Abstract: Distributions of microphytobenthos are highly heterogeneous at scales as small as a few centimetres. However, the sampling protocols currently used for the absolute determination of microphytobenthos biomass through chlorophyll a concentration measurements in surface sediments are too limited to take this variability into account, typically relying on 3-5 samples taken within a randomly located 1 m2 quadrat in a given environment. We address this issue by objectively and quantitatively inferring the minimum number of samples required to obtain reliable estimates of microphytobenthos biomass on the basis of high-resolution sub-sampling (225 regularly spaced samples) within each of nine 1 m2 quadrats at an unvegetated sheltered intertidal sandbank of the Gold Coast (Queensland, Australia). The results were generalised using data obtained in previous studies on an exposed sandy shore and on sheltered estuarine sandy muds of the Eastern English Channel. Estimates of chlorophyll a concentration exhibited a high degree of heterogeneity, both between and within quadrats. The number of samples needed to estimate the average chlorophyll a concentration, and hence mean microphytobenthos biomass with 95% confidence intervals, ranged from 15 to 115, and mainly depended on the presence of global and local gradients within the quadrats. These results have major implications for intertidal ecology by implying a possible systematic bias in the measurement of both microphytobenthos biomass and production of up to 40%. Finally, we emphasise that this issue can be circumvented using field spectrometry or PAM fluorescence measurements coupled with traditional sediment sampling techniques, and urge for unified protocols to be adopted for the routine use of these combined methods.

Abstract: A barotropic tidal model, with a parameterization term to account for the internal wave drag energy dissipation, is used to examine areas of possible M2 internal tide generation in the Kerguelen Plateau region. Barotropic energy flux and a distribution of wave drag dissipation are computed. The results suggest important conversion of barotropic energy into baroclinic tide generation over the northern Kerguelen Plateau shelf break, consistent with a theoretical criterion based on ocean stratification, tidal forcing frequency, and bathymetric gradients. The sea surface height signatures of time-coherent internal tides are studied using TOPEX/Poseidon and Jason-1 altimeter data, whose ascending tracks cross nearly perpendicular to the eastern and western Kerguelen Plateau shelf break. Oscillations of a few centimeters associated with phase-locked internal tides propagate away from the plateau over distances of several hundred kilometers with a ~110 km wavelength. When reaching the frontal area of the Antarctic Circumpolar Current, the internal tide cannot be identified because of the aliasing of mesoscale variability into the same alias band as M2. Finally, using altimeter data, we estimate the M2 barotropic tidal power converted through the internal tide generation process. We find consistent values with the barotropic model parameterization estimation, which is also in good agreement with global internal tide model estimates. Combined with modeling, this study has shown that altimetry can be used to estimate internal tide dissipation.

Abstract: Cross-correlation of continuous broadband records allows the retrieval of body waves at teleseismic distances. These continuous records mainly contain low-amplitude background noise that comes from ocean–crust interactions, although there are also many transient events of different magnitudes and their coda associated with reverberation and/or scattering. We present an analysis at the global scale of these different contributions in the context of body-wave retrieval using the cross-correlation technique. Specifically, we compare the correlation of long codas after strong earthquakes with those of the quietest days. In the long period range (25–100 s), several phases that propagate in the deep Earth are observed in the correlations of the signals recorded after earthquakes, with some of these phases showing non-physical polarization. At the same time, the global section of correlations shows a series of spurious branches. These features are reproduced with synthetic correlations. A stack of the quietest days of the year shows that body waves are still present, with relative amplitudes that are closer to those expected for the actual Earth response. When considering shorter periods (5–10 s), the reconstruction of the deep phases is not affected by the earthquake coda, due to the dominance of scattering over reverberation.

Abstract: Abstract : Exoplanetary transit and stellar oscillation surveys require a very high precision photometry. The instrumental noise has therefore to be minimized. First, we perform a semi-analytical model of different noise sources. We show that the noise due the CCD electrodes can be overcome using a Gaussian PSF (Point Spread Function) of full width half maximum larger than 1.6 pixels. We also find that for a PSF size of a few pixels, the photometric aperture has to be at least 2.5 times larger than the PSF full width half maximum. Then, we compare a front- with a back-illuminated CCD through a Monte-Carlo simulation. Both cameras give the same results for a PSF full width half maximum larger than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica Search for Transiting Extrasolar Planets) project. As a result, we choose a front-illuminated camera for A STEP because of its better resolution and lower price, and we will use a PSF larger than 1.6 pixels. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Abstract: Based on the high quality broadband data from Gräfenberg array in Germany, we recently detected a reliable PKJKP phase, for which four kinds of evidence (travel time, slowness, back-azimuth, and comparison with a pseudo-liquid inner core model) were simultaneously provided. Also, for the first time, a clear waveform of PKJKP was observed. This gives us an unprecedented opportunity to put constraints on the shear wave attenuation in the earth's inner core using body waves. In order to minimize the potential influence of dispersion and phase shift caused by mantle heterogeneity, we adopt an envelope modeling approach. Our results show that the estimated Q from the shear phase PKJKP is significantly larger (315 ± 150) than that from normal mode observations. Because PKJKP samples the deep inner core, this indicates an increase of Q with depth in the inner core, in agreement with what is generally observed for Q.