ationthe coastal line tends to landward migrate within the last hundred years.Coastline of Zhenzhu bay had migrated landward since 20th century.Qinzhou bay shows the trend of westward expansion and eastwardreduction. In the western coast area, there have a degradation of mangrovein the early 20th century. The area of tidal at reduces due to the restrictedspace by human activities such as building dykes in 1960s and 1970s. Theeast coastline has obviously migrated seaward, corresponding to the rapiddeposition with more materials from Qinjiang River since 1980s.
LATE NEOGENE EAST ASIAN MONSOON: FROM WINTER TO SUMMERDOMINATED SUB-REGIME AND PERIODICITY TRANSITION FROM 100KYR TO 41 KYR
Fengjiang Li. Key Laboratory of Cenozoic Geology and Environment, ChinaE-mail address: firstname.lastname@example.org
More and more evidence indicates that the onset of the East Asian (EA)monsoon can be traced back to the Oligocene-Miocene boundary.However, its evolutionary process is still less well known. Here weinvestigate its late Neogene evolution by analyzing a terrestrial mollusksequence, from the Chinese Loess Plateau, covering the period between 7.1and 3.5 Ma. Considering the modern ecological requirements of theseorganisms, we were able to dene two groups of cold-aridiphilous andthermo-humidiphilous species, representing the EA winter and summermonsoon variations, respectively. Variations in these two groups indicatetwo different monsoon dominated periods during 7.1-3.5 Ma. First,between 7.1 and 5.5 Ma, the EA winter monsoon, with a 100 kyr period-icity, was dominant. Second, between 5.1 and 4 Ma, the EA summermonsoon dominated, with a 41 kyr periodicity. Furthermore, our molluskrecord yields valuable evidence for a late Miocene-Pliocene transition ofabout 400 kyr from winter monsoon dominated towards summermonsoon dominated, associated with a periodicity transition from weak100 kyr to 41 kyr. The strengthened winter monsoon interval, with a 100kyr periodicity, is coeval with orbital-scale global ice volume changes, inconjunction with the uplift of the Tibetan Plateau which probably rein-forced the winter monsoon sub-regime. Conversely, closures of thePanama and Indonesian seaways, associated with changes in obliquitybetween 5.1 and 4 Ma, are probably major forcing factors for the observeddominant summer monsoon with 41 kyr frequency, favoring heat andmoisture transports between low and high latitudes to allow TH mollusksto grow and develop in the CLP. The transition from a 100 kyr dominatedinterval towards a 41 kyr dominated one is contrary to the mid-Pleistocenetransition (MPT), which corresponds to ice volume expansion at highlatitude and show a shift in the periodicity from 41 kyr to 100 kyr.
RELATIVE POLLEN PRODUCTIVITY ESTIMATES FOR HERBACEOUS TAXAIN THE HULUNBEIER STEPPE, INNER MONGOLIA
Yiyin Li. Peking University, ChinaE-mail address: email@example.com
The quantitative reconstruction of past vegetation in steppe with an openlandscape has been hampered by the lack of detailed information of pollenproduction and dispersal processes. Steppe is an important vegetation typein northern China. The Hulunbeier steppe is widely known as one of thelargest grasslands in Inner Mongolia with a rich biodiversity. Thirty-fourpollen trap samples matched with 34 soil surface samples were collectedfrom16 plots in the Hulunbeier steppe, InnerMongolia. The vegetationwassurveyed in concentric rings around each trap out to a 20m radius. Eightplotswith 14 trapswere located in Leymus chinensis steppe, three plotswith8 traps in Stipa Baicalensis steppe, one plot with 2 traps in mixed grasssteppe, and four plots with 10 traps in pastures. Pollen productivity esti-mates (PPEs) for 5 common taxa, Gramineae, Artemisia, Chenopodiaceae,Compositae and Cyperaceae, which are often found in Quaternary sedi-ments, were calculated using ERV model. Our results show that the pollenproductivity estimates relative to Gramineae, which is set as one are: forArtemisia, Chenopodiaceae, Compositae and Cyperaceae 15, 14, 10, and 6,respectively. Compositae and Cyperaceae with large pollen grains and highfall speeds are poorly dispersed and often deposited near the plants thatproduce the pollen. Gramineae, Artemisia and Chenopodiaceae with small
Abstracts / Quaternary Internpollen grains and slower fall speed arewell dispersed and often form a highproportion of the background pollen. The pollen taxa in trap and surfacesamples mainly come from plants growing within 15.5m radius as mostherbaceous plant pollen can not disperse for great distance.
DISPERSAL CHARACTERISTICS OF CHARCOAL PARTICLES OF DIFFERENTSIZES IN THE DAXING'AN MOUNTAIN OF NORTHERN CHINA AND THEIRIMPLICATIONS FOR FIRE ACTIVITIES
Yiyin Li. Peking University, ChinaE-mail address: firstname.lastname@example.org
Charcoal is one of the important proxies for reconstructing re history andecological processes. However, our knowledge of dispersal, deposition andpreservation of charcoal is still very limited. Located on forest-steppe witha wide distribution of Pinus pumila, a ammable species and with a longhistory of human activity, Daxing'an Mountain is known to have a highfrequency of re activity. This is an ideal place to study dispersal, depo-sition and preservation of charcoal for a better understanding of reactivities and their implications. We collected surface samples from recentres to the margin of 10km distance with 100m spacing along differentdirections. Charcoal was extracted from surface samples and divided into 4size fractions: macrofossil charcoal of greater than 500mm, large charcoal500- 180mm, small charcoal 180-125mm and microfossil charcoal of lessthan 125mm. The charcoal particle concentration for different sizes hasbeen estimated to understand the re intensity, frequency and spatialextent. We nd that the pattern of change in charcoal concentration ofdifferent sizes is similar: relatively high in the burning area and lowoutside burning area. However, a detailed comparison among the charcoalconcentration of inside and outside burning areas reveals certain differ-ences in their uctuations. The concentration of large charcoal seems touctuate with greater amplitude than that of the microfossil charcoal.
OXYGEN AND CARBON ISOTOPIC FRACTIONATION IN THE OSTRACODEUCYPRIS MAREOTICA: RESULTS FROM A CULTURE EXPERIMENT ANDIMPLICATIONS FOR PALEOCLIMATE RECONSTRUCTION
Xiangzhong Li. State Key Laboratory of Loess and Quaternary Geolo, ChinaE-mail address: email@example.com
Oxygen and carbon isotopic analysis of the adult ostracod Eucypris mar-eotica cultured at controlled temperatures (10, 15, and 19C) was used tomeasure isotopic fractionationduring shell calcication. Theostracod shellsthat precipitated at experimental temperatures are almost in isotopicequilibrium with the culture water as compared to the oxygen isotopefractionation of inorganic carbonates. Moreover, they had almost constantoffsets from equilibrium based on the oxygen isotope fractionation ofinorganic carbonates. The d18O values of ostracod shells from the 10Ccultureswere higher than those of the 15 and 19C cultures by 1.6 and 2.7&,respectively. The oxygen fractionation factors of E. mareotica are very closeto those of synthetic calcite formed in isotopic equilibrium. However, theostracod shells that precipitated at experimental temperatures are inisotopic non-equilibriumwith the water DIC , but the mean offset betweend13Cshells and d13CDIC becomemuchmore close to the fractionation betweencalcite and HCO3- with increasing pH of culture water.Therefore, the carbon isotopic fractionation of ostracods living in differentwater environment should be considered, if the d13C data for E. mareoticaare used in palaeoenvironmental reconstruction. However, the vitaloffsets of shells-d18O for E. mareotica is so small that we can neglect itseffect when using the d18O of E. mareotica living in lake waters with highpH and salinity to reconstruct the paleoenvironment. The paleotemper-ature or paleoisotopic composition of lake water interpreted from a core oflacustrine sediment may be closer to the true values when the d18O datafor E. mareotica are used.Keywords: Eucypris mareotica, temperature, culture experiment, oxygenand carbon isotope fractionation
POLLEN-VEGETATION-CLIMATE RELATIONSHIP IN SOME DESERT ANDSTEPPE COMMUNITIES IN NORTHERN CHINA
Yuecong Li. Hebei Normal University, China
al 279-280 (2012) 233345 279E-mail address: firstname.lastname@example.org