Paleovegetation inferred from the carbon isotope composition of long-chain n-alkanes in lacustrine sediments from the Song-nen Plain… · ORIGINAL PAPER Paleovegetation inferred

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Journal of Paleolimnology ISSN 0921-2728Volume 54Number 4 J Paleolimnol (2015) 54:345-358DOI 10.1007/s10933-015-9856-0

Paleovegetation inferred from the carbonisotope composition of long-chain n-alkanes in lacustrine sediments from theSong-nen Plain, northeast China

Zhifu Wei, Yongli Wang, Baoxiang Wu,Zixiang Wang & Gen Wang

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ORIGINAL PAPER

Paleovegetation inferred from the carbon isotopecomposition of long-chain n-alkanes in lacustrine sedimentsfrom the Song-nen Plain, northeast China

Zhifu Wei . Yongli Wang . Baoxiang Wu .

Zixiang Wang . Gen Wang

Received: 9 April 2014 / Accepted: 1 September 2015 / Published online: 5 September 2015

� Springer Science+Business Media Dordrecht 2015

Abstract Abundant n-alkanes were identified by

GC/MS analysis in core sediments from Xianghai

Lake and the Huola Basin, on the Song-nen Plain,

northeast China. The n-alkanes extracted from Xiang-

hai Lake samples showed unimodal and bimodal

distribution. The main peaks of unimodal distribution

were at n-C29 or n-C31, and the mid- and long-chain n-

alkanes had odd-carbon-number predominance, sug-

gesting they were derived mainly from terrestrial

higher plants. Bimodal distributions of n-alkanes had

maximum values centered at n-C17 and n-C31 in all

samples. The short-chain n-alkanes with a maximum

at n-C17 showed no odd–even predominance, however

there was a strong odd-carbon-number predominance

of long-chain n-alkanes, with a maximum at n-C31.

These results suggest that organic matter in Xianghai

Lake was derived from mixed sources, including

bacteria, algae and terrestrial plants. The n-alkanes

extracted from Huola Basin sediments were charac-

terized by a unimodal distribution, with the maximum

value at n-C31, and the long-chain n-alkanes had an

odd-carbon-number predominance, indicating that

they were derived mainly from terrestrial higher

plants. In addition, the compound-specific carbon

isotope composition was determined for C27, C29 and

C31 n-alkanes in the core sediments, and the relative

contributions of C3 and C4 plants were estimated using

a binary model. Calculations indicated that C3 plants

were the dominant input during the late glacial and

Holocene. The relative abundance of C3 and C4 plants

changed significantly through time, likely determined

by cool versus warm climate conditions.

Keywords n-Alkanes � d13C of long-chain n-alkanes � Paleovegetation � C3 and C4 plants �Northeast China

Introduction

Lacustrine sediments are excellent archives for study-

ing high-resolution paleoclimate changes because of

their precise chronology and the large variety of

proxies contained within them (Smol and Cumming

2000; Fagel et al. 2008). Organic molecules are

increasingly used in paleolimnological investigations

as they provide identifiable environmental informa-

tion from different sources (Cranwell et al. 1987;

Ficken et al. 2000; Huang et al. 1999; Castañeda et al.

Z. Wei (&) � Y. Wang (&) � B. Wu � Z. Wang �G. Wang

Key Laboratory of Petroleum Resources, Gansu Province/

Key Laboratory of Petroleum Resources Research,

Institute of Geology and Geophysics, Chinese Academy

of Sciences, 730000 Lanzhou, People’s Republic of China

e-mail: [email protected]

Y. Wang

e-mail: [email protected]

Z. Wang � G. WangUniversity of Chinese Academy of Sciences,

100049 Beijing, China

123

J Paleolimnol (2015) 54:345–358

DOI 10.1007/s10933-015-9856-0

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2007). Based on knowledge of n-alkane distributions

in plants, proxies such as the n-alkane average chain

length (ACL), ratio of non-emergent aquatic macro-

phytes to emergent aquatic macrophytes and terrestrial

plants (Paq), the ratio of trees to grasses (n-C27/n-C31),

and the carbon preference index (CPI) have been

developed to infer climate-induced changes recorded

in lake sediment and peat sequences (Cranwell et al.

1987; Ficken et al. 2000; Meyers 2003). Besides the n-

alkane distributions, compound-specific d13C valuescan be used to estimate relative contributions of C3 and

C4 plants and infer paleoclimate changes, and to

examine past primary productivity (Huang et al. 1999;

Castañeda et al. 2007).

The potential for n-alkanes and compound-specific

carbon isotope proxies to track specific environmental

information and disentangle processes led to paleo-

climate studies in different regions of China, including

the northern South China Sea (Zhou et al. 2012),

northeastern China (Zhou et al. 2010) and the Qinghai-

Tibet Plateau (Zhu et al. 2008; Aichner et al. 2010;

Mügler et al. 2010; Duan et al. 2011; Wang and Liu

2012). Changes in the relative abundances of C3/C4plants throughout geologic history were studied using

the carbon isotopic composition of long-chain n-

alkanes in loess/paleosol sequences (Zhang et al.

2003), lake sediments (Street-Perrott et al. 1997;

Huang et al. 2001; Lane et al. 2011) and marine

deposits (Yamada and Ishiwatari 1999; Huang et al.

2007).

Study area

The Song-nen Plain (43�300–48�410N, 121�300–127�00E) is one of the main regions for grainproduction and animal husbandry in northeast China.

The plain is surrounded by the Da Hinggan, Xiao

Hinggan and Changbai Mountains. The area is com-

posed of alluvial, lacustrine and aeolian deposits.

Tectonically, the plain was a large Mesozoic sediment

basin developed on the base of Paleozoic folds and

part of the Cenozoic Song-Liao Fault Basin (Sun

1990). It has a temperate, semi-arid continental

monsoon climate, with an average annual air temper-

ature of 4.9 ± 1.5 %, average annual precipitation of

450 ± 50 mm, and average annual evaporation of

1450 ± 203 mm (Yang 1996). Its hydrologic envi-

ronment is unique in that there are out-flows formed by

the Nenjiang River and the Songhuajiang River. The

most common soil types in the area include black soil

and chernozem, but there are also meadow soils,

swamp soils, halic soils, sandy soils, and paddy soils.

Owing to agricultural expansion, grasslands are

mainly distributed throughout the west of the Song-

nen Plain and interlace with farmland.

NortheasternChina has amix ofC3 andC4 plants and

is a zone that is sensitive to climate and vegetation

changes. The area possesses a number of lakes and

sediment cores from these water bodies can be analyzed

to reveal these vegetation and climate changes, inferred

from the distribution and compound-specific carbon

isotopic composition of n-alkanes. We analysed the

distribution and compound-specific d13C ofn-alkanes insediment cores from Xianghai Lake and the Huola

Basin, on the Song-nen Plain, northeast China. We also

investigated the distribution of paleovegetation and the

relative contribution of C3 and C4 plants during the late

glacial and Holocene. These data provide important

information for understanding the vegetation distribu-

tion pattern in the regional environment under a global

warming trend.

Study site

Xianghai Lake is located in the Xianghai Wetland

Nature Reserve (44�550–45�090N, 122�050–122�310E),a freshwater wetland that covers an area of 360 km2 in

the downstream reaches of the Huolin River (Fig. 1).

The wetland lies at low altitude (156–192 m asl) and

relatively high latitude. The average annual temper-

ature is *5.1 �C. Water and sediment in marshes arefrozen from late October to early April, but start to

melt in late April. Mean annual rainfall is 408 mm. As

the wetland is located in the semi-arid climate zone

and borders the Keerqin Desert, the main hydrologic

input (about 55 %) to the Xianghai wetlands, except

for rainfall, comes from the Huolin River. Because of

the complex landscape, there are diverse plant and

animal resources. According to preliminary field

investigations, there are [600 higher plant species,of which 263 are medicinal plants belonging to 256

genera in 76 families.

The Huola Basin is located in the north Da Hinggan

Mountains, and lies in the cold-temperate continental

climate zone. Conditions for cold artesian water exist

in the basin. The average temperature in this area is

-49 �C, with an annual temperature range of[75 �C.The lowest temperatures are typically-45 to-52 �C,

346 J Paleolimnol (2015) 54:345–358

123


and highest values are 30–37 �C. The average yearlyground temperature is -4.2 �C. The frost-free periodis \100 days, and the freeze period is as long as8 months. Over 80 % of the annual rainfall occurs in

the months of June to September.

Materials and methods

Sediment coring and radiocarbon dating

Two sediment cores were recovered from Xianghai

Lake and Huola Basin in December 2012 (Fig. 1). The

Xianghai Lake core site was at 45�04027.1200N,122�19034.3200E and the recovered core was 1420 cm

long. The Huola Basin lacustrine sediments were

collected from the Gulian River Open Pit Coal Mine,

Da Hinggan Mountains (53�00038.8800N,121�57048.2400E) and the core was 300 cm in length.Twenty-five samples were taken at varying intervals

from each core for analysis of total organic carbon

(TOC), distribution of n-alkanes and compound-

specific carbon isotope composition of n-alkanes.

Five charcoal samples in each sediment core were

collected for accelerator mass spectrometry (AMS)14C dating at the Australian Nuclear Science and

Technology Organisation Laboratory, Australia. All

samples underwent a standard hydrochloric acid wash

to remove carbonates. Radiocarbon ages were cali-

brated using CALIB software (Reimer et al. 2009).

Fig. 1 Location of study area and the cores

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123


Lipid and carbon isotope analysis

Samples were powdered (80–100 mesh) and extracted

with chloroform in a Soxhlet apparatus for 72 h, and

the solvent was removed by distillation. The extracts

were condensed and weighed. Asphalt fractions were

collected through precipitation separation with petro-

leum ether, and aliphatic, aromatic and resin fractions

were eluted by using silica gel-alumina column

chromatography with n-hexane, benzene and ethanol,

respectively. The organic matter analysis was carried

out in the Key Laboratory of Gas Geochemistry,

Institute of Geology and Geophysics, Chinese Acad-

emy of Sciences.

GC–MS analysis was performed using an HP 5973

MSD (Agilent Technologies, Wilmington, DE, USA)

interfaced to an HP 6890 gas chromatograph that was

fitted with a 30 m 9 0.25 mm-i.d., fused silica cap-

illary column coated with a film (0.25 lm) of 5 %phenyl-methyl-DB-5. For routine GC analysis, the

oven was programmed from 80 to 300 �C at 3 �C/minwith a final hold time of 20 min. Helium was used as

carrier gas at a linear velocity of 32 cm/s, with the

injector operating at a constant flow of 0.9 mL/min.

The MS was operated with an ionization energy of

70 eV, a source temperature of 230 �C and an electronmultiplier voltage of 1900 V over a range of 35–550

Dalton.

The carbon isotopic values of individual n-alkanes

were determined using a gas chromatography-isotope

ratio mass spectrometry (Thermo ScientificMAT 253)

system. d13C values of long-chain n-alkanes weremeasured by GC (HP6890) with an HP-5 MS silica

capillary column (60 m 9 0.32 mm 9 0.25 lm),connected to an isotope ratio mass spectrometer (GV

Instruments IsoPrime mass spectrometer). The oven

temperature was programmed to be initially held at

80 �C for 3 min, increased to 300 �C at a rate of3 �C/min and held for another 30 min. Each samplewas analyzed twice, and final averaged results were

expressed as % relative to the VPDB (Vienna PeedeeBelemnite) standard.

Calculation of C3 and C4 plant percentages

The relative contribution of C3 plants can be calcu-

lated with a binary model for C3 and C4 plant wax n-

alkanes. Long-chain n-alkanes produced by C3 and C4plants have characteristic d13C values:-32 to-39 %

and -18 to -22 %, respectively (Rieley et al. 1991;Collister et al. 1994; Kuypers et al. 1999; Chikaraishi

and Naraoka 2003). In this study we chose-36 % forC3 plant n-alkanes and -21 % for C4 plant n-alkanesas end members. These values are well accepted and

used for similar calculations (Zhao et al. 2000). The

percent C3 plant contribution (x) is calculated from the

following formula:

x� ð�36&Þ þ ð1� xÞ � ð�21&Þ ¼ d13Cmeanð1Þ

where d13Cmean is the weighted mean average of d13C

of C27, C29 and C31 n-alkanes, in order to reconstruct

vegetation change:

d13Cmean ¼ d13C27 � C27 þ d13C29 � C29 þ d13C31�

�C31Þ=ðC27 þ C29 þ C31Þ ð2Þ

where C27, C29 and C31 are the relative abundances of

n-C27, n-C29 and n-C31.

Results

Lithology and carbon content

Sediments of the Xianghai Lake core were composed

mainly of interbedded sand and mud (Fig. 2). The

TOC values of samples were relatively low, ranging

from 0.04 to 1.11 %, with an average value of 0.25 %

(Table 1). The Huola Basin core is composed mainly

of lacustrine silt (Fig. 2), and the TOC values of the

profile samples ranged from 0.56 to 3.68 %, with an

average value of 1.41 % (Table 1).

Core chronologies

Five charcoal samples from each sediment core were

dated by radiocarbon analysis (Table 2). The age at

the core top was assumed to be zero in both cases, and

age models were derived by linear interpolation

between AMS 14C dates on the five charcoal samples

in each sediment core. The age-depth relationship in

the two sediment cores is shown in Fig. 2.

Distribution of n-alkanes

Abundant n-alkanes were detected in the core sedi-

ments from Xianghai Lake and the Huola Basin

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(Table 1). The n-alkanes in the Xianghai Lake sam-

ples represent a suite of components ranging from n-

C13 to n-C33, with either unimodal or bimodal

distribution, and maxima at n-C29 or n-C31, or n-C17and n-C31, respectively. In contrast, the carbon

number distribution of n-alkanes in Huola Basin

deposits ranges from n-C14 to n-C33, and is character-

ized by a unimodal distribution, with the maximum at

n-C31 (Fig. 3).

Compound-specific carbon isotope composition

of n-alkanes

Compound-specific d13C values of the odd-carbon-number C27 to C31 n-alkanes are listed in Table 3. In

the Xianghai Lake core, d13C27 values are between-34.0 and -28.5 % (average -30.7 %), d13C29values are between -35.7 and -29.3 % (average-32.2 %), and d13C31 values are between -36.0 and-31.3 % (average -32.7 %). The Huola Basin coreshowed more 13C-depleted values. There, the d13Cvalues of the three primary long-chain n-alkanes

ranged from -35.7 to -32.0 %, -36.7 to -32.4 %,

and -36.9 to -32.9 %, and had average values of-33.2,-34.3 and-34.3 %, respectively for n-C27, n-C29 and n-C31. The d

13C values of the two cores show

that the n-alkanes get systematically more 13C-

depleted with increasing chain length.

Discussion

Origin of the sediment n-alkanes

The n-alkanes are widely present in plants and other

organisms. The source of organic matter can be traced

by distribution characteristics of n-alkanes because

different biological sources of n-alkanes possess differ-

ent distribution characteristics. Previous studies showed

that n-alkanes from lower organisms range from n-C15to n-C20, often with n-C17 or n-C19 as the dominant

compounds, and without obvious odd-over-even pref-

erence (Cranwell et al. 1987). In contrast, n-alkanes

from modern terrestrial higher plants are mainly long-

chain compounds, i.e. n-C27, n-C29 and n-C31, and show

an apparent odd-over-even preference, with CPI values

Fig. 2 Age-depth modelbased on a linear

interpolation between dates

of charcoal samples

a Xianghai Lake core,b Huola Basin core. Thecore top was assigned an age

of zero

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Table 1 The TOC and biomarker parameters of the Xianghai Lake and Huola Basin core sediment samples

Depth (cm) TOC (%) Most abundant

compound

CPI17–21a CPI23–31

b OEP27–31c ACL27–33

d Rn-C21- /Rn-C22

?

The Xianghai lake core samples

115 0.24 21 1.11 2.02 2.71 29.1 0.87

213 0.39 29 1.13 2.58 4.12 29.3 0.72

283 1.11 29 1.19 6.37 7.16 29.4 0.26

337 0.87 29 1.55 8.49 10.17 29.5 0.24

425 0.56 31 1.11 10.6 11.68 29.8 0.10

477 0.49 31 1.13 11.84 12.99 29.8 0.07

497 0.42 31 1.10 10.91 12.35 29.7 0.08

515 0.25 31 1.13 5.63 6.93 29.7 0.23

529 0.24 31 1.13 7.53 8.90 29.7 0.17

559 0.22 31 1.13 4.61 5.87 29.7 0.37

609 0.06 17/31 1.13 2.46 3.13 29.4 1.58

639 0.11 17/31 1.13 3.01 3.38 29.5 0.96

731 0.05 17/31 1.13 1.70 2.07 29.6 1.60

781 0.04 17/31 1.13 1.95 2.92 29.6 2.56

833 0.05 17/31 1.13 3.60 5.09 29.8 1.12

851 0.06 17/31 1.13 4.65 5.85 29.8 0.64

875 0.05 17/31 1.13 3.58 4.34 29.9 0.90

905 0.06 17/31 1.13 4.72 5.66 29.9 0.44

925 0.06 17/31 1.13 4.82 5.65 30.1 0.49

1067 0.30 17/31 1.13 6.99 7.64 29.8 0.08

1135 0.14 17/31 1.13 5.75 6.37 29.7 0.21

1207 0.06 17/31 1.13 3.90 5.51 30.0 1.07

1347 0.09 17/31 1.13 6.07 6.55 29.9 0.29

1356 0.28 17/31 1.13 6.67 7.24 29.9 0.15

1385 0.09 17/31 1.13 3.13 3.60 29.5 0.70

Average 0.25 1.15 5.34 6.31 29.7 0.64

The Huola Basin core samples

18 1.88 31 1.50 4.16 4.80 29.8 0.24

39 1.51 31 1.38 4.37 5.44 29.5 0.21

65 3.14 31 1.33 4.16 5.28 29.6 0.27

86 2.09 31 1.35 4.14 5.06 29.6 0.31

105 1.72 31 1.43 4.77 5.59 29.5 0.19

111 1.94 31 1.57 4.50 5.36 29.5 0.18

140 1.21 31 1.31 4.62 5.27 29.8 0.14

156 1.26 31 1.42 4.08 4.71 29.8 0.14

175 1.14 31 1.30 4.34 5.26 29.7 0.16

181 1.38 31 1.26 3.36 4.31 29.6 0.16

186 1.19 31 1.28 4.74 6.28 29.8 0.18

190 1.09 31 1.27 5.09 6.19 29.9 0.18

193 0.57 31 1.24 4.76 5.83 29.8 0.17

198 1.16 31 1.38 4.95 6.06 30.0 0.14

202 1.80 31 1.45 5.29 6.70 29.9 0.14

206 1.11 31 1.29 5.28 6.48 30.1 0.15

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generally[5 (Eglinton andHamilton 1967; Rieley et al.1991). The n-alkane distribution exhibits high odd-to-

even predominance in long-chain (C25–C35) n-alkanes,

which characterizes hydrocarbons from vascular land

plants versus those in petroleum and bacteria (Gearing

et al. 1976; Farrington 1980). One common variable

derived from this predominance is the carbon prefer-

ence index (CPI). The CPI is an indication of n-alkane

source. Hydrocarbons composed of a mixture of

compounds originating from land plant material show

a predominance of odd-numbered carbon chains with

CPI = 5–10 (Rieley et al. 1991; Hedges and Prahl

1993), whereas petrogenic inputs have a CPI of about

1.0 (Saliot et al. 1988; Pendoley 1992). CPI values close

to 1 are also thought to indicate greater input from

marine microorganisms and/or recycled organic matter

(Kennicutt et al. 1987). In organic geochemistry, CPI is

used to indicate the degree of diagenesis of straight-

chain geolipids, and is a numerical representation of

how much of the original biological chain length

specificity is preserved in geological lipids (Meyers and

Ishiwatari 1995).

Table 1 continued

Depth (cm) TOC (%) Most abundant

compound

CPI17–21a CPI23–31

b OEP27–31c ACL27–33

d Rn-C21- /Rn-C22

?

210 0.67 31 1.37 4.51 5.74 30.0 0.15

220 0.59 31 1.16 4.5 5.77 29.7 0.26

228 0.56 31 1.13 4.69 6.11 29.7 0.27

235 0.80 31 1.13 4.59 5.82 29.6 0.25

243 0.84 31 1.12 4.28 5.06 30.0 0.20

248 1.03 31 1.17 4.35 5.00 29.8 0.25

262 3.68 31 1.32 3.8 4.93 29.3 0.40

289 1.68 31 1.30 4.39 5.36 29.5 0.21

296 1.16 31 1.17 4.21 5.12 29.6 0.17

Average 1.41 1.31 4.48 5.50 29.7 0.25

a CPI17–21 = 0.5 9 [(C17 ? C19 ? C21)/(C16 ? C18 ? C20) ? (C17 ? C19 ? C21)/(C18 ? C20 ? C22)]b CPI23-31 = 0.5 9 [(C23 ? C25 ? C27 ? C29 ? C31)/

(C22 ? C24 ? C26 ? C28 ? C30) ? (C23 ? C25 ? C27 ? C29 ? C31)/(C22 ? C24 ? C26 ? C28 ? C30 ? C32)]c OEP27–31 = (C27 ? 6 9 C29 ? C31)/[4 9 (C28 ? C30)]d ACL27–33 = (27 9 C27 ? 29 9 C29 ? 31 9 C31 ? 33 9 C33)/(C27 ? C29 ? C31 ? C33)

Table 2 Dates in two cores Lab. code Depth (cm) AMS14C age (a BP) Calibrated age (a BP) Material

Xianghai Lake core

Ansto-XH-1 160–162 1800 ± 40 1550 ± 62 Charcoal



Ansto-XH-4 1150–1152 9880 ± 40 10,620 ± 93 Charcoal

Ansto-XH-5 1394–1396 12,580 ± 40 13,410 ± 102 Charcoal

Huola Basin core

Ansto-HL-1 18–20 120 ± 40 80 ± 31 Charcoal




Ansto-HL-5 296–298 19,270 ± 40 19,800 ± 63 Charcoal

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The n-alkanes extracted from Xianghai Lake sam-

ples show unimodal and bimodal distribution

(Table 1). The main peaks of unimodal distribution

were at n-C29 or n-C31, and the long-chain n-alkanes

had an obvious odd-carbon-number predominance

(CPI23–31: 2.58–11.84, average: 7.62; odd–even pre-

dominance (OEP)27–31:4.12–12.99, average: 8.91),

indicating that they were mainly derived from terres-

trial higher plants. The characteristic bimodal distri-

bution of n-alkanes had maximum values centered at

n-C17 and n-C31 in all samples. The short-chain

alkanes showed no obvious OEP, with a maximum

at n-C17 (CPI17-21: 0.91–1.18, average: 1.07). In

contrast, the long-chain alkanes had a strong odd-

carbon-number predominance of long chain n-alka-

nes, with a maximum at n-C31 (CPI23–31: 1.70–6.99,

average: 4.20). These results suggest that the organic

matter was derived from mixed sources of lower

bacteria and algae, as well as terrestrial higher plants.

The n-alkanes extracted from Huola Basin were

characterized by a unimodal distribution, with the

maximum value at n-C31, and the long-chain n-alkanes

had an obvious odd-carbon-number predominance.

Calculated OEP27–31 values throughout the entire

section ranged from 4.31 to 6.70 and had an average

value of 5.42 (Table 1), indicating that they were

mainly derived from terrestrial higher plants.

Paleovegetation types of the study area

Modern organic geochemistry of molecules shows that

the ratio Rn-C21-/Rn-C22

? reflects the proportion of

lower organisms such as bacteria and algae relative to

higher plants (Xie et al. 1999, 2003; Xie and Evershed

2001). As shown in Table 1, the ratio Rn-C21-/Rn-

C22? ranged from 0.07 to 2.56 (average 0.64) and 0.14

to 0.40 (average 0.25), respectively, for the Xianghai

Lake core and Huola Basin core sediments, suggesting

that terrestrial higher plants were the main source of

organic matter during the late glacial and Holocene.

From 8.0 to 6.0 cal ka BP, however, the ratio in

Xianghai Lake was[1.0 (Fig. 4), indicating relativelygreater input from bacteria, algae and aquatic plants

under warmer climate and lower lake level. During the

late glacial and late Holocene, the ratio was \1.0,suggesting that higher plants dominated under colder

climate conditions. The ratio of these n-alkanes in the

Xianghai Lake core sediments was high in the interval

11.5–8.0 cal ka BP (Fig. 4), indicating that higher

plants were replaced as an organic matter source by

bacteria, algae and aquatic plants. During

8.0–5.0 cal ka BP, the ratio declined, indicating that

bacteria, algae and aquatic plants were replaced by

higher plants as an organic matter source, whereas

from 5.0 cal ka BP to present, the ratio increased,

Fig. 3 The distribution ofn-alkanes in the Xianghai

Lake core and Huola Basin

core

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Table 3 The d13C valuesof three primary long-chain

n-alkanes (n-C27, n-C29 and

n-C31) and calculated

relative contribution of C3and C4 plants of the

Xianghai lake core and

Huola Basin core

Depth (m) d13C (%) C3 (%) C4 (%)

n-C27 n-C29 n-C31 Cmean

The Xianghai lake core samples

115 -30.3 -32.3 -32.5 -31.7 71 29

213 -29.3 -29.3 -31.8 -30.2 61 39

283 -29.0 -31.0 -32.6 -31.1 67 33

337 -28.4 -30.2 -31.8 -30.3 62 38

425 -30.7 -32.4 -33.1 -32.5 76 24

477 -31.5 -32.8 -33.7 -33.0 80 20

497 -30.9 -32.8 -33.4 -32.7 78 22

515 -31.5 -32.1 -33.0 -32.4 76 24

529 -32.4 -32.9 -33.8 -33.2 81 19

559 -32.0 -32.2 -32.1 -32.1 74 26

609 -30.0 -33.3 -32.6 -32.2 74 26

639 -32.5 -33.2 -33.0 -33.0 80 20

731 -28.5 -31.2 -31.5 -30.6 64 36

781 -30.1 -32.7 -32.6 -32.0 73 27

833 -31.6 -33.0 -33.5 -32.9 80 20

851 -30.0 -31.8 -32.0 -31.6 70 30

875 -29.4 -31.9 -30.8 -30.9 66 34

905 -31.1 -31.4 -33.1 -32.1 74 26

925 -29.3 -30.5 -31.3 -30.8 65 35

1067 -31.2 -32.3 -32.7 -32.2 75 25

1135 -34.0 -35.7 -36.0 -35.5 97 3

1207 -30.1 -32.3 -32.6 -32.1 74 26

1347 -31.1 -33.0 -33.0 -32.7 78 22

1356 -32.2 -33.0 -33.2 -33.0 80 20

1385 -29.8 -31.0 -31.8 -31.0 67 33

Average -30.7 -32.2 -32.7 -32.1 70 30

The Huola Basin core samples

18 -32.1 -33.3 -32.9 -32.8 78 22

39 -32.6 -33.9 -34.0 -33.5 83 17

65 -32.2 -32.4 -33.2 -32.7 78 22

87 -33.7 -34.4 -33.3 -33.7 85 15

105 -32.0 -32.8 -33.0 -32.6 78 22

111 -33.8 -35.5 -35.5 -34.9 93 7

139 -32.2 -33.1 -33.4 -33.0 80 20

157 -32.2 -33.7 -33.8 -33.3 82 18

176 -33.2 -34.7 -34.6 -34.2 88 12

180 -33.0 -34.7 -34.6 -34.1 87 13

186 -35.7 -36.7 -35.6 -35.9 99 1

190 -32.6 -33.4 -33.8 -33.4 82 18

193 -33.4 -34.6 -34.7 -34.3 89 11

198 -32.8 -34.1 -34.2 -33.8 85 15

202 -33.0 -34.9 -34.6 -34.3 89 11

206 -32.8 -33.5 -34.1 -33.7 84 16

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suggesting that bacteria, algae and aquatic plants were

again dominant as the source of organic matter. Ratios

in Huola Basin sediments were\1.0 throughout therecord and fluctuated little, suggesting that terrestrial

higher plants were the main source of organic matter

during the late glacial and Holocene.

The n-alkane average chain length (ACL) value is

the concentration-weighted mean chain length of the

C27, C29, C31, and C33 n-alkanes (Poynter et al. 1989).

In warmer climates, land plants biosynthesize longer-

chain compounds with higher melting points for their

waxy coatings, whereas in cool, temperate regions,

somewhat shorter-chain compounds are produced

(Gagosian and Peltzer 1986). The ACL values of n-

alkanes from plants that grow in warm climates are

consequently larger than those of plants from cooler

regimes (Zhou et al. 2010). A fundamental assumption

for using ACL as a proxy for past vegetation is that leaf

lipids derived from grasslands, on average, have

longer carbon chain lengths than leaf lipids from

forest plants (Cranwell 1973). But a comprehensive

review by Bush and McInerney (2013) summarized

ACL values for alkanes in modern plants from around

the world, and found that ACL was unable to

distinguish graminoids (grasses) from woody plants.

Wang et al. (2015) argued that considerable caution is

necessary in using ACL values as a proxy indicator for

vegetation dynamics, and for interpreting ACL vari-

ation in terms of past changes in environment and

climate.

The ACL values in the Holocene sediments are

overall relatively larger than those of the late glacial

deposits (Fig. 4). The ACL values of the two cores

display an increasing tendency during the late glacial,

whereas during the Holocene, the ACL values show a

decreasing trend. The ACL values of n-alkanes

derived from Xianghai Lake core sediments increased

during the interval 11.5–9.0 cal ka BP (Fig. 4), indi-

cating that woody plants were progressively replaced

by grasses, but that trend reversed from 9.0 to

6.0 cal ka BP, as ACL values declined, indicating

grasses were replaced by woody plants. In the interval

6.0–5.0 cal ka BP, the values again increased, sug-

gesting a replacement of forest by grassland plants, but

from 5.0 cal ka BP to present, the ACL value

decreased, suggesting that grasslands gave way to

the spread of woody plants. In contrast, the ACL

values of Huola Basin only ranged from 29.4 to 29.8

throughout the record, without significant fluctuation

(Fig. 4).

Seki et al. (2012) demonstrated that ACL values

can distinguish trees from shrubs and sedges, in that

shrubs and sedges have higher ACL values ([29) thantrees (*27), as summarized by Kirkels et al. (2013).The ACL values of Xianghai Lake and Huola Basin

samples are [29.0 and range from 29.1 to 30.1(mean = 29.7) (Table 1; Fig. 4), indicating that veg-

etation types of the study area were mainly shrubs and

sedges during the late glacial and Holocene.

Paleovegetation composition of the study area

The d13C records of long-chain alkanes have beenused to estimate the relative abundances of C3 and C4plants at some sites (Huang et al. 2006; Castañeda and

Schouten 2011; Seki et al. 2010; Sun et al. 2013).

Table 3 continued Depth (m) d13C (%) C3 (%) C4 (%)

n-C27 n-C29 n-C31 Cmean

210 -34.4 -35.4 -33.2 -34.1 87 13

220 -34.0 -35.7 -36.9 -35.7 98 2

228 -33.5 -35.1 -35.2 -34.7 91 9

235 -33.4 -34.0 -34.2 -33.9 86 14

244 -33.0 -34.1 -34.6 -34.1 87 13

248 -33.4 -34.1 -35.0 -34.3 89 11

263 -33.4 -34.3 -34.1 -33.9 86 14

290 -33.3 -34.0 -34.1 -33.8 86 14

297 -33.5 -34.2 -34.7 -34.2 88 12

Average -33.2 -34.3 -34.3 -34.0 86 14

354 J Paleolimnol (2015) 54:345–358

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Long-chain n-alkanes mainly derive from terrestrial

higher plants. Terrestrial higher plants assimilate

atmospheric CO2 mainly via two photosynthetic

pathways, i.e. the C3 and C4 pathways. The C4 or

Hatch-Slack pathway has evolved as a CO2-concen-

trating mechanism in which CO2 initially combines

with phosphoenol pyruvate to form a 4-carbon acid,

oxaloacetate (Raven et al. 1999). This CO2-concen-

trating mechanism gives C4 plants a competitive

advantage under low pCO2 conditions (Collatz et al.

1998). It is also generally agreed that C4 plants have

greater water-use efficiency than C3 plants (Raven

et al. 1999). Thus, modern C4 plants are commonly

distributed in hot and dry environments. Warm-season

grasses and sedges use the C4 pathway. Virtually all

trees, most shrubs, herbs, cool-season grasses and

sedges use the C3 pathway.

In this study, the percentages of C3 and C4 plants

(Table 3) were calculated using Eq. (1). Calculated C3plant percentages in the Xianghai Lake core varied

from 61 to 97 %, with an average value of 70 %,

whereas in the Huola Basin core, the percentage of C3plants ranged from 78 to 99 %, with an average value

of 90 % (Table 3). These calculations indicate that C3plants were a dominant input during the late glacial

and Holocene. The percentages of C3 plants in the late

glacial are overall greater than those of the Holocene

(Fig. 5), and thus the percentages of C4 plants in the

late glacial sediments are overall relatively smaller

than percentages in Holocene deposits. During the late

glacial, the percentages of C3 plants in the two cores

rose, whereas during the Holocene, percentages of C3plants in the two cores decreased through time.

Fluctuations in the percentages of C3 and C4 plants

in the two cores displayed differences during the

Holocene (Fig. 5). Highest C3 plant percentages,

however, were recorded in both cores during the

interval 11.5–10.5 cal ka BP, indicating an especially

cold and moist local climate in the Pre-Boreal portions

of the Xianghai Lake and Huola Basin sequences.

From 10.5 to 9.0 cal ka BP, relative abundance of C3plants in the Xianghai Lake core decreased dramati-

cally, while C4 plants increased, indicating the spread

of grasslands at the expense of forest. This transition

occurred in the Huola Basin from 10.5 to 8.0 cal ka

BP. Between 9.0 and 7.0 cal ka BP, C3 and C4 plant

Fig. 4 Depth profiles of the variation in the ratio of Rn-C21-/

Rn-C22? and the ACL values of n-alkanes. a Xianghai Lake

core, b Huola Basin core

J Paleolimnol (2015) 54:345–358 355

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percentages in the Xianghai Lake core fluctuated on a

sub-millennial timescale, suggesting unstable climate.

Such fluctuations occurred in the Huola Basin record

between about 8.0 and 6.0 cal ka BP. From 7.0 to

5.0 cal ka BP, the C3 plant percentage in the Xianghai

Lake core increased strongly relative to percentages

for C4 plants, indicating the expansion of forest at the

expense of grassland. From 5.0 to 2.0 cal ka BP,

however, relative abundance of C3 plants declined,

indicating expansion of grasses on the landscape. In

contrast, from about 6.0 to 1.0 cal ka BP, C3 and C4

plant percentages in the Huola Basin core fluctuated

little, with no discernible trend.

Conclusions

The n-alkanes and d13C values of long-chain n-alkaneswere analyzed in lacustrine sediment samples from

cores taken in Xianghai Lake and the Huola Basin, on

the Song-nen Plain, northeast China. The n-alkanes

extracted from the Xianghai Lake core were from a

mixed source composed of bacteria, algae and terres-

trial higher plants, whereas the n-alkanes extracted

from the Huola Basin sediments were derived mainly

from terrestrial higher plants. The carbon isotopic

composition of C27, C29 and C31 n-alkanes in the core

sediments yielded information about the relative

contribution of C3 and C4 plants to the sediment

organic matter. C3 plants were the dominant input

during the late glacial and Holocene, but the relative

abundances of C3 and C4 plants displayed fluctuations

through time, probably a response to alternating warm

and cool climate conditions. The percent of C3 plants

increased during the late glacial, while the percentage

for C4 plants decreased. During the Holocene, how-

ever, the percentage of C4 plants increased, while the

relative abundance of C3 plants decreased.

Acknowledgments We gratefully acknowledge Prof. MarkBrenner and two anonymous reviewers for thoughtful and

constructive comments. This research was supported by the

Chinese Academy of Sciences Key Project (Nos.

XDB03020405, XDA05120204), the National Science

Foundation (41172169, 41572350, 41503049), Western Light

General Project, Western Light Joint Scholars Project, and the

Key Laboratory Project of Gansu Province (Grant No.

1309RTSA041).

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Paleovegetation inferred from the carbon isotope composition of long-chain n-alkanes in lacustrine sediments from the Song-nen Plain, northeast ChinaAbstractIntroductionStudy areaStudy site

Materials and methodsSediment coring and radiocarbon datingLipid and carbon isotope analysisCalculation of C3 and C4 plant percentages

ResultsLithology and carbon contentCore chronologiesDistribution of n-alkanesCompound-specific carbon isotope composition of n-alkanes

DiscussionOrigin of the sediment n-alkanesPaleovegetation types of the study areaPaleovegetation composition of the study area

ConclusionsAcknowledgmentsReferences

Documents

Paleovegetation inferred from the carbon isotope composition of long-chain n-alkanes in lacustrine sediments from the Song-nen Plain… · ORIGINAL PAPER Paleovegetation inferred