How lake morphometry reflects environmental conditions in the permafrost-dominated Lena Delta Anne Morgenstern1*, Guido Grosse2, Lutz Schirrmeister1 1
Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Germany, 2 Geophysical Institute, University of Alaska Fairbanks, USA *Corresponding author:
[email protected]
I Lena Delta
The northeast Siberian Lena Delta is situated in the zone of continuous permafrost. It is characterized by numerous lakes (fig. 1), most of which are of thermokarst genesis. Three geomorphologic main terraces can be distinguished. The first main terrace including the lower and upper floodplains and the first terrace above the floodplain represents the modern active delta (east). The second terrace (northwest) consists of Late Pleistocene to Early Holocene homogeneous sands of fluvial genesis, but is mainly not influenced by fluvial processes nowadays. Relics of a Late Pleistocene accumulation plain with fine-grained and ice-rich deposits (Ice Complex) form the third terrace (south).
II Methods
The inventory of the Lena Delta lakes is based on Landsat-7 ETM+ image data and spatial analysis in ArcGIS. Morphometric lake attributes (area, perimeter, circularity, elongation, orientation, degree of deviation from mean orientation) were determined from the resulting data set and statistically analyzed regarding their mean characteristics on the three geomorphological main terraces of the Lena delta (tab. 2).
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Figure 2: Lakes on the first main terrace.
III Lake types
For all analyzed morphometric lake variables we found significant differences between the three geomorphological main units of the Lena Delta, so we could derive a mean lake type for each terrace. 1st terrace: Lakes are in average small, elongated, with irregular shapes and strong deviation from mean orientation (fig. 2). Those characteristics are typical for lakes in active floodplains like abandoned channel lakes. 2nd terrace: Large elongated lakes with a NNE-SSW orientation of their major axes prevail (fig. 3). 3rd terrace: Lakes are mainly characterized by regular shorelines and little deviation from circularity (fig. 4). These characteristics are typical for thermokarst lakes in icerich permafrost.
IV Orientation
The character of orientation varies greatly on the three main terraces (fig. 5). On the first terrace, modern fluvial processes are very active and may inhibit orientation processes. The differences in lake orientation between the second and the third terraces seem to be caused by endogenous factors as sedimentology and cryolithology. The homogenous sands of the second terrace allow for a uniform distribution of forces that drive orientation processes. In the Ice Complex of the third terrace, consisting of huge ice wedges, peat, silts and sands, orientation cannot develop as clearly. As for the cause of orientation wind data from a meteorological station near to the second terrace might indicate that the wind hypotheses proposed for North American oriented lakes might also be applicable to the second terrace lakes, but the detailed conditions and mechanisms of the evolution of the oriented lakes in the Lena Delta remain to be investigated.
Figure 1: Landsat-7 ETM+ mosaic of the Lena Delta (Band 3, by Schneider et al. in review) with analyzed lakes and main terraces. Table 1: Area calculations for the three geomorphologic main terraces of the Lena Delta (Morgenstern et al. in review).
Figure 3: Oriented lakes on the second main terrace.
Differences to 29,000 km² / 100% delta area arise from the marine and some fluvial areas which are not particularly associated with a geomorphological terrace. Table 2: Descriptive statistics for the analyzed morphometric lake variables (Morgenstern et al. in review).
Figure 5: Frequency distribution of orientation of the Lena Delta lakes (intervals = 1°) (Morgenstern et al. in review).
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Figure 4: Circular lakes on the third main terrace.
V Conclusions
The three main terraces of the Lena Delta vary largely in the occurrence of morphometric lake characteristics. These characteristics are consistent with the sedimentological and cryolithological conditions and geomorphologic processes prevailing on the according terrace.
References
Morgenstern, A. Grosse, G., Schirrmeister, L. (in review): Genetical, morphological, and statistical classification of lakes in the permafrost-dominated Lena Delta. Proceedings of the Ninth International Conference on Permafrost, Fairbanks, Alaska, June 29-July 3, 2008. Schneider, J., Grosse, G., Wcagner, D. (in review): Land cover classification of tundra environments in the Arctic Lena Delta based on Landsat-7 ETM+ data and ist application for upscaling of methane emissions. Remote Sensing of Environment.
