The Mars oxidant experiment (MOx) for Mars '96

The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants.     

A trophic model for the Danshuei River Estuary, a hypoxic estuary in northern Taiwan

The estuary of the Danshuei River, a hypoxic subtropical estuary, receives a high rate of untreated sewage effluent. The Ecopath with Ecosim software system was used to construct a mass-balanced trophic model for the estuary, and network analysis was used to characterize the structure and matter flow in the food web. The estuary model was comprised of 16 compartments, and the trophic levels varied from 1.0 for primary producers and detritus to 3.0 for carnivorous and piscivorous fishes. The large organic nutrient loading from the upper reaches has resulted in detritivory being more important than herbivory in the food web. The food-chain length of the estuary was relatively short when compared with other tropical/subtropical coastal systems. The shortness of food-chain length in the estuary could be attributed to the low biomass of the top predators. Consequently, the trophic efficiencies declined sharply for higher trophic levels due to low fractions of flows to the top predators and then high fractions to detritus. The low biomass of the top predators in the estuary was likely subject to over-exploitation and/or hypoxic water. Summation of individual rate measurements for primary production and respiration yielded an estimate of −1791 g WW m⁻² year⁻¹, or −95 g C m⁻² year⁻¹, suggesting a heterotrophic ecosystem, which implies that more organic matter was consumed than was produced in the estuary.     

Temperature lapse rate and methane in Titan's troposphere

We have reanalyzed the Voyager radio occultation data for Titan, examining two alternative approaches to methane condensation. In one approach, methane condensation is facilitated by the presence of nitrogen because nitrogen lowers the condensation level of a methane/nitrogen mixture. The resulting enhancement in methane condensation lowers the upper limit on surface relative humidity of methane obtained from the Voyager occultation data from 0.7 to 0.6. We conclude that in this case the surface relative humidity of methane lies between 0.08 and 0.6, with values close to 0.6 indicated. In the other approach, methane is allowed to become supersaturated and reaches 1.4 times saturation in the troposphere. In this case, surface humidities up to 100% are allowed by the Voyager occultation data, and thus the upper limit must be set by other considerations. We conclude that if supersaturation is included, then the surface relative humidity of methane can be any value greater than 0.08--unless a deep ocean is present, in which case the surface relative humidity is limited to less than 0.85. Again, values close to 0.6 are indicated. Overall, the tropospheric lapse rate on Titan appears to be determined by radiative equilibrium. The lapse rate is everywhere stable against dry convection, but is unstable to moist convection. This finding is consistent with a supersaturated atmosphere in which condensation-and hence moist convection-is inhibited.     

Towards a classification of organic enrichment in marine sediments based on biogeochemical indicators

A nomogram is developed to show that pH, redox potentials (Eh_NHE) and measures of dissolved sulfides (H₂S + HS⁻ + S²⁻)(total free S²⁻) can be used to classify organic enrichment impacts in marine sediments. The biogeochemical cycle of sulfur in marine sediments is described to show that changes in macrobenthic infauna community structure associated with high levels of organic matter supply result from stress due to oxygen deficiency (hypoxia and anoxia) and toxic effects of S²⁻. The changes reflect enhancement of microbial sulfate reduction under conditions of high organic matter sedimentation and the progressive formation of hypoxic–anoxic conditions measured by decreased Eh_NHE and increased concentrations of S²⁻. The nomogram provides a basis for classification of the oxic status of marine sediments based on changes in inter-related biological and biogeochemical variables along an organic enrichment gradient.     

Preliminary report on radiocarbon dating of cryptoendolithic microorganisms

The existence of microbial communities living inside desert rocks has been reported by FRIEDMANN et al. (1967, 1976), first in rocks collected from the hot and dry Negev desert and later in rocks in the frigid Ross Desert of Southern Victoria Land, Antarctica. The extremely inhospitable climatic conditions in both places has led to the suggestion that these organisms have very low rates of metabolism and may, in addition, be very old (FRIEDMANN 1982). Our preliminary measurements showed a 14C deficiency indicating a carbon age in the order of magnitude of 10(3) years.     

关岛联合台风警报中心及其多海域热带气旋预报任务

关岛联合台风警报中心及其多海域热带气旋预报任务ＣｈａｒｌｅｓＰ．Ｇｕａｒｄ等（美国关岛联合台风警报中心）１前宫１．概述关岛的联合台风警报中心（ＪＴＷＣ）成立于１９５９年５月１日。它是世界上最繁忙的热带气旋（ＴＣ）警报中心，平均每年制作和发布６０个热带...     

Heavy metal concentrations in growth bands of corals: a record of mine tailings input through time (Marinduque Island,Philippines)

The impact of copper mining along the western coast of Marinduque Island was investigated. Historic input of mine tailings in the coastal region was traced through variations in heavy metal concentrations in Porites growth bands. Five samples were collected from three reefs showing different modes and extent of exposure to mine tailings. Baseline metal concentrations in Porites were established using a coral from a reef that is least exposed to contamination. The lowest mean values of Cu (0.7 microg/g), Mn (0.8 microg/g), and Zn (1.0 microg/g) were calculated from annual skeletal bands representing five years of growth. Conversely, a sample from a reef adjacent to an old tailings stockpile displayed consistently elevated metal values in its growth bands. Mean Cu, Mn, and Zn values for this coral are 3.1, 1.0 and 1.8 microg/g, respectively. Corals from the Ihatub reef showed a distinct metal concentration peak in their 1996 growth ring. These peaks coincide with a documented release of mine tailings in the Ihatub area during that year. Other metal peaks observed in coral samples correlate with years of high precipitation which may have resulted in increased sediment transport in the region. The metals are presumed to be mostly bound to the aragonite lattice of the coral skeleton, however, contribution from incorporated detrital materials to the observed metal signal (mainly of Fe) could not be easily discounted.     

A coupled soil-atmosphere model of H2O2 on Mars

The Viking Gas Chromatograph Mass Spectrometer failed to detect organic compounds on Mars, and both the Viking Labeled Release and the Viking Gas Exchange experiments indicated a reactive soil surface. These results have led to the widespread belief that there are oxidants in the martian soil. Since H2O2 is produced by photochemical processes in the atmosphere of Mars, and has been shown in the laboratory to reproduce closely the Viking LR results, it is a likely candidate for a martian soil oxidant. Here, we report on the results of a coupled soil/atmosphere transport model for H2O2 on Mars. Upon diffusing into the soil, its concentration is determined by the extent to which it is adsorbed and by the rate at which it is catalytically destroyed. An analytical model for calculating the distribution of H2O2 in the martian atmosphere and soil is developed. The concentration of H2O2 in the soil is shown to go to zero at a finite depth, a consequence of the nonlinear soil diffusion equation. The model is parameterized in terms of an unknown quantity, the lifetime of H2O2 against heterogeneous catalytic destruction in the soil. Calculated concentrations are compared with a H2O2 concentration of 30 nmoles/cm3, inferred from the Viking Labeled Release experiment. A significant result of this model is that for a wide range of H2O2 lifetimes (up to 10(5) years), the extinction depth was found to be less than 3 m. The maximum possible concentration in the top 4 cm is calculated to be approximately 240 nmoles/cm3, achieved with lifetimes of greater than 1000 years. Concentrations higher than 30 nmoles/cm3 require lifetimes of greater than 4.3 terrestrial years. For a wide range of H2O2 lifetimes, it was found that the atmospheric concentration is only weakly coupled with soil loss processes. Losses to the soil become significant only when lifetimes are less than a few hours. If there are depths below which H2O2 is not transported, it is plausible that organic compounds, protected from an oxidizing environment, may still exist. They would have been deposited by meteors, or be the organic remains of past life.