Isotope and trace element geochemistry of Colorado Plateau volcanics

Basalts from the San Francisco Peaks and North Rim of Grand Canyon, nephelinites from the Hopi Buttes and Navajo minettes (Colorado Plateau) have been analyzed for trace element contents and Sr, Nd, Pb isotope compositions. The ages increase eastward from the Quaternary (basalt) to 5 Ma (nephelinite) and 30 Ma (minette) as does the depth of melt generation inferred from xenolith mineralogy and major element geochemistry.

The three rock types present an enrichment of incompatible elements (although minettes present negative concentration spikes for Nb, Zr, Ti, Ba, Sr) relative to other magma types. The chondrite-normalized Ce/Yb ratio changes from 8–22 (basalt) to 25–30 (nephelinite) and 33–60 (minette) and reflects small degrees of partial melting of a mantle source with a garnet/clinopyroxene ratio increasing with depth. The negative Eu anomaly present in minette, the low Sr/Nd and high Pb/Ce suggest the presence of a recycled continental crust component in their mantle source.

The ⁸⁷Sr/⁸⁶Sr ratio varies from 0.7032-0.7045 (basalt and nephelinite) to 0.7052-0.7071 (minette), while ε_Nd is remarkably more constant at +0.8 to +3.7 (nephelinite) and −2.6 to +2.2 (basalt and minette). Good linear correlations are observed in both ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagrams with basalt being the least and nephelinite the most radiogenic and indicate a 2.3 ±0.1 Ga age and a Th/U of 3.4.

Three lithospheric source components are indicated: a) an OIB-type depleted mantle source, b) an end-member with unradiogenic Sr, Nd and Pb for basalt and nephelinite and c) a recycled crustal component for minette.     

Sea Ice Leads Detection Using SARAL/AltiKa Altimeter

Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulation, geochemistry, and in ice dynamics. Their precise detection is crucial for altimetric estimations of sea ice thickness and volume. This study evaluates the performance of the SARAL/AltiKa (Satellite with ARgos and ALtiKa) altimeter to detect leads and to monitor their spatio-temporal dynamics. We show that a pulse peakiness parameter (PP) used to detect leads by Envisat RA-2 and ERS-1,-2 altimeters is not suitable because of saturation of AltiKa return echoes over the leads. The signal saturation results in loss of 6–10% of PP data over sea ice. We propose a different parameter—maximal power of waveform—and define the threshold to discriminate the leads. Our algorithm can be applied from December until May. It detects well the leads of small and medium size from 200 m to 3–4 km. So the combination of the high-resolution altimetric estimates with low-resolution thermal infra-red or radiometric lead fraction products could enhance the capability of remote sensing to monitor sea ice fracturing.     

Community collaboration and climate change research in the Canadian Arctic

Research on climate change impacts, vulnerability and adaptation, particularly projects aiming to contribute to practical adaptation initiatives, requires active involvement and collaboration with community members and local, regional and national organizations that use this research for policy-making. Arctic communities are already experiencing and adapting to environmental and socio-cultural changes, and researchers have a practical and ethical responsibility to engage with communities that are the focus of the research. This paper draws on the experiences of researchers working with communities across the Canadian Arctic, together with the expertise of Inuit organizations, Northern research institutes and community partners, to outline key considerations for effectively engaging Arctic communities in collaborative research. These considerations include: initiating early and ongoing communication with communities, and regional and national contacts; involving communities in research design and development; facilitating opportunities for local employment; and disseminating research findings. Examples of each consideration are drawn from climate change research conducted with communities in the Canadian Arctic.     

CoRoT-2a Magnetic Activity: Hints for Possible Star–Planet Interaction

CoRoT-2a is a young (≈0.5 Gyr) G7V star accompanied by a transiting hot-Jupiter, discovered by the CoRoT satellite (Alonso et al. Astron Astrophys 482:L21, 2008; Bouchy et al. Astron Astrophys 482:L25, 2008). An analysis of its photospheric activity, based on spot modelling techniques previously developed by our group for the analysis of the Sun as a star, shows that the active regions on CoRoT-2a arised within two active longitudes separated by about 180° and rotating with periods of 4.5221 and 4.5543 days, respectively, at epoch of CoRoT observations (112 continous days centered at ≈2007.6). We show that the total spotted area oscillates with a period of about 28.9 days, a value close to 10 times the synodic period of the planet with respect to the active longitude pattern rotating in 4.5221 days. Moreover, the variance of the stellar flux is modulated in phase with the planet orbital period. This suggests a possible star–planet magnetic interaction, a phenomenon already seen in other extrasolar planetary systems hosting hot-Jupiters.     

Fostering sustainable tribal economies in a time of climate change

In this article, we explore how Māori tribal organisations are responding to calls by other Indigenous peoples to become more sustainable in a time of climate change. From a close examination of tribal Environmental Management Plans, we move to a specific case study in the Bay of Plenty area, Ngāti Kea/Ngāti Tuara. Ultimately, we suggest that many tribal organisations are seeking to respond to climate change and transition to becoming producers of their own food and energy needs, and are often articulating these responses in relation to specific local resources and contexts.     

Quantifying felt events: A joint analysis of intensities, accelerations and dominant frequencies

Recent seismic events for which macroseismic intensities and accelerometric records are simultaneously available are investigated in order to derive empirical relationships between intensities and ground accelerations. 20 events with local magnitudes 3.0 to 5.4 are selected in a single country (France), in order to have homogeneous intensity data. Records are obtained in about 50 stations. Relationships are first established between intensities, magnitudes and distances on one side, between S-wave horizontal peak ground accelerations (PGA), magnitudes and distances R on the other side. They show that the PGA decays with distance roughly as R ⁻², in agreement with previous studies, and that PGA and intensities lead to different attenuation models. An intensity-acceleration relationship is established from direct observations, and from a combination of the previous relationships. It reveals that the intensity felt depends not only on the PGAs, but also on the distance. This may be explained by the frequency dependent attenuation of the waves, and by a different sensitivity of humans to the different frequencies. The influence of frequency on the felt intensity is then investigated, and a relation between intensity, PGA and frequency is established. It shows that the acceleration needed to be felt with a given intensity is larger at high frequency than at low frequency.Finally, as sound also contributes to earthquake perception, the P-wave displacement is analysed in an attempt to find in which conditions a perceptible sound is generated. The perturbation in air pressure induced by the P-wave is compared to the threshold of hearing in two frequency ranges, 20–40 Hz and 40–60 Hz. The maximum distance of perceptibility as a function of magnitude deduced from the P-wave displacement alone is found to be below the experimental distances of perception reported in the macroseismic enquiries.     

From networks to uses patterns: the digital divide as seen from Africa

This paper gives an account of the work carried out in the AFRICA’NTI research network, which gathered together a hundred, mostly African, researchers. The results were presented at the conference on “the North–South Digital Divide” in 2003 and 2004 (see www.africanti.org). From network to uses patterns, it first questions the way in which the subject is defined. This is a controversial question; should we speak of a “ditch” rather than of “fracture”? This depends on the point of view, but also on the geopolitical situation, and is difficult to measure. The digital divide may be less important than it is usually believed. This paper presents several types of approaches dealing with the opportunities of new technologies for Africa, geographical aspects stressing the diversity of the situations considered, and the importance of a multilevel systemic analysis based on case studies. It is shown that a slow down in the dynamics of equipment has been observed in Africa for both mobile telephony and the Internet. This then raises the question of a risk of regression for the continent, based on the idea that inequalities in access and uses of ICTs matter less than whether these uses improve the living conditions of the poor people concerned.     

Enregistrements sismologiques de l'explosion sur le site de l'usine AZF (Toulouse,France)Seismological records of an explosion at the AZF chemical complex in Toulouse,France

This study presents a detailed analysis of the seismic records of a strong explosion that occurred on 21 September 2001 at a chemical complex located south of Toulouse, France, and provoked important damages. The explosion, which is equivalent to a 3.4 magnitude earthquake, has been recorded at most of the stations of the National Seismological Network, as well as at a station under test at the ‘Observatoire Midi-Pyrénées’, 4.2 km away from the epicentre. The main seismic phases are interpreted using the known crustal structures, and a modelling with synthetic seismograms is performed. To cite this article: A. Souriau et al., C. R. Geoscience 334 (2002) 155–161.