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Weathering Sources in the Kaoping River Catchment, Southwestern Taiwan: Insights From Major and

Weathering Sources in the Kaoping River Catchment, Southwestern Taiwan: Insights From Major and Trace Elements, Sr Isotopes and Rare Earth Elements C.-F. You, K.-F. Huang, C.-H. Chung and R.-M. Wang Department of Earth Sciences Also at Earth Dynamic System Research Center

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Weathering Sources in the Kaoping River Catchment, Southwestern Taiwan: Insights From Major and

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  1. Weathering Sources in the Kaoping River Catchment, Southwestern Taiwan: Insights From Major and Trace Elements, Sr Isotopes and Rare Earth Elements C.-F. You, K.-F. Huang, C.-H. Chung and R.-M. Wang Department of Earth Sciences Also at Earth Dynamic System Research Center National Cheng Kung University

  2. Ching et al., 2007 Liu et al., 2007

  3. Outlines • Sr isotopes Non-conventional high precision Sr isotopic measurement • Major and trace elements • REEs

  4. Strontium Isotopes: 84Sr (0.56 %) 86Sr (9.86 %) 87Sr (6.99 %) 88Sr (82.54 %) 87Rb  87Sr＋β -＋anti-neutrino＋energy (t1/2＝4.88× 1010years)

  5. Geological Applications: 1. Geo-chronometer: Rb-Sr dating Seawater curve 2. 87Sr/86Sr Tracer: a. River water --- weathering process b. Sediments--- provenance and transportation c. Biogenic carbonate---seawater evolution 3. Environmental proxy SST or SSS

  6. Sr Isotopic Composition of Earth Systems Dissolved load in river 0.7119 Detrital load in river 0.7178 Sediment 0.724 Seawater 0.708 Hydrothermal vent 0.7035 Oceanic crust 0.702

  7. Geochemical Behaviors of Sr in the “Water World” • River water: • (a) Reflect the Rb/Sr ratio and “age” of the source rocks; • (b) Sources derived from silicate and carbonate weathering • 2. Seawater: • (a) Chemically and isotopically “uniform” because of its long residence time (~2 Ma); • (b) Small but considerable regional difference in flux and ICs occurred on time-scales shorter than the residence time; • (c) Non-conservative mixing in estuaries due to dynamic exchanges

  8. Oceanic Sr Budget 1, Steady or not? 2, How Sr ICs change with time? Total mass of Sr in seawater= 1.25×1017 mol (Assuming an average seawater concentration of 91.3 mM) After Basu et al., 2001

  9. Sampling Sites Reference sites- ST-1 (NEC) and St-C (SCS)

  10. South China Sea Sample Locality April Aug.

  11. Typhoon Toraji Modern Hydrography WRA., 2003 Liang et al., 2003

  12. Kao-Ping Canyon Sea Water Masses Water mass Depth Kuroshio 0 RW NPTW 100 SCS NPTW SCS 200 100 m SCS 400 SCS NPIW 200-300 m 600 NPIW 1300 400-600 m NPDW PDW bottom >1300 m Wang et al., 2002

  13. 3N HNO3 8N HNO3 3N HNO3 0.05N HNO3 High-Precision Sr Isotopic Measurement P- TIMS TRITON TI ORI 679_S6-10 m • 0.709196±03 • 0.709197±02 Seawater ORI 679_S3-10 m Recovery> 99.5% • 0.709195±03 • 0.709195±02 SB_09-12 (10.5 m) • 0.709195±03 • 0.709193±02

  14. The surface distributions of Sr ICs in the KPE Δ87Sr (ppm) After Typhoon Toraji

  15. Other Hydrographic Evidences (Lin et al., 2003)

  16. EM-1 Δ87Sr= -39.11*S+1338.7 r2=0.80 EM-2 Δ87Sr (ppm) 9.3 ppm (33.99‰) Δ87Sr= -10.82*S+377.08 r2=0.70 Freshening EM-3 Salinity (psu) Surface Seawater Sr ICs vs. Salinity 2σ EM-1: Most radiogenic Sr IC--- (1) intense water-sediment interaction caused by flood plume (2) release radiogenic Sr from silicates due to stronger erosion EM-2: Normal discharge of the Kao-ping river after heavy rainfalls

  17. Sr Isotopic Characteristics of the Taiwan River Δ87Sr (ppm)

  18. Mixing processes of the Water masses --- Evidence from the vertical profiles of the Sr ICs at the SOT S3 S6 S1 SOT 0.709176 0.709182 0.709176 Seawater Sr ICs is “not” isotopic uniform in the open ocean and marginal sea, but it seems to have a similar pattern in the same region.

  19. (a)

  20. (a)

  21. (a)

  22. (b) (a) (c)

  23. Summary • High precision Sr isotopic measurement can be applied as a new sensitive tracer for studying water mass mixing near estuary • Rather large variation in D87Sr, >60 ppm, was detected in the Kao-ping estuary and possibly were affected by flood plume, river discharge and surface seawater mass • Vertical seawater Sr ICs is “not” isotopic uniform in the open ocean and marginal sea • Dynamic exchange among freshwater, groundwater and seawater are occurring in the Kaoping River estuary and canyon

  24. Summary (continue) • High dissolved B and Sr in the Kaoping River emphasize the potential impact of mountainous island to the global oceanic chemical budget • The dissolved REE patterns of the Kaoping River at different tributaries show similar negative Ce anomaly and HREE enrichment • Strong positive Gd anomaly supports an anthropogenic pollution in the river. • The Sr isotopic variations are rather large, 0.712649~ 0.713592, and show systematically decreasing ratios with distance from the coastal region

  25. THANKS FOR YOUR ATTENTION EDSRC-NCKU, Taiwan

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