South Atlantic intermediate water advances into the North-east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period

Q. Dubois-Dauphin (1) , Lucile Bonneau (1, 2) , Christophe Colin (1) , J.C Montero Serrano (3) , P. Montagna (4) , D. Blamart (5, 6) , D. Hebbeln (7) , D. van Rooij (8) , E. Pons-Branchu (5, 9) , F. Hemsing (10) , A.M. Wefing (10) , Norbert Frank (10)

1 GEOPS - Géosciences Paris Sud
2 iSTeP - Institut des Sciences de la Terre de Paris
3 Géosystèmes - UMR 8217
4 ISMAR - Istituto di Scienze Marine [Bologna]
5 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
6 PALEOCEAN - Paléocéanographie
7 MARUM - Center for Marine Environmental Sciences [Bremen]
8 RCMG Ghent
9 GEOTRAC - Géochrononologie Traceurs Archéométrie
10 IUP - Institute of Environmental Physics [Heidelberg]

The Nd isotopic composition (εNd) of seawater and cold-water coral (CWC) samples from the Gulf of Cádiz and the Alboran Sea, at a depth of 280–827 m were investigated in order to constrain middepth water mass dynamics within the Gulf of Cádiz over the past 40 ka. εNd of glacial and Holocene CWC from the Alboran Sea and the northern Gulf of Cádiz reveals relatively constant values (−8.6 to −9.0 and −9.5 to −10.4, respectively). Such values are similar to those of the surrounding present-day middepth waters from the Mediterranean Outflow Water (MOW; εNd ∼ −9.4) and Mediterranean Sea Water (MSW; εNd ∼ −9.9). In contrast, glacial εNd values for CWC collected at thermocline depth (550–827 m) in the southern Gulf of Cádiz display a higher average value (−8.9 ± 0.4) compared to the present-day value (−11.7 ± 0.3). This implies a higher relative contribution of water masses of Mediterranean (MSW) or South Atlantic origin (East Antarctic Intermediate Water, EAAIW). Our study has produced the first evidence of significant radiogenic εNd values (∼ −8) at 19, 23–24, and 27 ka, which are coeval with increasing iceberg discharges and a weakening of Atlantic Meridional Overturning Circulation (AMOC). Since MOW εNd values remained stable during the last glacial period, it is suggested that these radiogenic εNd values most likely reflect an enhanced northward propagation of glacial EAAIW into the eastern Atlantic Basin.

Mots clés: Panoply

Domaines: Planète et Univers [physics]

Q. Dubois-Dauphin, Lucile Bonneau, Christophe Colin, J.C Montero Serrano, P. Montagna, et al.. South Atlantic intermediate water advances into the North-east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period. Geochemistry, Geophysics, Geosystems, 2016, 17 (6), pp.2236-2353. ⟨10.1002/2016GC006281⟩. ⟨hal-01417326⟩