1474 / 2019-08-10 21:15:22

Precession- and glacial-cycles regulate the iron-rich sediment supplies from Papua New Guinea to the equatorial Pacific

6、海洋地球科学 > 专题4：晚新生代大洋环流与碳循环

The equatorial Pacific is one of the largest high-nutrient low-chlorophyll regions in the global ocean. In such regions, iron (Fe) level is thought to limit the phytoplankton growth in the surface ocean and also affect the subsequent carbon sequestration at depth. It has been shown that Papua New Guinea (PNG) is the major Fe contributor for the western equatorial Pacific. However, the exact sources, transport processes and range along the equatorial Pacific remain unclear, especially regarding the long-term variability of this Fe supply related to hydroclimate and paleoceanographic changes. Using a set of cores collected offshore the northern PNG and from the Ontong-Java Plateau (OJP), thought to be along the pathway of Fe delivery by undercurrents, here we compile high-resolution records to explore how the Fe-rich sediment supplies varied and distributed on orbital time-scale during the past 400 ka. The core chronologies are established based on 14C datings and the stratigraphic correlations of foraminiferal δ18O records and carbonate contents. The sedimentary Fe and clay-mineral smectite in the offshore-PNG sites show a precession cycle alone, in phase with the boreal spring insolation change (5°S, March). Such precessional predominance suggests the control of local precipitation and river runoff on the PNG near-coast deposition. For the OJP sites, by contrast, the proxies derived from terrigenous detrital component display a temporal pattern having both precession and ~100-ka cycles. The stronger 100-ka cycle during glacial times is likely related to sea-level changes, which should have regulated the route and strength of the New Guinea Coastal Undercurrent. This variability may have influenced the long-distance Fe-rich sediment transport from the PNG to the OJP, and further eastwards.