Laurent Labeyrie

Parc Naturel Regional du Golfe du Morbihan

The idea of reconstructing the history of oceans and climates in the past using marine sediment cores arrived quite late after the beginnings of oceanography. It was initiated in the twentieth century, well after the first attempts to measure variations in seawater temperature down the water column, which date back to the eighteenth century with th...

The Holocene period (last 11,700 years BP) has been marked by significant climate variability over decadal to millennial timescales. The underlying mechanisms are still being debated, despite ocean–atmosphere–land connections put forward in many paleo-studies. Among the main drivers, involving a cluster of spectral signatures and shaping the climat...

In France, integrating adaptation to climate change into planning policies is a prerogative that has recently been delegated to municipalities. There are also various injunctions to engage the local population in this decision-making process. How can municipalities co-construct an adaptive future with their citizens? This article critically describ...

Spatially extensive and intense phytoplankton blooms observed off Iberia, in satellite pictures, are driven by significant nutrient supply by upper-ocean vertical mesoscale activity rather than by horizontal advection by coastal upwelling. Productivity of oligotrophic regions is still poorly depicted by discrete instrumental and model data sets. Th...

From the Glénan Island to Guérande plateau in south Brittany (France, Bay of Biscay), based on 10000 km of seismic lines, submerged rocky barriers/inherited structural elements were interpreted as the primary controls on variance of coastal topography and incision of palaeovalleys. Sediment infilling is regulated by valley morphology and fluctuatio...

We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns duri...

Well-dated benthic foraminifer oxygen isotopic records (d18O) from different water depths and locations within the Atlantic Ocean exhibit distinct patterns and significant differences in timing over the last deglaciation. This has two implications: on the one hand, it confirms that benthic d18O cannot be used as a global correlation tool with mille...

We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns duri...

Past glacial periods were punctuated by pseudoperiodical abrupt temperature oscillations (described as Dansgaard-Oeschger cycles and Heinrich events), which are particularly well marked in paleorecords from the middle to high latitudes of the Northern Hemisphere (Greenland ice cores, ocean and lacustrine sediments, and cave stalagmites). Associated...

We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns duri...

Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the es...

Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the es...

1] Well‐dated benthic foraminifer oxygen isotopic records (d 18 O) from different water depths and locations within the Atlantic Ocean exhibit distinct patterns and significant differences in timing over the last deglaciation. This has two implications: on the one hand, it confirms that benthic d 18 O cannot be used as a global correlation tool wit...

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of...

We present an eco-physiological model reproduc-ing the growth of eight foraminifer species (Neogloboquad-rina pachyderma, Neogloboquadrina incompta, Neoglobo-quadrina dutertrei, Globigerina bulloides, Globigeri-noides ruber, Globigerinoides sacculifer, Globigerinella si-phonifera and Orbulina universa). By using the main phys-iological rates of for...

Mg/Ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to reconstruct past sea surface temperatures (SST). However, additional factors that might have an influence on Mg/Ca, like dissolution, salinity, diagenesis, and carbonate ion effects have come into focus. In this paper, the occurrence of diageneti...

We present an eco-physiological model reproducing the growth of eight foraminifer species (Neogloboquadrina pachyderma, Neogloboquadrina incompta, Neogloboquadrina dutertrei, Globigerina bulloides, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera and Orbulina universa). By using the main physiological rates of foraminif...

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of...

Paleohydrological changes in the area of the southern part of the Mozambique channel were studied on the basis of isotopic and microfaunal analysis and radiocarbon dating (on planktonic microfauna) of a Quaternary core spanning the last 25,000 years. The results permit tracing the history of changes in the environment and paleohydrology since the l...

Abstract Available from http://www.agu.org

Variations in the interactions between marine ecosystems, thermohaline circulation, external forcing and atmospheric greenhouse gases concentrations are not yet fully represented in detailed models of the glacial-interglacial transitions. Most of the research on past productivity changes has been focused so far on high-productivity areas such as up...

Our study gives new constraints on the response of Atlantic Meridional Overturning Circulation (AMOC) export to various forcings during the Last Glacial Inception. The decay corrected excess sedimentary (231Pa/230Th) activity ratio (hereafter referred to as (Pa/Th)) has been measured over that period in two deep cores from the Western (SU90-11, 44°...

The planktonic foraminiferal record of core MD99-2346 (Gulf of Lion) shows a decrease of sea surface temperature (SST) at the time of Heinrich event H2 (24–23.5 cal kyr BP), Younger Dryas and during the early to middle Holocene. These events were associated with a decrease of surface water salinity. The salinity lowering events were similar and syn...

Studies from the subtropical western and eastern Atlantic Ocean, using the 231Pa/230Th ratio as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation (MOC) over the last deglaciation. In this study, we present a compilation of existing and new...

Variations in the assemblage and abundance of coccoliths reveal changes in oceanic and atmospheric dynamics in the Guyana Basin over the last climatic cycle, mainly linked to latitudinal variations in the ITCZ (Intertrop-ical Convergence Zone). Records of the N ratio (a palaeo-productivity index of coccolithophores) allowed us to monitor nutri-ther...

Variations in the assemblage and abundance of coccoliths reveal changes in oceanic and atmospheric dynamics in the Guyana Basin over the last climatic cycle, mainly linked to latitudinal variations in the ITCZ (Intertropical Convergence Zone). Records of the N ratio (a palaeoproductivity index of coccolithophores) allowed us to monitor nutri-thermo...

As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000 m; simultaneously a mooring line was deployed at the deepest...

The distribution of planktic foraminifera from the continental slope onto the shelf of the south-eastern Bay of Biscay is discussed in relation to environmental factors. Samples were obtained between March and November, 2006–2008, along a bathymetric transect from 2000 to 145m water depth, from 50km off the shelf-break onto the outer shelf. Live sp...

The Holocene is commonly referred to as a period of relatively stable climate conditions. It is however affected by a climate anomaly 8.2 kyr ago, postulated to be the result of weakened Meridional Overturning Circulation (MOC) triggered by a freshwater outburst. This time period offers then a good opportunity to study the relationship between inte...

Deep water circulation changes during the initiation of the last glacial period, and its role in the global cooling are still poorly known. We compare high-resolution oxygen and carbon isotope composition records of planktic and benthic foraminifera from Southern Ocean and North Atlantic cores for the 130-100 ka period in order to establish the dee...

1] We investigated deep water changes in the Southern Ocean during the last glacial inception, in relationship to surface hydrology and global climatology, to better understand the mechanisms of the establishment of a glacial ocean circulation. Changes in benthic foraminiferal d 13 C from three high-resolution cores are compared and indicate decoup...

Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was dev...

The temperature influence on foraminifera growth rate was analysed using a mechanistic formulation that take into account enzyme inactivation at extreme temperatures. Growth rates are calculated using available published and unpublished laboratory culture experiments for eight species, including Neogloboquadrina pachyderma (sinistral and dextral fo...

Respiration and photosynthesis of the planktonic foraminifera Globigerinoides ruber, Orbulina universa, and Globigerinella siphonifera and their symbiotic algae were calculated from measured dissolved oxygen gradients using microelectrodes, using different temperatures in dark and light (250 mu mol photon m(-2) s(-1)) conditions. At one temperature...

This dataset contains (1) the oxygen and carbon stable isotope compositions of the benthic foraminifera Cibicides kullenbergi (50-140 ka), (2) the oxygen stable isotope compositions of the planktic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma sinistral (0-140 ka), (3) the summer Sea Surface Temperatures reconstructed from the...

Studies from the subtropical western and eastern Atlantic Ocean, using the 231Pa/230Th ratio as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation (MOC) over the last deglaciation. In this study, we present a compilation of existing and new...

The evolution of Northern Hemisphere climate during the Last Interglacial (LIG) (129--118 ka) is significant for the study of future climate changes as it may provide information on the climate system responses and feedbacks to radiative forcing (Jansen et al. 2007). We present here a comparison of foraminiferal records from high latitude deep-sea...

Reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstruct past upper water column temperature gradients and past oceanic heat content. This work examines the relationships between trace element ratios in fossil shells and seawater temperature for surface-dwelling foraminifera species, Globigerinoides rub...

Copyrighted by American Geophysical Union. An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in th...

Variations in the assemblages and abundances of calcareous nannoplankton have allowed us to interpret changes in oceanic and atmospheric dynamics in the Guyana Basin, mainly linked to the southeast trades over the last climatic cycle. Records of the paleoproductivity index of coccolithophores ( N ratio) allowed us to monitor the nutri-thermocline...

Reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstruct past upper water column temperature gradients and past oceanic heat content. This work examines the relationships between trace element ratios in fossil shells and seawater temperature for surface-dwelling foraminifera species, Globigerinoides rub...

Past glacial periods were punctuated by pseudoperiodical abrupt temperature oscillations (described as Dansgaard–Oeschger cycles and Heinrich events), which are particularly well marked in paleorecords from the middle to high latitudes of the Northern Hemisphere (Greenland ice cores, ocean and lacustrine sediments, and cave stalagmites). Associated...

Reorganization of intermediate and deep water masses during the last deglaciation is still a matter of debate. Two radiocarbon dated cores located in the southern Indian Ocean (core MD 79-257, 20°24' S ; 36°20' E ; 1262 m water depth and core MD 84-527 43°49'3 S ; 51°19'1 E ; 3269 m water depth ) were studied to reconstruct the physical characteris...

The changes in the oceanic circulation at the initiation of the last glacial period, and its role in the chain of events linking the decrease of Northern summer insolation with the establishment of large ice continental sheets and global cooling are still poorly known. We present here new constraints on the deep-water circulation changes in the Sou...