Millennium Timescale Iceberg Discharges in the Irminger Basin During the Last Glacial Period : Relationship With the Heinrich Events and Environmental Settings

Mary Elliot; L. Labeyrie; N. TisnΘrat; E. Cortijo; J-C. Duplessy

(L.S.C.E., CNRS-CEA, Av. de la Terrasse, 91198 Gif sur Yvette Cedex, France; ph. 33-1-69-82-43-39; fax 33-1-69-82-35-68; Internet:elliot@lsce.cnrs-gif.fr); G. Bond (L.D.E.O., Rt 9w, Palisades, NY 10964, USA; ph. 914 365 8478; fax 914 365 8154; Internet: gcb@lamont.ldgo.columbia.edu); J-L. Turon (D.G.O., Av. des FacultΘs, 33405 Talence Cedex, France; ph.33-5-56-84-88-58;

fax 33-5-56-84-08-48; Internet: turon@geocean.u-bordeaux.fr) (AGU Sponsor: L. Labeyrie)

High resolution records of coarse lithic content and oxygen isotopehave been obtained in a piston core from the Irminger Basin at 62N. The lastGlacial period is characterised by numerous periods of increased iceberg dischargesoriginating partly from Iceland as attested by the presence of dark volcanic glass.A comparison with mid-latitude sediment cores shows that ice rafted materialcorresponding to the Heinrich events was deposited synchronously from 40 to 60N within

the error of radiocarbon dating and bioturbation effects. The more frequenticeberg discharges correspond to higher instabilities of the coastal ice sheetsand ice shelves in the Nordic area and may be linked with theDansgaard-Oeschger temperature oscillations. The evolution of sea surface hydrology at62N associated with these events has been reconstructed from the oxygenisotope record and changes in foraminiferal abundance. Light anomalies of the oxygen isotope ratio have been interpreted as a lowering of sea surfacesalinity which lag the lithic layers corresponding to HE2, HE3 and HE4 by a fewhundred years. This initial phase is rapidly followed by small increases in seasurface temperature within the range of the polar waters. In the Irminger Basin, bycontrast with the mid -latitudes, the foraminifera content increases with the lithic content.This has been interpreted as reflecting retreats of the sea ice edge synchronouswith periods of iceberg discharges. A comparison between high and mid-latitudesediment records of the North Atlantic Ocean suggests that the Heinrich events and themore frequent detrital events related to the Dansgaard-Oeschger cycles correspond totwo oscillating systems. The massive iceberg armardas which are released from large continental ice sheet every 5 to 10 ka and the more frequent instabilities of the coastal ice sheets in the high latitude Nordic regions which occur every 1,2 to 3,8 ka. At the time of the Heinrich events the synchroneity of the responsefrom all the northern hemisphere ice sheets attests of the existence of stronginteractions between the two systems.