392
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Within-basin variations
There are striking peculiarities of the diatom flora of larger lakes that must be regarded,
emphasized for instance by Stoermer (1993) from studies on the Great Lakes. The timing and
magnitude of limnological and biological responses to changes in temperature, precipitation,
runoff processes, external input, and nutrient content, for example, cannot necessarily be
assumed by analogy from the smaller lakes. Within-basin variations derive from the
establishment of microhabitats and factors influencing the deposition of diatoms such as mixing
regime, bottom morphology and transport by bottom currents (Thayer et aI., 1983) and topdown effects (Stoermer, 1993; Schelske, 1994).
For instance, the partly inverse trend in the curves of evenness and relative abundance of
euplanktonic diatoms could be the result of such variations. The observed differences in diatom
assemblage composition and species number result mainly from changes in rare periphytic
species. The marginal areas they inhabit are more strongly influenced by variations in ecological
parameters; microhabitats are therefore easily formed.
Also, the background level of taxa placed in the alpha-meso/eutrophic tolerance group (on the
order of7 %) is considered to derive from such microhabitats (e.g. shallow regions with higher
external nutrient input). This is substantiated by the generally non-planktonic life form of the
contributing taxa (e.g. Achnanthes clevei, Meridion circulare, Diatoms tenuis, Navicula
reinhardtii, Nitzschia pseudofonticola, Cymatopleura sole a, Rhopalodia gibba, Nitzschia
bacillum, Surirella sp.)
In order to investigate if and how such processes cause within-basin variations and influence
the representativity of diatom counts from sediment samples, the study of numerous surface
samples, plankton, and benthos samples is underway.
Ecological implications
Diatoms and pollen
The comparison of changes in pollen and diatom assemblages provides useful information
concerning the character of environmental changes. The timing of reaction of aquatic and
terrestrial ecosystems to changes is determined by different population dynamics, taphonomic
processes and the character of the change. The classical concept proceeds from a minor time lag
in the reaction of aquatic plants to rapid environmental changes, to terrestrial plants, where such
factors as pedogenesis and migration are important (Iversen, 1954; West, 1964; Wright, 1984;
Birks, 1986). Long-term climate changes, however, are found to cause a more or less
synchronous behaviour of both systems (Lotter et aI., 1992; MacDonald et aI., 1993; Lotter et
aI., 1995). A much higher temporal resolution in terms of sample distance is needed to resolve
such timing effects.
Nevertheless, from the evident parallels in the development of organisms inhabiting the two
ecosystems, some basic conclusions concerning the influencing environmental variables can be
drawn. Near the arctic treeline the relative abundance curve of arboreal pollen can indicate the
climate, corroborated as well by the correlation with the /) 18 0 - curve recorded from the
Academy of Sciences Glacier on Severnaya Zemlya (Klementev et aI., 1991; see Hahne and
Melles, this volume). In this context, the good correlation of the curves of relative abundance of
arboreal pollen and euplanktonic diatoms is interesting (Figure 10). Pollen counts, however, do
not exist for all samples with diatom records, resulting in a deficiency of this compilation.
Thus, the calculated correlation coefficient of 0.83 may be too high.
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Within-basin variations
There are striking peculiarities of the diatom flora of larger lakes that must be regarded,
emphasized for instance by Stoermer (1993) from studies on the Great Lakes. The timing and
magnitude of limnological and biological responses to changes in temperature, precipitation,
runoff processes, external input, and nutrient content, for example, cannot necessarily be
assumed by analogy from the smaller lakes. Within-basin variations derive from the
establishment of microhabitats and factors influencing the deposition of diatoms such as mixing
regime, bottom morphology and transport by bottom currents (Thayer et aI., 1983) and topdown effects (Stoermer, 1993; Schelske, 1994).
For instance, the partly inverse trend in the curves of evenness and relative abundance of
euplanktonic diatoms could be the result of such variations. The observed differences in diatom
assemblage composition and species number result mainly from changes in rare periphytic
species. The marginal areas they inhabit are more strongly influenced by variations in ecological
parameters; microhabitats are therefore easily formed.
Also, the background level of taxa placed in the alpha-meso/eutrophic tolerance group (on the
order of7 %) is considered to derive from such microhabitats (e.g. shallow regions with higher
external nutrient input). This is substantiated by the generally non-planktonic life form of the
contributing taxa (e.g. Achnanthes clevei, Meridion circulare, Diatoms tenuis, Navicula
reinhardtii, Nitzschia pseudofonticola, Cymatopleura sole a, Rhopalodia gibba, Nitzschia
bacillum, Surirella sp.)
In order to investigate if and how such processes cause within-basin variations and influence
the representativity of diatom counts from sediment samples, the study of numerous surface
samples, plankton, and benthos samples is underway.
Ecological implications
Diatoms and pollen
The comparison of changes in pollen and diatom assemblages provides useful information
concerning the character of environmental changes. The timing of reaction of aquatic and
terrestrial ecosystems to changes is determined by different population dynamics, taphonomic
processes and the character of the change. The classical concept proceeds from a minor time lag
in the reaction of aquatic plants to rapid environmental changes, to terrestrial plants, where such
factors as pedogenesis and migration are important (Iversen, 1954; West, 1964; Wright, 1984;
Birks, 1986). Long-term climate changes, however, are found to cause a more or less
synchronous behaviour of both systems (Lotter et aI., 1992; MacDonald et aI., 1993; Lotter et
aI., 1995). A much higher temporal resolution in terms of sample distance is needed to resolve
such timing effects.
Nevertheless, from the evident parallels in the development of organisms inhabiting the two
ecosystems, some basic conclusions concerning the influencing environmental variables can be
drawn. Near the arctic treeline the relative abundance curve of arboreal pollen can indicate the
climate, corroborated as well by the correlation with the /) 18 0 - curve recorded from the
Academy of Sciences Glacier on Severnaya Zemlya (Klementev et aI., 1991; see Hahne and
Melles, this volume). In this context, the good correlation of the curves of relative abundance of
arboreal pollen and euplanktonic diatoms is interesting (Figure 10). Pollen counts, however, do
not exist for all samples with diatom records, resulting in a deficiency of this compilation.
Thus, the calculated correlation coefficient of 0.83 may be too high.