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Registros recuperados: 6
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Atlantic Ocean circulation changes preceded millennial tropical South America rainfall events during the last glacial 5
Burckel, Pierre; Waelbroeck, Claire; Gherardi, Jeanne Marie; Pichat, Sylvain; Arz, Helge; Lippold, Joerg; Dokken, Trond; Thil, Francois.
During the last glacial period, Greenland's climate shifted between cold (stadial) and warm (interstadial) phases that were accompanied by ocean circulation changes characterized by reduced Atlantic Meridional Overturning Circulation (AMOC) during stadials. Here we present new data from the western tropical Atlantic demonstrating that AMOC slowdowns preceded some of the large South American rainfall events that took place during stadials. Based on 231Pa/230Th and Ti/Ca measurements in the same sediment core, we determine that the AMOC started to slowdown 1420 ± 250 and 690 ± 180 (1σ) years before the onset of two large precipitation events associated with Heinrich stadials. Our results bring unprecedented evidence that AMOC changes could be at the origin...
Tipo: Text Palavras-chave: Heinrich stadials; Dansgaard-Oeschger stadials; AMOC; ITCZ; Pa; Th.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00296/40711/39709.pdf
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Changes in the geometry and strength of the Atlantic meridional overturning circulation during the last glacial (20-50 ka) 5
Burckel, Pierre; Waelbroeck, Claire; Luo, Yiming; Roche, Didier M.; Pichat, Sylvain; Jaccard, Samuel L.; Gherardi, Jeanne; Govin, Aline; Lippold, Jörg; Thil, Francois.
We reconstruct the geometry and strength of the Atlantic meridional overturning circulation during the Heinrich stadial 2 and three Greenland interstadials of the 2050 ka period based on the comparison of new and published sedimentary Pa-231/Th-230 data with simulated sedimentary Pa-231/Th-230. We show that the deep Atlantic circulation during these interstadials was very different from that of the Holocene. Northern-sourced waters likely circulated above 2500 m depth, with a flow rate lower than that of the present-day North Atlantic deep water (NADW). Southern-sourced deep waters most probably flowed northwards below 4000 m depth into the North Atlantic basin and then southwards as a return flow between 2500 and 4000 m depth. The flow rate of this...
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Ano: 2016 URL: https://archimer.ifremer.fr/doc/00421/53212/54867.pdf
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GEOTRACES inter-calibration of the stable silicon isotope composition of dissolved silicic acid in seawater 5
Grasse, Patricia; Brzezinski, Mark A.; Cardinal, Damien; De Souza, Gregory F.; Andersson, Per; Closset, Ivia; Cao, Zhimian; Dai, Minhan; Ehlert, Claudia; Estrade, Nicolas; Francois, Roger; Frank, Martin; Jiang, Guibin; Jones, Janice L.; Kooijman, Ellen; Liu, Qian; Lu, Dawei; Pahnke, Katharina; Ponzevera, Emmanuel; Schmitt, Melanie; Sun, Xiaole; Sutton, Jill; Thil, Francois; Weis, Dominique; Wetzel, Florian; Zhang, Anyu; Zhang, Jing; Zhang, Zhouling.
The first inter-calibration study of the stable silicon isotope composition of dissolved silicic acid in seawater, delta Si-30(OH)(4), is presented as a contribution to the international GEOTRACES program. Eleven laboratories from seven countries analyzed two seawater samples from the North Pacific subtropical gyre (Station ALOHA) collected at 300 m and at 1000 m water depth. Sampling depths were chosen to obtain samples with a relatively low (9 mmol L-1, 300 m) and a relatively high (113 mmol L-1, 1000 m) silicic acid concentration as sample preparation differs for low- and highconcentration samples. Data for the 1000 m water sample were not normally distributed so the median is used to represent the central tendency for the two samples. Median delta...
Tipo: Text
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00381/49270/49681.pdf
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Neodymium isotopic composition in foraminifera and authigenic phases of South China Sea sediments: Implications for the hydrology of the North Pacific Ocean over the past 25 kyr 5
Wu, Qiong; Colin, Christophe; Liu, Zhifei; Thil, Francois; Dubois-dauphin, Quentin; Frank, Norbert; Tachikawa, Kazuyo; Bordier, Louise; Douville, Eric.
εNd and normalized Rare Earth Elements (REE) patterns of benthic and planktonic foraminifera and Fe-Mn coatings precipitated on sediments have been investigated for the South China Sea (SCS) to (1) assess the reliability of the extraction of past seawater εNd in the SCS and to (2) reconstruct past hydrological changes during the last 25 kyr. Reductively cleaned mono-specific planktonic foraminifera (Globigerinoides ruber) and mixed benthic foraminifera in core-top sediments from 1500 to 2400 m display similar εNd values to those of the modern Pacific Deep Water (PDW) (εNd of −3.9 to −4.4). Furthermore, the εNd of the reductive cleaning solutions shows similar εNd values to ones obtained on cleaned foraminifera. Combined with PAAS-normalized REE patterns,...
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Ano: 2015 URL: https://archimer.ifremer.fr/doc/00295/40582/39500.pdf
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Rbiative timing of precipitation and ocean circui In changes in the western equatorial Atlantic over the last 45 kyr 5
Waelbroeck, Claire; Pichat, Sylvain; Bohm, Evelyn; Lougheed, Bryan C.; Faranda, Davide; Vrac, Mathieu; Missiaen, Lise; Vazquez Riveiros, Natalia; Burckel, Pierre; Lippold, Joerg; Arz, Helge W.; Dokken, Trond; Thil, Francois; Dapoigny, Arnaud.
Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti / Ca). New sedimentary Pa / Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa / Th and ln(Ti/Ca) signals. We show that decreased water mass...
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Ano: 2018 URL: http://archimer.ifremer.fr/doc/00460/57126/59040.pdf
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Unveiling the Si cycle using isotopes in an iron fertilized zone of the Southern Ocean: from mixed layer supply to export 5
Closset, Ivia; Cardinal, Damien; Rembauville, Mathieu; Thil, Francois; Blain, Stephane.
A massive diatom-bloom is observed annually in the surface waters of the naturally Fe-fertilized Kerguelen Plateau (Southern Ocean). In this study, silicon isotopic signatures (δ30Si) of silicic acid (DSi) and suspended biogenic silica (BSi) were investigated in the whole water column with an unprecedented spatial resolution in this region, during the KEOPS-2 experiment (spring 2011). We use δ30Si measurements to track the silicon sources that fuel the bloom, and investigate the seasonal evolution of Si biogeochemical cycle in the iron fertilized area. We compare the results from a HNLC reference station with stations characterized by different degrees of iron enrichment and bloom conditions. Dissolved and particulate δ30Si signatures were generally highly...
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Ano: 2016 URL: https://archimer.ifremer.fr/doc/00344/45528/45085.pdf
Registros recuperados: 6
Primeira ... 1 ... Última
 

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