| 1. |
- Cohen, Timothy, et al.
(author)
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Continental aridification and the vanishing of Australia's mega-lakes
- 2011
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In: Geology. - 0091-7613 .- 1943-2682. ; 39, s. 167-170
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Journal article (peer-reviewed)abstract
- The nature of the Australian climate at about the time of rapid megafaunal extinctions and humans arriving in Australia is poorly understood and is an important element in the contentious debate as to whether humans or climate caused the extinctions. Here we present a new paleoshoreline chronology that extends over the past 100 k.y. for Lake Mega-Frome, the coalescence of Lakes Frome, Blanche, Callabonna and Gregory, in the southern latitudes of central Australia. We show that Lake Mega-Frome was connected for the last time to adjacent Lake Eyre at 50–47 ka, forming the largest remaining interconnected system of paleolakes on the Australian continent. The fi nal disconnection and a progressive drop in the level of Lake Mega-Frome represents a major climate shift to aridifi cation that coincided with the arrival of humans and the demise of the megafauna. The supply of moisture to the Australian continent at various times in the Quaternary has commonly been ascribed to an enhanced monsoon. This study, in combination with other paleoclimate data, provides reliable evidence for peri-ods of enhanced tropical and enhanced Southern Ocean sources of water fi lling these lakes at different times during the last full glacial cycle.
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| 2. |
- Cohen, Tim J., et al.
(author)
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Hydrological transformation coincided with megafaunal extinction in central Australia
- 2015
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In: Geology. - 0091-7613 .- 1943-2682. ; 43:3, s. 195-198
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Journal article (peer-reviewed)abstract
- Central to the debate over the extinction of many of Australia's last surviving megafauna is the question: Was climate changing significantly when humans arrived and megafauna went extinct? Here we present a new perspective on variations in climate and water resources over the last glacial cycle in arid Australia based on the study of the continent's largest lake basin and its tributaries. By dating paleoshorelines and river deposits in the Lake Eyre basin, we show that major hydrological change caused previously overflowing megalakes to enter a final and catastrophic drying phase at 48 +/- 2 ka just as the giant bird, Genyornis newtoni, went extinct (50-45 ka). The disappearance of Genyornis and other megafauna has been previously attributed to ecosystem collapse coincident with the spread of fire-wielding humans. Our findings suggest a climate-driven hydrological transformation in the critical window of human arrival and megafaunal extinction, and the results call for a re-evaluation of a human-mediated cause for such extinctions in arid Australia.
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| 3. |
- Cohen, Timothy, et al.
(author)
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Late Quaternary mega-lakes fed by the northern and southern river systems of central Australia : varying moisture sources and increased continental aridity
- 2012
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 356:Special Issue, s. 89-108
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Journal article (peer-reviewed)abstract
- Optically stimulated and thermoluminescence ages from relict shorelines, along with accelerator mass spectrometer 14C ages from freshwater molluscs reveal a record of variable moisture sources supplied by northern and southern river systems to Lake Mega-Frome in southern central Australia during the late Quaternary. Additional lacustrine, palynological and terrestrial proxies are used to reconstruct a record that extends back to 105 ka, confirming that Lakes Mega-Frome and Mega-Eyre were joined to create the largest system of palaeolakes on the Australian continent as recently as 50–47 ka. The palaeohydrological record indicates a progressive shift to more arid conditions, with marked drying after 45 ka. Subsequently, Lake Mega-Frome has filled independently at 33–31 ka and at the termination of the Last Glacial Maximum to volumes some 40 times those of today. Further sequentially declining filling episodes (to volumes 25–10 those of today) occurred immediately prior to the Younger Dryas stadial, in the mid Holocene and during the medieval climatic anomaly. Southern hemisphere summer insolation maxima are a poor predictor of palaeolake-filling episodes. An examination of multiple active moisture sources suggests that palaeolake phases were driven independently of insolation and at times by some combination of enhanced Southern Ocean circulation and strengthened tropical moisture sources.
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| 4. |
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| 5. |
- Cohen, Timothy, et al.
(author)
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Late Quaternary mega-lakes of central Australia: varying moisture sources and increased continental aridity.
- 2010
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In: <em>EOS Transactions, </em><em>American Geophysical Union</em>, PP31B-1624. San Francisco, USA, Dec. 2010.. - Washington DC : American Geophysical Union.
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Conference paper (other academic/artistic)abstract
- Optically stimulated (OSL) and thermoluminescence (TL) ages from relict shorelines, along with accelerator mass spectrometer (AMS) 14C ages from freshwater molluscs reveal a record of mega-lake phases over the late Quaternary for Lake Mega-Frome, situated in the arid zone of South Australia. Additional lacustrine, palynological and terrestrial proxies are used to reconstruct a record that extends as far back as 105 ka and demonstrates that Mega-Frome was last joined to the adjacent mega-Eyre at 50 - 47 ka forming the largest palaeolake on the Australian continent. This time interval for hydrological decline coincides with the arrival of humans on the Australian continent and the demise of the mega-fauna. Since then, Mega-Frome has filled independently at 33 - 31 ka (Heinrich event 3) and at the termination of the Last Glacial Maximum (LGM) to depths far in excess of those seen today (up to 15 - 20 times modern lake volumes). Further evidence of subsequent lake-filling episodes is recorded immediately prior to the Younger Dryas, the mid Holocene and during the medieval climatic anomaly. We present evidence for multiple moisture sources over this time period with lake phases being driven by either an enhanced Southern Ocean circulation or an enhanced tropical moisture source or a combination of both. We show however, that southern hemisphere summer insolation maxima (monsoon proxy) is a poor predictor for past palaeo-lake filling episodes. This is the first palaeohydrological record for a large area of southern semi-arid Australia indicating a progressive shift to more arid conditions throughout the last glacial cycle
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| 6. |
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| 7. |
- Fitzsimmons, Kathryn E., et al.
(author)
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Late Quaternary palaeoenvironmental change in the Australian drylands
- 2013
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 74, s. 78-96
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Journal article (peer-reviewed)abstract
- In this paper we synthesise existing palaeoenvironmental data from the arid and semi-arid interior of the Australian continent for the period 40-0 ka. Moisture is the predominant variable controlling environmental change in the arid zone. Landscapes in this region respond more noticeably to changes in precipitation than to temperature. Depending on their location, arid zone records broadly respond to tropical monsoon-influenced climate regimes, the temperate latitude westerly systems, or a combination of both. The timing and extent of relatively arid and humid phases vary across the continent, in particular between the westerly wind-controlled temperate latitudes, and the interior and north which are influenced by tropically sourced precipitation. Relatively humid phases in the Murray-Darling Basin on the semi-arid margins, which were characterised by large rivers most likely fed by snow melt, prevailed from 40 ka to the Last Glacial Maximum (LGM), and from the deglacial to the mid Holocene. By contrast, the Lake Eyre basin in central Australia remained relatively dry throughout the last 40 ka, with lake high stands at lake Frome around 35-30 ka, and parts of the deglacial period and the mid-Holocene. The LGM was characterised by widespread relative aridity and colder conditions, as evidenced by extensive desert dune activity and dust transport, lake level fall, and reduced but episodic fluvial activity. The climate of the deglacial period was spatially divergent. The southern part of the continent experienced a brief humid phase around similar to 17-15 ka, followed by increased dune activity around similar to 14-10 ka. This contrasts with the post-LGM persistence of arid conditions in the north, associated with a lapsed monsoon and reflected in lake level lows and reduced fluvial activity, followed by intensification of the monsoon and increasingly effective precipitation from similar to 14 ka. Palaeoenvironmental change during the Holocene was also spatially variable. The early to mid-Holocene was, however, generally characterised by moderately humid conditions, demonstrated by lake level rise, source-bordering dune activity, and speleothem growth, persisting at different times across the continent. Increasingly arid conditions developed into the late Holocene, particularly in the central arid zone.
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| 8. |
- Gliganic, Luke A., et al.
(author)
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Late-Holocene climatic variability indicated by three natural archives in arid southern Australia
- 2014
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 24:1, s. 104-117
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Journal article (peer-reviewed)abstract
- Three terrestrial climate proxies are used to investigate the evolution of Holocene palaeoenvironments in southern central Australia, all of which present a coherent record of palaeohydrology. Single-grain optically stimulated luminescence from sediments supplemented by C-14 from charcoal and lacustrine shells was obtained to date shoreline deposits (Lake Callabonna) and the adjacent Mt Chambers Creek alluvial fan. Our findings are complemented by a U/Th-based record of speleothem growth in the Mt Chambers Creek catchment, which we interpret to reflect increased precipitation. Together, these archives shed light on the timing of, and possible sources of water for, Holocene pluvial intervals. We identified several phases of elevated lake levels dated at similar to 5.8-5.2, 4.5, 3.5-2.7 and 1 kyr, most of which correspond to fluvial activity resulting from increased precipitation in the adjacent ranges. The enhanced hydrology during phases of the late Holocene likely increased the reliability of resources for regional human populations during a time of reduced winter rainfall. When considered within the framework of the current understanding of Holocene palaeoclimate in central Australia, our data suggest that the pattern of landscape response was broadly synchronous with larger scale climatic variability and punctuated by pluvial periods greater than today.
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| 9. |
- Jansen, John, 1967-, et al.
(author)
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Functional relationships between vegetation, channel morphology, and flow efficiency in an alluvial (anabranching) river
- 2010
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In: Journal of Geophysical Research. - Washington DC : American Geophysical Union. - 0148-0227 .- 2156-2202. ; 115:F04030
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Journal article (peer-reviewed)abstract
- Water and sediment flux interactions are examined in Magela Creek, an alluvial (anabranching) sand-bed river in the northern Australian tropics. Dense riparian vegetation stabilises the channels and floodplains thereby preventing erosional instability at flow depths up to 6.2-times bankfull and discharges up to 15-times bankfull. Narrow anabranching channels characterise >92% of the alluvial reach and transport bedload more efficiently than short reaches of wide single-channels, yet overall 29 ± 12% of the bedload is sequestered and the average vertical accretion rate is 0.41 ± 0.17 mm/y along the 12 km study reach. The most effective discharge for transporting sediment (40–45 m3/s) is consistent at all 5 stations (10 channels) examined and is equivalent to the channel-forming discharge. It has an average recurrence interval of 1.01 years, occurs for an exceptionally long 13–15% of the annual flow duration and averages a remarkable 2.1-times bankfull. The high flow efficiency (i.e., bedload transport rate to stream power ratio) of the anabranches is facilitated by low width/depth channels with banks reinforced by vegetation. Colonnades of bank-top trees confine high-velocity flows overbed (i.e. over the channel bed) at stages well above bankfull. At even larger overbank flows, momentum exchange between the channels and forested floodplains restrains overbed velocities, in some cases causing them to decline, thereby limiting erosion. Magela Creek exhibits a complicated set of planform, cross-sectional and vegetative adjustments that boost overbed velocities and enhance bedload yield in multiple channels while restraining velocities and erosion at the largest discharges.
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| 10. |
- Reeves, Jessica M., et al.
(author)
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Palaeoenvironmental change in tropical Australasia over the last 30,000 years - a synthesis by the OZ-INTIMATE group
- 2013
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 74, s. 97-114
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Journal article (peer-reviewed)abstract
- The tropics are the major source of heat and moisture for the Australasian region. Determining the tropics' response over time to changes in climate forcing mechanisms, such as summer insolation, and the effects of relative sea level on exposed continental shelves during the Last Glacial period, is an ongoing process of re-evaluation. We present a synthesis of climate proxy data from tropical Australasia spanning the last 30,000 years that incorporates deep sea core, coral, speleothem, pollen, charcoal and terrestrial sedimentary records. Today, seasonal variability is governed largely by the annual migration of the inter-tropical convergence zone (ITCZ), influencing this region most strongly during the austral summer. However, the position of the ITCZ has varied through time. Towards the end of Marine Isotope Stage (MIS) 3, conditions were far wetter throughout the region, becoming drier first in the south. Universally cooler land and sea-surface temperature (SST) were characteristic of the Last Glacial Maximum, with drier conditions than previously, although episodic wet periods are noted in the fluvial records of northern Australia. The deglacial period saw warming first in the Coral Sea and then the Indonesian seas, with a pause in this trend around the time of the Antarctic Cold Reversal (c. 14.5 ka), coincident with the flooding of the Sunda Shelf. Wetter conditions occurred first in Indonesia around 17 ka and northern Australia after 14 ka. The early Holocene saw a peak in marine SST to the northwest and northeast of Australia. Modern vegetation was first established on Indonesia, then progressively south and eastward to NE Australia. Flores and the Atherton Tablelands show a dry period around 11.6 ka, steadily becoming wetter through the early Holocene. The mid-late Holocene was punctuated by millennial-scale variability, associated with the El Nino-Southern Oscillation; this is evident in the marine, coral, speleothem and pollen records of the region.
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