Tracing Papua New Guinea imprint on the central Equatorial Pacific Ocean using neodymium isotopic compositions and Rare Earth Element patterns

The Nd isotopic composition (IC) and Rare Earth patterns of hydrodynamic st ructures of the Equatorial Pacific Ocean were characterized along 140 degre esW. The Nd IC of Antarctic Intermediate Water (AAIW) and of the lower laye r of the Equatorial Undercurrent (EUC) at 140 degreesW (13 degreesC Water) are much more radiogenic at the equator than at their origin in the South E quatorial Current (12 degreesS), revealing that these water masses have bee n in contact with the highly radiogenic Papua New Guinea (PNS) slope. In bo th cases, only a small fraction (less than 9%) of the sediment deposited on the PNG slope is required to be exchanged or dissolved to explain these Nd TC variations, whereas the hydrographic properties of the same water masse s remain unchanged. This confirms the usefulness of this tracer to identify pathways of water masses. These results emphasize the importance of jets i n transporting lithogenic material into the subsurface layers of remote are as, where aeolian inputs are particularly weak and corroborate the previous results on Fe and Al maximum in this area [M.L. Wells, G.K. Vallis, E.A. S ilver, Nature 398 (1999) 601-604]. The Nd IC of the upper layer of the EUC contrasts strongly to that of the subpycnocline layer, indicating that the equatorial upwelling only affects the surface waters and is not effective b etween 120 and 150 m. We calculate that the Nd imprint of the PNG input is likely to vanish from this surface layer as it traverses the basin, due to the replacement of upwelled waters by non-radiogenic ones, (C) 2001 Elsevie r Science B.V. All rights reserved.