Features of the Formation of Lakes in the Cryogenic Regions of the Upper Kolyma, Northeast Siberia

Abstract

Long-term observations of the evolution of the Elikchan lakes (Kolyma Upland, Maimandzha Mountains), which form a "chain" that stretches across the flat watershed separating the Upper Kolyma and the Sea of Okhotsk drainages, make it possible to determine how slope, thermokarst processes, and ecology affected landscape changes within this area. Clastic material coming from the slopes of the Maimandzha Mountains formed dams, which created large lakes within the Okhotsk basin (Elikchan-4 Lake, Elikchan-3 Lake). The origin of the lakes belonging to the Kolyma basin is the result of active thermokarst processes associated with the thawing of ice wedges, the development of bogs, the confluence of small lakes and the formation of new larger reservoirs. Such thermokarst processes were some of the main factors in the origin of Elikchan-1 Lake. The continuous palynological record and radiocarbon dating of the Elikchan-1 Lake sediments reflect the successive changes of biocenoses, which correspond to the general pattern of the evolution of the vegetation cover in the Upper Kolyma basin and in Northern Priokhotye. This record shows a change in plant communities over at least the past 9 000 years with a climatic optimum at ca. 8 000 - 6 100 years ago. Comprehensive analysis of Elikchan-1 Lake also emphasizes the significant discrepancies between the boundaries of Holocene subdivisions in the Far Eastern region and the European chrono-stratigraphy for the Holocene. Attempts to resolve the problems of Far East stratigraphy by comparison to the traditional divisions for Europe are a serious mistake. Moreover, a complete analogy of the Far Eastern subdivisions of the Holocene with the European chronological standard should not be expected, just as it is inappropriate to use the УEuropeanФ terminology in the Far Eastern reconstructions. The influences of the primary factors that determine the Holocene events in the Far East sharply differ from those of Europe, including the specific features of the regional climates as they respond to global forcing factors, diversity of the vegetation cover, and variations in the timing of changes in the biocenoses. Given such differences, it is quite natural that equating the Holocene divisions between the two regions is unacceptable. Radiocarbon dating at the base of the Elikchan-1 Lake sedimentary column indicates that the site was originally a peat bog in the Early Holocene with subsequent lake formation. Comparison of radiocarbon dates from the Elikchan-1 peat with other peat deposits in the region suggests that the Early Holocene was a time of active formation and fairly widespread development of peat bogs in the mountainous regions of the Kolyma and Northern Priokhotye.