Journal of Chemistry
Volume 2016 (2016), Article ID 4741939, 9 pages
http://dx.doi.org/10.1155/2016/4741939

Research Article

Composition and Distribution Characteristics and Geochemical Significance of n-Alkanes in Core Sediments in the Northern Part of the South Yellow Sea

Jinxian He,1,2 Shengyin Zhang,³ Xiaoli Zhang,1,2 Yu Qian,³ Haijun He,⁴ and Hongchen Wu1,2

¹Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China
²School of Resources and Geoscience, China University of Mining and Technology, Xuzhou 221116, China
³Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China
⁴Guangzhou Marine Geological Survey, Guangzhou 510760, China

Received 18 June 2016; Revised 27 September 2016; Accepted 18 October 2016

Academic Editor: Marc Schwientek

Copyright © 2016 Jinxian He et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The South Yellow Sea is an important carbon sink and a significant research area of carbon cycle. After studying the composition and distribution of n-alkanes in a 250 cm long sediment core in the northern part of South Yellow Sea, it can be found that all n-alkanes of sediment samples in this research are distributed in three types, that is, double peak groups, predominance of long-chain n-alkanes, and predominance of short-chain n-alkanes. The average values of C₂₅₋₃₅/C₁₅₋₂₁, C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉, /, and / are 1.92, 4.22, 0.51, and 0.35, respectively; all above outcomes indicate significant predominance of terrigenous inputs. The average values of C31/C29 and ACL are 1.04 and 29.92, respectively; these results reflect that herbaceous plants and ligneous plants account for similar percentages in the sediment core samples. The average values of CPI1 of short-chain alkanes are 0.80, reflecting the apparent even predominance, which is the result of microbial degradation. The average values of CPI2 of long-chain alkanes of most samples are 2.77, reflecting the apparent odd predominance. The average values of CPI and Pr/Ph, as well as the Pr/nC₁₇ and Ph/nC₁₈ correlation diagram, reflect that the organic matter is immature and suggest reductive sedimentary environment.

1. Introduction

The organic carbon deposition rate of continental margin sea is 8–30 times higher than that of the ocean, and over 80% deposited organic carbon is buried in the continental shelf and continental slope area [1, 2]. Therefore, the margin sea plays an important role in global carbon cycle [2]. Organic matter source of the margin sea is an important scientific subject in the research on carbon cycle [3, 4]. The South Yellow Sea is typical semiclosed continental margin sea, into which a large amount of terrigenous matter was transported along streams since Holocene [5, 6]. Influenced by runoff of Yellow River and Yangtze River, warm current and alongshore current of the Yellow Sea, and tidal action, South Yellow Sea became an important carbon sink with diverse organic matter and changeable sedimentary environment [7, 8]. Much research has been conducted for modern sediments of South Yellow Sea [9–14].

Predecessors conduct a large amount of research on source of organic matter and sedimentary environment of South Yellow Sea with stable carbon isotopes [15], content of elements and minerals [16–20], and biomarkers [5, 6, 21–23] and achieved abundant outcomes. Provenance study results show that organic matter of western and central part of the South Yellow Sea comes from modern Yellow River and ancient Yellow River; sediments in the eastern part are mainly influenced by the matter in Korean Peninsula; nearshore area in the northern part is mainly influenced by the matter in modern Yellow River [15–18, 24]. Research on organic matter source of sediments in the Yellow Sea shows that n-alkanes of South Yellow Sea are dominated by terrigenous inputs [5, 6, 21–23, 25, 26], and the terrigenous n-alkanes are mainly derived from higher plants waxiness [5]. Atmospheric deposition inputs account for a small percentage of n-alkanes, but the river input is a main contributor of n-alkanes [6, 27]. The distribution of n-alkanes is characterized by three types: predominance of short-chain n-alkanes, predominance of long-chain n-alkanes, and double-peak groups [5, 6, 22, 28]. Previous research on n-alkanes of organic matter in modern sediments of South Yellow Sea focuses on surface sediment samples [5, 6, 22, 23, 28]. Not much research on sediment core samples has been conducted, and the length of sediment cores in the research is short (only 35 cm) [22]. There is a lack of research on n-alkanes of long sediment core samples. This paper studies composition and distribution of n-alkanes of a 250 cm long sediment core in the northern part of South Yellow Sea and analyzes the geochemical significance.

2. Sample Collection and Analysis

2.1. Sample Collection

A 250 cm long sediment core sample was collected in the northern part of South Yellow Sea in August, 2013. Water depth of the sampling station is 40 m, and the sampling locations are shown in Figure 1. The sample spacing was 10 cm, and 25 sediment core samples wrapped with aluminium foil and plastic bags were brought to the laboratory at the ground temperature and put into the freezer for preservation at −20°C until organic analysis.

Figure 1: Core sediment sampling locations.

Foraminiferal sediments samples were selected from 3 sediments samples at different depths and delivered to Beta Analyses for foraminiferal AMS¹⁴C dating, and the obtained AMS¹⁴C dating data were converted into chronological age via the software Calib 5.5.2 (Table 1) [29]. Marine04 curve was used [30], the age of regional carbon reservoir was set to be 0 by referring to the method of Kong et al. [31], and the deposition rate at various depths was calculated according to depth and chronological age. It is shown in the results that this 250 cm long sediment core is representative of 3952-year-old sediments. Deposition rate at various depths is between 0.048 and 0.108 cm/a, which is in line with 0.026–0.67 cm/a [32, 33] or 0.013–0.119 cm/a [34, 35], the deposition rate range of South Yellow Sea obtained with ²¹⁰Pb isotope method or obtained with foraminiferal dating method by predecessors.

Table 1: AMS¹⁴C dating data and deposition rate of foraminiferal sediments samples.

Depths (cm)
Chronological age (aBP)
Depth range (cm)
Deposition rate (cm/a)

100
924
0–100
0.108

200
2126
100–200
0.083

250
3952
200–250
0.048

2.2. Sample Analysis

After freezing and drying of the sediment samples, Soxhlet extraction was performed for 20 g crushed sample for 72 h with dichloromethane. The extracting solution was concentrated and was isolated and purified with silica gel/aluminium oxide (1 : 1) chromatographic column and then eluted with mixed liquor of n-hexane and dichloromethane (V : V = 1 : 1). Saturated hydrocarbon in the sample was finally obtained. Saturated hydrocarbon sample was under full scan by Agilent GC-MSD (6890/5975) for analytical determination. The chromatographic column was a DB-5MS capillary column (column length: 30 m, inner diameter: 0.25 mm, coating thickness: 0.25 μm; J & W Scientific). The carrier gas was high-purity helium (He), column flow was 1.0 mL/min, and sample size was 1 μL with splitless sampling. The temperature of injection port and detector was 280°C and 300°C, respectively. Here is the heating procedure: maintain initial temperature 60°C for 1 min, increase temperature to 180°C with heating rate 8°C/min and remain so for 1 min, and increase temperature to 300°C with heating rate 3°C/min and remain so for 2 min. The ion source temperature was 250°C, and ionization energy was 70 eV. The relative standard deviation of the experiment was <±10%. The identification of compound was based on retention time and characteristic ion ( 85) of the standard sample and comparison with mass spectrometry scheme of reference material and mass spectral library (NIST2005).

3. Results and Discussion

3.1. Composition and Distribution Characteristics of n-Alkanes

The n-alkanes with chain length C₁₂–C₄₀ were tested. The C₁₂ alkane content of 13 samples was too low to be detected, and C₁₃ alkane content of 2 samples was too low to be detected. The C₃₇–C₄₀ alkane content of some samples was not detected due to low content (Table 2). The gas chromatogram of typical n-alkanes of core sediments is shown in Figure 2. The distribution of n-alkanes is characterized by three types: double-peak groups (Figure 3(a)), predominance of long-chain n-alkanes (Figure 3(b)), and predominance of short-chain n-alkanes (Figure 3(c)), which is in line with previous research results [6, 22, 23, 25–28]. The relative amount distribution of n-alkanes with different carbon number is shown in Figure 3.

Table 2: Geochemical parameters of n-alkanes and isoprenoid alkanes of sediment core samples.

Sample number
Deep/cm
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O

ZY1
10
13–40
16,31
0.45
28.54
53.68
1.88
0.91
0.82
0.89
0.76
0.58
0.70
0.21
1.01
29.96

ZY2
20
12–40
17,31
0.48
31.24
51.98
1.66
0.91
0.62
0.75
0.83
0.68
0.77
0.21
1.01
29.88

ZY3
30
14–40
16,31
0.58
35.96
50.38
1.40
0.85
0.74
0.94
1.28
0.65
1.21
0.25
1.05
29.92

ZY4
40
12–40
16,31
0.69
38.90
47.75
1.23
0.88
0.80
0.99
1.62
0.67
1.51
0.26
1.07
30.04

ZY5
50
12–40
16,31
0.68
38.07
50.06
1.31
0.92
0.73
0.99
2.02
0.75
1.93
0.31
1.06
29.91

ZY6
60
12–40
18,31
0.63
37.47
49.67
1.33
0.73
0.64
0.82
1.88
0.70
1.78
0.29
1.08
29.99

ZY7
70
13–40
17,29
0.42
29.52
56.95
1.93
0.68
0.70
1.07
1.91
0.82
1.85
0.32
0.87
29.61

ZY8
80
13–40
17,31
0.49
31.46
56.93
1.81
0.79
0.74
1.09
2.40
0.78
2.25
0.37
1.12
30.09

ZY9
90
13–40
17,31
0.83
43.79
45.58
1.04
0.91
0.69
1.02
2.75
0.86
2.61
0.30
1.08
30.05

ZY10
100
12–38
17,31
0.50
30.54
55.39
1.81
0.96
0.62
0.91
2.88
0.96
2.73
0.37
1.06
29.93

ZY11
110
13–37
17,31
0.34
23.97
64.91
2.71
0.94
0.61
0.77
3.64
0.86
3.52
0.47
1.11
29.98

ZY12
120
13–37
18,31
0.43
28.91
59.79
2.07
0.57
0.62
0.99
3.80
0.97
3.67
0.43
1.05
29.87

ZY13
130
12–40
18,31
0.32
22.55
61.95
2.75
0.35
0.45
0.71
2.47
0.75
2.38
0.40
1.04
29.81

ZY14
140
12–37
17,31
0.63
34.34
52.44
1.53
0.88
0.63
0.90
3.58
0.90
3.51
0.38
1.05
29.87

ZY15
150
13–37
17,31
0.69
39.58
48.83
1.23
0.70
0.66
0.87
2.10
0.71
2.02
0.30
1.05
30.01

ZY16
160
13–37
16,31
0.98
47.99
43.25
0.90
0.88
0.65
0.92
3.10
0.73
3.00
0.29
1.00
30.04

ZY17
170
13–37
18,31
0.54
33.86
55.71
1.65
0.75
0.57
0.88
3.17
0.91
3.04
0.39
1.08
30.02

ZY18
180
12–37
17,29
0.46
30.25
58.83
1.94
0.90
0.62
0.78
3.38
0.83
3.29
0.42
0.99
29.81

ZY19
190
13–37
18,31
0.29
22.07
67.35
3.05
0.69
0.67
0.86
4.03
0.94
3.95
0.49
1.05
29.93

ZY20
200
14–37
18,31
0.19
15.90
72.85
4.58
0.44
0.70
0.97
3.79
0.87
3.73
0.52
1.04
29.94

ZY21
210
12–37
18,31
0.41
27.75
61.72
2.22
0.64
0.62
0.96
3.38
0.90
3.27
0.44
1.10
29.95

ZY22
220
12–37
18,29
1.73
62.61
31.33
0.50
0.41
0.45
1.04
3.81
1.09
3.74
0.23
0.98
29.83

ZY23
230
13–36
18,31
0.57
36.03
55.28
1.53
0.59
0.66
1.06
3.83
0.78
3.73
0.40
1.04
29.91

ZY24
240
12–37
18,31
0.37
25.52
61.43
2.41
0.77
0.64
0.83
2.25
0.75
2.16
0.39
1.03
29.93

ZY25
250
12–40
18,29
0.23
17.74
65.90
3.72
0.57
0.55
0.70
1.13
0.57
1.06
0.31
0.99
29.85

A: carbon number range; B: carbon number of main peak; C: ; D: ; E: ; F: ; G: Pr/Ph; H: Pr/nC₁₇; I: Ph/nC₁₈; J: CPI; K: CPI1; L: CPI2; M: Alkterr; N: ; O: ACL;

;

;

;

;

.

Figure 2: Gas chromatogram of typical n-alkanes and isoprenoid alkanes of sediment core samples.

(a) ZY5

(b) ZY20

(c) ZY22

Figure 3: The three typical distribution patterns of n-alkane contents. ((a) Terrestrial and marine input; (b) stronger terrestrial input; (c) weaker terrestrial input).

The front peak group of n-alkanes, between C₁₂ and C₂₁, has main peak carbon of C₁₆, C₁₇, or C₁₈ and higher content of C₁₇–C₂₀. The back peak group, between C₂₂ and C₄₀, has main peak carbon of C₂₉ or C₃₁ and the highest content of C₃₁, followed by C₂₉ and then C₂₇. Among isoprenoid alkanes, the peak height of pristane (Pr) is generally lower than that of phytane (Ph).

3.2. Organic Matter Source of Sediments

3.2.1. Distribution of n-Alkanes and Their Significance

The distribution of n-alkanes of 25 sediment samples in this research is characterized by three types: double-peak groups (Figure 3(a)), predominance of long-chain n-alkanes (Figure 3(b)), and predominance of short-chain n-alkanes (Figure 3(c)). The short-chain n-alkanes (C₁₂–C₂₁) reflect marine inputs and long-chain n-alkanes (C₂₂–C₄₀) reflect terrigenous inputs. The double-peak suggests that both terrigenous organic matter and marine organic matter contribute to the n-alkanes of sediment core samples in this research (Figure 2). In this research, samples with double-peak groups are influenced by both terrigenous inputs and marine inputs (Figure 3(a)); samples with predominance of long-chain n-alkanes indicate higher terrigenous inputs (Figure 3(b)); samples with predominance of short-chain n-alkanes indicate lower terrigenous inputs (Figure 3(c)).

3.2.2. C₂₅₋₃₅/C₁₅₋₂₁ Value Distribution Characteristics and Their Significance

The sum of C₁₅–C₂₁ content of short-chain n-alkanes, C₁₅₋₂₁, represents marine alkane content [36]. The sum of C₂₅–C₃₅ content of long-chain n-alkanes, C₂₅₋₃₅, represents terrigenous alkane content [37]. The value of C₂₅₋₃₅/C₁₅₋₂₁ can be used to eliminate the influence of particle size and deposition rate and indicate organic matter source in the sediments more accurately [38]. The higher ratio indicates stronger influence of terrigenous inputs, while the lower ratio indicates weaker influence of terrigenous inputs.

The value distribution of C₁₅₋₂₁, C₂₅₋₃₅, and C₂₅₋₃₅/C₁₅₋₂₁ of samples in this research is shown in Table 2 and Figures 4 and 5. It is shown in Table 2 that C₁₅₋₂₁ ranges between 15.90% and 62.61%, averaging 32.58%, with the maximum value 3.9 times of the minimum value; C₂₅₋₃₅ ranges between 31.33% and 72.85%, averaging 55.20%, with the maximum value 2.3 times of the minimum value; C₂₅₋₃₅/C₁₅₋₂₁ ranges between 0.50 and 4.58, averaging 1.92. The above parameters suggest higher terrigenous organic matter input of studied sediment core samples.

Figure 4: Vertical distribution characteristics of geochemical parameters of n-alkanes of sediment core samples.

(a)

(b)

Figure 5: Biomarker characteristics of sediment core samples. (a) Generally contains squalene compound; (b) front peak group generally contains “UCM bumps.”

3.2.3. C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉ Value Distribution Characteristics and Their Significance

C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉, the ratio of the sum of terrigenous-dominated n-alkanes content to the sum of marine-dominated n-alkanes content, is also a common parameter to evaluate relative contribution of terrigenous n-alkanes and marine n-alkanes [39]. Therefore, C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉ can indicate organic matter source of sediments. In Table 2 and Figure 4, the ratio of C₂₇₊₂₉₊₃₁ to C₁₅₊₁₇₊₁₉ of studied samples ranges between 0.24 and 26, averaging 4.22. It is shown in Figure 4 that distribution characteristics of C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉ are very similar to those of C₂₅₋₃₅/C₁₅₋₂₁, with high ratio and low ratio areas basically the same. Both of them indicate higher terrigenous organic matter input.

3.2.4. C₂₁₋/C₂₂₊ Value, Alkterr Value, C₃₁/C₂₉ Value, and ACL Value Distribution Characteristics and Their Significance

Since C₂₁₋ reflects marine inputs [36] and C₂₂₊ reflects terrigenous inputs [37], C₂₁₋/C₂₂₊ is generally used to estimate that organic matter is terrigenous-dominated or marine-dominated. The C₂₁₋/C₂₂₊ distribution of studied samples is shown in Table 2 and Figure 4. Except the fact that C₂₁₋/C₂₂₊ of number ZY22 sample is 1.73 (indicating predominance of marine organic matter), C₂₁₋/C₂₂₊ of other 24 samples is between 0.19 and 0.98, averaging 0.51, and indicates significant predominance of terrigenous inputs.

/C₁₄₋₃₈ (Alkterr value for short) is an indicator of terrigenous inputs [23]. The Alkterr value of samples in this research ranges from 0.21 to 0.52, averaging 0.35, and indicates significant terrigenous inputs.

It is of great significance to further distinguish terrigenous organic matter, that is, ligneous plants dominated or herbaceous plants dominated. The main peak of ligneous plant-derived n-alkanes is mostly C₂₉, while that of herbaceous plant-derived n-alkanes is mostly C₃₁ [40, 41]. The main peak of back peak group of studied samples is mostly C₃₁. However, C₂₉ content is similar to C₃₁ content with C₃₁/C₂₉ between 0.87 and 1.12, averaging 1.04 (Table 2, Figure 4). Therefore, herbaceous plants and ligneous plants account for similar percentages in the sediment core samples, which is in line with previous research results [5, 23, 42].

The average carbon chain length (ACL) of n-alkanes reflects vegetation variation. n-Alkanes have smaller ACL when the formation is dominated by ligneous plants and have larger ACL when the formation is dominated by herbaceous plants [43]. It is shown in Table 2 that ACL of sediment core samples is distributed between 29.61 and 30.09, averaging 29.92, around 30. This reflects that herbaceous plants and ligneous plants account for similar percentages in the sediment core samples, which is in line with the above results indicated by C₃₁/C₂₉.

3.2.5. CPI Value Distribution Characteristics and Their Significance

The CPI value of organic matter is a common index determining the odd-even predominance (OEP) of carbon number of n-alkanes [44]. The short-chain n-alkanes group and long-chain n-alkanes group of double-peak n-alkanes have different odd-even predominance, which is defined by CPI1 and CPI2. The corresponding computational formulas and CPI of samples are shown in Table 2 and Figure 4. It is shown in Table 2 that, except for number ZY22 sample (CPI1: 1.09), CPI1 values of short-chain alkanes group of 24 samples are between 0.57 and 0.97 and are all below 1.0 and average 0.80, reflecting the apparent even predominance; CPI2 values of long-chain alkanes group are between 0.7 and 3.95, and the CPI2 values of numbers ZY1, ZY2, and ZY3 samples are 0.7, 0.77, and 1.06, respectively, reflecting the apparent even predominance; CPI2 values of other 22 samples are all above 1.20, and average 2.77, reflecting the apparent odd predominance.

The carbon number of n-alkanes contaminated by oil does not show the apparent odd-even predominance [44, 45]. However, all the sediments samples in this research show the apparent odd-even predominance. Thus, it is estimated that these samples were not contaminated by oil, and the parameters of n-alkanes of samples could reflect the characteristics of primitive sedimentary environment and source.

The short-chain n-alkanes are mainly from marine floating algae and bacteria [36], which are dominated by , C₁₇, and C₁₉ [39], and have odd predominance [46]. However, the short-chain n-alkanes of 24 samples show even predominance, which shows specialty apparently.

It is found in the previous research that medium-chain n-alkanes in sea areas like Bohai Sea and Yangtze Estuary show even predominance [47], and medium-chain n-alkanes of a few samples in southern part of South Yellow Sea also show even predominance [5], which possibly resulted from microbe, for example, bacteria [47, 48] or fresh water and marine macrophyte [40, 41].

All the samples in the research contain squalene compound (Figure 5(a)), and the squalene is from the microbe. Thus, it is proved that all the samples suffered from the degradation by microbe. Meanwhile, the unseparation complex mixture (UCM) is widely developed in the n-alkanes of front peak group (Figure 5(b)), and UCM indicates that the organic matter suffered from the degradation by microbe. However, UCM is only shown in the short-chain n-alkanes, but not in long-chain n-alkanes, which could be resulted from two reasons. The first reason is mixture of two periods of organic matter. The organic matter deposited in the early period suffered from the degradation by microbe, and then new terrigenous organic matter migrated here fast, showing the present characteristics after mixing. The second reason is selective degradation by microbe. The microbe degraded short-chain n-alkanes in a selective way. However, determination of genesis needs further study.

The long-chain n-alkanes show apparent odd predominance [37, 49], with C₂₇, C₂₉ and C₃₁ most abundant [37, 39], which shows that long-chain n-alkanes of sediment core samples are mainly derived from surface waxiness of continental higher plants.

Additionally, CPI is a parameter indicating the maturity of organic matter. Generally, CPI >1.2 indicates immaturity, but CPI <1.2 does not necessarily indicate maturity. The CPI of sediment cores is between 0.76 and 4.03 (only 3 samples below 1.20), averaging 2.63, which reflects immaturity and is in accordance with characteristics of modern marine sediments.

3.3. Sedimentary Environment of Organic Matter

Pr/Ph >1.0 indicates oxidized sedimentary environment, and Pr/Ph <1.0 indicates reductive sedimentary environment [50]. Pr/Ph of studied sediment core samples is distributed between 0.35 and 0.96, averaging 0.74, below 1.0 (Table 2, Figure 4), which suggests reductive sedimentary environment. Additionally, Pr/nC₁₇ and Ph/nC₁₈ correlation diagram (Figure 6) also suggests that studied sediment samples are from marine sedimentary environment with strong reducibility and are at immature stage, which corresponds to characteristics of modern marine sediments.

Figure 6: Pr/nC₁₇ and Ph/nC₁₈ correlation diagram.

4. Conclusions

(1)The distribution of n-alkanes of 25 sediment samples in this research is characterized by three types: double-peak groups influenced by both terrigenous inputs and marine inputs, predominance of long-chain n-alkanes which indicate higher terrigenous inputs, and predominance of short-chain n-alkanes which indicate lower terrigenous inputs; C₂₅₋₃₅/C₁₅₋₂₁ ranges between 0.50 and 4.58, averaging 1.92; C₂₇₊₂₉₊₃₁/C₁₅₊₁₇₊₁₉ ranges between 0.24 and 26, averaging 4.22; C₂₁₋/C₂₂₊ is between 0.19 and 0.98, averaging 0.51; ranges from 0.21 to 0.52, averaging 0.35; all above outcomes indicate significant predominance of terrigenous inputs.(2) It is also of great significance to further distinguish terrigenous organic matter, that is, ligneous plants dominated or herbaceous plants dominated. C₃₁/C₂₉ of samples is between 0.87 and 1.12, averaging 1.04; ACL is distributed between 29.61 and 30.09, averaging 29.92, around 30; these results reflect that herbaceous plants and ligneous plants account for similar percentages in the sediment core samples.(3) CPI1 values of short-chain alkanes of samples are between 0.57 and 0.97 and are all below 1.0 and average 0.80, reflecting the apparent even predominance; CPI2 values of long-chain alkanes are between 0.7 and 3.95, and CPI2 values of 22 samples are all above 1.20, and average 2.77, reflecting the apparent odd predominance. The apparent odd-even predominance of sediments samples in the research suggests that these samples were not contaminated by oil, and their biomarker indicators could reflect the characteristics of primitive sedimentary environment and source. All the samples in the research contain the squalene compound, and the unseparation complex mixture (UCM) is widely developed in the short-chain n-alkanes. Both facts indicate that the organic matter suffered from the degradation by microbe. The long-chain n-alkanes show apparent odd predominance, with C₂₇, C₂₉, and C₃₁ most abundant, which shows that long-chain n-alkanes are mainly derived from surface waxiness of continental higher plants.(4) The CPI of samples is between 0.76 and 4.03, averaging 2.63, which reflects immaturity. Pr/Ph of sediment core samples is distributed between 0.35 and 0.96, averaging 0.74, below 1.0. This suggests reductive sedimentary environment. Pr/nC₁₇ and Ph/nC₁₈ correlation diagram also suggests that studied sediment samples are from marine sedimentary environment with strong reducibility and that the organic matter is at immature stage.

Competing Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors would like to give sincere thanks for the continuous supply of funds. This research was supported by the China Postdoctoral Science Foundation (2015M571841), the Key Laboratory of Marine Ecology and Environmental Science and Engineering, SOA (MESE-2016-04), the Scientific Research Foundation of Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education (China University of Mining and Technology) (no. 2016-003), Foundation of Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education (TPR-2015-04), Foundation of Sichuan Key Laboratory of Natural Gas Geology (Southwest Petroleum University) (2015trqdz10), and A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

References

J. Chen, H. Zhang, H. Jin, M. Jin, and Z. Liu, “Accumulation of sedimentary organic carbonin the arctic shelves and its significance on global carbon budget,” Chinese journal of polar research, vol. 16, no. 3, pp. 193–201, 2004.

F. E. Muller-Karger, R. Varela, R. Thunell, R. Luerssen, C. Hu, and J. J. Walsh, “The importance of continental margins in the global carbon cycle,” Geophysical Research Letters, vol. 32, no. 1, 2005.

J. I. Hedges and R. G. Keil, “Sedimentary organic matter preservation: an assessment and speculative synthesis,” Marine Chemistry, vol. 49, no. 2-3, pp. 81–115, 1995.

R. A. Berner, “Burial of organic carbon and pyrite sulfur in the modern ocean: its geochemical and environmental significance,” American Journal of Science, vol. 282, no. 4, pp. 451–473, 1982.

M. Zhao, Y. Zhang, L. Xing, Y. Liu, S. Tao, and H. Zhang, “The composition and distribution of n-alkanes in surface sediments from the South Yellow Sea and their potential as organic matter source indicators,” Periodical of Ocean University of China, vol. 41, no. 4, pp. 90–96, 2011.

S. Zhang, S. Li, H. Dong, Q. Zhao, X. Lu, and J. Shi, “An analysis of organic matter sources for surface sediments in the central South Yellow Sea, China: evidence based on macroelements and n-alkanes,” Marine Pollution Bulletin, vol. 88, no. 1-2, pp. 389–397, 2014.

Y. Qin, Y. Zhao, and L. Chen, Geology of the Yellow Sea, China Ocean Press, Beijing, China, 1989.

X. Gao, J. Song, X. Li, A. Long, and S. Chen, “A review of the major progress on carbon cycle researches in the Chinese marginal seas and the analysis of the key influence factors,” Marine Sciences, vol. 32, no. 3, pp. 83–90, 2008.

X. Shi, C. Chen, Y. Liu, H. Ren, and H. Wang, “Trend analysis of sediment grain size and sedimentary process in the central South Yellow Sea,” Chinese Science Bulletin, vol. 47, no. 14, pp. 1202–1207, 2002.

S. Yang and J.-S. Youn, “Geochemical compositions and provenance discrimination of the central south Yellow Sea sediments,” Marine Geology, vol. 243, no. 1–4, pp. 229–241, 2007.

H. Wang, X. Zhang, X. Lan, Z. Zhang, Z. Lin, and G. Zhao, “Geochemistry characteristics of sediment and provenance relations of sediments in core NT1 of the South Yellow Sea,” Journal of China University of Geosciences, vol. 18, no. 4, pp. 287–298, 2007.

Y. Wang, G. Li, W. Zhang, and P. Dong, “Sedimentary environment and formation mechanism of the mud deposit in the central South Yellow Sea during the past 40 kyr,” Marine Geology, vol. 347, pp. 123–135, 2014.

J. Lu, A. Li, P. Huang, and Y. Li, “Mineral distributions in surface sediments of the western South Yellow Sea: implications for sediment provenance and transportation,” Chinese Journal of Oceanology and Limnology, vol. 33, no. 2, pp. 510–524, 2015.

X. Zhang, Y. Ji, Z. Yang, Z. Wang, D. Liu, and P. Jia, “End member inversion of surface sediment grain size in the South Yellow Sea and its implications for dynamic sedimentary environments,” Science China Earth Sciences, vol. 59, no. 2, pp. 258–267, 2016.

D. Cai, X. Shi, W. Zhou et al., “Material sources and transportation of sediments in the Southern Yellow Sea: the stable carbon isotope evidences,” Chinese Science Bulletin, vol. 46, no. 1, pp. 16–23, 2001.

X. Lan, X. Zhang, and Z. Zhang, “Material sources and transportation of sediments in the Southern Yellow Sea,” Transactions of Oceanology and Limnology, no. 4, pp. 53–60, 2005.

X. Lan, H. Wang, Z. Zhang, Z. Lin, R. Li, and Z. Wang, “Distributions of rare earth elements and provenance relations in the surface sediments of the South Yellow Sea,” Journal of the Chinese Rare Earthsociety, vol. 24, no. 6, pp. 745–749, 2006.

X. Lan, H. Wang, R. Li, Z. Lin, and Z. Zhang, “Major elements composition and provenance analysis in the sediments of the south yellow sea,” Earth Science Frontiers, vol. 14, no. 4, pp. 197–203, 2007.

X. Yin, W. Liu, X. Lian, and X. Wan, “Detrital minerals and geochemistry of the surface soft sediments and their provenance, South Yellow Sea, China,” Journal of Jilin University (Earth Science Edition), vol. 37, no. 3, pp. 491–499, 2007.

Z. Xu, D. Lim, J. Choi, S. Yang, and H. Jung, “Rare earth elements in bottom sediments of major rivers around the Yellow Sea: implications for sediment provenance,” Geo-Marine Letters, vol. 29, no. 5, pp. 291–300, 2009.

S. Zhang, S. Li, H. Dong, and J. Shi, “Characteristics of biomarkers composition and geochemical significance of surface sediments in the northern part of south Yellow Sea,” Marine Science Bulletin, vol. 31, no. 2, pp. 198–206, 2012.

L. Hu, X. Shi, Z. Guo, Y. Liu, and D. Ma, “Geochemical characteristics of hydrocarbons in the core sediments from the South Yellow Sea and its implication for the sedimentary environment,” Acta Sedimentologica Sinica, vol. 31, no. 1, pp. 108–119, 2013.

S. Zhang, S. Li, H. Dong, Q. Zhao, and Z. Zhang, “Distribution and molecular composition of organic matter in surface sediments from the central part of South Yellow Sea,” Acta Sedimentologica Sinica, vol. 31, no. 3, pp. 497–508, 2013.

K. Wang, X. Shi, and X. Jiang, “The source and partition of sediments in the Southern Yellow Sea: evidence from light minerals,” Chinese Science Bulletin, vol. 46, no. 1, pp. 24–29, 2001.

B. Li, Distribution of Polycyclic Aromatic Hydrocarbons and n-Alkane in Surface Sediments from Yellow Sea an Bohai Sea, University of Oceanology, Qingdao, China, 2000.

Y. Wu, Some Progresses on Organic Geoehemistry Study of Bohai, the Yellow Sea, the East China Sea and Large Estuaries, East China Normal University, Shanghai, China, 2001.

Y. Wu, J. Zhang, T.-Z. Mi, and B. Li, “Occurrence of n-alkanes and polycyclic aromatic hydrocarbons in the core sediments of the Yellow Sea,” Marine Chemistry, vol. 76, no. 1-2, pp. 1–15, 2001.

S. Li, S. Zhang, Q. Zhao, and H. Dong, “The geochemical characteristics and its significance of saturated hydrocarbon in Surface Sediments from the South Yellow Sea,” Marine Geology Letters, vol. 25, no. 12, pp. 1–7, 2009.

M. Stuiver and P. J. Reimer, “Extended ¹⁴C data base and revised CALIB 3.0 ¹⁴C age calibration program,” Radiocarbon, vol. 35, no. 1, pp. 215–230, 1993.

K. A. Hughen, M. G. L. Baillie, E. Bard et al., “Marine04 marine radiocarbon age calibration, 0–26 cal kyr BP,” Radiocarbon, vol. 46, no. 3, pp. 1059–1086, 2004.

G. S. Kong, S.-C. Park, H. C. Han, J. H. Chang, and A. Mackensen, “Late Quaternary paleoenvironmental changes in the southeastern Yellow Sea, Korea,” Quaternary International, vol. 144, no. 1, pp. 38–52, 2006.

Y. Zhao, F. Li, D. J. DeMaster, C. A. Nittrouer, and J. D. Milliman, “Preliminary studies on sedimentation rate and sediment flux of the South Huanghai Sea,” Oceanologia Et Limnologia Sinica, vol. 22, no. 1, pp. 38–43, 1991.

F. Li, S. Gao, J. Jia, and Y. Zhao, “Contemporary deposition rates of fine-grained sediment in the Bohai and Yellow Seas,” Oceanologia et Limnologia Sinica, vol. 33, no. 4, pp. 364–369, 2002.

J.-M. Kim and M. Kucera, “Benthic foraminifer record of environmental changes in the Yellow Sea (Hwanghae) during the last 15,000 years,” Quaternary Science Reviews, vol. 19, no. 11, pp. 1067–1085, 2000.

L. Zhuang, F. Chang, T. Li, and J. Yan, “Foraminiferal faunas and holocene sedimentation rates of core EY02-2 in the South Yellow Sea,” Marine Geology and Quaternary Geology, vol. 22, no. 4, pp. 7–14, 2002.

M. Blumer, R. R. L. Guillard, and T. Chase, “Hydrocarbons of marine phytoplankton,” Marine Biology, vol. 8, no. 3, pp. 183–189, 1971.

G. Eglinton and R. J. Hamilton, “Leaf epicuticular waxes,” Science, vol. 156, no. 3780, pp. 1322–1335, 1967.

Y. Duan, “Organic geochemistry of recent marine sediments from the Nansha Sea, China,” Organic Geochemistry, vol. 31, no. 2-3, pp. 159–167, 2000.

J. E. Silliman and C. L. Schelske, “Saturated hydrocarbons in the sediments of Lake Apopka, Florida,” Organic Geochemistry, vol. 34, no. 2, pp. 253–260, 2003.

K. J. Ficken, B. Li, D. L. Swain, and G. Eglinton, “An n-alkane proxy for the sedimentary input of submerged/floating freshwater aquatic macrophytes,” Organic Geochemistry, vol. 31, no. 7-8, pp. 745–749, 2000.

R. Mead, Y. Xu, J. Chong, and R. Jaffé, “Sediment and soil organic matter source assessment as revealed by the molecular distribution and carbon isotopic composition of n-alkanes,” Organic Geochemistry, vol. 36, no. 3, pp. 363–370, 2005.

W. Kai-Fa, Z. Yu-Lan, J. Hui, X. Jia-Sheng, and W. Youg-Ji, “The spore-pollen and algal assemblages from the surface sediments of Yellow Sea,” Acta Botanica Sinica, vol. 22, no. 2, pp. 182–190, 1980.

X. Huang, P. A. Meyers, W. Wu, C. Jia, and S. Xie, “Significance of long chain iso and anteiso monomethyl alkanes in the Lamiaceae (mint family),” Organic Geochemistry, vol. 42, no. 2, pp. 156–165, 2011.

X. Lv and S. Zhai, “The distribution and environmental significance of n-alkanes in the Changjiang River estuary sediments,” Acta Sientiae Circumstantiae, vol. 28, no. 6, pp. 1221–1226, 2008.

J. Han and M. Calvin, “Hydrocarbon distribution of algae and bacteria, and microbiological activity in sediments,” Proceedings of the National Academy of Sciences of the United States of America, vol. 64, no. 2, pp. 436–443, 1969.

L. Zhang, P. Gong, and X. Zhang, “A review of the study of estuarine organic carbon,” Periodical of Ocean University of China, vol. 35, no. 5, pp. 737–744, 2005.

C. M. Reddy, T. I. Eglinton, R. Palić et al., “Even carbon number predominance of plant wax n-alkanes: a correction,” Organic Geochemistry, vol. 31, no. 4, pp. 331–336, 2000.

W.-L. Jeng and C.-A. Huh, “A comparison of sedimentary aliphatic hydrocarbon distribution between East China Sea and southern Okinawa Trough,” Continental Shelf Research, vol. 28, no. 4-5, pp. 582–592, 2008.

M. A. Goni, K. C. Ruttenberg, and T. I. Eglinton, “Sources and contribution of terrigenous organic carbon to surface sediments in the Gulf of Mexico,” Nature, vol. 389, no. 6648, pp. 275–278, 1997.

K. E. Peters and J. M. Moldowan, The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments, Prentice Hall, New Jersey, NJ, USA, 1993.