Seasonal variation in long-range transported dust to a subtropical islet offshore northern Taiwan: Chemical composition and Sr isotopic evidence in rainwater |
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Authors: | Miao-Ching Cheng Chen-Feng You Fei-Jan Lin Chuan-Hsiung Chung Kuo-Fang Huang |
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Institution: | 1. Istanbul Technical University, Eurasia Institute of Earth Sciences, Istanbul, Turkey;2. Laboratoire d’Ae´rologie, 16 avenue E´douard Belin, 31400 Toulouse, France;3. The Abdus Salam, International Centre for Theoretical Physics, Strada Costiera, Trieste, Italy |
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Abstract: | We investigated chemical and Sr isotopic composition of monthly rainwater collected on Peng-Chia-Yu (PCY) in northern Taiwan. Rainwater 87Sr/86Sr ratios, Na/Cl, Ca/Cl, Sr/Cl, Sr/Ca, NH4/Cl, NO3/Cl, SO4/Cl and Na/Sr, showed clear seasonal cycles, reflecting mixture of loess carbonates (high Ca/Sr and more radiogenic 87Sr/86Sr) and seawater (low Ca/Sr and intermediate 87Sr/86Sr). Model results showed that the former source contributes up to 45% during the winter monsoon period, but seawater is the dominant Sr source in rainwater (>50%) at other times. Two anomalously low 87Sr/86Sr values occurred in July and August 1998, coinciding with the Merapi eruption in Indonesia. Air-mass backward trajectories and the geochemical and isotopic compositions in rainwater and Merapi lava (i.e. Ca/Sr = 100 and 87Sr/86Sr = 0.705400) suggested that the Merapi eruption delivered ash across the western equatorial Pacific to PCY. Aerosols leaching experiments were conducted to examine the impact of the 1998 eruption, demonstrating that only a minor terrestrial signature can be extracted by distilled water, implying rapid dispatch of volcanic gases or high-efficiency dissolution of ash related substance in acidic rains. |
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