Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO₂ rise

A rise in the atmospheric CO2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO2, and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO2 in the ocean interior, possibly explaining the Holocene atmospheric CO2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene

‘Sawtooth’ variation in magnetic intensity profiles and delayed acquisition of magnetization in deep sea cores

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Geomagnetic Polarity Reversals

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L'éducation musicale à l'école. Un point de vue sur la polyvalence des enseignants du premier degré

The teaching of music in schools often appears as a subject of minimal importance. The two surveys on professional practices of primary school teachers which the GRPPE has conducted between 1 997 and 2000 confirms this fact. In schools, music is a subject which is sometimes neglected, often delegated to outside contributors and for which institutional requirements (syllabus, instructions, hours) only constitute vague references for the teachers. However, the data collected by the GRPPE, make it possible to go further and to start perceiving the effect of the depreciation of certain subjects on the representations of primary school teachers. Thus, the status of music contributes to the blurring of the notion of professional expertise, to a considerable distancing of teachers from teaching contents and leads to an underestimate of the specific contribution of each subject to the construction of concepts. The institution seems to be willing to make some adjusments with the announcement of a plan to restore to favour the teaching of artistic subjects. Yet, the principles upon which it is based and the prospects it opens, especially in the field of teacher training, may or may not reverse the trend.L'éducation musicale en milieu scolaire apparaît souvent comme le parent pauvre de l'enseignement. Les deux enquêtes sur les pratiques professionnelles des enseignants du primaire auxquelles s'est livré le GRPPE entre 1 997 et 2000 confirment cet état de fait. À l'école, la musique est une discipline parfois occultée, souvent déléguée à des intervenants extérieurs et pour laquelle les prescriptions institutionnelles (programmes, instructions, horaires) ne constituent souvent, pour les maîtres, que de vagues références. Mais les données recueillies par le GRPPE permettent d'aller plus loin et de commencer à percevoir l'effet de la dévalorisation de certains champs disciplinaires sur les représentations des enseignants du premier degré. Ainsi, le statut de la musique contribue au brouillage de la notion d'expertise professionnelle, à une importante prise de distance des maîtres avec les contenus d'enseignement et conduit à une sous-estimation de l'apport propre de chaque discipline dans la construction des concepts. L'institution semble vouloir corriger le tir avec l'annonce d'un plan de réhabilitation des enseignements artistiques. Mais les présupposés sur lesquels il repose, et les perspectives qu'il ouvre, notamment en matière de formation des maîtres, contribueront-ils à inverser la tendance ?Baillat Gilles, Mazaud Alain. L'éducation musicale à l'école. Un point de vue sur la polyvalence des enseignants du premier degré. In: Recherche & Formation, N°40, 2002. Les savoirs entre pratique, formation et recherche, sous la direction de Annette Gonnin-Bolo. pp. 95-120

The 15 m.y. geomagnetic reversal periodicity: a quantitative test

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A geomagnetic chronology for antarctic ice accumulation

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The Matuyama-Brunhes and Upper Jaramillo transitions recorded in a loess section at Weinan, north-central China

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FIRST PALEOMAGNETIC RESULTS FROM NEOGENE FORMATIONS IN EVIA, SKYROS AND THE VOLOS REGION AND THE DEFORMATION OF CENTRAL AEGEA

International audiencePaleomagnetic results from Neogene volcanic and sedimentary formations in central Aegea indicate that Evia and Skyros have undergone a 48 ø and 26 ø clockwise rotation respectively. The Volos region does not show any significant rotation in the last 3 Ma. The rotation of Evia is about twice as large as the one measured from coeval formations in the external Hellenic arc. The results are interpreted in terms of a published model of distributed deformation by faulting, which also provides an explanation for the significant differential rotation of Evia and Skyros