Neodymium isotopic composition of deep-sea corals from Rockall Trough : implications for past changes of hydrology during the Holocene

ɛNd analyses have been performed on fossil deep-sea corals (L. pertusa and M. oculata) from a gravity core located on the Rockall Bank at 747 m water depth to reconstruct past hydrological changes of North Atlantic upper intermediate water. Corals ɛNd values range from -12.2 to -15.5 and demonstrate strong and systematic changes of seawater ɛNd during the Holocene. The ɛNd record displays a general trend with a small decrease from -14.5 to -15.3 during the time interval from 9400 to 6000 yrs. This is followed by an abrupt increase of ɛNd toward more radiogenic ɛNd values ranging from -13.5 to -12.2 about 6000 yrs ago. These variations suggest changes in the relative proportion of upper intermediate water originating in the subtropical and subpolar Atlantic characterized today by ɛNd of -10/-11.5 and -15, respectively. Hence, a wider eastward extension of the subpolar gyre induced by stronger westerlies occurs during the early-mid Holocene, which contributes likely a large amount of Labrador Sea water to the Nordic inflow. Beyond 6000 yrs BP, a weakening of the subpolar gyre circulation induces an extension of saline subtropical water masses into the NE Atlantic accompanied by a reduction of subpolar Atlantic waters flowing into the Nordic Seas. Such modifications could have affected deep-water convective activity of the Northern hemisphere through redistribution of freshwater from early Holocene melting northern hemisphere ice sheets. Superimposed to the long-term trend, rapid seawater ɛNd changes occurs suggesting centennial fluctuations of the subpolar and subtropical water mass balance.