Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

Germain Bayon,Yoan Germain,Sylvain Bermell,Patrick De Deckker,Kazuyo Tachikawa,John W Magee,Marc D Norman

doi:10.1038/srep44054

Abstract

Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.

Highlights

During the last glacial, episodes of massive iceberg discharges in the Northern Hemisphere were accompanied by substantial cooling and weakening of the Atlantic Meridional Oceanic Circulation (AMOC)[1], leading to out-of-phase warming periods in Antarctica[2,3]
Neodymium isotopes remain largely unaffected by erosion and transport processes[15], so that the average εNd composition of each potential provenance area is expected to have remained relatively unchanged over the last glacial period
Rainfall patterns in the tropics are strongly controlled by the position and intensity of the intertropical convergence zone (ITCZ), which varies on seasonal timescales from north to south of the Equator (Fig. 1)

Summary

OPEN Extensive wet episodes in Late

Glacial Australia resulting from high-latitude forcings received: 10 October 2016 accepted: 03 February 2017. The use of Nd/Ca ratios in planktonic foraminifera at this latter southern PNG site (MD05-2925; Fig. 3c), taken as an indicator for the intensity of REE-rich dissolved riverine inputs from Papua New Guinean rivers, shows that the sudden drops in precipitation recorded at Borneo and northern PNG were accompanied by more intense rainfall in the southerly tropical regions[19] This pattern agrees well with results obtained from dust flux reconstructions in the central equatorial Pacific[21], which provide evidence for a major latitudinal shift of the ITCZ by at least 4 degrees in this area during an earlier HS event. While the exact mechanism remains elusive, these interactions between northern and southern high-latitude climates most likely drove important fluctuations of interhemispheric temperature/pressure gradients[28], which may have resulted in protracted rainfall episodes in the Southern Hemisphere subtropical regions during the last glacial period

Methods

Author Contributions

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Additional Information