1. Among our Gaoping Slope and deep sea sites, most of measured trace metals have little variations over time and their ratios with Al (M/Al) reveal their natural variability in the sediments. However, Pb pollution signals can still be found in Gaoping Slope and the sedimentary record can clearly illustrate the onset of industrial development in Taiwan.
2. The comparable cumulative mass of the trace metals observed in the deep sea site and the relatively consistent Ti/Al molar ratio between Gaoping Slope and deep sea, all suggesting that the sediments could cross the narrow shelf and made a considerable amount to transport and accumulate in the deep sea. This transport mechanism could also be applied to those submarine canyons which have characteristics analogous to GPSC (developed on an active continental margin).
3. Natural hazards (earthquakes, typhoons, etc.) tend to be the major agents in Taiwan to cause grand output of sediments into the marine environment. Though they may cause lowered concentration of trace metals due to the dilution of coarser detrital materials, the absolute amount (cumulative mass) of the trace metals contributed from an event over a short time period (less than one year) could be much greater than those delivered from a long-term (year average) steady sedimentation condition, elucidating these natural hazards can also be the major agents to accelerate accumulation of trace metals off southwestern Taiwan.
4. Compared to previous studies conducted in the coastal and offshore region (Hung
& Hsu, 2004; Chen & Selvaraj, 2008), many trace metals are found highly enriched in the near source area, yet no significant enrichment of the trace metals is found in the further seaward regions (Gaoping Slope & deep sea) in this study.
Although no strong pollution signals are recorded beyond the Gaoping Shelf as the pollution signals could be largely diluted with the increasing distance they’ve been transported, footprints of pollution (Pb) can still be recorded in the Gaoping Slope.
5. Though the cross-shelf transport can deliver a huge amount of terrestrial materials into the deep sea, due to dilution of the pollution signals during the further seaward transport, no interferences from anthropogenic sources were found at the deep sea sites (MT6 & MT7), implying the impact of pollutants discharged from Gaoping River on the deep sea is insignificant.
6. The estimated increasing rates of anthropogenic Pb flux in different areas around the world indicate the pollution level in Taiwan can be compared to most countries in east Asia and the US, while China accounts for the highest increasing rate of the world.
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APPENDIX
The concentrations of the trace and major elements in all depth of each sediment core analyzed in this study.
PL02
Zn5.5 cm 99 71 19 12.1 31.4 19 0.20 393 4.1 1.29 8.5 2.49 0.41
15.5 cm 91 67 20 11.0 28.6 15 0.14 286 3.8 1.16 8.1 2.50 0.40
Minimum 95 59 18 11.9 30.3 17 0.11 311 4.0 1.16 7.7 2.19 0.39
16.5 cm 101 69 17 12.4 31.0 22 0.19 490 4.4 1.31 8.9 2.60 0.47
24.5 cm 101 68 19 12.6 31.7 24 0.12 391 4.4 1.42 9.1 2.58 0.42
25.5 cm 105 77 19 13.6 33.7 25 0.13 1663 4.3 1.32 8.8 2.46 0.41
29.5 cm 104 71 19 12.7 31.9 23 0.14 861 4.2 1.29 8.8 2.49 0.41
30.5 cm 106 77 20 14.5 33.5 24 0.14 1137 4.3 1.28 9.0 2.54 0.41
31.5 cm 105 72 23 14.7 31.5 21 0.12 1201 4.8 1.35 8.6 2.73 0.46
32.5 cm 100 75 20 13.0 31.9 22 0.13 658 4.2 1.26 8.9 2.45 0.42
33.5 cm 98 70 17 11.6 30.3 22 0.11 466 3.9 1.22 8.2 2.29 0.39
36.5 cm 103 59 18 12.9 33.2 24 0.24 505 4.0 1.27 8.4 2.38 0.40
40.5 cm 97 70 19 12.1 30.2 22 0.12 489 4.4 1.37 9.0 2.52 0.43
48.5 cm 97 69 20 12.3 30.7 21 0.12 446 4.4 1.32 8.9 2.53 0.42
56.5 cm 99 75 17 13.0 32.7 24 0.18 392 4.4 1.44 9.5 2.62 0.44
Minimum 93 59 16 11.5 29.3 18 0.09 355 3.6 1.14 7.5 2.09 0.36
Maximum 106 77 23 14.7 33.8 28 0.32 1663 4.8 1.44 9.5 2.73 0.46
Mean 100 70 19 12.7 31.6 23 0.15 547 4.1 1.29 8.5 2.41 0.40