CHIli – COccolithes: The Regime of Westerlies and Oceanic Fronts in the South Pacific Ocean since the Last Glacial Maximum

Funding

INSU-LEFE-IMAGO 2013 (2013-2016)

Project leader

S. Duchamp-Alphonse (GEOPS)

Collaborations

L. Beaufort (CEREGE), G. Siani (GEOPS), E. Michel (LSCE), N. Durand (LMC14), et C. Kissel (LSCE).

Measurements of CO₂ trapped in Antarctic ice reveal that the pCO₂ of the atmosphere during the Last Glacial Maximum (LGM) was 80 to 110 ppmv lower than the pCO₂ value recorded for the interglacial period, before any anthropic activity. It turns out that significant changes in the position and intensity of oceanic fronts and of winds from the west (westerlies) in the high latitudes of the Southern Hemisphere, could on their own explain these major changes in atmospheric pCO₂   by impacting on (i) the physical pump (ventilation of intermediate and deep ocean water masses); (ii) the effectiveness of the biological pump (variations in primary production); and (iii) ice coverage. In other words, these three mechanisms impact significantly on the amplitude of CO₂ exchanges between the ocean reservoir and the atmospheric reservoir. The objective of this project is to better define the impact of the ocean-atmosphere system of the southern high latitudes on global levels of pCO₂ in the Last Glaciation by simultaneously considering the physical and biological pumps. In particular, it aims to tackle the following issues: (i) the impact of the regime of westerly winds and oceanic fronts on the ventilation of intermediate and deep ocean water masses in the South Pacific Ocean (water stratification v upwelling); and (ii) the effectiveness of the biological pump (variations in primary production) since the LGM through the study of coccolithic assemblages (calcareous phytoplankton) and measurement of COT and CaCO₃ contents of three sedimentary cores taken from Sub Antarctic zone of the Pacific sector. Through a thesis being prepared by Elisabeth Teca (2019-2022), this project is completed by the study of diatom assemblages (siliceous phytoplankton) from sedimentary cores MD07-3088 and MD07-3082.

Figure : Map showing the geographical locations of cores studied in this project (MD07-3100, MD07-3088 and MD07-3082); the cores follow a latitudinal transect within the sub Antarctic zone of the Pacific sector and are likely to record the dynamic of oceanic fronts in the region since the Last Glacial Maximum.

Associated thesis

Elisabeth Teca

Circulation InTeRmédiaire dans l’Océan iNdien depuis le dernier maximum GLACiairE

Funding

INSU-LEFE-IMAGO 2017 (2017-2019)

Project leader

S. Sepulcre (GEOPS

Collaborations

C. Colin (GEOPS), R. Ma (GEOPS), F. Bassinot (LSCE), N. Tisnérat-Laborde (LSCE), L. Licari (CEREGE)

The objectives of this research project fall within a study on the role of ocean circulation in the modalities of heat and salt transfer between low and high latitudes during the glacial-interglacial terminations. In particular, we are interested in changes that occurred between the Last Glacial Maximum and the Holocene at intermediate depths within the Bay of Bengal. In fact, while the role of intermediate water masses in the processes of teleconnection involved in the terminations is increasingly being studied for the Atlantic, Pacific and Southern Oceans, it remains little studied in the case of the Indian Ocean despite the presence of globally significant water masses. In order to meet our objectives, we propose a combined study of benthic foraminifera assemblages, which are sensitive to geochemical variations in water masses and sediment (trophic level, oxygen concentration), and geochemical tracers for a key period of the Earth’s climate history, Termination I: 1) Oxygen  (δ¹⁸O) and Carbon (δ¹³C) isotopic composition; 2) element ratios measured in tests of benthic foraminifera (Cd/Ca, Mg/Ca, B/Ca, Sr/Ca et U/Ca); 3) Δ¹⁴C (the difference between the C¹⁴ of planktonic and benthic  foraminifera); 4) εNd. These different complementary records, which are unprecedented for the study zone, allow us to accurately characterize variations in circulation at intermediate depths in the Bay of Bengal. These measurements will be compared to changes occurring at the surface and at depth both at the study site and at the scale of the Indian Ocean; ultimately, this will allow us to integrate these variations at a global scale. We will thus improve our understanding of the role of intermediate water masses during Termination I and the teleconnections between high latitudes and low latitudes.

Reconstruction of the extension of Antarctic Intermediate Waters a) at present and b) during the Last Deglaciation and its relationships to ventilation in the Southern Ocean and to CO₂ degassing (Yu et al., EPSL, 2018.)

Associated thesis

Riufang Ma

ECOS Sud CONICYT Chili

Project leader

G. Siani (GEOPS) and Ricardo De Pol Holz (Centro de Investigación GAIA-Antárctica (CIGA) and Center for Climate and Resilience Research Universidad de Magallanes)

Other participants

S. Duchamp-Alphonse (GEOPS), E. Michel (LSCE), C. Kissel (LSCE), C. Latorre Hidalgo (Pontificia Universidad Católica de Chile).

Project / Programme

The impact of circulation changes and the melting of the Patagonian ice sheets on the regulation of atmospheric CO₂ by the Southern Ocean.

This project is based on very close cooperation between three teams from the Nucleo Milenio Paleoclima Hemisferio Sur (NMPHS) at the Universidad de Magallenes and the Universidad Católica de Chile in Chile, and the GEOPS and LSCE labs in France.

Objectives

The Southern Ocean (SO) and its circulation play a fundamental role in the global climate system. In fact, a key element of thermohaline circulation is the return route of water masses from the deep ocean to the surface via the dynamic of upwelling. This return route is in part controlled by latitudinal position and the intensity of westerly winds. In recent years, the study of the Southern Ocean and its upwellings has become a priority for a better understanding of the climate system since they control the quantities of heat and carbon transferred from the deepest ocean reservoir to the surface ocean and the atmosphere.

Up until now, most studies have considered either the role played by the physical pump, or that played by the biological pump, to explain this transfer of carbon from the ocean to the atmosphere. However, the increase in upwelling in the Southern Ocean over the last glacial transition has led to an increase in exported biological production. It is, therefore, desirable to study the interactions between the two CO₂ pumps by looking at high resolution climatic records sampled in key areas of the Southern ocean. The western part of South America and the adjacent South-East Pacific, are unique regions for answering key questions regarding the evolution of the world’s climate due to their transitional position between subtropical and subarctic climate regimes. This study region features important interactions between the various components of the climate system: large scale atmospheric circulation, Southern Ocean circulation, and CO₂ exchange between the atmosphere and the ocean.

Within the framework of the ECOS Sud-CONICYT cooperative programme, we propose a multi-tracer study of marine sedimentary cores from the South-East Pacific sector of the Southern Ocean. The last Glaciation and the transition to the Holocene are the most promising climate periods for studying the evolution of biological and physical CO₂ pumps because they are characterized by major changes in global-scale ocean circulation. In particular, we aim to gain a better understanding of the impacts of the melting of the Patagonian ice sheets and ocean circulation on the regulation of atmospheric CO₂ by the Southern Ocean. In addition, the high sedimentation rates of our climate archives will allow us to obtain high quality data with very robust temporal control.

Associated thesis

Margaux Brandon

Holocene North Atlantic Gyres and Mediterranean Overturning dynamic through Climate Changes

Funding

ANR (2013-2018)

Project leader

C. Colin

Partner Laboratories

GEOPS (Univ. Paris Saclay, campus Paris Sud Orsay)
Laboratoire des Sciences du Climat et de l’Environnement (LSCE/IPSL, CEA-CNRS-UVSQ)
EPOC-CNRS, Université de Bordeaux
CEREGE (CNRS-Univ. Aix-Marseille)
LPGNantes (Université de Nantes)
M2C (Université de Rouen)

Context

The North Atlantic plays a fundamental role in the European climate through its system of meridional ocean circulation, known as Atlantic Meridional Overturning Circulation (AMOC) the dynamics of which control the salt and heat budgets of the North Atlantic. The intensity of the sub-polar gyre, which is in turn principally governed by atmospheric dynamics and flows of fresh water, today controls the northern limit of the intrusion of salty Mediterranean waters and the flows of sub-tropical Atlantic water reaching northern latitudes. Its dynamics also have a primary impact on the climate of Northern Europe. In this context, changes in the thermohaline circulation of the Mediterranean over the course of sapropel deposition events and exchanges of water masses between the eastern and western basins, on the one hand, and between the North Atlantic and the Mediterranean, on the other, still remain relatively unexplored and poorly quantified. Furthermore, the impact of hydrological changes occurring on the European edge of the Mediterranean is poorly constrained even though these Mediterranean waters can have an impact on the salt budgets and on the formation of deep water in the North Atlantic.

Objectives

Our research aims to improve our knowledge of the hydrology of the Mediterranean and its European margin with a view to reconstructing the AMOC and thermohaline circulation in the Mediterranean during sapropel deposition events; we also aim to identify the impact that Mediterranean thermohaline circulation might have on circulation in the North Atlantic.

Associated missions

Mingulay-Rockall, Ice-CTD

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Associated thesis

Maxence Duhamel

MAGnesium thermometer Improvement for assessing Climate Sensitivity

Funding

INSU-LEFE-IMAGO 2016 (2016-2018)

Project leader

F. Bassinot (LSCE)

Collaborations

S. Sepulcre (GEOPS), X. Pang (LSCE/GEOPS), H. Dang (LSCE), D. Blamart (LSCE), T. de Garidel-Thoron (CEREGE)

One of the principal approaches used to gain a better understanding of climatic sensitivity involves comparing past changes in ocean temperature with variations in greenhouse gases (GHG) recorded in ice. This type of approach requires the compilation of a database of paleotemperature information covering key periods (e.g. the Last Glacial Maximum LGM) for which we have GHG data retrieved from ice cores. But recent compilation efforts have revealed a number of challenges: (i) the difficulty involved in combining estimations from different tracers, and (ii) a certain number of problems specific to each tracer. This is the case for ocean temperatures reconstructed on the basis of Mg/Ca ratios in foraminifera where three principal problems are encountered:

(i) Uncertainty regarding the taxonomy used by geochemists;

(ii) Heterogeneity of sample preparation protocols used combined with differences in the choice of calibrations;

(iii) The absence of a common strategy concerning the taking into account (or not) of salinity as a factor that might potentially affect the Mg/Ca signal.

In order the better constrain these difficulties, the MAGICS project adopts a three-pronged approach:

1. The development of a strategy which allows the integration of Mg/Ca data from various labs (i.e. obtained using different analysis protocols) and the application of a temperature conversion which is as robust and coherent as possible;
2. The creation of a new dataset, subject to taxonomic controls, which will allow us to draw conclusions regarding the potential impact of salinity on the Mg/Ca thermometer and to propose a method of correction;
3. The more precise reconstruction of differences in ocean surface temperatures between the LGM and the present, with a particular focus on the intertropical band and the Pacific Warm Pool of the western pacific, and the use of this data to fine tune estimations of climatic sensitivity.

Map of ocean surface temperatures showing the connection between the Pacific and Indian Oceans and the extent of the present-day Warm Pool (Temperatures greater than 28°C).

Associated thesis

X. Pang