Photosynthetic responses of the coral Montipora digitata to cold temperature stress

Coral bleaching events have become more frequent and widespread, largely due to elevated sea surface temperatures. Global climate change could lead to increased variability of sea surface temperatures, through influences on climate systems, e.g. El Nino Southern Oscillation (ENSO). Field observations in 1999, following a strong ENSO, revealed that corals bleached in winter after unusually cold weather. To explore the basis for these observations, the photosynthetic responses of the coral species Montipora digitata Studer were investigated in a series of temperature and light experiments. Small replicate coral colonies were exposed to ecologically relevant lower temperatures for varying durations and under light regimes that ranged from darkness to full sunlight. Photosynthetic efficiency was analyzed using a pulse amplitude modulated (PAM) fluorometer (F-0, F-m, F-v/F-m), and chlorophyll a (chl a) content and symbiotic dinoflagellate density were analyzed with spectrophotometry and microscopy, respectively. Cold temperature stress had a negative impact on M digitata colonies indicated by decreased photosynthetic efficiency (F-v/F-m), loss of symbiotic dinoflagellates and changes in photosynthetic pigment concentrations. Corals in higher light regimes were more susceptible to cold temperature stress, Moderate cold stress resulted in photoacclimatory responses, but severe cold stress resulted in photodamage, bleaching and increased mortality. Responses to cold temperature stress of M digitata appeared similar to that observed in corals exposed to warmer than normal temperatures, suggesting a common mechanism. The results of this study suggest that corals and coral reefs may also be impacted by exposure to cold as well as warm temperature extremes as climate change occurs.

Experimental study of phase equilibria in the PbO-ZnO-"Fe2O3"-(CaO+SiO2) system in air for the lead and zinc blast furnace sinters (CaO/SiO2 weight ratio of 0.933 and PbO/(CaO+SiO2) ratios of 2.0 and 3.2)

Experimental studies on phase equilibria and liquidus in the multicomponent system PbO-ZnO-CaO-SiO2-FeO-Fe2O3 in air have been conducted over the temperature range between 1323 K (1050 degreesC) and 1623 K (1350 degreesC) to characterize the phase relations of the complex slag systems encountered in lead and zinc blast furnace sinters. The liquidus in two pseudoternary sections ZnO-Fe2O3-(PbO + CaO + SiO2) with the CaO/SiO2 weight ratio of 0.933 and PbO/(CaO + SiO2) weight ratios of 2.0 and 3.2 have been constructed.

Effect of cold wire inclination on temperature fluctuation measurements in a heated jet

Hot-wire anemometers at low operating currents are used as fast response resistance thermometers for the study of heated turbulent flows. Simultaneous measurement of temperature and velocity is generally performed with multi-wire arrays. In order to give good spatial resolution a new layout has been tested which uses an inclined temperature wire positioned parallel to the nearest inclined velocity wire. This leads to an asymmetric wire arrangement relative to the mean flow direction. As expected, a reduction in thermal interference from the velocity wires results when compared with an array containing a temperature wire placed normal to the flow. However, measurement of higher order moments of fluctuating quantities in an axisymmetric jet shows considerable distortion of radial distributions which is traced to alteration of the temperature field sensed by the temperature wire. When inclined velocity sensitive wires contain a temperature component, the latter may be affected by the same phenomenon.

Skin-friction measurements in high-enthalpy hypersonic boundary layers

Skin-friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4-6.7, 3-13 MJ kg(-1) and 0.16 x 10(6)-21 x 10(6), respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1-0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new skin-friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent skin-friction levels were measured to within a typical uncertainty of +/-7%. The systematic uncertainty in measured skin-friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the skin-friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent skin-friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the skin-friction coefficient may be applied.

Numerical simulations of wind and temperature structure within an Alpine lake basin, Lake Tekapo, New Zealand

High-resolution numerical model simulations have been used to study the local and mesoscale thermal circulations in an Alpine lake basin. The lake (87 km(2)) is situated in the Southern Alps, New Zealand and is located in a glacially excavated rock basin surrounded by mountain ranges that reach 3000 m in height. The mesoscale model used (RAMS) is a three-dimensional non-hydrostatic model with a level 2.5 turbulence closure scheme. The model demonstrates that thermal forcing at local (within the basin) and regional (coast-to-basin inflow) scales drive the observed boundary-layer airflow in the lake basin during clear anticyclonic summertime conditions. The results show that the lake can modify (perturb) both the local and regional wind systems. Following sunrise, local thermal circulations dominate, including a lake breeze component that becomes embedded within the background valley wind system. This results in a more divergent flow in the basin extending across the lake shoreline. However, a closed lake breeze circulation is neither observed nor modelled. Modelling results indicate that in the latter part of the day when the mesoscale (coast-to-basin) inflow occurs, the relatively cold pool of lake air in the basin can cause the intrusion to decouple from the surface. Measured data provide qualitative and quantitative support for the model results.