Provenance and supply of Fe-enriched terrigenous sediments in the western equatorial Pacific and their relation to precipitation variations during the late Quaternary

摘要

Iron (Fe) deposition in the equatorial Pacific has important implications for the global carbon cycle, while the provenance of Fe supply and its change remain highly debated. Here, we geochemically characterize the provenance of terrigenous sediments deposited on the pathways of the Equatorial Undercurrent (EUC) and the New Guinea Coastal Undercurrent (NGCUC). The Fe-enriched sediments in the western equatorial Pacific are mostly derived from fluvial inputs of Papua New Guinea (PNG), while nearly negligible impact from eo-lian dust could be detected. Variability of the terrigenous Fe-enriched deposition (7.4-13.4%) for core KX21-2 in the western equatorial Pacific over the past 380 ka shows dominant precession periods, superimposed on a clear glacial-interglacial trend with higher input during glacials. The precession periods are correlated with the precipitation over PNG, in response to the local summer insolation (5°S, March) and meridional migration of the Intertropical Convergence Zone (ITCZ). The glacial-interglacial trend is induced by sea level fluctuations that significantly influence the fluvial input from southern PNG. The different expressions of precession periods between glacials and interglacials in core KX21 -2 are tightly associated with the undercurrent. The subdued precession periods during interglacials can be attributed to the weakness of the NGCUC, which may link to La Nina-like conditions. The enhanced precession periods during glacials should result from increased input from southern PNG on one hand, and an intensified NGCUC on the other hand, due to the El Nino-like conditions. Compared to Fe, the proxy In (Ti/Total) (XRF log-ratio of Ti/Total counts) for core KX21 -2 preferentially indicates the northern PNG input, and therefore could be used to reflect the glacial changes in the NGCUC. Our records imply that the NGCUC was particularly stronger in MIS 6 and 10, and weaker in MIS 8.