Respiration and Calcification of <Emphasis Type="Italic">Crassostrea gigas</Emphasis>: Contribution of an Intertidal Invasive Species to Coastal Ecosystem CO<Subscript>2</Subscript> Fluxes

Respiration and calcification rates of the Pacific oyster Crassostrea gigas were measured in a laboratory experiment in the air and underwater, accounting for seasonal variations and individual size, to estimate the effects of this exotic species on annual carbon budgets in the Bay of Brest, France. Respiration and calcification rates changed significantly with season and size. Mean underwater respiration rates, deducted from changes in dissolved inorganic carbon (DIC), were 11.4 μmol DIC g⁻¹ ash-free dry weight (AFDW) h⁻¹ (standard deviation (SD), 4.6) and 32.3 μmol DIC g⁻¹ AFDW h⁻¹ (SD 4.1) for adults (80–110 mm shell length) and juveniles (30–60 mm), respectively. The mean daily contribution of C. gigas underwater respiration (with 14 h per day of immersion on average) to DIC averaged over the Bay of Brest population was 7.0 mmol DIC m⁻² day⁻¹ (SD 8.1). Mean aerial CO₂ respiration rate, estimated using an infrared gas analyzer, was 0.7 μmol CO₂ g⁻¹ AFDW h⁻¹ (SD 0.1) for adults and 1.1 μmol CO₂ g⁻¹ AFDW h⁻¹ (SD 0.2) for juveniles, corresponding to a mean daily contribution of 0.4 mmol CO₂ m⁻² day⁻¹ (SD 0.50) averaged over the Bay of Brest population (with 10 h per day of emersion on average). Mean CaCO₃ uptake rates for adults and juveniles were 4.5 μmol CaCO₃ g⁻¹ AFDW h⁻¹ (SD 1.7) and 46.9 μmol CaCO₃ g⁻¹ AFDW h⁻¹ (SD 29.2), respectively. The mean daily contribution of net calcification in the Bay of Brest C. gigas population to CO₂ fluxes during immersion was estimated to be 2.5 mmol CO₂ m⁻² day⁻¹ (SD 2.9). Total carbon release by this C. gigas population was 39 g C m⁻² year⁻¹ and reached 334 g C m⁻² year⁻¹ for densely colonized areas with relative contributions by underwater respiration, net calcification, and aerial respiration of 71%, 25%, and 4%, respectively. These observations emphasize the substantial influence of this invasive species on the carbon cycle, including biogenic carbonate production, in coastal ecosystems.     

ISIS IR: The first infrared fibre-fed spectrograph

ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (1.8m). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.Département d'Astrophysique Extragalactique et de Cosmologie     

Heliocentric evolution of the degradation of polyoxymethylene: Application to the origin of the formaldehyde (H2CO) extended source in Comet C/1995 O1 (Hale-Bopp)

The H₂CO production rates measured in Comet C/1995 O1 (Hale-Bopp) from radio wavelength observations [Biver, N., and 22 colleagues, 2002a. Earth Moon Planets 90, 5-14] showed a steep increase with decreasing heliocentric distance. We studied the heliocentric evolution of the degradation of polyoxymethylene (formaldehyde polymers: (CH₂O)_n, also called POM) into gaseous H₂CO. POM decomposition can indeed explain the H₂CO density profile measured in situ by Giotto spacecraft in the coma of Comet 1P/Halley, which is not compatible with direct release from the nucleus [Cottin, H., Bénilan, Y., Gazeau, M.-C., Raulin, F., 2004. Icarus 167, 397-416]. We show that the H₂CO production curve measured in Comet C/1995 O1 (Hale-Bopp) can be accurately reproduced by this mechanism with a few percents by mass of solid POM in grains. The steep heliocentric evolution is explained by the thermal degradation of POM at distances less than 3.5 AU. This study demonstrates that refractory organics present in cometary dust can significantly contribute to the composition of the gaseous coma. POM, or POM-like polymers, might be present in cometary grains. Other molecules, like CO and HNC, might also be produced by a similar process.     

Large scale chaos and marginal stability in the solar system

Large scale chaos is present everywhere in the solar system. It plays a major role in the sculpting of the asteroid belt and in the diffusion of comets from the outer region of the solar system. All the inner planets probably experienced large scale chaotic behavior for their obliquities during their history. The Earth obliquity is presently stable only because of the presence of the Moon, and the tilt of Mars undergoes large chaotic variations from 0° to about 60°. On billion years time scale, the orbits of the planets themselves present strong chaotic variations which can lead to the escape of Mercury or collision with Venus in less than 3.5 Gyr. The organization of the planets in the solar system thus seems to be strongly related to this chaotic evolution, reaching at all time a state of marginal stability, that is practical stability on a time-scale comparable to its age.This lecture was given at the XIth International Congress of Mathematical Physics, Paris, july 1994     

Comments on the next generation of ground-based solar telescopes

The development of telescope capabilities tends to go in spurts. These are triggered by the availability of new techniques in optics, mechanics and/or instrumentation. So has nighttime telescope technology developed since the construction in the nineteen-forties of the 5-m Hale telescope, first by the introduction in the sixties of high efficiency electronic detectors, followed recently by the production of large 8- to 10-m mirrors and now by the implementation of adaptive optics. In solar astronomy, major steps were the introduction of the coronagraph by Lyot in the nineteen-thirties and the vacuum telescope concept by Dunn in the sixties. In the last thirty years, telescope developments in solar astronomy have relied primarily on improved instrumental capabilities. As in nighttime astronomy, these instruments and their detectors are reaching their limits set by the quantum nature of light and the telescope diffraction. Larger telescopes are needed to increase sensitivity and angular resolution of the observations. In this paper, I will review recent efforts to increase substantially the telescope capabilities themselves. I will emphasize the concept of a large all-wavelength, coronagraphic telescope (CLEAR) which is presently being developed.Dedicated to Cornelis de Jager     

TNOs are Cool: A Survey of the Transneptunian Region

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well.     

Thermoluminescence of the lunar surface

Observations of the lunar luminescence are reported for a dozen of specific Moon features using the line-depth method with a high resolution spectroscopic technique. The data indicate a variation of the Moon proper emission as a function of the phase angle which is interpreted as a proof of the thermoluminescent origin of this emission.     

Chromospheric inhomogeneities in sunspot umbrae

The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these ‘Umbral Flashes’:

1. A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness.
2. A diameter ranging from the resolution limit up to 2000 km.
3. A tendency to repeat every 145 sec.
4. A ‘proper motion’ of 40 km/sec generally directed towards the penumbra.
5. A Doppler shift of 6 km/sec.
6. A magnetic field of 2100 G.
7. A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.
8. At any instant an average of 3–5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100–120 sec after the flash, it shows a rapid red shift just before the flash repeats.

     

Magnesite growth rates as a function of temperature and saturation state

Magnesite growth rates and step velocities have been measured systematically as a function of temperature from 80 to 105 °C and saturation state in 0.1 M NaCl solutions using hydrothermal atomic force microscopy (HAFM). The observations indicate that at these conditions magnesite precipitation is dominated by the coupling of step generation via spiral growth at screw dislocations and step advancement away from these dislocations. As these two processes occur in series the slowest of these dominates precipitation rates. At 100 °C magnesite growth rates (r) determined by HAFM are consistent with

r=k(Ω-1)²,