THERMAL REGIME AND STABILITY OF JURUMIRIM RESERVOIR (PARANAPANEMA RIVER, SAO-PAULO, BRAZIL)

Thermal regime and stability in Jurumirim Reservoir (São Paulo, Brazil) were studied for a year. Isothermy and thermal stratification were observed from June to September and from October to March, respectively. The annual heat budget was 14.0 Kcal . cm-2 and average heat gain per day was 67.2 cal . cm-2 . day-1. Maximum stability and wind work reached 324.2 and 3,037.5 g . cm . cm-2, respectively. According to thermal structure and heat content, Jurumirim Reservoir was classified as a warm tropical monomictic lake.

Temperature and thermal regime effects on the specific dynamic action of Bothrops alternatus (Serpentes, Viperidae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal regime of the Southeast Indian Ridge between 88°E and 140°E: Remarks on the subsidence of the ridge flanks

The flanks of the Southeast Indian Ridge are characterized by anomalously low subsidence rates for the 0-25 Ma period: less than 300 m Ma(-1/2) between 101 degrees E and 120 degrees E and less than 260 m Ma(-1/2) within the Australian-Antarctic Discordance (AAD), between 120 degrees E and 128 degrees E. The expected along-axis variation in mantle temperature (similar to 50 degrees C) is too small to explain this observation, even when the temperature dependence of the mantle physical properties is accounted for. We successively analyze the effect on subsidence of different factors, such as variations in crustal thickness; the dynamic contribution of an old, detached slab supposedly present within the mantle below the AAD; and depletion in phi(m), a parameter here defined as the "ubiquitously distributed melt fraction" within the asthenosphere. These effects may all contribute to the observed, anomalously low subsidence rate of the ridge flanks, with the most significant contribution being probably related to the depletion in phi(m). However, these effects have a deep-seated origin that cannot explain the abruptness of the transition across the fracture zones that delineate the boundaries of the AAD, near 120 degrees E and near 128 degrees E, respectively.

Heat budgets, thermal structure and dissolved oxygen in Brazilian reservoirs

A comparison of the thermal regime and oxygen distribution patterns of some Brazilian reservoirs was made. A strong latitudinal dependence of surface temperature, annual mean and annual range was found. Except for Tucurui Reservoir, a reservoir of the Equatorial zone, the lowest surface temperature of the year in the other compared reservoirs was observed from June to August while the highest extended from October to February. The decreasing trend of annual mean temperatures and thermal ranges was due to the increasing seasonal variability of insolation with the latitude. A positive relationship between the increase on thermal surface-bottom differences and the depth of water column was found for reservoirs of similar latitudes. A long thermal stratification (around four months) was evidenced in the lacustrine zone of reservoirs with a residence time higher than 40 days. Low fluctuation (<2%) of the annual variability of heat contents was observed for the Tucurui Reservoir, while in das Garcas Reservoir a manmade lake located in the frontier between tropical and temperate regions, the annual coefficient of variation attained 13%. Concerning the heat budgets, the value for the Tucurui Reservoir was two times higher than in das Garcas Reservoir. Both the morphometric and climatological factors affected the heat contents of the two compared reservoirs. In deep eutrophic reservoirs, a significant reduction on the oxygen concentrations in the hypolimnetic zone was frequently observed. In some oligotrophic stratified reservoirs, a decrease on oxygen with depth occurred when the temperature of the hypolimnion was higher than 20 degrees C and caused a biochemical oxygen demand. In das Garcas Reservoir, the actual oxygen deficits ranged from 0.40 to 1.52 mg.O-2.cm(-2) and appear to be linked to oxygen consumption after the senescence of Microcystis aeruginosa populations in the spring. But, other factors such as the allochthonous loads of organic matter also had an important role on the oxygen balance of das Garcas Reservoir.

Short- and long-term consequences of thermal variation in the larval environment of anurans

To survive adverse or unpredictable conditions in the ontogenetic environment, many organisms retain a level of phenotypic plasticity that allows them to meet the challenges of rapidly changing conditions. Larval anurans are widely known for their ability to modify behaviour, morphology and physiological processes during development, making them an ideal model system for studies of environmental effects on phenotypic traits. Although temperature is one of the most important factors influencing the growth, development and metamorphic condition of larval anurans, many studies have failed to include ecologically relevant thermal fluctuations among their treatments. We compared the growth and age at metamorphosis of striped marsh frogs Limnodynastes peronii raised in a diurnally fluctuating thermal regime and a stable regime of the same mean temperature. We then assessed the long-term effects of the larval environment on the morphology and performance of post-metamorphic frogs. Larval L. peronii from the fluctuating treatment were significantly longer throughout development and metamorphosed about 5 days earlier. Frogs from the fluctuating group metamorphosed at a smaller mass and in poorer condition compared with the stable group, and had proportionally shorter legs. Frogs from the fluctuating group showed greater jumping performance at metamorphosis and less degradation in performance during a 10-week dormancy. Treatment differences in performance could not be explained by whole-animal morphological variation, suggesting improved contractile properties of the muscles in the fluctuating group.

Geochronological (U–Pb, U–Th–total Pb, Sm–Nd) and geochemical (REE, 87Sr/86Sr, δ18O, δ13C) tracing of intraplate tectonism and associated fluid flow in the Warburton Basin, Australia

The Warburton Basin of central Australia has experienced a complex tectonic and fluid-flow history, resulting in the formation of various authigenic minerals. Geochemical and geochronological analyses were undertaken on vein carbonates from core samples of clastic sediments. Results were then integrated with zircon U–Pb dating and uraninite U–Th–total Pb dating from the underlying granite. Stable and radiogenic isotopes (δ18O, Sr and εNd), as well as trace element data of carbonate veins indicate that >200 °C basinal fluids of evolved meteoric origin circulated through the Warburton Basin. Almost coincidental ages of these carbonates (Sm–Nd; 432 ± 12 Ma) with primary zircon (421 ± 3.8 Ma) and uraninite (407 ± 16 Ma) ages from the granitic intrusion point towards a substantial period of active tectonism and an elevated thermal regime during the mid Silurian. We hypothesise that such a thermal regime may have resulted from extensional tectonism and concomitant magmatic activity following regional orogenesis. This study shows that the combined application of geochemical and geochronological analyses of both primary and secondary species may constrain the timing of tectonomagmatic events and associated fluid flow in intraplate sedimentary basins. Furthermore, this work suggests that the Sm–Nd-isotopic system is surprisingly robust and can record geologically meaningful age data from hydrothermal mineral species.

Bottom simulating reflector and gas seepage in Okinawa Trough: Evidence of gas hydrate in an active back-arc basin

To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation: to help gather enough methane into a small area and to modulate the thermal regime.

南海北部陆缘深水区构造－热演化与烃源岩成熟度史研究

Abstract In order to provide basic data for evaluation of the petroleum potential in the deep water area of the northern margin of the South China Sea (SCS), present-day thermal regime and basin tectonothermal evolution are reconstructed and the maturation history of the Cenozoic major source rocks in the study area is derived. The present-day geothermal regime in the deep water area of the northern margin of SCS is defined according to the geothermal gradient, thermal properties and heat flow data. Tectonic subsidence history is reconstructed based on borehole and seismic data, and accordingly the stretching episodes are determined from the subsidence pattern. Heat flow history in the deep water area of the northern margin of SCS is estimated on a finite time, laterally non-uniform and multi-episode stretching model. Maturation history of the main source rocks in the study area is estimated through EASYRo% kinetic model and thermal history, and the potential of petroleum in the deep water area of the northern margin of SCS is evaluated based on the data above. The results show that the present-day geothermal regime in the deep water area of the northern margin of SCS is characterized by “hot basin” with high geothermal gradient (39.1±7.4℃/km) and high heat flow (77.5±14.8 mW/m2), and that the Qiongdongnan Basin (QDNB) underwent three stretching episodes and consequently suffered three heating episodes (Eocene, Oligocene and Pliocene time) with highest paleo-heat flow of 65～90 mW/m2 at the end of the Pliocene, that the Pearl River Mouth Basin (PRMB) two stretching and two heating episodes (Eocene, Oligocene time) with highest paleo-heat flow of 60～70 mW/m2 at the end of the Oligocene, and that the source rocks matured drastically responding to the heating episodes. There are four hydrocarbon generation kitchens in the deep water area of the northern margin of SCS which are favor of its bright petroleum perspective. Tectonothermal analysis indicates that the present-day geothermal regime which is characterized with “hot basin” in the deep water area of the PRMB resulted mainly from the Cenozoic stretching as well as faulting and magmatic activities during the Neotectonic period, and that the Pliocene heating episode of the QDNB is coupled with the transition from sinistral to dextral gliding of the Red Rive fault, and that the deep water basins in the northern margin of SCS are typical of multiple rifting which caused multi-episode heating process.

句容海安区块热史、成烃史与二次生烃

Jurong -Hai'an block of lower Yangtz area is one of the important petroleum exploration area among the residual marine basins in the south China. In the history of the basin's evolution, the strongly compressing, napping, folding and deforming during Indosinian to Yanshan epoch resulted in destruction of the early formed petroleum pool. Therefore, the strategy exploration of the secondary hydrocarbon generation and later formation of petroleum pool was brought forward for petroleum exploration and planning in the study area..On the basis of tectonic and sedimentary as well as present-day thermal regime evolution, using vitrinite reflectance and apatite fission track data and the paleo-heat flow based method, the basin's thermal history is reconstructed and hence the strata's temperature history are obtained. In addition, the maturation histories of the main four sets of marine hydrocarbon source rocks in the block are calculated. Furthermore, taking the maturity in the end of early Cretaceous as the original maturity and according to the formulas fitted by the secondary hydrocarbon generation model, the secondary hydrocarbon generation potential of the four sets of source rock is evaluated.The results of thermal history reconstruction show that Jurong-Hai'an block was under an uniform thermal setting during the Caledonian to Hercynian period and characterized by middle heat flow (52~57rnW/ m2). The uniform thermal setting was divided during and after Indosinian to Yanshan epoch. Wuwei area of southern Anhui province was under the high heat flow setting(~90 mW/m2)between 236Ma and 137Ma; Jurong area of southern Jiangsu ,Huangqiao area and Subei basin reached its maximum heat flow of 90,84 and 78-82 mW/m2 at 101Ma,157Ma and 56Ma respectivelyThe study of secondary hydrocarbon generation shows that the upper Paleozoic and Triassic source rocks have excellent secondary hydrocarbon generation potential. Silurian source rock posses some secondary hydrocarbon generation. Cambrian source rock, however, nearly has no secondary hydrocarbon generation. Overall there are no advantages of secondary hydrocarbon generation in the southern area of Jiansu. The intensity of secondary hydrocarbon generation in North Jiangsu basin is definitely better than that in the southern area of Jiangsu.

Climate effects and benthic-pelagic coupling in the North Sea

The North Sea is one of the most biologically productive ecosystems in the world and supports important fisheries. Climate-induced changes occurred in the pelagic ecosystems of the North Sea during the 1980s. These changes, which have been observed from phytoplankton to fish and among permanent (holoplankton) and temporary (meroplankton) plankton species, have resulted in alterations in plankton community composition and seasonality. Until now, the effects of climate-driven changes on biological linkages between pelagic and benthic ecosystems have not been examined. The present study indicates that changes in benthic organisms could have a profound effect on the trophodynamics of the pelagos. We demonstrate this by analyses of a long-term time series of North Sea plankton and sea surface temperature data. We discover that pronounced changes in the North Sea meroplankton, mainly related to an increased abundance and spatial distribution of the larvae of a benthic echinoderm, Echinocardium cordatum, result primarily from a stepwise increase in sea temperature after 1987 that has caused warmer conditions to occur earlier in the year than previously. Key stages of reproduction in E. cordatum, gametogenesis and spawning, appear to be influenced by winter and spring sea temperature and their larval development is affected by the quantity and quality of their phytoplankton food. Our analyses suggest that a new thermal regime in the North Sea in winter and spring may have benefited reproduction and survival in this benthic species. As a result, E. cordatum may be altering the trophodynamics of the summer pelagic ecosystem through competition between its larvae and holozooplankton taxa.

Unanticipated biological changes and global warming

Evidence of global warming is now unequivocal, and studies suggest that it has started to influence natural systems of the planet, including the oceans. However, in the marine environment, it is well-known that species and ecosystems can also be influenced by natural sources of large-scale hydro-climatological variability. The North Atlantic Oscillation (NAO) was negatively correlated with the mean abundance of one of the subarctic key species Calanus finmarchicus in the North Sea. This correlation was thought to have broken down in 1996, however, the timing has never been tested statistically. The present study revisits this unanticipated change and reveals that the correlation did not break down in 1996 as originally proposed but earlier, at the time of an abrupt ecosystem shift in the North Sea in the 1980s. Furthermore, the analyses demonstrate that the correlation between the NAO and C. finmarchicus abundance is modulated by the thermal regime of the North Sea, which in turn covaries positively with global temperature anomalies. This study thereby provides evidence that global climate change is likely to alter some empirical relationships found in the past between species abundance or the ecosystem state and large-scale natural sources of hydro-climatological variability. A theory is proposed to explain how this might happen. These unanticipated changes, also called ‘surprises’ in climatic research, are a direct consequence of the complexity of both climatic and biological systems. In this period of rapid climate change, it is therefore hazardous to integrate meteo-oceanic indices such as the NAO in models used in the management of living resources, as it has been sometimes attempted in the past.

Synchronous response of marine plankton ecosystems to climate in the Northeast Atlantic and the North Sea

Over the last few decades, global warming has accelerated both the rate and magnitude of changes observed in many functional units of the Earth System. In this context, plankton are sentinel organisms because they are sensitive to subtle levels of changes in temperature and might help in identifying the current effects of climate change on pelagic ecosystems. In this paper, we performed a comparative approach in two regions of the North Atlantic (i.e. the Northeast Atlantic and the North Sea) to explore the relationships between changes in marine plankton, the regional physico-chemical environment and large-scale hydro-climatic forcing using four key indices: the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO), the East Atlantic (EA) pattern and Northern Hemisphere Temperature (NHT) anomalies. Our analyses suggest that long-term changes in the states of the two ecosystems were synchronous and correlated to the same large-scale hydro-climatic variables: NHT anomalies, the AMO and to a lesser extent the EA pattern. No significant correlation was found between long-term ecosystem modifications and the state of the NAO. Our results suggest that the effect of climate on these ecosystems has mainly occurred in both regions through the modulation of the thermal regime.

Conséquences de l’acclimatation à différents régimes thermiques sur les taux métaboliques standards des tacons du saumon de l’Atlantique(Salmo salar)

Les poissons vivant au sein d’une rivière sont soumis à des variations circadiennes de température pouvant influencer la croissance, la digestion et le métabolisme standard. Les modèles bioénergétiques utilisant les fonctions métaboliques pour déterminer la croissance d’un poisson ont souvent été élaborés avec des poissons acclimatés à des températures constantes. Ces modèles pourraient sous-estimer l’énergie dépensée par un poisson soumis à des températures fluctuantes. En utilisant la respirométrie par débit intermittent, les objectifs de ce travail étaient : (1) de quantifier les différences entre les taux métaboliques standards de poissons acclimatés à une température constante (20.2 oC ± 0.5 oC) et à des fluctuations circadiennes de température (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) et (2) comparer deux méthodologies pour calculer les taux métaboliques standards de poissons sujets aux fluctuations circadiennes de températures : respirométrie (a) en température constante ou (b) en température fluctuante. Les poissons acclimatés à des fluctuations circadiennes de température ont des taux métaboliques standards plus élevés que des poissons acclimatés à une température constante. À 20.2 oC ± 0.5 oC, les taux métabolique standards ont été de 25% à 32% plus bas pour des poissons maintenus à une température constante que pour des poissons gardés sous des fluctuations circadiennes de température. Les méthodologies utilisées pour estimer les taux métaboliques standards de poissons sujets aux fluctuations de température offrent des résultats similaires.

Réponse métabolique du saumon Atlantique (Salmo salar) aux fluctuations journalières de température : rôles de la température d’acclimatation et de l’historique thermique

En général, le métabolisme des poissons est estimé à des valeurs de température constantes, mais les effets de fluctuations journalières de température similaires à celles retrouvées en milieu naturel semblent peu connus. Les objectifs du présent mémoire sont de quantifier les effets de la température moyenne d’acclimatation et d’évaluer les effets de l’historique thermique des individus, sur les réponses métaboliques de tacons de saumon Atlantique (Salmo salar) aux fluctuations journalières de la température. Des tacons provenant de deux rivières, une fraîche et une chaude, ont été acclimatés à un maximum de quatre régimes thermiques (constant 15 °C ou 20 °C, fluctuant 15 °C ± 2.5 °C ou 20 °C ± 2.5 °C) et leur taux métabolique standard estimés par respirométrie par débit-intermittent. Les fluctuations journalières de température (15 °C ± 2.5 °C) près de l’optimum thermique pour cette espèce (16 °C) n’affectent pas le taux métabolique standard. À l’opposé, les fluctuations journalières de température plus chaudes (20 °C ± 2.5 °C) augmentent de 35.4% le taux métabolique standard des tacons de la rivière plus chaude, mais pas ceux des poissons de la rivière fraîche. Ainsi, la température moyenne à laquelle sont acclimatés les poissons peut affecter leur réponse métabolique aux fluctuations journalières de température, mais cette réponse peut varier entre populations provenant de rivières présentant des régimes thermiques différents. Enfin, grâce aux données de métabolisme précédemment estimées, un modèle de métabolisme standard a été développé pour des tacons de saumon Atlantique soumis à des fluctuations journalières de température.

Évolution spatio-temporelle du pergélisol alpin marginal au mont Jacques-Cartier, massif des Chic-Chocs, Gaspésie (Qc)

L’objectif de ce mémoire est d’acquérir une connaissance détaillée sur l’évolution spatiale de la température de surface du sol (GST) au mont Jacques-Cartier et sur la réponse thermique de son îlot de pergélisol alpin aux changements climatiques passés et futurs. L’étude est basée sur un ensemble de mesures de température (GST, sous-sol) et de neige, ainsi que des modèles spatiaux de distribution potentielle de la GST et des simulations numériques du régime thermique du sol. Les résultats montrent que la distribution de la GST sur le plateau est principalement corrélée avec la répartition du couvert nival. Au-dessus de la limite de la végétation, le plateau est caractérisé par un couvert de neige peu épais et discontinu en hiver en raison de la topographie du site et l’action des forts vents. La GST est alors couplée avec les températures de l’air amenant des conditions froides en surface. Dans les îlots de krummholz et les dépressions topographiques sur les versants SE sous le vent, la neige soufflée du plateau s’accumule en un couvert très épais induisant des conditions de surface beaucoup plus chaude que sur le plateau dû à l’effet isolant de la neige. En raison de la quasi-absence de neige en hiver et de la nature du substrat, la réponse du pergélisol du sommet du mont Jacques-Cartier au signal climatique est très rapide. De 1978 à 2014, la température du sol a augmenté à toutes les profondeurs au niveau du forage suivant la même tendance que les températures de l’air. Si la tendance au réchauffement se poursuit telle que prévue par les simulations climatiques produites par le consortium Ouranos, le pergélisol pourrait disparaître d’ici à 2040-2050.