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Climatic impact of glacial cycle polar motion: Coupled oscillations of ice sheet mass and rotation pole position / Bruce G. Bills in Journal of geophysical research : Solid Earth, vol 104 n° 1 (01/01/1999)  

Public [article]  inJournal of geophysical research : Solid Earth > vol 104 n° 1 (01/01/1999) . - pp 1059 - 1075 Titre : Climatic impact of glacial cycle polar motion: Coupled oscillations of ice sheet mass and rotation pole position Type de document : Article/Communication Auteurs : Bruce G. Bills, Auteur ; T. James, Auteur ; J. Mengel, Auteur Année de publication : 1999 Article en page(s) : pp 1059 - 1075 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] axe de rotation de la Terre [Termes IGN] calotte glaciaire [Termes IGN] changement climatique [Termes IGN] masse [Termes IGN] mouvement du pôle [Termes IGN] oscillation Résumé : (Auteur) Precessional motion of Earth's rotation axis relative to its orbit is a well-known source of long-period climatic variation. It is less well appreciated that growth and decay of polar ice sheets perturb the symmetry of the global mass distribution enough that the geographic location of the rotation axis will change by at least 15 km and possibly as much as 100 km during a single glacial cycle. This motion of the pole will change the seasonal and latitudinal pattern of temperatures. We present calculations, based on a diurnal average energy balance, which compare the summer and winter temperature anomalies due to a 1° decrease in obliquity with those due to a 1° motion of the rotation pole toward Hudson Bay. Both effects result in peak temperature perturbations of about 1° Celsius. The obliquity change primarily influences the amplitude of the seasonal cycle, while the polar motion primarily changes the annual mean temperatures. The polar motion induced temperature anomaly is such that it will act as a powerful negative feedback on ice sheet growth. We also explore the evolution of the coupled system composed of ice sheet mass and pole position. Oscillatory solutions result from the conflicting constraints of rotational and thermal stability. A positive mass anomaly on an otherwise featureless Earth is in rotational equilibrium only at the poles or the equator. The two polar equilibria are rotationally unstable, and the equatorial equilibrium, though rotationally stable, is thermally unstable. We find that with a plausible choice for the strength of coupling between the thermal and rotational systems, relatively modest external forcing can produce significant response at periods of 104–106 years, but it strongly attenuates polar motion at longer periods. We suggest that these coupled oscillations may contribute to the observed dominance of 100 kyr glacial cycles since the mid-Pleistocene and will tend to stabilize geographic patterns that are suitable to glaciations. Numéro de notice : A1999-202 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1029/1998JB900004 Date de publication en ligne : 10/01/1999 En ligne : https://doi.org/10.1029/1998JB900004 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33332 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
194-99011	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Kinematics of the India-Eurasia collision zone from GPS measurements / K. Larson in Journal of geophysical research : Solid Earth, vol 104 n° 1 (01/01/1999)  

Public [article]  inJournal of geophysical research : Solid Earth > vol 104 n° 1 (01/01/1999) . - pp 1077 - 1093 Titre : Kinematics of the India-Eurasia collision zone from GPS measurements Type de document : Article/Communication Auteurs : K. Larson, Auteur ; R. Bürgmann, Auteur ; R. Bilham, Auteur ; et al., Auteur Année de publication : 1999 Article en page(s) : pp 1077 - 1093 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] Cinématique [Termes IGN] faille géologique [Termes IGN] Inde [Termes IGN] Népal [Termes IGN] positionnement par GPS [Termes IGN] risque naturel [Termes IGN] tectonique Résumé : (Auteur) We use geodetic techniques to study the India-Eurasia collision zone. Six years of GPS data constrain maximum surface contraction rates across the Nepal Himalaya to 18 + 2 mm/yr at 12°N +13° (1ó). These surface rates across the 150-km-wide deforming zone are well fitted with a dislocation model of a buried north dipping detachment fault striking 105°, which aseismically slips at a rate of 20 + 1 mm/yr, our preferred estimate for the India-to-southern-Tibet convergence rate. This is in good agreement with various geologic predictions of 18 + 7 mm/yr for the Himalaya. A better fit can be achieved with a two-fault model, where the western and eastern faults strike 112° and 101°, respectively, in approximate parallelism with the Himalayan arc and a seismicity lineament. We find eastward directed extension of 11 + 3 mm/yr between northwestern Nepal Lhasa, also in good agreement with geologic and seismic studies across the southern Tibetan plateau. Continuous GPS sites are used to further constrain the style and rates of deformation throughout the collision zone. Sites in India, Uzbekistan, and Russia agree within error with plate model prediction. Numéro de notice : A1999-203 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1029/1998JB900043 Date de publication en ligne : 10/01/1999 En ligne : https://doi.org/10.1029/1998JB900043 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33333 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
194-99011	RAB	Revue	Centre de documentation	En réserve L003	Disponible