Impact of iceberg melting on Mediterranean thermohalinecirculation during Heinrich events

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Hodell , A. D. , Francisco Javier , H. Jason , Villarejo Flores , Abel José , García Reguera , Hidalgo Colmenero , Elena , Angeles María , Grimalt , O. Joan , Lascorz Cacho , Isabel , Ferrer Frigola , Jaime , Miquel , Sánchez Sierro , Isabel María , Pernía Bárcena , Canals , Curtis

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Colecciones : DGL. Artículos del Departamento de Geología
Fecha de publicación : 29-jun-2005
Down-core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopesin International Marine Past Global Changes Study (IMAGES) core MD99-2343 in order to study theinteractions between climate change in the Northern Hemisphere and the western Mediterranean thermohalinecirculation at times of Heinrich events (HE). Our results confirm the antiphase correlation between enhancedNorth Atlantic Deep Water formation and low ventilation in the Mediterranean. However, this study reveals thatthis antiphase relationship in deepwater formation between the North Atlantic and Mediterranean wasinterrupted during times of HE when the injection of large volumes of water from melting icebergs reached theentrance to the Mediterranean. These events, which lasted less than 1000 years, are represented by pronounceddecreases in both planktonic d18O and benthic d13C signals. Lower salinities of Mediterranean surface waterresulted in a slowdown of western Mediterranean deepwater overturn even though cold sea surface temperaturesand drier climate should have resulted in enhanced deepwater formation.

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Sciences et techniques

PALEOCEANOGRAPHY, VOL. 20, PA2019, doi:10.1029/2004PA001051, 2005

Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events F. J. Sierro, 1 D. A. Hodell, 2 J. H. Curtis, 2 J. A. Flores, 1 I. Reguera, 1 E. Colmenero-Hidalgo, 1 M.A.B´arcena, 1 J. O. Grimalt, 3 I. Cacho, 4 J. Frigola, 4 and M. Canals 4 Received 11 May 2004; revised 25 February 2005; accepted 28 March 2005; published 29 June 2005. [ 1 ] Down-core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopes in International Marine Past Global Changes Study (IMAGES) core MD99-2343 in order to study the interactions between climate change in the Northern Hemisphere and the western Mediterranean thermohaline circulation at times of Heinrich events (HE). Our results confirm the antiphase correlation between enhanced North Atlantic Deep Water formation and low ventilation in the Mediterranean. However, this study reveals that this antiphase relationship in deepwater formation between the North Atlantic and Mediterranean was interrupted during times of HE when the injection of large volumes of water from melting icebergs reached the entrance to the Mediterranean. These events, which lasted less than 1000 years, are represented by pronounced decreases in both planktonic d 18 O and benthic d 13 C signals. Lower salinities of Mediterranean surface water resulted in a slowdown of western Mediterranean deepwater overturn even though cold sea surface temperatures and drier climate should have resulted in enhanced deepwater formation. Citation: Sierro, F. J., et al. (2005), Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events, Paleoceanography , 20 , PA2019, doi:10.1029/2004PA001051.

1. Introduction with all DO climatic oscillations, demonstrating that IRD [ 2 ] During the last glacial period evidence from Green- events occurred much more frequently than previously land ice cores and deep-sea sediments indicates that the thought, although they were recorded only in cores taken climate in the Northern Hemisphere was subject to rapid in the vicinity of the ice sheet margins. Iceberg melting coolings(stadials)andwarmings(interstadials)normallydOucreianng,pHaErtiacfufleacrtleydththeelahtiytdurdoelsogbyetowfeetnhe40N  oNrthanAdtl5a5nt  iNc referred to as Dansgaard-Oeschger (DO) millennial oscil-lations [ Dansgaard et al. , 1993; Bond and Lotti , 1995]. The [ Ruddiman , 1977] where the major IRD layers were depos-deposition of layers of ice-rafted detritus (IRD) indicates ited and planktonic foraminifera show pronounced thatmassiveicedischarges(Heinrichevents(HE))occurreddweactreera[s H es ei i n n ric d 1 h 8 ,O19v8a8l;ue G s, ro in us d s ic et at e i t ng al. t,he19p9r3e;se C n o c r e tij o o f e m t e a l l t . -, in the North Atlantic during some of the coldest stadials at the end of long-term cooling trends that include several DO 1997; Elliot et al. , 1998, 2001]. oscillations [ Heinrich , 1988; Bond et al. , 1992, 1993; [ 3 ] The injection of large volumes of freshwater slowed Broecker et al. ,1992].IthasbeenpostulatedthatthetrheedufcoerdmantoirotnheorlfyNaodrvtehctAiotlnanotfictheDeweaprmWastuebrtr(oNpAicDalWw)ataenrds deposition of these major IRD layers resulted from cata- that would normally heat the atmosphere of Greenland and strophic iceberg calving along the ice sheet margins of the western Europe [ Broecker et al. , 1985, 1992; Bond et al. , North Atlantic [ Bond et al. , 1992; Broecker et al. , 1992]. AlthoughalargefractionoftheIRDcamefromthei1n9fl9u2e,nc1e99o3f;i V c i e d b a e l rg e s t a al n . ,d1m99el7t;wa E t l e l r iot m e a t y a h l. a,ve20e0x2t]e.ndTehde Laurentide ice sheet, it has been suggested that at least in southward and eastward into the subtropics and offshore the northeast Atlantic, icebergs were calved first from the Eurasian ice sheets [ Grousset et al. , 2000]. Moreover, minor Portugal [ Shackleton et al. , 2000; Sch¨onfeldandZahn , IRD events were found [ Bond and Lotti ,1995]associatedp2r0e0s0e;nt Ba o r x d yg e e t n al. a,nd20c0a0r;bo Sc n ho¨ is n o f t el o d pe et d a a l t . a,2o0f0f3o]r.amHienriefewrae from the deep northern margin of the Balearic Islands in the 1 Department of Geology, University of Salamanca, Salamanca, Spain. western Mediterranean Sea suggesting that the meltwater 2 iences, University of Florida, Gainesville, released by icebergs from the Laurentide or Eurasian ice FloridDae,paUrtSmAe.ntofGeologicalSc sheets had a profound effect on Mediterranean surface 3 Department of Environmental Chemistry, Institute of Chemical and salinity and thermohaline circulation at times of HE. Environmental Research, Barcelona, Spain. [ 4 ] Previous data [ Cacho et al. , 2000] have shown during 4 Department of Stratigraphy, Paleontology and Marine Geosciences, University of Barcelona, Barcelona, Spain. gwlaascicallospeelryiocdosutphlaetdMtoedaibtreurrpatncelainmattheercmhaonhagleisneincitrhceulNatoirotnh Copyright 2005 by the American Geophysical Union. Atlantic and subpolar regions. The Mediterranean surface 0883-8305/05/2004PA001051$12.00 waters cooled and sank in response to the decreasing SST of PA2019 1 of 13

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