642
Land-Ocean Systems in the Siberian Arctic: Dynamics and Historr
19:0 fatty acid methyl ester as internal standard which was added to the samples before any
analytical step.
The abundance of the tetrapyrrolic pigments was determined by measuring the absorbance of
the solvent extract (80% acetone) at a wavelength of 410 nm (Rosell-Mele, 1994; Rosell-Mele
and Koc, 1997). In addition, the measurement was carried out at 645 and 663 nm to determine
chlorophyll abundances. The turbidity factor (absorbance at 750 nm) has been substracted.
The carbon-preference-index (CPI), i.e., the relation of odd-to-even chain lengths of nalkanes between C21 and C32 (Bray and Evans, 1961), is used as a measure for the maturity of
terrigenous organic matter. Fresh terrigenous organic material has a CPI-index of 3 to 10
(Brassell et a!., 1978; Hollerbach, 1985), whereas fossil material varies around 1 depending on
the state of diagenesis.
Calculation of accumulation rates
Bulk (BAR) and total organic carbon (TOCAR) accumulation rates were calculated for the
Holocene using a mean wet bulk density (WBD) value of 1.43 g/cm3 determined in Core
PS2474 (Ftitterer, 1994), and a grain density (GD) of 2.65 g/cm3 (cf., Table 2):
(1) PO (%) = «GD - WBD) / (GD - 1.026» * 100
(2) BAR (g / cm 2 / ky) = LSR * (WBD - 1.026 PO/lOO)
(3) TOCAR (g C / cm 2 / ky) = BAR * TOC/IOO
(Weber et a!., 1997)
(van Andel et aI., 1975)
For calculation of mean linear sedimentation rates (LSR) see above.
Results
The TOC record of Core PS2476 displays very constant values ranging between 0.9 and
1.2%. Only in the lowermost part of the record (600 - 625 cmbsf), lower values of about 0.5%
occur (Figure 5).Based on the TOC values, the sedimentary record of Core PS2474 can be
divided into three intervals (Figure 5). In the lower part (500 - 780 cmbsf) TOC values vary
between 0.6 and 1.1 % with one single spike of 1.6% at 660 cmbsf. In the middle part most of
the TOC values are around 0.5%. The uppermost 200 cm of the record are dominated by high
TOC values of 1-1.5%.
In Core PS2471 from the lower slope, maximum TOC values of 0.6 to 2% occur in the three
turbidites at 350 - 390 cmbsf, 280 - 320 cmbsf, and 180 - 230 cmbsf (Unit C, Figure 5). The
intervals inbetween the turbidites as well as the interval between 50 and 180 cmbsf (Unit B) are
characterized by low TOC values around 0.3%. The uppermost 50 cm (Unit A) display higher
TOC values of 0.5 - 0.9%.
The correlation of the three cores based on the magnetic susceptibility records (Figure 4), is
supported by the TOC data, suggesting a Holocene interval of elevated TOC values in all three
cores (Unit A, Figure 5).
The total organic carbon/total nitrogen (CIN) ratios which may give informations about the
organic carbon source (i.e., marine vs. terrigenous; see above), do not show any major
variations in the upper slope Core PS2476 sediments; most of the values are around 8 (Figure
6). In Core PS2474, CIN ratios fluctuate around 10 (total range between 5 and 13), with one
very high ratio of> 20 at 660 cmbsf. In Core PS24 71, CIN ratios are low in the (pelagic) silty
clay intervals (4 to 8), whereas the three turbidites are characterized by significantly higher
ratios of 10 to 17, with one single value of up to 28 (Figure 6). Based on the C/N ratios, the
Land-Ocean Systems in the Siberian Arctic: Dynamics and Historr
19:0 fatty acid methyl ester as internal standard which was added to the samples before any
analytical step.
The abundance of the tetrapyrrolic pigments was determined by measuring the absorbance of
the solvent extract (80% acetone) at a wavelength of 410 nm (Rosell-Mele, 1994; Rosell-Mele
and Koc, 1997). In addition, the measurement was carried out at 645 and 663 nm to determine
chlorophyll abundances. The turbidity factor (absorbance at 750 nm) has been substracted.
The carbon-preference-index (CPI), i.e., the relation of odd-to-even chain lengths of nalkanes between C21 and C32 (Bray and Evans, 1961), is used as a measure for the maturity of
terrigenous organic matter. Fresh terrigenous organic material has a CPI-index of 3 to 10
(Brassell et a!., 1978; Hollerbach, 1985), whereas fossil material varies around 1 depending on
the state of diagenesis.
Calculation of accumulation rates
Bulk (BAR) and total organic carbon (TOCAR) accumulation rates were calculated for the
Holocene using a mean wet bulk density (WBD) value of 1.43 g/cm3 determined in Core
PS2474 (Ftitterer, 1994), and a grain density (GD) of 2.65 g/cm3 (cf., Table 2):
(1) PO (%) = «GD - WBD) / (GD - 1.026» * 100
(2) BAR (g / cm 2 / ky) = LSR * (WBD - 1.026 PO/lOO)
(3) TOCAR (g C / cm 2 / ky) = BAR * TOC/IOO
(Weber et a!., 1997)
(van Andel et aI., 1975)
For calculation of mean linear sedimentation rates (LSR) see above.
Results
The TOC record of Core PS2476 displays very constant values ranging between 0.9 and
1.2%. Only in the lowermost part of the record (600 - 625 cmbsf), lower values of about 0.5%
occur (Figure 5).Based on the TOC values, the sedimentary record of Core PS2474 can be
divided into three intervals (Figure 5). In the lower part (500 - 780 cmbsf) TOC values vary
between 0.6 and 1.1 % with one single spike of 1.6% at 660 cmbsf. In the middle part most of
the TOC values are around 0.5%. The uppermost 200 cm of the record are dominated by high
TOC values of 1-1.5%.
In Core PS2471 from the lower slope, maximum TOC values of 0.6 to 2% occur in the three
turbidites at 350 - 390 cmbsf, 280 - 320 cmbsf, and 180 - 230 cmbsf (Unit C, Figure 5). The
intervals inbetween the turbidites as well as the interval between 50 and 180 cmbsf (Unit B) are
characterized by low TOC values around 0.3%. The uppermost 50 cm (Unit A) display higher
TOC values of 0.5 - 0.9%.
The correlation of the three cores based on the magnetic susceptibility records (Figure 4), is
supported by the TOC data, suggesting a Holocene interval of elevated TOC values in all three
cores (Unit A, Figure 5).
The total organic carbon/total nitrogen (CIN) ratios which may give informations about the
organic carbon source (i.e., marine vs. terrigenous; see above), do not show any major
variations in the upper slope Core PS2476 sediments; most of the values are around 8 (Figure
6). In Core PS2474, CIN ratios fluctuate around 10 (total range between 5 and 13), with one
very high ratio of> 20 at 660 cmbsf. In Core PS24 71, CIN ratios are low in the (pelagic) silty
clay intervals (4 to 8), whereas the three turbidites are characterized by significantly higher
ratios of 10 to 17, with one single value of up to 28 (Figure 6). Based on the C/N ratios, the