Jiantao Xue

Paleotemperature variability in central China during the last 13 ka recorded by a novel microbial lipid proxy in the Dajiuhu peat deposit

The Asian summer monsoon is a very important climatic component affecting the land ecosystem on the eastern Asian continent. Here we assess microbe-derived lipid biomarker evidence from a well-dated peat core from Dajiuhu to reconstruct paleotemperature changes in central China through the last 13 ka. The branched fatty alcohol ratio BNA15, which is defined as the relative contribution of branched C15 fatty alcohols over their straight-chain homolog, shows a positive correlation with air temperature (R= 0.83, n=11, p<0.001) in an altitude transect at Shennongjia Mountain, central China. This correspondence suggests that the microbial activities associated with branched fatty alcohol synthesis are sensitive to differences in temperature. The BNA15 sequence in the Dajiuhu peat deposit shows a trend similar to the paleotemperature record derived from pollen results over the last 13 ka, further supporting that BNA15 is a sensitive proxy of paleotemperature. Absolute temperatures estimated from BNA15 values of modern surface peats are about 3–4°C lower than the modern annual mean air temperature in the peatland, which may result from the influences of factors other than temperature or from the different microbial communities in the mountain soils used to calibrate the BNA15 acidic peats. Fluctuations in the continuous 13 ka BNA15-derived record of relative temperature change from the Dajiuhu peat core imply that solar activity is the dominant cause for most cold events at multicentennial to submillennial timescales.

Molecular Paleoclimate Reconstructions over the Last 9 ka from a Peat Sequence in South China

To achieve a better understanding of Holocene climate change in the monsoon regions of China, we investigated the molecular distributions and carbon and hydrogen isotope compositions (δ13C and δD values) of long-chain n-alkanes in a peat core from the Shiwangutian (SWGT) peatland, south China over the last 9 ka. By comparisons with other climate records, we found that the δ13C values of the long-chain n-alkanes can be a proxy for humidity, while the δD values of the long-chain n-alkanes primarily recorded the moisture source δD signal during 9–1.8 ka BP and responded to the dry climate during 1.8–0.3 ka BP. Together with the average chain length (ACL) and the carbon preference index (CPI) data, the climate evolution over last 9 ka in the SWGT peatland can be divided into three stages. During the first stage (9–5 ka BP), the δ13C values were depleted and CPI and Paq values were low, while ACL values were high. They reveal a period of warm and wet climate, which is regarded as the Holocene optimum. The second stage (5–1.8 ka BP) witnessed a shift to relatively cool and dry climate, as indicated by the more positive δ13C values and lower ACL values. During the third stage (1.8–0.3 ka BP), the δ13C, δD, CPI and Paq values showed marked increase and ACL values varied greatly, implying an abrupt change to cold and dry conditions. This climate pattern corresponds to the broad decline in Asian monsoon intensity through the latter part of the Holocene. Our results do not support a later Holocene optimum in south China as suggested by previous studies.

Testate amoebae as indicators of water quality and contamination in shallow lakes of the Middle and Lower Yangtze Plain

Testate amoebae are micro-organisms characterized by an agglutinated or autogenous shell enclosing the cytoplasm. Testate amoebae have been widely proposed as valuable bioindicators in a range of ecosystems (such as soils, peatlands and lakes). The use of testate amoebae as bioindicators of water quality in aquatic ecosystems is much less developed than for other microorganisms and previous research is geographically restricted. We investigated a large range of environmental variables and their relations to testate amoeba communities from 37 shallow lakes in the middle and lower Yangtze River Plain of China. Multiple factor analysis, redundancy analysis (RDA) and a forward-selection approach were used to explore the overall community structure and the links between the environmental variables and testate amoeba composition. Results showed that testate amoebae are widely distributed in most of the lakes despite often high levels of pollution. Our data highlight some links between water quality variables and testate amoeba communities. In particular, our results suggest that heavy metals have a role in shaping testate amoeba assemblage structure, although correlations are comparatively weak, perhaps due to lagged responses. Our results support previous suggestions that testate amoebae may be useful bioindicators in aquatic ecosystems but emphasize the need for an improved mechanistic understanding.

Paleohydrological changes over the last 4000 years in the middle and lower reaches of the Yangtze River: Evidence from particle size and n-alkanes from Longgan Lake

We have reconstructed the history of late-Holocene paleohydrological changes in the middle and lower reaches of the Yangtze River using grain size and n-alkane data from a sediment core retrieved from Longgan Lake. We employ changes in the grain size distribution to reflect the water level in the floodplain lake, with a higher percentage of the finer fraction indicating higher water level and vice versa. The n-alkane molecular distribution, average chain length (ACL), and Paq ratio (C23+C25)/(C23+C25+C29+C31) are used to reflect mainly vegetation composition that is also sensitive to water depth. Our results reveal that the lake water level was relatively low and gradually increased from 4 to 2.7 ka. The period from 2.7 to 1.2 ka exhibited the highest late-Holocene lake water level in this region. The water level then decreased toward the present. This paleohydrological reconstruction agrees with existing paleoclimate reconstructions of the middle and lower reaches of the Yangtze River, confirming that the intensity of Asian monsoon rains is an important factor in affecting paleohydrological changes in this region.

Correction: Molecular Paleoclimate Reconstructions over the Last 9 ka from a Peat Sequence in South China

[This corrects the article DOI: 10.1371/journal.pone.0160934.].