Orbital and sea-level changes regulate the iron-associated sediment supplies from Papua New Guinea to the equatorial Pacific

Abstract

Iron (Fe) supplied to the equatorial Pacific are thought to play a critical role in marine biogeochemical cycle and the related air–sea CO2 flux. Previous studies have shown that Papua New Guinea (PNG) is a major Fe contributor for the western equatorial Pacific. However, key issues of this Fe supply including the exact sources, transport processes and distribution range remain unclear, especially its long-term variability associated with hydroclimatic and paleoceanographic changes. Using a set of cores collected offshore the northern PNG and from the Ontong-Java Plateau (OJP), shown to situate along the pathway of Fe delivery by undercurrents, here we compile high-resolution records to explore how the Fe-associated sediment supplies varied and distributed on orbital time-scale during the past 400 ka. The chronologic frameworks of these cores are established by using 14C datings and stratigraphic correlations of foraminiferal δ18O records and carbonate contents. The sedimentary Fe and clay-mineral smectite in the offshore-PNG sites show a prominent precession cycle, in phase with the March insolation change at 5°S. Such precessional predominance suggests the control of local precipitation and river runoff on the offshore deposition of the Fe-associated sediment. For the OJP sites the proxies derived from terrigenous detrital component give a spectral pattern, however, prevailed by ∼100-ka cycle with secondary precessional highs. The significant 100-ka cycle can best be attributed to glacial–interglacial changes in oceanic transports, likely caused by sea-level regulated variability in the strength and/or route of the coastal undercurrents off PNG. This variability may have influenced the long-distance transport of Fe-rich particulates from the PNG to the OJP, and further eastwards via the Equatorial Undercurrent.