Vast laminated diatom mat deposits from the west low-latitude Pacific Ocean in the last glacial period

Diatoms are one of the predominant contributors to global carbon fixation by accounting for over 40% of total oceanic primary production and dominate export production. They play a significant role in marine biogeochemistry cycle. The diatom mat deposits are results of vast diatoms bloom. By analysis of diatom mats in 136°00′--140°00′E, 15°00′--21°00′N, Eastern Philippines Sea, we identified the species of the diatoms as giant Ethmodiscus rex （Wallich） Hendey. AMS 14C dating shows that the sediments rich in diatom mats occurred during 16000--28600 a B.P., which means the bloom mainly occurred during the last glacial period, while there are no diatom mat deposits in other layers. Preliminary analysis indicates that Antarctic Intermediate Water （AAIW） expanded northward and brought silicate-rich water into the area, namely, silicon leakage processes caused the bloom of diatoms. In addition, the increase of iron input is one of the main reasons for the diatom bloom.     

14C dating of moss peat banks in Fildes Peninsula, Antarctica

Based on the radiocarbon data of the moss peat banks in Fildes Peninsula, Antarctica, it was calculated that the mean rates of peat accumulation in the upper layer and the lower layer are 0.195 and 0.069 4 mm · a^™1 respectively. Based on the radiocarbon date (3 265 ± 120 aBP) and the mean rate of peat accumulation in the lower peat layer, it was calculated that the age of the coast terrace on which the moss peat bank occurs is earlier than 4 300 aBP. During the past 4 300 years the coast terrace has risen about 18 m without apparently being destroyed, and the age of the glacier retreating process in this area is also earlier than 4 300 aBP.     

14C measurement of forest soils in Dinghushan Biosphere Reserve

Organic carbon in forest soils of Qingyunsi and Wukesong profiles can be divided into fast and slow components. Δ 14C values of these profiles decrease with increasing of depth. The Δ 14C values in 30-40 cm depth interval of Wukesong profile are decreasing sharply until a very low value, showing that a strong geological environment change occurred about 1 560 years ago. The 14C apparent ages of Wukesong profile show that the coniferous and broad-leaf mixed forests around Wukesong profile have been developing since 425 a BP, which is consistent with historical documents. The penetrating depths of "bomb 14C" in Qingyunsi and Wukesong profiles are 10 and 20 cm, respectively.     

Geological records of marine environmental changes in the southern Okinawa Trough

Indexes of sediment grain size,sedimentation rates,geochemical composition,heavy,minerals,benthic foraminiferal fauna,indicator species of the Kuroshio Current,paleo-SST and carbonate dissolution of core E017 conformably suggest a great marine environmental change occurring at about 10.1-9.2cal.kaBP in the southern Okinawa Trough,which may correspond to the strengthening of the Kuroshio Warm Current and re-entering the Okinawa Trough through the sea area off northeast Taiwan.The invasion of Kuroshio current has experienced a process of gradual strengthening and then weakening,and its intensity became more fluctuation during the last 5000 years.Compared to the transition of sediment grain size,geochemical composition and heavy minerals,the foraminiferal faunas show a 900-year lag,which may indicate that the invasion of Kuroshio Current and the consequent sea surface and deep-water environmental chanages is a gradual process,and fauna has an obvious lag compared to environment altering.The carbonate dissolution of the Okinawa Trough has had an apparent strengthening since 9.2cal.kaBP,and reached a maximum in the late 3000 years,which may be caued by the deep-water environmental changes due to the invasion of Kuroshio Current.     

Biomarker reconstruction of phytoplankton productivity and community structure changes in the middle Okinawa Trough during the last 15 ka

Biomarkers have been widely used to reconstruct phytoplankton productivity and community structure changes, and this method has been applied for the first time in the middle Okinawa Trough during the transition from the last deglaciation to the Holocene. The total content of all marine phytoplankton biomarkers, used as a total productivity indicator, reveals higher productivity during the deglaciation. The ratios of the biomarkers are used as community structure indicators which show that, compared with the Holocene, the contribution from haptophytes decreased while the contributions from diatoms and dinoflagellates increased during the deglaciation. The increased productivity during the deglaciation was likely caused by the stronger winter monsoon. Also increased nutrient supply from terrestrial sources contributes to the higher productivity due to lower sea-level, which is consistent with higher terrestrial biomarker （long-chain n-alkanols） content. These changes in the nutrient supply also con- tributed to the community structure changes in the Okinawa Trough.     

Carbon isotopic composition,turnover and origins of soil CO<Subscript>2</Subscript> in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir,South China

Carbon isotopic compositions of soil CO2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO₂ are preliminarily discussed in this paper. Results show that the content of soil CO2 varies between 6120 and 18718 ppmv, and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO₂ δ¹³C ranges from −24.71‰ to −24.03‰, showing a significant inverse correlation (R²＝0.91) with the soil CO₂ content in the same layer. According to a model related to soil CO₂ δ¹³C, the soil CO₂ is mainly derived from the root respiration (>80%) in DHLS. While in DHS, where soil CO₂ ? 13C ranges from −25.19‰ to −22.82‰, soil CO₂ is primarily originated from the decomposition of organic matter (51%–94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO₂ is modern carbon in both DHLS and DHS. Differences in ¹⁴C ages between the “oldest” and “youngest” soil CO₂ in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO₂ in DHLS has a faster turnover rate than that in DHS. The ¹⁴C values of soil CO₂, which range between 100.0‰ and 107.2‰ and between 102.5‰ and 112.1‰ in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO₂ and SOC in the same layer, suggesting that soil CO₂ is likely an important reservoir for Bomb-¹⁴C in the atmosphere.     

冲绳海槽火山岩同位素特征及铀系组分法测年

借助多种分析方法,对采自冲绳海槽北段和中段的火山岩进行了常量元素、稀土元素、Sr-Nd同位素组成分析及铀系组分法年龄测定,在此基础上对此地区的海槽岩浆的起源、演化及岩石类型进行了研究。结果表明:(1)海槽晚更新世(大约10万年)以来有一期广泛的酸性火山喷发活动;(2)受板块俯冲的控制,此期火山活动年龄按照与琉球岛弧距离的由近到远而由新到老;(3)海槽北、中段岩浆演化过程相似,其下很可能存在有巨大的、统一的岩浆房,但与海槽南段岩浆作用差异明显,岩浆物质很可能来源于PREMA地幔源区;(4)此地区的黑色浮岩为钙碱性系列流纹岩,岩石化学组成与海槽产出的白色浮岩相似,形成年代为17.7±2.1 ka。     

The elemental carbon record in Weinan loess section since the last 21 ka

We studied the records of elemental carbon (EC) of the last 21 ka in the Weinan loess section, Shanxi Province. The variations of EC abundance and δ¹³C_EC value along with depth (or age) were presented. There are four large peaks of EC abundance around the following years: 20.16 ka, 17.76 ka, 11.97 ka and 4.49 ka. Climatic situation was changed rapidly during these periods. The peaks around 11.97 ka and 20.16 ka are particularly sharp, occurring over intervals of tens to hundreds of years, which could represent short-duration intense events. δ¹³C_EC values in the upper 4 m of the Weinan loess section vary between −11.71‰ and −21.34‰, which suggests that the vegetation pattern of the last 21 ka on the Loess Plateau is C₄-dominated grasses.     

Further support for a Cretaceous age for the feathered-dinosaur beds of Liaoning,China:New 40Ar÷39Ar dating of the Yixian and Tuchengzi Formations

We report new ⁴⁰Ar÷³⁹Ar dating results obtained from total fusion and incremental-heating analyses of sanidine and biotite from three tuffs found interbedded within the fossil-bearing deposits of Liaoning, northeast China. The first is a new sample of the Bed 6 Sihetun tuff from the Yixian Formation, previously dated by our team as middle Early Cretaceous, and recently considered by Lo et al., partially reset due to metamorphism from a nearby basaltic sill. The second is the Yixian Bed 9 tuff from Hengdaozi considered by Lo et al. to be unaffected by metamorphism and whose age, based on total fusion ⁴⁰Ar÷³⁹Ar dating of biotite, argues for a Jurassic age for the Yixian Formation. The third tuff is a previously undated tuff from the upper part of the underlying Tuchengzi Formation. Single crystal total fusion ⁴⁰Ar÷³⁹Ar analyses of the Sihetun sanidine showed homogeneous radiogenic Ar, Ca÷K ratios, excellent reproducibility and gave a mean age of 125.0±0.18 (1SD)±0.04 (SE) Ma. Single sanidine crystal total fusion ⁴⁰Ar÷³⁹Ar analyses of the Hengdaozi tuff gave a mean age of 125.0±0.19 (1SD)±0.04 (SE) Ma, which is indistinguishable from the Sihetun tuff. The Tuchengzi Formation tuff gave a mean age of 139.4±0.19 (1SD)±0.05 (SE) Ma. Detailed laser incremental-heating analyses of biotite from Sihetun, Hengdaozi, and Tuchengzi tuffs show disturbed Ar release patterns and evidence of trapped argon components. We conclude from these analyses that the total fusion dates on biotite by Lo et al. are erroneously old and isotopic dating of both biotite and sanidine from tuffs of the Yixian Formation point to a middle Early Cretaceous age. The upper part of the Tuchengzi Formation can be referred to the Early Cretaceous.     

CO<Subscript>2</Subscript> gas emplacement age in the Songliao Basin: Insight from volcanic quartz <Superscript>40</Superscript>Ar-<Superscript>39</Superscript>Ar stepwise crushing

Due to a lack of suitable minerals, the gas/oil emplacement ages have never been accurately obtained before. CH₄-CO₂-saline- bearing secondary inclusions are found in quartz from the volcanic rocks of the Yingcheng Formation, the container rocks of the deep CO₂ gas reservoir in the Songliao Basin. The inclusion fluid was trapped into microcracks in quartz during the gas emplacement and accumulation, providing an optimal target for the ⁴⁰Ar-³⁹Ar stepwise crushing technique to determine the CO₂ gas emplacement age. ⁴⁰Ar-³⁹Ar dating results of a quartz sample by stepwise crushing yield a highly linear-regression isochron with an age of 78.4±1.3 Ma, indicating that the accumulation of the deep CO₂ gas reservoir in the Songliao Basin occurred in the late Cretaceous. This is the first time to report an exact isotopic age for a CO₂ gas reservoir, which indicates that the ⁴⁰Ar-³⁹Ar dating can serve as a new technique to date the oil/gas emplacement ages.     

Further support for a Cretaceous age for the feathered-dinosaur beds of Liaoning, China: New 40Ar/39Ar dating of the Yixian and Tuchengzi

We report new ⁴⁰Ar/³⁹Ar dating results obtained from total fusion and incremental-heating analyses of sanidine and biotite from three tuffs found interbedded within the fossil-bearing deposits of Liaoning, northeast China. The first is a new sample of the Bed 6 Sihetun tuff from the Yixian Formation, previously dated by our team as middle Early Cretaceous, and recently considered by Lo et al., partially reset due to metamorphism from a nearby basaltic sill. The second is the Yixian Bed 9 tuff from Hengdaozi considered by Lo et al. to be unaffected by metamorphism and whose age, based on total fusion ⁴⁰Ar/³⁹Ar dating of biotite, argues for a Jurassic age for the Yixian Formation. The third tuff is a previously undated tuff from the upper part of the underlying Tuchengzi Formation. Single crystal total fusion ⁴⁰Ar/³⁹Ar analyses of the Sihetun sanidine showed homogeneous radiogenic Ar, Ca/K ratios, excellent reproducibility and gave a mean age of 125.0 ± 0.18 (1SD) ± 0.04 (SE) Ma. Single sanidine crystal total fusion ⁴⁰Ar/³⁹Ar analyses of the Hengdaozi tuff gave a mean age of 125.0 ± 0.19 (1SD) ± 0.04 (SE) Ma, which is indistinguishable from the Sihetun tuff. The Tuchengzi Formation tuff gave a mean age of 139.4 ± 0.19 (1SD) ± 0.05 (SE) Ma. Detailed laser incremental-heating analyses of biotite from Sihetun, Hengdaozi, and Tuchengzi tuffs show disturbed Ar release patterns and evidence of trapped argon components. We conclude from these analyses that the total fusion dates on biotite by Lo et al. are erroneously old and isotopic dating of both biotite and sanidine from tuffs of the Yixian Formation point to a middle Early Cretaceous age. The upper part of the Tuchengzi Formation can be referred to the Early Cretaceous.     

Lasing on pyroclastic rocks: A case study of <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating on Moshishan Group,eastern Zhejiang Province

It is difficult to date pyroclastic rocks, for almost all the dating methods, due to the multiple sources during their formation. ^40Ar/^39gAr incremental heating results on groundmass selected from the samples show that the age spectra are meaningless geologically. However, singe crystal total fusions of CO2 lasing on the sanidine separates could yield rational 4^40Ar/^39Ar results and distinguish their sources in this study. Timing on three formations of the Moshishan Group, after avoiding the exotic and altered grains by lasing on the single sanidine separate, was reported in this paper. The lowermost portion of the Chawan Formation gives an age of 113.7±0.3 Ma; the lower part of the Xishantou Formation was formed 116.4±0.4 Ma ago and the bottom of the Gaowu Formation took its shape at 118.4±0.4 Ma. These new ages are much younger than the previous ones, suggesting that these thick volcanic formations had been formed in very short durations.     

I2C总线在单片机串行扩展中的应用

介绍I²C总线的结构、工作原理、数据传输方式和优点,对于不带I²C总线接口的单片机,利用其常规的I/O口来模拟I²C总线接口,消除了串行扩展的局限性,并设计了数字温度传感器DS1624与不带I²C总线接口的单片机AT89C52的硬件系统,给出了软件实现的流程图及汇编语言程序.     

Carbon and nitrogen stable isotope analyses of mammal bone fossils from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River,China

Based on AMS ¹⁴C dating data, carbon and nitrogen isotope analyses were conducted on mammal bone collagen of deer, cattle and pigs from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River. These analyses were conducted to reconstruct palaeodiets of mammals, palaeoecology, palaeoenviroment and previous human activities in the study area. Results show that the collagen loss of bone did not change the in vivo isotopic composition of carbon and nitrogen stable isotopes, and most of the bone fossils were well preserved. The bone collagen of samples from deer had a mean δ¹³C of -23.1‰ and a mean δ¹⁵N of 4.7‰, suggesting that deer subsisted in a closed habitat and fed on branches and leaves. The bone collagen of cattle had a mean δ¹³C of –19.6‰ and a mean δ¹⁵N of 5.2‰, which indicates that cattle subsisted in an open habitat and fed on grasses and stems. The δ¹³C values show that both deer and cattle fed on C₃ plants and lived in the same ecosystem, but the t-test results show that deer δ¹³C and δ¹⁵N values were both more negative than those of cattle, indicating that they inhabited different niches. The δ¹³C and δ¹⁵N values of cattle partially overlapped those of deer, suggesting some competition in diets between them. The t-tests show that the δ¹³C and δ¹⁵N values of pigs were more positive than those of cattle and deer, which signifies that pigs occupied a higher trophic level compared to cattle and deer. The wide range of pig δ¹³C values demonstrates that pig trading had been taking place from early Neolithic Age to late Bronze Age. There were no significant differences in deer δ¹³C and δ¹⁵N values among different archaeological periods, making it clear that climatic, ecological and environmental conditions were kept relatively stable from 2200 to 4200 a BP. This stability may have been responsible for the extensive and complete cultural layers at the Zhongba site. The minimum number of samples required to estimate the mean δ¹³C values of deer, pigs and cattle are 8, 73 and 16, respectively, and for mean δ¹⁵N values of deer, pigs and cattle, the minimum numbers are 4, 5 and 6, respectively.     

High-resolution multi-proxy records of Asian monsoon activities from terrestrial sediments over the last 75,000 years

Our research group have investigated chronology and sedimentology of terrestrial sediments including loess-paleosols sediments over the last 75 ka at Lanzhou, northwestern China, and over the last 45ka at Tokyo, central Japan. Based on chronology of high resolution dating of ESR, TL, and IRSL and tephrochronology in these sediments, we investigated to reconstruct activities of Asian summer and winter paleomonsoons by using magnetic susceptibility, color reflectance and eolian dust concentrations over the last 75ka. Relations between standard curves of delta ~(18)O in GISP2 and color reflectance in loess-paleosol sediments of Linxia over last 140 ka shows that color reflectances are good proxy records indicating Asian summer paleomonsoon activity in time and are closely related to standard curve of delta ~(18)O in GRIP since the last interglacial. Also, relations between standard curve of delta ~(18)O in GISP2 and eolian dust concentrations over the last 75 ka at Lanzhou shows the Asian winter paleomonsoon activities have coincided with climatic changes in North Atlantic by GISP2 ice cores, and suggests that response of winter monsoon was rapid in global cooling stages, but slow in warming stage. Other results of our research in terrestrial sediments show as follows; 1) Horizons of Heinrich events from H1 to H4 in loess-paleosol sequences at Lanzhou. 2) Magnetic susceptibility and MS frequency dependent are possible to be available as proxy records for pedogenesis of tile Kanto Loam in Japan. 3) 8.2ka cooling event was recognized in Holocene loess-paleosol sequences at Lanzhou.     

Regional difference of aridity/ humidity conditions change over China during the last thirty years

Scientists have found that the global average surface temperature has increased by 0.6±0.2℃ since the late 19th century based on various evidence[1]. From the 1980s, temperature has experienced the most rapid warming to an extent of abrupt change statistically[2,3]. Global warming has attracted extensive attention from multiple depart-ments and has been an important issue related to global politics. Many scientific communities have made great efforts on climate change research and global env…     

Reconstruction of flood events over the last 150 years in the lower reaches of the Changjiang River

The reconstruction of paleofloods in the Holocene has become one research highlight for the present global change study. The core sediments from one newly-emerged bar in the lower Changjiang River (Yangtze River) mainstream were collected for grain size and organic elemental measurements, with aim to reconstruct the flood events over the past 150 years. Major grain size parameters such as mean grain size, probability cumulative curve and C-M diagram of the core sediments clearly indicate the flood event deposition. Furthermore, the TOC/TN ratios in the sediments can indicate flood events considering that during the flash floods, strong surface erosion in the upper and lower reaches of the Changjiang River can transport a large amount of undecomposed plant debris and organic components with relatively low C/N ratios into the lower mainstream. Based on 210Pb dating and sedimentary geochemical results, the research profile recorded several large floods happened from 1850 to 1954, which agrees well with the historical documents and hydrological observations. Interesting to note that the flood events since the 1960s cannot be distinctly recognized on the basis of sediment grain size and organic elemental compositions of the profile, which mainly reflects the intensive human activities over the last fifty years, especially condense dam construction, have significantly changed the characters of suspended sediment into the lower mainstream.     

Modeling studies on the changes of the Subtropical High over the Western Pacific during the last 100 years

Intensity index series of Subtropical High over the Western Pacific was constructed according to modeling results by using of CCM3.6 atmospheric model with climatologically SST forcing for 30 years, and with observed SST forcing from 1900 to 2000. The index series constructed by modeling closely correlated to the observations for 1951-1999 (c.c. 0.72) and to the statistically reconstructed one for 1900-1950 (c.c. 0.51). The index series for 1900-1999 showed significant 80 a and 40 a periodicity. A minimum of persistence in seasonal variations of the index occurred in Autumn, which was called "Autumn Barrier". It may relate to the "Spring Barrier", found in the seasonal variations of SST over the Eastern Equatorial Pacific. The increasing trend shown in the index series for the 20th century may associate with the global warming caused by enhancement of greenhouse effect.     

The40Ar/39Ar age record of formation and uplift of the blueschists and eclogites in the western Tianshan Mountains

The⁴⁰Ar/³⁹Ar ages indicate that the eclogite facies rocks of the Hasiate slice in the western Tianshan Mountains were formed at the early stage of Devonian (401 Ma) and had been uplifted to the greenschist facies tectonic level in the middle stage of Devonian (381 Ma). The formation and uplift of the blueschists of the Akesayi slice are constrained to the late stage of Devonian (370-364 Ma). The different tectonic slices in the high-pressure metamorphic belt have experienced the different uplift history.