Chung-Che Wu


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Wu

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Chung-Che

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0000-0003-0189-5208

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2020 - 20247
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Publications 1 - 7 of 7
  • Coral Record of Increased Soil Erosion Since East and Southeast Asia Economic Boom
    Item type: Journal Article
    Li, Xiaohua; Zeng, Zhen; Liu, Yi; et al. (2023)
    Journal of Geophysical Research: Oceans
    Soil erosion in East and Southeast Asia is believed to have increased significantly since the regional economic boom of the 1970s-1980s. However, limited records of soil erosion make it difficult to understand and indeed verify such changes. Here we present two new monthly resolved Ba/Ca records from Porites coral skeletons from southern Taiwan and central Vietnam, supplemented with some sporadic monthly and annually resolved coral delta Ba-138/134 data. Our records span the 1980s to the 2000s and suggest that there were intervals of elevated seawater Ba concentrations (Ba-sw) during the intervals 1987-1995 in southern Taiwan and 1992-2001 in central Vietnam. In combination with evidence for insignificant changes in regional seawater delta Ba-138/134 values, model simulations, and other published coral Ba/Ca records from Lanyu (offshore southeast Taiwan) and Hainan, we infer that the intervals of high Ba-sw values are linked to soil erosion associated with land use changes and socioeconomic developments. The increased sediment loads are also likely responsible for the recent degradation of regional coral reefs. Our study provides new insights into regional soil erosion histories, which may prove useful for guiding soil conservation and sustainable land management.
  • Subannual-to-biannual-resolved travertine record of Asian Summer Monsoon dynamics in the early Holocene at the eastern margin of Tibetan Plateau
    Item type: Journal Article
    Sun, Hailong; Shen, Chuan-Chou; Wu, Chung-Che; et al. (2022)
    Applied Geochemistry
    In this study, we present a subannual–biannual-resolved (0.9–2 years) ASM intensity record spanning from 11.6 to 10.0 ka BP (before 1950 AD) inferred from a 230Th-dated travertine δ18O record at Zhangjia Ravine on the eastern margin of the Tibetan Plateau. The ZJG-1 δ18O sequence is characterized by high-frequency fluctuations at decadal to centennial scales. Fluctuating between −11.15‰ and −14.78‰ over the δ18O sequence, the fluctuation range gradually decreased from 11.6 to 10.0 ka BP. There are several abrupt changes in the δ18O sequence, which indicate that the ASM in the early Holocene was highly unstable. Comparison with marine records suggests that the Preboreal oscillation (PBO) event could be triggered by a freshwater outburst which led to/resulted in a sudden release of thousands of cubic kilometers of the meltwater to the North Atlantic Ocean. Furthermore, the climate oscillations during the PBO were associated with the complex interplay of solar activity and freshwater outburst, the freshwater outburst may amplify the effect of solar activity when it was in the minima. The rapid warming after the PBO event may be controlled by the common mechanism that induced the Dansgaard–Oeschger warming events during the last glacial period. The further pronounced increases of the travertine δ18O values occurred at about 10.3 ka BP, coinciding roughly with Bond 7 event, also caused by the freshwater outburst and solar activity. This study is not only important to understand the primary driving force of the ASM intensity in the early Holocene, but also essential for evaluate the probability of abrupt climate changes in the future.
  • LA-ICPMS for In Situ U−Th Dating of Holocene Stalagmites
    Item type: Journal Article
    Wu, Chung-Che; Shen, Chuan-Chou; Günther, Detlef; et al. (2024)
    Analytical Chemistry
    Here, we present an in situ U–Th dating approach of carbonate speleothems using laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) with a detection efficiency of 1–2%. By online addition of a 229Th–233U–236U isotope triple spike to the laser-generated aerosol, instrumental mass discrimination and U/Th elemental fractionation could be monitored and corrected. With this approach, the 234U/238U and 230Th/238U activity ratios of a flowstone sample in secular equilibrium could be accurately reproduced as unity with two-sigma uncertainties ±0.053 and ±0.050, respectively. The method was used for the determination of the formation ages of individual layers in natural stalagmites ranging between 210 and 1 thousand years ago (ka). The determined ages corresponded well with those obtained using conventional solution multi collector-ICPMS techniques after isotope separation. Particularly, Holocene stalagmites, as young as 1 ka, could be accurately dated with 2 standard error of ±76 years. This developed microdomain U–Th dating approach thus can be applicable for diverse research areas, such as paleoclimatology, oceanography, geomagnetism, and archeology.
  • Stalagmite-inferred European westerly drift in the early Weichselian with centennial-scale variability in marine isotope stage 5a
    Item type: Journal Article
    Chung, Yun-Chuan; Menviel, Laurie; Marchionne, Arianna; et al. (2022)
    Quaternary Science Reviews
    he Weichselian glaciation is characterized by significant ocean circulation variations starting from ∼115 thousand years ago (ka) and terminating at ∼11.5 ka. The early Weichselian (115–74 ka), especially marine isotope stage (MIS) 5a at 85–74 ka, provides a window for understanding the linkage between the European westerlies and Mediterranean climate. However, lack of highly-resolved paleoclimate records with absolute chronologies hampers our knowledge of decadal-to-centennial-scale climate changes and forcings in the circum-Mediterranean realm. Here, we present 230Th-dated stalagmite-inferred hydroclimate records from Observatoire cave (43°44′ N, 7°25’ E), Monaco, for the period between 88.7 ± 0.4 and 80.3 ± 0.1 ka, covering portions of MIS 5b and 5a. Agreement between Observatoire and circum-Mediterranean stalagmite records confirm large-scale warming over the Atlantic-Europe territory during the transition from MIS 5b to 5a. Subdecadally-resolved Observatoire δ18O and δ13C records express four multi-centennial arid intervals in southern Europe at 84–80 ka in the first-half of MIS 5a, suggesting centennial westerly drifts, a finding supported by a model simulation. Westerly changes and associated arid events can be attributed to slowdowns of the Atlantic meridional overturning circulation, North Atlantic Oscillation states, and solar activity.
  • A Century of Reduced ENSO Variability During the Medieval Climate Anomaly
    Item type: Journal Article
    Lawman, Allison E.; Quinn, Terrence M.; Partin, Judson W.; et al. (2020)
    Paleoceanography and Paleoclimatology
    Climate model simulations of El Niño–Southern Oscillation (ENSO) behavior for the last millennium demonstrate interdecadal to centennial changes in ENSO variability that can arise purely from stochastic processes internal to the climate system. That said, the instrumental record of ENSO does not have the temporal coverage needed to capture the full range of natural ENSO variability observed in long, unforced climate model simulations. Here we demonstrate a probabilistic framework to quantify changes in ENSO variability via histograms and probability density functions using monthly instrumental and coral‐based sea surface temperature (SST) anomalies from 1900–2005 and 1051–1150 CE. We find that reconstructed SST anomalies from modern corals from the southwest Pacific capture changes in ENSO variability that are consistent with instrumental SST data from the central equatorial Pacific. Fossil coral records indicate 100 years of relatively lower ENSO variability during part of the Medieval Climate Anomaly. Our results demonstrate that periods of reduced ENSO variability can last a century, far longer in duration than modern observations in the instrumental record of ENSO, but consistent with results from unforced climate model simulations.
  • Coevolutions of terrestrial temperature and monsoonal precipitation amounts from the latest Pleistocene to the mid-Holocene in Japan: Carbonate clumped isotope record of a stalagmite
    Item type: Journal Article
    Kato, Hirokazu; Mori, Taiki; Amekawa, Shota; et al. (2023)
    Chemical Geology
    Quantitative paleotemperature reconstruction is a challenging and important issue in paleoenvironmental studies, for which carbonate clumped isotope (Δ47) thermometry is a promising approach. Here we analyzed Δ47 values from 66 layers of OT02 stalagmite from Ohtaki Cave in central Japan, covering two separate time intervals (2.6–8.8 and 34.8–63.5 ka) to reconstruct terrestrial temperature and meteoric δ18O records. The average Δ47 temperatures of the Holocene interval and the latest Pleistonece interval were 16.3 °C ± 5.6 °C and 9.7 °C ± 4.6 °C, respectively. The Δ47 thermometry also revealed that the cold intervals (5 °C–10 °C) correspond to the Heinrich stadials HSs4–6, and the warm interval (up to 19.9 °C ± 6.0 °C) in middle Holocene (approximately 6–5 ka) accompanied by the Hypsithermal climate optimum. We also reconstructed past meteoric δ18O by subtracting the temperature effect from stalagmite δ18O. Average meteoric δ18O was −8.2‰ ± 1.0‰ vs. VSMOW in the Holocene interval and − 8.8‰ ± 0.8‰ in the latest Pleistocene interval. Over centennial timescales, meteoric δ18O was more negative during colder periods, such as Heinrich stadials and a cooling event around 7 ka, and less negative in warmer periods, such as Hypsithermal warming. A temperature dependency of total 18O fractionation from sea water to precipitation is a likely reason for the negative correlation between temperature and meteoric δ18O. Additionally, East Asian summer monsoon (EASM) brought larger rainfall of less negative δ18O during the warm periods, whereas larger snow/rainfall of more negative δ18O brought from East Asian winter monsoon (EAWM) in colder periods. The relative influences from EASM and EAWM were changing in a centennial timescale. δ18O of OT02 had reflected changes in terrestrial temperature and meteoric δ18O, which are both strongly related to EASM and EAWM.
Publications 1 - 7 of 7