Rachold and Hubberten: Carbon Isotope Composition of Particulate Organic Material
229
addition, two peat samples collected in the Lena and Yana deltas and two coal samples from a
river terrace near Zhigansk at the Lena and from a Khatanga tributary - the Kotuy - were
included in the isotope analysis. Total SPM concentrations were calculated from the weight
difference between the clean and the sediment loaded filters after freeze-drying. C, N
concentrations were measured using a LECO elemental analyzer. l3C/ 12 C isotope ratios were
measured using a FINNIGAN DELTA S mass spectrometer after removal of carbonate with I
N HCI in Ag-cups and combustion to CO2 in a Heraeus elemental analyzer (Fry et aI., 1992).
Sample volumes were chosen to contain about 0.2 mg C. Ac.curacy of the analytical methods
was checked by parallel analysis of international standard reference material (IAEA-CH-7).
Results are expressed vs. V-PDB in the form:
13
13
12
13
12
13
12
cS C (%0) = [( C/ Csample- C/ Cstandard)/( C/ Cstandard)]· 1000.
The precision of the SPM determination is better than ± I %, and that of the C and N analyses
better than ± 4 %. The analytical precision of the carbon isotope analyses is ± 0.2 %0.
Results
The results are presented in Table I. Since some locations were sampled on two expeditions,
both the station number and the sampling year are indicated. The "Iocation" column indicates
the distance (river-km) of the station from the river mouth in the Laptev Sea. For the tributaries,
the distance of the confluences to the river mouth is given. If sampling was performed on cross
sections, average values, standard deviation of cS I3 C values, and number of samples are listed.
Total SPM content (turbidity) and organic C concentrations of the SPM of the three studied
rivers varied within the wide range of 1.2 mg/I (one Lena tributary) to 1140 mg/l (Yana) and
1.6 % C (Yana) to 36.8 % C (one Lena tributary), respectively. Figure 3 displays the
correlation between turbidity and organic C concentrations of the SPM. In general high SPM
content corresponded to low organic C concentrations in all of the studied rivers. This general
relationship between turbidity and particulate organic carbon (PaC) has been reported for
several other rivers (Meybeck, 1982; Cauwet and Mackenzie, 1993) including the Lena
(Cauwet and Sidorov, 1996).
Figure 4 presents the cS I3 C values of the paM along the Lena (a), Yana (b), and Khatanga (c)
as well as along their tributaries. The scale on the x-axis corresponds to the distance (river-km)
of the station from the river mouth. The stable carbon isotope ratio of Lena paM ranged from
-25.7 %0 to -28.8 %0 with an average value of -27.1 %0 and a standard deviation of ± 0.9 %0 (n
= 19) (Figure 4a). In the Lena delta, the paM was isotopically lighter (average: -28.2 %0,
standard deviation: ± 1.4 %0, n = 9) ranging from -26.5 %0 to -31.3 %0. The data of most of the
tributaries fell within the range of the Lena itself. The Dzhardzhan was characterized by a I3C
enrichment (cSl3C = -25.0 %0) and the Olekma and Aldan by a depletion in I3 C (cSuC = -30.1 %0
in both cases). Except for the lowermost Lena, the variations between samples collected at the
same locations in 1994 and 1995 were small. In the upper Lena and the Vilyuy the differences
did not exceed 0.4 %0. The stations of the lowermost Lena (12-1994, 19-1995 and 15-1994,
20-1995) exhibited more pronounced displacements of 1.4 and 1.7 %0. Our Lena average of
-27.1 %0 is in general agreement with carbon isotope data of marine sediments located within
the main Lena outflow into the Laptev Sea. While surface sediments of the southern Laptev Sea
close to the Lena delta are characterized by cSl3C values of -26.4 %0 that may be attributed to
paM exported by the Lena, in the northern Laptev Sea cS I3 C values increase to -23.7 %0,
reflecting the marine paM contribution (Erlenkeuser, 1996). CIN ratios in the Lena basin are in
229
addition, two peat samples collected in the Lena and Yana deltas and two coal samples from a
river terrace near Zhigansk at the Lena and from a Khatanga tributary - the Kotuy - were
included in the isotope analysis. Total SPM concentrations were calculated from the weight
difference between the clean and the sediment loaded filters after freeze-drying. C, N
concentrations were measured using a LECO elemental analyzer. l3C/ 12 C isotope ratios were
measured using a FINNIGAN DELTA S mass spectrometer after removal of carbonate with I
N HCI in Ag-cups and combustion to CO2 in a Heraeus elemental analyzer (Fry et aI., 1992).
Sample volumes were chosen to contain about 0.2 mg C. Ac.curacy of the analytical methods
was checked by parallel analysis of international standard reference material (IAEA-CH-7).
Results are expressed vs. V-PDB in the form:
13
13
12
13
12
13
12
cS C (%0) = [( C/ Csample- C/ Cstandard)/( C/ Cstandard)]· 1000.
The precision of the SPM determination is better than ± I %, and that of the C and N analyses
better than ± 4 %. The analytical precision of the carbon isotope analyses is ± 0.2 %0.
Results
The results are presented in Table I. Since some locations were sampled on two expeditions,
both the station number and the sampling year are indicated. The "Iocation" column indicates
the distance (river-km) of the station from the river mouth in the Laptev Sea. For the tributaries,
the distance of the confluences to the river mouth is given. If sampling was performed on cross
sections, average values, standard deviation of cS I3 C values, and number of samples are listed.
Total SPM content (turbidity) and organic C concentrations of the SPM of the three studied
rivers varied within the wide range of 1.2 mg/I (one Lena tributary) to 1140 mg/l (Yana) and
1.6 % C (Yana) to 36.8 % C (one Lena tributary), respectively. Figure 3 displays the
correlation between turbidity and organic C concentrations of the SPM. In general high SPM
content corresponded to low organic C concentrations in all of the studied rivers. This general
relationship between turbidity and particulate organic carbon (PaC) has been reported for
several other rivers (Meybeck, 1982; Cauwet and Mackenzie, 1993) including the Lena
(Cauwet and Sidorov, 1996).
Figure 4 presents the cS I3 C values of the paM along the Lena (a), Yana (b), and Khatanga (c)
as well as along their tributaries. The scale on the x-axis corresponds to the distance (river-km)
of the station from the river mouth. The stable carbon isotope ratio of Lena paM ranged from
-25.7 %0 to -28.8 %0 with an average value of -27.1 %0 and a standard deviation of ± 0.9 %0 (n
= 19) (Figure 4a). In the Lena delta, the paM was isotopically lighter (average: -28.2 %0,
standard deviation: ± 1.4 %0, n = 9) ranging from -26.5 %0 to -31.3 %0. The data of most of the
tributaries fell within the range of the Lena itself. The Dzhardzhan was characterized by a I3C
enrichment (cSl3C = -25.0 %0) and the Olekma and Aldan by a depletion in I3 C (cSuC = -30.1 %0
in both cases). Except for the lowermost Lena, the variations between samples collected at the
same locations in 1994 and 1995 were small. In the upper Lena and the Vilyuy the differences
did not exceed 0.4 %0. The stations of the lowermost Lena (12-1994, 19-1995 and 15-1994,
20-1995) exhibited more pronounced displacements of 1.4 and 1.7 %0. Our Lena average of
-27.1 %0 is in general agreement with carbon isotope data of marine sediments located within
the main Lena outflow into the Laptev Sea. While surface sediments of the southern Laptev Sea
close to the Lena delta are characterized by cSl3C values of -26.4 %0 that may be attributed to
paM exported by the Lena, in the northern Laptev Sea cS I3 C values increase to -23.7 %0,
reflecting the marine paM contribution (Erlenkeuser, 1996). CIN ratios in the Lena basin are in