364
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
(As, Cd, Pb)_ The organic carbon content was measured on decarbonated samples by using a
columetric method (ELTRA). All instruments have a precision ~ 1 % reI. for the measured
concentrations. International standard reference materials (SRM) as well as double analyses
were used to check the external precision. These measurements yielded an accuracy of ±5% for
major element concentrations (wt. %) and of ± 1 0% for trace element concentrations (ppm) and
Corg (wt. %). The water content of each core section was determined from the mass difference
between wet and dry sediment, assuming a specific density of 1 g cm- 3 for water. Grain size
determination was carried out using the classical method of wet sieving and Atterberg
separation.
Results
Coring site and lithology
The coring site was located in the middle part of the lake, about 5 km south of the Mikchangdo
river inflow. Depth measurements on various points around the coring site (Figure 1) and new
seismic data collected during 1997, indicated pelagic sedimentation at the sampling area. A
description of the lithology and change in water content is given in Figure 4. The main mineral
components of the sediment were feldspar and pyroxene. The grain size composition « 0.1 %
sand, 54% silt and 46% clay) was homogeneous over the investigated sediment column. Three
visible boundary layers at 7.5 cm, 12.5 cm and 22 cm depth were observed. Within these
layers a strong decrease in water content and change in color from brown to dark-brown
occurs.
0.252.25
5
7
9
11
13 15 depth (em)
0.35
If!4
0.30
+ 210Pb
.....
... 214Pb
I
CJ)
0_25
0• 226Ra
e1 0.20
Wh0 210Pbsupported
>:t:
> 0.15
U
f
ro
0.10
0.05
T+
w///////~//////////.t/// 4wj;//~/...w/// #'.-?W/ AY/"/"/.h
0
o 2
4
6
8
10
12
14
cumulative mass (g cm- 2 )
Figure 2: 2iOPb, 226Ra and 2l4Pb activities (Bq g-l) versus cumulative mass (core PGl111-1). Also shown is
the supported 210Pb activity (Bq g-l) estimated from the lower part of core (below 8 cm).
2JOPb dating
The results of alpha and gamma spectroscopy and calculated accumulation rates in the core
sections are shown in Figure 2 and Table 2. The measured total 210Pb (21oPbtotal) activity is
composed of 210Pb from the atmospheric input (2lOPbunsupported) and from the in situ decay of
238U in the sediment (2lOPbsupported). Since the accumulation rates and ages were calculated
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
(As, Cd, Pb)_ The organic carbon content was measured on decarbonated samples by using a
columetric method (ELTRA). All instruments have a precision ~ 1 % reI. for the measured
concentrations. International standard reference materials (SRM) as well as double analyses
were used to check the external precision. These measurements yielded an accuracy of ±5% for
major element concentrations (wt. %) and of ± 1 0% for trace element concentrations (ppm) and
Corg (wt. %). The water content of each core section was determined from the mass difference
between wet and dry sediment, assuming a specific density of 1 g cm- 3 for water. Grain size
determination was carried out using the classical method of wet sieving and Atterberg
separation.
Results
Coring site and lithology
The coring site was located in the middle part of the lake, about 5 km south of the Mikchangdo
river inflow. Depth measurements on various points around the coring site (Figure 1) and new
seismic data collected during 1997, indicated pelagic sedimentation at the sampling area. A
description of the lithology and change in water content is given in Figure 4. The main mineral
components of the sediment were feldspar and pyroxene. The grain size composition « 0.1 %
sand, 54% silt and 46% clay) was homogeneous over the investigated sediment column. Three
visible boundary layers at 7.5 cm, 12.5 cm and 22 cm depth were observed. Within these
layers a strong decrease in water content and change in color from brown to dark-brown
occurs.
0.252.25
5
7
9
11
13 15 depth (em)
0.35
If!4
0.30
+ 210Pb
.....
... 214Pb
I
CJ)
0_25
0• 226Ra
e1 0.20
Wh0 210Pbsupported
>:t:
> 0.15
U
f
ro
0.10
0.05
T+
w///////~//////////.t/// 4wj;//~/...w/// #'.-?W/ AY/"/"/.h
0
o 2
4
6
8
10
12
14
cumulative mass (g cm- 2 )
Figure 2: 2iOPb, 226Ra and 2l4Pb activities (Bq g-l) versus cumulative mass (core PGl111-1). Also shown is
the supported 210Pb activity (Bq g-l) estimated from the lower part of core (below 8 cm).
2JOPb dating
The results of alpha and gamma spectroscopy and calculated accumulation rates in the core
sections are shown in Figure 2 and Table 2. The measured total 210Pb (21oPbtotal) activity is
composed of 210Pb from the atmospheric input (2lOPbunsupported) and from the in situ decay of
238U in the sediment (2lOPbsupported). Since the accumulation rates and ages were calculated