Prokaryotic Community Structure, Abundances, and Potential Ecological Functions in a Mars Analog Salt Lake.

Barkol Lake, situated northeast of the Tianshan Mountains, Xinjiang, is a hypersaline lake with abundant sulfate and chloride minerals, which can be a potential analog for microbial saline paleolakes on Mars. The lake water, sediments, and surrounding soils of Barkol Lake were sampled for geochemical analysis and 16S rRNA gene sequencing to investigate the prokaryotic community structure, abundances, interactions, and ecological functions. Results show that (1) prokaryotic community structure differs significantly between biotopes (water, sediment, and soil), with the highest abundances of archaea occurring in water samples and highest prokaryotic diversities in soil samples; (2) archaeal communities are dominated by Halobacterota, Nanoarchaeota, Thermoplasmatota, and Crenarchaeota, while bacterial communities are mainly Proteobacteria, Bacteroidetes, Actinobacteria, Desulfobacterota, Chloroflexi, Gemmatimonadetes, Firmicutes, and Cyanobacteria; (3) the prokaryotic community network for soil is far more complicated and stable than those for water and sediment; (4) soil prokaryotic communities could be significantly affected by environmental factors such as salinity, pH, total sulfur, and Ca2+; (5) archaeal communities may play an important role in the nitrogen cycle, while bacterial communities may mainly participate in the sulfur cycle. This study extends the data set of prokaryotic communities for hypersaline environments, which will provide perspectives into identification of the counterparts and help to understand potential microbial interactions and biogeochemical cycles occurring on Mars.

Regional characteristics of atmospheric δ34S-SO42- over three parts of Asia monitored by quartz wool-based passive samplers.

A new method is presented for measuring atmospheric contents and δ34S-SO42- in airborne particulate matter using quartz wool disk passive air samplers (Pas-QW). The ability of Pas-QW samplers to provide time-integrated measurements of atmospheric SO42- was confirmed in a field calibration study. The average sampling rate of SO42- measured was 2.3 ± 0.3 m3/day, and this was not greatly affected by changes in meteorological parameters. The results of simultaneous sampling campaign showed that the average SO42- contents in Pakistan and the Indochina Peninsula (ICP) were relatively lower than that of China. The spatial distribution of SO42- concentrations was largely attributed to the development of the regional economies. The range of δ34S values observed in Pakistan (4.3 ± 1.4‰) and the ICP (4.5 ± 1.2‰) were relatively small, while a large range of δ34S values was observed in China (3.9 ± 2.5‰). The regional distribution of sulfur isotope compositions was significantly affected by coal combustion. A source analysis based on a Bayesian mixing model showed that 80.4 ± 13.1% and 19.6 ± 13.1% of artificial sulfur dioxide (SO2) sources in China could be attributed to coal combustion and oil combustion, respectively. The two sources differed greatly between regions, and the contribution of oil combustion in cities was higher than previously reported data obtained from emission inventories. This study confirmed that the Pas-QW is a promising tool for simultaneously monitoring atmospheric δ34S-SO42- over large regions, and that the results of the isotope models can provide a reference for the compilation of SO2 emission inventories.

New sedimentary evidence reveals a unique history of C4 biomass in continental East Asia since the early Miocene.

Pyrogenic carbon (PyC) and n-alkane data from sediments in the northern South China Sea reveal variations in material from C4 plants in East Asia over the last ~19 Ma. These data indicate the likely presence of C4 taxa during the earliest part of the record analysed, with C4 species also prominent during the mid and late Miocene and especially the mid Quaternary. Notably the two records diverge after the mid Quaternary, when PyC data indicate a reduced contribution of C4 taxa to biomass burning, whereas plant-derived n-alkanes indicate a greater abundance of C4 plants. This divergence likely reflects differences in the predominant source areas of organic materials accumulating at the coring site, with PyC representing a larger source area that includes material transported in the atmosphere from more temperate (relatively cooler and drier) parts of East Asia. Variations in the relative abundances of C3 and C4 taxa appear to be linked to a combination of environmental factors that have varied temporally and geographically and that are unique to East Asia. A major expansion of C4 biomass in warmer subtropical parts of eastern Asia from ~1 Ma and particularly from ~0.4 Ma is later than other parts of the world.

Purification of BaSO4 precipitate contaminated with organic matter for oxygen isotope measurements (δ18 O and Δ17 O).

RATIONALE: Sulfate precipitates are often contaminated with nitrates and organic materials (OM), which reduce the precision and accuracy of measurements of δ18 O and Δ17 O values in the sulfate. Although nitrates can be effectively removed using diethylenetriaminepentaacetic acid solution, removing OM from the precipitates is often difficult. One effective approach is to heat powdered precipitates to high temperatures. In this study, the effect of this procedure on the δ18 O and Δ17 O values of BaSO4 precipitate was fully examined. METHODS: OM-contaminated BaSO4 precipitates and 18 O- and 17 O-labeled purified BaSO4 precipitates were loaded into alumina and gold crucibles and heated at 450 °C, 600 °C and 800 °C for 2 h. The nitrogen and carbon contents in the initial and the final BaSO4 were measured using an elemental analyzer. The values of δ18 O and Δ17 O were measured using a temperature conversion/elemental analyzer coupled with an isotope ratio mass spectrometer, and a CO2 laser system coupled with an isotopic ratio mass spectrometer. RESULTS: OM was effectively (88 ± 17%) removed from the BaSO4 precipitates by this treatment, and heating at 800 °C had the highest removal efficiency (98%). The differences in δ18 O and Δ17 O values between the final and initial BaSO4 precipitates was -0.6‰ to 0.3‰ (average of -0.1‰) and -0.24‰ to 0.10‰ (average of -0.02‰), respectively. Significant positive relationships between the δ18 O and Δ17 O values of the initial BaSO4 precipitate and those of the high-T-treated aliquots were found, with slopes having mean values of 0.96 ± 0.06 and 1.04 ± 0.01, respectively. CONCLUSIONS: The result demonstrates high removal efficiency for OM in BaSO4 precipitates and no significant differences in the oxygen isotopic compositions between high-T treated BaSO4 and initial BaSO4 . This study indicates that the modified high-T treatment (800 °C, 2 h) is an effective method for purifying BaSO4 precipitated from geological and environmental samples with a high OM content for δ18 O and Δ17 O measurements. Copyright © 2016 John Wiley & Sons, Ltd.

Acceleration of modern acidification in the South China Sea driven by anthropogenic CO2.

Modern acidification by the uptake of anthropogenic CO2 can profoundly affect the physiology of marine organisms and the structure of ocean ecosystems. Centennial-scale global and regional influences of anthropogenic CO2 remain largely unknown due to limited instrumental pH records. Here we present coral boron isotope-inferred pH records for two periods from the South China Sea: AD 1048-1079 and AD 1838-2001. There are no significant pH differences between the first period at the Medieval Warm Period and AD 1830-1870. However, we find anomalous and unprecedented acidification during the 20th century, pacing the observed increase in atmospheric CO2. Moreover, pH value also varies in phase with inter-decadal changes in Asian Winter Monsoon intensity. As the level of atmospheric CO2 keeps rising, the coupling global warming via weakening the winter monsoon intensity could exacerbate acidification of the South China Sea and threaten this expansive shallow water marine ecosystem.

[Chemical characteristics of precipitation in South China Sea].

Rainwater samples were collected in the summer on "Shiyan 3" during the 2012 South China Sea Sectional Scientific Survey. The concentrations of anion and cation, and pH in precipitation were determined and backward trajectories of air mass were simulated to analyze the chemical characteristics of ions and examine the source of ions. The results indicated that the mean pH value of precipitation was 6.3, with 5.6 of minimal value in summer in South China Sea. The order of anion and cation abundance was Cl(-) > S04(2-) > NO3(-) and Na(+) > Mg(2+) > Ca(2+) > K(+). Cl(-) was the major anion and Na(+) was the major cation, with concentrations of 2 637.5 microeq x L(-1) and 2095.5 microeq x L(-1), respectively, showing that they were the characteristics of marine atmospheric precipitation. There was a good linear relationship between each pair of 7 ions, with correlation coefficient above 0.9, suggesting that they may have a common source. However, the correlation coefficients were lower between NO3(-) and other ions than the others, suggesting that NO3(-) had more complex sources. The concentrations of Ca(2+) and K(+) in precipitation may be related to coral environment in South China Sea. The backward trajectories in 6 stations showed that the air mass was from south and southwest of South China Sea, without passing through above the continent. These results suggested that precipitation affected by human ion source can be ignored in summer in South China Sea.