640
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
will be proven, however, by future determinations of other, more precise stratigraphic
parameters such as lOBe and 234Th, microfossils, and amino acids. In this paper, both age
models will be discussed and suggestions about the stratigraphy will be made according to the
organic geochemical parameters.
Methods
Determination of bulk parameters
Total carbon, total nitrogen, and total organic carbon (TOC) contents were determined on both
ground bulk samples and HCI-treated carbonate-free samples, using a HERAEUS CHN
analyser (for details see Stein, 1991). C/N ratios were calculated as total organic carbon/total
nitrogen ratios based on weight percentages. The Rock-Eval parameters hydrogen index (HI in
mg HC / g TOC) and oxygen index (mg C02 / g TOC) were determined as described by
Espitalie et al. (1977). Although HI values and C/N ratios determined on organic-carbon-poor
sediments (TOC <0.5%) have to be interpreted with caution (e.g., Stein, 1991 and further
references therein), the records are used as indicators for organic-carbon composition because
they are strongly supported by the biomarker records (see results and discussion).
Determination of biomarkers
For the determinations of specific biomarkers gas chromatography (GC) and gas
chromatrography/mass spectrometry (GC/MS) techniques were used.
For the lipid analyses the sediment samples were stored at -80°C or in dichloromethane:
methanol (2: I, by vol.) at -23°C until further treatment. The sediment (2 g) was homogenised,
extracted and purified as recommended by Folch et al. (1957) and Bligh and Dyer (1959). An
aliquot of the total extract was used for analysing n-alkanes and alkenones. Both lipid classes
were separated from the other fractions by column chromatography (n-alkanes with hexane,
alkenones with hexane:ethyl acetate, 95:5 and 90: 10, by vol.). To provide a separation of the
alkenone compounds (C37:2, C37:3, and C37:4) from co-occurring alkenoates by gas
chromatography, a saponification step with I M potassium hydroxide in 95 % methanol for 2
hours at 90°C was applied. The alkenone composition was analysed with a Hewlett Packard gas
chromatograph (HP 5890, column 30 m x 0.25 mm; film thickness 0.25 11m; stationary phase:
HP I) using a temperature program for analysing n-alkanes as follows: 60°C (l min), 150°C
(rate: 10°C/min), 300°C (rate: 4°C/min), 300°C (45 min isothermal); for alkenones: 60°C (1
min), 270°C (rate: 20°C/min), 320°C (rate: 1°C/min), 320°C (20 min isothermal). A volume of 1
III was injected (cold injection system: 60°C (5 s), 300°C (60 s, rate: 100C/s) and helium was
used as carrier gas. As internal standards squalane and octacosanoic acid methyl ester were
added to the samples before any analytical step. Because of the low alkenone concentrations
results obtained by GC were checked for a selected set of samples by GCIMS technique. The
GC/MS consists of a gaschromatograph (HP 5890, column 30 m x 0.25 mm; film thickness
0.25 11m; stationary phase: HP 5) and a mass spectrometer (MSD, HP 5972, 70 eV electronimpact-ionisation, Scan 50-650 mlz, 1 scants, ion source temperature 175°C). The injection
volume is 1 III (splitless). Helium was used as carrier gas (l mllmin at 60°C).
For preparing fatty acid methyl esters and free alcohols by transesterification an aliquot of the
total extract was treated with 3 % concentrated sulfuric acid in methanol for 4 hours at 80°C.
After extraction with n-hexane the product was analysed by GC (as above) but using DB-FFAP
as stationary phase. The temperature program was as follows: 160°C, 240°C (rate: 4°C/min),
240°C (15 min isothermal) (modified after Kattner and Fricke, 1986). The injection volume was
1 Ill. The fatty acids and alcohols were identified by standard mixtures and quantified using
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
will be proven, however, by future determinations of other, more precise stratigraphic
parameters such as lOBe and 234Th, microfossils, and amino acids. In this paper, both age
models will be discussed and suggestions about the stratigraphy will be made according to the
organic geochemical parameters.
Methods
Determination of bulk parameters
Total carbon, total nitrogen, and total organic carbon (TOC) contents were determined on both
ground bulk samples and HCI-treated carbonate-free samples, using a HERAEUS CHN
analyser (for details see Stein, 1991). C/N ratios were calculated as total organic carbon/total
nitrogen ratios based on weight percentages. The Rock-Eval parameters hydrogen index (HI in
mg HC / g TOC) and oxygen index (mg C02 / g TOC) were determined as described by
Espitalie et al. (1977). Although HI values and C/N ratios determined on organic-carbon-poor
sediments (TOC <0.5%) have to be interpreted with caution (e.g., Stein, 1991 and further
references therein), the records are used as indicators for organic-carbon composition because
they are strongly supported by the biomarker records (see results and discussion).
Determination of biomarkers
For the determinations of specific biomarkers gas chromatography (GC) and gas
chromatrography/mass spectrometry (GC/MS) techniques were used.
For the lipid analyses the sediment samples were stored at -80°C or in dichloromethane:
methanol (2: I, by vol.) at -23°C until further treatment. The sediment (2 g) was homogenised,
extracted and purified as recommended by Folch et al. (1957) and Bligh and Dyer (1959). An
aliquot of the total extract was used for analysing n-alkanes and alkenones. Both lipid classes
were separated from the other fractions by column chromatography (n-alkanes with hexane,
alkenones with hexane:ethyl acetate, 95:5 and 90: 10, by vol.). To provide a separation of the
alkenone compounds (C37:2, C37:3, and C37:4) from co-occurring alkenoates by gas
chromatography, a saponification step with I M potassium hydroxide in 95 % methanol for 2
hours at 90°C was applied. The alkenone composition was analysed with a Hewlett Packard gas
chromatograph (HP 5890, column 30 m x 0.25 mm; film thickness 0.25 11m; stationary phase:
HP I) using a temperature program for analysing n-alkanes as follows: 60°C (l min), 150°C
(rate: 10°C/min), 300°C (rate: 4°C/min), 300°C (45 min isothermal); for alkenones: 60°C (1
min), 270°C (rate: 20°C/min), 320°C (rate: 1°C/min), 320°C (20 min isothermal). A volume of 1
III was injected (cold injection system: 60°C (5 s), 300°C (60 s, rate: 100C/s) and helium was
used as carrier gas. As internal standards squalane and octacosanoic acid methyl ester were
added to the samples before any analytical step. Because of the low alkenone concentrations
results obtained by GC were checked for a selected set of samples by GCIMS technique. The
GC/MS consists of a gaschromatograph (HP 5890, column 30 m x 0.25 mm; film thickness
0.25 11m; stationary phase: HP 5) and a mass spectrometer (MSD, HP 5972, 70 eV electronimpact-ionisation, Scan 50-650 mlz, 1 scants, ion source temperature 175°C). The injection
volume is 1 III (splitless). Helium was used as carrier gas (l mllmin at 60°C).
For preparing fatty acid methyl esters and free alcohols by transesterification an aliquot of the
total extract was treated with 3 % concentrated sulfuric acid in methanol for 4 hours at 80°C.
After extraction with n-hexane the product was analysed by GC (as above) but using DB-FFAP
as stationary phase. The temperature program was as follows: 160°C, 240°C (rate: 4°C/min),
240°C (15 min isothermal) (modified after Kattner and Fricke, 1986). The injection volume was
1 Ill. The fatty acids and alcohols were identified by standard mixtures and quantified using