380
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Sampling and laboratory techniques
The sediment core was sampled at least at every 10 cm for diatom analysis. In general, sample
processing of 0.5 g of freeze-dried sediment followed the method outlined in Schrader and
Gersonde (1978). Briefly, the organic and calcareous compounds were removed by digestion
in U)SOL (washing benzine) followed by boiling with HCl (conc.) and H202 (30%) at 170°C.
Repeated flushing with distilled water (up to 10 times) removed finer particles and residual
acid. The remaining suspension was filled to 50 III and stored in plastic bottles.
Preparation of slides began with 0.4 III aliquots taken from the stored suspension and
followed an evaporation method developed in the laboratory of the Alfred Wegener Institute,
Bremerhaven and outlined in Zielinski (1993). For permanent slides, the mounting medium
MOUNTEX (n = 1.67) was used.
Counting and Taxonomy
Diatoms were identified using a ZEISS Axioplan microscope (equipped with differential
interference contrast) at 1000x magnification. The diatom valves were counted along transects
measured by stage micrometer until 40 mm of transect were examined or until at least 400 to
500 valves per sample were counted. In samples extremely poor in diatoms, at least 100 valves
were counted. Since aliquots from sample material and suspension were used for all slides, the
number of valves encountered per millimetre of microscope transect in each sample gives a
semi-quantitative approximation of diatom concentration (Bradbury, 1997). Taxa with less than
five occurrences and with a relative maximum abundance of less than 2% were excluded from
graphical illustration.
The following literature was used for determination of diatom taxa: Cleve-Euler (1951-1955),
Kling and Hakansson (1988), Krammer and Lange-Bertalot (1986, 1988, 1991a, 1991b),
Lange-Bertalot (1993), Round et al. (1990).
Table I: Terminology used for relative abundance of diatom species.
percentage proportion
I individual
<1%
1 to 5%
5 to 10%
> 10%
Relative abundance
terminology
sparse
rare
few
frequent
abundant
According to the percentage proportions of species in diatom assemblages, the terminology
listed in Table 1 is used.
Sequence splitting
The numerical zonation of the sequence is performed using the CONISS subprogram of the
TILIA version 1.10 (stratigraphically CONstrained cluster analysis by the method of
Incremental Sum of Squares; Grimm, 1987). Prior to application of the procedure, data are
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Sampling and laboratory techniques
The sediment core was sampled at least at every 10 cm for diatom analysis. In general, sample
processing of 0.5 g of freeze-dried sediment followed the method outlined in Schrader and
Gersonde (1978). Briefly, the organic and calcareous compounds were removed by digestion
in U)SOL (washing benzine) followed by boiling with HCl (conc.) and H202 (30%) at 170°C.
Repeated flushing with distilled water (up to 10 times) removed finer particles and residual
acid. The remaining suspension was filled to 50 III and stored in plastic bottles.
Preparation of slides began with 0.4 III aliquots taken from the stored suspension and
followed an evaporation method developed in the laboratory of the Alfred Wegener Institute,
Bremerhaven and outlined in Zielinski (1993). For permanent slides, the mounting medium
MOUNTEX (n = 1.67) was used.
Counting and Taxonomy
Diatoms were identified using a ZEISS Axioplan microscope (equipped with differential
interference contrast) at 1000x magnification. The diatom valves were counted along transects
measured by stage micrometer until 40 mm of transect were examined or until at least 400 to
500 valves per sample were counted. In samples extremely poor in diatoms, at least 100 valves
were counted. Since aliquots from sample material and suspension were used for all slides, the
number of valves encountered per millimetre of microscope transect in each sample gives a
semi-quantitative approximation of diatom concentration (Bradbury, 1997). Taxa with less than
five occurrences and with a relative maximum abundance of less than 2% were excluded from
graphical illustration.
The following literature was used for determination of diatom taxa: Cleve-Euler (1951-1955),
Kling and Hakansson (1988), Krammer and Lange-Bertalot (1986, 1988, 1991a, 1991b),
Lange-Bertalot (1993), Round et al. (1990).
Table I: Terminology used for relative abundance of diatom species.
percentage proportion
I individual
<1%
1 to 5%
5 to 10%
> 10%
Relative abundance
terminology
sparse
rare
few
frequent
abundant
According to the percentage proportions of species in diatom assemblages, the terminology
listed in Table 1 is used.
Sequence splitting
The numerical zonation of the sequence is performed using the CONISS subprogram of the
TILIA version 1.10 (stratigraphically CONstrained cluster analysis by the method of
Incremental Sum of Squares; Grimm, 1987). Prior to application of the procedure, data are