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Geochemistry of alkaline earth elements (Mg, Ca, Sr, Ba) in the surface sediments of the Yellow Sea
Chemical Geology 153 Ž1999. 1–10
Geochemistry of alkaline earth elements žMg, Ca, Sr, Ba / in the surface sediments of the Yellow Sea Guebuem Kim a
a,b,)
, Han-Soeb Yang a , Thomas M. Church
b
Department of Oceanography, Bukyong National UniÕersity, Namgu, Daeyeondong, Pusan 608-737, South Korea b College of Marine Studies, UniÕersity of Delaware, Newark, DE 19716, USA Received 8 April 1998; accepted 21 July 1998
Abstract The concentrations of alkaline earth elements were measured in the surface sediments of the Yellow Sea in an attempt to establish their sources from horizontal distributions. The maximum concentrations of Mg are found in the central Yellow Sea, and its horizontal distribution is mainly controlled by quartz dilution. The concentrations of Ca and Sr increase toward the southeastern Yellow Sea region. The relatively higher enrichment of Ca and Sr in the southeastern Yellow Sea, with SrrCa ratios of 0.0053, suggests the presence of carbonates which are comprised of foraminifera andror coccoliths, like deep-sea carbonates. On the other hand, the concentrations of Ba increase toward the northeastern Yellow Sea. The higher Ba enrichment in the sandy region of the northeastern Yellow Sea is associated with the presence of feldspar as evidenced by excellent correlations among BarMg, AlrMg, and SrrCa ratios. Our results suggest that the transgressive and relict sand occurring in the eastern parts of the Yellow Sea contains Al, Sr, and Ba enriched feldspars which originated from Arprock River, Korea and thus can be distinguished from sand occurring in the western parts of the Yellow Sea which originated from Yellow and Yangtze Rivers. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Yellow Sea; Sediment; Mg; Sr; Ba; Ca
1. Introduction Alkaline earth elements in marine sediments have received a considerable attention in view of their assimilation up by marine organisms such as foraminifera, corals, and molluscs. The calcium ion in seawater is used by shellfish to form an outer shell of calcium carbonate, and accumulates over geological time in marine sediments by forming limestone deposits. As such, Mg, Sr, and Ba are associated )
Corresponding author. Tel.: q1-302-8313049; Fax: q1-3028314575; E-mail: [email protected]
with carbonates by forming magnesite ŽMgCO 3 ., strontianite ŽSrCO 3 ., and witherite ŽBaCO 3 . in the marine environment. The Sr and Ba also form celestite ŽSrSO4 . and barite ŽBaSO4 . in association with marine organisms ŽEbbing and Wrighton, 1990.. The Mg, Sr, and Ba may also substitute for Ca in calcite Žespecially Mg. and aragonite Žespecially Sr and Ba.. The Yellow Sea Ž4 = 10 5 km2 in dimension, 50 m in mean depth. is semi-enclosed by the landmasses of China and Korea and is one of the best examples of an epicontinental sea ŽPark and Khim, 1992.. The circulation pattern of the East China Sea
0009-2541r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 5 4 1 Ž 9 8 . 0 0 1 4 9 - 1
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G. Kim et al.r Chemical Geology 153 (1999) 1–10
including the Yellow Sea can be characterized by the strong northward flowing Taiwan Warm Current, the northwestward flowing Yellow Sea Warm Current, the northeastward spreading of the Yangtze Diluted Water in summer, the presence of Yellow Sea Cold Water in summer, and the presence of a cyclonic gyre occurring to the southwest of Cheju Island throughout the year ŽYuan and Su, 1984.. The Yellow and Yangtze Rivers discharge a tremendous volume of sediments and are ranked the second Ž1080 = 10 6 tonsryr. and the fourth Ž478 = 10 6 tonsryr., respectively, in the world ŽMilliman and Meade, 1983; Suk, 1989.. Also, sediments discharged from a number of small-scale rivers in the Korean Peninsula influence the sedimentology of the eastern Yellow Sea ŽChough, 1983.. Therefore, the Yellow Sea provides various textural, structural, and mineralogical characteristics of sediments and has a number of different sources Ži.e., the rivers, atmosphere, and open ocean. for chemical components ŽLee and Chough, 1989; Zhao et al., 1989a,b; Park and Khim, 1990; Zhao et al., 1995.. However, geochemical studies in the Yellow Sea covering coastal regions off both Korea and China have been limited to specific regions due to a long period of political strife between Korea and China. Especially, the geochemistry of alkaline earth elements is poorly understood in the Yellow Sea sediments. Recently, the geographical distribution of sediment grain-size has been successfully mapped by compiling the available data measured by Korean and Chinese workers ŽPark et al., 1986; Lee et al., 1992.. Also, the origins of clay in the Yellow Sea have been well documented using mineralogical characteristics ŽPark et al., 1986; Lee and Chough, 1989; Suk, 1989; Park and Khim, 1990.. For example, the clay sediments accumulating in the central Yellow Sea originate from the Yellow River with an accumulation rate of 2.2 = 10 8 tonsryr, and those in the southeastern Yellow Sea originate from Keum and Youngsang Rivers, Korea ŽLee and Chough, 1989; Park and Khim, 1992; Khim and Park, 1992.. However, the origin of sand, which particularly predominates in the northeastern Yellow Sea, has not been documented by geochemical studies. In this study, we aim to Ž1. establish the sources of alkaline earth elements ŽMg, Sr, Ba, Ca. which
can be affected by complex weathering processes and different sediment origins and also by biological productivity in the overlying surface ocean, based on their horizontal distributions and Ž2. elucidate the factors controlling the distribution of each element based on various geochemical parameters such as grain size, organic content, etc.
2. Materials and methods Surface sediments were obtained in 1992 using a Van Veen grab from 49 sites of the Yellow Sea ŽFig. 1.. Soon after sampling, the samples were packed in polyethylene bags, and frozen at y208C. Grain-size analysis was carried out by a sieving method for the sediments larger than 4f, and by a pipette method for the sediments smaller than 4f. The samples were dried to a constant weight at 608C and ground to a fine powder using an agate mortar. About 5 g of dried sediments were ignited for 5 h at 4508C to obtain loss on ignition. For the analysis of chemical elements, 0.5–5 g of dried sediments were digested with a mixture of 6 ml of conc. HF, 3 ml of conc. HNO 3 , and 2 ml of conc. HClO4 . The samples were digested with lids for 6 h and dried without lids. These steps were repeated until only a negligible amount of white residue remained following the addition of the acids again. The solution was centrifuged at 3000 rpm for 20 min to obtain clear leachate for the following measurements. The Al, Mg, Ba, Ca, and Sr along with transition elements were measured by an ICP-AES ŽInductively Coupled Plasma Atomic Emission Spectrophotometer, Model JY58P-1, Seiko Instruments and Electronics. following an appropriate dilution necessary for each element. For three reagent blanks, the concentration of each element was less than 1% of the mean concentration of all sediment samples. Although the certified standard materials were not measured, the previously reported results ŽZhao et al., 1995. in the eastern and central Yellow Sea overlapping with this study area fall onto our regression line within 95% prediction level on the metal versus Al plots. They showed very low relative errors Ž- 5%. compared with the highest-grade national standard samples, supporting the accuracy of the absolute values. The measured concentrations in
G. Kim et al.r Chemical Geology 153 (1999) 1–10
3
Fig. 1. Bathymetry and location of sediment sampling stations in the Yellow Sea.
this study may represent mean values of surface sediments up to 20 cm since a grab sampler was used for sampling ŽCauwet, 1987..
3. Results and discussions Results for LOI, Al, Mg, Ca, Ba, and Sr are presented in Table 1. The grain size displays large horizontal variation ranging from 1% Žnortheastern Yellow Sea. to 100% Žcentral Yellow Sea. of silt
plus clay ŽFig. 2.. It has been suggested that the clay minerals in the central Yellow Sea originate mainly from the old and present Yellow River, whereas the clay minerals in the southeastern Yellow Sea are associated with the Keum and Yeongsan Rivers in Korea, based on the clay mineral characteristics in the Chinese and Korean rivers ŽPark and Khim, 1992; Khim and Park, 1992.. On the other hand, the sandy areas occurring in the northeastern Yellow Sea and southwest of Shandong Peninsula are considered as transgressive and relict sediments, whereas those
G. Kim et al.r Chemical Geology 153 (1999) 1–10
4
Table 1 Contents of SqC Žsilt plus clay., LOI Žloss on ignition., Al, Mg, Ca, Ba, and Sr in the surface sediments of the Yellow Sea Stn.
SqC Ž%.
LOI Ž%.
Al Ž%.
Mg Ž%.
Ca Ž%.
Ba Žppm.
Sr Žppm.
A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 C1 C2 C3 C4 C5 C6 C7 C8 C9 D1 D2 D3 D4 D5 D6 D7 D8 E1 E2 E3 E4 E5 E6 E7 F1 F2 F3 F4 F5 F6 F7 F8
1 1 24 38 17 64 66 31 16 9 38 97 100 100 100 100 93 41 51 73 93 100 100 100 82 36 64 82 69 68 82 90 91 94 84 78 79 73 81 99 38 98 100 87 69 61 26 45 67
0.38 0.57 1.33 1.12 1.07 3.89 1.61 1.60 0.89 0.86 1.68 6.48 6.72 5.09 8.09 4.21 3.16 6.71 0.70 3.41 5.70 6.70 7.43 7.56 4.99 4.81 1.39 2.59 5.89 3.63 3.02 6.10 5.04 6.18 4.89 7.71 6.83 5.95 4.64 5.74 7.13 1.96 6.06 6.56 6.60 2.98 4.15 1.38 1.58
3.49 4.33 5.54 5.77 6.01 7.19 6.73 5.98 4.67 4.95 5.71 8.86 11.19 9.28 9.36 8.84 7.82 4.90 6.18 7.93 8.38 8.77 8.76 8.28 6.71 5.28 3.23 5.89 5.65 6.81 7.40 7.91 7.99 7.63 7.39 7.08 6.86 6.80 7.07 7.15 5.46 7.41 8.34 7.03 5.92 6.17 5.27 6.07 5.29
0.11 0.14 0.45 0.45 0.43 1.09 1.01 0.56 0.33 0.29 0.49 1.60 2.21 1.87 1.88 1.88 1.49 0.45 0.68 1.23 1.47 1.68 1.73 1.63 1.22 0.54 0.61 1.06 0.87 1.00 1.26 1.46 1.41 1.57 1.46 1.34 1.37 1.42 1.19 1.54 1.24 1.55 1.81 1.42 1.17 1.20 0.91 1.15 0.95
0.21 0.34 0.63 0.55 0.70 1.98 1.83 0.72 0.50 0.53 0.62 0.88 1.16 1.18 1.46 1.61 2.32 0.82 0.84 1.23 1.44 1.68 1.75 1.74 1.41 1.02 7.43 4.39 3.42 1.95 2.37 2.87 2.11 2.55 3.75 3.49 2.97 2.92 1.96 4.15 3.24 6.34 3.89 3.15 1.44 2.29 1.55 2.09 1.72
756 810 777 816 803 574 533 734 765 811 769 527 643 521 542 542 512 682 688 568 523 488 483 482 522 622 315 426 541 616 537 506 532 441 471 509 439 432 477 429 415 403 444 450 444 455 495 468 441
133 165 201 213 226 222 213 204 176 189 195 154 187 152 164 161 203 171 195 183 178 169 167 171 192 216 488 316 292 221 217 204 198 194 241 230 207 206 176 200 221 351 229 206 193 206 201 204 213
Fig. 2. Horizontal distributions of SqC Žsilt plus clay. and LOI Žloss on ignition. in the bottom sediments of the Yellow Sea.
in the north of the Yangtze River mouth are considered as a remnant of tidal current winnowing ŽPark and Khim, 1990.. The maximum concentrations of Mg are observed in the central Yellow Sea, where clay minerals predominate ŽFig. 3.. However, all other measured alkaline earth elements show different horizontal distributions. For examples, Ca and Sr concentrations
G. Kim et al.r Chemical Geology 153 (1999) 1–10
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Fig. 3. Horizontal distributions of Mg, Ca, Ba, and Sr in the bottom sediments of the Yellow Sea.
increase toward the southeastern Yellow Sea, and Ba concentrations increase toward the northeastern Yellow Sea where the sand predominates ŽFig. 3.. To examine factors controlling Mg distribution in the surface sediment of the Yellow Sea, Mg is plotted against silt plus clay content ŽFig. 4.. Most of the samples fall on or close to the 95% confidence level by regression analysis, except for some samples, indicating that silt plus clay dilution by quartz is the most important factor controlling Mg distribution in the Yellow Sea. The abnormally lower ratios
are observed in the southeastern Yellow Sea Žstations D1, D2, and D3.. This can be attributed to the dilution of Mg by calcium carbonates. On the contrary, exceptionally larger Mg versus silt plus clay at stations E7, F6, and F7 are located in the plume area of Yangtze River where sand predominates Žsand ) 40%.. This suggests either the presence of authigenic compounds such as MgO andror MgCO 3 in the sediments or relatively high Mg-enriched suspended matter inputs from the Yangtze River. Alternatively, Calvert Ž1976. suggested that the ion ex-
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G. Kim et al.r Chemical Geology 153 (1999) 1–10
Fig. 4. Plots between silt plus clay versus Mg in the bottom sediments of the Yellow Sea, with a 95% prediction interval.
change of Mg for Fe produces higher MgrFe ratios in anoxic sediments in the South West African continental regions. In order to define the occurrence and enrichment mechanism of Mg in the Yangtze River plume region, more studies are necessary. Based on the assumption that Mg is only controlled by quartz and carbonate dilution, we plotted Ca against Mg ŽFig. 5a.. As expected from their horizontal distributions, the plot shows a large scatter. The Ca shows a good correlation with Sr, within the range from 3–8% of Ca contents ŽFig. 5b.. Turekian Ž1964. has documented SrrCa ratios for seawater Ž0.0202., stream Ž0.0045–0.0082., corals Žy0.020., molluscs Ž0.00375., and deep-sea carbonates Ž0.00525.. The observed SrrCa ratio for carbonates in the southeastern Yellow Sea is close to that in deep-sea carbonates, which are mainly composed of foraminifera and coccoliths ŽFig. 5b.. This result is consistent with the result from Niino and Emery
Ž1961. that foraminifera are the main contributor of carbonates in the Yellow Sea. We also found increases of Ba, Al, and Sr with respect to the continental sediment in the northeastern Yellow Sea where sand predominates ŽFig. 5b–d.. First, we examined the possibility of marine barite presence in the northeastern Yellow Sea, based on Ba and Sr enrichment. However, this is unlikely considering the fact that the lowest LOI content is observed in this sandy region ŽFig. 2.. Alternatively, such high contents of Ba, along with Al and Sr, can be found if Ba enriched feldspar is present. We hypothesize that if all the ‘excess’ Ba, Al, and Sr over the dilution line ŽFig. 5b–d. between clay and quartzrcarbonates are associated with feldspar which originates from the same source region, there should be correlations among their ratios. Indeed, we found excellent correlation between BarMg versus AlrMg ratios and between SrrCa versus AlrMg ratios
G. Kim et al.r Chemical Geology 153 (1999) 1–10
7
Fig. 5. Plots between Ca versus Mg Ža. and Sr Žb., and Mg versus Al Žc. and Ba Žd., in the bottom sediments of the Yellow Sea. The solid lines in plots between Mg vs. Ca Ža., Al Žc., and Ba Žd. represent the dilution of a Chinese continental sediment component by quartz. The solid line in plots between Sr vs. Ca Žb. represents the dilution of CaCO 3 Žforaminifera. by quartz.
ŽFig. 6., suggesting the presence of feldspars ŽSmith and Brown, 1988.. Zhao et al. Ž1989a,b. also found high enrichments of K and Rb in recent sand occurring in the most northeastern Yellow Sea, which originates from the Arprock River ŽYalu River., and attributed this to the presence of K-feldspar. However, they could not find
such a feldspar signature in the relict sand occurring in the Old Yellow River mouth, and north of Shandong Peninsula. Based on their results and our observations, it is evident that the transgressive and relict sand ŽPark and Khim, 1990. occurring in the eastern parts of the Yellow Sea contains Al, Sr, and Ba enriched feldspars. These feldspars appear to origi-
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G. Kim et al.r Chemical Geology 153 (1999) 1–10
Fig. 6. Plots of AlrMg versus BarMg Ža., and AlrMg versus SrrCa Žb., in the bottom sediments of the Yellow Sea, with a 95% prediction interval.
G. Kim et al.r Chemical Geology 153 (1999) 1–10
nate from Arprock River, Korea Žsee sand-distribution map in Lee and Chough, 1989. and can be clearly differentiated from sand originating in the Yellow and Yangtze rivers, which show much lower K and Rb contents. We suggest the possibility of dispersion of K-feldspar produced from the volcanic mountain Baegdu, which is located closely to the Arprock River, in the course of the weathering processes. To confirm this hypothesis, the measurements of K, Rb, Ba, Sr, and Al from possible sand-source regions, as well as direct determination of feldspar in the entire Yellow Sea sediment, are necessary.
4. Conclusion The distribution of Mg is mainly controlled by quartz and carbonate dilution of clay minerals in the Yellow Sea. However, relatively high Mg over the clay and sand mixing line is observed in the plume region of Yangtze River. This requires more extensive studies to define the Mg enrichment mechanism in these coastal sediments. The distributions of Ca and Sr are mainly controlled by the presence of carbonate shells which are comprised of foraminifera andror coccoliths, inferred from SrrCa ratios Ž0.0052., with their maximum occurrence in the southeastern Yellow Sea. The direct measurements of foraminifera contents over the extent of entire Yellow Sea may be necessary to confirm its contribution to the carbonate contents. The presence of Ba, Al, and Sr enriched feldspar is found in the sandy region of the northeastern Yellow Sea, and these feldspars appear to originate from the Arprock River, Korea. However, such feldspar signature is not observed in sand occurring in the western part of the Yellow Sea which originates from the Yellow or Yangtze Rivers. Therefore, we suggest that such a feldspar-labeled sand originating from Arprock River can serve as an excellent tracer of its dispersion throughout the Yellow Sea.
Acknowledgements We thank Prof. Jae-Sang Hong ŽIn-ha Univ., Korea. who collected the Van Veen Grab samples for
9
this study as a part of ‘The Exploitation Research of Marine Resources on the Yellow Sea’. We also indebted to Prof. Y. Nozaki and Y. Kodama ŽUniv. of Tokyo. for their assistance in ICP measurements and further discussions regarding the data analyses. We also thank Drs. M.M. Sarin, N. Hussain, J.J.G. Zwolsman, and G. Douglas who gave valuable comments on the manuscript.
References Calvert, S.E., 1976. The mineralogy and geochemistry of nearshore sediments. In: Riley, J.P., Chester, R. ŽEds.., Chemical Oceanography. Academic Press, London, pp. 187–271. Cauwet, G., 1987. Influence of sedimentological features on the distribution of trace metals in marine sediments. Mar. Chem. 22, 221–234. Chough, S.K., 1983. Marine Geology of Korean Seas. IHRDC, Boston. Ebbing, D.D., Wrighton, M.S., 1990. General Chemistry. Houghton Mifflin, Boston, 1035 pp. Khim, B.K., Park, Y.A., 1992. Smectite as a possible source-indicative clay mineral in the Yellow Sea. Geo-Mar. Lett. 12, 228–231. Lee, C.B., Jung, H.S., Jeong, K.S., 1992. Distribution of some metallic elements in surface sediments of the southeastern Yellow Sea. J. Oceanol. Soc., Korea 27, 55–65. Lee, H.J., Chough, S.K., 1989. Sediment distribution, dispersal and budget in the Yellow Sea. Mar. Geol. 87, 195–205. Milliman, J.D., Meade, R.H., 1983. World-wide delivery of river sediment to the oceans. J. Geol. 91, 1–21. Niino, H., Emery, K.O., 1961. Sediments of shallow portions of East China Sea and South China Sea. Geol. Soc. Am. Bull. 72, 731–762. Park, Y.A., Khim, B.K., 1990. Clay minerals of the recent finegrained sediments on the Korean continental shelves. Cont. Shelf. Res. 12, 1179–1191. Park, Y.A., Khim, B.K., 1992. Origin and dispersal of recent clay minerals in the Yellow Sea. Mar. Geol. 104, 205–213. Park, Y.A., Kim, S.C., Choi, J.H., 1986. The distribution and transportation of fine-grained sediments on the inner continental shelf off the Keum River estuary, Korea. Cont. Shelf. Res. 5, 499–519. Smith, J.V., Brown, W.L., 1988. Feldspar Minerals. Crystal Structures, Physical, Chemical and Microtextural Properties, Vol. 1. Springer-Verlag, Berlin, 828 pp. Suk, B.C., 1989. Sedimentology and history of sea level changes in the East China Sea and adjacent seas. In: Taira, A., Masuda, F. ŽEds.., Sedimentary Facies in the Active Plate Margin. Terra Scientific Publishing, Tokyo, pp. 215–231. Turekian, K.K., 1964. The marine geochemistry of strontium. Geochim. Cosmochim. Acta 28, 1479–1496. Yuan, Y., Su, J., 1984. Numerical modeling of the circulation in
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the East China Sea. In: Ichiye, T. ŽEd.., Ocean Hydrodynamics of the Japan and East China Seas. Elsevier, pp. 167–186. Zhao, Y., Li, F., Han, G., 1989a. Chemical differences among various sediments of the Huanghai Sea ŽYellow Sea.. In: Developments in Geoscience ŽChinese Academy of Science., Contribution to 28th International Geological Congress, Washington, DC, USA. Science Press, Beijing, China, pp. 299–307.
Zhao, Y., He, L., Chen, Y., 1989b. On regional distribution patterns of elements in sediments of the Haunghai Sea. Mar. Sci. ŽChina. 1, 15–22. Zhao, Y.-Y., Yan, M.-C., Jiang, R.-H., 1995. Abundance of chemical elements in continental shelf sediment of China. Geo-Mar. Lett. 15, 71–76.
Geochemistry of alkaline earth elements žMg, Ca, Sr, Ba / in the surface sediments of the Yellow Sea Guebuem Kim a
a,b,)
, Han-Soeb Yang a , Thomas M. Church
b
Department of Oceanography, Bukyong National UniÕersity, Namgu, Daeyeondong, Pusan 608-737, South Korea b College of Marine Studies, UniÕersity of Delaware, Newark, DE 19716, USA Received 8 April 1998; accepted 21 July 1998
Abstract The concentrations of alkaline earth elements were measured in the surface sediments of the Yellow Sea in an attempt to establish their sources from horizontal distributions. The maximum concentrations of Mg are found in the central Yellow Sea, and its horizontal distribution is mainly controlled by quartz dilution. The concentrations of Ca and Sr increase toward the southeastern Yellow Sea region. The relatively higher enrichment of Ca and Sr in the southeastern Yellow Sea, with SrrCa ratios of 0.0053, suggests the presence of carbonates which are comprised of foraminifera andror coccoliths, like deep-sea carbonates. On the other hand, the concentrations of Ba increase toward the northeastern Yellow Sea. The higher Ba enrichment in the sandy region of the northeastern Yellow Sea is associated with the presence of feldspar as evidenced by excellent correlations among BarMg, AlrMg, and SrrCa ratios. Our results suggest that the transgressive and relict sand occurring in the eastern parts of the Yellow Sea contains Al, Sr, and Ba enriched feldspars which originated from Arprock River, Korea and thus can be distinguished from sand occurring in the western parts of the Yellow Sea which originated from Yellow and Yangtze Rivers. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Yellow Sea; Sediment; Mg; Sr; Ba; Ca
1. Introduction Alkaline earth elements in marine sediments have received a considerable attention in view of their assimilation up by marine organisms such as foraminifera, corals, and molluscs. The calcium ion in seawater is used by shellfish to form an outer shell of calcium carbonate, and accumulates over geological time in marine sediments by forming limestone deposits. As such, Mg, Sr, and Ba are associated )
Corresponding author. Tel.: q1-302-8313049; Fax: q1-3028314575; E-mail: [email protected]
with carbonates by forming magnesite ŽMgCO 3 ., strontianite ŽSrCO 3 ., and witherite ŽBaCO 3 . in the marine environment. The Sr and Ba also form celestite ŽSrSO4 . and barite ŽBaSO4 . in association with marine organisms ŽEbbing and Wrighton, 1990.. The Mg, Sr, and Ba may also substitute for Ca in calcite Žespecially Mg. and aragonite Žespecially Sr and Ba.. The Yellow Sea Ž4 = 10 5 km2 in dimension, 50 m in mean depth. is semi-enclosed by the landmasses of China and Korea and is one of the best examples of an epicontinental sea ŽPark and Khim, 1992.. The circulation pattern of the East China Sea
0009-2541r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 5 4 1 Ž 9 8 . 0 0 1 4 9 - 1
2
G. Kim et al.r Chemical Geology 153 (1999) 1–10
including the Yellow Sea can be characterized by the strong northward flowing Taiwan Warm Current, the northwestward flowing Yellow Sea Warm Current, the northeastward spreading of the Yangtze Diluted Water in summer, the presence of Yellow Sea Cold Water in summer, and the presence of a cyclonic gyre occurring to the southwest of Cheju Island throughout the year ŽYuan and Su, 1984.. The Yellow and Yangtze Rivers discharge a tremendous volume of sediments and are ranked the second Ž1080 = 10 6 tonsryr. and the fourth Ž478 = 10 6 tonsryr., respectively, in the world ŽMilliman and Meade, 1983; Suk, 1989.. Also, sediments discharged from a number of small-scale rivers in the Korean Peninsula influence the sedimentology of the eastern Yellow Sea ŽChough, 1983.. Therefore, the Yellow Sea provides various textural, structural, and mineralogical characteristics of sediments and has a number of different sources Ži.e., the rivers, atmosphere, and open ocean. for chemical components ŽLee and Chough, 1989; Zhao et al., 1989a,b; Park and Khim, 1990; Zhao et al., 1995.. However, geochemical studies in the Yellow Sea covering coastal regions off both Korea and China have been limited to specific regions due to a long period of political strife between Korea and China. Especially, the geochemistry of alkaline earth elements is poorly understood in the Yellow Sea sediments. Recently, the geographical distribution of sediment grain-size has been successfully mapped by compiling the available data measured by Korean and Chinese workers ŽPark et al., 1986; Lee et al., 1992.. Also, the origins of clay in the Yellow Sea have been well documented using mineralogical characteristics ŽPark et al., 1986; Lee and Chough, 1989; Suk, 1989; Park and Khim, 1990.. For example, the clay sediments accumulating in the central Yellow Sea originate from the Yellow River with an accumulation rate of 2.2 = 10 8 tonsryr, and those in the southeastern Yellow Sea originate from Keum and Youngsang Rivers, Korea ŽLee and Chough, 1989; Park and Khim, 1992; Khim and Park, 1992.. However, the origin of sand, which particularly predominates in the northeastern Yellow Sea, has not been documented by geochemical studies. In this study, we aim to Ž1. establish the sources of alkaline earth elements ŽMg, Sr, Ba, Ca. which
can be affected by complex weathering processes and different sediment origins and also by biological productivity in the overlying surface ocean, based on their horizontal distributions and Ž2. elucidate the factors controlling the distribution of each element based on various geochemical parameters such as grain size, organic content, etc.
2. Materials and methods Surface sediments were obtained in 1992 using a Van Veen grab from 49 sites of the Yellow Sea ŽFig. 1.. Soon after sampling, the samples were packed in polyethylene bags, and frozen at y208C. Grain-size analysis was carried out by a sieving method for the sediments larger than 4f, and by a pipette method for the sediments smaller than 4f. The samples were dried to a constant weight at 608C and ground to a fine powder using an agate mortar. About 5 g of dried sediments were ignited for 5 h at 4508C to obtain loss on ignition. For the analysis of chemical elements, 0.5–5 g of dried sediments were digested with a mixture of 6 ml of conc. HF, 3 ml of conc. HNO 3 , and 2 ml of conc. HClO4 . The samples were digested with lids for 6 h and dried without lids. These steps were repeated until only a negligible amount of white residue remained following the addition of the acids again. The solution was centrifuged at 3000 rpm for 20 min to obtain clear leachate for the following measurements. The Al, Mg, Ba, Ca, and Sr along with transition elements were measured by an ICP-AES ŽInductively Coupled Plasma Atomic Emission Spectrophotometer, Model JY58P-1, Seiko Instruments and Electronics. following an appropriate dilution necessary for each element. For three reagent blanks, the concentration of each element was less than 1% of the mean concentration of all sediment samples. Although the certified standard materials were not measured, the previously reported results ŽZhao et al., 1995. in the eastern and central Yellow Sea overlapping with this study area fall onto our regression line within 95% prediction level on the metal versus Al plots. They showed very low relative errors Ž- 5%. compared with the highest-grade national standard samples, supporting the accuracy of the absolute values. The measured concentrations in
G. Kim et al.r Chemical Geology 153 (1999) 1–10
3
Fig. 1. Bathymetry and location of sediment sampling stations in the Yellow Sea.
this study may represent mean values of surface sediments up to 20 cm since a grab sampler was used for sampling ŽCauwet, 1987..
3. Results and discussions Results for LOI, Al, Mg, Ca, Ba, and Sr are presented in Table 1. The grain size displays large horizontal variation ranging from 1% Žnortheastern Yellow Sea. to 100% Žcentral Yellow Sea. of silt
plus clay ŽFig. 2.. It has been suggested that the clay minerals in the central Yellow Sea originate mainly from the old and present Yellow River, whereas the clay minerals in the southeastern Yellow Sea are associated with the Keum and Yeongsan Rivers in Korea, based on the clay mineral characteristics in the Chinese and Korean rivers ŽPark and Khim, 1992; Khim and Park, 1992.. On the other hand, the sandy areas occurring in the northeastern Yellow Sea and southwest of Shandong Peninsula are considered as transgressive and relict sediments, whereas those
G. Kim et al.r Chemical Geology 153 (1999) 1–10
4
Table 1 Contents of SqC Žsilt plus clay., LOI Žloss on ignition., Al, Mg, Ca, Ba, and Sr in the surface sediments of the Yellow Sea Stn.
SqC Ž%.
LOI Ž%.
Al Ž%.
Mg Ž%.
Ca Ž%.
Ba Žppm.
Sr Žppm.
A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 C1 C2 C3 C4 C5 C6 C7 C8 C9 D1 D2 D3 D4 D5 D6 D7 D8 E1 E2 E3 E4 E5 E6 E7 F1 F2 F3 F4 F5 F6 F7 F8
1 1 24 38 17 64 66 31 16 9 38 97 100 100 100 100 93 41 51 73 93 100 100 100 82 36 64 82 69 68 82 90 91 94 84 78 79 73 81 99 38 98 100 87 69 61 26 45 67
0.38 0.57 1.33 1.12 1.07 3.89 1.61 1.60 0.89 0.86 1.68 6.48 6.72 5.09 8.09 4.21 3.16 6.71 0.70 3.41 5.70 6.70 7.43 7.56 4.99 4.81 1.39 2.59 5.89 3.63 3.02 6.10 5.04 6.18 4.89 7.71 6.83 5.95 4.64 5.74 7.13 1.96 6.06 6.56 6.60 2.98 4.15 1.38 1.58
3.49 4.33 5.54 5.77 6.01 7.19 6.73 5.98 4.67 4.95 5.71 8.86 11.19 9.28 9.36 8.84 7.82 4.90 6.18 7.93 8.38 8.77 8.76 8.28 6.71 5.28 3.23 5.89 5.65 6.81 7.40 7.91 7.99 7.63 7.39 7.08 6.86 6.80 7.07 7.15 5.46 7.41 8.34 7.03 5.92 6.17 5.27 6.07 5.29
0.11 0.14 0.45 0.45 0.43 1.09 1.01 0.56 0.33 0.29 0.49 1.60 2.21 1.87 1.88 1.88 1.49 0.45 0.68 1.23 1.47 1.68 1.73 1.63 1.22 0.54 0.61 1.06 0.87 1.00 1.26 1.46 1.41 1.57 1.46 1.34 1.37 1.42 1.19 1.54 1.24 1.55 1.81 1.42 1.17 1.20 0.91 1.15 0.95
0.21 0.34 0.63 0.55 0.70 1.98 1.83 0.72 0.50 0.53 0.62 0.88 1.16 1.18 1.46 1.61 2.32 0.82 0.84 1.23 1.44 1.68 1.75 1.74 1.41 1.02 7.43 4.39 3.42 1.95 2.37 2.87 2.11 2.55 3.75 3.49 2.97 2.92 1.96 4.15 3.24 6.34 3.89 3.15 1.44 2.29 1.55 2.09 1.72
756 810 777 816 803 574 533 734 765 811 769 527 643 521 542 542 512 682 688 568 523 488 483 482 522 622 315 426 541 616 537 506 532 441 471 509 439 432 477 429 415 403 444 450 444 455 495 468 441
133 165 201 213 226 222 213 204 176 189 195 154 187 152 164 161 203 171 195 183 178 169 167 171 192 216 488 316 292 221 217 204 198 194 241 230 207 206 176 200 221 351 229 206 193 206 201 204 213
Fig. 2. Horizontal distributions of SqC Žsilt plus clay. and LOI Žloss on ignition. in the bottom sediments of the Yellow Sea.
in the north of the Yangtze River mouth are considered as a remnant of tidal current winnowing ŽPark and Khim, 1990.. The maximum concentrations of Mg are observed in the central Yellow Sea, where clay minerals predominate ŽFig. 3.. However, all other measured alkaline earth elements show different horizontal distributions. For examples, Ca and Sr concentrations
G. Kim et al.r Chemical Geology 153 (1999) 1–10
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Fig. 3. Horizontal distributions of Mg, Ca, Ba, and Sr in the bottom sediments of the Yellow Sea.
increase toward the southeastern Yellow Sea, and Ba concentrations increase toward the northeastern Yellow Sea where the sand predominates ŽFig. 3.. To examine factors controlling Mg distribution in the surface sediment of the Yellow Sea, Mg is plotted against silt plus clay content ŽFig. 4.. Most of the samples fall on or close to the 95% confidence level by regression analysis, except for some samples, indicating that silt plus clay dilution by quartz is the most important factor controlling Mg distribution in the Yellow Sea. The abnormally lower ratios
are observed in the southeastern Yellow Sea Žstations D1, D2, and D3.. This can be attributed to the dilution of Mg by calcium carbonates. On the contrary, exceptionally larger Mg versus silt plus clay at stations E7, F6, and F7 are located in the plume area of Yangtze River where sand predominates Žsand ) 40%.. This suggests either the presence of authigenic compounds such as MgO andror MgCO 3 in the sediments or relatively high Mg-enriched suspended matter inputs from the Yangtze River. Alternatively, Calvert Ž1976. suggested that the ion ex-
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Fig. 4. Plots between silt plus clay versus Mg in the bottom sediments of the Yellow Sea, with a 95% prediction interval.
change of Mg for Fe produces higher MgrFe ratios in anoxic sediments in the South West African continental regions. In order to define the occurrence and enrichment mechanism of Mg in the Yangtze River plume region, more studies are necessary. Based on the assumption that Mg is only controlled by quartz and carbonate dilution, we plotted Ca against Mg ŽFig. 5a.. As expected from their horizontal distributions, the plot shows a large scatter. The Ca shows a good correlation with Sr, within the range from 3–8% of Ca contents ŽFig. 5b.. Turekian Ž1964. has documented SrrCa ratios for seawater Ž0.0202., stream Ž0.0045–0.0082., corals Žy0.020., molluscs Ž0.00375., and deep-sea carbonates Ž0.00525.. The observed SrrCa ratio for carbonates in the southeastern Yellow Sea is close to that in deep-sea carbonates, which are mainly composed of foraminifera and coccoliths ŽFig. 5b.. This result is consistent with the result from Niino and Emery
Ž1961. that foraminifera are the main contributor of carbonates in the Yellow Sea. We also found increases of Ba, Al, and Sr with respect to the continental sediment in the northeastern Yellow Sea where sand predominates ŽFig. 5b–d.. First, we examined the possibility of marine barite presence in the northeastern Yellow Sea, based on Ba and Sr enrichment. However, this is unlikely considering the fact that the lowest LOI content is observed in this sandy region ŽFig. 2.. Alternatively, such high contents of Ba, along with Al and Sr, can be found if Ba enriched feldspar is present. We hypothesize that if all the ‘excess’ Ba, Al, and Sr over the dilution line ŽFig. 5b–d. between clay and quartzrcarbonates are associated with feldspar which originates from the same source region, there should be correlations among their ratios. Indeed, we found excellent correlation between BarMg versus AlrMg ratios and between SrrCa versus AlrMg ratios
G. Kim et al.r Chemical Geology 153 (1999) 1–10
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Fig. 5. Plots between Ca versus Mg Ža. and Sr Žb., and Mg versus Al Žc. and Ba Žd., in the bottom sediments of the Yellow Sea. The solid lines in plots between Mg vs. Ca Ža., Al Žc., and Ba Žd. represent the dilution of a Chinese continental sediment component by quartz. The solid line in plots between Sr vs. Ca Žb. represents the dilution of CaCO 3 Žforaminifera. by quartz.
ŽFig. 6., suggesting the presence of feldspars ŽSmith and Brown, 1988.. Zhao et al. Ž1989a,b. also found high enrichments of K and Rb in recent sand occurring in the most northeastern Yellow Sea, which originates from the Arprock River ŽYalu River., and attributed this to the presence of K-feldspar. However, they could not find
such a feldspar signature in the relict sand occurring in the Old Yellow River mouth, and north of Shandong Peninsula. Based on their results and our observations, it is evident that the transgressive and relict sand ŽPark and Khim, 1990. occurring in the eastern parts of the Yellow Sea contains Al, Sr, and Ba enriched feldspars. These feldspars appear to origi-
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Fig. 6. Plots of AlrMg versus BarMg Ža., and AlrMg versus SrrCa Žb., in the bottom sediments of the Yellow Sea, with a 95% prediction interval.
G. Kim et al.r Chemical Geology 153 (1999) 1–10
nate from Arprock River, Korea Žsee sand-distribution map in Lee and Chough, 1989. and can be clearly differentiated from sand originating in the Yellow and Yangtze rivers, which show much lower K and Rb contents. We suggest the possibility of dispersion of K-feldspar produced from the volcanic mountain Baegdu, which is located closely to the Arprock River, in the course of the weathering processes. To confirm this hypothesis, the measurements of K, Rb, Ba, Sr, and Al from possible sand-source regions, as well as direct determination of feldspar in the entire Yellow Sea sediment, are necessary.
4. Conclusion The distribution of Mg is mainly controlled by quartz and carbonate dilution of clay minerals in the Yellow Sea. However, relatively high Mg over the clay and sand mixing line is observed in the plume region of Yangtze River. This requires more extensive studies to define the Mg enrichment mechanism in these coastal sediments. The distributions of Ca and Sr are mainly controlled by the presence of carbonate shells which are comprised of foraminifera andror coccoliths, inferred from SrrCa ratios Ž0.0052., with their maximum occurrence in the southeastern Yellow Sea. The direct measurements of foraminifera contents over the extent of entire Yellow Sea may be necessary to confirm its contribution to the carbonate contents. The presence of Ba, Al, and Sr enriched feldspar is found in the sandy region of the northeastern Yellow Sea, and these feldspars appear to originate from the Arprock River, Korea. However, such feldspar signature is not observed in sand occurring in the western part of the Yellow Sea which originates from the Yellow or Yangtze Rivers. Therefore, we suggest that such a feldspar-labeled sand originating from Arprock River can serve as an excellent tracer of its dispersion throughout the Yellow Sea.
Acknowledgements We thank Prof. Jae-Sang Hong ŽIn-ha Univ., Korea. who collected the Van Veen Grab samples for
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this study as a part of ‘The Exploitation Research of Marine Resources on the Yellow Sea’. We also indebted to Prof. Y. Nozaki and Y. Kodama ŽUniv. of Tokyo. for their assistance in ICP measurements and further discussions regarding the data analyses. We also thank Drs. M.M. Sarin, N. Hussain, J.J.G. Zwolsman, and G. Douglas who gave valuable comments on the manuscript.
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