Vertical Distribution of the Metals

3.3.1 S2 (Gaoping Slope Site)

S2 is located on the west side of GPSC with a deeper water depth of 1205 m, and the concentration of each element at this site are as follow, Al: 7.7-8.7%, with a mean of 8.2%; Fe: 3.8-4.3%, with a mean of 4.1%; Mn: 335-2022 µg/g, with a mean of 513 µg/g; Zn: 95-103 µg/g, with a mean of 99 µg/g; Cr: 51-77 µ g/g, with a mean of 68 µ g/g;

Pb: 16-27 µg/g, with a mean of 19 µg/g; Co: 11.7-13.9 µg/g, with a mean of 12.5 µg/g;

Ni: 30.0-34.2 µg/g, with a mean of 31.4 µg/g; Cu: 17-20 µg/g, with a mean of 18 µg/g;

Cd: 0.12-0.20 µg/g, with a mean of 0.15 µ g/g (see Appendix).

Except for Cr and Cd, most of the trace metals at this site shows little variations over time, and their ratio to Al all appears around or under the ratio of natural backgrounds (Figure 3-16), implying most of them are from natural sources. However, Mn and Pb show a sharp increase in the uppermost layer of this sediment core, and their ratios to Al indicate a slight (Pb) and significant (Mn) enrichment with respect to the natural backgrounds (Figure 3-16).

Figure 3-16 Vertical distribution of the metals in core S2. The concentration of Mn and Pb have a sharp increase in the surface layer (red shaded area) and their ratio to Al shows different extent of enrichment with respect to the natural backgrounds (straight lines).

3.3.2 S6 (Gaoping Slope Site)

S6 is also located on the west side of GPSC with a shallower water depth of 618 m, and the concentration of each element at this site are as follow,

Al: 8.1-9.3%, with a

Most of the trace metals at this site also shows less variations over time, and their ratio to Al all appears around or below the natural backgrounds (Figure 3-17), showing

the natural variability of these elements. The concentration of Zn and Pb have a slight increase over time, and the trend disappeared after normalizing to Al for Zn yet there is still a slight increase in the surface layer for Pb. However, both of their ratio to Al still fall within the range of natural backgrounds (Figure 3-17). Like in core S2, there is also a sharp increase of Mn concentration observed in the surface layer in S6, but their ratio to Al is all below the natural backgrounds (Figure 3-17).

Figure 3-17 Vertical distribution of the metals in core S6. Mn has a sharp increase (red shaded area) at top of this sediment column while its ratio to Al is all below the natural backgrounds.

3.3.3 S1 (Gaoping Slope Site)

S1 is located on the east side of GPSC with a water depth of 822 m, and the

concentration of each element at this site are as follow, Al: 7.7-10.2%, with a mean of 8.7%; Fe: 4.0-5.2%, with a mean of 4.5%; Mn: 311-527 µg/g, with a mean of 379 µ g/g;

Zn: 95-111 µ g/g, with a mean of 103 µg/g; Cr: 59-85 µg/g, with a mean of 72 µg/g; Pb:

18-30 µg/g, with a mean of 23 µg/g; Co: 11.9-15.1 µg/g, with a mean of 12.9 µg/g; Ni:

30.3-36.9 µg/g, with a mean of 31.9 µ g/g; Cu: 17-24 µg/g, with a mean of 19 µg/g; Cd:

0.11-0.18 µg/g, with a mean of 0.14 µ g/g (see Appendix).

Most of the trace metals at this site also oscillates around a constant level (Zn and Pb have a slight increase) over time, and their ratio to Al all appears around or below the natural backgrounds, suggesting a natural variability of these elements (Figure 3-18). In this core, Mn has a small peak in the subsurface layer while the ratio to Al all appears below the natural backgrounds (Figure 3-18). The most obvious feature of this core is Pb has a sharp increase in the surface layer, below which the Pb content seems to fall back to a relatively constant level, and its ratio to Al indicates a slight enrichment in the surface layer (Figure 3-18).

Figure 3-18 Vertical distribution of the metals in core S1. Pb has a sharp increase in the surface layer (red shaded area) and its ratio to Al shows a slight enrichment with respect to the natural backgrounds.

3.3.4 B4G (Gaoping Slope Site)

B4G is also located on the east side of GPSC with a deeper water depth of 863 m, and the concentration of each element at this site are as follow, Al: 6.8-7.4%, with a mean of 7.1%; Fe: 3.5-3.93%, with a mean of 3.6%; Mn: 248-308 µg/g, with a mean of 282 µg/g; Zn: 77-87 µ g/g, with a mean of 81 µ g/g; Cr: 62-70 µg/g, with a mean of 65 µg/g; Pb: 14-20 µg/g, with a mean of 16 µ g/g; Co: 9.0-9.9 µg/g, with a mean of 9.5 µg/g; Ni: 26.1-29.1 µg/g, with a mean of 27.1 µg/g; Cu: 11-14 µ g/g, with a mean of 12 µg/g; Cd: 0.13-0.26 µ g/g, with a mean of 0.20 µ g/g (see Appendix).

Most of the trace metals have little variations over time, and their ratio to Al is all around or below the natural backgrounds, showing a dominated natural source at this site (Figure 3-19). Pb and Cd seem to have a slight increase over time, but their ratios

to Al are all around or below the natural backgrounds (Figure 3-19).

Figure 3-19 Vertical distribution of the metals in core B4G.

3.3.5 PL02 (Penghu Submarine Canyon Site)

PL02 is sampled on the Palm Ridge at head of the Penghu Submarine Canyon with a water depth of 931 m, and the concentration of each element at this site are as follow,

Al: 4.7-7.4%, with a mean of 6.2%; Fe: 3.2-3.8%, with a mean of 3.5%; Mn: 250-595

At the Penghu Submarine Canyon site, except that Mn has a sharp increase in the surface layer, other metals show a nearly constant concentration over time (Figure 3-20).

After normalizing to Al, most of the metal/Al ratios show a small peak in the subsurface

and bottom layer. However, since their concentrations stay nearly constant over time, these peaks are resulted from the variation of Al concentration along the depth (can also see these small peak layers is characterized with a relatively low concentration of Al, Figure 3-20), and most of the metals to Al ratio still appear around the natural backgrounds, showing their primary sources from crustal materials. Zn/Al ratio is slightly higher than the natural backgrounds in this core.

Figure 3-20 Vertical distribution of the metals in core PL02.

3.3.6 MT6 (Deep Sea Site)

MT6 is a deep sea site at lower reach of GPSC with a water depth of 3078 m, and the concentration of each element at this site are as follow, Al: 7.2-9.6%, with a mean of 8.6%; Fe: 3.6-4.8%, with a mean of 4.4%; Mn: 393-1160 µg/g, with a mean of 516 µg/g; Zn: 86-113 µ g/g, with a mean of 100 µg/g; Cr: 62-76 µ g/g, with a mean of 70 µg/g; Pb: 9-23 µg/g, with a mean of 18 µg/g; Co: 11.0-13.1 µg/g, with a mean of 12.2

µg/g; Ni: 28.2-33.9 µg/g, with a mean of 31.2 µ g/g; Cu: 16-24 µg/g, with a mean of 21 µg/g; Cd: 0.13-0.25 µ g/g, with a mean of 0.19 µ g/g (see Appendix).

Most of the trace metals at this site also possess small temporal fluctuations, and their ratio to Al all drops around or below the natural backgrounds, showing no interference from anthropogenic sources (Figure 3-21). At top of this sediment column, it is also found a sharp increase of Mn, and its ratio to Al shows its enrichment with respect to the natural backgrounds (Figure 3-21). Due to the dilution of coarser detrital materials, lowered concentration of most trace metals are found in the event layers (yellow shaded area).

Figure 3-21 Vertical distribution of the metals in core MT6. Mn has a sharp increase at top of this sediment column and its ratio to Al shows its enrichment with respect to the natural backgrounds. Lowered concentration of most trace metals is found in the event layer (yellow shaded area).

3.3.7 MT7 (Deep Sea Site)

MT7 is a deep sea site on the Tsan-Yao Ridge with a water depth of 2654 m, and the concentration of each element at this site are as follow, Al: 7.5-9.5%, with a mean of 8.5%; Fe: 3.6-4.8%, with a mean of 4.1%; Mn: 355-1663 µg/g, with a mean of 547 µg/g; Zn: 93-106 µg/g, with a mean of 100 µg/g; Cr: 59-77 µg/g, with a mean of 70 µg/g; Pb: 16-23 µg/g, with a mean of 19 µg/g; Co: 11.5-14.7 µg/g, with a mean of 12.7 µg/g; Ni: 29.3-33.8 µg/g, with a mean of 31.6 µ g/g; Cu: 18-28 µg/g, with a mean of 23 µg/g; Cd: 0.09-0.32 µ g/g, with a mean of 0.15 µ g/g (see Appendix).

Most of the trace metals at this site also presents little variations over time, and their ratio to Al also falls within or below the natural backgrounds (Figure 3-22). At this site, it can be noticed that the high content of Mn, unlike other cores, all appearing in the surface layer, it appears right below the event layer, and their ratio to Al also indicates their enrichments with respect to the natural backgrounds (Figure 3-22). In contrast, Cd shows increased and frequent changes within the event layer.

Figure 3-22 Vertical distribution of the metals in core MT7. The yellow shaded area is the event layer. Mn is enriched right below the event layer and Cd followed more variations in the event layer.