Category Archives: Projects

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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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 Br_XRF/Ca_XRF 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.

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.

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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