中国科技论文在线 http://www.paper.edu.cn Marine Pollution Bulletin 64 (2012) 1940–1946
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Marine Pollution Bulletin
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Baseline Use of aliphatic hydrocarbons to infer terrestrial organic matter in coastal marine sediments off China ⇑ Liang-Ying Liu a,b, Ji-Zhong Wang a, Yu-Feng Guan a, Eddy Y. Zeng a,
a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China b Graduate School of Chinese Academy of Sciences, Beijing 100049, China
article info abstract
Keywords: Sediment samples from the marine systems along the coast of China, covering Yellow Sea, inner shelf of Terrestrial organic matter the East China Sea (ECS) and the South China Sea (SCS), were analyzed for n-alkanes and organic carbon. n-Alkanes À1 À1 The concentrations of Rn–C15–35 were 120–1680 ng g dry weight with an average of 560 ng g . Short- Atmospheric deposition chain n-alkanes (
Approximately 70% of the Earth’s surface is covered by oceans, ocean current systems (Fig. 1)(Hu, 1984; Wu et al., 2001). On whereas 80% of the global organic carbon in oceans is buried in the other hand, long-range atmospheric transport can introduce coastal marine systems adjacent to rivers (Goni et al., 2006; terrestrial organic materials to areas distant from the points of Hedges and Keil, 1995). Therefore, nearshore coastal areas, espe- discharge. cially estuaries and continental shelves, play an important role in One approach to understanding the sources and transport global cycling of organic matter (Goni et al., 2006). In this regard, mechanisms of organic materials accumulated in continental shelf examining the potential sources and transport mechanisms of sediments is to utilize molecular organic geochemical methods, organic matter in continental shelf sediments is of great signifi- among which aliphatic hydrocarbons (n-alkanes) have been widely cance in understanding the environmental fate of terrestrial organ- utilized (Colombo et al., 2005; Doskey, 2001; Tolosa et al., 1996). ic materials. There are allochthonous and autochthonous sources for n-alkanes The coast of China is largely surrounded by marginal seas, from preserved in sediments (Doskey, 2001). Allochthonous n-alkanes north to south including Bohai Sea, Yellow Sea, the East China Sea largely stem from terrestrial higher plant waxes and petroleum (ECS) and the South China Sea (SCS). Both terrestrially and aquati- residues, whereas autochthonous ones mainly originate from cally produced organic materials could deposit and be preserved in aquatic organisms, such as planktons and bacteria. Therefore, coastal marine sediments. Terrestrial organic materials can be n-alkanes can be used as molecular tracers to diagnose potential transported to coastal areas via hydrodynamic and/or atmospheric sources and transport mechanisms, as well as to assess the relative flows. On one hand, the abundant water systems of China (Fig. S1, importance of terrestrial and aquatic origins, for organic materials Supplementary material), e.g., from north to south the Yellow (Doskey, 2001). River, Yangtze River, Min River and Pearl River, play an important Comprehensive studies of aliphatic hydrocarbons in surface role in transporting terrestrial materials into the coastal marine sediments have been conducted in the entire Bohai Sea (Hu environment. For example, a previous study estimated that et al., 2009b), the ECS and southern Okinawa Trough (Jeng and 9.2 Â 105 tons of total organic carbon (TOC) were annually dis- Huh, 2008), and the northern SCS (Hu et al., 2009a). To our knowl- charged from the Pearl River Delta of South China to the coastal edge, there has been only one study concerning the historical ocean through riverine runoff (Ni et al., 2008). Furthermore, estu- records of aliphatic hydrocarbons in Yellow Sea (Wu et al., 2001), arine organic materials may be redistributed under the effect of and no study has been conducted to examine the spatial diver- gence of sediment aliphatic hydrocarbons within the coastal mar- ine systems (Yellow Sea, the ECS and the SCS) of China. The present ⇑ Corresponding author. Tel.: +86 20 85291421; fax: +86 20 85290706. study was conducted to investigate the spatial divergence of E-mail address: [email protected] (E.Y. Zeng). n-alkanes and TOC in coastal marine sediments off China, with
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L.-Y. Liu et al. / Marine Pollution Bulletin 64 (2012) 1940–1946 1941
40oN 1
2
3 C Shandong 4 W
5 S o Y Y 35 N S 6 C Yellow Sea C 7 8 YRE
o 9 30 N C a W Zhejiang T a Se in 10 h shio Kuro 11 East C Fujian 25oN 12 Guangdong 13 Taiwan 14 16 ary Estu ver 15 17 arl Ri o Pe 1921 20 N 18 20 ea Hainan 24 a S 26 25 23 22 in 31 27 h 30 28 C th 29 Sou 15oN
110oE 115oE 120oE 125oE
Fig. 1. Map showing the sampling sites on the continental shelf of China. The straight arrow along the ECS inner shelf indicates the southward decreasing trendof sedimentation rate (Huh and Su, 1999) and the direction of coastal current (Liu et al., 2007). The fingerprints in Yellow Sea and along the shelf of the East China Sea represent the mud area, while the curve arrows point to the direction of ocean currents. YSCC and YSWC refers to Yellow Sea coastal current and Yellow Sea warm current, respectively. This schematic diagram of mud areas and ocean currents is adopted from Refs. (Hu, 1984; Wu et al., 2001). the aims of examining the potential input sources and transport column packed with silica/alumina. Five milliliters of hexane were mechanisms of terrestrial organic materials. used to wash the column and the eluent was discarded. The frac- A set of surface sediment samples from the continental shelf of tion containing n-alkanes was eluted with an additional 20 mL of China, from north to south covering Yellow Sea, the ECS inner shelf hexane; the eluent was concentrated to 0.5 mL and spiked with a and the SCS (Fig. 1), were collected on board the South China Sea known amount of the internal standard (n–C30–d62) for subsequent Open Cruise (R/V SHIYAN III) and the Open Research Cruise Off- instrumental analysis. shore China (R/V KEXUE I) from August to September in 2007 using The concentrations of n-alkanes were determined with a Shima- a stainless steel grab sampler. For ease of comparison, samples are dzu Model 2010 gas chromatograph–mass spectrometer equipped grouped on a geographical basis as follows: (a) Yellow Sea (sites 1– with an AOC-20i auto injector (Shimadzu, Japan). The chromato- 8); (b) the ECS inner shelf (sites 9–13); (c) Southwest Taiwan with- graphic separation of the target analytes was achieved with a in the SCS (sites 14–17); (d) the SCS adjacent to the Pearl River 30 m  0.25 mm-i.d. (0.25-lm film thickness) DB-5 column (J&W Estuary (PRE) (sites 18–23); (e) Southeast Hainan within the SCS Scientific, Folsom, CA, USA). Extract injection was performed in (sites 24–30), and (f) Northwest Philippines within the SCS (site the splitless/split mode with a splitless injection time of 1 min. 31; Philippines is not shown). On a large scale, sites 14–31 are also Column temperature was programmed from 80 °C (held for considered being located within the SCS. 1 min) to 290 °C at a rate of 5 °C/min, and held for 30 min at the The procedures for sample extraction and extract purification/ final temperature. The interface and ion source temperatures were fractionation of n-alkanes used in the present study were detailed maintained at 250 °C. Peak confirmation of n-alkane congeners in a previous study (Wang et al., 2008) with slight modifications. was achieved with mass spectra acquired in the full scan mode,
Upon addition of a surrogate standard n–C24–d50 (n–Ci–dj, where while quantification was based on characteristic ion at m/z 85 ‘n’ designates normal alkane and subscripts ‘i’ and ‘j’ indicate car- and 71. bon number and deuterium number, respectively), freeze-dried The contents of TOC in the sediment samples (Table S1, Supple- and homogenized sediment samples were Soxhlet-extracted with mentary material) were measured with an elemental analyzer 200 mL of a mixture of hexane:acetone (1:1 in volume) for 48 h. (Vario EL III Elementar, Germany) after inorganic carbon was re- Prior to extraction, copper sheets were added to each sample for moved with 10% HCl. removal of elemental sulfur. Each extract after Soxhlet extraction Standards of pristane (Pri) and phytane (Phy) obtained from the was concentrated to approximately 1 mL with a Zymark TurboVap Laboratories of Dr. Ehrenstorfer (Augsburg, Germany), and a stan-
500 (Hopkinton, MA, USA) and purified/fractionated with a glass dard mixture containing n–C14, n–C15, n–C16, n–C17, n–C18, n–C19,
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1942 L.-Y. Liu et al. / Marine Pollution Bulletin 64 (2012) 1940–1946
n–C20, n–C22, n–C24, n–C26, n–C28, n–C30, n–C32, and n–C34 pur- Sea, the ECS and the SCS estimated in previous studies (Chen et al., chased from AccuStandard (New Haven, CT, USA) were used for 2006; Huh and Su, 1999; Lim et al., 2007; Wu et al., 2001) were qualitative and quantitative analyses. Any odd-numbered carbon used, and a detailed description is given in the Supplementary n-alkane with carbon number greater than 20 was quantified with material.
the average response factor of two adjacent even-numbered car- The Rn–C15–35 concentrations obtained in the present study bon n-alkane as their standards were not available. Along with were 120–1680 ng gÀ1 (mean: 560 ng gÀ1), varying in a consider- each batch of 15 field samples, a procedural blank, a spiked blank ably narrow range excluding a few low values (Table S1, Supple- and a matrix spiked sample were also processed. The recoveries of mentary material). Detailed comparison with the available data of
the surrogate standard n–C24–d50 were 68 ± 16% for sediment sam- sedimentary n-alkanes acquired worldwide (Table 1) suggested ples and 61 ± 5% for QA/QC samples. Because the concentration of that the concentrations of n-alkanes in the coastal marine sedi- each n-alkane component was higher than the lowest level in the ments off China were at the low end of the global range. A prelimin- calibration curve, this lowest calibration level (50 ppb) divided ary data analysis obtained a large variability (0–48,000 ng gÀ1)in by the average sample weight (22 g) and corrected with a final ex- UCM contents (Table S1, Supplementary material), low levels tract volume of 0.5 mL was treated as the reporting limit, which (30–130 ng gÀ1; mean: 74 ng gÀ1) of marine planktonic markers À1 was 1.1 ng g for each n-alkane in the present study. (the sum of n–C15, n–C17, and n–C19), and moderate levels The measured concentrations of n-alkanes were not surrogate (10–600 ng gÀ1; mean: 160 ng gÀ1) of terrestrial markers (the sum
standard recovery corrected but blank corrected; i.e., the average of n–C27, n–C29 and n–C31) in coastal marine sediments off China. concentrations of n-alkanes detected in the procedural blanks were The levels of planktonic and terrestrial markers accounted for 3–
subtracted from all measured concentrations to derive reporting 26% and 8–56% of Rn–C15–35 concentrations, with averages of 14% concentrations, which were normalized to dry sample weights. and 33%, respectively. The planktonic marker levels in the SCS The concentrations of unresolved complex mixture (UCM) were (30–130 ng gÀ1; mean: 75 ng gÀ1) were generally higher than those estimated from the UCM area and the average response factor of in Yellow Sea (12–110 ng gÀ1; mean: 50 ng gÀ1) and the ECS inner the individual n-alkanes with retention times embraced within shelf (10–92 ng gÀ1; mean: 50 ng gÀ1). The aquatically derived
the UCM (Doskey, 2001). In the present study, Rn–Ci–j is defined short-chain n-alkanes are friable thus prone to degradation (Meyers as the sum of n-alkanes with carbon numbers from i to j. Carbon et al., 1984). A previous study (Doskey, 2001) suggested that
preference index (CPI24–34) was calculated on a molar basis (Bray autochthonous organic matter was better preserved in areas with and Evans, 1961), while other compositional indices such as great primary productivity and rapid sedimentation. The generally
CPI15–20, odd–even preference (OEP), plant wax alkane (%waxCn), higher levels of planktonic marker in the SCS than in Yellow Sea was natural n-alkane ratio (NAR) (Mille et al., 2007), Pri/n–C17, Phy/n– in contrast to the generally lower primary productivity in the SCS C18 and Pri/Phy were calculated on a mass fraction basis and de- than in Yellow Sea (Tan and Shi, 2006). This inconsistency might fined in the Supplementary material. The n–C29/n–C17 value was suggest that other sources rather than aquatic planktons mainly ac- used to reveal the relative importance of allochthonous and autoch- counted for the occurrence of short-chain n-alkanes. Another plau- thonous inputs of hydrocarbons (Doskey, 2001). Depositional flux sible reason for the spatial distribution of planktonic marker is the of n-alkanes was estimated as the product of the sediment n-alkane geographical difference in biotransformation of aliphatic hydrocar- concentration, sediment density (q; assumed to be 1.5 g cmÀ3) and bons. On one hand, the environmental conditions, such as water sedimentation rate (c;cmyrÀ1). The sedimentation rates in Yellow depth (Table S2, Supplementary material), water temperature,
Table 1 Concentration levels and carbon preference index (CPI) of n-akanes in continental shelf sediments off China in comparison with other regions.
Study area n-Alkanes (ng gÀ1) CPI References Global areas Santos, Brazil 100–14,560a Medeiros and Caruso Bíego (2004) São Sebastião, SP-Brazil 30–4770a Medeiros and Caruso Bíego (2004) Black Sea 100–3400b Readman et al. (2002) Kara Sea 2–7c Fernandes and Sicre (2000) Coastal zone-China Jiaozhou Bay, Qingdao 500–8120(1910)a 0.9–2.0h Wang et al. (2006) Yangtze River Estuary 160–1880(1000)f 1.13–4.75i Bouloubassi et al. (2001) PRE and SCS 106–2670e 1.45–4.98i Hu et al. (2009a) Marginal seas-China Bohai Sea 390–4940d Hu et al. (2009b) Bohai Sea 4.0–5.9 Bigot et al. (1989) Northern Yellow Sea 240–420g 1.88–3.74j Present study Central Yellow Sea 390–1340g 1.81–3.87j Present study East China Sea (ECS) 70–3000g 1.41–5.82 Jeng and Huh (2008) Inner shelf of the ECS 130–1680g 1.29–2.57j Present study South China Sea 140–1100g 0.68–4.39j Present study South China Sea 2300–4600 Carles Pelejero (2003)
a Rn–C12–4. b Rn–C14–34. c Rn–C16–36. d Rn–C12–35. e Rn–C13–35. f Rn–C15–38. g Rn–C15–35. h 2 Â (n–C27 + n–C29)/[n–C26 +(2Â n–C28)+n–C30]. i CPI25–35. j CPI24–34 in the present study on a mole fraction basis which is described in the Supplementary material. The northern and central Yellow Sea refer to sampling sites 1–3 and 4–8, respectively (Fig. 1).
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L.-Y. Liu et al. / Marine Pollution Bulletin 64 (2012) 1940–1946 1943 and dissolved organic carbon contents and constituents are pre- commonly observed in uncontaminated sediments (Steinhauer sumably different among the three marine systems. On the other and Boehm, 1992). Except for sites 4 and 5, other samples were hand, the species and/or populations of microorganisms, such as characterized with the low UCM levels (11–48 lggÀ1; mean: Pseudomonas putida CA-3 (Dunn et al., 2005), which are able to 22 lggÀ1) and high Pri/Phy values (1.11–7.26; mean: 3.42) (Table transform aliphatic hydrocarbons, are potentially different among S1, Supplementary material), suggesting predominant biogenic the three marine systems as well. The terrestrial marker levels in (zooplanktons and/or marine animals) rather than petrogenic Yellow Sea (64–560 ng gÀ1; mean: 290 ng gÀ1; Table S1, Supple- sources. On the other hand, isoprenoids are less susceptible to bio- mentary material) were slightly higher than those in the ECS inner degradation than n-alkanes, resulting in high Pri/n–C17 and Phy/n– À1 À1 shelf (23–550 ng g ; mean: 210 ng g ; Table S1, Supplementary C18 values in degraded oil (Mille et al., 2007). The low Pri/n–C17 À1 À1 material) and the SCS (10–600 ng g ; mean: 150 ng g ; Table and Phy/n–C18 values (generally lower than 1; Table S1, Supplemen- S1, Supplementary material). The spatial distribution of terrestrial tary material) also suggested that most sediments analyzed in the marker levels suggested that hydrocarbons of terrestrial origin present study were free of petroleum contamination. were relatively more abundant in Yellow Sea than in the SCS. This Short chain n-alkanes ( The occurrence of UCM may be reflective of petroleum contami- planktonic origins are predominated by even (n–C14, n–C16 and nation and/or chronically degraded complex mixture of hydrocar- n–C18)(Nishimura and Baker, 1986) and odd (n–C15, n–C17 and bons (Mille et al., 2007). A previous study suggested that a level of n–C19)(Youngblood and Blumer, 1973) carbon n-alkanes, respec- À1 UCM lower than 10 lgg in marine sediments indicated no petro- tively. The CPI14–20 values for aliphatic hydrocarbons of nonsilli- leum contamination (Tolosa et al., 1996). In the present study, 16 out ceous planktonic origin were greater than 1 (Doskey, 2001; of the 31 sediment samples contained UCM at <10 lggÀ1 (Table S1, Youngblood and Blumer, 1973). In the present study, short chain Supplementary material). Other indicators of petroleum contamina- n-alkanes in five sediments (sites 10–13 in the ECS inner shelf tion are isoprenoids, pristane and phytane, with Pri/Phy value close and site 23 in the SCS adjacent to the PRE) showed an apparent to 1 indicating a petrogenic origin (Wu et al., 2001). However, large odd–even carbon number preference with CPI15–20 ranging from uncertainties may be incurred using Pri/Phy ratio as an indicator of 1.21 to 1.8 (Table S1, Supplementary material), suggesting the pre- petroleum sources because pristane can originate from zooplank- dominance of planktonic sources. On the other hand, the short tons and/or marine animals (Gomez-Belinchon et al., 1988) and chain n-alkanes in the remaining 26 samples (mainly in Yellow oxidation or reduction of chlorophyll can also produce pristane Sea and the SCS) contained no obvious odd–even carbon number and phytane (Mille et al., 2007). High Pri/Phy values (3–5) were preference with CPI15–20 around 1 (0.86–1.25; mean: 1.07; Table 40oN 35oN 30oN 25oN 20oN 6.5 15oN 110oE 115oE 120oE 125oE Fig. 2. Spatial distribution of n–C29/n–C17 values in coastal marine sediments off China. 中国科技论文在线 http://www.paper.edu.cn 1944 L.-Y. Liu et al. / Marine Pollution Bulletin 64 (2012) 1940–1946 1.4 (1.46–4.39) were statistically higher (t < 0.05) than those in the 9 samples (1.54–2.03). Four (sites 9, 13, 18 and 21) out of the 1.2 (a) remaining 5 samples were characterized by the highest relative 1.0 abundance at n-C16 and no apparent odd–even carbon preference .8 in the long-chain carbon number. The short-chain n-alkanes .6 peaked at even carbon number (n–C16) in the above-mentioned .4 13 samples (mainly in the SCS) further elaborated the importance of bacteria derived hydrocarbons in the SCS. Finally, n-alkanes in .2 site 11 sediment peaked at n–C25, suggesting submerged and/or 0.0 floating plant sources (Ficken et al., 2000). A summary of the -.2 above-discussed results suggested that long-chain n-alkanes were 1.4 (b) mainly derived from terrestrial higher plants in most samples. This 1.2 conclusion was also supported by the high levels of OEP, %waxCn 1.0 Compositional Profiles and NAR (Table S1, Supplementary material). .8 The mean depositional fluxes of Rn–C21–35 were À2 À1 À2 À1 .6 310 ng cm yr (range: 160–470 ng cm yr ) at central Yellow À2 À1 À2 À1 .4 Sea (sites 4–8), 97 ng cm yr (range: 18–270 ng cm yr )at the SCS (sites 14–31), and 100 ng cmÀ2 yrÀ1 (range: .2 60–140 ng cmÀ2 yrÀ1) at northern Yellow Sea (sites 1–3) (Fig. 4). 0.0 The lowest depositional fluxes (25–34 ng cmÀ2 yrÀ1) were ob- -.2 tained at the lower reach of the ECS inner shelf (site 13) and South- 7 0 3 6 9 2 15 16 1 18 19 2 21 22 2 24 25 2 27 28 2 30 31 3 33 34 east Hainan within the SCS (sites 24 and 25). In general, the Carbon Number depositional fluxes of Rn–C21–35 were lower in marine sediments off China than those in Rhone Prodelta (mean: 11000 ng cmÀ2 yrÀ1; Fig. 3. Compositional profiles of aliphatic hydrocarbons in coastal marine sedi- range: 5000–18000 ng cmÀ2 yrÀ1) and Ebro Prodelta (mean: ments (a) sites 2–8 in Yellow Sea, sites 10 and 12 in the inner shelf of ECS, and sites À2 À1 À2 À1 14, 17, 19, 20, 22, 23, 29, and 30 in the SCS (Fig. 1) and (b) site 1 in Yellow Sea, sites 470 ng cm yr ; range: 270–690 ng cm yr )(Tolosa et al., 15, 16, 24–28, and 31 in the SCS (Fig. 1). In (a) and (b), each n-alkane congener was 1996) which received large amounts of terrestrial inputs from normalized to n–C31 and n–C16, respectively. The numbers on x-axis represent the Rhone River and Ebro River, respectively, but were higher than carbon number of n-alkanes. those in the western (mean: 53 ng cmÀ2 yrÀ1; range: 46– 62 ng cmÀ2 yrÀ1) and eastern (mean: 18 ng cmÀ2 yrÀ1; range: 10– S1, Supplementary material), signaling a mixed source from bacte- 27 ng cmÀ2 yrÀ1) deep basins of Mediterranean Sea (Tolosa et al., ria and planktons (Bouloubassi et al., 2001). 1996). Terrestrial higher plants generally produce long-chain n-al- Organic carbon in marine sediments is derived from both ter- kanes with CPI values ranging from 5 to 10 (Rielley et al., 1991), restrial and marine sources (Prahl et al., 1994). Fluvial transport while n-alkanes from petrogenic inputs typically show a CPI value is the main input mechanism for the accumulation of terrestrial close to one (Pendoley, 1992). Generally, aliphatic hydrocarbons in TOC in marine sediments, while contributions from atmospheric 26 out of 31 sediment samples analyzed in the present study were deposition may be neglected (Chen et al., 2004). In the present characterized with an obvious odd–even carbon preference, with study, although there is no correlation between the concentrations 2 CPI24–34 greater than 1 (1.46–4.39; Table S1, Supplementary mate- of TOC and Rn–C15–35 (r = 0.06), the samples with low levels of À1 rial) but lower than 5–10. The difference was that hydrocarbons in Rn–C15–35 (120–420 ng g ) generally also contained low TOC con- 17 out of the 26 sediments (sites 2–8, 10, 12, 14, 17, 19, 20, 22, 23, tents (0.26–0.39%). Therefore, TOC may have some effects on the 29 and 30) contained the highest relative abundance at n–C29 or n– spatial distribution of n-alkanes in coastal marine sediments off C31 (Fig. 3a) and that hydrocarbons in 9 out of the 26 samples (sites China. To uncover any possible correlation between TOC and n-al- 1, 15, 16, 24–28, and 31) peaked at n–C16 (Fig. 3b). Furthermore, kanes, samples from the same geographical region (described in the CPI24–34 values in the above-mentioned 17 sediment samples Field Sampling) were assessed separately. As a result, significant 13500 ) -1 13000 yr -2 12500 (a) Yellow Sea 12000 (b) ECS inner shelf (c) Southwest Taiwan 400 (e) Southeast Hainan 200 (d) SCS adjacent to the PRE Depositional Fluxes (ng cm 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Site Number À2 À1 Fig. 4. Depositional fluxes (ng cm yr ) of terrestrial aliphatic hydrocarbons (Rn–C21–35) in coastal marine sediments off China. 中国科技论文在线 http://www.paper.edu.cn L.-Y. Liu et al. / Marine Pollution Bulletin 64 (2012) 1940–1946 1945 600 90 American continent (Gagosian and Peltzer, 1986) were used to roughly estimate the contributions of atmospheric loading to the 80 500 coastal marine sediments off China. This atmospheric loading on 70 average accounted for 22% (range: 8–56%), 32% (range: 1–100%), ) ) 400 -1 -1 Ter = 500 *TOC - 56 and 55% (range: 13–180%) of the depositional fluxes of Rn–C21–35 2 r = 0.92 60 in Yellow Sea, the ECS inner shelf, and the SCS, respectively. 300 50 Clearly, these estimates neglected possible regional divergence Mar = 69 *TOC + 8.1 Ter (ng g Mar (ng g for atmospheric n-alkane concentrations among the northern 2 200 r = 0.91 40 (Shandong and further north), eastern (Zhejiang and Fujian) and 30 southern (Guangdong, Hainan and Taiwan) parts of China. In addi- 100 tion, the locations of sediments sampled in the present study were 20 much closer (approximately 40–440 km) to the continent (main- .2 .4 .6 .8 1.0 1.2 1.4 land China) than those of the deep sea ocean (5000 km) (Gagosian TOC (%) and Peltzer, 1986). Therefore, the percent contributions from atmospheric loadings of terrestrial n-alkanes to the coastal marine Fig. 5. Correlation between the concentrations of TOC (%) and terrestrial marker À1 sediments are expected to be greater than the estimated values, (Ter; the sum of n–C27, n–C29 and n–C31;ngg ) in sediments from Yellow Sea (sites 1–8) and between the concentrations of TOC (%) and planktonic marker (Mar; the suggesting that long-range atmospheric transport may have played À1 sum of n–C15, n–C17 and n–C19;ngg ) in sediments from Southeast Hainan within an important role in the accumulation of terrestrial n-alkanes in the SCS (sites 24–30). the coastal marine sediments off China. Acknowledgements positive correlations were found between the concentrations of TOC and the terrestrial marker in sediments from Yellow Sea This work was financially supported by the Earmarked Fund of (r2 = 0.92) and between the concentrations of TOC and the plank- the State Key Laboratory of Organic Geochemistry (SKLOG2009A04), tonic marker in sediments from Southeast Hainan within the SCS National Natural Science Foundation of China (No. 41121063), (r2 = 0.91) (Fig. 5). These results possibly suggested that organic Chinese Academy of Sciences (KZCX2-YW-Q02-06-01). We thank matter in sediments from these two areas was principally of terres- the crews of the South China Sea Open Cruise and the Open Research trial and marine sources, respectively. Cruise Offshore China, administrated by the South China Sea The percent fractions of organic carbon can be estimated from Institute of Oceanology and the Institute of Oceanology, Chinese the concentrations of n-alkanes divided by the slope of the correl- Academy of Sciences, respectively, for sample collection. This is ative regression between the concentrations of TOC and n-alkanes contribution No. IS-1499 from GIGCAS. (Prahl et al., 1994). Based on the regression equations in Fig. 5, the percent fractions of terrestrial organic carbon in Yellow Sea sedi- ments and marine organic carbon in sediments from Southeast Appendix A. Supplementary data Hainan within the SCS were estimated to be 13–110% and 48– 110%, with a mean of 58% and 86%, respectively. Supplementary data associated with this article can be found, in No significant correlations were found either between the con- the online version, at http://dx.doi.org/10.1016/j.marpolbul.2012. centrations of TOC and the terrestrial marker or between the 04.023. concentrations of TOC and the planktonic marker in the remaining geographical regions, possibly suggesting mixed sources of TOC in these areas. This notion is somewhat supported by the generally References higher sediment TOC levels (0.84–1.32%) in the SCS adjacent to Bigot, M. et al., 1989. Organic geochemistry of surface sediments from the Huanghe the PRE than in Yellow Sea and Southeast Hainan within the SCS estuary and adjacent Bohai Sea (China). Chem. Geol. 75, 339–350. (0.26–1.11% and 0.29–0.98%, respectively), where organic carbon Bouloubassi, I. et al., 2001. Hydrocarbons in surface sediments from the changjiang was mainly of terrestrial and marine origins, respectively. (Yangtze River) estuary, East China Sea. Mar. 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