late quaternary climates of the australian arid zone a review abstract aridity in australia has generally been associated with glacial intervals of the last few glacial cycles the causes and nature of aridity varied from north to south over the continent in northern and central australia reduced monsoon rain in global cold stages caused lakes and rivers to dry vegetation to become more sparse sand dunes to become active and dust advection to increase while the monsoon is correlated with warmer global temperatures and high sea levels overall the exact timing of the greatest development of the monsoon in stage 5 remains uncertain in southeastern australia the proxy records give a less clear picture while vegetation seems to have been more sparse in cold stages and sand dune activity and dust flux consequently greater records of runoff in rivers and lakes have mixed or opposite behaviour to northern or central australia the nature of aridity in southeastern australia is not analogous to conditions anywhere on the continent today greatly reduced temperatures over the central and southern interior greater influence of snow and periglaciation on runoff high groundwater tables lower rainfall and reduced atmospheric carbon dioxide levels may all have contributed to and interacted to produce the reconstructed picture of a cold sparsely vegetated arid landscape with large rivers and perennial lakes the largest changes in circulation patterns over the glacial cycle probably occurred in the location and or intensity of summer tropical convergence in northern australia over southern australia changes to the temperature and humidity of the westerly circulation have been more significant than the small fluctuations in latitude of the sub tropical high pressure ridge

land surface feedbacks and palaeomonsoons in northern africa we ran a sequence of climate model experiments for 6000 years ago with land surface conditions based on a realistic map of palaeovegetation lakes and wetlands to quantify the effects of land surface feedbacks in the saharan region vegetation induced albedo and moisture flux changes produced year round warming forced the monsoon to 17 25 n two months earlier and shifted the precipitation belt 300 km northwards compared to the effects of orbital forcing alone the addition of lakes and wetlands produced localised changes in evaporation and precipitation but caused no further extension of the monsoon belt diagnostic analyses with biome and continental hydrology models showed that the combined land surface feedbacks although substantial could neither maintain grassland as far north as observed 26 n nor maintain lake megachad 330 000 km

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

glacial to holocene swings of the australian indonesian monsoon the australian indonesian monsoon is an important component of the climate system in the tropical indo pacific region 1 however its past variability relation with northern and southern high latitude climate and connection to the other asian monsoon systems are poorly understood here we present high resolution records of monsoon controlled austral winter upwelling during the past 22 000 years based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern java we show that glacial interglacial variations in the australian indonesian winter monsoon were in phase with the indian summer monsoon system consistent with their modern linkage through cross equatorial surface winds likewise millennial scale variability of upwelling shares similar sign and timing with upwelling variability in the arabian sea on the basis of element composition and grain size distribution as precipitation sensitive proxies in the same archive we infer that austral summer monsoon rainfall was highest during the bolling allerod period and the past 2 500 years our results indicate drier conditions during heinrich stadial 1 due to a southward shift of summer rainfall and a relatively weak hadley cell south of the equator we suggest that the australian indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere the seasonality of the global monsoon is of central importance to the global hydrologic cycle and its environmental influence on human societies palaeoclimate reconstructions generally agree that the strengths of the east asian monsoon and the indian monsoon are tightly coupled to the northern hemisphere climate through zonal migrations of the monsoon convection centres also interpreted as intertropical convergence zone itcz migration 26 the mechanism of the australianindone

holocene depositional history of the burdekin river delta of northeastern australia a model for a low accommodation highstand delta abstract the burdekin river of northeastern australia has constructed a substantial delta during the holocene delta plain area 1260 km2 the vertical succession through this delta comprises 1 a basal coarse grained transgressive lag overlying a continental omission surface overlain by 2 a mud interval deposited as the coastal region was inundated by the postglacially rising sea in turn overlain by 3 a generally sharp based sand unit deposited principally in channel and mouth bar environments with lesser volumes of floodplain and coastal facies the holocene burdekin delta was constructed as a series of at least thirteen discrete delta lobes formed as the river avulsed each lobe consists of a composite sand body typically 5 8 m thick the oldest lobes formed during the latter stages of the postglacial sea level rise 10 5 5 kyr bp are larger than those formed during the highstand 5 5 3 kyr bp which are in turn larger than those formed during the most recent slight sea level lowering and stillstand 3 0 kyr bp radiocarbon ages and other stratigraphic data indicate that inter avulsion period has decreased through time coincident with the decrease in delta lobe area the primary control on holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12 4 kyr bp to the present drier enso dominated climate in addition to decreasing the sediment supply via lower rates of chemical weathering this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge more frequent avulsion may also have been facilitated by the lengthening of the delta plain channels as the system prograded seaward

initiation of the australian summer monsoon 14 000 years ago abstract definitive evidence for the onset of monsoon moisture in northern australia following the arid phase of the last glacial maximum has been elusive in large part due to the lack of long continuous sediment records here we report new evidence from two separate drainage basins in the kimberley region of monsoonal northwestern australia at both sites radiocarbon ages on basal biogenic materials in flood deposits indicate stream flow as high or higher than maximum historic levels began about 14 cal ka bp these results suggest that the australian summer monsoon was fully active several millennia earlier than previously expected the early onset of the monsoon and the widespread evidence for diminished monsoon activity in the late holocene cannot be reconciled with primary forcing of the australian monsoon by changes in low latitude summer insolation over australia

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

δ13c values and radiocarbon dates of microbial biomarkers as tracers for carbon recycling in peat deposits this paper describes the first application of compound specific stable carbon isotope and radiocarbon isotope analyses to the investigation of microbial processes in peat deposits

the use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical australia implications to paleoclimate abstract the lynch s crater peat deposit in ne australia is a sensitive environmental archive located in the tropical southern hemisphere this unique deposit illustrates that local and regional changes had a profound effect on the local australian ecosystem over the past 55 kyr to obtain a proxy of past climate changes trace and major element geochemistry analyses were applied to a 13 m peat core from the crater principle component analysis pca was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements for example sc al cu and pb were found to be related to increased erosion of the basin soils and from this several periods of significant flux from atmospheric input and or terrigenous run off were identified geochemically mobile elements during rock weathering and pedogenesis such as mg ca and sr helped to identify the peat ombrotrophic minerotrophic boundary at 1 5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit arsenic and v comparisons between the peat record high concentrations in some peat sections and in local basin rocks very low concentrations suggested the presence of a long range atmospheric dust source early in the formation of the mire the lynch s crater peat record presents a continuous record of environmental change in tropical australia and contributes new understanding to geochemical processes in peatlands

insolation forcing of the australian monsoon as controls of pleistocene mega lake events 1 during the last c 300 000 years mega lakes with areas an order of magnitude greater than those of today occurred in the monsoon region of northern australia the results of an atmosphere global circulation model agcm sensitivity experiment show that the repeated occurrence of mega lake phases during the pleistocene and the strong monsoon flow that this implies can be related to milankovitch insolation forcing the agcm experiment is centred on the southern hemisphere low latitude summer insolation high of 115 000 years ago the details of the results indicate a strong response of the australian monsoon to the higher insolation at that time with a longer monsoon season increased precipitation and higher resultant runoff than at present

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

sensitivity of the australian summer monsoon to tilt and precession forcing abstract the response of the australian summer monsoon to orbital forcing is studied using a coupled general circulation model gcm with the focus on the relative roles of tilt and precession on the forcing of the northern australian summer monsoon it was found that unlike the northern hemisphere monsoons which are dominated by precession forcing the australian monsoon can be enhanced significantly not only by precession forcing but also by tilt forcing coupled to oceanic feedback the new insights obtained from a series of experiments with differing tilt precession configurations allow an interpretation of the australian late quaternary monsoon record in which insolation forcing plays a significant role

a high resolution record of vegetation and climate through the last glacial cycle from caledonia fen southeastern highlands of australia a blocked tributary has provided a rare site of long term sediment accumulation in montane southeastern australia this site has yielded a continuous detailed pollen record through the last ca 140 000 years and revealed marked vegetation and environmental changes at orbital to sub millennial scales radiocarbon and optically stimulated luminescence osl or optical ages provide some chronological control for the last ca 70 000 years most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice covered lake conditions the lake was surrounded by low growing plants with an alpine character exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment the two major periods of forest expansion are related to the last interglacial and the holocene with the third shorter period considered to represent an interstadial in the early part of marine isotope stage mis 3 the latter part of the last glacial period is characterised by abrupt sub millennial amelioration events that may relate to documented global oscillations emanating from the north atlantic there are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to a long term trend towards climatic drying copyright 2007 john wiley sons ltd

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

time slice analysis of the australian summer monsoon during the late quaternary using the fast ocean atmosphere model we use the fast ocean atmosphere model foam to investigate the variation in the australian summer monsoon over the last 55 000 years a synthesis of palaeoenvironmental observations is used to constrain the model for six time slices 55 35 21 11 6 and 0 ka both inter hemispheric forcing and the seasonal timing of local insolation changes play key and interacting roles on the evolution and intensity of the monsoon during the onset to the monsoon a heat low develops to the west of australia over the indian ocean in all time slices but with varying strengths divergent outflow from asia converges with the cyclonic flow to bring increased rainfall to northern australia and the maritime continent the relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies only in the middle holocene is the low pressure pull the dominant forcing mechanism at 21 ka the climate shift to colder mean temperatures determines the large scale dynamics of the monsoon the general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times copyright 2006 john wiley sons ltd

redating the onset of burning at lynch s crater north queensland implications for human settlement in australia lynch s crater preserves a continuous high resolution record of environmental changes in north queensland this record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries this increase is accompanied or closely followed by the virtually complete replacement of rainforest by sclerophyll vegetation the absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area the age for this increase in burning on the basis of conventional radiocarbon dating was previously thought to be approximately 38000 c 14 yr bp supporting the traditional model for human arrival in australia at 40 000 c 14 yr bp here we have applied a more rigorous pre treatment and graphitisation procedure for radiocarbon dating samples from the lynch s crater sequence these new dates suggest that the increase in fire frequency occurred at 45 000 c 14 yr bp supporting the alternative view that human occupation of australia occurred by at least 45 000 55 000 cal yr bp copyright c 2001 john wiley sons ltd

abrupt increase in east indonesian rainfall from flooding of the sunda shelf 9500 years ago we present a precisely dated multi proxy stalagmite record from liang luar cave flores southeast indonesia that reveals a rapid increase in indonesian monsoon rainfall at 9 5 ka a ramp fitting method for detecting statistically significant inflections in a time series was applied to the stalagmite 18o mg ca and sr ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of 350 years previously published lake level records from the monsoon affected australian interior show a sudden intensification of the australian monsoon at 14 ka however our records indicate that monsoon intensification in flores occured 4 5 kyr later the timing of the monsoon shift in flores is synchronous with the rapid expansion of rainforest in northeast australia and regional freshening of the southern makassar strait which under present day conditions is sensitive to monsoon variability the freshening of southern makassar was coeval with an abrupt 1 5 c cooling in the upper thermocline of the timor sea 9 5 ka indicative of reduced surface heat transport by the indonesian throughflow itf when the java sea opened during postglacial sea level rise this suggests that the abrupt increase in monsoon rainfall on flores was not due to a change in the itf because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures ssts but rather by the sudden increase in ocean surface area and or temperature in the monsoon source region as the sunda shelf flooded during deglaciation we propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the itf following the flooding of the sunda shelf at 9 5 ka

alluvial evidence for major climate and flow regime changes during the middle and late quaternary in eastern central australia as a low gradient arid region spanning the tropics to the temperate zone the lake eyre basin has undergone gentle late cenozoic crustal warping leading to substantial alluvial deposition thereby forming repositories of evidence for palaeoclimatic and palaeohydrological changes from the late tertiary to the holocene auger holes and bank exposures at five locations along the lower 500 km of cooper creek a major contributor to lake eyre in the eastern part of the basin yielded 85 luminescence dates tl and osl that combined wit a further 142 luminescence dates from northeastern australia have established a chronology of multiple episodes of enhanced flow regime from about 750 ka to the holocene mean bankfull discharges on cooper creek upstream of the innamincka dome at 250 230 ka or oxygen isotope stages ois 7 6 are estimated to have been 5 to 7 times larger than those of today however substantially less reworking has occurred during and after ois 5 than before lower cooper creek appears to have similarly declined in the tirari desert adjacent to lake eyre there is evidence of widespread alluvial activity perhaps during but certainly before the middle pleistocene yet the river became laterally restricted in ois 7 to 5 while the quaternary has been characterised by a dramatically oscillating wet dry climate since oxygen isotope stage ois 7 or 6 there has been a general decline in the magnitude of the episodes of wetness to which the eastern part of central australia has periodically returned during the last full glacial cycle cooper creek s periods of greatest runoff and sand transport were not during the last interglacial maximum of ois 5e 132 122 ka but later in ois 5 when sea levels and global temperatures were substantially below those of 5e or today fluvial activity returned in ois 4 and 3 but not to the extent of mid and late ois 5 strongly seasonal but still powerful flows transported sand and fed source bordering dunes in ois 5 and 3 this chronology of fluvial activity in the late quaternary broadly coincides with that for rivers of southeastern australia and suggests that the wet phases in eastern central australia have not been governed as much by the northern monsoon as by conditions in the western pacific close to the east coast both north and south flow confinement within the innamincka dome has locally amplified cooper creek s energy and here evidence exists for short but high magnitude episodes of flow during the last glacial maximum and in the early to middle holocene conditions that were capable of forming large palaeochannels but that were not long lived enough to rework the river s extensive floodplains elsewhere along its length

wetting and drying of australia over the past 300 ka alternately dry and wet climatic episodes across central and eastern australia during the past 300 ka have greatly affected australia9s rivers lakes and dune fields evidence of widespread climate and flow regime changes has been provided by 75 thermoluminescence tl dates and 18 u th dates from alluvial and eolian sediments fluvial conditions dominated part of the last two interglacials stage 5 and 7 resulting in large sand loads in rivers in the present simpson desert and southeastern australia during the last interglacial fluvial activity in central australia peaked at 110 ka stage 5 pluvial probably 5 10 ka behind world temperature and sea level maxima following the last late interglacial wet phase aridity associated with dune building spread from central australia toward its margins achieving greatest intensity during the last glacial maximum a less widespread wet phase identified at about 55 35 ka stage 3 subpluvial is associated with high lake levels and paleochannel activity in southeastern australia this tl record of variable continental aridity in australia correlates well with global changes including the variable eolian dust flux into central china the northern pacific ocean and antarctica

emergence of anomalous transport in stressed rough fractures abstract we report the emergence of anomalous non fickian transport through a rough walled fracture as a result of increasing normal stress on the fracture we show that the origin of this anomalous transport behavior can be traced to the emergence of a heterogeneous flow field dominated by preferential channels and stagnation zones as a result of the larger number of contacts in a highly stressed fracture we show that the velocity distribution determines the late time scaling of particle spreading and velocity correlation determines the magnitude of spreading and the transition time from the initial ballistic regime to the asymptotic anomalous behavior we also propose a spatial markov model that reproduces the transport behavior at the scale of the entire fracture with only three physical parameters our results point to a heretofore unrecognized link between geomechanics and particle transport in fractured media

extending the record of lacustrine phases beyond the last interglacial for lake eyre in central australia using luminescence dating abstract we show with multiple luminescence dating techniques that the sedimentary record for lake eyre australia s largest lake extends beyond 200 thousand years ka to marine isotope stage mis 7 transgressive clayey sand and finely laminated clays overlying the miocene etadunna formation in lake eyre north document the deep lake phases of central south australia in the past until now unresolved chronology has hampered our ability to interpret these sedimentary records which are important for understanding the timing of the wettest phase of central australia s late quaternary climate in this study we apply quartz optically stimulated luminescence osl dating thermally transferred osl tt osl dating and k feldspar post infrared infrared stimulated luminescence pirir dating to lake floor sediments near williams point in madigan gulf to provide new age constraint for the lacustrine sediments of lake eyre methodological studies on quartz and k feldspar demonstrate that these luminescence dating procedures are suitable for the lake eyre lacustrine samples and produce consistent replicate ages a bayesian model applied to the new dating results provides a chronological model of lacustrine deposition and shows that the transgressive clayey sand were deposited 221 19 ka to 201 10 ka and that the deep water sediments were laid down in early mis 6 191 9 ka to 181 9 ka we also find evidence for a potential depositional hiatus in mid mis 6 and the likely formation of a palaeo playa later in mis 6 from 158 11 ka to 143 15 ka in contrast the mis 5 sediments are characterised by oscillating deep and shallow water lacustrine units deposited 130 16 ka to 113 20 ka this study is the first of its kind to provide evidence for a wet desert interior in australia beyond the last glacial cycle using comprehensive numerical dating our results show that past deep lake episodes of central south australia which were previously thought to represent peak interglacial conditions are actually associated with both warm interglacial and cold glacial periods with all the wettest episodes generally coinciding with the intervening periods between the glacial and interglacial maximums we assume from these results that orbital forcing is not a first order control for the long term dynamics of the lake eyre basin and the indo australian monsoon the high lake level events of lake eyre are well correlated with millennial scale cooling events and stadials of the north atlantic and coincide with weakened episodes events for the east asia summer monsoon this may imply an important role for the northern high latitudes in influencing the indo australian monsoon which may be associated with a southward migration of the intertropical convergence zone itcz during cooling periods in the north atlantic

glacial aridity in central indonesia coeval with intensified monsoon circulation abstract the last glacial maximum was cool and dry over the indo pacific warm pool ipwp a key region driving global oceanic atmospheric circulation both low and high latitude teleconnections with insolation ice sheets and sea level have been suggested to explain the pervasive aridity observed in paleoecological and geomorphic data however proxies tracking the h and o isotopic composition of rainfall e g speleothems sedimentary biomarkers suggest muted aridity or even wetter conditions than the present complicating interpretations of glacial ipwp climate here we use multiproxy reconstructions from lake sediments and modern rainfall isotopic measurements from central indonesia to show that contrary to the classical amount effect intensified australian indonesian monsoon circulation drove lighter h and o isotopic composition of ipwp rainfall during the lgm while at the same time dry conditions prevailed precipitation isotopes are particularly sensitive to the apparent increase in monsoon circulation and perhaps also decreased moisture residence time implied by our data explaining contrasts among proxy records while illuminating glacial ipwp atmospheric circulation a key target for climate models

dynamics of acacia aneura triodia boundaries using carbon 14c and δ 13c and nitrogen δ15n signatures in soil organic matter in central australia abstract soil organic matter som was sampled from soil profiles on a near level sandsheet at the southern limit of the tanami desert in central australia to determine if boundaries of triodia hummock grassland acacia aneura shrublands had changed in the holocene accelerator mass spectrometry ams 14c dating of 16 soil profiles showed that som that had accumulated at 100 to 140 cm depth near the base of most profiles had ages between 1175 and 2630 14c years averaging 1906 14c years the stable carbon isotopic a13c composition of som from the upper 50 cm soil profiles in the a aneura shrubland inhabited by plants with predominantly c3 photosynthetic pathway was significantly more 13c depleted than the comparable soil interval beneath a triodia grassland predominantly c4 photosynthetic pathway mean age of som at 50 cm depth was 830 14c years suggesting the vegetation has been stable for about 1000 years however soil profiles in triodia grassland adjacent to the shrubland boundary had slightly more depleted a13c relative to sites 0 5 km from the boundary with respect to stable nitrogen isotopic values only surface soils in the acacia shrublands were found to be 15n enriched relative to all other soil depths although there were no obvious environmental discontinuities such as change in soil type or slope angle associated with the ecosystem boundaries the acacia shrublands were found to occur on more clayrich soils with higher concentrations of total phosphorus nitrogen and potassium compared with the surrounding grasslands and these trends became more pronounced with increasing distance from the ecotone it is unclear if these differences are a cause or an effect of the vegetation mosaic the concordance of the vegetation boundaries with the a13c and a15n and of soil nutrients are consistent with only minor attrition of the a aneura shrublands in the late holocene at this site

glacial and deglacial climatic patterns in australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract this study forms part of a wider investigation of late quaternary environments in the southern hemisphere we here review the terrestrial and near shore proxy data from australia indonesia papua new guinea png new zealand and surrounding oceans during 35 10 ka an interval spanning the lead up to the last glacial maximum lgm the lgm proper 21 2 ka and the ensuing deglaciation sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval a stratigraphically consistent chronology and one or more sources of proxy climatic data tropical australia indonesia and png had lgm mean annual temperatures 3 7 c below present values and summer precipitation reduced by at least 30 consistent with a weaker summer monsoon and a northward displacement of the intertropical convergence zone the summer monsoon was re established in northwest australia by 14 ka precipitation in northeast australia was reduced to less than 50 of present values until warmer and wetter conditions resumed at 17 16 ka followed by a second warmer wetter phase at 15 14 ka lgm temperatures were up to 8 c lower than today in mainland southeast australia and up to 4 c cooler in tasmania winter rainfall was much reduced throughout much of southern australia although periodic extreme flood events are evident in the fluvial record glacial advances in southeast australia are dated to 32 2 5 19 1 1 6 and 16 8 1 4 ka with periglacial activity concentrated towards 23 16 ka deglaciation was rapid in the snowy mountains which were ice free by 15 8 ka minimum effective precipitation in southern australia was from 14 to 12 ka in new zealand the glacial advances date to 28 21 5 and 19 ka with the onset of major cooling at 28 ka or well before the lgm there is no convincing evidence for a younger dryas cooling event in or around new zealand but there are signs of the antarctic cold reversal in and around new zealand and off southern australia there remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of new zealand sites one explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids sea surface temperatures ssts were up to 5 c cooler during the lgm with rapid warming after 20 ka to attain present values by 15 ka the increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation warmer ssts and steeper thermal gradients between land and sea the postglacial increase in winter rainfall in southern australia is probably related to the southward displacement of the westerlies as ssts around antarctica became warmer and the winter pack ice and antarctic convergence zone retreated to the south

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

early to middle miocene monsoon climate in australia the present day australian monsoon delivers substantial moisture to the northern regions of a predominantly arid continent however the pre quaternary history of the australian monsoon is poorly constrained due to sparse and often poorly dated paleoclimate proxy evidence sedimentological and paleontological data suggest that warm humid and seasonal environments prevailed in central and north australia during the miocene though it is unclear whether these were products of the australian monsoon we perform a series of sensitivity experiments using an atmospheric general circulation model combined with an offl ine equilibrium vegetation model to quantitatively constrain the areal extent of the miocene monsoon our results suggest a weaker than modern monsoon climate during the miocene this result is insensitive to atmospheric co 2 although somewhat sensitive to vegetation interactions and the presumed distribution of inland water bodies none of our miocene experiments exhibit precipitation rates greater than modern over north australia in disagreement with paleoclimate record interpretations vegetation modeling indicates that inferred precipitation values from fossil fl ora and fauna could only support miocene vegetation patterns if atmospheric co 2 was twice the modern concentration this suggests that elevated co 2 was critical for sustaining miocene vegetation

orbital time scale circulation controls of the australian summer monsoon a possible role for mid latitude southern hemisphere forcing abstract discussions of the quaternary paleoclimatology of the northwestern australian summer monsoon have emphasized inter hemispheric forcing of the northern australian summer monsoon by the east asian winter monsoon here we draw on the results of general circulation model experiments to examine southern hemisphere circulation characteristics that controlled the australian summer monsoon in response to milankovitch insolation forcing the experiments suggest that during tilt and precession driven southern hemisphere low latitude insolation highs the monsoon regime has the potential to be forced by inflow from the mid latitudes of the southern hemisphere to lend credence to the general circulation model results we employ a simple force balance model to demonstrate the dynamics controlling southern hemisphere inflow into the monsoon region of northwestern australia and draw attention to work that suggests this mechanism may explain recent precipitation trends in the region our findings caution against drawing correlations of stratigraphic events in the east asian australian monsoon records without first having a full appreciation of the dynamics that controlled paleoclimate states

the human colonisation of australia optical dates of 53 000 and 60 000 years bracket human arrival at deaf adder gorge northern territory the date at which people entered australia has important implications for the debate on modern human origins thermoluminescence dates of 50 60 ka reported for initial occupation of the malakunanja ii site in northern australia have been used as a means of calibrating the rate of mitochondrial and nuclear dna evolution in modern humans optical dating of unburnt quartzose sediments from a rock shelter site nauwalabila i lindner site in deaf adder gorge 70 km south of malakunanja ii provides new evidence for the timing of the colonisation of the continent optical dates were determined for several stratigraphic levels within a 3 m deep excavation in which flaked stone artefacts and ground pigments were found in primary depositional setting the lowest human occupation levels are bracketed by dates of 53 4 5 4 ka and 60 3 6 7 ka while the upper levels show good agreement between optical and calibrated 14c age estimates high quality haematite with ground facets and striations is associated directly with the 53 ka level and indicates the use of pigments by these early australians the optical dates independently confirm evidence for the colonisation of northern australia shortly after 60 ka and should be seen in the context of this region as having been a likely entry route for the first human movements into sahul