Dramatic reduction in size of the lowland Macquarie River in response to Late Quaternary climate-driven hydrologic change

Abstract

Palaeochannels of lowland rivers provide a means of investigating the sensitivity of river response to climate-driven hydrologic change. About 80 palaeochannels of the lower Macquarie River of southeastern Australia record the evolution of this distributive fluvial system. Six Macquarie palaeochannels were dated by single-grain optically stimulated luminescence. The largest of the palaeochannels (Quombothoo, median age 54 ka) was on average 284 m wide, 12 times wider than the modern river (24 m) and with 21 times greater meander wavelength. Palaeo-discharge then declined, resulting in a younger, narrower, group of palaeochannels, Bibbijibbery (125 m wide, 34 ka), Billybingbone (92 m, 20 ka), Milmiland (112 m, 22 ka), and Mundadoo (86 m, 5.6 ka). Yet these channels were still much larger than the modern river and were continuous downstream to the confluence with the Barwon-Darling River. At 5.5 ka, a further decrease in river discharge led to the formation of the narrow modern river, the ecologically important Macquarie Marshes, and Marra Creek palaeochannel (31 m, 2.1 ka) and diminished sediment delivery to the Barwon-Darling River as palaeo-discharge fell further. The hydrologic changes suggest precipitation was a driving forcing on catchment discharge in addition to a temperature-driven runoff response.

Minimum founding populations for the first peopling of Sahul

“…To translate net primary production into a carrying capacity expressed in units of humans the landscape was capable of supporting, we used data derived from archaeological sites and the assumption of a putative population low (nadir) that occurred during and immediately after the Last Glacial Maximum (23-18 ka) 64-67 , when conditions were cooler than today and much (but not all [68][69][70][71] ) of the continent was drier [72][73][74][75][76][77][78][79] . Demographic reconstructions based on the spatial distribution of dated archaeological sites suggest that up to 80% of Australia could have been abandoned or experienced reduced occupation at some point during this interval , or at least a major spatial thinning of populations (perhaps as much as 60%) during this period .…”

The morphology and geomorphic evolution of a large chain‐of‐ponds river system

“…The second time period is presented for ~60-15 ka (Figure 7). At this time, the river is likely still a high-energy, gravel-bed river but may have shifted towards a more sinuous, single-thread planform akin to that documented elsewhere Kemp and Rhodes, 2010;Hesse et al, 2018aHesse et al, , 2018b. Large pools occur on meander bends and riffle zones occur between pools.…”

Significantly enhanced mid Holocene fluvial activity in a globally important, arid‐zone wetland: The Okavango Delta, Botswana

“…smaller rivers with greater lateral stability within the confines of larger channels), river pattern transformations, deactivation or breakdown of channels and the establishment or transformation of large wetland complexes, and/or increasing fluvial-aeolian interactions (e.g. Hesse et al, 2018aHesse et al, , 2018bIsla & Espinoza, 2021;Mehl et al, 2022;Nanson et al, 1995Nanson et al, , 2008Tooth, 1997). Similarly, in the Northern Hemisphere, orbitally controlled northward shifts of the ITCZ during the early to mid Holocene, and/or intensification of monsoon weather systems, resulted in enhanced fluvial activity in many drylands, including North Africa, the Mediterranean, and Asia, with subsequent late Holocene reductions in fluvial activity evidenced by the development of smaller channels, river pattern transformations, and/or burial by aeolian deposits (e.g.…”