Pollen, biomarker and stable isotope evidence of late Quaternary environmental change at Lake McKenzie, southeast Queensland

Unravelling links between climate change and vegetation response during the Quaternary is important if the climate–environment interactions of modern systems are to be fully understood. Using a sediment core from Lake McKenzie, Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over the last ca. 36.9 cal kyr. Evidence is drawn from multiple sources, including pollen, micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to gain a better understanding of the nature and timing of past ecological changes that have occurred at the site. The glacial period of the record, from ca. 36.9 to 18.3 cal kyr BP, is characterised by an increased abundance of plants of the aquatic and littoral zone, indicating lower lake water levels. High abundance of biomarkers and microfossils of the colonial green alga Botryococcus occurred at this time and included large variation in individual botryococcene d13C values. A slowing or ceasing of sediment accumulation occurred during the time period from ca. 18.3 to 14.0 cal kyr BP. By around 14.0 cal kyr BP fire activity in the area was reduced, as was abundance of littoral plants and terrestrial herbs, suggesting wetter conditions from that time. The Lake McKenzie pollen record conforms to existing records from Fraser Island by containing evidence of a period of reduced effective precipitation that commenced in the mid-Holocene

Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie

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 18.3 cal ka BP and 14.0 cal ka BP 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 18.3 cal ka BP 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

Climate instability during the last deglaciation in central Asia, reconstructed by pollen data from Yili Valley, NW China

An extended pollen record with grain size analysis and AMS C-14 dating is provided for a palaeolake section which is located in an intermountain basin in Yili Valley, Xinjiang, NW China. Covering the late MIS 3, early MIS 2 and the last deglaciation, vegetation variations and climate events are discussed in relation to changes in pollen assemblages and Artemisia/Chenopodiaceae (A/C) ratios. The presence of montane forest-steppe dominated by Picea and Taraxacum indicates a relative humid climate in the study area during late MIS 3 (before 31.5 cal kyr BP). Picea forest disappeared and the vegetation dominated by Chenopodiaceae shows the climate became dry from 31.5 to 14.7 cal kyr BP. The sediments of Last Glacial Maximum (LGM) period are absent in the section probably. Betula-Picea mixed forest occurred at 14.7 cal kyr BP and corresponds to the onset of the warm Bolling period in the North Atlantic. A long dry period was detected from 14.5 to 13.6 cal kyr BP on the basis of the occurrence of Chenopodiaceae desert. A subalpine meadow community dominated by Geranium covered the area during 13.6-13.4 cal kyr BP, suggesting lower temperatures at this time. This may coincide with the Older Dryas (OD). The most humid period in the record occurred between 13.4 and 12.9 cal kyr BP, which coincides with the warm Allerod period. Dry conditions prevailed from similar to 12.9 to 11.7 cal kyr BP in the area, coinciding with the Younger Dryas (YD) in the North Atlantic. Within this period a three-phase climate fluctuation was detected, which can be summarized as follows: a dry early YD (12.9-12.6 cal kyr BP), a slightly moister mid-YD (12.6-12.0 cal kyr BP) and a very dry late YD (12.0-11.7 cal kyr BP). These millennial to century-scale climatic events in Yili Valley correlate well with other palaeoclimate records in North Hemisphere, suggesting that these events probably originate from same mechanisms.</p

Evolution of prehistoric dryland agriculture in the arid and semi-arid transition zone in northern China.

Based on chronological and archaeobotanical studies of 15 Neolithic and Bronze Age sites from the northern Chinese Loess Plateau and southern Inner Mongolia-the agro-pastoral zone of China-we document changes in the agricultural system over time. The results show that wheat and rice were not the major crops of the ancient agricultural systems in these areas, since their remains are rarely recovered, and that millet cultivation was dominant. Millet agriculture increased substantially from 3000 BC-2000 BC, and foxtail millet evidently comprised a high proportion of the cultivated crop plants during this period. In addition, as the human population increased from the Yangshao to the Longshan periods, the length and width of common millet seeds increased by 20-30%. This demonstrates the co-evolution of both plants and the human population in the region. Overall, our results reveal a complex agricultural-gardening system based on the cultivation of common millet, foxtail millet, soybeans and fruit trees, indicating a high food diversity and selectivity of the human population

Mid-Holocene palaeolimnological record of a Southern Hemisphere subtropical lake spanning the last ~6000 years: Lake Jennings, Fraser Island, Australia

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

Climatic variations over the last 4000 cal yr BP in the western margin of the Tarim Basin, Xinjiang, reconstructed from pollen data

The nature of Holocene climate patterns and mechanisms in central Asia are open areas of inquiry. In this study, regional vegetation and climate dynamics over the last ca. 4000 years are reconstructed using a high resolution pollen record from the Kashgar oasis, on the western margin of the Tarim Basin, central Asia. Ephedra, Chenopodiaceae and Cannabaceae dominate the pollen assemblages, and Chenopodiaceae/Ephedra ratios and percentages of long-distance transported pollen taxa are used to infer regional variations in moisture and vegetation density. Three periods of increased humidity are identified, from ca. 4000-2620 cal yr BP, ca. 1750-1260 cal yr BP and ca. 550-390 cal yr BP and these periods coincide with the respective Holocene Bond Events 2,1 and 0, which are reported in the North Atlantic. Any increase in strength, or southward migration, of the mid-latitude westerlies would result in more precipitation and meltwater on mountains surrounding the study site. Warm and dry conditions are detected between ca.1260 and 840 cal yr BP (AD 690-1110), and cool and wet conditions are detected between ca. 840 and 680 cal yr BP (AD 1110-1270), during the Medieval Warm Period (ca. AD 800-1200). The climate variations in the Kashgar region over the last 4000 years appear to have been dominated by changes to the westerly circulation system and glacier dynamics on surrounding mountains. However, the question of whether the Asian monsoon delivers precipitation to the western Tarim Basin, a region that is influenced by several climate systems, is still open to debate.</p

Origin and spread of wheat in China

Wheat was added as a new crop to the existing millet and rice based agricultural systems of China. Here we present 35 radiocarbon ages from wheat seeds collected from 18 sites between western (Xinjiang Province) and eastern (Henan Province) China. The earliest wheat ages cluster around 2100-1800 BCE in northern China&#39;s Hexi corridor of Gansu Province, where millet was already a well-established crop. Wheat first appears in Xinjiang and Henan about 300-400 years later, and perhaps a little earlier than this in Xinjiang, and we hypothesize that the likely route of wheat into China was via Russia through Gansu.</p

Subsistence and the isotopic signature of herding in the Bronze Age Hexi Corridor, NW Gansu, China

Dietary patterns at two Bronze Age sites in the Hexi Corridor are investigated by the analysis of stable carbon and nitrogen isotopes in faunal bone collagen. The findings are compared with archaeobotanical remains from one of the sites which include high proportions of millet (Panicum miliaceum and Setaria italica) as well as the western derived cereals wheat (Triticum aestivum), barley (Hordeum vulgare) and oat (Avena sativa). The isotopic data indicate domestic omnivores (Canis and Sus) had diets dominated by millet. Minimally offset delta(15)N values between herbivore and omnivore fauna suggest low consumption of animal protein by omnivores. Diets of herded animal (Bos and Caprinae) included only low proportions of C4 foods, suggesting that these animals were not regularly foddered with millet plants, and that their grazing areas were mostly beyond the agricultural zone. The wide range in delta(15)N values amongst herbivore fauna (4.1 parts per thousand-11.8 parts per thousand) suggests grazing occurred in a variety of ecological zones, and this would be consistent with the occurrence of long-distance transport of livestock in the region.</p

Morphological characteristics (average length and width) of carbonized seeds of foxtail millet (<i>Setaria italica</i>) and common millet (<i>Panicum miliaceum</i>).

<p>Morphological characteristics (average length and width) of carbonized seeds of foxtail millet (<i>Setaria italica</i>) and common millet (<i>Panicum miliaceum</i>).</p

Results of AMS radiocarbon dating of samples from cultural horizons at the studied archaeological sites.

<p>All results are reported with 2 sigma error. ¹⁴C ages are calibrated to calendar years using Calib Rev 5.1 and OxCal v4.3.6, with the r:5 IntCal 13 atmospheric curve.</p