Oceanic productivity variations during rapid climatic changes (Heinrich events)

LA DERNIERE GLACIATION A CONNU DE NOMBREUSES DEBACLES MASSIVES D'ICEBERGS DANS L'ATLANTIQUE NORD, (EVENEMENTS DE HEINRICH (HE)). CEUX CI ONT CHANGE FORTEMENT LES PROPRIETES DES EAUX SUPERFICIELLES, ET CREE DES INSTABILITES DE LA CIRCULATION THERMO-HALINE. ILS ONT AUSSI PRODUIT UN IMPACT SIGNIFICATIF SUR L'ECOSYSTEME MARIN, EN LIMITANT LA PENETRATION DE LUMIERE, ET MODIFIANT TEMPERATURE ET APPORT DES NUTRITIFS DANS LES EAUX DE SURFACE. TOUTEFOIS, ILS ONT AUSSI PU CONTRIBUER A DES SOURCES ADDITIONNELLES DE NUTRITIFS, PAR LA FONTE DES ICEBERGS, OU PAR LES CHANGEMENTS DANS L'HYDROLOGIE QU'ILS ONT PROVOQUE. CE TRAVAIL PORTE SUR UNE ETUDE A HAUTE RESOLUTION DE LA PRODUCTIVITE (DIATOMEES ET CONTENU EN CARBONE ORGANIQUE) PENDANT DEUX HE PARTICULIEREMENT ABRUPTES (H4 ET H1). IL S'AGIT DE COMPRENDRE LES LIENS ENTRE VARIABILITE DE LA PRODUCTIVITE PRIMAIRE, DEBACLES D'ICEBERGS, CHANGEMENTS DE L'HYDROLOGIE DE SURFACE ET CIRCULATION PROFONDE. CETTE ETUDE A MIS EN EVIDENCE UNE DIMINUTION DE LA PRODUCTIVITE SILICEUSE PENDANT LES HE, PARTICULIEREMENT DANS LA REGION DE FORTE ARRIVEE ET DEPOSITION DES DETRITIQUES, QUE NOUS ATTRIBUONS A L'AUGMENTATION DE STRATIFICATION DES EAUX SUPERFICIELLES.THE LAST GLACIAL PERIOD WAS PUNCTUATED BY DRAMATIC ICE SHEET SURGES IN THE NORTH ATLANTIC, KNOWN AS HEINRICH EVENTS (HE). THEY CAUSED MAJOR CHANGES IN SURFACE WATER PROPERTIES AND DESTABILIZATION OF THERMOHALINE CIRCULATION. BESIDES, THEY HAD ALSO MAJOR IMPACTS ON MARINE ECOSYSTEM AS THE LATER IS HIGHLY DEPENDENT ON LIGHT, TEMPERATURE AND NUTRIENTS SUPPLY. ADDITIONAL NUTRIENT SOURCES FROM ICEBERG MELTING OR LINKED TO A STRONGER SOUTHERN INTERMEDIATE WATER COMPONENT REACHING THE NORTHERN ATLANTIC MAY HAVE OCCURRED DURING HE, THUS INCREASING PRIMARY PRODUCTIVITY. AT THE OPPOSITE, PRODUCTIVITY MAY HAVE BEEN HAMPERED BY THE COOLING AND INCREASED STRATIFICATION ASSOCIATED WITH HE. ALSO, WE PRESENT HERE A HIGH-RESOLUTION ANALYSIS OF PALEOPRODUCTIVITY (DIATOMS AND ORGANIC CARBON CONTENT) IN THE NORTH ATLANTIC, DURING THE TWO MAJOR ICEBERG SURGES (H1 AND H4) IN ORDER TO UNDERSTAND LINKS BETWEEN VARIABILITY OF PRIMARY PRODUCTIVITY, ICEBERG DISCHARGES, CHANGES ON SURFACE HYDROLOGY AND DEEP-WATER CONVECTION. RESULTS SHOWS A STRONG DECREASE ON PRODUCTIVITY DURING HE ESPECIALLY IN THE AREA OF MAXIMUM ICE-RAFTED DEPOSITION, BUT ALSO SOUTH OF THAT LATITUDINAL BAND THAT IS PROBABLY DUE TO REDUCED NUTRIENT SUPPLY LINKED TO UPPER LAYER STRATIFICATION.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF