Yonghua Wu

State Oceanic Administration, Tsingtao, Shandong Sheng, China

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Publications (6)5.69 Total impact

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    ABSTRACT: A total of six δ 13C minimum events, i.e., VI, V, IV, III, II, and I, were observed via a stable carbon and oxygen isotope analysis of infaunal benthic foraminifera Uvigerina spp. in gravity core OS03-1 in the southeastern Okhotsk Sea over the last 180 ka. These events occurred at 112–109, 102–90, 85–76, 57–54, 44–40, and 17–10 ka BP. The largest negative excursions reached 2.5 ‰ in event V and were greater than 1 ‰ in the other events. We proposed that all δ 13C minimum events were caused by the increase in sea surface water productivity, the weakened formation of Okhotsk Sea intermediate water, and the enhancement of the oxygen minimum zone. The negative excursions were unaffected by methane hydrate destabilization and subsequent methane release based on the results obtained by using archaeal lipid markers.
    Chinese Science Bulletin 08/2014; 59(24). · 1.37 Impact Factor
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    ABSTRACT: We present a paleoclimatic reconstruction of the mid-Holocene by geochemical analysis of a sediment core MZ01 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). Our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes. Relatively higher ratios of CIA, Ba/Sr and a lower ratio of CaO/MgO coincide with major regional warm and humid climate episodes, and vice versa. Therefore, these geochemical indicators are useful in reconstructing the paleoclimate in eastern China. Using the geochemical records of core MZ01, which are well constrained by AMS 14C dating, we found that from 8300 yr BP to 4200 yr BP the regional climate was moderately warm and humid, and from 4200 yr BP to 2300 yr BP the climate was cool and dry, with large fluctuations between cool-dry (3700 yr BP, 2850 yr BP and 2400 yr BP) and warm-wet (3250 yr BP and 2650 yr BP). Since 2300 yr BP, our records indicate that the climate has gradually become warmer, although a cold event centered at around 250 yr BP (the Little Ice Age, LIA) interrupted this warming trend. We also found significant 238 yr cycles in our CIA records that imply a possible solar influence on the regional climate changes since the mid-Holocene.
    Journal of Asian Earth Sciences 06/2013; · 2.38 Impact Factor
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    ABSTRACT: Paleoclimate record was revealed in Core MZ01 covering the mid-Holocene in age, located in the mud area of the inner continental shelf of the East China Sea. The ancient environment featured low-energy shallow sea shelf deposition formed mainly by coastal currents. The results show that temporal variation in geochemistry corresponds with the climate changes inferred from historical record. Relatively low MgO/Al2O3, CaO/K2O and high Al2O3/Na2O, K2O/Na2O, MnO/CaO values reflected a warm and humid climate in general, and vice versa. Therefore, these chemical indices could be applied to identify the variation of palaeoclimate in eastern China. The authors reconstructed the history of mid-Holocene climatic variation of the inner continental shelf of the East China Sea. From 8 300 a BP to 4 200 a BP, the climate was moderately warm and humid. From 4 200 a BP to 2 000 a BP, the climate turned cool and dry, and the regional climate frequently fluctuated in alternation of cool-dry periods (3 700 a BP, 2 850 a BP and 2 400 a BP) and warm-wet periods (3 250 a BP and 2 650 a BP). After 2 000 a BP, the climate of the study area gradually turned warm again, while the Little Ice Age, a cold event centered at around 250 a BP was indicated by those geochemical indices as mentioned above. Key wordsHolocene–East China Sea–mud area–major element–palaeoclimate–East Asia monsoon
    Acta Oceanologica Sinica -English Edition- 01/2011; 30(4):43-52. · 0.58 Impact Factor
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    ABSTRACT: AMS14C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 μm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ18O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300–6300 a BP, strong and unstable; 6300–3800 a BP, strong but stable; 3800–1400 a BP, weak and unstable; after 1400 a BP, weak but stable. KeywordsHolocene-inner shelf of the East China Sea-mud areas-grain size-clay mineral-elemental analysis-East Asia winter monsoon
    Chinese Science Bulletin 01/2010; 55(21):2306-2314. · 1.37 Impact Factor
  • Shulan Ge, Xuefa Shi, Gang Yang, Yonghua Wu
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    ABSTRACT: We conducted rock magnetic and paleomagnetic research on two deep-sea sediment cores from the west Philippine Sea, located to the east of Benham Rise with the length of 4 m and water depth of over 5000 m. At the bottom of core 146 occurs a reversal of inclination and deflection of relative declination, which is recognized as Brunhes-Matuyama Polarity Boundary (MBPB). No reversal occurs in core 89, which implies a younger bottom age than that of core 146. Rock magnetic results reveal magnetic uniformities in mineralogy, concentration and grain size along the two cores, thus relative paleointensity variations are acquired. The three normalizers-anhysteresis remanent magnetization (ARM), magnetic susceptibility (k) and saturation isothermal remanent magnetization (SIRM) are used for normalization to obtain relative paleointensities. The three normalization results are averaged to indicate the paleoitensity of the cores and are further stacked together to get a synthetic curve for west Philippine Sea (named asWPS800 in this paper). Based on the magnetic correlation between cores and paleointensity to Sint800, we transfer the changes of rock magnetic parameters from depth to time. Furthermore, the astronomically tuned oxygen isotope from ODP site 1143 in the south China Sea is used for the glacial and interglacial indicator. Three concentration proxies (ARM, k and SIRM) and grain size indicators (k ARM/SIRM, k ARM/k) are examined according to the paleointensity-assisted chronology. The grain size changes in the two cores display a consistent pattern with the climatic changes embodied by oxygen isotope. The magnetic sizes are usually coarser in glacial periods and finer in interglacial times, which may reflect the influence of chemical erosion rather than fining from sea level rising on the source sediment. Furthermore, the sub-peaks and sub-troughs in interglaciations almost correspond with that of oxygen isotope records, which means sedimentation can reflect the subtle changes in interglaciations. This kind of revelation of climatic fluctuation by magnetic size is also found in the South China Sea, which shows a common pattern of magnetic signals to climate at least within East Asia. The concentration of ARM (representing more about fine grain) also shows similar response to glacial and interglacial cycles, that is, high in interglacial cycle and low in glacial cycle; but k and SIRM (reflecting more about coarse grain) lack the response to the climatic cycles. At the same time, S-ratio lacks the correlation with aeolian dust record and rhythmic changes, indicating the dominant source of main magnetic carrier (low coercivity magnetite) is the suspended matter instead of dust. The decreasing trend of sedimentation rate from west to east also reveals that the sediments are mainly from west Luzon and adjacent land. Grain sizes first became coarse and then stable around 400 ka B.P., and at the same time all the magnetic contents lowered and amplitude of magnetic mineral changes increased. The magnetic transition around 400 ka B.P. is simultaneous with the decreases of carbonate content, reflecting a global carbonate dissolution event, i.e. mid Brunhes event. The synchronization of magnetic content and grain size with climatic cycles of glacials and interglacials imply the validity of paleointesnityassisted chronology. Also, the response of rock magnetic signals to stable oxygen isotope changes and carbonate variation reveals that rock magnetismmethod can be an effective tool for paleoclimatic and paleoceanographic research.
    Frontiers of Earth Science in China 08/2008; 2(3):314-326.
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    ABSTRACT: Based on results of nannofossil analysis and 10Be dating in ferromanganese crusts M1-1 and A1-1 (no nannofossils were found in it), from the western and central Pacific respectively, it is found that the crust growth ages from nannofossil biostratigraphy agree well with those based on 10Be isotope analysis. Both crusts have three growth layers, and the oldest layer was deposited in Miocene at about 12.80 Ma. The maximum, minimum, and average growth rates of crust A1-1 (from the central Pacific) are 8.11, 1.92 and 3.47 mm/Ma, and those of crust M1-1 (from the western Pacific) are 2.93, 0.47, and 0.94 mm/Ma.
    Chinese Science Bulletin - CHIN SCI BULL. 01/2006; 51(24):3035-3040.