542
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Thalassiosira hyperborea and Thalassiosira baltica: these two species were also counted
together because of their similarities in ecology. Both species inhabit brackish environments
(mesohalobous-euryhaline habitats; Pankow, 1990) in circumpolar to temperate waters of the
northern hemisphere. They are especially abundant in the vicinity of the large Siberian and
Canadian rivers (Hasle and Lange, 1989). T. hyperborean. baltica have their highest
abundance in the western region of the 74°30'N-transect, reaching between 20 and 30% (Figure
6). In coastal sediments both species occur with 5 to 25% (Figure 5) whereas their portion on
the northernmost transect has a maximum abundance of 10% (Figure 7).
Thalassiosira nordenskioeldii: this species is a typical cold water diatom (marine-neritic) of
polar to temperate waters of the northern hemisphere. According to Has1e (1976) this species
occurs down to 35°N. T. nordenskioeldii is a resting spore forming diatom and grows best at
temperatures between 0 and 5°C (Durbin, 1974, 1978). In samples of the southern transect T.
nordenskioeldii is nearly missing (Figure 5). On the other hand this species shows a generally
high abundance in sediments of the central Laptev Sea shelf (Figures 6 and 7).
Factor analysis
In order to describe well defined diatom assemblages and their occurrence in sediments of the
Laptev Sea shelf a factor analysis was carried out. Factor analyses were used to investigate
micropaleontological datasets (e.g. Imbrie and Kipp, 1971; Maynard, 1976; Williams, 1986;
Koy Karpuz and Schrader, 1990; Pichon et aI., 1992; Koy et aI., 1993; Matthiessen, 1994). A
factor analysis reduces a great number of variables (here: relative abundance of diatom species)
to a small number of factors (here: diatom assemblages), which can replace the original
variables in further investigations. Thus, the dataset becomes reduced and simplified, and
interpretations are easier.
The factor analysis was carried out on 75 surface sediment samples and 21 species and
species groups (Figure 3, Table 2). To reduce the data set species with similar environmental
characteristics were grouped. After this clustering all species and groups with a relative
abundance generally less than 2 % of the total assemblage were removed. Table 2 lists the 21
species and species groups used in this factor analysis. Results of the factor analysis are given
in tables 3 and 4. Table 3 contains the varimax factor matrix in which the portion of each factor
in each sediment sample is expressed as a factor loading. The communality indicates to what
degree the factor model explains the original information in each sediment sample. The factor
score matrix (Table 4) explains the composition of each factor (of each diatom assemblage)
determined by the analysis. The factor score value is a measure for the significance of each
species and species group in the defined assemblages. The distribution of the diatom sediment
assemblages is shown in figure 8.
The factor analysis yielded four factors which explain 81,4% of the variance in the original
dataset (Table 3). The communality is higher than 0.70 in 60 (= 80%) of the samples.
However, the species composition of 15 sediment samples (= 20%) cannot be sufficiently
explained by the model of four factors, indicated by relatively low communalities (Table 3).
Reasons may be local differences in ecological conditions, selective opal dissolution processes,
local species blooms, or changes of the species composition through resuspension and input of
fossil taxa (Imbrie and Kipp, 1971; Matthiessen, 1994).
Species assemblages
Factor 1 (ice algae assemblage) explains 43.9% of the variance and consists mainly of the
Fragilariopsis-group and Fossula arctica (Table 4). These species are the main components of
sea-ice communities in the Arctic (Poulin, 1990; Hasle et aI., 1996). This assemblage shows
highest factor loadings in sediments from the central and northeastern regions of the Laptev Sea
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Thalassiosira hyperborea and Thalassiosira baltica: these two species were also counted
together because of their similarities in ecology. Both species inhabit brackish environments
(mesohalobous-euryhaline habitats; Pankow, 1990) in circumpolar to temperate waters of the
northern hemisphere. They are especially abundant in the vicinity of the large Siberian and
Canadian rivers (Hasle and Lange, 1989). T. hyperborean. baltica have their highest
abundance in the western region of the 74°30'N-transect, reaching between 20 and 30% (Figure
6). In coastal sediments both species occur with 5 to 25% (Figure 5) whereas their portion on
the northernmost transect has a maximum abundance of 10% (Figure 7).
Thalassiosira nordenskioeldii: this species is a typical cold water diatom (marine-neritic) of
polar to temperate waters of the northern hemisphere. According to Has1e (1976) this species
occurs down to 35°N. T. nordenskioeldii is a resting spore forming diatom and grows best at
temperatures between 0 and 5°C (Durbin, 1974, 1978). In samples of the southern transect T.
nordenskioeldii is nearly missing (Figure 5). On the other hand this species shows a generally
high abundance in sediments of the central Laptev Sea shelf (Figures 6 and 7).
Factor analysis
In order to describe well defined diatom assemblages and their occurrence in sediments of the
Laptev Sea shelf a factor analysis was carried out. Factor analyses were used to investigate
micropaleontological datasets (e.g. Imbrie and Kipp, 1971; Maynard, 1976; Williams, 1986;
Koy Karpuz and Schrader, 1990; Pichon et aI., 1992; Koy et aI., 1993; Matthiessen, 1994). A
factor analysis reduces a great number of variables (here: relative abundance of diatom species)
to a small number of factors (here: diatom assemblages), which can replace the original
variables in further investigations. Thus, the dataset becomes reduced and simplified, and
interpretations are easier.
The factor analysis was carried out on 75 surface sediment samples and 21 species and
species groups (Figure 3, Table 2). To reduce the data set species with similar environmental
characteristics were grouped. After this clustering all species and groups with a relative
abundance generally less than 2 % of the total assemblage were removed. Table 2 lists the 21
species and species groups used in this factor analysis. Results of the factor analysis are given
in tables 3 and 4. Table 3 contains the varimax factor matrix in which the portion of each factor
in each sediment sample is expressed as a factor loading. The communality indicates to what
degree the factor model explains the original information in each sediment sample. The factor
score matrix (Table 4) explains the composition of each factor (of each diatom assemblage)
determined by the analysis. The factor score value is a measure for the significance of each
species and species group in the defined assemblages. The distribution of the diatom sediment
assemblages is shown in figure 8.
The factor analysis yielded four factors which explain 81,4% of the variance in the original
dataset (Table 3). The communality is higher than 0.70 in 60 (= 80%) of the samples.
However, the species composition of 15 sediment samples (= 20%) cannot be sufficiently
explained by the model of four factors, indicated by relatively low communalities (Table 3).
Reasons may be local differences in ecological conditions, selective opal dissolution processes,
local species blooms, or changes of the species composition through resuspension and input of
fossil taxa (Imbrie and Kipp, 1971; Matthiessen, 1994).
Species assemblages
Factor 1 (ice algae assemblage) explains 43.9% of the variance and consists mainly of the
Fragilariopsis-group and Fossula arctica (Table 4). These species are the main components of
sea-ice communities in the Arctic (Poulin, 1990; Hasle et aI., 1996). This assemblage shows
highest factor loadings in sediments from the central and northeastern regions of the Laptev Sea