Australian Summer Monsoon variability in the past 14,000\u2009years revealed by IODP Expedition 356 sediments

Takeshige Ishiwa,Cecilia M Mchugh,Yusuke Yokoyama,David De Vleeschouwer,Lars Reuning,Stephen J Gallagher

doi:10.1186/s40645-019-0262-5

Abstract

The International Ocean Discovery Program (IODP) Expedition 356 Site U1461 cored a Miocene to Holocene sedimentary sequence in the upper bathyal carbonate offshore northwestern Australia (NWA). The siliciclastic component of these strata is primarily derived from the Australian continent. Radiocarbon dating on macrofossils and planktonic foraminifera shows that the upper 14 m section at Site U1461 preserves Holocene sediments, recording regional climate variability. K/Ca ratios determined by X-ray fluorescence elemental analyses and %K determined by shipboard natural gamma ray analysis are interpreted as indicators of riverine run-off from the Australian continent. We document the consequences of the variability of the Australian Summer Monsoon (ASM) on the continental shelf of NWA. We report an increase in terrigenous input due to a riverine run-off after 11.5 ka, which reaches a maximum at ~ 8.5 ka. This maximum is the result of the enhanced ASM-derived precipitation in response to the southern migration of the Intertropical Convergence Zone (ITCZ). A decrease in riverine run-off due to a weakening of precipitation in the NWA region after 8.5 ka was caused by the northern migration of the ITCZ. We conclude that the ITCZ reached its southernmost position at 8.5 ka and enhanced precipitation in the NWA region. This Holocene record shows that even during interglacial periods, monsoonal variability was primarily controlled by the position of the ITCZ.

Highlights

Northwestern Australia (NWA) is located at the edge of the Indo-Pacific Warm Pool (IPWP), which is the largest source of moisture and heat on Earth (Gagan et al 2004; De Deckker et al 2014; De Deckker 2016)
Modelling studies show that the exposure of the Sunda Shelf during the Last Glacial Maximum (LGM) and its flooding during the Holocene global sea level rise have influenced the hydrological cycle in the tropical Pacific and the eastern Indian Ocean and have caused rainfall variation in NWA (Di Nezio and Tierney 2013)
Riverine run-off records at Site U1461 The %K contribution to the total Natural gamma radiation (NGR) on the shelf of NWA is interpreted to indicate the presence of fluvial-derived clays and feldspar, reflecting the Variability in the Australian Summer Monsoon from the Pleistocene and the Holocene It has been suggested that the ASM was weak or inactive during glacial periods (Wyrwoll and Miller 2001; Gallagher et al 2014; De Deckker et al 2014)

Summary

Introduction

Northwestern Australia (NWA) is located at the edge of the Indo-Pacific Warm Pool (IPWP), which is the largest source of moisture and heat on Earth (Gagan et al 2004; De Deckker et al 2014; De Deckker 2016). Discovery Program (IODP) Expedition 356 Indonesian Throughflow recovered a proximal ASM terrigenous proxy record by coring a series of sites in the shallow continental shelf to the upper bathyal region part of offshore NWA (Fig. 1), recovering a sequence of Miocene to Holocene sediments at Site U1461 over 1 km thick (Gallagher et al 2015, 2017a). Due to their proximity to the Australian coast, the siliciclastic component of the sediments is derived from the NWA continent via the Fortescue and De Grey rivers (Fig. 1; James et al 2004). The Bchron algorithm uses Monte Carlo methods to produce a continuous age-depth model and interpolates ages of outlier intervals using obtained ages

Results

Discussion

Conclusions