climate and collapse agro ecological perspectives on the decline of the tiwanaku state abstract after approximately 700 years of growth and colonial expansion the tiwanaku state disintegrated as a regional political force in the south central andes between c ad 1000 1100 this paper examines the collapse of the state of tiwanaku through the lens of its agricultural history we argue that the proximate cause of tiwanaku s decline as a politically integrated expansive state society was the deterioration and ultimate abandonment of its regional scale agricultural systems both in its core area in the andean altiplano and in its economic colonies in the lower altitude yungas zones we present evidence that the collapse of tiwanaku intensive agriculture was triggered by regional change in climatic conditions recorded in highly resolved palaeoenvironmental data derived from the quelccaya ice cap of southern peru and in sediment cores from lake titicaca our analysis of the quelccaya data documents a radical climate change in the south central andes during the post ad 1000 era in the form of a statistically significant decrease in mean precipitation level that persisted until c ad 1400 by defining vulnerability classes for various agricultural technologies used in different regions of the tiwanaku state we then relate this palaeoclimatic data to performance of specific core area and colonial tiwanaku agricultural systems we demonstrate that chronic drought conditions led to sequential collapse of these distinct agricultural systems irrigation based agriculture in tiwanaku colonies at lower altitude failed first followed by groundwater dependent raised field systems in the altiplano agricultural and settlement pattern changes in the post ad 1000 period are correlated with the palaeoenvironmental data to present an integrated view of the coupling of climate and cultural process the full implications of the agro ecological collapse model presented here reach well beyond an explanation for the decline of tiwanaku alone

arid zone groundwater recharge and salinisation processes an example from the lake eyre basin australia in arid central australia the 1 14 m km2 endorheic lake eyre basin leb experiences sporadic floods and contains saline shallow groundwater in this basin where on ground physical and chemical data are very sparse new observations of major ion chemistry stable isotopes 2h 18o 13c radiogenic isotopes 3h 14c and remote sensing modis data were used to investigate groundwater recharge and salinisation processes in 2006 2007 in january 2007 there was a large and intense local rainfall event followed by flooding to the normally dry lake eyre resulting from heavy rainfall in the northern leb that took 2 months to arrive at lake eyre groundwater chemistry from this study show no evidence of recharge from the floodwaters or the local rainfall however this does not preclude the process low transit times and low infiltrating volumes may mean that the recharge event has not yet been detected over the longer term the stable isotope chemistry indicates that groundwater is predominantly diffusely recharged during heavy local rainfall events 100 150 mm month and radiogenic isotopes reflect an older shallow groundwater efficiently mixing with recent decadal recharge the high total dissolved solids tds of regional shallow groundwater up to 52 5 g l is intrinsically linked with these recharge processes where infiltrating diffuse rainfall is evaporated and heavy rainfall events transport saline pore water saline due to evaporation in the unsaturated zone to the groundwater system the high tds of shallow groundwater beneath the dry lake eyre bed up to 322 g l is also controlled by evaporation however although evaporite minerals are prolific in the lake area the non conservative behaviour of br in pore water limits analysis of the role of halite mineral dissolution and precipitation reactions controlling groundwater salinity evaporation driven salinisation of shallow groundwater in arid central australia is distinct from the transpiration driven salinisation of groundwater in the australian murray basin located in a semi arid climate and results in relatively high groundwater salinity values compared with many other large arid zone endorheic basins across the world

the effect of sparse vegetation on the transport of dune sand by wind the precise effect of a sparse plant cover on the transport of dune sand by wind is a critical factor in understanding the morphology evolution and global distribution of aeolian dunes1 3 it is also of considerable practical importance in sand stabilization rehabilitation and restoration ecology here i report the first detailed experimental quantification of this effect using living plants in patterns approximating natural vegetation for wind velocities v at 0 5 m elevation up to 15 m s 1 and plant covercup to 17 the rate of aeolian sand transport q g cm 1 s 1 is closely approximated by q b v 1 kc vt 3 where b is bagnold s constant4 vt is a threshold velocity and k is a constant dependent on plant geometry for typical small erect or spreading herbaceous dune plants k 0 018 for small rounded stemless plants k 0 046

dating methods and geomorphic evidence of palaeoenvironmental changes at the eastern margin of the south peruvian coastal desert 14 30 s before and during the little ice age abstract the atacama desert is known to be one of the driest places on earth however in the study area between ica and nasca south peru 75 76 w 14 15 s palaeoclimate proxies show several semi arid phases during the holocene a more humid period during the early holocene favoured an open grass land which allowed the accumulation of desert loess eitel b hecht s machtle b schukraft g kadereit a wagner g kromer b unkel i reindel m 2005 geoarchaeological evidence from desert loess in the nazca palpa region southern peru palaeoenvironmental changes and their impact on pre columbian cultures archaeometry 47 137 158 the paracas and nasca cultures existing in that region between the 9th century bc and 7th century ad had propitious conditions to evolve and to settle close to the rivers fed by the monsoonal precipitation in the cordillera occidental culminating aridity after 600 ad might have caused the collapse of the nasca civilization the onset of semi arid climate towards the end of the late intermediate period 14th century ad allowed a reoccupation of the area here we present 14c and osl data from sediments of river terraces a debris flow and loess snails scutalus sp indicating appreciable geomorphic activity between 1390 and 1714 cal ad this phase is isochronous to the little ice age period on the northern hemisphere and to an increase in the ice accumulation on the quelccaya glacier in the peruvian altiplano thompson l g mosley thompson e bolzan j f koci b r 1985 a 1500 year record of tropical precipitation in ice cores from the quelccaya ice cap peru science 229 971 973

late quaternary mega lakes fed by the northern and southern river systems of central australia varying moisture sources and increased continental aridity 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

la nina de australia contemporary and palaeo hydrology of lake eyre abstract the available records of inflows to lake eyre cover only forty five years their quality is questionable as longer time series of precipitation records are available the observed series of inflows to lake eyre can be extended with the help of a rainfall runoff model further reconstruction of the inflow series can be achieved by examining local evidence or with the help of proxy data however the limitations of these extensions and reconstructions of inflows are severe the inflows to lake eyre could be considered one of the most convincing manifestations of hydrological uncertainty however it is apparent that major flooding episodes in the lake eyre basin are most often associated with la nina phases of the el nino southern oscillation enso phenomenon the paper presents a hydrological description of the lake eyre basin and large scale contemporary and palaeo climatic patterns which affect the water balance of the catchment a simple water balance model has been constructed to determine storages of the lake when annual evaporation reaches equilibrium with annual runoff

hydroclimatic interpretation of quaternary shorelines on south australian playas abstract the catchment of lake eyre is one of the world s largest internally drained basins the playas near its depocentre the driest region of australia contain a partial record of quaternary climatic and hydrologic events for the last full glacial cycle and probably beyond ancient beach ridges marginal to lakes eyre frome callabonna and blanche have been dated using thermoluminescence tl to provide evidence for major changes in the hydrological regime of the basin beach ridges around lake eyre provide evidence of high lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of marine oxygen isotope stage 5 there is evidence also for even higher lake stands associated with earlier isotope stages three tl dates identify a period of aeolian activity during stage 4 and a further 5 tl dates from lakes eyre and frome indicate that high lake stands occurred between about 55 and 40 ka corresponding with stage 3 the stage 5 and stage 3 high stands both relate to periods of enhanced fluvial activity previously identified in the lake eyre basin and elsewhere in australia in contradiction with other work a few tl dates from some playas suggest a possible major episode of high lake levels immediately preceding or at the start of the last glacial maximum lgm 26 22 ka this may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north while a set of relatively low elevation late holocene beaches have been dated on two of the playas a period of enhanced precipitation and stream flow in the early to mid holocene appears not to have formed higher beaches possibly due to high temperatures and evaporation rates at that time the filling of lake eyre during and since stage 5 appears to have been to no more than to a level of 12 m australian height datum ahd possibly due a spillway at about this elevation in the form of the warrawoocara channel connecting lake eyre with playas to the southeast lakes gregory blanche callabonna and frome such overflows from one large basin to another would have had a major impact on the hydrology of the region in addition to enhanced runoff essential for the maintenance of high lake levels must have been local temperatures and evaporation rates significantly reduced from present day levels

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction tooth s nanson g c 2004 forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction geological society of america bulletin 116 7 8 802 816 rae2008

australian desert dune fields initiated with pliocene pleistocene global climatic shift development of continental aridity has been linked to late cenozoic global cooling but the evidence is indirect based on terrestrial loess deposits and eolian silt in marine sediments whereas direct dating of the inception of arid landforms has been frustrated by a lack of suitable methods here we report the first age determination of a major arid zone dune field based on cosmogenic 10 be and 26 al measurements of drill cores from dunes in the simpson desert central australia results show that the dune field began to form ca 1 ma whereas dating using quartz optically stimulated luminescence indicates episodic dune building during late quaternary ice ages less intense desertification began earlier the previous cosmogenic exposure dating showed that neighboring stony deserts began to form at the onset of quaternary ice ages 2 4 ma aridity deepened and the dune field formed when ice age cycles increased their amplitude and switched their periods from 40 k y to 100 k y ca 1 ma

pedosedimentary cultural and environmental significance of paleosols within pre hispanic agricultural terraces in the southern peruvian andes paleosols were exposed in sections through four abandoned pre hispanic agricultural terraces surrounding an infilled mire basin in the southern peruvian andes the two paleosols beneath the tocotoccasa terrace represent the original natural solum and a later soil formed after construction of the agricultural terrace probably during the early middle horizon cultural period 615 695 ad the soil at the current surface developed subsequent to the building up and reconstruction of the terrace possibly during the late late intermediate period 1200 1400 ad micromorphology revealed an unexpected abundance of clay coatings within the upper terrace paleosol and surface terrace soil a phenonemon attributed to the migration and or accumulation of neoformed clay produced from the weathering of very unstable volcanic clasts perhaps fuelled by arid humid climatic oscillations and or seasonal input of irrigation waters the paleosols at tocotoccasa could not be correlated with any degree of confidence with those beneath the other three terraces due to differences in pedosedimentary properties and uncertainties over chronological controls thus it seems likely that either the terraces were re constructed and utilised over different cultural periods or that there is significant variation in the extent of weathering of material used for reconstruction of the terraces unfortunately it cannot be ascertained from the data available whether the terraces were abandoned for any significant period of time prior to reconstruction and if so whether this was a regional phenomenon related to climate social or economic changes

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

hydrology of lake eyre australia el nino link abstract all major ephemeral rivers of australia lie in the lake eyre basin dry for years on occasions they carry enormous floods with annual volumes of 40 km 3 and instantaneous discharges of the order of 30 000 m 3 s 1 mean annual runoff of the basin is 4 km 3 or 3 5 mm significantly less than the 57 mm for the whole of australia this paper examines lake eyre and its drainage basin describing the historical hydrology of the catchment both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs beyond the instrument period the burdekin river catchment runoff history is strongly paralleled by the volumes of lake eyre inflows during the period of common reliable instrument gaugings the burdekin runoff data have been extended back to 1735 a d using the correlation between river discharge and annual growth band fluorescence in an old coral from pandora reef off the north queensland coast for the instrument period 1952 to 1980 73 of the variance between coral fluorescence and burdekin discharge is common during the period 1949 1980 41 of the variance between coral fluorescence and lake eyre inflow data is common modelled inflows to lake eyre for the period 1885 1948 are based on the latter data set

tl chronology and stratigraphy of riverine source bordering sand dunes near wagga wagga new south wales australia abstract riverine source bordering dunes are found throughout the murray basin of southeastern australia at the eastern and northern margins of late quaternary palaeochannels the dunes are dominated by locally derived sand but often contain a minor calcareous clay component originating from a distant westerly source in the bedrock confined valley of the murrumbidgee river near wagga wagga the dunes occur as discrete mounds on the floodplain or as drapes over the marginal valley side slopes tl dating of three stratigraphic units within the dunes shows that phases of sand accumulation occurred between 15 and 25 ka in oxygen isotope stage 2 clarendon unit between 35 and 60 ka in stage 3 glenfield unit and between 80 and 120 ka in stage 5 yarragundry unit the tl ages here which show excellent agreement with those determined respectively for the yanco kerarbury and coleambally phases of palaeochannel activity on the riverine plain j quat sci 11 1996 311 extend the emerging regional model of late quaternary climatic and hydrologic change for southeastern australia

pre industrial human and environment interactions in northern peru during the late holocene the result of long term environmental and human interaction is a variety of potential human responses to major natural crises population aggregation or dispersal changes in economic strategies an

climate variability over the last 35 000 years recorded in marine and terrestrial archives in the australian region an oz intimate compilation abstract the australian region spans some 60 of latitude and 50 of longitude and displays considerable regional climate variability both today and during the late quaternary a synthesis of marine and terrestrial climate records combining findings from the southern ocean temperate tropical and arid zones identifies a complex response of climate proxies to a background of changing boundary conditions over the last 35 000 years climate drivers include the seasonal timing of insolation greenhouse gas content of the atmosphere sea level rise and ocean and atmospheric circulation changes our compilation finds few climatic events that could be used to construct a climate event stratigraphy for the entire region limiting the usefulness of this approach instead we have taken a spatial approach looking to discern the patterns of change across the continent the data identify the clearest and most synchronous climatic response at the time of the last glacial maximum lgm 21 3 ka with unambiguous cooling recorded in the ocean and evidence of glaciation in the highlands of tropical new guinea southeast australia and tasmania many terrestrial records suggest drier conditions but with the timing of inferred snowmelt and changes to the rainfall runoff relationships driving higher river discharge at the lgm in contrast the deglaciation is a time of considerable south east to north west variation across the region warming was underway in all regions by 17 ka post glacial sea level rise and its associated regional impacts have played an important role in determining the magnitude and timing of climate response in the north west of the continent in contrast to the southern latitudes no evidence for cooling during the younger dryas chronozone is evident in the region but the antarctic cold reversal clearly occurs south of australia the holocene period is a time of considerable climate variability associated with an intense monsoon in the tropics early in the holocene giving way to a weakened monsoon and an increasingly el nino dominated enso to the present the influence of enso is evident throughout the southeast of australia but not the southwest this climate history provides a template from which to assess the regionality of climate events across australia and make comparisons beyond our region

paleoenvironmental catastrophies on the peruvian coast revealed in lagoon sediment cores from pachacamac abstract paleoenvironmental reconstruction combining data from diatom pollen macrophytic and archaeological analyses had not been attempted previously for coastal peru we analyzed two radiocarbon dated sediment cores extracted from the sacred urpi kocha lagoon at the pre hispanic religious center of pachacamac ca ad 350 1533 near lima to characterize the paleoenvironment of the site the data reveal an environmental history characterized by alternating periods of severe drought and catastrophic flood recurrent pulses with distinctive sediment diatom pollen and macrophytic characteristics reflecting variations in water depth substrate turbidity and salinity usually contain a thick basal sandy storm deposit overlain by thin organic accumulations of peat gyttja and snails the most intense of these disturbance pulses when correlated with pollen plant macrofossils radiocarbon dates and regional proxy data provide local evidence of four major floods associated with sustained catastrophic el nino events tsunamis and or severe storms in the andean highlands over the last 2000 years

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

spectral properties 0 4 to 25 microns of selected rocks associated with disseminated gold and silver deposits in nevada and idaho visible near infrared vnir reflectance spectra and midinfrared mir transmission spectra 2 5 25 m were measured for selected rock types from disseminated gold and silver deposits in northern nevada and southern idaho samples from the open pit mines at pinson nevada and delmar idaho were compared to weathered surface samples from a prospect at preble nevada eight characteristics of the disseminated deposits were proposed that could be identified by remote sensing applications of these eight characteristics jasperoids the siliceous replacement of limestones were readily distinguishable from the carbonate host rock and other associated silicate rocks by their spectral characteristics in the mir active or fossil hot spring sites where present near the deposit display similar vnir spectral features at the surface as hydrothermally altered rocks found at depth in the open pit mines however most of the host rocks at the surface above a disseminated gold prospect show few vnir absorption features because of the presence of organic matter vnir spectral features of carbonate were detectable in a few cases immediately adjacent to a jasperoid ammonium spectral features are observed on some of the hydrothermally altered shale surrounding the prospect also suggesting the presence of organic matter because organic matter exerts such a large influence on the spectral character of the host rocks the combined mir and vnir wavelengths are needed for remote discrimination of disseminated gold prospects in the western u s

hazard risk and agrarian adaptations in a hyperarid watershed el nino floods streambank erosion and the cultural bounds of vulnerability in the andean middle horizon abstract peru s osmore drainage also known as the moquegua valley is one of the driest regions on earth yet agricultural development has supported complex societies in the basin for almost 4000 yrs because of canal construction and irrigation we compare the distinct agrarian and settlement systems of three coeval archaeological cultures in this arid region huaracane wari and tiwanaku and how each adapted or failed to adapt to geomorphic and climatic hazards systematic settlement pattern survey and radiocarbon dating along with geomorphological analysis of flood history and riverine processes permit detailed discussion of agrarian strategies during the formative 1800 bc ad 500 and middle horizon ad 500 1000 periods with distinct settlement niches in terms of agricultural practices and longitudinal position in the drainage and lateral location relative to the floodplain these adaptive strategies each manifest distinct bounds of adaptability to natural hazard climate events and social stressors and thus varying risk profiles besides the continual risk associated with sustained droughts the atacama and peruvian coastal desert and culturally connected highland altiplano are also vulnerable to the vagaries of the el nino southern oscillation enso leading to catastrophic floods in the mid valley during warm phase ensos in tandem with simultaneous hazards in other regions inhabited by these transregional cultures by comparing the archaeological record of wari huaracane and tiwanaku culture settlements with geomorphic signatures of catastrophic el ninos we show that the viability of each cultural sequence depended on specific relationships to floodplain streambank erosion construction and reworking over multiple time scales

human environment interactions in australian drylands exploratory time series analysis of archaeological records exploratory time series analysis of radiocarbon data from archaeological contexts is used to reconstruct the population history of arid australia allowing this to be read in concert with records of climatic variability over the last 20 000 years probability distribution plots of 971 radiocarbon ages from 286 sites in five dryland regions the arid west coast pilbara and murchison nullarbor arid interior and the southeastern arid zone provide a proxy record of prehistoric population fluctuations in these areas there is regional variation but the radiocarbon density plots suggest a step wise pattern of population growth and expansion with significant thresholds at 19 8 and 1 5 cal kyr bp within this the plots suggest a saw tooth pattern of rapid population growth and decline on a 1 3 kyr frequency with a marked collapse of dryland hunter gatherer populations around 3 2 5 cal kyr bp affecting most regions comparison with climate data shows broad correlations with past temperature and rainfall

a reconstruction of extratropical indo pacific sea level pressure patterns during the medieval climate anomaly subtropical and extratropical proxy records of wind field sea level pressure slp temperature and hydrological anomalies from south africa australia new zealand patagonian south america and antarctica were used to reconstruct the indo pacific extratropical southern hemisphere sea level pressure anomaly slpa fields for the medieval climate anomaly mca 700 1350 ce and transition to the little ice age lia 1350 1450 ce the multivariate array of proxy data were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data the mean slp and slp anomaly patterns derived from these analogues illustrate the evolution of low frequency changes in the extratropics the indo pacific extratropical mean climate state was dominated by a strong tropical interaction with antarctica emanating from 1 the eastern indian and south west pacific regions prior to 1100 ce then 2 the eastern pacific evolving to the central pacific la nina like pattern interacting with a ve sam to 1300 ce a relatively abrupt shift to ve sam and the central pacific el nino like pattern occurred at 1300 a poleward equatorward shift in the subtropical ridge occurred during the mca mca lia transition the hadley cell expansion in the australian and southwest pacific region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported hadley cell expansion in the north pacific and atlantic regions and suggests that bipolar climate symmetry was a feature of the mca

fluvial history of the rio ilave valley peru and its relationship to climate and human history fluvial strata and landforms in the rio ilave valley peru document a history of holocene aggradation and downcutting that is correlative with regional climatic events and provides an environmental context for human occupation of the river valley periods of aggradation correspond to periods of high or rising level in lake titicaca and elsewhere on the altiplano and increased sediment accumulation in the rio ilave valley downcutting episodes correspond to periods of low level in lake titicaca and low or rapidly decreasing sedimentation rates in the ilave delta there are five terrace tracts t1 through t5 present in this southwestern lake titicaca tributary these tracts occur as both paired and unpaired terraces and have average heights from 1 4 to 24 3 m above the valley floor the major part of the fluvial sequence was deposited during the time period from prior to the last glacial maximum until about 8300 calendar years before present cal bp a period of generally high but variable precipitation on the altiplano and high water level in lake titicaca initial deposition aggradation was followed by successive downcutting to the t4 and t3 terrace surfaces initial downcutting began immediately after precipitation runoff and sediment load decreased while base level dropped it was followed by a period of episodic equilibrium and minor downcutting that included a prolonged period of soil formation between v8350 and 6780 cal bp the major pulses of downcutting likely occurred between v6000 and 4500 cal bp and were coincident with periods of decreased precipitation on the altiplano and decreasing levels of lake titicaca two final periods of infilling resulting in deposition of the t2 and t1 terrace sediments at v4000 to 2500 cal bp and v2000 to 1600 cal bp during periods of rising water level in lake titicaca lacustrine sedimentation in the rio desaguadero valley and increased sedimentation offshore the ilave delta were separated by brief equilibrium stages and a brief downcutting event this fluvial history when coupled with regional paleoclimatic data relates to the region s preceramic through tiwanakuperiod archeological records archeological evidence indicates that humans occupied the ilave valley as early as 10 000 cal bp the higher terraces t3 t4 and t5 were occupied for at least 5000 years but humans did not utilize the lower terraces t1 and t2 until after v4400 3700 cal bp our results confirm that these lower terraces would not have been available for either occupation or agriculture until after v4000 cal bp 2003 published by elsevier science b v

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

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

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

freshwater recharge into a shallow saline groundwater system cooper creek floodplain queensland australia freshwater lenses have been identified as having penetrated the shallow regional saline groundwater beneath the cooper creek floodplain near ballera south west queensland piezometers were installed to evaluate the major element chemistry along a floodplain transect from a major waterhole goonbabinna to a smaller waterhole chookoo associated with a sand dune complex the floodplain consists of 2 7m of impermeable mud underlain by unconsolidated fluvial sands with a saline watertable waterholes have in places scoured into the floodplain the transect reveals that groundwater recharge takes place through the base of the waterholes at times of flood scour but not through the floodplain mud total dissolved solids rise with distance from the waterhole and independently of the presence of sand dunes stable water isotopes 2h and 18o confirm that recharge is consistent with and dependant on monsoonal flooding events following floods the waterholes self seal and retain water for extended periods with sulfate 34s and 18o isotopes suggesting bacterial reduction processes within the hyporheic zone and limited interaction between the surface water and groundwater during no flow conditions the area occupied by the freshwater lenses tds 5000 mg l is locally asymmetrical with respect to the channel flow direction extending down gradient along distances of 300 m

quaternary aeolian dust processes and sediments in the australian region abstract aeolian dust processes have played an important role in the evolution of the australian landscape yet little is known of the processes and their sediments two major dust transport pathways are described based upon paleo dune patterns and present day dust storms and related processes these dust pathways have been fed by alluvium deposited in internally draining river basins during the period leading up to and including the late pleistocene aridity rates of dust entrainment transport and deposition were significantly higher than at present the ocean sediments of the tasman sea the pacific and indian oceans received massive amounts of aeolian sediment dust contributions to some australian soils have also been considerable

anabranching rivers on the northern plains of arid central australia anabranching rivers are a widespread feature of the northern plains in the alice springs region of central australia but their unusual characteristics previously have not been described on the northern plains anabranching occurs on rivers transporting bedloads of coarse sand and gravel and is characterised by channels of variable size and shape which occur within a broader typically well defined channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands ridges and islands are either depositional features formed in situ by accretionary processes or erosional features formed by excision from once continuous areas of floodplain vegetation plays a key role in the initiation survival and growth of depositional forms through its influence on flow sediment transport and ridge and island stability anabranching is also related to the influence of tributaries for some large rivers alternate from single thread to anabranching along their length in response to tributary inputs of water and sediment tributary inputs occur during flow events that are either independent from or in concert with floods in the trunk channel ridges and islands form in association with tributaries as a result of various hydrological depositional and erosional processes including irrigation of enhanced numbers of in channel trees and resulting lee side sediment accretion floodplain scour and the formation and maintenance of deferred junction tributaries the change from single thread to anabranching downstream of tributary junctions occurs in the absence of any significant change in channel gradient or degree of channel confinement on the northern plains anabranching appears to be a stable river pattern that helps to maintain the throughput of relatively coarse sediment in low gradient typically 0 0005 0 002 channels characterised by an abundance of within channel vegetation and subject to declining downstream discharges

an improved bathymetric model for the modern and palaeo lake eyre abstract here we demonstrate the applicability of using altimetry data and landsat imagery to provide the most accurate digital elevation model dem of australia s largest playa lake lake eyre we demonstrate through the use of geospatial techniques a robust assessment of lake area and volume of recent lake filling episodes whilst also providing the most accurate estimates of area and volume for larger lake filling episodes that occurred throughout the last glacial cycle we highlight that at a depth of 25 m lake mega eyre would merge with the adjacent lake mega frome to form an immense waterbody with a combined area of almost 35 000 km2 and a combined volume of 520 km3 this would represent a vast water body in what is now the arid interior of the australian continent the improved dem is more reliable from a geomorphological and hydrological perspective and allows a more accurate assessment of water balance under the modern hydrological regime the results presented using glas icesat data suggest that earlier historical soundings were correct and the actual lowest topographic point in australia is 15 6 m below sea level the results also contrast nicely the different basin characteristics of two adjacent lake systems lake eyre and lake frome

splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia abstract splays are common features of many rivers and deltas forming as a result of overbank flooding and sediment deposition but they have rarely been described from modern dryland settings this paper investigates splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia here splays vary from small lobate or tongue shaped features 1 km long to larger elongate features up to 4 km long and are supplied with rare floodwater and sediment through well defined breaches in the upper parts of the main channel banks in proximal and medial parts splay channels are incised up to 2 m into pre splay fine grained floodplain sediments but remain elevated between 0 5 m and 2 m above the main channels only in the very distal parts are splay channels less deeply incised either grading into the floodplain surface or terminating as sediment lobes that are deposited upon the floodplain aerial photographs and field observations indicate that many splays develop rapidly during large floods and are modified during infrequent subsequent floods four main stages of splay development are proposed 1 aggressive overbank flow results in bank line breaching and channel scour on the floodplain but little sediment deposition 2 coarse bed sediment is diverted from the main channel preventing further deepening at the bank line breach and slowing channel scour 3 increasing coarse sediment transport through the bank line breach and scoured channels leads to the formation of distal sediment lobes 4 subsequent floods divert around these distal lobes sometimes leading to further channel scour and lobe formation on the northern plains splays contribute to downstream decreases in the discharge and size of the main channels and splay deposits form local accumulations of gravelly sand in the predominantly fine grained floodplain successions some splays ultimately may evolve into distributaries or anabranches the dominantly erosional bases of these splay channels contrast with typical descriptions of many humid region splays but they do not display any geomorphological or sedimentological features that are necessarily diagnostic of formation in a dryland setting

a pluvial episode identified in arid australia during the medieval climatic anomaly optically stimulated luminescence osl ages from a relict shoreline on lake callabonna record a major pluvial episode in southern central australia between 1050 70 and 1100 60 common era ce w

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

geomorphological study of the cafayate dune field northwest argentina during the last millennium abstract the cafayate depression is a dry valley located in the pre andean region of northwest argentina the area shows the development of a large dune field its significance has been established from geomorphological and mineralogical evidence grain shape characteristics and chronological data osl dating archaeological remains and historical data the dating results were between 1000 1100 ad to1740 1830 ad showing that the aeolian dynamics remained active during the last millennium it was not possible to identify stabilised phases marked by ruptures or paleosol development nevertheless other regional and local proxies from northwest argentina archaeological documentary etc were used to complete the interpretative framework to propose the paleoenvironmental evolution of the area in addition human activity and land use must be considered as a complementary factor affecting aeolian dynamics during the most recent stage

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

environmental character and history of the lake eyre basin one seventh of the australian continent abstract one of the world s largest internally drained endorheic basins the 1 14 million km 2 lake eyre hydrological basin leb covers nearly 15 of the australian continent palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial aeolian and lacustrine sediments that are particularly accessible for deposits from the past 300 ka and are especially relevant for the past 50 ka during which humans have inhabited australia due to its great size economic resources and diverse latitudinal extent it has for over six decades been the focus of environmental scientific and resource based studies across numerous disciplines with an emphasis on assessing the scientific and environmental research over this period this paper is divided into four parts part a provides an introduction and background part b provides the geological history including evidence of substantial tertiary and quaternary climate change part c covers the contemporary environmental conditions and part d presents a conclusion and summary this not only represents the first comprehensive review of current knowledge of any of the world s truly large dryland drainage basins but also highlights how more multi disciplinary research is required key remaining questions revolve around the impact of global weather systems on the leb the lake level story in relation to a more precise picture of late quaternary climate change the role of humans and climate in the demise of the megafauna modern hydrological changes the role of vegetation in altering channel morphology and flow efficiencies and nature of flood transmissions

lake eyre palaeohydrology from 60 ka to the present beach ridges and glacial maximum aridity lake eyre is presently an ephemeral playa lake in an extremely large 1 3 million km2 internal drainage basin with most of its inflow derived from monsoon watered northern australia the hydrologic state of the lake has varied in the past in response to climate change from a perennial lake up to 25 metres deep to a groundwater controlled playa marked by substantial sediment deflation this paper is concerned with the stratigraphic record of the last 60 ka of that hydrologic history particularly the character and age of a playa marginal unit formed by deflation from the playa and of stranded high beach ridges a major deflation episode between 60 and 50 ka excavated the present lake eyre basin and deposited a gypsum and clay rich aeolian phase the williams point aeolian unit at a number of sites around the lake after deflation ceased a thick secondary gypsum profile developed on the dune early in oxygen isotope stage 3 evidence for the state of lake eyre at this time is equivocal preliminary results from a substantial suite of amino acid racemization aar analyses of mollusc shell and bird eggshell samples from beach ridges at 5 and 10 m australian height datum ahd suggest that they are oxygen isotope stage 5 in age sedimentologic evidence suggests that it is unlikely that the shells are reworked from older deposits these aar results apparently conflict with early oxygen isotope stage 3 thermoluminescence tl dates from the 5 m ahd beach ridge nanson et al this volume however the age difference is not substantial the calibration of the aar is still at a preliminary stage and only one site was sampled for both techniques further stratigraphic and chronologic work is required to fully assess the apparent discrepancy between about 30 000 and 12 000 yr b p lake eyre was at least as dry as it is today at many sites around madigan gulf a lunette like playa marginal aeolian unit the shelly island unit was deposited during this period formed by material deflated from the playa floor forty ams radiocarbon dates span the period 35 000 to 10 000 yr b p from the shelly island unit 11 and from aeolian sediment close to playa level 29 indicating that the lake was dry during this period this evidence conflicts strongly with 2 tl dates from latest oxygen isotope stage 3 and oxygen isotope stage 2 from the 5 and 10 m ahd beach ridges nanson et al this volume additionally the aar results from the high beach ridges cannot be reconciled with these tl dates after 10 000 yr b p a minor lacustral phase occurred until the modern ephemeral playa regime became established at 3000 4000 yr b p

downstream changes in dryland river channels the northern plains of arid central australia abstract many dryland rivers undergo marked downstream changes owing to factors such as infrequent floods flow transmission losses and typically few tributary inflows beyond the headwaters along the sandover bundey sandover bundey and woodforde rivers on the northern plains of arid central australia downstream channel changes are broadly similar in upland zones small rocky channels transporting sand and gravel gradually increase in size before entering piedmont zones where channels and narrow floodplains are confined by bedrock alluvial terraces or aeolian dunes in lower gradient lowland zones channels and floodplains remain confined and in the absence of tributary inflows channel cross sectional areas and discharges decrease downstream confining landforms are not present in floodout zones which results in splay formation increased floodplain widths and marked overall downstream decreases in cross sectional areas eventually channelised flow and bedload transport terminate although occasional large floods continue across extensive unchanneled alluvial surfaces termed floodouts these broad similarities apart downstream changes along the three rivers differ in detail the sandover is largely a single thread channel whereas many reaches of the sandover bundey and woodforde are anabranched on the small woodforde river downstream decreases in parameters such as cross sectional area and width are roughly linear on the larger sandover and sandover bundey downstream changes are more irregular particularly through the floodout zones where there are marked fluctuations in widths depths and bed slopes the irregular downstream changes typical of the lower reaches of these large rivers may be due to the reduced influence of vegetation on bankline stability and width adjustment relative to that of smaller rivers on the northern plains as in other drylands complex interactions between discharge sediment transport slope patterns of tributary drainage bank sediment type and vegetation result in variable patterns of downstream channel change

palaeoclimatic and archaeological evidence for a 200 yr recurrence of floods and droughts linking california mesoamerica and south america over the past 2000 years conspicuous grey clay rich flood deposits in the predominantly olive varved sediment in the central santa barbara basin california were dated via varve counting to c ad 212 440 603 1029 1418 and 1605 the 200 yr quasi periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented 200 yr periodicity in palaeoclimate records elsewhere the floods of c ad 440 and ad 1418 occurred during global reorganizations of atmospheric circulation cold spells seem to have accompanied the floods of c ad 1029 and ad 1605 california floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a 200 yr periodicity our compilation of palaeoclimatic and mesoamerican and south american archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in 200 yr steps the matching patte

climate variation and the rise and fall of an andean civilization paleolimnological and archaeological records that span 3500 years from lake titicaca and the surrounding bolivian peruvian altiplano demonstrate that the emergence of agriculture ca 1500 b c and the collapse of the tiwanaku civilization ca a d 1100 coincided with periods of abrupt profound climate change the timing and magnitude of climate changes are inferred from stratigraphic evidence of lake level variation recorded in14c dated lake sediment cores paleo lake levels provide estimates of drainage basin water balance archaeological evidence establishes spatial and temporal patterns of agricultural field use and abandonment prior to 1500 b c aridity in the altiplano precluded intensive agriculture during a wetter period from 1500 b c to a d 1100 the tiwanaku civilization and its immediate predecessors developed specialized agricultural methods that stimulated population growth and sustained large human settlements a prolonged drier period ca a d 1100 1400 caused declining agricultural production field abandonment and cultural collapse