@article {6805, title = {Modern drought conditions in western Sahel unprecedented in the past 1600~years}, journal = {Climate Dynamics}, volume = {52}, year = {2019}, month = {Jan-02-2019}, pages = {1949 - 1964}, abstract = {As climate model uncertainties remain very large for future rainfall in the Sahel, a multi-centennial perspective is required to assess the situation of current Sahel climate in the context of global warming. We present here the first record of hydroclimatic variability over the past 1600\ years in Senegal, obtained from stable oxygen isotope analyses (δ18O) in archaeological shell middens from the Saloum Delta. During the preindustrial period, the region was relatively humid, with maximum humidity reached during the period from AD 1500 to AD 1800, referred to as the Little Ice Age. A significant negative link is observed at the centennial scale between global temperature and humidity in the Sahel that is at odds with the expected effects of latitudinal shifts of the intertropical convergence zone during the last millennium. In the context of the past 1600\ years, the Western Sahel appears to be experiencing today unprecedented drought conditions. The rapid aridification that started ca. AD 1800 and the recent emergence of Sahel drought from the natural variability point to an anthropogenic forcing of Sahel drying trend. This new long-term perspective suggests that the recovery of Sahel rainfall in the last decade may only result from short-term internal variability, and supports climate models that predict an increase of Sahel drought under future greenhouse climate.}, issn = {0930-7575}, doi = {10.1007/s00382-018-4311-3}, url = {https://hal.archives-ouvertes.fr/hal-02349321}, author = {Carr{\'e}, Matthieu and Azzoug, Moufok and Zaharias, Paul and Camara, Abdoulaye and Cheddadi, Rachid and Chevalier, Manuel and Fiorillo, Denis and Gaye, Amadou T. and Janicot, Serge and Khodri, Myriam and Lazar, Alban and Claire E. Lazareth and Mignot, Juliette and Mitma Garc{\'\i}a, Nancy and Patris, Nicolas and Perrot, Oc{\'e}ane and Wade, Malick} } @article {6107, title = {Seasonal oxygen isotope variations in freshwater bivalve shells as recorders of Amazonian rivers hydrogeochemistry}, journal = {Isotopes in Environmental and Health Studies}, year = {2019}, pages = {1-15}, type = {Journal Article}, abstract = {

Freshwater bivalve shell oxygen isotope values (δ18OS) may act as a recorder of river δ18O variations that can then be interpreted in terms of hydrology (e.g. precipitation{\textendash}evaporation balance, precipitation and river discharge patterns). We investigated the potential of this proxy measured across the hinge of South American unionid shells: Anodontites elongatus collected in Peru and A. trapesialis in Brazil. The isotopic signatures were reproducible between individuals of the same species. A. trapesialis clearly showed a strong δ18OS cyclicity in accordance with its growth patterns while A. elongatus presented less clear δ18OS with lower amplitude. We confirm that the deposition of successive growth lines and increments is annual, with growth line corresponding to the wet season. Also, we suggest that low amplitude of δ18OS in the A. elongatus shells indicates a habitat close to the river while large amplitude of δ18OS cycles observed in A. trapesialis shells would reflect a floodplain lake habitat, seasonally disconnected from the river and thus subjected to higher seasonal fluctuations in water δ18O. Considering these promising first results, future studies could be directed towards the use of fossil shells to reconstruct the past and present hydrological and geochemical conditions of the Amazon.

}, keywords = {Amazon basin, freshwater bivalve shells, hydroclimate, isotope ecology, isotope hydrology, oxygen isotopes}, issn = {1025-6016 1477-2639}, doi = {10.1080/10256016.2019.1666120}, url = {https://hal.archives-ouvertes.fr/hal-02314885v1}, author = {Gaillard, Blandine and Claire E. Lazareth and Lestrelin, Hugo and Dufour, Elise and Santos, Roberto V. and Carlos E.C. Freitas and Marc Pouilly} } @article {6806, title = {Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical South Pacific}, journal = {Nature Communications}, volume = {9}, year = {2018}, month = {Jan-12-2018}, abstract = {Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH records in the world{\textquoteright}s oceans, seawater pH variability at the decadal and centennial scale remains largely unknown and requires documentation. Here we present evidence of striking secular trends of decreasing pH since the late nineteenth century with pronounced interannual to decadal{\textendash}interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE. High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Ni{\~n}o/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.}, doi = {10.1038/s41467-018-04922-1}, url = {https://hal.archives-ouvertes.fr/hal-01839951}, author = {Wu, Henry C. and Dissard, Delphine and Douville, Eric and Blamart, Dominique and Bordier, Louise and Tribollet, Aline and Le Cornec, Florence and Pons-Branchu, Edwige and Dapoigny, Arnaud and Claire E. Lazareth} } @mastersthesis {6807, title = {High-resolution climatic reconstruction in the tropical Pacific based on biocarbonate archives}, volume = {HDR}, year = {2017}, pages = {110}, abstract = {In the current context of global change and the associated need to provide forecasts on the future evolution of the climate as precise as possible, it is crucial to have a deep understanding of the earth climate system. Pacific Ocean is an important compartment of this system. It is the place of strong ocean-atmosphere interactions and the birthplace of the El Ni{\~n}o Southern Oscillation (ENSO), the impacts of which are catastrophic for the environments and the populations. The current knowledge on ENSO partly relies on observations which are however limited in time. To increase this dataset and understand the natural climate variability, additional data are acquired for past periods, based on various type of archives. Because ENSO occurrences are connected with the seasonal variability and last several months, high temporal resolution information, are necessary. In this manuscript I shall describe how I tried to develop, and to apply, environmental proxies from biocarbonate archives in the tropical Pacific Ocean to reconstruct the monthly or infra-monthly variability of the sea surface temperatures (SSTs) and the evaporation/precipitation balance. To do that, I focused my works on the mollusk shells and Porites sp coral skeleton. These archives contain various tracers (growth and geochemical variations) of the sought environmental variables. I will show that the thicknesses of growth decreases of the Protothaca thaca bivalve shells (East Pacific) indicate occurrences of El Nino events. In the Western part of the Pacific basin, changes in daily increment thicknesses in two Tridacnidae species, Tridacna maxima and Hippopus hippopus are related to SST changes but also depend on physiological condition of the animals. While certain geochemical tracers (Sr/Ca, δ18O) within Porites sp. Skeleton can be used with a certain confidence, this is not always the case for the mollusk shells. I will show that the use of Mg/Ca as a SST proxy depends on the species and that physiology and very early diagenesis are obstacles in the use of this proxy. In T. maxima and H hippopus, δ18O can be used as a tracer of SST and of the evaporation/precipitation balance. To reconstruct variations of these parameters during the Mid-Holocene, I worked on fossil giant clams and corals, after diagenesis assessment. I will show how various types of diagenesis impact the microstructure, the geochemistry, and the reconstructed environmental parameter. I will also propose hypotheses on the diagenesis process itself. Based on results obtained from Mid-Holocene archives, I will show that the post-glacial SST rise was reached at around 6.5-6 ka BP in the Southwest Pacific, that the South Pacific Convergence Zone influence was more probably reduced, the Hadley circulation enhanced, and that ENSO variability was probably reduced. The work done on Lapita (3 ka BP) Tridacnidae confirmed that the Lapita migration has probably been favored by an increase in climatic variability.The last chapter deals with the future directions I would like to give to my research that include i/ better understand the incorporation of proxies in mollusk and ii/ try to propose solution for sustainable management of tropical ecosystems based on the use of biocarbonate as recorder of the environment and its disturbances.
\ }, url = {http://hal.ird.fr/tel-01572677}, author = {Claire E. Lazareth} } @article {6811, title = {Saving Our Marine Archives}, journal = {Eos}, year = {2017}, month = {Dec-02-2018}, doi = {10.1029/2017EO068159}, url = {https://eos.org/project-updates/saving-our-marine-archives}, author = {Dassi{\'e}, Emilie and DeLong, Kristine and Kilbourne, Hali and Williams, Branwen and Abram, Nerilie and Brenner, Logan and Brahmi, Chlo{\'e} and Cobb, Kim and Corr{\`e}ge, Thierry and Dissard, Delphine and Emile-Geay, Julien and Evangelista, Heitor and Evans, Michael and Farmer, Jesse and Felis, Thomas and Gagan, Michael and Gillikin, David and Goodkin, Nathalie and Khodri, Myriam and Lavagnino, Ana and LaVigne, Mich{\`e}le and Claire E. Lazareth and Linsley, Braddock and Lough, Janice and McGregor, Helen and Nurhati, Intan and Ouellette, Gilman and Perrin, Laura and Raymo, Maureen and Rosenheim, Brad and Sandstrom, Michael and Sch{\"o}ne, Bernd and Sifeddine, Abdelfettah and Stevenson, Samantha and Thompson, Diane and Waite, Amanda and Wanamaker, Alan and Wu, Henry} } @article {6812, title = {Development of laser ablation multi-collector inductively coupled plasma mass spectrometry for boron isotopic measurement in marine biocarbonates: new improvements and application to a modern Porites coral}, journal = {Rapid Communications in Mass Spectrometry}, volume = {30}, year = {2016}, month = {Mar-02-2017}, pages = {359 - 371}, abstract = {RATIONALE: Laser Ablation coupled to Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MCICPMS)
is a powerful tool for the high-precision measurement of the isotopic ratios of many elements in geological
samples, with the isotope ratio (11B/10B) of boron being used as an indicator of the pH of oceanic waters. Most geological
samples or standards are polished and ablation occurs on flat surfaces. However, the shape and the irregularities of
marine biocarbonates (e.g., corals, foraminifera) can make precise isotopic measurements of boron difficult. Even after
polishing, the porosity properties and the presence of holes or micro-fractures affect the signal and the isotopic ratio
when ablating the material, especially in raster mode.
METHODS: The effect of porosity and of the crater itself on the 11B signal and the isotopic ratio acquired by LA-MCICPMS
in both raster and spot mode was studied. Characterization of the craters was then performed with an optical
profilometer to determine their shapes and depths. Surface state effects were examined by analyzing the isotopic
fractionation of boron in silicate (NIST-SRM 612 and 610 standards) and in carbonate (corals).
RESULTS: Surface irregularities led to a considerable loss of signal when the crater depth exceeded 20 μm. The stability
and precision were degraded when ablation occurred in a deep cavity. The effect of laser focusing and of blank correction
was also highlighted and our observations indicate that the accuracy of the boron isotopic ratio does not depend on the
shape of the surface. After validation of the analytical protocol for boron isotopes, a raster application on a Porites coral,
which grew for 18 months in an aquarium after field sampling, was carried out.
CONCLUSIONS: This original LA-MC-ICPMS study revealed a well-marked boron isotope ratio temporal variability,
probably related to growth rate and density changes, irrespective of the pH of the surrounding seawater.}, doi = {10.1002/rcm.7448}, url = {http://doi.wiley.com/10.1002/rcm.7448}, author = {Thil, Fran{\c c}ois and Blamart, Dominique and Assailly, Caroline and Claire E. Lazareth and Leblanc, Thierry and Butsher, John and Douville, Eric} } @article {6814, title = {Ideas and perspectives: Southwestern tropical Atlantic coral growth response to atmospheric circulation changes induced by ozone depletion in Antarctica}, journal = {Biogeosciences}, volume = {13}, year = {2016}, month = {Jan-01-2016}, pages = {2379 - 2386}, abstract = {Recent Southern Hemisphere (SH) atmospheric
circulation, predominantly driven by stratospheric ozone de-
pletion over Antarctica, has caused changes in climate across
the extratropics. Here, we present evidence that the Brazilian
coast (southwestern Atlantic) may have been impacted from
both wind and sea-surface temperature changes derived from
this process. Skeleton analysis of massive coral species liv-
ing in shallow waters off Brazil are very sensitive to air{\textendash}sea
interactions, and seem to record this impact. Growth rates
of Brazilian corals show a trend reversal that fits the ozone
depletion evolution, confirming that ozone impacts are far
reaching and potentially affect coastal ecosystems in tropical
environments}, doi = {10.5194/bg-13-2379-2016}, url = {http://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers16-05/010067169.pdf}, author = {Evangelista, Heitor and Wainer, Ilana and Sifeddine, Abdelfettah and Corr{\`e}ge, Thierry and Cordeiro, Renato C. and Lamounier, Saulo and Godiva, Daniely and Shen, Chuan-Chou and Le Cornec, Florence and Turcq, Bruno and Claire E. Lazareth and Hu, Ching-Yi} } @article {6813, title = {Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process}, journal = {Geochimica et Cosmochimica Acta}, volume = {176}, year = {2016}, month = {Jan-03-2016}, pages = {279 - 294}, abstract = {Geochemical proxies measured in the carbonate skeleton of tropical coral Porites sp. have commonly been used to reconstruct sea surface temperature (SST) and more recently seawater pH. Nevertheless, both reconstructed SST and pH depend on the preservation state of the skeleton, here made of aragonite; i.e., diagenetic processes and its related effects should be limited. In this study, we report on the impact of the presence of intra-skeletal calcite on the skeleton geochemistry of a live-collected Porites sp. The Porites skeleton preservation state was analyzed using X-ray diffraction and scanning electron microscopy. Sr/Ca, Mg/Ca, U/Ca, Ba/Ca, Li/Mg, and B/Ca ratios were measured at a monthly and yearly resolution using quadrupole ICP-MS and multi-collector ICP-MS. The δ11B signatures and the calcite percentages were acquired at a yearly timescale. The coral colony presents two parts, one with less than 3\% calcite (referred to as {\textquotedblleft}no-calcite{\textquotedblright} skeleton), the other one, corresponding to the skeleton formed during the last 4 years of growth, with calcite percentages varying from 13\% to 32\% (referred to as {\textquotedblleft}with calcite{\textquotedblright} skeleton). This intra-skeletal calcite replaces partly or completely numerous centers of calcification (COCs). All investigated geochemical tracers are significantly impacted by the presence of calcite. The reconstructed SST decreases by about 0.1 {\textdegree}C per calcite-percent as inferred from the Sr/Ca ratio. Such impact reaches up to 0.26 {\textdegree}C per calcite-percent for temperature deduced from the Li/Mg ratio. So, less than 5\% of such intra-skeletal calcite does not prevent SST reconstructions using Sr/Ca ratio, but the percentage and type of calcite have to be determined before fine SST interpretation. Seawater pH reconstruction inferred from boron isotopes drop by about -0.011 pH-unit per calcite-percent. Such sensitivity to calcite presence is particularly dramatic for fine paleo-pH reconstructions. Here we suggest that after being brought to shallow waters following a cyclone, the studied coral was seasonally subjected to rainfall-related water freshening that could have mimicked a vadose environment like can be encountered on raised fossil coral reefs. Nevertheless, the process of calcite precipitation remains to be determined.}, issn = {00167037}, doi = {10.1016/j.gca.2015.12.020}, url = {https://hal.archives-ouvertes.fr/hal-01253864v1}, author = {Claire E. Lazareth and Soares-Pereira, Caroline and Douville, Eric and Brahmi, Chlo{\'e} and Dissard, Delphine and Le Cornec, Florence and Thil, Fran{\c c}ois and Gonzalez-Roubaud, C{\'e}cile and Caquineau, Sandrine and Cabioch, Guy} } @article {6815, title = {Calibration of seawater temperature and δ18Oseawater signals in Tridacna maxima{\textquoteright}s δ18Oshell record based on in situ data}, journal = {Coral Reefs}, volume = {34}, year = {2015}, month = {Jan-06-2015}, pages = {437 - 450}, issn = {0722-4028}, doi = {10.1007/s00338-014-1245-z}, url = {http://link.springer.com/10.1007/s00338-014-1245-z}, author = {Duprey, N. and Claire E. Lazareth and Dupouy, C. and Butscher, J. and Farman, R. and Maes, C. and Cabioch, G.} }