Geochemical compositions of river and shelf sediments in the Yellow Sea: Grain-size normalization and sediment provenance

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1 ARTICLE IN PRESS Continental Shelf Research 26 (2006) Geochemical compositions of river and shelf sediments in the Yellow Sea: Grain-size normalization and sediment provenance D.I. Lim a,, H.S. Jung b, J.Y. Choi c, S. Yang d, K.S. Ahn e a Southern Coastal Environment Research Department, Korea Ocean Research and Development Institute, 391 Jangmok-ri Jjangmok-myun, Geoje , Korea b Korea Ocean Research and Development Institute, Ansan, P.O. Box 29, Seoul , Korea c Department of Oceanography, Kunsan National University, Kunsan , Korea d Department of Marine Geology, Tongji University, 1239 Siping Road, Shanghai , PR China e Department of Earth Sciences, Chosun University, Gwangju , Korea Received 17 March 2005; received in revised form 2 September 2005; accepted 5 October 2005 Available online 14 November 2005 Abstract The geochemistry of sediment samples from Korean and Chinese rivers provides source indicators enabling these river materials to be identified within the sediment load of the Yellow Sea. Elements enriched in Chinese river sediments relative to those in Korean rivers include Ca, Na, Sr, and Cu. Korean river sediments have higher Al, K, Ba, and Li concentrations, but extremely low Ca concentrations. Direct comparisons of these elemental concentrations in Yellow Sea sediments become difficult due to grain-size effects and the presence of biogenic materials and pollutants that produce significant variation in the data. The concentrations of Fe, Mg, Ti, V, and Co with respect to Al are distinctly different in both groups of river sediments and the correlations of these elements with Al display different linear regression trends for both groups of river sediments indicating differences in composition. These differences, especially in Fe and Mg, provide a basis for discriminating sediment sources of the Yellow Sea. Further, the grain-size normalization, using these two liner regression lines, enables the source areas to be differentiated more clearly in the Yellow and East China Seas. r 2005 Elsevier Ltd. All rights reserved. Keywords: Geochemical composition; Sediment provenance; Grain-size normalization; Korean and Chinese river sediments; Yellow Sea 1. Introduction The Yellow Sea (West Sea of Korea) is a semienclosed, western Pacific marginal sea, occupying the broad continental shelf between China and Korea (Fig. 1). It receives a vast amount of sediment, 410% of the world s fluvial sediment Corresponding author. Tel.: ; fax: address: oceanlim@kordi.re.kr (D.I. Lim). discharge (Hay, 1998), which comes mainly from two of the largest rivers in the world, the Changjiang and Huanghe Rivers of China, along with some input from the Korean Han, Geum, and Yeongsan Rivers. The sediment provenance of the Yellow Sea is much debated and has generated some quite controversial opinions (Yang et al., 2003). For example, most of the Yellow Sea sediments have been inferred to be derived from Chinese rivers given their huge sediment discharge and circulation patterns (e.g., Schubel et al., 1984; Milliman et al., /$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi: /j.csr

2 16 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Fig. 1. Map showing Korean and Chinese river systems and sampling sites. 1985a, b, 1987; Ren and Shi, 1986; Wells, 1988; Qin et al., 1989; Alexander et al., 1991; Chen et al., 2000; Park et al., 2000). However, there is no direct evidence that Chinese river sediments are supplied to the eastern Korean portion of the Yellow Sea and some researchers have argued that the sediments in this part of the Yellow Sea are supplied mainly from Korean rivers (e.g., Park and Khim, 1992; Lee and Chu, 2001; Chough et al., 2002). Various attempts have been made to ascertain the spatial variability in elemental composition of Yellow Sea sediments in order to determine the proportion and distribution patterns of sediments derived from Korea and China (Hu et al., 1982; Li et al., 1984; Zhang et al., 1990; Huang and Zhang, 1990; Lee et al., 1992; Kim et al., 1998; Cho et al., 1999). However, none of these established the criteria necessary to demonstrate specific sediment origins, or the range in geochemistry of the entire Yellow Sea sedimentary suite. The causes of this failure lie primarily in inconsistencies in the different databases. These included different sampling and analytical procedures, the limited attention paid to grain-size effects, and even an insufficiency of data (Yang et al., 2003). Further, the majority of previous provenance studies in the Yellow Sea concerned themselves with the marine sediments themselves. They took little account of the river sediments being supplied from Korea and China. Systematic differences are to be expected between these two potential sources due to differences in the rock compositions and weathering patterns in the different river basins. In Korea, the bedrock is dominated by Precambrian granite and gneiss and in China by carbonates and loess. Consequently, any attempt to determine the origin of the Yellow Sea sediments must firstly characterize the geochemical compositions of these two potential source end-members. The granulometric characters of sediment exert considerable influence on its elemental concentrations as a result of the so-called silica-dilution effect, and hence it is most important to compensate for any grain-size effects when interpreting elemental concentrations in provenance studies. Normalizing the element concentrations with respect to the concentration of Al (C Element /C Al )isa widely accepted procedure used to minimize sediment grain-size effects. However, the ratio (C Element / C Al ) can give misleading information for determining the provenance of sediments as a result of differences in the basal concentrations of different elements (value of C Element when C Al ¼ 0 or value of C Al when C Element ¼ 0). Consequently, a more robust and comprehensive approach to Al-normalization is required. This study compares and contrasts the geochemical composition of Korean and Chinese river sediments and uses the results to propose a new approach to the interpretation of geochemical data

3 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) as a means of distinguishing sediment provenances in the Yellow Sea. 2. Materials and analytical methods Ninety-three surface sediment samples were taken from the Geum and Yeongsan Rivers of Korea and the Huanghe and Changjiang Rivers of China along with 59 samples of sediments from the Korean coast at Yeongkwang and Haenam Bays and from the Yellow and East China Seas (Fig. 1). Each sediment sample was divided into two to allow for grain-size and geochemical analysis. Grain-size analysis was carried out using standard sieving methods for particles larger than 64 mm and by pipetting for particles smaller than 64 mm (Carver, 1971). For elemental analysis, the sediments were dried in an oven at less than 70 1C and then powdered in an agate mortar. The powered samples were digested with a mixture of HF HNO 3 HClO 4 in sealed Teflon bombs for 10 h and then taken to dryness. These digestion steps were repeated with additional acid until only a negligible amount of white residue remained. Each sample was then leached with dilute HNO 3 and the solution analyzed for Al, Na, Mg, K, Fe, Ca, Ti, Ba, Sr, V, Li, Co, and Cu using ICP-AES in the Isotope Laboratory of the Korea Basic Science Institute (KBSI). Standard reference material (MAG-1) was analyzed with the sample sets to provide a control on analytical precision and accuracy. The results showed that Table 1 Analyses of standard reference material for the major and trace elements concentrations Elements Recommended Measured (n ¼ 3) Na (%) Mg (%) Al (%) K (%) Ca (%) Ti (%) Fe (%) Ba (ppm) Sr (ppm) V (ppm) Li (ppm) Co (ppm) Cu (ppm) s is the standard deviation of measured values; a is accuracy estimated as accuracy ¼ 1 (Element measured in standard / Element recommended for standard ) s a major and trace element concentrations were accurate to within 75% and 78%, respectively (Table 1). The elemental compositions of some river sediments were also analyzed using XRF at KBSI to provide a further check on analytical quality. All procedures were performed simultaneously on all samples to minimize errors between analytical batches. 3. Results and discussion 3.1. Elemental composition of Korean and Chinese river sediments The textural and elemental compositions of Korean and Chinese river sediments are presented in Table 2. Grain-size distribution in the two river sediments varied non-uniformly among sampled stations. In general, the Chinese river sediments were silt-dominant, consisting of more than 73% silt and 14% clay, with a mean grain size ranging from 4 to 7 phi. By contrast, the Korean river sediments consisted of a mixture of silt (average 46%) and clay (average 31%), with a mean grain size ranging from 4 to 9 phi. Most metallic elements analyzed in this study were enriched in the Chinese river sediments, particularly Ca, Na, Sr, and Cu, while some elements were higher in Korean sediments, including Al, K, Ba, and Li (Fig. 2). Lee et al. (1992) reported that Fe was enriched in Chinese river sediments, but this was not the case in our study (Fig. 2). These simply averaged values cannot be used directly as a means of differentiating Korean from Chinese river sediments, partly as a result of grain-size effects, and also due to the large biogenic and anthropogenic contributions, as well as the wide range in elemental concentrations in both the river sediments and those of the Yellow Sea. The concentrations of Al and other elements are plotted in pair diagrams in Fig. 3. The concentrations of Fe, Mg, Ti, V, and Co show strong linear relationships with that of Al in both Korean and Chinese river sediments and highlight the extent to which grain size can affect the concentrations of these elements. Ca and Cu, which have very high concentrations in Chinese river sediments, fail to show such a good correlation. K and Ba are highly enriched in the Korean river sediments and have poor correlation with Al. The most obvious feature of these correlations is the clear separation in the linear regression lines of both groups of river sediments. This same effect occurs in the XRF data

4 18 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Table 2 Comparison of textural compositions and elemental concentrations between the Chinese (the Changjiang and the Huanghe) and Korean (the Geum and the Yeongsan) river sediments Sample no. Sand Silt Clay Na Mg Al K Ca Ti Fe Sr Ba Li V Co Cu (%) (ppm) Chinese river sediments CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ CJ MH MH MH MH MH MH MH MH MH MH MH MH Korean river sediments YS YS YS YS GR GR GR GR GR6* GR7* GR10* GR19* GR30* GR34* GR42* GR44* GR49* GR50* GR54* CJ: Changjiang River; MH: Modern Huanghe River; YS: Yeongsan River; GR: Geum River; asterisk is data obtained from Cho (1994). (Fig. 4) and such differences must reflect differences in the geochemistry of Korean and Chinese rive sediments. Further, most elements of both the Huanghe and the Changjiang River sediments of China plot on the same linear regression line, indicating that there is no geochemical difference

5 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Fig. 2. Average value and standard deviation of mean grain size (Mz) and elemental concentrations in Korean and Chinese river sediments. in the composition of the sediments of these two rivers. This result differs from that found in previous studies of Yang et al. (2002, 2003) reporting that most of the elements, except Na, Ca, Sr, and Ba, were enriched in Changjiang sediments compared to those of Huanghe. This inconsistency may reflect inadequate attention to be differences in grain size when interpreting the analyses of the Changjiang and Huanghe sediments. Our results demonstrate that some elements, including Fe, Mg, Ti, V, and Co, are more enriched in Chinese river sediments than in those of Korea, although both groups have similar grain sizes. Such differences in concentrations are to be expected given the different provenances. The drainage basins of the Chinese rivers (about km 2 in total) are primarily covered by loess, carbonate rock, and clastic deposits (Qu and Yan, 1990; Yang et al., 2004), whereas those of Korean rivers (about km 2 in total) consist mostly of Precambrian igneous and metamorphic rocks, and Jurassic and Cretaceous granite and schist (Lee and Chough, 1989; Chough et al., 2000) Grain-size normalization and sediment provenance discrimination Despite the enrichment in Fe, Mg, Ca, Ti, V, Cu, and Co of Chinese river sediments, other factors need to be considered when tracing these sediments within the Yellow Sea. For example, the high concentrations of Ca and detrital calcite in Chinese river sediments have been used as source indicators (e.g., Milliman et al., 1985a, 1987; Ren and Shi, 1986; Alexander et al., 1991) and we found that both Ca and Sr were much higher in Chinese river sediments than in those of Korea (Fig. 3). However, these two elements can be used to differentiate Korean from Chinese sediments only in limited areas of the Yellow Sea because of strong dilution effects that arise from biogenic components (Li and Qin, 1991; Martin et al., 1993; Cho et al., 1999). As shown in Fig. 5, in fact, Ca concentration in marine sediments is significantly higher than that in river sediments and further its spatial variation in the Yellow Sea displays no systematic gradient. Moreover, the sediments in the eastern part of the Yellow Sea show about 3% of Ca concentration, which is similar to that of western Chinese part. This result is well consistent with distribution patterns of Ca and CaCO 3 concentrations mapped in the whole Yellow Sea by Yang et al. (2003). Therefore, it should be prudent on using Ca as a source indicator in the whole Yellow and East China Seas because of the ubiquitous biogenic carbonates therein. Any calcite in marine sediments can be either detrital or biogenic in origin, and it is nigh on impossible to identify a specific calcitic clast from a given area as having been contributed by a Chinese river (Li and Qin, 1991). Similarly, the concentrations and distribution patterns of some trace elements, such as Cu and Co, are strongly influenced by anthropogenic activity and these elements are generally significantly higher in coastal areas (Yang et al., 2003). In this study, Cu is highly enriched in the Changjiang

6 20 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Fig. 3. Pair diagrams of the concentrations of Al and other elements in Korean and Chinese river sediments (ICP data). Note that the correlations of some elements with Al show different trends for groups of river sediments, suggesting a distinct compositional difference between them.

7 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Fig. 4. Pair diagrams of the concentrations of Al and other elements in Korean and Chinese river sediments (XRF data). River sediments, up to 2 5 factors higher than that in Huanghe and other Korean rivers (Table 2) and has poor correlation with Al in the Chinese river. So, the metallic elements are not an appropriate tracer for provenance discriminations, especially in the highly contaminated and fertile coastal areas of the Yellow Sea. As a result, only Fe, Mg, Ti, and V remain to be used as possible tracers with which to undertake provenance discrimination within the Yellow Sea, assuming that any impact of grain size is given due consideration in analyzing these data. Cho et al. (1999) have already found that V/Al ratios provide good tracers for differentiating sediments of Chinese origin from those of Korean origin in the Yellow Sea. Until now, any compensation for grain size has been undertaken largely by normalizing element concentrations to those of Al. However, a general element/al ratio must be used judiciously. The assumption is usually made that a best-fit linear regression line involving this ratio passes through the origin (0, 0), as shown by the dotted lines in Fig. 6. In general, sediment samples have different granulometric characters and consequently their associated linear regression lines do not necessarily pass through the origin. For example, consider two sets of sediments of different geochemical compositions. The data points of each can be plotted in a pair diagram in terms of their Al concentrations. The two sets of data generate two different regression lines, as shown in Fig. 6. The point where the two regression lines intersect may not be at the origin (0, 0) owing to differences in the elemental and mineralogical compositions of each sample. For practical grainsize normalization it becomes necessary to move the origin to the point of intersection, as shown by the solid lines in Fig. 6.

8 22 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) Fig. 5. Regional distribution map of Ca concentration in the Yellow Sea sediments. The circled data are the average Ca concentrations of the river sediments and numbers indicate Ca concentrations in each station. Fig. 6. Correlations between the concentrations of Al and Fe, Mg in Korean and Chinese river sediments. For Al-normalization, in this study, the intersection point of the two regression lines of Korean and Chinese river sediments is used as the point of origin (0, 0). CR: Chinese river sediments; KR: Korean river sediments. Such revised linear regression lines can be derived for the Fe and Mg values of our data (solid lines in Fig. 6). The corrected Mg/Al and Fe/Al ratios are plotted in Fig. 7. In Fig. 7a, the conventional, uncorrected Mg/Al and Fe/Al ratios show only limited differentiation between Korean and Chinese river sediments and other sediments. However, the corrected Mg/Al and Fe/al ratios clearly differentiate the sediments into distinct groups (Fig. 7b): lower Korean river samples from the eastern part of

9 ARTICLE IN PRESS D.I. Lim et al. / Continental Shelf Research 26 (2006) influence on sediments in the East China Sea, consistent with those previous researchers who concluded that sediments in this area were derived directly from the Chinese rivers, in particular the Changjiang River (Yang, 1989; Lin et al., 2002; Liu et al., 2003; Youn et al., 2005). 4. Conclusions Fig. 7. Comparison of discrimination plots between general Alnormalizing ratio (a) and newly calculated Al-normalizing ratio (b). Note that the revised normalization method provides the advanced geochemical gradient for better understanding of sediment provenance in the Yellow and East China Seas as well as these rivers. the Yellow Sea, central Yellow Sea samples, western Yellow Sea and East China Sea shelf samples, and upper Chinese river samples. Until now, most Yellow Sea sediments, including sediments close to the western coast of Korea, i.e., in the eastern part of the Yellow Sea, have been considered to be derived primarily from Chinese rivers (e.g., Milliman et al., 1985a, b, 1987; Alexander et al., 1991; Park et al., 2000). However, Fig. 7 indicates that sediments discharged from Korean rivers also have a wide influence on the sedimentology of the Yellow Sea and its sediments are formed by a mixing of the material originating from both Korean and Chinese rivers. Material from Korean rivers has little A detailed study of the geochemical characteristics of Korean and Chinese river sediments has provided a means of clearly discriminating the provenance of sediments in the Yellow Sea (West Sea of Korea). There is a distinct compositional difference between the two river sediments that is evident when the concentrations of the different elements are normalized with respect to Al. The Chinese river sediments prove to be enriched in Fe, Mg, Ti, V, and Co compared to their Korean equivalents when allowance is made for grain-size effects. A revised Al-normalization procedure in which the intersection point of the two regression lines of Korean and Chinese river sediments is used as the point of origin (0, 0) provides an improved procedure for discriminating the provenance of sediments in the Yellow Sea. The results indicate that much of the Yellow Sea sediments are a mixture from two distinct sources originating in Korea and China, with the East China Sea sediments predominately of Chinese river origin. The revised grain-size normalization procedure offers an excellent tool for differentiating the source of sediments in the Yellow and East China Seas. Acknowledgement This work was supported by Korea Ocean Research and Development Institute (KORDI) research program (Grant Nos. E94400 and E95800) in Korea. References Alexander, C.R., DeMaster, D.J., Nittrouer, C.A., Sediment accumulation in a modern epicontinental-shelf setting: the Yellow Sea. Marine Geology 98, Carver, R.E., Procedures in Sedimentary Petrology. Wiley- Interscience, New York (653pp). Chen, Z.H., Chen, Z.H., Shi, X.F., Wang, X.Q., Distribution characteristics of carbonate as well as Ca, Sr and Ba in the surface sediments in the south Yellow Sea. Marine Geology and Quaternary Geology 20, 9 16 (in Chinese).

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