Luc Beaufort

• PhD
• Research Director at French National Centre for Scientific Research

Plain Language Summary Today, the atmospheric circulation over the Indo‐Pacific Warm Pool exhibits strong convective updraft and heavy precipitation. In this study, we found evidence that the response of this atmospheric convection to Last Glacial Maximum conditions may have exhibited spatial variability, weakening in the central part associated wi...

Throughout the Cenozoic, calcareous nannoplankton and planktonic foraminifera have been the main producers of pelagic carbonate preserved on the seafloor. While past variability in pelagic carbonate production has been previously studied, relatively little is known about the variability in the relative contribution of the two components. This is im...

Diatom communities preserved in sediment samples are valuable indicators for understanding the past and present dynamics of phytoplankton communities, and their response to environmental changes. These studies are traditionally achieved by counting methods using optical microscopy, a time‐consuming process that requires taxonomic expertise. With th...

The amount of radiative energy received at the Earth's surface depends on two factors: Earth–Sun distance and sunlight angle. Because of the former, high-eccentricity cycles can induce the appearance of seasons in the tropical ocean. In this paper, we use the Earth system model IPSL-CM5A2 to investigate the response of the low-latitude ocean to var...

Automated pollen analysis is not yet efficient on environmental samples containing many pollen taxa and debris, which are typical in most pollen‐based studies. Contrary to classification, detection remains overlooked although it is the first step from which errors can propagate. Here, we investigated a simple but efficient method to automate pollen...

The fossil record of coccolithophores dates back approximately 225 million years, and the production of their calcite platelets (coccoliths) contributes to the global carbon cycle over short and geological timescales. Variations in coccolithophore parameters (e.g. community composition, morphology, size and coccolith mass) are a key factor for ocea...

Diatom communities preserved in sediment samples are valuable indicators for understanding the past and present dynamics of phytoplankton communities, and their response to environmental changes. These studies are traditionally achieved by counting methods using optical microscopy, a time-consuming process that requires taxonomic expertise. With th...

The fossil record of coccolithophores dates back approximately 225 million years and the production of their calcite platelets (coccoliths) contributes to the global carbon cycle over short and geological time scales. Variations in coccolithophore parameters (e.g., community composition, morphology, size and coccolith mass) have been used as paleop...

The amount of radiative energy received at the Earth's surface depends on two factors: Earth-Sun distance and sunlight angle. Because of the former factor, high eccentricity cycles can induce the appearance of seasons in the tropical ocean. In this paper, we use the Earth System model IPSL-CM5A2 to investigate the response of the low-latitude ocean...

Marine phytoplankton play important roles in the global ecosystem, with a limited number of cosmopolitan keystone species driving their biomass. Recent studies have revealed that many of these phytoplankton are complexes composed of sibling species, but little is known about the evolutionary processes underlying their formation. Gephyrocapsa huxley...

The partial melting of Earth’s bi-polar ice sheets since the Last Glacial Maximum (LGM) has translated into a ~ 120 m amplitude stepwise sea-level rise punctuated by three major meltwater pulses that were tracked and recorded with some of the best accuracy by coral reefs. However, the initial meltwater pulse marking the end of the LGM, at 19 ka, is...

Although the role of Earth’s orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abund...

Carbon isotope records from alkenone biomarkers (εp37:2) produced by haptophyte algae are frequently used for atmospheric CO2 paleobarometry, but this method has yielded inconsistent results during periods where CO2 variations are known independently. Recent syntheses of algal cultures have quantitatively demonstrated that εp37:2 indeed records CO2...

Heterococcoliths are calcite platelets produced inside diploid coccolithophore cells and extruded to form a covering on the cell surface called a coccosphere. The size of coccoliths is an important parameter sometimes used to identify species, and it is observed to be influenced in extant species by abiotic parameters (e.g., CO2, light). However, t...

Oxygen minimum zones (OMZs) are oceanic areas largely depleted in dissolved oxygen, nowadays considered in expansion in the face of global warming. To investigate the relationship between OMZ expansion and global climate changes during the late Quaternary, quantitative oxygen reconstructions are needed but are still in their early development. Here...

In tropical and sub‐tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf o...

Coccoliths are calcite platelets produced inside coccolithophore cells and extruded to form a covering on the cell surface called a coccosphere. The size of coccoliths is an important parameter often used to identify species, and observations on extant species have shown an influence of abiotic parameters (e.g., CO2, light, nutrient concentration)...

Oxygen Minimum Zones (OMZs) are oceanic areas largely depleted in dissolved oxygen, nowadays considered in expansion in the face of global warming. Their ecological and economic consequences are being debated. The investigation of past OMZ conditions allows us to better understand biological and physical mechanisms responsible for their variability...

Coccoliths are major contributors to the particulate inorganic carbon in the ocean that is a key part of the carbon cycle. The coccoliths are a few micrometres in length and weigh a few picogrammes. Their birefringence characteristics in polarized optical microscopy have been used to estimate their mass. This method is rapid and precise because cam...

Calcareous nannofossils are micrometric calcite platelets secreted by the photosynthetic algae named coccolithophores and incertae sedis. Calcareous nannoplankton inhabit the photic zone from coast to open-ocean and have left an abundant fossil record since the Triassic. Therefore, they constitute an interesting material for geochemical studies alt...

Identification of microfossils is usually done by expert taxonomists and requires time and a significant amount of systematic knowledge developed over many years. These studies require manual identification of numerous specimens in many samples under a microscope, which is very tedious and time-consuming. Furthermore, identification may differ betw...

The effect of global climate cycles driven by Earth’s orbital variations on evolution is poorly understood because of difficulties achieving sufficiently-resolved records of past evolution. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable an exceptional assessment of the impact of cyclic orbital-scale climate cha...

At present, variations of primary productivity (PP) in the Bay of Bengal (BoB) are driven by salinity-related stratification, which is controlled by the Indian summer monsoon (ISM). The relationships between PP, precipitation, and more generally climate in the past are not clearly understood. Here, we present a new record of PP based on the examina...

Identification of microfossils is usually done by expert taxonomists and requires time and a significant amount of systematic knowledge developed over many years. These studies require manual identification of numerous specimens in many samples under a microscope, which is very tedious and time consuming. Furthermore, identification may differ betw...

Calcareous nannofossils are micrometric calcite platelets secreted by coccolithophores and incertae sedis photosynthetic algae. Calcareous nannoplankton inhabit the photic zone from coast to open-ocean and have left an abundant fossil record since the Triassic. Therefore, they constitute an interesting material for geochemical studies although it h...

Pollen grains are valuable paleoclimate and paleovegetation proxies which require extensive knowledge of morphotypes and long acquisition time under the microscope. The abundance of damaged, folded, and broken pollen grains in the fossil register and sometimes also in modern soil and sediment samples, has so far prevented automation of pollen ident...

Abstract. At present, variations of primary productivity (PP) in the Bay of Bengal (BoB) are responding to salinity-related-stratification which is controlled by the Indian Summer Monsoon (ISM). The relationships between PP, ISM, and to a broader scale, North Atlantic climate rapid variability in the past, are not clearly understood. Here, we prese...

Abstract. The coccoliths are major contributors to the particulate inorganic carbon in the ocean that is a key part of the carbon cycle. The coccoliths are few microns in length and weigh few picograms. Their birefringence characteristics in polarized optical microscopy has been used to estimate their mass. This method is rapid and precise because...

Abstract: The Deep Biomass (DB), located in the lowest part of the euphotic zone (approx. 80 m to 300 m) primarily in the subtropical gyres is an unexplored part of primary production (PP). It is one of the largest biomes on our planet considering that subtropical regions occupy 60% of the total ocean. Recent observations indicate that the major oc...

Coccolithophores are one of the most abundant and widespread groups of calcifying plankton and have attracted extensive study in terms of their likely response to ocean acidification. Conflicting results concerning coccolithophore calcification have been reported from both experimental and field studies. Due to their minute size, it is difficult to...

The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) is one of the most severe greenhouse warming events in Earth's history. Thousands of petagrams of carbon were released into the atmosphere-ocean system in only a few thousand years, ultimately causing ocean acidifi cation (Zachos et al., 2005). The gradual sequestration of this light carbon took p...

When micron-sized particles are suspended into the dense brine waters of a deep hypersaline basin, in the absence of biological packaging, their settling velocities should be greatly attenuated. We observed this phenomenon in the anoxic brine water of the Urania Basin in the eastern Mediterranean. We found that the deepest part of this basin is fil...

Geophysical Research Abstracts Vol. 21, EGU2019-4538-2, 2019 EGU General Assembly 2019 © Author(s) 2019. CC Attribution 4.0 license. We focus on an unexplored part of primary production (PP), the Deep Biomass (DB), located in the lowest part of the euphotic zone (approx. 80 m to 300 m) primarily in the subtropical gyres. The DB is one of the large...

Coccolithophores of the Noëlaerhabdaceae family are covered by imbricated coccoliths, each composed of multiple calcite crystals radially distributed around the periphery of a grid. The factors that determine coccolith size remain obscure. Here, we used synchrotron-based three-dimensional Coherent X-ray Diffraction Imaging to study coccoliths of 7...

The need to accurately recreate how Oxygen Minimum Zones (OMZs) changed through time requires a combined use of classic and novel proxy approaches. Proxy qualities of U are usually attributed to authigenic enrichment during early diagenesis. Evidence from modern OMZs show that U authigenesis can occur in the water column adding significant amounts...

Several synergistic mechanisms were likely involved in the last deglacial atmospheric pCO 2 rise. Leading hypotheses invoke a release of deep-ocean carbon through enhanced convec-tion in the Southern Ocean (SO) and concomitant decreased efficiency of the global soft-tissue pump (STP). However, the temporal evolution of both the STP and the carbonat...

The Eastern Tropical North Pacific (ETNP) is sensitive to climatic changes that either strengthen or weaken the Oxygen Minimum Zone (OMZ). Paleoproxy and model evidence indicate that the shifts from cold stadials (LGM, MIS4) to warm interstadials are often accompanied by sudden sea level rise, intensification of marine productivity and enhanced oce...

The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) account for a large part of modern climate variability. Over the last decades, understanding of these modes of climate variability has increased but prediction in the context of global warming has proven difficult because of the lack of pertinent and reproducible pale...

Landsliding processes are relatively well-constrained on clastic sedimentary margins but remain poorly documented along carbonate slope and guyots. The southern central Mozambique Channel, between Mozambique and Madagascar, hosts several isolated carbonate platforms called the “Iles Eparses” and adjacent seamounts, which developed in shallow-water...

We developed a new automated procedure for measuring several pore parameters of benthic foraminiferal calcareous tests. Crushed test fragments are mounted on microscope slides and observed with an optical microscope under natural transmitted light, allowing the observation of pores and fragment outlines. Images are automatically acquired and proces...

Our ability to track the sensitivity of major Oxygen Minimum Zones (OMZs) to rapid perturbations in climate and productivity can be compromised by (1) global sea level change, (2) insufficient temporal resolution, (3) inadequate age models, and (4) strong microbially mediated transformations and diagenetic overprints. As a consequence, short-term p...

The current-climate Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from palaeo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for eight contrasted clim...

The intensity of the Oxygen Minimum Zone (OMZ) of the Eastern North Pacific (ENP) experienced strong variations during the last Glacial, mirroring changes in the balance between export production (O2-consumption) and water mass ventilation (O2-renewal). In this paper we present a new benthic foraminiferal assemblages record from Core MD02-2508, rec...

Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth’s climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosyntheti...

Authigenic 10 Be/ 9 Be ratios from three equatorial ocean cores are stacked and averaged  The 10 Be cosmogenic nuclide overproduction episodes are systematically associated with Geomagnetic Dipole Lows  The 10 Be signatures of the Brunhes/Matuyama transition and Brunhes geomagnetic excursions yield distinct rates and durations Abstract Geomagneti...

Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth’s climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosyntheti...

The Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from paleo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for 8 contrasted climates from the last gl...

Intensity of the Oxygen Minimum Zone of the Eastern North Pacific experienced strong variations during the last Glacial that mirror changes in the balance between export production (O2-consumption) and ventilation (O2-renewal). Here, we present a new record of benthic foraminiferal assemblages from Pacific Core MD022508. That record reflects oxygen...

Calcifying marine phytoplankton—coccolithophores— are some of the most successful yet enigmatic organisms in the ocean and are at risk from global change. To better understand how they will be affected, we need to know “why” coccolithophores calcify. We review coccolithophorid evolutionary history and cell biology as well as insights from recent ex...

Calcifying marine phytoplankton—coccolithophores— are some of the most successful yet enigmatic organisms in the ocean and are at risk from global change. To better understand how they will be affected, we need to know “why” coccolithophores calcify. We review coccolithophorid evolutionary history and cell biology as well as insights from recent ex...

Oscillations of water column chemistry (especially dissolved oxygen) in coastal marine basins and open seas are controlled by a complex interplay among circulation, climate, productivity, and sea level variability, which can also bear anthropogenic impacts. The underlying marine sediments are capable of recording such changes but often in dissimila...

The geochemistry of Upper Quaternary organic-rich (Corg 3.7–10.0%) sediments recovered by the 40-m-long Core MD02-2508 from the upper continental slope of Baja California is compared to the chemical composition of sedimentary rocks from the Miocene Monterey Formation, California. It is ascertained that concentrations of most macroelements (Al, Ti,...

The Last Glacial Maximum represents the most recent major sea level low stand in Earth history. Such changes in eustatic sea level impacted the oxygenation of marine basins, yet the characteristics and mechanisms of those impacts remain poorly known. Specific basin conditions are needed to develop, record, and preserve those paleoredox changes thro...

Approximately half of the world's population lives in the tropics, and future changes in the hydrological cycle will impact not just the freshwater supplies but also energy production in areas dependent upon hydroelectric power. It is vital that we understand the mechanisms/processes that affect tropical precipitation and the eventual surface hydro...

Changes in Late Quaternary oceanic primary productivity in the western tropical Pacific were reconstructed using coccolith counts from the improved SYRACO system in piston core MD01-2386 retrieved from the Halmahera Sea near northwest New Guinea. The calculated primary productivity exhibits cycles on obliquity and precession timescales over the las...

Nannofossil assemblages from core MD02-2510 provide a ~ 22 ka record of past oceanographic variability in Alfonso Basin (Gulf of California, east subtropical Pacific). In this area, environmental conditions depend on a monsoonal system heavily influenced by changes in the location of the ITCZ and nearby atmospheric pressure centers. To reconstruct...

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 time scales at low resolution. Here, we document a new high-resolution set of reconstructed past sea surface and subsurface waters...

Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking th...

Coccolithophores, major pelagic carbonate producers, underwent important changes during the latest Aalenian-Early Bajocian (ca.-170 Ma, Middle Jurassic). Specifically, a new genus called Watznaueria diversified and started dominating the coccolith assemblages. While this change in the coccolith assemblages is already known, the impact on coccolith...

Ocean acidification is a result of the uptake of anthropogenic CO2 from the atmosphere into the ocean and has been identified as a major environmental and economic threat. The release of several thousands of petagrams of carbon over a few hundred years will have an overwhelming effect on surface ocean carbon reservoirs. The recorded and anticipated...

As oceans take up more carbon dioxide, their increasing acidity could be decreasing the weight of one of the most abundant calcium-producing marine phytoplankton.

Coccolithophores are one of the most abundant eukaryotic phytoplankton in the oceans and are distinguished by their ability to build calcitic platelets (coccoliths). Of the numerous species, Emiliania huxleyi is considered one of the major calcifiers in the pelagic ocean. There is growing concern that increasing levels of CO2 in the atmos- phere an...

We describe a procedure for measuring the thickness and mass of calcite particles that works for most calcite particles <4.5-μm thick. The calcite particles are observed in cross-polarized light, which enables the light transmitted through the calcite particles to be correlated with their thickness. Three polarizing planes are used to minimize the...

During the Last Glacial Maximum, tropical sea surface temperatures were 1 to 3 °C cooler than present, but the altitude of the snowlines of tropical glaciers was lower than would be expected in light of these sea surface temperatures. Indeed, both glacial and twentieth-century snowlines seem to require lapse rates that are steeper than a moist adia...

During the last deglaciation, coralgal reefs established themselves on newly flooded continental shelf, accurately recording the stepwise character of the deglacial sea level rise (meltwater pulses). This study, conducted along the Papua New Guinea Peninsula outer shelf (Gulf of Papua), focuses on the analyses of a Calypso core, MD05-2945 (MD-45),...

Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking th...