- Email: [email protected]
Isolation of individual fatty acids in sediments using preparative capillary gas chromatography (PCGC) for radiocarbon analysis at NIES-TERRA
Nuclear Instruments and Methods in Physics Research B 172 (2000) 583±588
www.elsevier.nl/locate/nimb
Isolation of individual fatty acids in sediments using preparative capillary gas chromatography (PCGC) for radiocarbon analysis at NIES-TERRA Masao Uchida a,b,*, Yasuyuki Shibata a, Kimitaka Kawamura b, Minoru Yoneda a, Hitoshi Mukai a, Atsushi Tanaka a, Takashi Uehiro a, Masatoshi Morita a a
National Institute for Environmental Studies (NIES), Onogawa 16-1, 305-0053 Tsukuba, Ibaraki, Japan b Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
Abstract Compound-speci®c radiocarbon analysis (CSRA) of individual fatty acids (140±1190 lg C) in an estuarine sediment sample collected from Tokyo Bay was carried out using a recently developed preparative capillary gas chromatography (PCGC) system and accelerator mass spectrometry (AMS). The results showed that the estimated 14 C ages of four components greatly varied from modern age (combined iso and anteiso C15:0 , C16:0 ) to 17 000 years BP (C22:0 ), while a bulk-phase 14 C age of organic matter is 5000 years BP. The 14 C ages of the fatty acids derived from phytoplankton and bacteria are much younger than that of the bulk phase. On the other hand, the fatty acid originated from terrestrial higher plants (C22:0 ) shows an older 14 C age of 17 000 years BP. Ó 2000 Elsevier Science B.V. All rights reserved.
1. Introduction Compound-speci®c radiocarbon analysis (CSRA) is now available using a preparative capillary gas chromatography (PCGC) system, which requires separate target compounds from natural samples with sucient quantities for 14 C measurements by accelerator mass spectrometry (AMS) [1±3].
*
Corresponding author. Tel.: +81-298-50-2450; fax: +81298-50-2574. E-mail address: [email protected] (M. Uchida).
Here we report preliminary results on the CSRA of fatty acids in Tokyo Bay surface sediments using PCGC system. Fatty acids are widely occurring compounds and play a variety of roles, such as membrane structure (phospholipids) and energy storage compounds (long-chain alkyl esters or wax esters and triacylglycerols). Fatty acids in marine sediments are derived from several sources, such as bacteria, phytoplankton and terrestrial higher plants. The CSRA study of fatty acids as a proxies for sources of organic matters in marine sediments will provide further information on sources and depositional history, ®xation and utilization in carbon cycle in marine ecosystems, and reconstruction of paleoceanographic environments.
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 3 6 0 - 8
584
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
2. Experimental and methods 2.1. Sample and compound selection We used surface sediment (5±10 cm in depth) collected from Sanbanze, Tokyo Bay, which is located at the estuary of the Edogawa River. The sampling site is close to the shore near the industrial area. The water depth is about 3 m. The sediments are sandy and the total organic carbon content is approximately 0.3%. Salinity varies from about 25& to 30& according to input of freshwater from the river. Freezed-dried and homogenized sediment samples were treated to isolate lipids (20±25 g each sediment; total weight 1.5 kg) using both ultrasonic extraction and accelerated solvent extraction (Dionex ASE200 system). The samples were extracted at 100°C and 6.9 MPa (1000 psi) with CH2 Cl2 /MeOH (2:1 v/v) as the solvent in accelerated solvent extraction, or three times with MeOH/CH2 Cl2 (2:1), CH2 Cl2 and MeOH/ CH2 Cl2 (1:9) in an ultrasonicator [4]. Then the total extracts were saponi®ed with 0.5 M KOH/ methanol for 2 h under re¯ux. Neutral lipids were separated by an extraction with CH2 Cl2 /nhexane (10:1), whereas acidic lipids were extracted with CH2 Cl2 after the remaining solution was acidi®ed
terface (320°C) and six 10 ll glass traps and are one 100 ll waste glass trap supported in liquid nitrogen-cooled units ()20°C ) [1]. The injection volume was approximately 10 ll per injection. The injection port was set at 60°C (hold time: 1 min) and temperature programmed to 70°C at a rate of 12°C/min (hold time: 2 min) and to 300°C at a rate of 12°C/min. Individual compounds were separated on a 30 m megabore (0.53 mm I.D.) fused silica capillary column coated with a cross-bonded methyl silicone phase (RTXÿ1 , RESTEK; ®lm thickness 0.5 lm). The GC oven temperature was programmed from 50°C (hold time: 1 min) to 120°C at a rate of 10°C/min and to 320°C at a rate of 4°C/min (hold time: 10 min). Run time was about 60 min. Helium was used as carrier gas with a ¯ow rate of 2.4 ml/min. 2.3. Conversion of trapped samples to graphite targets for AMS After PCGC isolation, the U-tubes containing the trapped components were recovered by addition of CH2 Cl2 (1 ml) and transferred to 2 ml glass vials. For combustion, each trapped compounds was transferred to a pre-combusted quartz tube using CH2 Cl2 and the solvent was removed under a stream of high purity helium. Then they were combusted at 850°C. As a precaution to remove the residual solvent from the quartz tubes, the tubes were evacuated to 10ÿ6 Torr while immersed in a dry ice/EtOH [1]. The tubes were combusted by the same procedure mentioned above. Preparation of graphite targets was conducted according to the batch preparation method [5]. Radiocarbon analysis was made at AMS facility at National Institute for Environmental Studies (NIES-TERRA) [6,7]. To remove the in¯uence of the derivative carbon, we used a simple isotopic mass balance approach by measuring D14 C value (41 950 240 years BP) of the derivative reagent (BF3 /MeOH). Stable carbon isotopes of isolated compounds were measured by isotope ratio monitoring gas chromatography/mass spectrometry (GC/IRMS), consisted of a HP6890GC and a Finnigan MAT252. We determined the stable carbon iso-
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
585
Fig. 1. HRGC traces of fatty acid methyl ester fraction and aliquots of the isolated esters in each trap by a 106 consecutive PCGC run. The numbers mean the fatty acid ME trapped.
106 106
106 106 106 106 106
)26.6
na )18.6
na na na na na
d13 C (&)d
31.90±32.40 38.59±39.00
24.80±25.10 26.10±26.50 26.10±26.50 28.30±28.75 28.75±29.25
Trap window (min)
180 1570
100 120 100 190 480
Yield GC (lg C)e
)464 13
nd )878 26
)154 4 +2 31
240 360 150 1190
nd )52 2
D14 C (&)g
140 200
Yield CO2 (lg C)f
nd )873
)101 +65
nd +11
D14 C corr (&)h
5000 230
nd 17000 200
1400 200 Modern
nd 400 200
14 C age (yr BP)i
nd 16900
900 Modern
nd modern
14 C agecorr (yr BP)h
b
Iso and anteiso C15:0 fatty acids were analyzed as a composite sample to maximize yield and because they were insuciently resolved to be isolated as pure compounds. Phyt. ± phytoplankton; Zoo. ± zooplankton; Bac. ± bacteria; Vas. ± vascular higher plant. c Total numbers of consecutive PCGC runs. d Determined after sealed-tube combustion after PCGC isolation. Isotope ratio is relative to the PDB standard material and is corrected by measuring isotope ratio of derivative reagent. e Determined by response relative to an n-C18 monocarboxylic acid external standard. f Determined after sealed quartz tube combustion after PCGC isolation. g Radiocarbon concentration. h Radiocarbon measurements corrected for the presence of derivative carbon sample preparation background have been subtracted, based on measurements of samples of 14 C free marble. i Radiocarbon age (years BP) reported using the Libby half-life of 5568 years. j Bulk-phase organic matter was analyzed after removal of inorganic carbon in the sediment sample.
a
Bulk-phase OMj
C18:0 C22:0
Phyt. Bac. Bac. Phyt. Phyt., Zoo. Phyt. Vas., Fos.
C14:0 Iso C15:0 Antiso C15:0 C16:1 C16:0
Inj.c
C ages of bulk-phase organic matter and fatty acids in the Tokyo Bay sediments by AMS
Inferred sourceb
14
Target compounds (fatty acids)a
Table 1 PCGC conditions and
586 M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
topic compositions of bulk phase and after PCGC isolation by combustion in the sealed quartz tube with CuO/Ag, 850°C, 4 h. All stable carbon isotope ratios are relative to the PDB carbonate reference material (NBS-19). 3. Results and discussion HRGC trace of fatty acid methyl ester fraction (A-1) is shown in Fig. 1. Straight-chain saturated C12 ±C34 fatty acids were detected in the Tokyo Bay sediments. The monocarboxylic acids in the Tokyo Bay sediments showed a bimodal pattern with maxima at C16 and C22 and a predominance of even-carbon number. A high concentration of C22:0 is not typical in marine sediments. The procedural blank showed that the C22 is not a contamination. Except for this acid, the distribution was also dominated by the lower molecular weight (C14 ± C18 ) fatty acids, which are mostly derived from marine organisms [8]. Also, monounsaturated fatty acids (palmitoleic: C16:1 and oleic: C18:1 ) and branched-fatty acids (C15:0 ) were detected in the sediments. They originate from phytoplankton and bacteria, respectively. Prior to CSRA, trapped compounds isolated by PCGC were analyzed by GC and GC/MS in order to determine their amounts and purities. The results (Fig. 1) certify that the puri®cation was achieved enough for CSRA. We also investigated to con®gure repeated reproducibility of replicate injection on PCGC. Standard deviations of retention times for the selected compounds from the 106 consecutive PCGC runs ranged from 0.02 min for C14:0 fatty acid to 0.07 min for C22:0 fatty acid. The deviations seemed to increase with progress of retention time. These results suggested that we need to set up wider trapped window (retention time) in PCGC program in order to isolate the target compounds without contamination of next peak each other in PCGC runs. Moreover, in order to attain the reliability of isolation and enrichment of target compounds by PCGC, we examined a yield for the individual compounds. Yields determined after sealed quartz tube combustion, following PCGC isolation were necessarily inconsistent with those determined by the
587
response relative to external standard before PCGC isolation (Table 1). The amounts of compounds except for target compound in isolated fraction were less than 0.1%. 14 C ages of four fatty acids and bulk organic carbon are given in Table 1. Their 14 C ages of compounds were found to vary from modern age to 17 000 years BP. Bulk-phase organic carbon age in sediment was dated as 5000 (230) years BP. The 14 C ages of two marine biomarkers (C16:0 , C16:1 ) as allochthonous source ranged from modern age to 900 years BP. On the other hand, C22 fatty acid which originated from terrestrial higher plant showed much older age of 17 000 years BP. This older age of C22 fatty acid may be explained by two factors: changes in primary input (variation of input amount of terrestrial organic matter); past environment changes of the estuary and its surroundings. Moreover, an overlap of both higher plant-modern carbon and old carbon stored in soils should also be taken into consideration in this case. Since C22 fatty acid shows relatively heavier d13 C (Table 1), this acid may be in part derived from C4 plants such as seashore or riverside grasses. Our preliminary CSRA results support the dierent source inputs of organic matter to the marine sediment, which raises a question on how dierent sources of organic carbon can aect the bulk-phase 14 C age. The resolution of this problem should provide a breakthrough for understanding biogeochemical processes to elucidate the carbon dynamics of organic matter in biomarker-levels in the ocean.
Acknowledgements We thank T. Hiwatari and K. Kohata for sample collection and M. Ito and Y. Nagano for GC/MS analysis. We also gratefully appreciated H. Sekiguchi and M. Hirota for assistance for AMS analyses. The authors gratefully acknowledge helpful discussions with K. Yamada and K. Okuda. The authors gratefully thank also Y. Yokouchi, Y. Abe, A. Haibara and N. Takemoto for their help.
588
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
References [1] T.I. Eglinton, L.I. Aluwihare, J.E. Bauer, Z.R.M. Druel, A.P. McNichol, Anal. Chem. 68 (1996) 904. [2] T.I. Eglinton, B.C. Benitez-Nelson, A. Pearson, A.P. McNichol, J.E. Bauer, Z.R.M. Druel, Science 277 (1997) 796. [3] L.A. Currie, T.I. Eglinton, B.A. Benner Jr., A. Pearson, Nucl. Instr. and Meth. B 123 (1997) 475. [4] K. Kawamura, in: H. Sakai, Y. Nozaki (Eds.), Biogeochemical Processes of Ocean Flux in the Western Paci®c, Terra Sci., Tokyo, 1995, p. 31.
[5] K. Kitagawa, T. Masazawa, T. Nakamura, E. Matsumoto, Radiocarbon 35 (2) (1993) 295. [6] H. Kume, Y. Shibata, A. Tanaka, M. Yoneda, Y. Kumamoto, M. Morita, Nucl. Instr. and Meth. B 123 (1997) 31. [7] A. Tanaka, M. Yoneda, M. Uchida, T. Uehiro, Y. Shibata, M. Morita, AMS-8, Nucl. Instr. and Meth. B 172 (2000) 107. [8] J.K. Volkman, R.B. Jhons, F.T. Gillan, G.J. Perry, H.J. Bavor Jr., Geochim. Cosmochim. Acta. 44 (1980) 1133.
www.elsevier.nl/locate/nimb
Isolation of individual fatty acids in sediments using preparative capillary gas chromatography (PCGC) for radiocarbon analysis at NIES-TERRA Masao Uchida a,b,*, Yasuyuki Shibata a, Kimitaka Kawamura b, Minoru Yoneda a, Hitoshi Mukai a, Atsushi Tanaka a, Takashi Uehiro a, Masatoshi Morita a a
National Institute for Environmental Studies (NIES), Onogawa 16-1, 305-0053 Tsukuba, Ibaraki, Japan b Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
Abstract Compound-speci®c radiocarbon analysis (CSRA) of individual fatty acids (140±1190 lg C) in an estuarine sediment sample collected from Tokyo Bay was carried out using a recently developed preparative capillary gas chromatography (PCGC) system and accelerator mass spectrometry (AMS). The results showed that the estimated 14 C ages of four components greatly varied from modern age (combined iso and anteiso C15:0 , C16:0 ) to 17 000 years BP (C22:0 ), while a bulk-phase 14 C age of organic matter is 5000 years BP. The 14 C ages of the fatty acids derived from phytoplankton and bacteria are much younger than that of the bulk phase. On the other hand, the fatty acid originated from terrestrial higher plants (C22:0 ) shows an older 14 C age of 17 000 years BP. Ó 2000 Elsevier Science B.V. All rights reserved.
1. Introduction Compound-speci®c radiocarbon analysis (CSRA) is now available using a preparative capillary gas chromatography (PCGC) system, which requires separate target compounds from natural samples with sucient quantities for 14 C measurements by accelerator mass spectrometry (AMS) [1±3].
*
Corresponding author. Tel.: +81-298-50-2450; fax: +81298-50-2574. E-mail address: [email protected] (M. Uchida).
Here we report preliminary results on the CSRA of fatty acids in Tokyo Bay surface sediments using PCGC system. Fatty acids are widely occurring compounds and play a variety of roles, such as membrane structure (phospholipids) and energy storage compounds (long-chain alkyl esters or wax esters and triacylglycerols). Fatty acids in marine sediments are derived from several sources, such as bacteria, phytoplankton and terrestrial higher plants. The CSRA study of fatty acids as a proxies for sources of organic matters in marine sediments will provide further information on sources and depositional history, ®xation and utilization in carbon cycle in marine ecosystems, and reconstruction of paleoceanographic environments.
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 3 6 0 - 8
584
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
2. Experimental and methods 2.1. Sample and compound selection We used surface sediment (5±10 cm in depth) collected from Sanbanze, Tokyo Bay, which is located at the estuary of the Edogawa River. The sampling site is close to the shore near the industrial area. The water depth is about 3 m. The sediments are sandy and the total organic carbon content is approximately 0.3%. Salinity varies from about 25& to 30& according to input of freshwater from the river. Freezed-dried and homogenized sediment samples were treated to isolate lipids (20±25 g each sediment; total weight 1.5 kg) using both ultrasonic extraction and accelerated solvent extraction (Dionex ASE200 system). The samples were extracted at 100°C and 6.9 MPa (1000 psi) with CH2 Cl2 /MeOH (2:1 v/v) as the solvent in accelerated solvent extraction, or three times with MeOH/CH2 Cl2 (2:1), CH2 Cl2 and MeOH/ CH2 Cl2 (1:9) in an ultrasonicator [4]. Then the total extracts were saponi®ed with 0.5 M KOH/ methanol for 2 h under re¯ux. Neutral lipids were separated by an extraction with CH2 Cl2 /nhexane (10:1), whereas acidic lipids were extracted with CH2 Cl2 after the remaining solution was acidi®ed
terface (320°C) and six 10 ll glass traps and are one 100 ll waste glass trap supported in liquid nitrogen-cooled units ()20°C ) [1]. The injection volume was approximately 10 ll per injection. The injection port was set at 60°C (hold time: 1 min) and temperature programmed to 70°C at a rate of 12°C/min (hold time: 2 min) and to 300°C at a rate of 12°C/min. Individual compounds were separated on a 30 m megabore (0.53 mm I.D.) fused silica capillary column coated with a cross-bonded methyl silicone phase (RTXÿ1 , RESTEK; ®lm thickness 0.5 lm). The GC oven temperature was programmed from 50°C (hold time: 1 min) to 120°C at a rate of 10°C/min and to 320°C at a rate of 4°C/min (hold time: 10 min). Run time was about 60 min. Helium was used as carrier gas with a ¯ow rate of 2.4 ml/min. 2.3. Conversion of trapped samples to graphite targets for AMS After PCGC isolation, the U-tubes containing the trapped components were recovered by addition of CH2 Cl2 (1 ml) and transferred to 2 ml glass vials. For combustion, each trapped compounds was transferred to a pre-combusted quartz tube using CH2 Cl2 and the solvent was removed under a stream of high purity helium. Then they were combusted at 850°C. As a precaution to remove the residual solvent from the quartz tubes, the tubes were evacuated to 10ÿ6 Torr while immersed in a dry ice/EtOH [1]. The tubes were combusted by the same procedure mentioned above. Preparation of graphite targets was conducted according to the batch preparation method [5]. Radiocarbon analysis was made at AMS facility at National Institute for Environmental Studies (NIES-TERRA) [6,7]. To remove the in¯uence of the derivative carbon, we used a simple isotopic mass balance approach by measuring D14 C value (41 950 240 years BP) of the derivative reagent (BF3 /MeOH). Stable carbon isotopes of isolated compounds were measured by isotope ratio monitoring gas chromatography/mass spectrometry (GC/IRMS), consisted of a HP6890GC and a Finnigan MAT252. We determined the stable carbon iso-
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
585
Fig. 1. HRGC traces of fatty acid methyl ester fraction and aliquots of the isolated esters in each trap by a 106 consecutive PCGC run. The numbers mean the fatty acid ME trapped.
106 106
106 106 106 106 106
)26.6
na )18.6
na na na na na
d13 C (&)d
31.90±32.40 38.59±39.00
24.80±25.10 26.10±26.50 26.10±26.50 28.30±28.75 28.75±29.25
Trap window (min)
180 1570
100 120 100 190 480
Yield GC (lg C)e
)464 13
nd )878 26
)154 4 +2 31
240 360 150 1190
nd )52 2
D14 C (&)g
140 200
Yield CO2 (lg C)f
nd )873
)101 +65
nd +11
D14 C corr (&)h
5000 230
nd 17000 200
1400 200 Modern
nd 400 200
14 C age (yr BP)i
nd 16900
900 Modern
nd modern
14 C agecorr (yr BP)h
b
Iso and anteiso C15:0 fatty acids were analyzed as a composite sample to maximize yield and because they were insuciently resolved to be isolated as pure compounds. Phyt. ± phytoplankton; Zoo. ± zooplankton; Bac. ± bacteria; Vas. ± vascular higher plant. c Total numbers of consecutive PCGC runs. d Determined after sealed-tube combustion after PCGC isolation. Isotope ratio is relative to the PDB standard material and is corrected by measuring isotope ratio of derivative reagent. e Determined by response relative to an n-C18 monocarboxylic acid external standard. f Determined after sealed quartz tube combustion after PCGC isolation. g Radiocarbon concentration. h Radiocarbon measurements corrected for the presence of derivative carbon sample preparation background have been subtracted, based on measurements of samples of 14 C free marble. i Radiocarbon age (years BP) reported using the Libby half-life of 5568 years. j Bulk-phase organic matter was analyzed after removal of inorganic carbon in the sediment sample.
a
Bulk-phase OMj
C18:0 C22:0
Phyt. Bac. Bac. Phyt. Phyt., Zoo. Phyt. Vas., Fos.
C14:0 Iso C15:0 Antiso C15:0 C16:1 C16:0
Inj.c
C ages of bulk-phase organic matter and fatty acids in the Tokyo Bay sediments by AMS
Inferred sourceb
14
Target compounds (fatty acids)a
Table 1 PCGC conditions and
586 M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
topic compositions of bulk phase and after PCGC isolation by combustion in the sealed quartz tube with CuO/Ag, 850°C, 4 h. All stable carbon isotope ratios are relative to the PDB carbonate reference material (NBS-19). 3. Results and discussion HRGC trace of fatty acid methyl ester fraction (A-1) is shown in Fig. 1. Straight-chain saturated C12 ±C34 fatty acids were detected in the Tokyo Bay sediments. The monocarboxylic acids in the Tokyo Bay sediments showed a bimodal pattern with maxima at C16 and C22 and a predominance of even-carbon number. A high concentration of C22:0 is not typical in marine sediments. The procedural blank showed that the C22 is not a contamination. Except for this acid, the distribution was also dominated by the lower molecular weight (C14 ± C18 ) fatty acids, which are mostly derived from marine organisms [8]. Also, monounsaturated fatty acids (palmitoleic: C16:1 and oleic: C18:1 ) and branched-fatty acids (C15:0 ) were detected in the sediments. They originate from phytoplankton and bacteria, respectively. Prior to CSRA, trapped compounds isolated by PCGC were analyzed by GC and GC/MS in order to determine their amounts and purities. The results (Fig. 1) certify that the puri®cation was achieved enough for CSRA. We also investigated to con®gure repeated reproducibility of replicate injection on PCGC. Standard deviations of retention times for the selected compounds from the 106 consecutive PCGC runs ranged from 0.02 min for C14:0 fatty acid to 0.07 min for C22:0 fatty acid. The deviations seemed to increase with progress of retention time. These results suggested that we need to set up wider trapped window (retention time) in PCGC program in order to isolate the target compounds without contamination of next peak each other in PCGC runs. Moreover, in order to attain the reliability of isolation and enrichment of target compounds by PCGC, we examined a yield for the individual compounds. Yields determined after sealed quartz tube combustion, following PCGC isolation were necessarily inconsistent with those determined by the
587
response relative to external standard before PCGC isolation (Table 1). The amounts of compounds except for target compound in isolated fraction were less than 0.1%. 14 C ages of four fatty acids and bulk organic carbon are given in Table 1. Their 14 C ages of compounds were found to vary from modern age to 17 000 years BP. Bulk-phase organic carbon age in sediment was dated as 5000 (230) years BP. The 14 C ages of two marine biomarkers (C16:0 , C16:1 ) as allochthonous source ranged from modern age to 900 years BP. On the other hand, C22 fatty acid which originated from terrestrial higher plant showed much older age of 17 000 years BP. This older age of C22 fatty acid may be explained by two factors: changes in primary input (variation of input amount of terrestrial organic matter); past environment changes of the estuary and its surroundings. Moreover, an overlap of both higher plant-modern carbon and old carbon stored in soils should also be taken into consideration in this case. Since C22 fatty acid shows relatively heavier d13 C (Table 1), this acid may be in part derived from C4 plants such as seashore or riverside grasses. Our preliminary CSRA results support the dierent source inputs of organic matter to the marine sediment, which raises a question on how dierent sources of organic carbon can aect the bulk-phase 14 C age. The resolution of this problem should provide a breakthrough for understanding biogeochemical processes to elucidate the carbon dynamics of organic matter in biomarker-levels in the ocean.
Acknowledgements We thank T. Hiwatari and K. Kohata for sample collection and M. Ito and Y. Nagano for GC/MS analysis. We also gratefully appreciated H. Sekiguchi and M. Hirota for assistance for AMS analyses. The authors gratefully acknowledge helpful discussions with K. Yamada and K. Okuda. The authors gratefully thank also Y. Yokouchi, Y. Abe, A. Haibara and N. Takemoto for their help.
588
M. Uchida et al. / Nucl. Instr. and Meth. in Phys. Res. B 172 (2000) 583±588
References [1] T.I. Eglinton, L.I. Aluwihare, J.E. Bauer, Z.R.M. Druel, A.P. McNichol, Anal. Chem. 68 (1996) 904. [2] T.I. Eglinton, B.C. Benitez-Nelson, A. Pearson, A.P. McNichol, J.E. Bauer, Z.R.M. Druel, Science 277 (1997) 796. [3] L.A. Currie, T.I. Eglinton, B.A. Benner Jr., A. Pearson, Nucl. Instr. and Meth. B 123 (1997) 475. [4] K. Kawamura, in: H. Sakai, Y. Nozaki (Eds.), Biogeochemical Processes of Ocean Flux in the Western Paci®c, Terra Sci., Tokyo, 1995, p. 31.
[5] K. Kitagawa, T. Masazawa, T. Nakamura, E. Matsumoto, Radiocarbon 35 (2) (1993) 295. [6] H. Kume, Y. Shibata, A. Tanaka, M. Yoneda, Y. Kumamoto, M. Morita, Nucl. Instr. and Meth. B 123 (1997) 31. [7] A. Tanaka, M. Yoneda, M. Uchida, T. Uehiro, Y. Shibata, M. Morita, AMS-8, Nucl. Instr. and Meth. B 172 (2000) 107. [8] J.K. Volkman, R.B. Jhons, F.T. Gillan, G.J. Perry, H.J. Bavor Jr., Geochim. Cosmochim. Acta. 44 (1980) 1133.