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Millennial-scale dynamics of the East Asian winter monsoon during the last 200,000 years

Thibault de Garidel-ThoronL Beaufort, BK Linsley, and S Dannenmann
Journal Paper Paleoceanography, 16, no. 5, January 2001, 491–502


The primary productivity dynamics of the last 200,000 years in the Sulu Sea was reconstructed using the abundance of the coccolithophore Florisphaera profunda in the IMAGES MD97-2141 core. We find that primary productivity was enhanced during glacial periods, which we suggest is due to a stronger East Asian winter monsoon. During the last 80 kyr, eight significant increases in primary productivity (PP) in the Sulu Sea are similar to East Asian winter monsoon changes recorded in Chinese loess. The PP maxima are not linked with Heinrich events (HE) in the North Atlantic, although four PP peaks are synchronous with HE. The PP oscillations have frequencies near those of the Dansgaard-Oeschger cycles in Northern Hemisphere ice records and indicate a teleconnection of the East Asian winter monsoon with Greenland climate. In this Sulu Sea record the East Asian winter monsoon oscillates with periodicities of similar to6, 4.2-3.4, 2.3, and 1.5 kyr. In particular, the 1.5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the Holocene without any ice volume modulation. This stationarity suggests that the 1.5 kyr cycle is not driven by some high-latitude forcing.

Biomass burning and oceanic primary production estimates in the Sulu Sea area over the last 380 kyr and the East Asian monsoon dynamics

L. Beaufort, T. de Garidel-Thoron, B Linsley, D Oppo, and N Buchet.
Journal Paper Marine Geology, 201, no. 1 (January 1, 2003): 53–65


Coccolithophorid assemblages and micro-charcoal content were analysed in giant piston core MD97-2141 recovered in the Sulu Sea (Philippines). These proxies help to reconstruct respectively the dynamics of the oceanic primary production (PP) and biomass burning in that area. PP in the Sulu Sea intensifies during the East Asian winter monsoon (EAWM) and therefore PP constitutes a proxy for EAWM dynamics. Most of the precipitation in the Sulu Sea region occurs during the East Asian summer monsoon (EASM). Because the intensity of biomass burning is related to dryness of the surrounding area, the sedimentary micro-charcoal content can be used as an inverse proxy for EASM intensity. Our results show that the EAWM intensifies during glacial times in agreement with previous studies. Precessional forcing appears to act directly on EAWN because of the early response of PP in that frequency band. The micro-charcoal record exhibits complex dynamics, which we attribute to the competing influence of the long-term El Nino Southern Oscillation (ENSO)-like forcing and the glacial/interglacial cycle on EASM. These influences create an unusual frequency spectrum with power around 30 kyr and 19 kyr attributed to the non-linear response to the 100-kyr cycle (glacial) and the 23-kyr (ENSO) cycle. A factor of two increase in the amplitude of the micro-charcoal variability between 51 and 10 ka BP could correspond to Homo sapiens biomass burning in the style of the fire-stick farming of the Australian Aborigines. We also find, on precession cycles, an opposite phase between EASM and EAWM records and an advance of -delta(18)O and delta(18)O respectively by 2000 yr.

Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Thibault de Garidel-ThoronLuc Beaufort, Franck Bassinot, and Pierre Henry
Journal PaperProceedings of the National Academy of Sciences, 101, no. 25 (2004): 9187–9192.


Past atmospheric methane-concentration oscillations recorded in polar ice cores vary together with rapid global climatic changes during the last glacial episode. In the ‘‘clathrate gun hypothesis,’’ massive releases of deep-sea methane from marine gas-hydrate dissociation led to these well known, global, abrupt warmings in the past. If evidence for such releases in the water column exists, however, the mechanism and eventual transfer to the atmosphere has not yet been documented clearly. Here we describe a high- resolution marine-sediment record of stable carbon isotopic changes from the Papua Gulf, off Papua New Guinea, which exhibits two extremely depleted excursions (down to 􏰖9‰) at 􏰗39,000 and 􏰗55,000 years. Morphological, isotopic, and trace metal evidence dismisses authigenic calcite as the main source of depleted carbon. Massive methane release associated with deep- sea gas-hydrate dissociation is the most likely cause for such large depletions of 􏰍13C. The absence of a 􏰍13C gradient in the water column during these events implies that the methane rose through the entire water column, reaching the sea–air interface and thus the atmosphere. Foraminiferal 􏰍18O composition suggests that the rise of the methane in the water column created an upwelling flow. These inferred emission events suggest that during the last glacial episode, this process was likely widespread, including tropical regions. Thus, the release of methane from the ocean floor into the atmosphere cannot be dismissed as a strong positive feedback in climate dynamics processes.

ENSO-Like Forcing on Oceanic Primary Production During the Late Pleistocene

Beaufort, L, T. de Garidel-Thoron, AC Mix, and NG Pisias.
Journal PaperScience, 293, no. 5539 (January 1, 2001): 2440–2444.


Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores. We show that variations in equatorial productivity are primarily caused by glacial-interglacial variability and by precession-controlled changes in the east-west thermodine slope of the Indo-Pacific. The precession-controlled variations in productivity are linked to processes similar to the Southern Oscillation phenomenon, and they precede changes in the oxygen isotopic ratio, which indicates that they are not the result of ice sheet fluctuations. The 30,000-year spectral peak in the tropical Indo-Pacific Ocean productivity records is also present in the Antarctica atmospheric CO2 record, suggesting an important rote for equatorial biological productivity in modifying atmospheric CO2.

Stable sea surface temperatures in the western Pacific warm pool over the past 1.75 million years

T. de Garidel-Thoron, Y. Rosenthal, F. Bassinot, L. Beaufort
Journal PaperNature 433, no. 7023 (January 1, 2005): 294–298. doi:10.1038/nature03189.


About 850,000 years ago, the period of the glacial cycles changed from 41,000 to 100,000 years. This mid-Pleistocene climate transition has been attributed to global cooling, possibly caused by a decrease in atmospheric carbon dioxide concentrations(1,2). However, evidence for such cooling is currently restricted to the cool upwelling regions in the eastern equatorial oceans(3,4), although the tropical warm pools on the western side of the ocean basins are particularly sensitive to changes in radiative forcing(5,6). Here we present high-resolution records of sea surface temperatures spanning the past 1.75 million years, obtained from oxygen isotopes and Mg/Ca ratios in planktonic foraminifera from the western Pacific warm pool. In contrast with the eastern equatorial regions, sea surface temperatures in the western Pacific warm pool are relatively stable throughout the Pleistocene epoch, implying little long-term change in the tropical net radiation budget. Our results challenge the hypothesis of a gradual decrease in atmospheric carbon dioxide concentrations as a dominant trigger of the longer glacial cycles since 850,000 years ago. Instead, we infer that the temperature contrast across the equatorial Pacific Ocean increased, which might have had a significant influence on the mid-Pleistocene climate transition.

Fidelity of radially viewed ICP-OES and magnetic-sector ICP-MS measurement of Mg/Ca and Sr/Ca ratios in marine biogenic carbonates: Are they trustworthy together?

Andreasen, D, S Perron-Cashman, CH Lear, S Sosdian, T de Garidel-Thoron, P Field, and Yair Rosenthal
Journal Paper Geochemistry Geophysics Geosystems 7 (January 1, 2006): Q10P18. doi:10.1029/2005GC001124.


Improving interlaboratory reproducibility (in both precision and accuracy) of Mg/Ca and Sr/Ca determination in marine biogenic carbonates is critical in optimizing their utility as paleothermometers. Coupled with a need for uniform sample cleaning practices, there is a need for more exacting methods and procedures across laboratories using varied instrumentation. Here we employ an intensity ratio/matrix-effect correction methodology to a suite of solution standards and biogenic carbonates (foraminifera tests and a gastropod shell) to investigate short-term and long-term Mg/Ca and Sr/Ca precision and accuracy by different instruments: a magnetic-sector inductively coupled plasma-mass spectrometer (ICP-MS) and a radially viewed inductively coupled plasma-optical emission spectrophotometer (ICP-OES). Over an extended 1.0-24.5 mM Ca concentration range, both instruments have significant Ca matrix effects for Mg/Ca and somewhat less for Sr/Ca. Over our working Ca range (1-8 mM Ca), Mg/Ca matrix effects are significant, requiring correction, and Sr/Ca matrix effects are small to negligible, occasionally requiring correction (linear or logarithmic fit) using a suite of matrix standards for both instruments. The short-term (intrarun) precision for a suite of solution standards is <0.2% (1 sigma %RSD) for Mg/Ca and Sr/Ca for both instruments. A long-term (interrun) precision of <0.9% is demonstrated for Mg/Ca and <0.6% for Sr/Ca on both instruments. The accuracy of measured Mg/Ca and Sr/Ca values for short- and long-term standards is similar on both instruments at better than 1 +/- 0.5%, on par with our long-term precision. An interinstrument comparison of the same measured suite of biogenic carbonates demonstrates that after accounting for matrix effects, data generated on either instrument are essentially interchangeable (within analytical precision) to a high degree of fidelity.

Late Quaternary paleoceanography of the northwestern Pacific: Results from IMAGES program

Y. RosenthalT. de Garidel-Thoron, L. Beaufort
Journal PaperGlobal and Planetary Change 53, no. 1 (January 1, 2006): 1–4. doi:10.1016/j.gloplacha.2006.05.001


Evidence for multiple paleomagnetic intensity lows between 30 and 50 ka BP from a western Equatorial Pacific sedimentary sequence

Cécile L. Blanchet, N. Thouveny, T. de Garidel-Thoron
Journal PaperQuaternary Science Reviews 25, no. 9 (January 1, 2006): 1039–1052. doi:10.1016/j.quascirev.2005.09.001.


A paleomagnetic study was carried out on the radiocarbon dated MD97-2134 core located in the western Equatorial Pacific (Southern Papua New Guinea margin). Rock magnetic investigations revealed changes of the magnetic mineralogy along the hemi-pelagic sedimentary sequence but the reconstruction of past direction and relative paleointensity variations of the geomagnetic field remained feasible. Four successive paleointensity drops are recorded between 30 and 50 ka BP. The largest one is associated with an abrupt swing of declination and inclination interpreted as a smoothed signature of the Laschamp excursion (similar to 41 ka BP). The Succession of four events of weak intensity between 30 and 50 ka BP introduces a complex behaviour of the geomagnetic field in the time interval spanning over the Laschamp and the Mono Lake excursions.

Low-latitude hydrological cycle and rapid climate changes during the last deglaciation

Levi, Camille, Laurent Labeyrie, Franck Bassinot, Francois Guichard, Elsa Cortijo, Claire Waelbroeck, Nicolas Caillon, Josette Duprat, Thibault de Garidel-Thoron, and Harry Elderfield. .Cécile L. Blanchet, N. Thouveny, T. de Garidel-Thoron
Journal PaperGeochemistry Geophysics Geosystems 8 (January 1, 2007): Q05N12. doi:10.1029/2006GC001514


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 the northern hemisphere ice sheets, and El Nino-Southern Oscillation variability, through changes in the position of the Intertropical Convergence Zone. This interaction generated an oscillator with millennial time response that operated at times of sufficient northern hemisphere ice sheets extent.

A multiproxy assessment of the western equatorial Pacific hydrography during the last 30 kyr

de Garidel-Thoron, Thibault, Yair Rosenthal, Luc Beaufort, Edouard Bard, Corinne Sonzogni, and Alan C Mix.
Journal PaperPaleoceanography 22, no. 3 (January 1, 2007): PA3204. doi:10.1029/2006PA001269.


Sea surface temperature (SST) and salinity of the Western Pacific Warm Pool (WPWP) reflect global climate effects such as the El Nino - Southern Oscillation phenomenon. However, reconstructions of past changes in the WPWP from the geologic record vary depending on the specific proxy record used. Here we develop a multiproxy record of the last deglaciation from a radiocarbon-dated sediment core (MD97-2138) retrieved in the heart of the WPWP. SST reconstructions for the past 30,000 years based on planktonic foraminiferal Mg/Ca (Globigerinoides ruber and Globigerinoides sacculifer), alkenone unsaturation index, and foraminiferal transfer functions differ notably. Mg/Ca-based SST estimates from the surface dwelling species G. ruber in MD97-2138 indicate a larger surface cooling (3 degrees +/- 0.6 degrees C) during the Last Glacial Maximum (LGM) than inferred from Mg/Ca ratios in G. sacculifer (2.3 degrees +/- 0.7 degrees C), statistical transfer functions based on planktonic foraminiferal species assemblages, and Uk(37)' (1 degrees-2 degrees C). These estimates are consistent with estimates from other WPWP cores, thereby suggesting that the discrepancy is due to proxy compatibility rather than differences in cores qualitity. Postdepositional dissolution above the lysocline might have altered the Mg/Ca-based temperature estimates in our site, but this effect is insufficient to resolve discrepancies between Mg/Ca in G. ruber and the other proxies. We suggest that the lower estimates obtained from Mg/Ca in G. sacculifer, faunal transfer functions, and Uk(37)' might reflect subsurface temperature changes rather than strict surface estimates. Accounting for potential artefacts, including dissolution and bioturbation, we suggest that the glacial WPWP SST was about 2.5 degrees +/- 0.7 degrees C cooler than during the Holocene, whereas the subsurface/upper thermocline temperature change was only about 1.8 degrees +/- 0.7 degrees C. Interpreting variations in delta O-18(SW) in terms of salinity changes suggests a possibly slight decrease in surface salinity at the site of MD97-2138 during the LGM. Though LGM freshening in MD97-2138 is not robust to postdeposition dissolution effects, this inferred freshening appears to be a general feature of the western equatorial Pacific.

Morphological recognition of cryptic species in the planktonic foraminifer Orbulina universa

Morard, Raphaël, Frédéric Quillévéré, Gilles Escarguel, Yurika Ujiie, Thibault de Garidel-Thoron, Richard D Norris, and Colomban de Vargas
Journal PaperMarine Micropaleontology 71, no. 3 (April 22, 2009): 148–165. doi:10.1016/j.marmicro.2009.03.001


One of the key hypotheses of paleoceanography is that planktonic foraminiferal morphospecies record reasonably stable and homogeneous oceanographic and climatic characteristics over their geographic and stratigraphic ranges. The discovery of numerous genetically-defined cryptic species challenges the morphospecies concept in planktonic foraminifera and paleoceanographic interpretations based on them. Here, we present a combined genetic and biometric analysis of Orbulina universa specimens in the Atlantic, Indian and Pacific Oceans. Our study is based on shells retained after DNA extractions. On those genotyped shells, we perform biometric analyses (shell size and thickness, inner porosity and pore surface distribution). Our genetic data confirm the presence of three cryptic species of O. universa in the world ocean, whose distributions are primarily correlated to the productivity of the surface waters. The Mediterranean species of O. universa is most abundant in the vertically mixed and nutrient-rich areas of the low to mid-latitudes, whereas the Caribbean and Sargasso species occur in stratified and oligotrophic subtropical waters. Our biometric data show no correlation between shell size and inner porosity within each cryptic species of O. universa. Combining Principal Component Analyses with MANOVAs performed on shell pore surface distribution, we demonstrate that the three different cryptic species are characterized by significant morphological differentiation. The Caribbean species typically exhibits large pores and higher porosity values, while the Mediterranean and Sargasso species are characterized by smaller pore areas and shell porosity. A model based upon pore surface distribution correctly assigns 60% to 90% of the specimens to their corresponding genotype. Although the inner shell surface of the Sargasso species resembles that of the Mediterranean species, our model demonstrates that the pore surface distributions of these two cryptic species can be distinguished. Finally, the Sargasso species exhibits significantly thinner shells than the two other cryptic species.

Coiling dimorphism within a genetic type of the planktonic foraminifer Globorotalia truncatulinoides

Ujiie, Yurika, Thibault de Garidel-Thoron, Silvia Watanabe, Peter Wiebe, and Colomban de Vargas.
Journal PaperMarine Micropaleontology 77 (2010): 145–153. doi:10.1016/j.marmicro.2010.09.001


The coiling direction sinistral (left-coiled) or dextral (right-coiled) of planktonic foraminiferal shells is a classical proxy used to assess past environmental changes and to understand their evolutionary patterns. Globorotalia truncatulinoides is composed of five different genetic types (I to V), each with a specific biogeographic distribution. So far, type II is the only type within which both coiling types have been frequently found. Here we examine the coiling direction as a dimorphic variation in a single genetic type, and show that the two forms with different coiling directions differ in ecology. The studied 140 left- and 137 right-coiled specimens from eight depth layers at four stations in the Sargasso Sea all belonged to Type II, based on the phylogenetic analyses of the ITS (internal transcribed spacer) region of ribosomal DNA. The distributions of left- and right-coiled Type II (Type II-L and II-R) differed strongly: Type II-L dominated between 400 and 200 m depth in the central water mass, whereas Type II-R was common in the top 200 m of the subtropical gyre. The left- and right-coiled forms are thus associated with different water masses. However, the vertical distribution along a temperature gradient indicates that their coiling direction is not determined by temperature, and might have some genetic basis. Our molecular phylogenetic analyses showed that the two forms probably share the same gene pool through their dispersals between different water masses. Moreover, the lineage of G. truncatulinoides is young (<3 Ma), which might not be long enough to evolve into two lineages with opposite coiling direction. We discuss the practical and theoretical usefulness of a simple genetic model for coil dimorphism, in order to build testable hypotheses regarding the evolutionary history of planktonic foraminifera at the population level.

Sensitivity of coccolithophores to carbonate chemistry and ocean acidification

Beaufort, L, I Probert, Thibault de Garidel-Thoron, E M Bendif, D Ruiz-Pino, N Metzl, C Goyet, N. Buchet, P. Coupel, M. Grelaud, B. Rost, REM Rickaby and C. de Vargas
Journal PaperNature 476, no. 7358 (August 3, 2011): 80–83. doi:10.1038/nature10295


About one-third of the carbon dioxide (CO2) released into the atmosphere as a result of human activity has been absorbed by the oceans, where it partitions into the constituent ions of carbonic acid. This leads to ocean acidification, one of the major threats to marine ecosystems and particularly to calcifying organisms such as corals, foraminifera and coccolithophores. Coccolithophores are abundant phytoplankton that are responsible for a large part of modern oceanic carbonate production. Culture experiments investigating the physiological response of coccolithophore calcification to increased CO2 have yielded contradictory results between and even within species. Here we quantified the calcite mass of dominant coccolithophores in the present ocean and over the past forty thousand years, and found a marked pattern of decreasing calcification with increasing partial pressure of CO2 and concomitant decreasing concentrations of CO32-. Our analyses revealed that differentially calcified species and morphotypes are distributed in the ocean according to carbonate chemistry. A substantial impact on the marine carbon cycle might be expected upon extrapolation of this correlation to predicted ocean acidification in the future. However, our discovery of a heavily calcified Emiliania huxleyi morphotype in modern waters with low pH highlights the complexity of assemblage-level responses to environmental forcing factors.

Worldwide Genotyping in the Planktonic Foraminifer Globoconella inflata: Implications for Life History and Paleoceanography

Morard, Raphaël, Frédéric Quillévéré, Christophe J Douady, Colomban de Vargas, Thibault de Garidel-Thoron, and Gilles Escarguel.
Journal Paper PLos ONE Edited by Anna Stepanova. 6, no. 10 (October 20, 2011): e26665. doi:10.1371/journal.pone.0026665.t003


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 other hand, sediment data show that G. inflata was restricted to transitional and subtropical environments since the early Pliocene, and expanded its geographic range to southern subpolar waters ~700 kyrs ago, during marine isotopic stage 17. This datum may correspond to a peripatric speciation event that led to the partition of an ancestral genotype into two distinct evolutionary units. Biometric measurements performed on individual G. inflata from plankton tows north and south of the Antarctic Subpolar Front indicate that Types I and II display slight but significant differences in shell morphology. These morphological differences may allow recognition of the G. inflata pseudo-cryptic species back into the fossil record, which in turn may contribute to monitor past movements of the Antarctic Subpolar Front during the middle and late Pleistocene.

Longitudinal Differentiation Among Pelagic Populations in a Planktic Foraminifer

Ujiie, Yurika, Asami TakahiroThibault de Garidel-Thoron, Hui Liu, Yoshiyuki Ishitani, and Colomban de Vargas
Journal Paper Ecology and Evolution (June 22, 2012): 1–13. doi:10.1002/ece3.286


Evolutionary processes in marine plankton have been assumed to be dependent on the oceanic circulation system, which transports plankton between populations in marine surface waters. Gene flow facilitated by oceanic currents along longitudinal gradients may efficiently impede genetic differentiation of pelagic populations in the absence of confounding marine environmental effects. However, how responsible oceanic currents are for the geographic distribution and dispersal of plankton is poorly understood. We examined the phylogeography of the planktic foraminifer Pulleniatina obliquiloculata in the Indo-Pacific Warm Pool (IPWP) by using partial small subunit ribosomal DNA (SSU rDNA) sequences. We found longitudinal clines in the frequencies of three distinct genetic types in the IPWP area. These frequencies were correlated with environmental factors that are characteristic of three water masses in the IPWP. Noteworthy, populations inhabiting longitudinally distant water masses at the Pacific and Indian sides of the IPWP were genetically different, despite transportation of individuals via oceanic currents. These results demonstrate that populations of pelagic plankton have diverged genetically among different water masses within a single climate zone. Changes of the oceanic circulation system could have impacted the geographic patterns of dispersal and divergence of pelagic plankton.

The cryptic and the apparent reversed: lack of genetic differentiation within the morphologically diverse plexus of the planktonic foraminifer Globigerinoides sacculifer

Aurore André, Agnes Weiner, Frédéric Quillévéré, Ralf Aurahs, Raphaël Morard, Christophe J. Douady, Thibault de Garidel-Thoron, Gilles Escarguel, Colomban de Vargas, and Michal Kucera
Journal Paper Paleobiology Winter 2013, Vol. 39, No. 1, pp. 21-39. 10.1666/0094-8373-39.1.21


Previous genetic studies of extant planktonic foraminifera have provided evidence that the traditional, strictly morphological definition of species in these organisms underestimates their biodiversity. Here, we report the first case where this pattern is reversed. The modern (sub)tropical species plexus Globigerinoides sacculifer is characterized by large morphological variability, which has led to the proliferation of taxonomic names attributed to morphological end-members within the plexus. In order to clarify the taxonomic status of its morphotypes and to investigate the genetic connectivity among its currently partly disjunct (sub)tropical populations, we carried out a global survey of two ribosomal RNA regions (SSU and ITS-1) in all recent morphotypes of the plexus collected throughout (sub)tropical surface waters of the global ocean. Unexpectedly, we find an extremely reduced genetic variation within the plexus and no correlation between genetic and morphological divergence, suggesting taxonomical overinterpretation. The genetic homogeneity within the morphospecies is unexpected, considering its partly disjunct range in the (sub)tropical Atlantic and Indo-Pacific and its old age (early Miocene). A sequence variant in the rapidly evolving ITS-1 region indicates the existence of an exclusively Atlantic haplotype, which suggests an episode of relatively recent (last glacial) isolation, followed by subsequent resumption of unidirectional gene flow from the Indo-Pacific into the Atlantic. This is the first example in planktonic foraminifera where the morphological variability in a morphospecies exceeds its rDNA genetic variability. Such evidence for inconsistent scaling of morphological and genetic diversity in planktonic foraminifera could complicate the interpretation of evolutionary patterns in their fossil record.

Ecological modeling of the temperature dependence of cryptic species of planktonic Foraminifera in the Southern Hemisphere

Morard, Raphaël, Frédéric Quillévéré, Gilles Escarguel, Thibault de Garidel-Thoron, Colomban de Vargas,and Michal Kucera.
Journal Paper Palaeogeography Palaeoclimatology Palaeoecology 391, no. Part A (2013): 13–33. doi:10.1016/j.palaeo.2013.05.011


Previous genetic studies of extant planktonic foraminifera have provided evidence that the traditional, strictly morphological definition of species in these organisms underestimates their biodiversity. Here, we report the first case where this pattern is reversed. The modern (sub)tropical species plexus Globigerinoides sacculifer is characterized by large morphological variability, which has led to the proliferation of taxonomic names attributed to morphological end-members within the plexus. In order to clarify the taxonomic status of its morphotypes and to investigate the genetic connectivity among its currently partly disjunct (sub)tropical populations, we carried out a global survey of two ribosomal RNA regions (SSU and ITS-1) in all recent morphotypes of the plexus collected throughout (sub)tropical surface waters of the global ocean. Unexpectedly, we find an extremely reduced genetic variation within the plexus and no correlation between genetic and morphological divergence, suggesting taxonomical overinterpretation. The genetic homogeneity within the morphospecies is unexpected, considering its partly disjunct range in the (sub)tropical Atlantic and Indo-Pacific and its old age (early Miocene). A sequence variant in the rapidly evolving ITS-1 region indicates the existence of an exclusively Atlantic haplotype, which suggests an episode of relatively recent (last glacial) isolation, followed by subsequent resumption of unidirectional gene flow from the Indo-Pacific into the Atlantic. This is the first example in planktonic foraminifera where the morphological variability in a morphospecies exceeds its rDNA genetic variability. Such evidence for inconsistent scaling of morphological and genetic diversity in planktonic foraminifera could complicate the interpretation of evolutionary patterns in their fossil record.

Global scale same-specimen morpho-genetic analysis of Truncorotalia truncatulinoides: A perspective on the morphological species concept in planktonic foraminifera

Frédéric Quillévéré, Morard, Raphaël, , Gilles Escarguel, Christophe J. Douady, Yurika Ujiié, Thibault de Garidel-Thoron, and Colomban de Vargas.
Journal Paper Palaeogeography Palaeoclimatology Palaeoecology 391 (December 2013): 2–12. doi:10.1016/j.palaeo.2011.03.013.


Genetic analyses of planktonic foraminifera have unveiled significant levels of cryptic diversity, thus calling into question the usefulness of the morphological species concept for paleoceanographic reconstructions. Here, we present single-specimen combined genetic and morphological analyses performed on living Truncorotalia truncatulinoides collected across the world oceans. A combined morphogenetic analysis allows us to (1) detect five different genetic types (Types I to V) within the morphospecies T. truncatulinoides, (2) statistically analyze shape variations among these genotypes, and (3) assess the biogeographic patterns and the links between surface ocean properties and the distribution of morphological and genetic diversity within T. truncatulinoides. Of the five genetic types, Type I appears to inhabit the warm (sub)tropical waters of the South Hemisphere, Types II and V are found in the warm (sub)tropical waters of the Atlantic and NW Pacific, respectively, and Types III and IV appear to be restricted to the productive subtropical and the cold subpolar frontal zones of the Southern Ocean, respectively. Same-specimen morphogenetic comparisons reveal significant differences in test morphology between the warm (sub)tropical cluster of genotypes (Types I, II, and V) and the colder subpolar cluster of genotypes (Types III and IV). These results indicate that changes in shell conicalness, observed across the subtropical fronts in the Southern Ocean and for a long time interpreted as ecophenotypic variation, reflect genetic differentiation, with large, highly conical left (Indian Ocean) or right-coiled (Pacific Ocean) specimens north of the North Subtropical Front representing genetic Type I, and small, axially compressed and biconvex left-coiled specimens south of this front representing genetic Types III and IV. Our morphogenetic data are consistent with the scenario of a late Pleistocene invasion of the Southern Ocean by newly evolved T. truncatulinoides genotypes, specifically adapted to cold water masses. Finally, we build a model based upon test outline analyses, which correctly assigns up to 75% of the specimens to their corresponding cluster of genotypes. Application of this model to sediment samples may contribute to the reconstruction of migrations of the Subtropical Front during the late Pleistocene.

SSU rDNA Divergence in Planktonic Foraminifera: Molecular Taxonomy and Biogeographic Implications

Aurore André, Frédéric Quillévéré, Ralf Aurahs, Raphaël Morard, Yurika Ujiié, Gilles Escarguel, Colomban de Vargas, , Thibault de Garidel-Thoron, Christophe J. Douady
Journal Paper Plos ONE 9(8): e104641. doi:10.1371/journal.pone.0104641


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 morpho-species 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, suggesting that genetic types have been sometimes inconsistently defined. We further apply two quantitative and independent methods, ABGD (Automatic Barcode Gap Detection) and GMYC (General Mixed Yule Coalescent) to a dataset of published and newly obtained partial SSU rDNA for a more objective assessment of the species status of these genetic types. Results of these complementary approaches are highly congruent and lead to a molecular taxonomy that ranks 49 genetic types of planktonic foraminifera as genuine (pseudo)cryptic species. Our results advocate for a standardized sequencing procedure allowing homogenous delimitations of (pseudo)cryptic species. On the ground of this revised taxonomic framework, we finally provide an integrative taxonomy synthesizing geographic, ecological and morphological differentiations that can occur among the genuine (pseudo)cryptic species. Due to molecular, environmental or morphological data scarcities, many aspects of our proposed integrative taxonomy are not yet fully resolved. On the other hand, our study opens up the potential for a correct interpretation of environmental sequence datasets.

Progressive shoaling of the equatorial Pacific thermocline over the last eight glacial periods

Fabienne Regoli, Thibault de Garidel-Thoron, Kazuyo Tachikawa, Zhiming Jian,, Liming Yen André W. Droxler, Guillaume Lenoir, Michel Crucifix, Nicolas Barbarin, Luc Beaufort
Journal Paper Paleoceanography 10.1002/2014PA002696


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 800ka. 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 thermocline to both direct orbital forcing and glacial-interglacial changes. Our stratification record shows a systematic shallower glacial thermocline, whereas sea surface temperatures are characterized by precessional forcing. The record is indicative of a progressive long-term shoaling of the thermocline during the glacial stages during the late Pleistocene. The shoaling of the subequatorial Pacific thermocline is consistent with regional estimates. An enhanced South Pacific shallow overturning wind-driven circulation could have driven this progressive shoaling. We speculate that this late Pleistocene glacial shoaling of the thermocline could be related to an increase in the amplitude of the obliquity.