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| Regoli, Fabienne; De Garidel-thoron, Thibault; Tachikawa, Kazuyo; Jian, Zhiming; Ye, Liming; Droxler, Andre W.; Lenoir, Guillaume; Crucifix, Michel; Barbarin, Nicolas; Beaufort, Luc. |
| The depth of equatorial Pacific thermocline is diagnostic of the main modes of tropical climates. Past estimates of Pacific thermocline dynamics have been reconstructed either for the Last Glacial Maximum or on longer timescales at low resolution. Here we document a new high-resolution set of reconstructed past sea surface and subsurface waters temperatures from the southwestern subequatorial Pacific, core MD05-2930, in the Gulf of Papua, over the last 800 ka. We used two morphotypes of Globigerinoides ruber known to live at different water depths to reconstruct past stratification. We estimated calcification temperature of each morphotypes by Mg/Ca paleothermometry. Our subequatorial Pacific thermocline paleotemperature record indicates a response of the... |
| Tipo: Text |
Palavras-chave: Equatorial Pacific; Thermocline; Pleistocene. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00295/40572/39477.pdf |
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| Levi, Camille; Labeyrie, Laurent; Bassinot, Franck; Guichard, Francois; Cortijo, Elsa; Waelbroeck, Claire; Caillon, Nicolas; Duprat, Josette; De Garidel-thoron, Thibault; Elderfield, Harry. |
| Sea surface temperature and oxygen isotopic records from two well-dated Indian Ocean cores covering the last deglaciation show the occurrence of two periods of increased salinity along the route of warm surface water transport from the Indian to the Atlantic Ocean, one between 18 and 14.5 ka and the other during the Younger Dryas. Our results imply that during these periods, salt accumulated in the tropical Atlantic, creating favorable conditions for an abrupt resumption of the thermohaline circulation and abrupt northern hemisphere warming. Furthermore, we suggest that the observed pattern of millennial climate variability during the last glacial and deglaciation resulted from the interaction between the relatively slow rhythm of expansion and decay of... |
| Tipo: Text |
Palavras-chave: Rapid climate changes; Low-latitude hydrological cycle; Last deglaciation. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00235/34611/32960.pdf |
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| Andre, Aurore; Quillevere, Frederic; Morard, Raphael; Ujiie, Yurika; Escarguel, Gilles; De Vargas, Colomban; De Garidel-thoron, Thibault; Douady, Christophe J.. |
| The use of planktonic foraminifera in paleoceanography requires taxonomic consistency and precise assessment of the species biogeography. Yet, ribosomal small subunit (SSUr) DNA analyses have revealed that most of the modern morphospecies of planktonic foraminifera are composed of a complex of several distinct genetic types that may correspond to cryptic or pseudo-cryptic species. These genetic types are usually delimitated using partial sequences located at the 3'end of the SSUrDNA, but typically based on empirical delimitation. Here, we first use patristic genetic distances calculated within and among genetic types of the most common morpho-species to show that intra-type and inter-type genetic distances within morpho-species may significantly overlap,... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40107/38859.pdf |
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| Marchant, Ross; Tetard, Martin; Pratiwi, Adnya; Adebayo, Michael; De Garidel-thoron, Thibault. |
| Manual identification of foraminiferal morphospecies or morphotypes under stereo microscopes is time consuming for micropalaeontologists and not possible for nonspecialists. Therefore, a long-term goal has been to automate this process to improve its efficiency and repeatability. Recent advances in computation hardware have seen deep convolutional neural networks emerge as the state-of-the-art technique for image-based automated classification. Here, we describe a method for classifying large foraminifera image sets using convolutional neural networks. Construction of the classifier is demonstrated on the publicly available Endless Forams image set with a best accuracy of approximately 90 %. A complete automatic analysis is performed for benthic species... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00655/76687/77826.pdf |
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| Morard, Raphaël; Füllberg, Angelina; Brummer, Geert-jan A.; Greco, Mattia; Jonkers, Lukas; Wizemann, André; Weiner, Agnes K. M.; Darling, Kate; Siccha, Michael; Ledevin, Ronan; Kitazato, Hiroshi; De Garidel-thoron, Thibault; De Vargas, Colomban; Kucera, Michal. |
| The planktonic foraminifera genus Globigerinoides provides a prime example of a species-rich genus in which genetic and morphological divergence are uncorrelated. To shed light on the evolutionary processes that lead to the present-day diversity of Globigerinoides, we investigated the genetic, ecological and morphological divergence of its constituent species. We assembled a global collection of single-cell barcode sequences and show that the genus consists of eight distinct genetic types organized in five extant morphospecies. Based on morphological evidence, we reassign the species Globoturborotalita tenella to Globigerinoides and amend Globigerinoides ruber by formally proposing two new subspecies, G. ruber albus n.subsp. and G. ruber ruber in order to... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00595/70719/68946.pdf |
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| Moreno, Eva; Caroir, Fabien; Fournier, Lea; Fauquembergue, Kelly; Zaragosi, Sébastien; Joussain, Ronan; Colin, Christophe; Blanc-valleron, Marie-madeleine; Baudin, François; De Garidel-thoron, Thibault; Valet, Jean Pierre; Bassinot, Franck. |
| We present here a study based on the Anisotropy of Magnetic Susceptibility (AMS) and magnetic mineralogy carried out on the composite core MD17&18taken from the eastern levee of the active channel of the middle Bengal Fan in the Indian Ocean. Based on C-14 dating, the sedimentary sequence covers 9.8 ka in 39 m of sediment. It therefore records at very high resolution the variations in continental material exported to the ocean by the Ganges-Brahmaputra river system during the Holocene. This sequence was divided into two units according to turbidite activity: Unit 1 from 9.8 to 9.2 ka cal. Representing 39 m of coarse-grained turbidite sequences (coarse silts to fine sands) and extremely high sedimentation rates. Unit 2 of 9.2 ka cal. BP to the present... |
| Tipo: Text |
Palavras-chave: Bengal fan; Holocene; Turbidite activity; Magnetic fabric; Magnetic mineralogy. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00652/76388/77402.pdf |
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| Morard, Raphael; Escarguel, Gilles; Weiner, Agnes K. M.; Andre, Aurore; Douady, Christophe J.; Wade, Christopher M.; Darling, Kate F.; Ujiie, Yurika; Seears, Heidi A.; Quillevere, Frederic; De Garidel-thoron, Thibault; De Vargas, Colomban; Kucera, Michal. |
| Investigations of biodiversity, biogeography, and ecological processes rely on the identification of "species" as biologically significant, natural units of evolution. In this context, morphotaxonomy only provides an adequate level of resolution if reproductive isolation matches morphological divergence. In many groups of organisms, morphologically defined species often disguise considerable genetic diversity, which may be indicative of the existence of cryptic species. The diversity hidden by morphological species can be disentangled through genetic surveys, which also provide access to data on the ecological distribution of genetically circumscribed units. These units can be identified by unique DNA sequence motifs and allow studies of evolutionary and... |
| Tipo: Text |
Palavras-chave: Cryptic species; Genetic diversity; Planktonic foraminifera; Molecular nomenclature; MOTUs. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00383/49408/49900.pdf |
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| Morard, Raphael; Quillevere, Frederic; Douady, Christophe J.; De Vargas, Colomban; De Garidel-thoron, Thibault; Escarguel, Gilles. |
| The planktonic foraminiferal morpho-species Globoconella inflata is widely used as a stratigraphic and paleoceanographic index. While G. inflata was until now regarded as a single species, we show that it rather constitutes a complex of two pseudo-cryptic species. Our study is based on SSU and ITS rDNA sequence analyses and genotyping of 497 individuals collected at 49 oceanic stations covering the worldwide range of the morpho-species. Phylogenetic analyses unveil the presence of two divergent genotypes. Type I inhabits transitional and subtropical waters of both hemispheres, while Type II is restricted to the Antarctic subpolar waters. The two genetic species exhibit a strictly allopatric distribution on each side of the Antarctic Subpolar Front. On the... |
| Tipo: Text |
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| Ano: 2011 |
URL: https://archimer.ifremer.fr/doc/00144/25559/23704.pdf |
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