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Paleoclimate research in the Maya region of Mesoamerica provides compelling evidence of drought during key periods of cultural transition in Maya society. These include the transition from the Preclassic to the Classic, and from Classic to the Postclassic. Previous research emphasized a causal relationship between drought and cultural change, or so-called “collapse” in the Maya region. Recent advances in the range and precision of climate-sensitive proxies and the development of new archives have enabled quantitative reconstructions of past hydroclimate, as well as providing evidence of high impact, short-duration events, such as tropical cyclones. Simultaneously, archaeological research has unearthed widespread evidence of technologies used by the Maya to exert control over water resources in urban, rural, and agricultural settings. Evidence suggests that many of these water features were in use for multiple generations, possibly centuries, and many were constructed during the Terminal Preclassic and Terminal Classic periods. We suggest that, given the availability of new archaeological and paleoclimate records, these data can be combined to identify the full complexity of Maya adaptation to hydroclimate variability to emphasize adaptation and resilience to both water scarcity and over-abundance (e.g., flooding). Such syntheses, which can offer lessons for present-day efforts to grapple with regional climate change, will benefit from additional studies in data-poor zones of the Maya region, as well as public archiving of paleoclimate and archaeological data.

Previous syntheses of palaeoclimate and archaeological data from the Kashmir Valley have proposed that climate changes drove prehistoric settlement of the valley, based on the adaptation of West Asian winter crops to mid-Holocene warm-humid conditions ca. 5000 BP. It has been argued that these conditions enabled population growth that became unsustainable following the onset of a cold-arid phase ca. 3000 BP, with these cycles of growth and collapse again repeating ca. 2000 and 1000 BP. Here we present multi-proxy palynomorph, charcoal and sediment data indicating that from ca. 4500-1500 BP the environment of the valley was characterised by drier conditions, comparable to other regional records indicating weakening Westerly precipitation over Central Asia. Considering recent archaeobotanical data indicating the presence of both West Asian winter crops and East Asian summer millets in the valley as early as 4500 BP, we argue that rather than Malthusian cycles of growth and collapse in Kashmir, early populations likely drew on a broad range of available domesticates and varied ecotopes across the valley to allow a Boserupian response to changing Holocene climate conditions. These adaptations were likely more oriented towards flexible systems of agro-pastoralism practiced throughout the Inner Asian mountains, rather than towards developing large urban settlements as was the case in the river basins and plains south of Kashmir.

Debate about the nature of climate and the magnitude of ecological change across Australia during the last glacial maximum (LGM; 26.5–19 ka) persists despite considerable research into the late Pleistocene. This is partly due to a lack of detailed paleoenvironmental records and reliable chronological frameworks. Geochemical and geochronological analyses of a 60 ka sedimentary record from Brown Lake, subtropical Queensland, are presented and considered in the context of climate-controlled environmental change. Optically stimulated luminescence dating of dune crests adjacent to prominent wetlands across North Stradbroke Island (Minjerribah) returned a mean age of 119.9 ± 10.6 ka; indicating relative dune stability soon after formation in Marine Isotope Stage 5. Synthesis of wetland sediment geochemistry across the island was used to identify dust accumulation and applied as an aridification proxy over the last glacial-interglacial cycle. A positive trend of dust deposition from ca. 50 ka was found with highest influx occurring leading into the LGM. Complexities of comparing sedimentary records and the need for robust age models are highlighted with local variation influencing the accumulation of exogenic material. An inter-site comparison suggests enhanced moisture stress regionally during the last glaciation and throughout the LGM, returning to a more positive moisture balance ca. 8 ka.

The River Murray Estuary, South Australia exhibits a morphology typical of a wave-dominated estuary and comprises two large, shallow central basin lakes – Lakes Alexandrina and Albert. Contested interpretations of the estuary’s limnological history and uncertainty surrounding the sustainability of current basin water usage practice warrant a robust investigation into how the system has evolved. Here we combine lithostratigraphic, geochemical and sedimentological evidence from a transect of sediment cores to reconstruct the sediment infill history of the system. We uncover multiple stages of sediment infill over the history of the system, associated with (1) the low gradient morphology of the estuary and lower river channel, (2) the mid- to late-Holocene sea-level regression and (3) anthropogenic modifications to the fluvio-estuarine system. We show that while estuarine conditions in the system were fully established during the mid-Holocene highstand (~6.4 kyr BP), central basin facies sedimentation was focussed further inland before prograding with the lowering of base level and shifting of tidal influence as sea-level fell. Central basin facies sedimentation within northern Lake Albert occurred from 5.4 to 4.0 cal kyr BP at ~0.25 cm yr-1. The uppermost accumulation of this unit was eroded by continued reduction in base level until sea-level regression concluded at 3.5 cal kyr BP. Barrage and weir installation (1940 CE) re-initiated and expanded central basin facies sedimentation in the estuary (~0.32 cm yr-1). Recently deposited sediments exhibit geochemical markers of increased trophy and more frequent acid sulfate soil acidification, exposing human impacts on the estuary.

Mangrove forests sequester organic carbon, nutrients and toxic metals sorbed to fine sediment, and thus restrict the mobility of pollutants through estuarine environments. However, mangrove removal and environmental degradation caused by industrial activity and urban growth can impact the ability of mangrove communities to provide these critical ecosystem services. Here, we use sediment profiles from an impacted tropical estuary in southwest India to provide a c. 70-year record of carbon, nutrient and trace metal burial in the context of rapid urban development and the systemic removal of mangrove communities. Our results show that carbon and nutrient accumulation rates increase sharply during the 1990's in accordance with the high rates of deforestation. Nitrogen and phosphorus accumulation rates increased fourfold and twofold, respectively, during the same period. Organic carbon accumulation was fivefold higher than the global average during this period, reflecting intense deforestation during the last three decades. The enrichment of Hg, Zn, Pb, Mo, Ni, Cu and Mn demonstrate clear anthropogenic impact starting in the 1950's and peaking in 1990. Mercury, the trace metal with the highest enrichment factor, increased sevenfold in the most recent sediments due to increased fossil fuel emissions, untreated water and incineration of medical waste and/or fertilizers used in aquaculture. Organic carbon isotope (δ

Mangrove ecosystems are dynamic and biodiverse environments with the capacity to sequester more organic carbon per unit area, per time, than terrestrial forests, yet are among one of the most heavily degraded ecosystems on Earth. Here, we quantify trace metal, nutrient and carbon accumulation rates in a tropical mangrove environment in northeast Brazil, a region that has been rapidly developed over the past seven decades. Carbon accumulation rate results show modest or no increase since the 1950's, when major development occurred in the region. Organic carbon isotope (δ

Large, low-density settlements of the tropical world disintegrated during the first and second millennia of the CE. This phenomenon, which occurred in South Asia, Southeast Asia, and Mesoamerica, is strongly associated with climate variability and extensive landscape transformation. These profound social transformations in the tropical world have been popularized as “collapse,” yet archaeological evidence suggests a more complex and nuanced story characterized by persistence, adaptation, and resilience at the local and regional scales. The resulting tension between ideas of climate-driven collapse and evidence for diverse social responses challenges our understanding of long-term resilience and vulnerability to environmental change in the global tropics. Here, we compare the archetypal urban collapse of the Maya, in modern Belize, Guatemala, Honduras, and Mexico, during the 8th to 11th centuries CE, and the Khmer in modern Cambodia, Laos, Thailand, and Vietnam during the 14th to 15th centuries CE. We argue that the social response to environmental stress is spatially and temporally heterogenous, reflecting the generation of large-scale landesque capital surrounding the urban cores. Divergences between vulnerable urban elite and apparently resilient dispersed agricultural settlements sit uncomfortably with simplistic notions of social collapse and raise important questions for humanity as we move deeper into the Anthropocene.

The Dipterocarpaceae family is ubiquitous across mainland and maritime south-east Asia. Species within the family are often so well-adapted to - and prolific within - ecologically distinct forest types, that they are used as habitat indicators within forestry and ecological research. The limited work on the classification of Dipterocarpaceae pollen under light microscopy, however, means that paleoecologists working in the region are currently unable to link fossil pollen to indicator species/assemblages with any confidence. As a consequence, ecologically meaningful and habitat-specific data are homogenized in the paleorecord.This study explores whether the classification of pollen from representative south-east Asian Dipterocarpaceae species can be resolved at a higher taxonomic resolution. This will provide paleoecologists with a tool to (1) better assess shifts in forest types (and hence climate/elevation envelopes) through time, and (2) predict species response to future regional change. Our revised classification scheme is based on an analysis of the pollen morphology of Dipterocarpaceae species from two globally significant ecoregions in south-east Asia - the seasonally dry tropical forests of mainland south-east Asia, and the Sulawesi lowland rainforests of Wallacea - under the light microscope. Results of this analysis show that, using a range of morphological metrics - notably grain size, size-to-wall thickness ratios and exine structure - mainland and Wallacean Dipterocarpaceae pollen can be readily classified into three taxonomic groups - Vatica, Dipterocarpus and Shorea/Hopea/Anisoptera/Pentacme types. At an intra-ecoregional scale, each assemblage can be further broken down into six groups. Some of these groupings appear useful for the classification of certain indicator pollen types within the family, including those taxa representative of key open - and closed - canopy dry forest habitats in the mainland seasonal tropics, the delimitation of peat/swamp forest types in both ecoregions, and the identification of lowland mafic forest types in Sulawesi. Additionally, being able to split the Dipterocarpaceae within these ecologically important ecoregions at a higher taxonomic resolution is of potential conservation significance, permitting long-term assessment of the adaptation capacity of different genera/species to climatic change or disturbance events. (C) 2019 Elsevier B.V. All rights reserved.

During the Angkor period (9th to 15th centuries C.E.) the Khmer kingdom extended across much of mainland Southeast Asia. The primate city of Angkor was located on the floodplains to the north of the Tonle Sap and connected to a network of secondary cities across the kingdom via formal road or navigable river systems. Preah Khan of Kompong Svay was one such secondary city, and was positioned on the eastern margins of Khmer territory approximately 100 km from Angkor. Stylistic dating of Preah Khan's temple architecture revealed that the majority of building works was conducted between the 11th and 13th centuries C.E., however only minimal archaeological evidence for occupation during this period has been found. This paper presents a record of environmental change that re-evaluates the settlement history of Preah Khan, and suggests that occupation and land use change was occurring at least between the early 12th and late 14th centuries C.E. Signs of gradual land use attenuation and a reduction in water infrastructure management are evident from the late 13th century through to the late 14th century C.E., and during the mid-14th century an apparent shift in the utilisation of the city occurs. This study helps to address the relative lack of research into cities outside the Angkor region, and demonstrates the value of using palaeoecological evidence for unravelling the complexity of settlement history in Angkor-period cities, particularly through the waning phases of occupation.

The sedimentology, geochemistry, and plant microfossils of volcanic lake sediments from Cambodia were analysed to reconstruct a 4700 year record of change in moisture availability. This site sits at the heart of the intersection zone of the East Asian and Indian summer monsoons – a climatic system that is socio-ecologically important but poorly understood. Proxies for lake deepening and shallowing indicate a stepwise weakening of the summer monsoon from c. 4700 to 1700 cal. years BP, after which it appears to gradually strengthen. This trend is punctuated by seven dry events between 4300 and 1540 cal. years BP. The results present one of the longest, continuous records of palaeo-hydrological change in the Asian monsoon intersection zone. In doing so, they suggest that the climate of the region was broadly comparable to the East Asian summer monsoon (EASM) province to approximately 2240 cal. years BP, and the Indian summer monsoon (ISM) province between 2240 and 1700 cal. years BP. The subsequent, late Holocene hydroclimate appears to reflect a combination of both subsystems. These findings highlight dynamism in EASM and ISM dominance over mainland southeast Asia over the past five thousand years, but overall demonstrate regional vs. local scale influence on the hydroclimate of the region. The multi-decadal periods of strong drying that punctuate longer-term monsoon patterns demonstrate the natural variability of the mid- to late- Holocene climate of the intersection zone. This is of consequence given that apparently less severe drought events of the last millennium have had dramatic socio-economic consequences. Resultantly, planning for the resilience of socio-ecological systems within the region needs to account for the real potential of similar scale events occurring in the future, particularly given the increased extremes predicted for Asian summer monsoon region over the 21st century.

The consequences of protected areas for proximal human communities are diverse. Protected areas can alleviate poverty by providing a range of economic opportunities for people that live and work within them. Equally, however, they may also disempower and disposes local communities. For communities adapting to systemic environmental change, proximity to protected areas can act to limit potential adaptive pathways. Here, we employ social science methods to explore the impact of an internationally significant protected area on adjacent communities in the Tonle Sap Lake basin, Cambodia. Semi-structured interviews, informed by a scenario framework, reveal an awareness of declining fish yields and a perceived lack of economic alternatives. Vulnerability to hydroclimatic extremes, particularly storms, flood, drought and – increasingly – fire, are exacerbated as a result of proximity to the protected area. We conclude that the impact of protected areas on local communities is heterogenous, and that the development of adaptive and effective management policies requires sensitivity to local conditions and impacts.

Few Australian wetlands have persisted since the Last Glacial Maximum, with fewer still in existence through the entire last glacial cycle. The absence of wetlands, which itself indicates periods of moisture deficit, means there are few continuous climate and environmental change records covering this critical period. The lack of wetland persistence also raises the question of how plant and animal species that require permanent wetlands survived the last glacial cycle. Sixteen wetlands have been cored and dated on North Stradbroke Island (Minjerribah) – a large east Australian sand island – with basal dates reported from 10 sites for the first time. These wetlands range in age to over 200 000 years old, with six dating to the Last Glacial Maximum or earlier. There is no evidence of a stratigraphic discontinuity in the radiocarbon-based age–depth profiles, suggesting continuous deposition of highly organic sediment through the period covered by these ages (c. 40 ka). The persistence of these wetlands suggests that for much of the last 40 000 years, and for perhaps much longer, the regional moisture balance has been positive. Over the last glacial cycle, persistently wet conditions may have provided a refuge from regional drying, and thus contributed to the high genetic diversity of rainforest plants in the region. Vegetation and climate records from these sites will allow hypothesis testing about the drivers of both local and regional climate variability. Copyright © 2017 John Wiley & Sons, Ltd.

Extreme prolonged drought over south-eastern Australia a decade ago (the Millennium Drought, 1996–2010) triggered extensive acid sulfate soil oxidation and associated acidification. Whilst the significant release of metal-enriched drainage has been documented during this event, the fate of these elements in receiving systems is still largely unknown. Here we investigate the spatial distribution, chemical partitioning, and potential bioavailability of S, Fe, Mn, Al, trace metals (V, Cr, Co, Ni, Cu, Pb) and rare earth elements in the surficial sediments of Lake Albert, South Australia; a system that received prolonged (2007–2011) acidic drainage during the Millennium Drought. The highest concentrations of all metals (Enrichment Factors ranging from 1.06–1.97) were observed in the sediments closest to shorelines where sulfidic material were oxidised, generating metal-enriched acidic drainage. Localised enrichment indicates metals have not been completely redistributed across the system following their initial deposition by physical (wind-driven resuspension) or chemical (diagenetic and redox changes) processes. Based on selective extraction data, these metals are likely partitioned as discrete sulfides (Pb) or are with organic material (V, Cr, Cu, Pb, REEs), Fe monosulfides (V, Co, Ni), or pyrite (Co, Ni, Pb). Lake-wide enrichment of trace metals Cr (mean concentration 57 ppm), Ni (39 ppm), Cu (36 ppm), and Pb (24 ppm) relative to other Lower Murray River sites is also evident, suggesting that metal contamination associated with acidic drainage is not restricted to near-source sites. Importantly, the mobilisation, transport, and accumulation of metals is controlled by sediment transport pathways and system hydrology and will thus function differently under varying states of geomorphology, climate, and anthropogenic modification. Our study shows that extreme drought is recorded as a lasting geochemical signature in estuarine sediments, demonstrating that metal and rare earth element geochemistry provides insights into the distribution and behaviour of contaminants mobilised into dynamic, anthropogenically altered estuaries.

Mangrove ecosystems can record biogeochemical and sedimentary signatures in their stratigraphic column. This study examines a mangrove sediment core to evaluate the potential environmental impact of a large-scale port-industrial construction in a tropical lagoonal–estuary near Recife, NE Brazil. Here, we measure sediment accretionrate (SAR), carbon and nitrogen stable isotopes ( δ 13 C and δ 15 N), total organic matter (TOM), total nitrogen (TN), total organic carbon (TOC), and carbonate content (CaCO 3) to determine the impact of Suape’s Port-Industrial Complex in the adjacent estuarine system. We identify a high SAR (1.37 cm yr −1) and propose three main depositional phases in the 82 cm sediment core. The first phase (circa 1956–1973) corresponds to the period prior to the installation of the Suape port complex, where the sediments are characterized by containing sand and organic material derived from terrestrial sources. The second phase (c. 1976–1986) shows signatures that reflect the installation of the Suape port complex and the intensification of the sugarcane monoculture in the catchment area. This phase shows an increase of mud and carbonate content, interpreted as a predominance of marine sediment source due to the morphological changes along the estuary. The third and final phase (c. 1986–2015) contains fluctuating results, reflecting an increase of land use, but not as intense as the period after the installation of the port complex (phase 2). Our results show a biogeochemical and sediment signature shifts directly related to anthropogenic impacts and natural factors. Overall, this study reveals a shift in the sediment sources and composition in the Suape estuarine system as a consequence of human development adjacent to estuarine areas and the resilience of mangrove ecosystems to adapt to anthropogenic impact.

Mangrove environments are important for maintaining biodiversity and carbon cycling. However, these systems are being degraded at alarming rates around the world, particularly in rapidly developing regions. Here, we examine a sediment profile from a mangrove forest near a large port complex at Suape, northeast Brazil, in order to assess the impact of rapid urbanization and industrialization. We find that total organic carbon (TOC) and total nitrogen (TN) accumulation rates have increased in the estuary since the 1980's, directly related to rapid urban development. The TN and heavy δ15N values in the sediment column suggest increasing anthropogenic influences. In contrast, heavy metal fluxes did not increase during these transitions. The increase in TOC and TN accumulation rates during the past four decades highlight the significant role mangrove areas play as sinks for anthropogenically enhanced nutrients in poorly-understood tropical areas.

Prior to the investigations in 2004–2005 of the West Mebon and subsequent analysis of archaeological material in 2015 it was presumed that the Mebon was built in the mid-11th century and consecrated only once. New data indicates a possible re-use of the water shrine and a refurbishment and reconsecration in the early 12th century, at which time a large sculpture of Viṣṇu was installed. Understanding the context of the West Mebon is vital to understanding the complex hydraulic network of Angkor, which plays a crucial role in the history of the Empire.

Yeak Loam is a volcanic crater lake in Cambodia’s northeastern uplands, and represents an important economic and cultural resource for local ethnic minority groups. The lake and the surrounding crater rim are currently protected as part of a community based natural resource management scheme. Despite this, development pressure remains high, and visible deterioration of the lake’s water quality is of great concern for the local community, visiting tourists, and the Cambodian Ministry of Environment. In this paper we blend scientific analyses with vernacular, place-based knowledge – coherent with the critical physical geography concept – to provide an integrated understanding of water quality change over more than 50 years. We find that changes in water quality have occurred episodically and irregularly over that period. Further, we find that these events are triggered by natural biogeochemical cycles within the lake, and in this instance are unlikely to be related to the type of land use within the protected area.

Preah Khan of Kompong Svay (Preah Khan) was a vast peripheral outpost of the Angkorian Khmer Empire, managed with either strong influence from the capital or semi-autonomously between the 11th and 13th centuries AD. It is believed to have held significant economic importance to the Angkorian elite given its assumed trade partnerships with the neighbouring Kuay hill tribes as well as its proximity to Phnom Dek, or “Iron Mountain”, one of Cambodia's richest known sources of iron oxide. However, the dating of a number of iron metallurgy sites found within the complex placed the heaviest period of industrial activity between the 13th and 17th centuries AD — during the decline of the Angkorian period and beyond into Cambodia's Middle Period. In this paper we present a more extensive record of occupation and use of the site, using a series of geoarchaeological and geochemical records, and show that occupation likely occurred in three stages (Stage 1, Stage 2 and Stage 3). We suggest that in Stage 1 Preah Khan was initially established as a politico-religious expression of power in this strategically important region, and during this time maintained a small, non-industrial population. By the mid-late 14th century AD (Stage 2) macrocharcoal levels increase suggesting that Preah Khan's purpose may have shifted as it became increasingly occupied or utilised for iron smelting activity, before it was finally abandoned in Stage 3, approximately half a century before the supposed abandonment of Angkor. An important question raised from this transition is whether the increased activity in the later phase represents a new wave of Khmer occupants or parasitic occupation of an abandoned temple complex by neighbouring forest-based minority groups. These results highlight the benefit of using geoarchaeological approaches in reconstructing the histories of Angkorian settlements and in increasing our understanding of the response of Khmer peripheral cities to the abandonment of the capital.

Tropical forests are the most biodiverse terrestrial ecosystems on earth, yet are particularly susceptible to future climatic and human-induced change. Identifying tipping points at which tropical ecosystems will reorganise is therefore an important research goal. Limited research within the seasonally dry tropical forests of south-east Asia means that much uncertainty exists around the resilience of these systems to future global change. This is a critical research gap because these forests should – given their physiognomic attributes, current bioclimatic envelope and the range of stressors – be very sensitive to a stable-state shift to savanna. Here we adopt a palaeoecological approach to examine the interaction between key drivers of change (decreased precipitation and heightened fire activity) and forest response over ∼4700 years though interrogation of sediment-based proxies from volcanic crater lakes within north-east Cambodia – in the core range of southeast Asia’s tropical dry forests. Our results suggest that rapidly regenerating, secondary forest taxa are important for maintaining a forested state when the landscape is subject to moderate fire and climatic disturbance. However, when these stressors are amplified, recovery and resistance traits associated with key deciduous dipterocarp forest taxa appear critical for forest stability. Notably, shifts from more closed, seasonal evergreen forest formations to more open secondary/deciduous dipterocarp formations appear reversible when the stressors are removed, suggesting that these transitions are not analogous with the difficult-to-reverse, forest-to-savanna stable state shifts that occur elsewhere in Neotropical and Afrotropical settings. Our results indicate that the resilience of south-east Asian forests to climatic forcing appears contingent on the maintenance of secondary forest, deciduous forest, and seasonal evergreen dry forest mosaics across the ecoregion. This has implications for the conservation and wise-use of mainland south-east Asia’s lowland dry forests.

Significance Contrasting models exist to explain the movement of urban populations following the 15th-century demise of Angkor. Here we present geoarchaeological data from the urban core of Angkor that indicate a protracted decline in land use intensity during the 14th century rather than an abrupt demographic collapse. These results argue against traditional explanations for the demise of Angkor, which emphasize the role of interventionist foreign powers in forcing collapse, and imply a more complex and protracted transformation., Alternative models exist for the movement of large urban populations following the 15th-century CE abandonment of Angkor, Cambodia. One model emphasizes an urban diaspora following the implosion of state control in the capital related, in part, to hydroclimatic variability. An alternative model suggests a more complex picture and a gradual rather than catastrophic demographic movement. No decisive empirical data exist to distinguish between these two competing models. Here we show that the intensity of land use within the economic and administrative core of the city began to decline more than one century before the Ayutthayan invasion that conventionally marks the end of the Angkor Period. Using paleobotanical and stratigraphic data derived from radiometrically dated sediment cores extracted from the 12th-century walled city of Angkor Thom, we show that indicia for burning, forest disturbance, and soil erosion all decline as early as the first decades of the 14th century CE, and that the moat of Angkor Thom was no longer being maintained by the end of the 14th century. These data indicate a protracted decline in occupation within the economic and administrative core of the city, rather than an abrupt demographic collapse, suggesting the focus of power began to shift to urban centers outside of the capital during the 14th century.

The historic urban collapse of Angkor is linked to infrastructural complexity and climatic variability., Complex infrastructural networks provide critical services to cities but can be vulnerable to external stresses, including climatic variability. This vulnerability has also challenged past urban settlements, but its role in cases of historic urban demise has not been precisely documented. We transform archeological data from the medieval Cambodian city of Angkor into a numerical model that allows us to quantify topological damage to critical urban infrastructure resulting from climatic variability. Our model reveals unstable behavior in which extensive and cascading damage to infrastructure occurs in response to flooding within Angkor’s urban water management system. The likelihood and extent of the cascading failure abruptly grow with the magnitude of flooding relative to normal flows in the system. Our results support the hypothesis that systemic infrastructural vulnerability, coupled with abrupt climatic variation, contributed to the demise of the city. The factors behind Angkor’s demise are analogous to challenges faced by modern urban communities struggling with complex critical infrastructure.

Throughout the Angkor period (9th to 15th centuries CE), the Khmer kingdom maintained a series of interconnected cities and smaller settlements across its territory on mainland Southeast Asia. One such city was Koh Ker, which for a brief period in the 10th century CE even served as a royal capital. The complexity of the political landscape meant the Khmer kings and the elite were particularly mobile through the Angkor period, and rupture in royal houses was common. However, while the historical record chronicles the 10th century migration of the royal seat from Koh Ker back to Angkor, the fate of Koh Ker's domestic population has remained unknown. In this article, we reconstruct the settlement history of Koh Ker, using palaeoecological and geoarchaeological techniques, and show that human activity and land use persisted in the city for several centuries beyond the city's abandonment by the royal court. These results highlight the utility of multi-proxy environmental reconstructions of Khmer urban settlements for re-evaluating prevailing assumptions regarding the use and occupation of Angkor-period cities.

Persistent drought over eastern Australia at the turn of the last millennium reduced stream flow in Australia's largest and most economically important drainage basin. Low water levels in the basin's terminal lakes triggered widespread pyrite oxidation, which altered surface water chemistry and released metals into the environment. The frequency of these events, and the links between drought and acid sulfate soil activation, are not known because the historical and instrumental records are short. Here, we present a Holocene-aged record of trace metal enrichment from Lake Albert—part of the terminal Lower Lakes system of the Murray-Darling Basin, Australia—that demonstrates the potential of trace elements mobilised during acidification events for palaeodrought reconstructions. Symptomatic metals were measured from a core of clayey sediment to form a multi-element assemblage that reveals acidification events in the geological past. Correlation with regional climate proxies suggests that climate forcing is significant in driving metal flux to estuarine sinks in acid sulfate soil rich landscapes, although the intensity of a drought is not the only variable responsible for acidification intensity. The constructed record indicates that regional climate moved from a generally humid climate phase with intermittent droughts, to a more arid climate at ~ 5.2 ka which prevailed until ~ 1.7 ka. Following conditions were relatively wet with low climatic variability through till European Settlement. Enrichment is observed coincident with both the 1982–83 drought and Millennium Drought, the latter of which reaching an intensity unsurpassed in the last ~ 4.8 ka, likely a product of anthropogenic changes to the Lower Murray-Darling Basin system.

SUMMARYReconstructing the environmental history of protected areas permits an empirically-based assessment of the conservation values ascribed to these sites. Ideally, this long-term view can contribute to evidence-based management policy that is both ecologically ‘realistic’ and pragmatically feasible. Lachlan Nature Reserve, a protected wetland in Centennial Park, Sydney, is claimed to be the final remnant of early and pre-European swamplands that were once extensive in the area, and the site is thus considered to have indigenous cultural and natural conservation significance. This study uses palynological techniques to reconstruct vegetation communities at the Reserve from the late Holocene to the present in order to assess whether these values adequately reflect the history, character and development of the site. The findings indicate that the modern site flora is a modified Melaleuca quinquenervia low forest assemblage formed in response to aggregated anthropogenic disturbance since colonial settlement. This assemblage replaces an Epacris-dominated heath-swampland community that was extirpated in the mid-20th century. These results emphasize the value of long-term studies in contributing to a realistic management policy that explicitly reflects the normative basis of conservation, and values the influence of past land-uses on contemporary protected ecosystems.

We report the chronological construction for the top portion of a speleothem, PC1, from southern Cambodia with the aim of reconstructing a continuous high-resolution climate record covering the fluorescence and decline of the medieval Khmer kingdom and its capital at Angkor (~9th–15th centuries AD). Earlier attempts to date PC1 by the standard U-Th method proved unsuccessful. We have therefore dated this speleothem using radiocarbon. Fifty carbonate samples along the growth axis of PC1 were collected for accelerator mass spectrometry (AMS) analysis. Chronological reconstruction for PC1 was achieved using two different approaches described by Hua et al. (2012a) and Lechleitner et al. (2016a). Excellent concordance between the two age-depth models indicates that the top ~47 mm of PC1 grew during the last millennium with a growth hiatus during ~1250–1650 AD, resulting from a large change in measured14C values at 34.4–35.2 mm depth. The timing of the growth hiatus covers the period of decades-long droughts during the 14th–16th centuries AD indicated in regional climate records.

Clastic spring sediments, the product of groundwater transport by fissure or conduit flow, remain largely uninvestigated. Yet such sediments may be much more common than has generally been realised and examples within the stratigraphic record are likely to have been widely overlooked. This study investigates the potential of these deposits for preserving a history of past floods. Clastic spring sediments at Mount McKinlay Spring in the hot, arid Gammon Ranges of northeast South Australia were dated by 14C analysis. Five samples of pollen grains taken from sediments interpreted on geomorphic grounds as post-dating European contact (AD 1843) all yielded dates of AD 1955–1958. These are likely to be the product of sedimentation in March 1956 following the greatest single day’s rainfall in the instrumental record. This event, with a return period of around 100 years, may have caused the undercutting of the banks of the creek downstream of the springs, the collapse of mature River Red Gums growing adjacent to the channel and the accumulation of a jam of logs across the creek. The spring deposits appear to represent solely the product of high-magnitude, long return-period floods. A series of older spring sediments at the site dating from the first millennium BC to the mid-18th century may therefore provide an opportunity to establish event magnitude and frequency, to determine return periods, and to assess the role of climatic change and human environmental impact on flood frequency. This approach may offer a valuable means of reconstructing the chronology of floods, particularly in locations affording few other sources of palaeoenvironmental information.

Of the many myths surrounding the medieval city of Angkor, Cambodia, one of the most obscure but pervasive is the existence of a road built across the Tonle Sap Lake. This road supposedly ran from the Angkorian ‘port’ at Phnom Krom to the temples situated in the Battambang district some 70 km southwest of capital. New geoarchaeological information demonstrates that the ‘road’ is actually a series of localised occurrences of authegenic calcite, which probably formed approximately 5500 years Before Present. Our results demystify this intractable Cambodian legend expand on the dynamic history of this important water body in mainland Southeast Asia.

The “hydraulic city” of Angkor, the capitol of the Khmer Empire in Cambodia, experienced decades-long drought interspersed with intense monsoons in the fourteenth and fifteenth centuries that, in combination with other factors, contributed to its eventual demise. The climatic evidence comes from a seven-and-a-half century robust hydroclimate reconstruction from tropical southern Vietnamese tree rings. The Angkor droughts were of a duration and severity that would have impacted the sprawling city’s water supply and agricultural productivity, while high-magnitude monsoon years damaged its water control infrastructure. Hydroclimate variability for this region is strongly and inversely correlated with tropical Pacific sea surface temperature, indicating that a warm Pacific and El Niño events induce drought at interannual and interdecadal time scales, and that low-frequency variations of tropical Pacific climate can exert significant influence over Southeast Asian climate and society.

Meticulous survey of the banks, channels and reservoirs at Angkor shows them to have been part of a large scale water management network instigated in the ninth century AD. Water collected from the hills was stored and could have been distributed for a wide variety of purposes including flood control, agriculture and ritual while a system of overflows and bypasses carried surplus water away to the lake, the Tonle Sap, to the south. The network had a history of numerous additions and modifications. Earlier channels both distributed and disposed of water. From the twelfth century onwards the large new channels primarily disposed of water to the lake. The authors here present and document the latest definitive map of the water network of Angkor.

It has been claimed that Tonle Sap Lake is rapidly filling with sediment as a result of increasing sediment yields from the catchment. Infilling of the lake basin would have serious implications for the magnitude of flooding in central Cambodia and the Mekong Delta region and threaten the lake's unique ecosystem. In this article, we synthesize the results of radiocarbon dating of sediment cores and hydrodynamic modeling results to provide an empirically based assessment of this issue. We find that current sedimentation rates within the lake basin proper are low and have been for several millennia. However, sedimentation at the lake margin and in its floodplain is relatively high, which presents a range of issues for riparian communities.

A new global synthesis and biomization of long (> 40 kyr) pollen-data records is presented and used with simulations from the HadCM3 and FAMOUS climate models and the BIOME4 vegetation model to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial–interglacial cycle. Simulated biome distributions using BIOME4 driven by HadCM3 and FAMOUS at the global scale over time generally agree well with those inferred from pollen data. Global average areas of grassland and dry shrubland, desert, and tundra biomes show large-scale increases during the Last Glacial Maximum, between ca. 64 and 74 ka BP and cool substages of Marine Isotope Stage 5, at the expense of the tropical forest, warm-temperate forest, and temperate forest biomes. These changes are reflected in BIOME4 simulations of global net primary productivity, showing good agreement between the two models. Such changes are likely to affect terrestrial carbon storage, which in turn influences the stable carbon isotopic composition of seawater as terrestrial carbon is depleted in 13C.

Angkor was the capital city of the Khmer kingdom from the latter half of the first millenniumAD. At its peak in the eleventh to twelfth century AD, the Khmer kingdom incorporated Cambodia, southern Vietnam, southern Laos, and parts of Thailand. Angkor was the primate city of this vast kingdom and was connected to a network of smaller, satellite cities by an extensive road system (Hendrickson, 2010). King Jayavarman II founded Angkor, it is commonly said, in 802 AD, proclaiming himself the universal king and unifying a constellation of smaller chiefdoms that were grouped by Chinese visitors under the generic names “Funan” and “Chenla.” However, this date comes from a stone inscription (K235; Coedes & Dupont, 1943–1946) written hundreds of years after the events it depicts, and its veracity is widely questioned (Vickery, 1998). Indeed, many of the early state temples that characterized Angkor’s urban form may be much older than the epigraphic evidence suggests (Penny et al., 2006; Pottier, 1996). Whatever the date of Angkor’s establishment as a city, it likely emerged from a long period of occupation in the area that dates back to the second millennium BC. No primary historical documents (stone inscriptions in Khmer and Sanskrit) from Angkor are known after the end of the thirteenth century AD. Monumental construction in the capital also ceased at this time. It is not until the late sixteenth century that European visitors – initially Portuguese missionaries and merchants – began to describe Angkor (Groslier, 1958). At that time, the city was in ruin, almost completely abandoned and overgrown with forest. More detailed accounts emerged in the nineteenth century from explorers such as Henri Mouhot – often incorrectly credited with the “discovery” of Angkor in 1860 – and in the subsequent and ultimately ill-fated “Mekong Expedition” of 1866, led by Doudart de Lagree (Osborne, 1996). The romantic notion of the ruined city conjured in nineteenth-century Europe by these reports from the Far East was, in part, fanciful. Angkor was never completely abandoned by the Khmer, and in fact the city was re-occupied – if only briefly – by a Khmer king in the 1550s. AngkorWat was probably continuously occupied by Theravāda Buddhist monks, and significant construction occurred in the sixteenth century at Angkor Wat and extensively within the enclosure of Angkor Thom (Jacques, 2007).

Angkorian temples are characterised by one or more encircling moats that are excavated into the alluvial substrate. As a key part of the overall design of the temple, the moats are important symbolically and are presumed to be contemporaneous with the associated temple. They also represent important depositional basins for sediment and other materials and can therefore yield vertical profiles of sediment that has accumulated since the moat was originally excavated. Unconformities in these moat profiles can be dated absolutely using small-sample, high-precision AMS radiocarbon techniques. These unconformities are likely to represent periodic re-excavation or maintenance of the moat and therefore indicate the presence of large, presumably centrally organised workforces. In some instances, presumed anthropogenic unconformities occur centuries after Angkor was supposedly abandoned. In this way, radiocarbon dates themselves are being used as a proxy indicator of cultural activity and are being used to challenge the historiography of Angkor's famous demise. (c) 2007 Elsevier B.V. All rights reserved.

Work to apply luminescence dating to archaeological sites in the Lower Mekong Delta has continued with a programme aimed at dating ancient canal sediments and brick monuments in the vicinity of ancient city of Angkor Borei. Following the successful application of OSL dating to the Paris 2 canal near Angkor Borei further fieldwork and analysis has been undertaken. The infill and substrate of the larger Paris 4 canal connecting Angkor Borei to Oc Eo, some 80 km to the south in Vietnam has been sampled and subjected to luminescence analysis. Field spectroscopy and underwater bleaching experiments were also conducted in the Baray and Angkor Borei in 2004. The results show that both illumination intensities and spectral distributions are severely altered by as little as 1.5 m of turbid water, and that OSL bleaching rates for both quartz and feldspars are reduced. Since quartz resetting is heavily dependant on the UV components in daylight, which have preferentially attenuated the effects of turbid water on OSL zeroing rates are especially marked. The new data from the Paris 4 canal, which has been dated by OSL to be between the first millenium BC and the late first millenium AD are significant to understanding the archaeological development of the Fu Nan state in the Lower Mekong Delta, and the sequence of development of the canal network linking inland agrarian sites and coastal trading centres.

Pollen and diatom analyses of organic sediments from Three-Quarter Mile Lake, a perched lake on Cape York Peninsula, north Queensland, indicate that significant changes in vegetation and hydrology occurred during the Holocene. Early Holocene grass-dominated landscapes were replaced in mid-Holocene times by increasingly woody vegetation comprising tropical heathlands, savanna and rainforest. Early-Holocene lake levels fluctuated widely. From mid-Holocene times, lake levels stabilized and water became increasingly acidic as a mature swamp forest developed adjacent to the lake and contributed tannins to the lake water. The timing and character of changes are consistent with those described from the Atherton Tableland in wet tropical Queensland. Holocene dry phases described from the Northern Territory and the western shores of Cape York cannot be identified from Three-Quarter Mile Lake. Rainforest is currently close to its greatest Holocene extent, suggesting that the rainforest-dependent endemic fauna of northern Cape York have been isolated from rainforest blocks to the south throughout the last 10 000 years and, by inference, throughout at least the 120 000 years beyond that.

The Tonle Sap, the ‘Great Lake’ of central Cambodia, is the central component of wetland ecosystems in the lower Mekong River basin, and is of enormous conservation value. The lake's unusual hydraulic relationship with the Mekong River, and its consequent sensitivity to monsoon variability, makes the Tonle Sap sensitive to climate change. Exploring the dynamics and development of this system under different climate regimes of the past offers a perspective on possible future impacts, which is critical for sound management. Biostratigraphic and sedimentological data derived from cores of lake sediment indicate that during the period >7000 to ca. 5500 14 C years Before Present the lake was less variable than present in terms of depth during the annual cycle of flood, and may have been strongly influenced by saline tidal waters associated with higher-than-present seas levels. As regional environments became drier and more seasonal in the late Holocene, more sediment was re-suspended during the increasingly marked dry season lake level minimum, lowering the effective sediment accumulation rate. Contrary to current interpretations of the history of the lake and associated wetland ecosystems, the data presented here imply that regional hydraulic connections between the lake and the Mekong River existed from at least the early Holocene.

The Tonle Sap is an invaluable resource for the people of Cambodia, and is a globally significant ecological site. Much of the literature published on the environmental health and management of the lake suggests that its sustainability is threatened by accelerated rates of infilling related to unfettered land-use in the catchment. However, the evidence for supposedly increased sedimentation rates is confused and contradictory, and there have been very few studies that have attempted to actually measure the rate at which sediment is accumulating on the bed of the lake. This research measures long-term sedimentation rates in the Tonle Sap in an attempt to provide an empirically derived ‘baseline’ against which more recent and allegedly accelerated sedimentation rates can be compared. Radiometric dating techniques (14C, 210Pb, 137Cs) reveal that sediment has been accumulating in the lake at an average long-term rate of less than 1 mm per year. There is a clear and consistent decline in the rate of sediment accumulation in the lake basin over time, with the highest rates recorded in the middle to early Holocene epoch. It is recommended that research be directed toward measuring changes in the morphology of the lake margin over time, rather than focus on changes in the bathymetry of the lake basins themselves, which are here shown to be effectively stable in terms of sediment accumulation.

Palaeo-environmental data from accumulated lake sediments at Phayao, northwest Thailand, provide a record of vegetation and environmental change from approximately 20,000 years Before Present. This is an important region archaeologically, with claims in the 1970s for an ‘early’ transition to domestication having arisen from a number of cave sites. Multiple indices are used to determine if people had an observable impact on the natural environment, and to determine the timing and magnitude of impacts associated with the development of agricultural land use in the region. An initial increase in sedimentation rate is apparent from ca. mid-2nd C AD. Changes in phytoplankton concentrations are apparent from the late 3rd C AD, and evidence for initial forest disturbance is apparent from the 5th or 6th C AD, with impacts becoming more severe over time to reach a pre-modern maximum in the 11th to the 13th C AD. Changes in agricultural practices are apparent during the 14th C AD, with an increased emphasis on rice agriculture and incipient management of the regenerating forests. Based on these data we suggest that agricultural intensification in the early part of the 1st millennium AD destabilised catchment slopes, through clearance of dryland vegetation and swidden agriculture. There is no direct evidence for the impacts of earlier peoples on the vegetation of the area, which we take to indicate that agricultural intensification was later here than in the lowlands to the east and south.

Aim: This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid- Holocene and at the last glacial maximum (LGM). Methods: Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 14C yr BP. Results: 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad-scale patterns of vegetation distribution. The north-south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed-canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad-scale pattern emerges. 2. Differences between the modern and mid-Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south-eastern Australia some sites show a shift towards more moisture-stressed vegetation in the mid-Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm- temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture- demanding vegetation in the mid-Holocene than today. South-western Australia was slightly drier than today. The single site in north-western Australia also shows conditions drier than today in the mid-Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid-Holocene, in sites occupied today by cool- temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9°C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions: This study provides the first continental-scale reconstruction of mid-Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project.

Reconstruction of the environmental history of mainland Southeast Asia from the late Pleistocene is a relatively recent endeavor. Beginning in the mid-1990s, lacustrine sediments in Thailand with deposits dating from the late Pleistocene have been cored and analyzed for palaeoenvironmental indicators. The three cores reported here were extracted by the Thailand Palaeoenvironment Project, whose objective was to retrieve empirical data on vegetation and sedimentary sequences that can in turn be related to the growing archaeological record from this part of monsoonal Asia. This evidence, along with data from other recently analyzed cores, is beginning to develop a picture of regionally diverse environmental/cultural trajectories. Possible relationships between the environmental changes and cultural and/or climatic impacts are discussed.