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Registros recuperados: 8
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A mid-Holocene transition in the nitrogen dynamics of the western equatorial Pacific: Evidence of a deepening thermocline? ArchiMer
Kienast, M.; Lehmann, M. F.; Timmermann, A.; Galbraith, E.; Bolliet, T.; Holboum, A.; Normandeau, C.; Laj, C..
Sedimentary delta(15)N records from the oligotrophic western equatorial Pacific (WEP) off Mindanao show that late Holocene sedimentary delta(15)N is substantially lower than that of the early Holocene, following a gradual >3 parts per thousand decrease that occurred between 7 and 3 kyrs ago. Analyses of modem day nitrate isotope profiles from the same region indicate the sensitivity of the WEP N pools towards (1) the advection of (15)N-enriched nitrate from the Eastern Equatorial Pacific (EEP) by the North Equatorial Current (NEC) and the Mindanao Current in subsurface waters and, (2) at shallow depths, the input of new and (15)N-depleted nitrate through N, fixation. We suggest that the Holocene decrease in sedimentary delta(15)N reflects a diminished...
Tipo: Text Palavras-chave: Tropical Pacific; El Nino; Surface temperature; Fresh water; Nitrate; Mindanao; Ocean; Variability; Holocene; Seawater.
Ano: 2008 URL: https://archimer.ifremer.fr/doc/00207/31843/30257.pdf
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An accreted continental terrane in Northwestern Peru IRD
Mourier, T.; Laj, C.; Mégard, F.; Roperch, Pierrick; Mitouard, P.; Farfan Medrano, A..
Cet article présente une étude paléomagnétique des échantillons de plusieurs formations du bassin de Lancones (province de Piura). Les auteurs formulent l'hypothèse de l'accrétion d'une terrane sur la marge péruvienne au cours du Néocomien. Un régime de cisaillement aurait également produit des rotations in situ. L'évolution géodynamique du nord du Pérou est donc comparable aux processus observés sur les Andes septentrionales, en Equateur
Tipo: Text Palavras-chave: PALEOMAGNETISME; ACCRETION; EVOLUTION; GEODYNAMIQUE; NEOCOMIEN; TERRANE.
Ano: 1988 URL: http://www.documentation.ird.fr/hor/fdi:25070
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Le carbone 14 : progrès récents et limitations de la méthode de datation IRD
Duplessy, J.C.; Arnold, M.; Bard, E.; Cortijo, E.; Labeyrie, L.; Laj, C.; Lehman, B.; Mazaud, A.; Paterne, M.; Tisnerat, N.; Vidal, L..
La méthode de datation par le carbone 14 a permis l'établissement d'une échelle chronologique du Quaternaire Supérieur et a contribué à la découverte de phénomènes insoupçonnés comme l'existence de variations climatiques abruptes et de grande amplitude pendant la dernière période glaciaire et la déglaciation qui l'a terminée. L'effort continu pour comparer les âges carbone 14 avec les âges calendaires a été maintenant étendu au delà de 30 000 ans, même si le nombre de mesures est encore trop petit pour permettre l'établissement d'une courbe de calibration précise au delà des dix mille dernières années. La comparaison des variations du rapport 14C/12C de l'atmosphère avec celles du champ magnétique terrestre (déduites de l'analyse des carottes de sédiments...
Tipo: Text Palavras-chave: QUATERNAIRE; DATATION ABSOLUE; C 14; GEOCHRONOLOGIE; PALEOCLIMAT; CHAMP MAGNETIQUE.
Ano: 1998 URL: http://www.documentation.ird.fr/hor/fdi:010013863
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L'Occident équatorien : un terrain océanique pacifique accolé au continent sud-américain IRD
Mégard, F.; Roperch, Pierrick; Lebrat, Michel; Laj, C.; Mourier, T.; Noblet, Christophe.
Cet article présente les principaux traits géologiques de la partie occidentale de l'Equateur et les premiers résultats d'une étude paléomagnétique entreprise dans cette région en 1985. Selon les auteurs, la partie occidentale de l'Equateur se serait formée dans le Pacifique, puis elle serait venue se coller au vieux continent sud-américain sous la forme d'un terrain exotique semblable à ceux connus ailleurs, notamment dans les chaînes péripacifiques
Tipo: Text Palavras-chave: GEODYNAMIQUE; MARGE CONTINENTALE; SUBDUCTION; ACCRETION; PALEOMAGNETISME; FORMATION PINON; FORMATION MACUCHI.
Ano: 1987 URL: http://www.documentation.ird.fr/hor/fdi:26205
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Magnetic Fingerprints of Modern Sediments in the South China Sea Resulting from Source-to-Sink Processes ArchiMer
Kissel, C.; Sarnthein, M.; Laj, C.; Wang, P. X.; Wandres, C.; Egli, R..
More than 650 million tons/year of fluvial sediment are delivered from continental regions into the South China Sea (SCS). Previous studies have shown that the composition of the magnetic fraction of riverine sediments drained into the SCS is significantly variable from north to south. On the basis of this evidence, we now examine a full set of magnetic properties for a number of core‐tops taken at water depth comprised mostly between 800 and 3500 m. Room‐temperature magnetic parameters and thermal spectra are used to obtain information about the concentration and mineralogical magnetic composition. Spatial changes are observed in the relative proportion of magnetite and hematite with an increase of the latter toward the south, similarly to the observation...
Tipo: Text Palavras-chave: South China Sea; Magnetic mineralogy; Marine sediments.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00443/55502/57048.pdf
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Millennial-scale sea surface temperature and Patagonian Ice Sheet changes off southernmost Chile (53 degrees S) over the past similar to 60 kyr ArchiMer
Caniupan, M.; Lamy, F.; Lange, C. B.; Kaiser, J.; Arz, H.; Kilian, R.; Baeza Urrea, O.; Aracena, C.; Hebbeln, D.; Kissel, C.; Laj, C.; Mollenhauer, G.; Tiedemann, R..
Glacial millennial-scale paleoceanographic changes in the Southeast Pacific and the adjacent Southern Ocean are poorly known due to the scarcity of well-dated and high resolution sediment records. Here we present new surface water records from sediment core MD07-3128 recovered at 53 degrees S off the Pacific entrance of the Strait of Magellan. The alkenone-derived sea surface temperature (SST) record reveals a very strong warming of ca. 8 C over the last Termination and substantial millennial-scale variability in the glacial section largely consistent with our planktonic foraminifera oxygen isotope (delta(18)O) record of Neogloboquadrina pachyderma (sin.). The timing and structure of the Termination and some of the millennial-scale SST fluctuations are...
Tipo: Text Palavras-chave: Patagonian Ice Sheet; Alkenones; Ice rafted debris; Millennial-scale changes; Southeast Pacific.
Ano: 2011 URL: https://archimer.ifremer.fr/doc/00214/32516/31000.pdf
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Paleomagnetic study of upper cretaceous and tertiary formations from the central Andes (Southern Ecuador and Peru) IRD
Kissel, C.; Laj, C.; Mitouard, P.; Macedo, O.; Roperch, Pierrick; Surmont, J..
Tipo: Text Palavras-chave: PALEOMAGNETISME; CRETACE; CENOZOIQUE; GEODYNAMIQUE; TECTONIQUE; ROTATION.
Ano: 1990 URL: http://www.documentation.ird.fr/hor/fdi:30991
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Variations of the ACC-CDW during MIS3 traced by magnetic grain deposition in midlatitude South Indian Ocean cores: Connections with the northern hemisphere and with central Antarctica ArchiMer
Mazaud, A.; Kissel, C.; Laj, C.; Sicre, M. A.; Michel, E.; Turon, J. L..
We examine the magnetic mineral deposition in three cores located at midlatitude sites in the South Indian Ocean, in an area where sediment eroded from the Kerguelen-Crozet plateau and transported by the marine currents, principally the Antarctic Circum Current, accumulates at a high sedimentation rate. We focus on Marine Isotopic Stage 3, characterized by large climatic fluctuations at northern latitudes, and compare the obtained records to the climatic records at Byrd ( Antarctica) and Summit (GISP2, Greenland) and to the North Atlantic Deep Water variations in the North Atlantic. Magnetic mineral deposition at the studied sites exhibits a profile with maxima at the time of Heinrich events H4 and H5, which suggests a strong Antarctic Circum Current when...
Tipo: Text Palavras-chave: Paleoceanography; South; Indian; Ocean; Paleoclimatology and paleoceanography; Environmental magnetism; Interhemispheric phasing.
Ano: 2007 URL: https://archimer.ifremer.fr/doc/00235/34612/32954.pdf
Registros recuperados: 8
Primeira ... 1 ... Última
 

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