest Sweden using pollen–climate calibration functions and converted into anomalies relative to modern temperatures. The anomalies were applied to 28 meteorological stations in Denmark, with each station adjusted to account for spatial variability in both TJuland TJan. The resulting reconstructions were merged to create composite TJuland TJanrecords. The individual reconstructions were also used to establish the parameterization of the TJuland TJanvalues, resulting in Holocene temperature maps for all of Denmark. Low TJulvalues characterised southern Sweden and Denmark at the start of the Holocene, followed by an increase during the early Holocene. Likewise, TJanwas initially low at the start of the Holocene, followed by an increase between 10 500 and 9900 cal. BP. Thereafter, TJanwas relatively stable between 9900 and 8000 cal. BP. The general increase in temperature during the early Holocene was accompanied by a decrease in the amplitude of the mean monthly temperature record, indicating that a maritime climate was established at this time. Maximum TJuland TJanare recorded during the mid-Holocene interval from 8000 to 4500 cal. BP, with consistently high July temperatures (>18°C) between 6700 and 5400 cal. BP. During the late Holocene, both TJuland TJangradually decreased. The Holocene temperature maps of Denmark reveal spatial patterns in both summer and winter temperature. In the summer, an east–west decreasing temperature gradient, related to a maritime effect, has persisted in Denmark throughout the Holocene. In contrast, the temperature in winter has varied spatially along subtle coastal–inland and topographical gradients. Various mechanisms have been invoked to explain the Holocene trends in temperature, including the melting of the Scandinavian Ice Sheet, changes in insolation, and changes in the dominant type of atmospheric circulation affecting northern Europe.

Reply

Reply: We would like to thank Dr Dahlqvist and colleagues for their interest and insightful commentaries regarding our review. As stated in the article, our purpose with the article was to summarize the parameters most commonly used in clinical practice to guide volemic resuscitation in the scenarios of severe sepsis/septic shock. We agree with the authors that there may be important limitations concerning macrocirculatory variables as end points of fluid resuscitation during sepsis and that perfusional parameters must be taken considerably into account. However, every parameter used to guide resuscitation in critical illness, whether hemodynamic or perfusional, is subject to criticisms. As the authors appropriately acknowledged, the correlation between most macrocirculatory parameters and tissue perfusion is weak. In addition, the precise relationship between global hemodynamics and microcirculatory blood flow remains incompletely understood. For instance, some studies demonstrated that increasing MAP from 65 to 85 mmHg does not significantly affect microcirculatory blood flow or tissue perfusion (1, 2). Although normalization of macrocirculatory hemodynamic variables is often insufficient to guarantee microcirculatory optimization of septic patients, one must remember that MAP is a key feature of the cardiovascular system and that the occurrence of hypotension of less than 60 mmHg during the course of sepsis is independently associated with mortality (3). We believe, therefore, that the initial approach should be optimization of macrohemodynamic variables, but the therapy obviously should not be limited to these parameters. Besides the variables described in the review, clearly several other hemodynamic and perfusional parameters may be used to guide fluid resuscitation during sepsis. We agree that the markers of skin perfusion are among these end points. Markers such as capillary refill time and gradient temperatures have been described as indicators of inadequate tissue perfusion in circulatory shock (4) and after initial resuscitation (5). Nevertheless, to our knowledge, no prospective randomized large study has been reported that evaluated these variables as end points for fluid resuscitation in early stages of severe sepsis/septic shock. Skin perfusion parameters may be subject to biases such as room temperature and derangements in thermoregulatory response (like in anesthetized patients) and even distributive shock may intervene in skin temperature and capillary refill time (4). Vincent et al. (6) described that a cardiac index less than 1.8 L/min−1 m−2 was associated with a decrease in toe ambient temperature gradient of 5°C and that the increase in this gradient precedes the augmentation in skin oxygen partial pressure during recovery. A similar correlation, however, was not found in septic shock patients (6). Recently, new devices such as capillary microscopy, laser Doppler flowmetry, and sidestream dark field were incorporated to research in intensive care. These techniques allowed the evaluation of microcirculation in "real time" and demonstrated that even when macrohemodynamic variables and global parameters of perfusion are "normalized," regional microcirculation dysfunction could persist and lead to irreversible tissue damage. However, microcirculatory imaging is still investigational in humans and has not been incorporated into routine practice. In addition, important issues related to the limitations of these technologies in "real life" are the limited number of human microcirculatory studies; the visualization only of body surface microcirculation, which might not reflect vital organs microcirculatory dysfunction; the complex interpretation of microcirculatory imaging data; and the difficulty in depicting a parallel to the clinical sepsis stages (7). An intact microcirculatory network is a critical intermediary between the cardiovascular system and tissue oxygenation. Once microcirculation serves as the bridge between macrocirculation and tissue oxygenation, by tracking the response of variables related to tissue perfusion such as acid-base parameters, lactate, and venous oxygen saturation, we are indirectly evaluating the effectiveness of tissue perfusion (8). In our opinion, until now the best evidence-based therapeutic approach for hemodynamic optimization in sepsis is based on the adjustment of circulatory support and the evaluation of global tissue perfusion. We hope that briefly new important studies focused on therapeutic interventions concerning microcirculation may allow a significant improvement in the management of septic patients based on the interplay between macrocirculatory parameters, global perfusion markers, and direct microcirculatory optimization. Fernando José da Silva Ramos Luciano Cesar Pontes Azevedo Research and Education Institute Hospital Sírio-Libanê São Paulo, Brazil

Transport and consumption of oxygen and methane in different habitats of the Håkon Mosby Mud Volcano (HMMV)

The Håring;kon Mosby Mud Volcano is a highly active methane seep hosting different chemosynthetic communities such as thiotrophic bacterial mats and siboglinid tubeworm assemblages. This study focuses on in situ measurements of methane fluxes to and from these different habitats, in comparison to benthic methane and oxygen consumption rates. By quantifying in situ oxygen, methane, and sulfide fluxes in different habitats, a spatial budget covering areas of 10–1000‐m diameter was established. The range of dissolved methane efflux (770– 2 mmol m−2 d−1) from the center to the outer rim was associated with a decrease in temperature gradients from 46°C m−1 to < 1°C m−1, indicating that spatial variations in fluid flow control the distribution of benthic habitats and activities. Accordingly, total oxygen uptake (TOU) varied between the different habitats by one order of magnitude from 15 m−2 d−1 to 161 m−2 d−1. High fluid flow rates appeared to suppress benthic activities by limiting the availability of electron acceptors. Accordingly, the highest TOU was associated with the lowest fluid flow and methane efflux. This was most likely due to the aerobic oxidation of methane, which may be more relevant as a sink for methane as previously considered in submarine ecosystems.

Influence of thermal stabilization on the solute concentration of the melt in directional solidification

Experiments on Al–25 at%Ni peritectic alloy consisting of melting followed by thermal stabilization ranging from 0 to 2 h were carried out in a Bridgman-type furnace. Temperature distribution, microstructure evolution and solute concentration in the mushy zone are characterized. An analytical model is proposed to evaluate the Ni concentration of the melt after thermal stabilization. Effect of temperature gradient and volume fraction of liquid phase in the mushy zone on the Ni concentration of the melt is discussed. The steady state Ni concentration of the melt is inappropriately below the initial Ni concentration of the sample. The deviation increases with decreasing temperature gradient. Finally, the influence of thermal stabilization on the solute concentration of the melt is discussed based on a comparison of Al–Ni peritectic alloys with Al–Ni hyper-eutectic alloys and Al–Cu hypo-eutectic alloys.

Modeling on Dendrite Growth of Medium Carbon Steel during Continuous Casting

AbstractDendrite growth is an important phenomenon during steel solidification. In the current paper, a numerical method was used to analyse and calculate the dendrite tip radius, dendrite growth velocity, liquid concentration, temperature gradient, cooling rate, secondary dendrite arm spacing, and the dendrite tip temperature in front of the solid/liquid (S/L) interface for the solidification process of medium carbon steels during continuous casting. The current model was well validated by published models and measurement data. The results show that in the continuous casting process, the dendrite growth rate is dominated by the casting speed. Dendrite growth rate, liquid concentration at the S/L interface, temperature gradient and cooling rate decrease with proceeding solidification and solid shell thickness growth, while other parameters such as dendrite tip radius, secondary dendrite arm spacing, and dendrite tip temperature in front of the S/L interface become larger with solidification progress and solid shell thickness growth. Parametric investigations were carried out. The effects of the stability coefficient, temperature gradient and casting speed on the micro‐structural parameters were discussed. Under the same conditions, higher casting speed promotes coarser secondary dendrite arm spacing and enlarges the dendrite tip radius, while decreasing temperature gradient, reducing the dendrite growth rate and making the solute distribute more uniform.

Comparative effect of texture and microstructure on the magnetostriction of directionally solidified Tb 0.3Dy 0.7Fe 1.95 alloy

Adopting modified Bridgman technique, alloy of Tb 0.3Dy 0.7Fe 1.95 was directionally solidified at 70 cm/h under decreasing temperature gradient, starting from 100 °C/mm and studied for microstructural features, grain orientation and magnetostriction. At the onset of solidification, <110> texture nucleates and grows. As the solidification front moves away from the chilled end, the texture changes to <211>, which is favourable for obtaining large magnetostriction. However, a contradictory effect is seen in the microstructure, wherein the deleterious pro-peritectic (Tb,Dy)Fe 3 starts appearing, when the solidification front moves away from the chilled end. As a result, the beneficial effect of achieving <211> texture is subdued by the detrimental effect caused by the formation of pro-peritectic phase.

Studies of protein folding pathways

Protein folding is a problem of great importance in both the life sciences and biotechnology industries. This review begins with a brief summary of the physics of protein folding in vivo, which we believe would provide a theoretical basis for the kinetic control of protein folding. This is followed by a summary of the established refolding methods, which are categorized according to their process kinetics. Molecular simulations are used to present the concept of establishing dynamic solution environments that mimic the molecular machinery employed for high efficiency protein folding in vivo to enhance the kinetic partitioning of the native conformation. In practice, the use of “SMART” polymers for protein folding in a decreasing temperature gradient mimics the capture-release mechanism of GroEL/GroES/ATP and promotes protein folding and inhibits protein aggregation. Oscillation of the oxidative/reductive potential of the solution by periodic loading of redox chemicals promotes the reshuffling of disulfide bridges, mimicking the action of protein disulfide isomerase (PDI), and results in increased refolding yields. Realization of the simulated “oscillatory hydrophobic driving force” that mimics the quality control system in the endoplasmic reticulum (ER) may be of enormous practical value for protein folding at high concentrations.

Thermal Structure of Laminar Methane/Air Flames: Influence of H2 Enrichment and Reactants Preheating

The Rayleigh scattering technique has been applied to a V-shaped laminar flame in order to investigate the effect of reactant temperature on the thickness and thermal structure of an H2-enriched laminar methane-air flame. A systematic comparison of experimental and numerical results obtained with the GRI3.0 chemical mechanism is provided. First, the effects of reactant temperature on the pure methane-air flame are presented. A decrease in flame thickness and higher temperature gradients in the flame front are observed, and the maximum temperature gradient is shifted toward lower progress variable values. The preheat zone is substantially modified by the reactant preheating. Globally, the numerical predictions are in good agreement with the experimental results and validate the measurements. In addition, the effects of H2 enrichment on the thermal methane/air flame thickness are presented for a reactant temperature of 300 K. We show that the main role of H2 enrichment is to increase the temperature gradient and to shift toward lower values of the thermal progress variable c the location of the maximum temperature gradient. The reactivity of the mixture is strongly increased. At constant equivalence ratio, the burnt gas temperature is not modified by the H2 enrichment, and the analysis can be done either in c or T space. Finally, the effect of reactant preheating on H2/CH4/air flames (40% H2 dilution in volume) is investigated. The flame thickness is found to be lowered when reactant temperature is increased, but unlike the preheated methane-air flame, the localization of the maximum temperature gradient is not found to be markedly shifted. The reactivity of the mixture is rather controlled by the H radicals produced by H2 dilution than the reactant preheating.

Effects of temperature gradients on elastic modulus and compression strength of the saturated frozen clay

The uniaxial compression tests for the deep remolded saturated clay at various temperature gradients and average temperatures were performed. The test results indicate that the elastic modulus of frozen clay at different average temperature increases with the decrease of temperature gradients and the increasing rates are enhanced as average temperature increases. The compression strength at different average temperature also increases with the decreasing of temperature gradients, but the increasing rates are enhanced as temperature gradient decreases. The linear models for estimating the elastic modulus and the compression strength of the saturated clay are presented by considering the effects of the average temperature and the temperature gradient.

Columnar to equiaxed transition during growth of a univariant eutectic

In this work the transition from columnar to equiaxed growth is studied during the solidification of the univariant eutectic L→ α(Al) + θ-Al2Cu in the ternary Al–Cu–Ag system. The experimental technique used is upwards solidification with a controlled cooling rate. In the lower part of the sample where the temperature gradient is high, a cellular eutectic is observed. When the temperature gradient decreases, the morphology first changes into two-phase dendrites and finally into an equiaxed eutectic. When the amount of Ag is increased, the formation of eutectic colonies becomes easier. Also, a higher cooling rate facilitates the formation of eutectic colonies. The addition of TiB2 does not influence the nucleation of eutectic colonies. Although the composition is on the eutectic groove, primary α(Al)-dendrites are found in the samples with TiB2. This leads to segregation effects due to the density difference between α(Al) and the liquid.

Dose-dependent benefit of nitroglycerin on microcirculation of patients with severe heart failure

Microcirculatory abnormalities are frequently observed in patients with severe heart failure and correlate to worse outcomes. We tested the hypothesis that nitroglycerin dose-dependently improves perfusion in severe heart failure and that this could be monitored by measuring central-peripheral temperature gradient and with Sidestream Dark Field imaging of the sublingual mucosa. A dose-response study was performed in 17 patients with cardiogenic shock (n = 9) or end-stage chronic heart failure (n = 8) admitted to Erasmus University Medical Center. We did hemodynamic measurements at baseline and during increasing infusion rates of nitroglycerin (up to a maximum dose of 133 microg min(-1)). As parameters of tissue perfusion, we measured central-peripheral temperature gradient (delta-T) and sublingual perfused capillary density (PCD). Nitroglycerin dose-dependently decreased mean arterial pressure (p < 0.001) and cardiac filling pressures (both central venous pressure (CVP) and pulmonary capillary wedge pressure: p < 0.001). It increased cardiac index (p = 0.01). Nitroglycerin decreased delta-T (p < 0.001) and increased sublingual PCD (p < 0.001). Significant changes in delta-T and PCD occurred earlier, i.e., at a lower doses of NTG, than changes in global hemodynamics. Macrohemodynamic and microcirculatory responses to nitroglycerin infusion were consistent in patients with either cardiogenic shock or end-stage chronic heart failure. Changes in microcirculatory parameters occurred independently of changes in cardiac index. Nitroglycerin dose-dependently increases tissue perfusion in patients with severe heart failure, as observed by a decrease in central-peripheral temperature gradient and an increase in sublingual perfused capillary density.

Influence of bottom frictional effects in sill regions upon lee wave generation and implications for internal mixing

A cross-sectional nonhydrostatic model using idealized sill topography is used to examine the influence of bottom friction upon unsteady lee wave generation and flow in the region of a sill. The implications of changes in shear and lee wave intensity in terms of local mixing are also considered. Motion is induced by a barotropic tidal flow which produces a hydraulic transition, associated with which are convective overturning cells, wave breaking, and unsteady lee waves that give rise to mixing on the lee side of the sill. Calculations show that, as bottom friction is increased, current profiles on the shallow sill crest develop a highly sheared bottom boundary layer. This enhanced current shear changes the downwelling of isotherms downstream of the sill with an associated increase in the hydraulic transition, wave breaking, and convective mixing in the upper part of the water column. Both short and longer time calculations with wide and narrow sills for a number of sill depths and buoyancy frequencies confirm that increasing bottom friction modifies the flow and unsteady lee wave distribution on the downstream side of a sill. Associated with this increase in bottom friction coefficient, there is increased mixing in the upper part of the water column with an associated decrease in the vertical temperature gradient. However, this increase in mixing and decrease in temperature gradient in the upper part of the water column is very different from the conventional change in near-bed temperature gradient produced by increased bottom mixing that occurs in shallow sea regions as the bottom drag coefficient is increased.

Changes in the Interannual Surface Air Temperature Variability in the Northern Hemisphere in Response to Global Warming

This paper examines long-term change in the interannual variability in surface air temperature and its cause by using monthly data generated in climate change experiments (1851-2100) performed using two models. Regions north of 20°N are analyzed. Anomalies are defined as high-pass filtered values with a cutoff period of 30 years. Interannual variabilities of anomalies are expressed as the root mean square value for a 30 year period.Before global warming (around year 1900), the interannual variability in temperature is large over sea areas north of 50°N. This is because a large gradient of sea ice concentration brings about a large temperature gradient there. The interannual variability decreases generally in a cold season at high latitudes with global warming. In contrast to the general decrease of the interannual variability, there are some regions where it increases locally north of regions that show significant decrease around the Arctic. It can be understood that these phenomena are brought about by the decrease in the sea ice concentration gradient (i.e., the decrease in the temperature gradient) in the southern part of the polar region and the increase in the sea ice concentration gradient (i.e., the increase in the temperature gradient) in the northern part, due to the northward shift of sea ice edges. However, the degree of the decrease of the interannual variability is larger than that of the increase. This is because the global decrease of the temperature gradient strengthens the decrease of the interannual variability and weakens the increase. In addition, even over regions without sea ice, there are some areas where the interannual variability decreases. This is also because the temperature gradient decreases globally.

In-situ sediment temperature measurements and geochemical porewater data suggest highly dynamic fluid flow at Isis mud volcano, eastern Mediterranean Sea

Isis mud volcano is located on the upper slope of the Nile deep-sea fan and has been described as the surface expression of a deep-seated gas chimney [Loncke, L., Gaullier, V., Mascle, J., Vendeville, B., 2002. Shallow structure of the Nile deep-sea fan: interactions between structural heritage and salt tectonics; consequences on sedimentary dispersal. In: CIESM (Ed.), Turbidite systems and deep-sea fans of the Mediterranean and the Black seas. CIESM Workshop Series. vol. 17. Monaco]. Detailed geothermal and geochemical investigations of Isis MV have been carried out during the NAUTINIL (2003) and MIMES (2004) cruises within the framework of the Euro-margins/Mediflux project. Sediment temperatures of more than 40 °C at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity. Rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of Isis MV. The microbathymetry along dive tracks of the submersible Nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology. At the center, porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments, whereas the chlorinity of cores taken at short distances away is equal to bottom water values. Applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies, which points to a transient regime of variable fluid flow, possibly accompanied by episodic mud eruptions. Numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud.