Dan Penny

Climate as a contributing factor in the demise of Angkor, Cambodia

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.

Late Quaternary palaeoecology, palynology and palaeolimnology of a tropical lowland swamp: Rawa Danau, West-Java, Indonesia

Abstract Sedimentological, limnological and palynological analyses of a sediment core from a lowland site in West-Java, Indonesia, provide a detailed palaeoenvironmental record for the Late Glacial and the Holocene. The record suggests open vegetation under inferred drier climatic conditions for the Late Glacial. However, there is no unequivocal evidence for cooler conditions at this time. The onset of the Holocene coincides with a change to more humid climatic conditions, with the development of a fern-rich closed forest vegetation type. Dramatic changes in diatom community composition provide a striking record of habitat change associated with lake shallowing, but this process appears to be a result of basin in-filling rather than variations in precipitation/evaporation balance associated with climatic fluctuations. Evidence for human impact on the vegetation development is restricted to the last few hundred years.

Sediment: Curse or Blessing for Tonle Sap Lake?

Abstract 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 lakes 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.

The water management network of Angkor, Cambodia

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.

Vegetation and land-use at Angkor, Cambodia : a dated pollen sequence from the Bakong temple moat

Investigating the use of land during the medieval period at the celebrated ceremonial area of Angkor, the authors took a soil column over 2.5m deep from the inner moat of the Bakong temple. The dated pollen sequence showed that the temple moat was dug in the eighth century AD and that the agriculture of the immediate area subsequently flourished. In the tenth century AD agriculture declined and the moat became choked with water-plants. It was at this time, according to historical documents, that a new centre at Phnom Bakeng was founded by Yasovarman I.

Holocene palaeoenvironments and change at Three-Quarter Mile Lake, Silver Plains Station, Cape York Peninsula, Australia

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 Mekong at Climatic Crossroads: Lessons from the Geological Past

Abstract The wetlands of the lower Mekong River Basin are ecologically and socioeconomically significant, but they are threatened by predicted climatic change. The likely response of wetland ecosystems to altered flooding regimes and surface-water chemistry is unknown in detail and difficult to model. One way of exploring the impact of climate change on wetland ecosystems is to utilize proxy environmental data that reveal patterns of change over geological time. In recent years, the coverage and resolution of proxy climatic data have improved markedly in the region. Recent evidence of the South China Sea transgression into southern and central Cambodia and paleobotanical evidence from the Tonle Sap (“Great Lake”) and elsewhere allow us to explore how periods of higher-than-present sea level and increased monsoon rainfall in the past have impacted the wetland ecology of the lower Mekong River Basin.

The Environmental Impact of Cambodia's Ancient City of Mahendraparvata (Phnom Kulen)

The Khmer kingdom, whose capital was at Angkor from the 9th to the 14th-15th century, was founded in 802 by king Jayavarman II in a city called Mahandraparvata, on Phnom Kulen. Virtually nothing more is known of Mahandraparvata from the epigraphic sources, but systematic archaeological survey and excavation have identified an array of cultural features that point to a more extensive and enduring settlement than the historical record indicates. Recent remote sensing data have revolutionized our view, revealing the remains of a city with a complex and spatially extensive network of urban infrastructure. Here, we present a record of vegetation change and soil erosion from within that urban network, dating from the 8th century CE. Our findings indicate approximately 400 years of intensive land use, punctuated by discrete periods of intense erosion beginning in the mid 9th century and ending in the late 11th century. A marked change in water management practices is apparent from the 12th century CE, with implications for water supply to Angkor itself. This is the first indication that settlement on Mahendraparvata was not only extensive, but also intensive and enduring, with a marked environmental impact.

Ecological history of Lachlan Nature Reserve, Centennial Park, Sydney, Australia: a palaeoecological approach to conservation

SUMMARY Reconstructing 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 preEuropean 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.

Radiocarbon dating of a speleothem record of paleoclimate for Angkor, Cambodia

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 measured 14 C 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.