Origin of chaos in the Prometheus-Pandora system

We demonstrate that the chaotic orbits of Prometheus and Pandora are due to interactions associated with the 121:118 mean motion resonance. Differential precession splits this resonance into a quartet of components equally spaced in frequency. Libration widths of the individual components exceed the splitting, resulting in resonance overlap which causes the chaos. Mean motions of Prometheus and Pandora wander chaotically in zones of width 1.8 and 3.1 deg yr⁻¹, respectively. A model with 1.5 degrees of freedom captures the essential features of the chaotic dynamics. We use it to show that the Lyapunov exponent of 0.3 yr⁻¹ arises because the critical argument of the dominant member of the resonant quartet makes approximately two separatrix crossings every 6.2 year precessional cycle.     

Microwave and hard X-Ray observations of a solar flare with a time resolution better than 100 ms

Simultaneous microwave and X-ray observations are presented for a solar flare detected on May 8, 1980 starting at 19:37 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28–490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms, respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive peaks in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240 ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5 s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model.     

TEM evidence for intracellular accumulation of lead by bacteria in subsurface environments

We monitored near-surface atmospheric fallout (15-cm above ground) and soil solution (at 15, 35 and 55 cm below ground) derived nanoparticles over an 8-month period by collecting the particles directly onto TEM grids in anthropogenically-influenced (vineyard) and pristine (native forest) sites in France. Particle clusters trapped on the grid were selected randomly and individual particles were binned into eight different groups (euhedral clays, weathered clays, salts, oxi-hydroxides, bacteria, non-living organic matter, aggregates and undetermined). Bacteria represent 9–23% of the collected nanoparticle area (ave. 9.4% and 18% for two atmospheric collection sites and ave. 23% for soil infiltration samples). Bacteria were most often associated with non-living organic matter and comprised a variety of morpho-types. Interestingly, 45% of all the bacteria analyzed by transmission electron microscopy and electron dispersive spectroscopy (TEM-EDX) showed the presence of intracellular grains significantly enriched in lead and phosphorus. Intracellular sequestration of Pb into polyphosphate bodies has been observed in the laboratory, but this is the first observation of this phenomenon in a natural environment. Furthermore, this suggests that microbial-bound Pb may be an important transport mechanism in subsurface environments.     

Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures

Stable isotope analyses (δ¹³C and δ¹⁵N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ¹³C values of Zostera capensis and surface sediments near the salt marsh, the δ¹³C and δ¹⁵N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ¹³C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ¹³C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ¹⁵N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ¹³C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.     

Variability in the nutritional value of the major copepods in Cape Cod Bay (Massachusetts, USA) with implications for right whales

The North Atlantic right whale, a seriously endangered species, is found in Cape Cod Bay (Massachusetts, USA) during the winter and early spring. During their residency in these waters, these whales are frequently observed feeding. This study evaluated spatial and temporal changes in the chemical composition (carbon weight and C/N ratio) of the food resource targeted by the right whales in Cape Cod Bay. The three taxa measured (Centropages typicus, Pseudocalanus spp., and Calanus finmarchicus) had highly variable chemical compositions resulting from the different life strategies and from fluctuations in their surrounding environment. The impact of seasonal variability in the energy densities of the food resource of right whales was calculated and compared to the energetic requirements of these whales. Calculations indicated that differences in the nutritional content of the zooplankton prey in Cape Cod Bay could have a considerable effect on the nutrition available to the right whales. Therefore, it is likely that using more precise estimates of the energetic densities of the prey of right whales would lead to a re‐evaluation of the adequacy of the food resource available to these whales in the North Atlantic.     

Immediate profile and planform evolution of a beach nourishment project with hurricane influences

In this study, planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration. Weekly beach profiles, shoreline surveys, and nearshore wave measurements were conducted before, during, and immediately after construction of the 1100-m long Upham Beach nourishment project on the low-energy, west coast of Florida. This project was constructed in three segments: the wide north segment, the central segment, and the narrow south segment. With the exception of the relatively distant passage of Hurricane Charley, calm weather prevailed for 45 days following completion of the south and central segments. Construction of the wide north segment was completed on August 27, 2004. Substantial planform diffusion occurred prior to construction completion via formation of a 300-m long spit extending from the wide north segment. The shoreline orientation was changed abruptly due to this diffusion spit formation, as opposed to the gradual adjustment predicted by most long-term models. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. A simple vector sum model for determining the orientation of a potential diffusion spit was developed. This study recommends designing end transitions at the predicted diffusion spit orientation to avoid post-nourishment spit formation during future projects.     

Effects of water-borne copper on metallothionein and lipid peroxidation in the marine amphipod Gammarus locusta

The aim of the current work was to determine over 10 days the effects of water-borne exposure of the marine amphipod Gammarus locusta to 4 microgCu l(-1) on the metallothionein (MT; measured by differential pulse polarography) protection system and lipid peroxidation (LP: thiobarbituric acid-reactive malondialdehyde equivalents) as a measure of oxidative damage. MT levels in exposed animals increased significantly at day 2 (36% > control; P < 0.001) and remained high at days 6 and 10 (55 and 38%, respectively, P < 0.001). The maximum level of MT at day 6 coincided with the highest Cu body-burden. LP increased within I day of exposure, indicative of Cu as an oxidative stressor. However, in contrast to MT, the highest LP level was seen at day 4 (68% > control, P < 0.001) before returning to control values by day 6, indicating a protective role of MT against the pro-oxidant effects of Cu.     

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: II. Organism and population-level endpoints

This study aimed to test the performance of the amphipod Gammarus locusta (L.) in chronic sediment toxicity tests. It constitutes part of a multi-level assessment of chronic toxicity of estuarine sediments, integrating organism and population-level endpoints with biochemical markers responses. Here we account for organism and population-level effects, while biomarker responses were reported in a companion article. Five moderately contaminated sediments from Sado and Tagus estuaries were tested, comprising 3 muddy and 2 sandy sediments. These sediments either did not show acute toxicity or were diluted with control sediment as much as required to remove acute toxicity. Subsequent chronic tests consisted of 28-day exposures with survival, individual growth and reproductive traits as endpoints. Two of the muddy sediments induced higher growth rates in the amphipods, and improved reproductive traits. This was understood to be a consequence of the amount of organic matter in the sediment, which was nutritionally beneficial to the amphipods, while concurrently decreasing contaminant bioavailability. Biomarker responses did not reveal toxicant-induced stress in amphipods exposed to these sediments. One of the sandy sediments was acutely toxic at 50% dilution, but in contrast stimulated amphipod growth when diluted 75%. This was presumed to be an indication of a hormetic response. Finally the two remaining contaminated sediments showed pronounced chronic toxicity, affecting survival and reproduction. The sex ratio of survivors was highly biased towards females, and offspring production was severely impaired. The particulars of the responses of this amphipod were examined, as well as strengths versus limitations of the sediment test. This study illustrates the utility of this chronic test for toxicity assessment of contaminated estuarine sediments, with potential application all along Atlantic Europe.     

The P-T-fO 2 stability of deerite,Fe 12 2+ Fe 6 3+ [Si12O40](OH)10

New equilibrium experiments have been performed in the 20–27 kbar range to determine the upper thermal stability limit of endmember deerite, Fe ₁₂ ²⁺ Fe ₆ ³⁺ [Si₁₂O₄₀](OH)₁₀. In this pressure range, the maximum thermal stability limit is represented by the oxygen-conserving reaction: deerite(De)=9 ferrosilite(Fs)+3 magnetite(Mag)+3 quartz(Qtz)+5 H₂O(W) (1). Under the oxygen fugacities of the Ni-NiO buffer the breakdown-reduction reaction: De=12 Fs+2 Mag+5 W+1/2 O₂ (10) takes place at lower temperatures (e.g. T=63° at 27 kbar). The experimental brackets can be fitted using thermodynamic data for ferrosilite, magnetite and quartz from Berman (1988) and the following 1 bar, 298 K data for deerite (per gfw): V^o=55.74 J.bar^-1, S^o=1670 J.K^-1, H _f ^o =-18334 kJ, =2.5x10^-5K^-1, =-0.18x10^-5 bar^-1. Using these data in conjunction with literature data on coesite, grunerite, minnesotaite, and greenalite, the P-T stability field of endmember deerite has been calculated for P _s=P _{H 2}O. This field is limited by 6 univariant oxygenconserving dehydration curves, from which three have positive dP/dT slopes, the other three negative slopes. The lower pressure end of the stability field of endmember deerite is thus located at an invariant point at 250±70°C and 10+-1.5 kbar. Deerite rich in the endmember can thus appear only in environments with geothermal gradients lower than 10°C/km and at pressures higher than about 10 kbar, which is in agreement with 4 out of 5 independent P-T estimates for known occurrences. The presence of such deerite places good constraints on minimum pressure and maximum temperature conditions. From log f _{O 2}-T diagrams constructed with the same data base at different pressures, it appears that endmember deerite is, at temperatures near those of its upper stability limit, stable only over a narrow range of oxygen fugacities within the magnetite field. With decreasing temperatures, deerite becomes stable towards slightly higher oxygen fugacities but reaches the hematite field only at temperatures more than 200°C lower than the upper stability limit. This practically precludes the coexistence deerite-hematite with near-endmember deerite in natural environments.