Southern Hemisphere control on Australian monsoon variability during the late deglaciation and Holocene

Abstract

The evolution of the Australian monsoon in relation to high-latitude temperature fluctuations over the last termination remains highly enigmatic. Here we integrate high-resolution riverine runoff and dust proxy data from X-ray fluorescence scanner measurements in four well-dated sediment cores, forming a NE-SW transect across the Timor Sea. Our records reveal that the development of the Australian monsoon closely followed the deglacial warming history of Antarctica. A minimum in riverine runoff documents dry conditions throughout the region during the Antarctic Cold Reversal (15-12.9 ka). Massive intensification of the monsoon coincided with Southern Hemisphere warming and intensified greenhouse forcing over Australia during the atmospheric CO 2 rise at 12.9-10 ka. We relate the earlier onset of the monsoon in the Timor Strait (13.4 ka) to regional changes in landmass exposure during deglacial sea-level rise. A return to dryer conditions occurred between 8.1 and 7.3 ka following the early Holocene runoff maximum.

The Indo-Pacific Warm Pool: critical to world oceanography and world climate

“…Nevertheless, ancient river systems did operate during the LGM. A relict system of river channels had already been identified by Molengraaf and Weber (1919) and further documented by several other investigators, including Kuenen (1950) and more recently by Solihuddin (2014) who reviewed past evidence together with new bathymetric data. An attempt was made here to provide a new map of the exposed Sunda Shelf using published maps as well as information obtained from the Shuttle Radar Topography Mission (STRM) that was downloaded from https://dds.cr.usgs.gov/srtm/ (USGS 2004).…”

“…showing an significantly exposed Sahul Shelf and also the exposed Sunda Shelf spanning from the Gulf of Thailand down to south of Borneo and north of the tip of Java. Plotted on this LGM topography is a system of palaeo-rivers, some of which had already been delineated by Molengraaf and Weber (1919), Kuenen (1950) and updated by Solihuddin (2014), all plotted in white, with a new interpretation of additional rivers shown here in red. The map was generated using the ETOPO1 global relief data set available at the following web site: http://www.ngdc.noaa.gov/mgg/global/ relief/ETOPO1/docs/.…”

“…Ocean transgression, which was really rapid for short periods, such as during the global 'meltwater pulses' occurring at 14.08-13.61 ka and 11.4-11.1 ka (Camoin et al 2012), and which have affected human occupation on the shelves in places (for more information, refer to Oppenheimer 1998), was a pertinent feature when deglaciation commenced until about 6000 years ago when sea levels were approximately the same as today and remained so for 6 millennia. Kuhnt et al (2015) identified that monsoonal activity became fully established by 14-15 ka in the Banda Sea and at 13.4 ± 0.3 ka in the Timor Strait. De Deckker et al (2014) determined that northwestern Western Australia came under the influence of monsoonal rains by 13 ka.…”

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“…The site is situated on seismic Line BR98-117, 1300 m northeast of the intersection with seismic Line BR98-168 and ~0.8 nmi southeast of the ~40 m long piston Core MD01-2378, which provides insights into late Pleistocene sedimentation and stratigraphy at this location (e.g., Holbourn et al, 2005;Kuhnt et al, 2015). The interpretation of Miocene seismic reflectors is based on comparison to the Australian Geological Survey Organisation regional seismic survey Line 119-04 (well control by Buffon 1 and Brewster 1A) and the BBHR Line 175/10 (well control by Argus 1).…”

“…Yellow arrows indicate main eolian dust paths in September (from Hesse and McTainsh, 2003). Figure modified from Kuhnt et al (2015). Base map was generated with GeoMapApp (http://www.geomapapp.org) using the Global Multi-Resolution Topography synthesis database (Ryan et al, 2009 …”