late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

onset of aridity and dune building in central australia sedimentological and magnetostratigraphic evidence from lake amadeus abstract sediments from lake amadeus a groundwater discharge playa in central australia comprise a surface playa sequence the winmatti beds varying between 0 6 and 3 m in thickness overlying a long sequence of fairly uniform fluvial lacustrine clays the uluru clay the latter extends down to at least 15 m the maximum depth cored during this study and possibly down to 65 m below the present playa surface in the cores studied the brunhes matuyama boundary 0 73 ma was identifiable in all the upper sediments typically at a depth of between 1 and 2 m but below this there are two plausible chronological interpretations of the palaeomagnetic data deposition rates are very low typically no more than 1 5 cm ka in the uluru clay beds and down to 0 2 cm ka in the winmatti beds these rates suggest that the fluvial lacustrine phase lasted for at least 5 ma the boundary between the uluru clay and the winmatti beds bears a close correspondence to the boundary between the blanchetown clay a lacustrine sequence and the tyrrell beds a playa sequence in palaeo lake bungunnia in what is now the murray basin in southeastern australia however the transition occurs at about 0 9 ma or possibly 1 6 ma at lake amadeus whereas it has been dated palaeomagnetically at less than 0 73 ma probably 0 5 ma in lake bungunnia records from other locations in southeastern australia likewise support a major change from wetter to drier conditions at or shortly after the matuyama brunhes polarity transition thus the current evidence from lake amadeus indicates that in central australia the onset of aeolian and saline gypseous deposits characteristic of arid zone facies may have pre dated the corresponding change in the southeastern part of the continent by about 0 4 ma or possibly by about 1 1 ma in common with most playas in central australia lake amadeus is surrounded by a ring of gypseous dunes derived from material deflated from the surface of the playa magnetostratigraphic evidence from auger island in the middle of lake amadeus suggests that the oldest gypseous dune formation on the island must have pre dated the start of the jaramillo subchron at 0 98 ma or possibly the start of the brunhes epoch 0 73 ma thus making these the oldest dated dunes in australia the age of the auger island dunes is probably characteristic of other gypseous dunes around the margins of playas in central australia

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

stratigraphy and sedimentology of the lower neales river west lake eyre central australia from palaeocene to holocene abstract the stratigraphy of the lower neales river to the west of lake eyre australia s largest internal drainage system preserves a detailed record of fluvial lacustrine and aeolian deposits of early tertiary to holocene age this stratigraphic framework provides a summary of the region s cainozoic sedimentary units three units have been identified an early tertiary fluvial unit a mid tertiary lacustrine unit and a quaternary unit composed of interbedded fluvial lacustrine and aeolian facies dramatic changes in depositional styles within and between these three major groups of sediments reflect the basin s response to changes in climate and sediment supply fluvial facies include perennial multi channel single channel and ephemeral river sequences lacustrine and deltaic facies reflect continuous fine grained sedimentation during periods of high water tables the aeolian facies are evidence of aridity and sediment deflation in the basin the early tertiary fluvial unit is the result of late palaeocene eocene epeirogenic movements a dramatic shift in facies to the mid tertiary lacustrine unit reflects a significant change in the basins climatic controls quaternary sediments reflect major changes in fluvial discharge regimes which may reflect major climatic and associated hydrological changes during past interglacial and glacial cycles

high ground water levels and dune development in central australia tl dates from gypsum and quartz dunes around lake lewis napperby northern territory abstract an episode of high lake levels prior to the last maximum glaciation has been identified at many localities in wastern australia similar events have been recognized at playa lakes in central australia where gypsum dunes along playa margins formed during one or more episodes of high groundwater discharge with a large influx of calcium sulphate at lake lewis exposures at two islands show similar sediment sequences three pedogenic gypcrete layers interbedded with aeolian quartz and gypsum sand horizons form three units within gypsum dunes up to 7 m high the lowest unit has cliffed edges buried by the upper units indicating a significant time break four tl dates coarse grained quartz show that this lowest unit was deposited at or before 70 80 ka the middle unit of mixed gypsum and quartz sand capped by gypcrete represents the major phase of gypsum dune formation and 6 tl dates range from 33 to 46 ka with overlapping error bars these are slightly younger but statistically similar to tl dates from 39 to 59 ka of the shoreline gypsum dune at lake amadeus in the same region the top unit of the two islands up to 1 m thick has not yet been well dated one date is inconsistent with the well dated middle layer below possibly because of incomplete bleaching and has been rejected the other date 17 5 ka is much younger which possibly indicates a minor and local reactivation of old gypsum sediments at the lake margin there are quartz dunes overlying the gypsum dunes and a buried aeolian quartz sand layer occurs in a lake margin terrace these represent reactivation of the regional quartz dune field after the major gypsum dune formation two consistent tl dates 21 4 ka and 23 6 ka indicate that regional dunes were active at about the time of the last glacial maximum

late quaternary environments of the carpentaria basin australia abstract quaternary variations in the level of the sea have exposed the shallow 29 000 km2 but shallow maximum depth s 4 0 kyr the pollen assemblages closely resemble the black soil plains presently found along the southern gulf thus the biogeographic and climatic barrier across the australia papua new guinea land bridge has remained largely intact in spite of the range of environmental conditions that have occured during the last

processes of deep water renewal in lake baikal deep water renewal in lake baikal siberia the world s deepest lake and largest lake by volume is relatively fast water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr relative saturation of dissolved oxygen typically exceeds 80 the equation of state of baikal water was determined including the effect of dissolved ions and silicic acid based on nearly 600 ctd profiles taken between 1993 and 1995 two mechanisms of deep water mixing were identified 1 in spring cold and relatively saline water from the selenga the major inflow to the lake forms a density plume that reaches the bottom of the central basin during april and early may due to entrainment of lake water the plume transports about 125 km of water per year to the deepest part of the basin later in spring the river water forms the thermal bar observed along the eastern shore there are indications that parts of the selenga are also plunging to the deep part of the southern basin 2 at academician ridge separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin horizontal mixing results in a water mass that can sink on either side of the sill whereas in the central basin the water mass stays at intcrmediatc depth in the northern basin it sinks to the decpcst part more detailed data are needed to quantify this density flux no indication of a wind induced thermobaric instability was found

the timing of linear dune activity in the strzelecki and tirari deserts australia abstract linear dunes occupy more than one third of the australian continent but the timing of their formation is poorly understood in this study we collected 82 samples from 26 sites across the strzelecki and tirari deserts in the driest part of central australia to provide an optically stimulated luminescence chronology for these dunefields the dunes preserve up to four stratigraphic horizons bounded by palaeosols which represent evidence for multiple periods of reactivation punctuated by episodes of increased environmental stability dune activity took place in episodes around 73 66 35 32 22 18 and 14 10 ka intermittent partial mobilisation persisted at other times throughout the last 75 ka and dune activity appears to have intensified during the late holocene dune construction occurred when sediment was available for aeolian transport in the strzelecki and tirari deserts this coincided with cold arid conditions during marine isotope stage mis 4 late mis 3 and mis 2 and the warm dry climates of the late pleistocene holocene transition period and late holocene localised influxes of sediment on active floodplains and lake floors during the relatively more humid periods of mis 5 also resulted in dune formation the timing of widespread dune reactivation coincided with glaciation in southeastern australia along with cooler temperatures in the adjacent oceans and antarctica

26al 10be dating of an aeolian dust mantle soil in western new south wales australia abstract aeolian dust mantle soils are an important element of many landscapes in south eastern australia though the age of these aeolian deposits has not been radiometrically determined at fowlers gap in western new south wales surface cobbles of silcrete and quartz overlie a stone free aeolian dust mantle soil which has a thickness of about 1 6 m the clay rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer modelling in situ cosmogenic 26 al and 10 be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks reveals that each has experienced a complex exposure burial history due to the absence of quartz stones or sand at intermediate depths our cosmogenic 26 al and 10 be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial various scenarios of stone formation transport burial and exhumation were tested that constrain the age of the deposit to range from 0 9 0 2 ma to 1 8 0 2 ma based largely on different assumptions taken for the time dependency of the net sedimentation rate this corresponds with the initiation of the simpson desert dune fields and the deflation of lakes in central australia which probably responded to the shift to longer wavelength larger amplitude quaternary glacial cycles at around 1 ma sensitivity analyses were carried out to identify those parameters which better constrained model outputs within model errors which largely are the result of analytical errors in measured 26 al and 10 be concentrations all three competing theories of colluvial wash upward displacement of stones and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement

measurement of equivalent doses in quartz from contemporary water lain sediments using optically stimulated luminescence the single aliquot technique and its derivatives are very attractive for the measurement of the very small doses found in young materials because they inherently avoid concerns about low dose non linearity and can offer high precisions a modification is outlined to the single aliquot regeneration and added dose sara protocol mejdahl and botter jensen 1994 quaternary geochronology quaternary science reviews 13 551 5541 to permit its application to sedimentary quartz using the optically stimulated luminescence signal this revised protocol is then used to determine the doses found in several contemporary fluvial sediments and one coastal beach sand thought to be deposi ted by recent wave action two over bank river deposits were both homogeneously well bleached with doses of 0 4 gy although most of the grains in three channel deposits from a range of catchment sizes were also well bleached contamination by a small proportion of very poorly bleached quartz grains prevented the measurement of the dose in the majority the beach deposit was homogeneously bleached and contained a dose of about 0 02 gy it is concluded that over bank sites may provide accurate dates for samples older than a few hundred years but that the heterogeneity of the channel sites limits the accuracy of dates less than a few thousand years

aeolian landscapes in central australia gypsiferous and quartz dune environments from lake amadeus there are two different dune systems in central australia regional quartz dunefields and transverse gypsiferous dunes associated with playa lakes these two systems especially gypsiferous dunes at lake amadeus the largest playa in central australia provide a sedimentary geomorphological and environmental history of the region during the late quaternary the gypsifierous dunes consist of a surficial gypcrete overlying an aeolian sediment sequence below a mixture of gypsum sand and quartz sand no clay pellets have been found in the dune sequence in significant contrast to the gypsiferous clay dunes in other parts of australia three possible models of the environmental controls of gypsiferous dune formation are discussed the most plausible one suggests simultaneous gypsum precipitation and deflation sandsized gypsum was precipitated in a groundwater seepage zone around the playa margin during seasonally high water tables and these crystals were deflated onto land during dry intervals forming the marginal gypsiferous dunes these processes require conditions of high regional water table strong climatic seasonality and probably a windier and overall wetter climate at least two separate gypsiferous duneforming episodes can be recognized the age of formation of the younger one has been dated by thermoluminescence at 44 54 ka the gypcrete crust capping the dunes is characterized by intergrown microcrystalline gypsum crystals showing evidence of leaching dissolution and recrystallization it is interpreted as a pedogenic product formed during a stable period after accumulation of the gypsiferous dune after the construction of the younger gypsiferous dune there was a major episode of activation of regional quartz dunefields which formed thick quartz sand mantles overlying gypsiferous dunes on both playa margins and the dune islands within the playa an equivalent aeolian sand layer was deposited within the playa soil structures in this unit indicate that the sand sheet over the playa was later colonized by vegetation activation of the regional dunefields suggests a major period of dry climate which although not dated may correlate with the last glacial maximum identified as a period of maximum aridity from 25 to 18 ka at other sites in australia

quaternary sandstones northeast jordan age depositional environments and climatic implications abstract osl dating of weakly consolidated root bound non calcareous quartz arenites in northeast jordan currently assigned to the plio pleistocene azraq formation suggests a middle pleistocene 652 47 ka age the sandstones are up to 15 5 m thick and overlain by a 2 5 m thick holocene gypcrete caprock facies and textural analyses suggest that the sandstones are predominantly aeolian in origin mainly derived from tertiary sediments exposed close to the depositional site the sands were transported by the prevailing nw winds and deposited in a broad relatively flat sand sheet environment rhizoliths occur throughout the sandstones mainly as long downward tapering vertical tap roots rarely branched and with few laterals microscopic examination of root cores replaced by carbonate reveals the presence of alveolar fabrics possible needle fibre calcite calcified organic filaments of fungal root vessel and root hair origins characteristic of low magnesium beta calcretes typical of humid climates morphologically the roots resemble modern shrub like species typical of desert environments where water availability at the surface and in the subsurface was sufficient to support an effective vegetation cover plots of stratigraphic variations in root length root spacing and root frequency reflect temporal variations in the water table level and precipitation during sand deposition all three parameters show a similar crude cyclicity consistent with fluctuations in the level of the water table with the most moist phase beneath the predominantly waterlain holocene gypcrete when trees appeared for the first time the gypcrete signifies a change to temporary wetter conditions and may mark the boundary between the pleistocene and holocene in this area although pedogenic horizonation is poorly developed especially in desert sands the beta calcretes and rhizocretions typically form within active soil zones soils do not form where rainfall is

formation of analcime and moganite at lake lewis central australia significance of groundwater evolution in diagenesis abstract lake lewis basin in the northern territory is a hydrologically closed intermontane basin in which clay rich palaeolacustrine sediments are infused with highly evolved brines acquisition of dissolved silica and sodium by groundwaters from the proterozoic arunta granite gneiss terrain and from arkosic alluvium and weathering products sourced from these bedrocks is important to diagenesis at the salt lake supersaturation of groundwaters with respect to sio 2 and the availability of catalytic ions coupled with high rates of evaporation favour neoformation of opal and chalcedonic silica from solution near the groundwater discharge zone moganite a distinctive silica polymorph that is commonly associated with evaporites has been identified amongst precipitated silica species down gradient from the zone of silica precipitation beneath the playa brines are sio 2 deficient long periods of weathering and diagenesis of lacustrine clays immersed in semi stagnant brines has transformed detrital minerals into substantial proportions of amorphous or gelatinous aluminosilicate material aluminosilicate phases have become metastable in the presence of evolved sio 2 deficient interstitial brine analcime a sodium bearing zeolite group mineral is stable in the presence of the na rich brine and is crystallizing authigenically below the watertable from the amorphous aluminosilicate material in the lacustrine sediment no volcanic rocks or pyroclastic sediments are involved in this diagenetic occurrence of analcime the appearance of analcime in the evolution of the salt lake system probably commenced within the last 100 000 years and is occurring in the present day hydrologic and climatic regime of this arid zone area

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

stratigraphy sedimentology chronology and palaeohydrology of quaternary lacustrine deposits at madigan gulf lake eyre south australia abstract madigan gulf is a large bay at the southern end of lake eyre north a major ephemerally flooded playa in arid central australia at the southwestern margin of a vast 1 300 000 km2 internal drainage basin the stratigraphy and chronology of the quaternary sequence in the gulf is described from 8 cores and a cliff exposure at the gulf margin a number of depositional environments are recognised and their distinctive sedimentary components are described facies recognised include deep and shallow water lacustrine environments dominated by surface water processes and dry or ephemerally flooded playa environments dominated by groundwater controlled processes sedimentary components include terrigenous clastics from river inflow and shoreline erosion carbonates of detrital inorganic or biological origin and gypsum and halite evaporites carbonates and gypsum evaporites precipitated within the basin are frequently reworked as clastic components the establishment of a preliminary chronology for the sequence by the application of thermoluminescence uranium thorium disequilibrium amino acid racemization and radiocarbon dating techniques has allowed a reconstruction of the last 130 ka of lake eyre palaeohydrology the wettest phase occurred during the last interglacial early in oxygen isotope stage 5 when an enlarged lake eyre was up to 25 m deep subsequently there has been a number of dry periods separating successively less effective wet phases culminating in the deposition of a substantial halite salt crust around the time of the glacial maximum the dry interludes are characterised by deflation of salts and sediment from the basin a process controlled by lowering of the watertable the record from madigan gulf demonstrates the dramatic and repetitive impact of lake deflation on the quaternary record of lake eyre in the early holocene a minor but mostly perennial lacustrine event was terminated at about 3 4 ka when the modern ephemeral playa regime was established the major catchment of lake eyre is located in the monsoon watered areas of northern australia as demonstrated by large floodings of the modern ephemeral regime major lacustrine episodes must indicate enhanced monsoon precipitation in northern australia in the holocene the lake has not risen to levels achieved during the early stage 5 lacustral phase indicating a marked reduction in the effectiveness of the monsoon in the present interglacial by comparison with its predecessor

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

low latitude glacial cooling in the southern hemisphere from amino acid racemization in emu eggshells the record of natural climate variability over glacial interglacial timescales provides a framework from which a better mechanistic understanding of the climate system may be derived but this approach is limited by the number and distribution of well dated and reliable palaeoenvironmental archives particularly vexing is the conflicting evidence for low latitude cooling during the last glacial maximum and the apparent synchrony in glacial activity between the hemispheres despite out of phase insolation forcing1 4 here we utilize the temperature dependent amino acid racemization reaction in radiocarbon dated emu eggshell fragments from the continental interior of australia to reconstruct low altitude subtropical temperatures for the past 45 kyr racemization rate changes indicate that millennial scale average air temperatures were at least 9 c lower between 45 and 16 kyr bp than since 16 kyr bp a temperature change of this magnitude coupled with other low latitude palaeotemperature records that indicate substantial cooling3 4 must reflect global processes which we speculate involved glacial age reduction in atmospheric water vapour content

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

biostabilization of sediments by microbial mats in a temperate siliciclastic tidal flat bahia blanca estuary argentina abstract extensive microbial mats have been found in the siliciclastic tidal flats of the temperate bahia blanca estuary in the atlantic coast of buenos aires province argentina several microbially induced sedimentary structures miss occur especially in the upper intertidal and lower supratidal flats among which the most conspicuous are erosional pockets gas domes microbial mat chips and polygonal oscillation cracks biostabilization processes by epibenthic and endobenthic mats are also analyzed endobenthic mats occur in the upper intertidal area stabilizing ripples that despite the occurrence of severe storms persist in a fixed position for at least 2 months epibenthic mats occurring in the lower supratidal area also protect the substrate forming a thick microbial cover through the studied period this thick cover was only affected by a strong storm that formed areas with erosional pockets and mat pieces nevertheless the loose sediment within the erosional pockets was quickly colonized by microorganisms that developed a thin biofilm layer after a week changes in sediment accumulation were also recorded all over the upper tidal flat during a year showing an important increase due to bioturbation activities of crabs this situation also affected microbial mat growth which evolved from a thin microbial biofilm into a thick stratified microbial mat community in almost 2 years mainly in the lower supratidal areas the results of this study not only help us to better characterize the complex interactions between the microorganisms forming microbial mats the tidal flat sediment and the physical parameters that control this setting but also have important implications for the understanding of analogous fossil sedimentary successions

subdividing the pleistocene using the matuyama brunhes boundary mbb an australasian perspective abstract the last major reversal of the earth s magnetic field the matuyama brunhes boundary mbb dated at 0 78 ma is widely identified in australian and new zealand pleistocene deposits in new zealand the mbb is precisely located in shallow marine sediments of wanganui basin where it corresponds with the base of the new zealand putikian substage a combination of marine biostratigraphy sequence stratigraphy and tephrostratigraphy permit correlation from wanganui basin to other on land sections and deep sea cores in australia the mbb is identified in many continental sequences particularly saline lake basins however chemical weathering has resulted in variable brunhes age normal overprints that are sometimes difficult to remove australasian tektites are a potential lithostratigraphic marker just prior to the mbb but have yet to be identified in the same on land section as the mbb in australia identification of reverse polarity magnetisation in weathered deposits including soils provides a minimum age of 0 78 ma for these materials a widespread arid shift in paleoclimate succeeded the mbb in australia placement of the lower middle pleistocene boundary at the mbb would constitute the most recognisable chronostratigraphic marker in weathered continental deposits

aeolian fluvial interaction evidence for late quaternary channel change and wind rift linear dune formation in the northwestern simpson desert australia in central australia the most easterly extent of the macdonnell ranges border the simpson desert dunefield where widely spaced strike ridges intercept and isolate pockets of broad crested linear dunes that reflect regional changes in late quaternary climate flow regime and channel avulsion an energetic todd river reworked the eastern part of camel flat basin from 75 65 ka until the last glacial maximum lgm when it shifted eastwards but with some flows persisting through the basin until about 10 ka resulting desert surfaces of different age facilitate temporal comparisons of linear dune formation fine grained red dunes 75 65 ka in age occur on the western floor of the basin and are ramped against the foot slopes of the range after the lgm and especially during the holocene the river s departure enabled small pale coloured closely spaced coarser textured linear dunes to form on the abandoned floodplain in the eastern basin their orientation 20 farther west than the larger and older red dunes this realignment indicates that the australian wind whorl shifted southwards some 160 km or 1 5 after the lgm linear dunes in the northwestern simpson desert were formed by wind rifting involving vertical accretion of sand from a proximal source not by long distance sand transport with linear extension the blocking ranges have caused negligible downwind sediment accumulation over the past 75 ka

comparison of 14c and luminescence chronologies at puritjarra rock shelter central australia abstract at puritjarra rock shelter a long comparative sequence permits detailed comparisons of luminescence and radiocarbon chronologies over 35 000 years both techniques produce self consistent chronologies for the puritjarra deposit but observed discrepancies between luminescence dates on unburnt sediments and 14c assays on charcoal are greater than reported elsewhere tl ages are generally older than 14c ages but dates converge at depths below 70 cm dating first significant human occupation of the rock shelter 35 000 years ago the discrepancies are not removed by calibrating 14c dates or adjusting tl ages for lower water content of sediments the 14c chronology is broadly supported by sedimentary or palaeobotanical evidence stone artefact typology and other archaeological data radiocarbon dates on intact hearths agree with those on detrital charcoal tl ages were arrived at using both total bleach and selective bleach methods and the latter agree with optical ages for the same samples incomplete bleaching of sediments during deposition can be ruled out incorporation of old material into the luminescence samples via in situ disintegration of local sandstone remains a possibility and will be an important issue to resolve as luminescence techniques are increasingly deployed to date archaeological deposits in rock shelters

aeolian fluvial interaction and climate change source bordering dune development over the past 100 ka on cooper creek central australia abstract this study provides an interpretation of interrelated quaternary fluvial and aeolian activity related to climate change on cooper creek in the lake eyre basin in southwestern queensland central australia the extensive muddy floodplain is characterised by buried sandy palaeochannels now almost entirely invisible but stratigraphically connected to source bordering dunes that emerge as distinctive sandy islands through the floodplain surface luminescence dating has identified pronounced periods of fluvial activity represented by abundant sandy alluvium from marine isotope stages mis 8 3 while all these sandy fluvial episodes on cooper creek were much more powerful than anything subsequent they appear to be ranked in order of declining activity mis 8 6 saw reworking of almost the entire floodplain whereas subsequent phases of reworking were far less extensive source bordering dunes were derived from active sandy channels in late mis 5 85 80 ka and mid mis 3 50 40 ka after 40 ka sand channel activity largely ceased and the floodplains and channels were inundated with mud isolating the dunes as emergent features although aeolian reworking of the upper parts of some dunes has continued to the present they show remarkable resilience having survived without appreciable migration for at least 40 ka whilst the channels once determined the location of source bordering dunes in an interesting role reversal the remnant dunes now determine the position of many contemporary flood channels and waterholes by deflection and confinement of overbank flows