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The study of climate mechanisms in the Southern Hemisphere during the Holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of Northern Hemisphere research. The subtropical/temperate climate transition zone of eastern Australia provides a unique location to investigate long-term environmental changes during the Holocene. Lake Jennings on Fraser Island was used to investigate climate change in this transition zone using palaeolimnological techniques. The beginning of the Lake Jennings record (~6000 to 3500 cal. yBP), is characterised by fluctuations in geochemical signals, an abundance of sponge spicules, and a lack of diatom species. Results suggest gradually increasing precipitation and water depth, which affect nutrient cycling. However, the biological functioning of the lake is difficult to interpret due to the absence of diatoms, possibly a result of turbidity, dissolution and/or predation by freshwater sponges. During the late Holocene, ~3500 cal. yBP to present, precipitation and water depth of the lake decreases to present day levels. Within this section of the core nutrient cycling changes, as indicated by the geochemical results, and a series of more intense wet and dry events took place before stabilising at present day levels. Other palaeoecological studies within the Southern Hemisphere have noted changes in geochemical and biological attributes within similar latitudes, confirming the notion of climate forced environmental change in aquatic ecosystems. This continuous ~6000 year record from Lake Jennings shows distinct changes in aquatic communities, confirming a trend of drying in subtropical eastern Australia through the late Holocene. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3calkaBP and 14.0calkaBP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3calkaBP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene. [ABSTRACT FROM AUTHOR]

New pollen, phytolith, charcoal and diatom data from 14C AMS-dated sediments from three clusters of former occupation sites on the southern Yangtze Delta – Liangzhu, Majiabang and Chuodun – reveal that hydrological conditions were a key factor influencing early food production on the southern Yangtze Delta. At least two episodes of inundation are recognized, the first occurring at c. 7200–5700 cal. yr BP and a second from c. 4700 cal. yr BP. The first involved increasing salinity of surface waters, likely associated with marine intrusion linked to post-glacial sea-level change (meltwater pulse (MWP) 2). The second appears to have been freshwater in nature and driven at least in part by extreme meteorological events of high levels of precipitation in combination with impeded drainage. These two episodes had profound impacts on Neolithic settlement and farming. Further hydrological changes, presumably linked to changes in sedimentary regime, geomorphology and drainage of the Taihu depression, recorded at the Chuodun site after c. 3000 cal. yr BP, appear to have had a major effect on technologically relatively advanced food production systems. While environmental pressures appear to have played an important role in shaping human activities and settlement on the southern Yangtze Delta, people responded by adopting strategies that included an increased reliance on food production, migration to more clement locations and implementation of new technologies, which possibly included the construction of flood defence works. [ABSTRACT FROM AUTHOR]

Abstract: Analyses of sedimentary evidence in the form of spores, pollen, freshwater algae, dinoflagellate cysts, phytoliths and charcoal from AMS 14C-dated, Holocene-aged sequences provide an excellent opportunity to examine the responses of Neolithic agriculturalists in the lower Yangtze to changing environments. Evidence from two sites close to the southern margin of the Yangtze delta and separated by what is now Hangzhou Bay attests the critical importance to early attempts at food production of access to freshwater resources. More readily, if episodically, available freshwater resources during the early to mid-Holocene on the Hangjiahu plain may have encouraged an early reliance on rice-based agriculture, which in turn facilitated the accumulation of agricultural surpluses and cultural diversification. Cultural change was relatively attenuated and human population pressures possibly lower on the Ningshao plain, seemingly because of much more profound environmental impacts of variations in local hydrological conditions, and because predominantly saline conditions, associated with rising relative sea level, hampered the early development of irrigated agriculture. The evidence, although largely dating to the early and middle parts of the Holocene, provides a timely warning of the complexity of vulnerability to climate change-induced processes of agriculture, and indeed human activities more generally, on megadeltas in Asia. [ABSTRACT FROM AUTHOR]

Multiproxies of past environmental conditions, comprising 53 sediment samples analysed for their lithostratigraphic properties (mainly their charcoal, phytoliths and pollen contents) from an AMS 14C-dated sequence of sediments accumulating at Guangfulin, Yangtze delta, are presented. The oldest sediments recovered date to the Lateglacial when a mosaic of mixed (conifer-deciduous) temperate forest and wetland vegetation characterized the study area. The Lateglacial-Holocene transition and much of the early Holocene record to c. 7400 yr BP appears to be missing from the sequence. The earliest evidence possibly representing human activities in the study area (the remains of cereals and indicators of forest) date to c. 7000 yr BP. A large increase in macrocharcoal remains c. 4700 yr BP is a more certain indication of human activities close to the study site, and may indicate the first occupation of what is now the location of a major archaeological excavation at Guangfulin. Technological changes during the Eastern Zhou Dynasty (770-221 BC) may be responsible for an increased abundance of rice (Oryza sp.), and possibly also foxtail or Chinese millet (Setaria italica), detected in the Guangfulin record after c. 2400 yr BP. An abrupt sedimentary change at c. 4000 yr BP may represent a short-lived episode of catchment instability. Aside from this, the sediment record from Guangfulin contains no evidence of dramatic environmental changes that could have led to a major decline in agricultural productivity c. 4000 yr BP, as has been suggested for the lower Yangtze by some researchers, who associate this with the cultural transition from Liangzhu to Maqiao. The findings do, however, add weight to the argument that developments in rice-based agriculture on the Yangtze delta varied both spatially and temporally. [ABSTRACT FROM AUTHOR]

The lower Yangtze, eastern China, was colonized by several Neolithic and Bronze Age cultures giving rise to possibly the highest concentration of prehistoric sites in the world. Early Neolithic cultures in the delta region cultivated rice (Oryza sativa) and agricultural developments appear to have occurred throughout the Neolithic with abrupt socio-economic changes possibly associated with the terminal Neolithic. Given the extensive history of environmental exploitation and well-preserved archaeological sites, the Yangtze delta is an ideal setting to explore the complex interactions between humans and their environment. Multiproxies of environmental changes, namely pollen, charcoal and phytoliths, in a 14C AMS-dated sequence of sediments from an exposed profile at Qingpu, Yangtze delta, were investigated. 14C AMS dating indicates that the age range of the sedimentary sequence analysed is from c. 1800 to 6000 BP, and therefore encompasses the terminal Neolithic and subsequent Bronze Age in the region. This paper reviews this sediment-based evidence in the light of current understanding of human-environment interactions during a critical phase of the development of the Yangtze delta and associated human cultures. [ABSTRACT FROM AUTHOR]