Geochemical composition and provenance discrimination of coastal sediments around Cheju Island in the southeastern Yellow Sea

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1 Marine Geology 206 (2004) Geochemical composition and provenance discrimination of coastal sediments around Cheju Island in the southeastern Yellow Sea S.Y. Yang a,b, *, D.I. Lim a, H.S. Jung a, B.C. Oh c a Marine Environment and Climate Change Laboratory, Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul , South Korea b Laboratory of Marine Geology, Department of Marine Geology, Tongji University, Shanghai , PR China c Coastal and Harbor Engineering Laboratory, Korea Ocean Research and Development Institute, Ansan P.O. Box 29, Seoul , South Korea Received 16 June 2003; received in revised form 29 October 2003; accepted 23 January 2004 Abstract Sediments from the northern coastal area of Cheju Island (South Sea of Korea, southeastern Yellow Sea) were analyzed for grain size composition, elemental compositions and clay mineralogy in order to investigate their provenance. Rare earth element (REE) compositions and geochemical discrimination diagrams were revealed to be useful indices for identifying the origin of sediments in the study area. These indices, together with clay mineral compositions, suggest that both the sandy and muddy sediments originated from weathering of the volcanic rocks of Cheju Island, whereas sediments originating from the Changjiang and Huanghe rivers cannot be traced in the study area. Similarly, river-borne matter from the Korea Peninsula has little influence on the sediment deposited. Therefore, the suggestion that fine-grained Changjiang sediments can reach the nearshore area of Cheju Island (the Cheju strait) suggested by oceanic circulation patterns in the Yellow and East China Seas cannot be supported by this study based on geochemical and mineralogical analyses. D 2004 Elsevier B.V. All rights reserved. Keywords: provenance discrimination; Cheju coastal sediment; Geochemistry; Yellow Sea 1. Introduction The distribution and dispersal patterns of Changjiang (Yangtze River) and Huanghe (Yellow River) sediments in the Yellow and East China Seas have been investigated extensively (Milliman et al., 1985a,b, * Corresponding author. Laboratory of Marine Geology, Department of Marine Geology, Tongji University, 1239 Siping Road, Shanghai , PR China. Tel.: ; fax: address: syyang@online.sh.cn (S.Y. Yang). 1987; Ren and Shi, 1986; Alexander et al., 1991; Martin et al., 1993; Zhang, 1999; Yang et al., 2002b, 2003). It has been postulated that the sediments around Cheju Island, located in the southeastern Yellow Sea and the northern margin of the East China Sea, are supplied mostly from the Huanghe River (fine-grained sediments) and from Cheju Island (coarse-grained sediments) (Nittrouer et al., 1984; Milliman et al., 1985a; Youn and Go, 1987; Alexander et al., 1991). Particularly, a mud patch located just southwest of Cheju Island has been interpreted as the distal deposition of Huanghe-derived materials in the East China /$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi: /j.margeo

2 42 S.Y. Yang et al. / Marine Geology 206 (2004) Sea, based on oceanic circulation patterns, sediment accumulation rates and diagnostic occurrence of calcite peaks in clay fraction (DeMaster et al., 1985; Milliman et al., 1985a; Alexander et al., 1991). Thus, Huanghe-derived sediments have been thought to dominate the southern part of the Yellow Sea, including most areas around Cheju Island (Yang et al., 2003). Nevertheless, the sediments from the Korean rivers are Fig. 1. Bathymetric map showing the study area, the oceanic circulation patterns in the Yellow Sea, the sampling locations and the sediment types around Cheju Harbor. Water depth in meters. Round symbols represent samples for grain size analysis alone, whereas square symbols are samples for geochemical and grain size analyses together. YSCC: Yellow Sea Coastal Current; CDFW: Changjiang Diluted Freshwater; YSWC: Yellow Sea Warm Current; KCC: Korea Coastal Current.

3 S.Y. Yang et al. / Marine Geology 206 (2004) suggested by others to exert a great influence on the sedimentation of the southeastern Yellow Sea around the southwestern area of Korea Peninsula (Park and Khim, 1992; Lee and Chu, 2001). Recent study of magnetic properties revealed that both the Changjiang and the old Huanghe sediments are the major source of surface sediment from the fine-grained depositional area on the outer shelf of the East China Sea (Liu et al., 2003). Furthermore, the study on satellite images suggests that a turbid water mass from the southwestern Yellow Sea may reach Cheju Island after mixing with a water mass from the Changjiang estuary in the East China Sea (Lee et al., 1998; Ahn et al., 1999; Sun et al., 2000). In addition, it has been reported that most of the suspended particulate matter from the Changjiang River is dispersed southwards, but some is transported northeastwards as far as about 124j30VE by the Changjiang Dilute Freshwater (CDFW, Fig. 1) during the summer (Milliman et al., 1985b; Zhang, 1999). Therefore, whether and to what extent the suspended particulate matter from the Changjiang and the old Huanghe can reach the Cheju Strait (South Sea of Korea) remains controversial. Cheju Island is the largest (80 km long by 40 km wide) among the numerous islands embraced the Korea Peninsula, and is in a Quaternary shield volcano, composed of hawaiite, alkaline basalt, mugearite and trachyte (Park and Kwon, 1993a,b). It is intuitively considered that the sediments in the vicinity of Cheju Island may be at least partly locally derived. Indeed, this has been suggested for the coarse-grained sediments by Youn and Go (1987). In this study, we present the geochemical and clay mineral compositions of sediments collected around Cheju Island in order to identify the sediment origin. 2. Materials and methods A total of 34 surface sediment samples (upper 5 cm of the bottom) were collected by boat in and around Cheju Harbor, which is located on the northern coast of Cheju Island (Fig. 1). The surface sediments were collected by grab sampler and kept in pre-cleaned polyethylene bag and transferred to laboratory quickly. Sediment grain size was analyzed using a Sedigraph 5100 analyzer for the fine fraction < 63 Am, and standard sieving methods for the >63 Am fraction, after pretreating with 10% H 2 O 2 and 0.1 N HCl to dissolve organic matter and biogenic carbonate. For the analysis of clay minerals, the < 2 Am fraction was separated from the bulk sediment by the pipette method. X-ray diffractograms were obtained from untreated and ethylene-glycol-treated samples, using a Mac Science MXP-3 X-ray diffraction (XRD) system with Ni-filtered CuKa radiation. The relative abundances of major clay minerals were estimated semiquantitatively by peak area on ethylene-glycolated diffractograms (Biscaye, 1965). Powdered particulate splits of 0.2 g bulk samples selected from nine stations were digested for chemical measurements with the method by Yang et al. (2002a). To separate labile and residual fractions of elements in bulk sediment, 0.2 g bulk sediments were leached with 20 ml 1 N HCl for 24 h, and the residues of the leached samples were totally digested with concentrated HF HNO 3 HClO 4 in an airtight Teflon container. Concentrations of major and trace elements in labile and residual fractions were determined by ICP MS (VG Plasma Quad model) and ICP AES (ICPS1000-Ø, Shimazu). The bulk concentration was defined as the sum of labile and residual fractions of a given element. The precision and accuracy of concentrations were monitored by repeated analyses of international geostandard MAG-1. Differences between the determined and recommended values were less than 5%, and the leaching efficiency checked by MAG-1 was about 90%. 3. Results and discussions 3.1. Elemental concentrations of the coastal sediments Mean grain size and elemental concentrations of the Cheju coastal sediments are presented in Table 1, with averaged elemental concentrations of the Cheju volcanic rocks and sediments from the Changjiang, Huanghe and Keum Rivers listed for comparison. The bulk sediments in Cheju Harbor are mud dominant (average 6.8 A in mean grain size), while coarsegrained sands with gravels (average 1.1 A in mean grain size) are dominant outside the harbor (Fig. 1). Mineralogical examination shows that lithological fragments occupy a large proportion in the sandy

4 44 S.Y. Yang et al. / Marine Geology 206 (2004) Table 1 Mean grain size (Mz) and elemental concentrations of the Cheju sediment and the river sediments (unit: A for Mz, *in wt.% and Ag/g for the other elements) Sample Mz K* Na* Ca* Fe* Mg* Al* Ti Mn Sr Ba Sc Li St. 25-res St. 34-res St. 4-res St. 12-res St. 21-res St. 28-res St. 17-res St. 29-res St. 18-res St. 25-lea St. 34-lea St. 4-lea St. 12-lea St. 21-lea St. 28-lea St. 17-lea St. 29-lea St. 18-lea St. 25-bulk St. 34-bulk St. 4-bulk St. 12-buk St. 21-bulk St. 28-bulk St. 17-bulk St. 29-bulk St. 18-bulk Keum River a Cheju volcanic b Changjiang a Huanghe a Sample V Cr Zn Co Ni Cu Rb Y Zr Nb Hf Pb Th St. 25-res St. 34-res St. 4-res St. 12-res St. 21-res St. 28-res St. 17-res St. 29-res St. 18-res St. 25-lea St. 34-lea St. 4-lea St. 12-lea St. 21-lea St. 28-lea St. 17-lea St. 29-lea St. 18-lea St. 25-bulk

5 S.Y. Yang et al. / Marine Geology 206 (2004) Table 1 (continued) Sample V Cr Zn Co Ni Cu Rb Y Zr Nb Hf Pb Th St. 34-bulk St. 4-bulk St. 12-buk St. 21-bulk St. 28-bulk St. 17-bulk St. 29-bulk St. 18-bulk Keum River Cheju volcanic Changjiang Huanghe Sample La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu St. 25-res St. 34-res St. 4-res St. 12-res St. 21-res St. 28-res St. 17-res St. 29-res St. 18-res St. 25-lea St. 34-lea St. 4-lea St. 12-lea St. 21-lea St. 28-lea St. 17-lea St. 29-lea St. 18-lea St. 25-bulk St. 34-bulk St. 4-bulk St. 12-buk St. 21-bulk St. 28-bulk St. 17-bulk St. 29-bulk St. 18-bulk Keum River Cheju volcanic Changjiang Huanghe Note that res and lea denote residual and leached fractions, respectively; bulk is the total values of leached fraction plus residual fraction. a Data from Yang et al. (2003) and this study. b Data from Park and Kwon (1993a,b). sediments. Clay minerals in sediments from Stations 17, 28 and 29 consist primarily of illite (60 62% with an average of 61%), with moderate amounts of chlorite and kaolinite (31 40% in total with an average of 34%), and minor amounts of smectite (< 8%, averaging 5%). Except for rare earth elements

6 46 S.Y. Yang et al. / Marine Geology 206 (2004) (REEs), concentrations of other elements vary considerably with coefficients of variation (CVs) ranging from 15% to 78%. Especially, elements including Pb, Li, Rb, Cu, Th, Ba and Cr exhibit large compositional variations with CVs higher than 30%. Leaching experiments show that elements including K, Al, Ti, Ba, Sc, V, Cr, Rb, Zr, Hf and Nb are primarily enriched in residual fractions (>80% in concentration, Fig. 2), indicating that they behave conservatively in supergene environment and are less diagenetically active. By contrast, elements such as Ca, Sr, Pb, Mg and most REEs were more enriched in the leached (labile) fractions (>75%), indicating that these elements are mainly resided in reactive phases and may be mobile during surficial sediment deposition. Overall, there is no clear relationship between grain size compositions and elemental concentrations in the bulk sediments although concentrations of some trace elements such as Zn, Pb, Rb, Co, V, Fe, Mn and REEs increased with a decrease in mean grain size (Fig. 3). It was particularly difficult to find a linear relationship between mean grain size and Al concentration, shown by higher concentrations in the very coarse- and finegrained sediments (Fig. 3). This observation implies that grain size may not be a dominant controlling factor for elemental composition of the Cheju coastal sediments. Linear relationships, however, exist between many elements in the leachable, residual and bulk fractions (Fig. 4). For example, good correlations are found between Ca and Sr, and between Al and some elements. A positive correlation between Al and Ca exists in the residual fractions, while a negative correlation exists in the leached fractions, which suggest different behaviors of Al and Ca during the acid attack. Al-bound minerals such as aluminosilicates are resistant to acid leaching, whereas main Cacontaining minerals including calcium carbonate (CaCO 3 ) and apatite can be dissolved by acid (Yang Fig. 2. Concentration ratios of acid-leachable and residual fractions of major and trace elements in the Cheju coastal sediments. Note that different elements bear obviously different characters in the 1 N HCl leaching experiments.

7 S.Y. Yang et al. / Marine Geology 206 (2004) Fig. 3. Relationship of elemental concentrations (leached and residual fractions and bulk sediment, being the sum of the former two fractions) with mean grain size (Mz) in the Cheju coastal sediments. No clear trends can be observed between them. Unit of Mz: A. et al., 2002a). A negative correlation between Al and Ca is probably due to carbonate dilution in finegrained sediment, whereas a positive correlation suggests that the clay fraction may contain part of Ca. Overall, REEs yield poor relationship with other trace elements. Compared to the Cheju volcanic rocks and the Chinese (Changjiang and Huanghe) and Korean (Keum) river sediments, the coarse-grained sediments (<2 A in mean grain size, Sts. 4, 12, 21, 25 and 34) from the Cheju coast are characterized by much higher concentrations of Ca and Sr (Table 1), mainly because of the abundant shell fragments in the sediment samples. For most elements, the fine-grained and coarse-grained sediments show similar variation trends in concentrations relative to the Cheju volcanic rocks and the river sediments. Except for K, Ba, Li, Rb, Cu and REEs, other elemental concentrations in the Cheju coastal sediments are higher than or close to those in the river sediments. However, most elements, with the exception of Ca, Sr, Li and Cu, yield lower concentrations in the Cheju coastal sediments relative to the Cheju volcanic rocks (Table 1). The REE distribution patterns (normalized by upper continental crust (UCC)) in Cheju bulk sediments exhibit weak Ce and positive Eu anomalies and a weak enrichment of light rare earth elements (LREEs) with (La/Yb) ranging from 0.99 to 1.60 (Fig. 5). The anomalies of Ce (dce) and Eu (deu) are respectively defined as Ce N /(La N Pr N ) 1/2 and Eu N /(Sm N Gd N ) 1/2, with N being chondrite normalization. The leached fractions show obvious enrichment of middle rare earth elements (MREEs) and stronger REE fractionations relative to the bulk sediments, while the residual fractions bear linear patterns except for distinct Eu anomalies. Especially, the residual fractions of the coarse sandy sediments display stronger positive Eu anomaly with deu varying from 1.86 to Relatively, the anomalies of Ce are very weak in the Cheju coastal sediments witnessed

8 48 S.Y. Yang et al. / Marine Geology 206 (2004) Fig. 4. Comparisons of elemental concentrations in leached and residual fractions and bulk sediments of the Cheju coastal sediments. by averaged dce of 0.93, 0.92 and 0.92 in leached, residual and bulk fractions, respectively Provenance discrimination of the coastal sediments In this study, elemental ratios including Ti/Al, Rb/ Al, Ti/Sc and Zr/Nb were applied to identifying the source of the Cheju coastal sediments in view of the relatively conservative behaviors of these elements during sediment formation and thereby their enrichments in residual fractions. Pair diagrams between Ti/ Al vs. Rb/Al and Ti/Al vs. Zr/Nb clearly indicate that the Cheju coastal sediments bear close resemblance to the Cheju volcanic rocks, but obviously different from the sediments from the Changjiang, Huanghe and Keum Rivers (Fig. 6). Relatively, the elemental compositions of the coarse sandy sediments are closer to those of the Cheju volcanic rocks. The coarse sandy sediments, composed mainly of coarse sand and

9 S.Y. Yang et al. / Marine Geology 206 (2004) Fig. 5. UCC-normalized patterns of REEs of the leachable, residual and bulk fractions in the Cheju coastal sediments. Note that the consistent presence but different degree of positive Eu anomaly in the residual and bulk fractions. gravel, contain a high proportion of rock fragments (up to 70%), which are transported by small rivers and/or storm erosion in the coast (Youn and Go, 1987; Ji and Woo, 1995). REE distribution pattern and fractionation parameters can be good indicators for identifying the sediments originated from Chinese and/or Korean rivers (Yang et al., 2003). Both the bulk samples and leached fractions of all Cheju coastal sediments show very similar UCC-normalized distribution patterns of REE (Fig. 5), suggesting the predominance of leached fractions in bulk REE compositions. The REE fractionations of the Cheju coastal sediments are very similar with that of the Cheju volcanic rocks, with a strong positive Eu anomaly that is absent in the sediments from Chinese and Korean rivers (Fig. 7). Despite the similar REE patterns of the leached fractions between the Cheju coastal sediments and Chinese and Korean river sediments, REE fractionations of the residual fractions of the Cheju coastal sediments are obviously different from those of the river sediments (Fig. 7). Acidleaching experiment indicated that most REEs in the Cheju coastal sediments (30 65% of bulk concentrations for coarse sediments and 34 62% for fine sediments) can be dissolved, whereas only about 20 43% of REEs in the Changjiang and Huanghe sediments are leachable (Yang et al., 2002a). Such different leaching efficiencies of REEs also suggest different compositions of REE-bearing minerals and phases between the Cheju coastal sediments and Chinese and Korean river sediments, which in turn depend on different sediment sources. The calcite peak in the XRD pattern of the clay fraction of sediments around Cheju Island has been suggested as an indicator of Huanghe provenance (Milliman et al., 1985a; Youn and Go, 1987). In this study, calcite peaks occurred in two Cheju coastal sediment samples (Sts. 17 and 29), but not in another

10 50 S.Y. Yang et al. / Marine Geology 206 (2004) Fig. 6. Discrimination plots Ti/Al vs. Ti/Sc, Ti/Al vs. Zr/Nb and Ti/Al vs. Rb/Al. The compositions of the Cheju coastal sediments are very close to that of the Cheju volcanic rocks, but different from those of the river sediments. sample (St. 28) (Fig. 8). The sampling locations of these three samples were all located in the harbor and very close to each another (Fig. 1), and consequently, one would expect the clay mineral compositions to be similar, assuming that the three sediment samples are of the same origin. Therefore, the calcite peaks in the Fig. 7. Comparisons of UCC-normalized REE patterns between the Cheju coastal sediments, Cheju volcanic rocks, the river sediments. The leached fractions have similar distribution patterns between the Cheju coast and river sediments, whereas the residual fractions are distinguishable.

11 S.Y. Yang et al. / Marine Geology 206 (2004) Fig. 8. Representative X-ray diffraction patterns of fine sediments around Cheju Island. Note the occurrence and absence of calcite peak in the patterns. As XRD has been done on the < 2 Am fraction, its mineral contents correspond to this fraction alone. two sediment samples are assumed to have originated from biogenic calcite, which occurs often in the Cheju coastal sediments, and not from detrital calcite of the Huanghe sediments. Furthermore, the low smectite contents in the Cheju sediment samples (< 1% in St. 28, 6% in St. 17 and 7% in St. 29) do not correspond well with high smectite in the Huanghe sediments (generally >10%, Ren and Shi, 1986; Yang et al., 2003), which further suggests that the Huanghe-origin matter cannot be a primary source of the Cheju coastal sediments. Aoki and Qinema (1983) suggested that fine-grained Changjiang sediments are distributed around Cheju Island on the basis of a clay mineral analysis of East China Sea sediments. Clay mineralogy in this study seems to support that the Changjiang and Keum river sediments can be supplied to this area, considering similar clay mineral suits of the Cheju coastal sediments with those of both river sediments (Yang et al., 2003). Geochemical study, however, did not identify the Changjiang- and/or Keum-origin sediments in the study area. Furthermore, smectite can also be derived from weathering alteration of basaltic parent materials under temperate, warm to cool climate conditions, while kaolinite predominates in hot to temperate climate zones (Chamley, 1989). Cheju Island is located in the subtropical climate zone, with an annual average temperature of about 15.5 jc and precipitation of 1500 mm. Therefore, the hot and humid weathering conditions in Cheju Island are responsible for the low contents of smectite and relatively abundant kaolinite in the Cheju coastal sediments. Variable clay mineral assemblages in the Cheju coastal sediments are probably due to different degrees of chemical weathering during the formations of these sediments. The oceanic circulation patterns in the Yellow Sea and the East China Sea are important for an understanding of sediment transport to the Cheju coastal area. During the spring and summer, the northward Taiwan Warm Current may merge with residual tidal currents around the Changjiang estuary, and then split into two branches, with one flowing eastward through the Cheju Strait (Jung et al., 2001). On the basis of drift data and model calculations, the Cheju Warm Current was suggested to circulate clockwise around the island (Lee et al., 2000; Lie et al., 2000). Kim et

12 52 S.Y. Yang et al. / Marine Geology 206 (2004) al. (1991) revealed that low salinity water, originating from the river plume over the Changjiang Bank and extending northeastward towards Cheju Island, separated warm and saline water of oceanic origin around Cheju Island from the surface water of the Yellow Sea. Furthermore, Yang (1997) suggested that the Changjiang Diluted Freshwater is even fed into the East Sea through the South Sea of Korea during the summer. These studies imply that the oceanic circulation patterns in the Yellow and East China Seas may transport fine-grained Changjiang and/or old- Huanghe sediments to the nearshore area of Cheju Island. Satellite data also indicate that turbid water derived from the old Huanghe delta and the Changjiang estuary can intermittently reach the southwestern tip of the Korea Peninsula (Lee et al., 1998; Ahn et al., 1999). However, the present study based on geochemical and mineralogical analyses did not identify the Changjiang- and/or Huanghe-origin sediments in the northern part of Cheju Island, i.e., the Cheju Strait. The Korean river sediments likewise cannot be traced in the study area although they have been suggested to primarily deposit around the southwestern tip of Korea Peninsula transported by the Korea Coast Current (Park and Khim, 1992; Lee and Chu, 2001). 4. Conclusions The elemental characteristics of the coastal sediments around Cheju Island are generally similar to those of the Cheju volcanic rocks, but are clearly different from the sediments from Chinese (Changjiang and Huanghe) and Korean (Keum) Rivers. Discrimination diagrams of Ti/Al vs. Rb/Al, Ti/Al vs. Zr/Nb and Ti/Al vs. Ti/Sc show that both the sandy and muddy sediments around Cheju Island have geochemical compositions similar to the Cheju volcanic rocks. REE distribution patterns of the residual and bulk fractions of the Cheju coastal sediments are very uniform and also similar to that of the Cheju volcanic rock by showing strong positive Eu anomalies, whereas moderate Eu depletion are observed in the Chinese and Korean river sediments. The clay mineral suites of the Cheju coastal sediments are variable and different from those of Chinese and Korean river sediments. The XRD calcite peak of the clay fractions discussed in other studies cannot be used to identify sediments as of Huanghe origin, because of the ubiquitous biogenic carbonate in the fine fraction. Therefore, we infer that not only the coarse sandy sediments but also the very fine particles in the Cheju strait close to Cheju Island are derived from the weathering of volcanic rocks on Cheju Island. Recent studies on oceanic circulation in the Yellow and East China Seas suggest that a branch of the Taiwan Warm Current may reach and possibly turn around the north of Cheju Island, and that turbid water can connect the Changjiang estuary and the southwestern tip of the Korea Peninsula. Our preliminary study, however, did not support that the fine particles from the Changjiang and/or old Huanghe can be transported to the Cheju Strait (the South Sea of Korea). Acknowledgements The authors would like to thank Y.S. Chu, I.K. Um and E.S. Park for field and laboratory assistance. Thanks are extended to G. de Lange, J.J. Middelburg and an anonymous reviewer for their constructive comments. This study is supported by KORDI program (PE 83400) and the MOST research fund (PN 51000) in Korea and partly by the National Foundation of Natural Science of China (Grant No ). References Ahn, Y.H., Lee, H.J., Moon, J.E., Variations of water turbidity in Korean waters. International Symposium on Progress in Coastal Engineering and Oceanography, Seoul, 9 11 September Seoul National University, Seoul, pp Alexander, C.X., DeMaster, D.J., Nittrouer, C.A., Sediment accumulation in a modern epicontinental-shelf setting in the Yellow Sea. Mar. Geol. 98, Aoki, S., Qinema, K., Clay mineral composition in surface sediment and the concentration of suspended matter of the East China Sea. Proceedings of the International Symposium on Sedimentation on the Continental Shelf. China Ocean Press, Beijing, Springer-Verlag, Heidelberg, vol. 1, pp Biscaye, P.E., Mineralogy and sedimentation of recent deepsea clay in the Atlantic Ocean and adjacent seas and oceans. Bull. Geol. Soc. Am. 76, Chamley, H., Clay Sedimentology. Springer-Verlag, Berlin. DeMaster, D.J., Mckee, B.A., Nittrouer, C.A., Qian, J.G., Cheng,

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