South-Est Pacific Ocean Reservoir Age – Quantification of C14 ages for the South-East Pacific ocean reservoir

Funding

INSU-LEFE-IMAGO 2016 (2016-2018)

Project leader

G. Siani (GEOPS)

Collaborations

G. Delpech (GEOPS), S. Duchamp-Alphonse (GEOPS), E. Michel (LSCE)

Project / Programme

Action “Interactions Multiples dans l’Atmosphère, la Glace et l’Océan” (IMAGO) [Multiple Interactions in the Atmospheres, Ice and Ocean]

The Southern Ocean (SO) plays a fundamental role in the global climatic system. In fact, a key element in thermohaline circulation is the return route of water masses from the ocean depths to the surface via upwelling. This process is largely controlled by latitudinal position and the intensity of winds from the west (westerlies).  In recent years the study of the SO and these upwelling has become a priority in order to obtain a better understanding of the climatic system because, in particular, they control the quantity of heat and carbon transferred from the deepest ocean reservoir to the surface ocean and the atmosphere. The development of accurate age models for the marine and continental archives is therefore essential for better understanding the mechanisms, the temporal frequency, and the geographical repercussions which govern ocean-climate interactions. An essential prerequisite for establishing robust age models in the marine context, is the quantification of C14 ages for the surface ocean reservoir (Rsurf) which is principally linked to the reduction of C14 in the water column and to the mixing of different water masses, in other words ocean circulation. Regional stratigraphic markers, such as volcanic tephras retrieved from marine cores and terrestrial archives, are used to reconstruct past (Rsurf). The project’s scientific goal depends on the detailed study of the marine and continental tephrachronology using sedimentary series sampled along a N-S transect off the southern coast of Chile (Figure 1; 40°S and 46°S). Using laser ablation in conjunction with LA-ICP-MS-HR analysis allows more accurate identification of the volcanic sources and thus ensures that robust correlations are made between marine and continental tephras. This allows an independent estimation of Rsurf variations and makes it easier to establish accurate age models of marine climatic records on the South-East Pacific rim. This data is necessary in order to constrain: (i) the ventilation time of intermediate and deep ocean water ventilation and the depth at which the upwelling cell ascends within the SO; (ii) the climatic mechanisms controlling ocean circulation in this region and, at a larger scale, the carbon cycle since the last glacial period.

This project is being undertaken within the framework of a PhD thesis by Consuelo Martinez Fontaine (Estimation of C14 ages of the surface and deep ocean reservoir in the South-eastern Pacific sector of the Southern Ocean since the last glacial period)

Projet SEPORAFigure 1: Map of South America and the South-eastern Pacific Ocean representing: white arrows, the principal ocean currents (ACC: Arctic Circumpolar Current; CHC: Cape Horn Current; PCC: Peru-Chile Current; AAIW: Antarctic Intermediate Waters; CPDW: Pacific Deep Water); red arrows, the westerly winds; SVZ: South Volcanic Zone; AVZ: Austral Volcanic Zone. The locations of terrestrial sites are indicated by white dots. Marine core sites are indicated by yellow stars apart from reference core MD07-3088 (4, red dot). Also included is a salinity/latitude/depth section representing the positions of the cores as a function of their bathymetry and the main ocean water masses.

Associated thesis

Consuelo Martinez Fontaine

The post-glacial evolution of Lake Urmia (Iran) : current context and paleoenvironmental reconstructions for a better understanding of natural and anthropic impacts

Funding

INSU-TelluS-SYSTER 2019

Project leader

A. Tudryn (GEOPS)

Collaborations

E. Gibert-Brunet (GEOPS), P. Tucholka (GEOPS), A. Noret (GEOPS), S. Miska (GEOPS), M. Massault (GEOPS), O. Dufaure (GEOPS), M. Djamali (IMBE), H. Motavallianbaran (Univ de Téhéran), M. Lankarani (Univ. Téhéran), H. Ahmady-Birgani (Univ. Urmia), H. Lahijani (INIOAS, Téhéran), A. Sharifi (INIOAS), M. Shah-Hosseini (INIOAS).

projet Epure

Lake Urmia is one of the largest salt-water lakes in the world. Since the1980s it has suffered severe environmental damage that has seen its level drop by 7 m over the past 15 years. Still the subject of controversy, this drop in water level has variously been attributed to a 10% drop in precipitation and to anthropic causes (the construction of several dams on rivers that feed into the lake, over-pumping of subterranean water, etc.). However, despite the clear over-exploitation of water, the respective impacts of natural and anthropic factors on the lake’s watershed have still not been quantified.

The principal objective of this project is to decipher the trends in the environmental evolution of the lake since the Last Glacial Maximum and to identify the natural and anthropic changes that have occurred over the course of the Holocene. Our approach is based on analyses of lacustrine sediments and of the waters of the lake and aquifers. The results (1) will be used  to formulate sustainable management plans for water sources and ecology on a regional scale, and (2) will be integrated within supra-regional (Western Iran, and Anatolia are situated within the zone of influence of the Eastern Mediterranean and act as a link between Europe, North Africa and Northern Asia) and global scale climate studies in order to accurately correlate climatic variations with other terrestrial and marine records.

These objectives will be achieved by means of three main steps:

  • The establishment of a hydrological reference system for the lake, which encodes all current aspects such as water testing and hydrogeochemical characterization for each fluctuation;
  • The reconstruction, at a high temporal resolution (certified chronology), of Late Quaternary environmental changes in the lake zone by verifying sedimentological, hydrochemical and biological indicators/markers;

The identification of past human and natural (climate, seismic activity) impacts on the hydroenvironments of the lake and its watershed

REconstructing the influence of Climate change on lAterite formation

Funding

ANR 2017 (2018-2021)

Project leader

C. Gautheron (GEOPS)

Collaborations

S. Sepulcre (GEOPS), F. Haurine, C. Quantin (GEOPS), D. Calmels (GEOPS), R. Pinna-Jamme (GEOPS), G. Monvoisin (GEOPS), J. Nouet (GEOPS), J. Roques (IPN), T. Allard (IMPMC), G. Morin (IMPMC), E. Balan (IMPMC), M. Guillaumet (IMPMC), J. Bouchez (IPGP), C. Rollion-Bard (IPGP), P. Agrignier (IPGP), Z. Fekiacova (CEREGE), I. Basile-Doelsch (CEREGE), A. Guihou (CEREGE), B. Angeletti (CEREGE), J.-Y. Roig (BRGM), G. Aertgeerts (BRGM), M. Dall’Asta (TOTAL), J.-P. Girard (TOTAL), J. Braun (GFZ, Germany), A. Horbe (IG, Brazil), G. Bueno (LABOGEF, Brazil), L. Cherem (LABOGEF, Brazil)

Laterites are deep weathering covers of the critical zone that occupy 80% of the total soil-mantle volume of the Earth’s landscape and significantly contribute to the global geochemical budget of weathering and erosion, and greenhouse gas consumption. Despite their factual importance on Earth surface, the timing of their formation and their evolution in response to climatic and geodynamic forcing are still not fully understood. The originality of the RECA project is to combine chronometric, weathering and climatic proxies developed in the recent years in order to build a comprehensive and predictive scenario of laterite formation and evolution. We will concentrate our effort on geodynamically stable Guyana Shield and Central Amazonia regions, where laterites formed through the whole Cenozoic and can be associated with major geomorphological units. This ambitious multidisciplinary project proposes, for the first time, to perform absolute dating of lateritic duricrusts associated to five episodes of planation in the South American subcontinent. We will date mineralogically well-identified populations of iron oxides and oxyhydroxides (hematite, goethite) and clays (kaolinites) by using (U-Th)/He, (U-Th)/Ne and electron paramagnetic resonance spectroscopy, respectively. The inherent complexity of weathering materials, which may contain different populations of a same secondary mineral related to distinct stages of lateritization will be taken into account. The timing of duricrust formation will then be related to paleoclimatic conditions (temperature, rainfall) derived from a combination of geochemical or mineralogical indices and proxies: (i) at global scale, through, for example, the known continental drainage curves; (ii) at a more regional scale through the intensity of weathering, the ratio hematite/goethite or O and H isotope systems of kaolinite and iron oxides and oxyhydroxides. We will also associate non-conventional Li, Si and Fe isotopic methods that will help to decipher the evolution of weathering processes linked to the various stages of laterite formation. Coupling weathering budget and the ages of weathering profiles will yield average weathering and erosion rates, allowing comparison with other weathering environments or paleo-environments at the Earth surface.

Projet RECA

Interactions between the various processes (climat, global geodynamics) operating at several timescales on the evolution of lateritic surfaces of the Amazonian shield, the establishment of which is estimated by various geochronometers and geochemical tracers (Ar/Ar dating, 36Cl) Yu et al., Elements, 2015.

PALeoventilation MEDiterranean Sea – Tracing and paleoventilation of intermediate and deep water masses in the Mediterranean since the last glacial period.

Funding

INSU-LEFE-IMAGO 2019 (2019-2021)

Project leader

C. Colin (GEOPS)

Collaborations

C. Colin (GEOPS), G. Siani (GEOPS), M. Duhamel (GEOPS), S. Zouari (GEOPS/GEOGLOB – Univ. Sfax) N. Tisnerat-Laborde (LSCE), F. Thil (LSCE), Dapoigny (LSCE), M. Revel (Géoazur, Nice), K. Tachikawa (CEREGE, Aix-Marseille), S. Toucanne (IFREMER, Brest), E. Ducassou (EPOC, Bordeaux), M. Paterne (LSCE, Gif-Sur-Yvette), N. Kallel (GEOPS/GEOGLOB – Univ. Sfax).

This project aims to test the various hydrological scenarios that have led to changes in the thermohaline circulation in the Mediterranean over the last glacial period and last deglaciation. The object is to better constrain the mechanisms that underlie these hydrological changes which occurred during rapid climatic events of the last glacial period and their potential impacts on the deposition of organic-rich deposits (i.e. ORL, sapropels). In order to do this, we propose to reconstruct the hydrological variations of the intermediate and deep water masses in the central Mediterranean (the Ionian Sea, the Straits of Sicily, the western Mediterranean around the Sardinian Channel and Corsica). We use the difference in C14 ages between deep and intermediate waters and the surface in order to identify changes in the ventilation of intermediary and deep water masses. These analyses are carried out using a new generation of accelerator mass spectrometers, the ECHoMICADAS, which allows us to use carbon 14 to date samples containing as little as 20 µg of carbon. These results are then combined with the trace evidence for the origin of the water masses based on the isotopic composition of the Nd in planktonic foraminifera (for the period post 30 ka). Analyses of foraminifera Nd and benthic foraminifera δ13C will also be carried out for sapropel S3 (beyond the scale of C-14 dating) in order to constrain the hydrology that gave rise to this anoxic event which occurred under glacial environmental conditions (sea level, inputs of fresh water from the African continent and the hydrological connection at the Straits of Gibraltar) that differ from the environmental conditions prevailing at the time when sapropel S1 was deposited.

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Projet palmeds

General outline of the hydrology of intermediate water masses in the Mediterranean and the locations of cores selected for the PALMEDS project.

 

Associated thesis

Maxence Duhamel, Sounda Zouari

BIOlogical Productivity changes and their leverage on the Carbon and Oxygen cycles during the last Deglaciations

Funding

INSU-LEFE-IMAGO 2019 (2019-2022)

Project leader

S. Duchamp-Alphonse (GEOPS) and A. Landais (LSCE)

Collaborations

M. Brandon (GEOPS/LSCE), M. Kageyama (LSCE), L. Bopp (LMD), E. Michel (LSCE), D. Roche (LSCE), G. Siani (GEOPS), F. Prié (LSCE), T. Extier (LSCE), T. Blunier (Université de Copenhague) et F. Manssouri (LSCE).

Since the 1950s, increasing CO2 emissions have amplified the natural greenhouse effect of the Earth, which is evident in a decrease in ice cover, a rise in sea level and the recurrence of extreme meteorological and climatic events, all of which have considerable consequences for natural and human systems. The important roles played by ocean circulation (particularly in the Southern Ocean) and biospheric productivity in variations of atmospheric pCO2 have been clearly identified. However, the processes that led to these variations and the impacts on the ecosystem since the industrial revolution, and also in pre-anthropic contexts, remain poorly understood. This fact limits our understanding of the climatic system of the future.
More particularly, over the past 800 ka, while an important part of the increases of atmospheric pCO2 recorded during the deglaciations can be attributed to the reinvigoration of austral upwelling which favours the degassing of CO2 from the deep ocean reservoir to the atmosphere, the scale of the changes in pCO2 is also a function of biological productivity, the past dynamics of which are still poorly understood.
The aim of this project is to more accurately quantify the changes in biological productivity and their impacts on the carbon- (C) and oxygen (O) cycles during the Quaternary deglaciations, by combining the expertise of several laboratories in the Isle de France (GEOPS, LSCE, LMD) in order to couple new, complementary empirical approaches with global climate modelling experiments. Specifically, measurements of the ∆17O composition of the EDC core, retrieved from the Antarctic, will allow us to quantify global photosynthetic oxygen for the past 800 ka. The calibration of the BrXRF/CaXRF signal of a Southern Ocean sedimentary core in terms of exported COT/CaCO3, through a micropaleontological and geochemical approach, will allow us to quantify changes in the efficiency of the biological pump in a key region for CO2 exchanges between the ocean and the atmosphere over this time period. The use of the outputs from oceanic bio-geochemistry and vegetation models will facilitate comparisons of the empirical results.

projet biocod

AFrican humid periods Recurrence and aeOlian dust signal over West Africa during the last two CLIMatic cycles

Funding

INSU-LEFE-IMAGO 2018 (2018-2021)

Project leader

C. Skonieczny (GEOPS)

Collaborations

A. Bory (LOG, Université de Lille), V. Bout-Roumazeilles (LOG, Université de Lille), B. Malaizé (EPOC, Université de Bordeaux), C. Colin (GEOPS).

Over the course of the Quaternary, variations in received insolation on the African continent have governed the dynamics of the Monsoon in this region causing a recurrence of intense periods of precipitation. These African Humid Periods (AHPs) are characterized by a major transformation of the hydrological cycle of the Sahara favouring the development of vast river networks and tropical flora and fauna in a region that is currently hyper-arid. In the current context of climatic warming, it is crucial that we understand the environmental mechanisms and responses associated with these dramatic swings between two extreme climatic states if we are to improve our climatic projections. During the last two climatic cycles, which span the past 240 ka, eight AHPs have been identified. Numerous studies have targeted the mechanisms associated with the initiation and termination of the last AHP which occurred at the beginning of the Holocene, but, despite all of these efforts, a degree of disagreement still surrounds the subject. A factor that complicates our understanding of this Holocene AHP perhaps lies in the fact that it corresponds to a period when obliquity and local insolation reach their maxima in a relatively synchronous manner thus making it difficult to clearly ascertain their respective roles. In the context of this project, we propose to examine the seven other AHPs identified with the aim of bringing new elements to the debate. We propose to study the aeolian terrigenous material in the continuous record of a marine sediment core taken off the coast of West Africa in the north-east Tropical Atlantic. The study of this terrigenous material, which had been carried by means of the atmosphere from the Sahara and Sahel during these AHPs, will provide information not only regarding atmospheric circulation (wind direction and intensity), but also valuable information regarding the provenance of the material and the changes in environmental conditions that prevailed in the source areas. The ultimate aim is to improve our understanding of the mechanisms associated with the recurrence of such rapid climatic variations in this particularly vulnerable part of the world.

 

­projet afroclim

Source Figure:  Skonieczny et al., 2019 – Science Advances. Mises en évidence de l’expression des AHPs sur différents engistrements paléoclimatiques africains et contexte orbital au cours des deux derniers cycles climatiques.

 

 

Associated thesis

Maxime Leblanc