Search

Developing continuous chronologies of paleoenvironmental change in northern areas of the Far East using 14C can be problematic because of the low organic content in lake sediments. However, Holocene age-models can be supplemented by widespread tephra deposits reported in the Magadan region. The best documented of these tephras has been correlated to the KO tephra from southern Kamchatka dated to 7600 BP. Although a key chronostratigraphic marker, no detailed compendium of the distribution of this tephra and its associated 14C dates has been available from sites in the northern Far East. We provide such a summary. Known locally as the Elikchan tephra, lake cores indicate an ash fall that extended ~1800 km north of the Kamchatkan caldera with a ~500 km wide trajectory in the Magadan region. Other Holocene tephras preserved in lake sediments have poorer age control and possibly date to ~2500 BP, ~2700 BP and ~6000 BP. These ashes seem to be restricted to coastal or near-coastal sites. A single record of a ~25,000 BP tephra has also been documented ~100 km to the northeast of Magadan.

The palynological investigations of sediments of the crater of El’gygytgyn Lake (67°30′ N, 172°05′ E), which provided a continuous record of interglacial and glacial events in Polar Chukotka, revealed significant climate warming corresponding to Marine Isotope Stage 31 (MIS 31) lasting from 1.062 to 1.081Ma ago. Its upper limit is placed within the Jaramillo paleomagnetic episode (0.99–1.07 Ma) registered in the sedimentary section of the lake. During MIS 31, the vegetation community was dominated by Betula-Alnus forests with subordinate Larix trees. These forests included also coniferous (Picea, Pinus) and broad-leaved trees and shrubs (Quercus, Carpinus, Corylus). The interglacial of MIS 31 was characterized by the warmest climate for the entire Quaternary Period. The warming episode established in the continuous record of the section of El’gygytgyn Lake implies relations between climatic events in the Arctic and Antarctic regions.

Investigations of glacial lake sediments located near the modern altitudinal boundary of a larch forest (between 750–810 m absolute elevation) reveal continuous records of the vegetation and climate changes over the last 12000 years in the area of the Okhotsk-Kolyma divide. For the first time, the pollen accumulation rates (PAR), which are suggestive of pollen productivity, were used as a key indicator to interpret the response of alpine plant communities to climate changes. The palynological data imply that several forest line fluctuations of ∼100–200 m occurred during the Holocene. A belt of tundra dominated by shrub pine was first established beyond the forest line near 7650 ± 50 BP. The abrupt appearance of the shrub pine in the studied area is characteristic of a sharp vegetation boundary found in other records from the north of the Far East that corresponds to the Boreal-Atlantic boundary of the Holocene. The birch pollen zone, which occurs in the earlier portions of the records, is characteristic of the transition from the Pleistocene to the Holocene.

Lake Pernatoe is located on Paramushir Island, Kuril Arc, in the area of sand dunes. The 7-m-thick sediments of this lake pertain to the Holocene and contain palustrine, marine, and lacustrine facies. The rock magnetic properties of the sediments are analyzed for tracking the changes in sedimentation conditions. Marine facies are noted with low content of magnetic minerals; their magnetization is dominated by the paramagnetic component; pseudo-single-domain particles of magnetic material and iron sulfides (pyrite) are present. Pyrite frequently occurs in diatoms in the form of chains, spherules, and crystals. The lacustrine facies show high values of the magnetic parameters; they contain multidomain particles, mostly titanomagnetite and magnetite. Sands and sandy silts have the maximum values of magnetic parameters and reflect the stages of aeolian activity, corresponding to climatic cooling and marine regressions. On the basis of magnetic properties, four stages of active aeolian sedimentation are identified in the Holocene.

The comprehensive study of the upper 1283 cm of sediment from Lake El’gygytgyn, which formed nearly 4 Ma ago following a meteorite impact in northern Chukotka, yielded the first continuous record of the extreme changes in the Beringian climate and vegetation from the middle Middle Pleistocene to recent time (equivalent of marine isotope stages of 1–7 and the upper part of isotope stage 8). During this period, the climate was warmer than at present between 8600 and 10 7000 14C years and during the Late Pleistocene (isotope substage 5e, 116–128 ka ago). In 2003, the German-Russian-USA expedition continued studying sediments of Lake El’gygytgyn to obtain new evidence of the change in the vegetation cover in the Middle Pleistocene and the first information on the Middle Pleistocene interglacial (isotope stage 9; 297–347 ka ago). Pollen spectra characterizing the Middle Pleistocene interglacial are similar to spectra of the early stage of the Early Pleistocene interglacial and the climatic optimum in the Pleistocene to Holocene transitional period. The climatic history of Lake El’gygytgyn is basic for stratigraphic interpretations and correlations in the eastern sector of the Arctic. These data also expand our understanding of climatic changes that are studied within the framework of the “Pole-Equator-Pole Paleoclimate,” “Past Global Changes,” and other international projects.

Investigation of Pernatoe Lake sediments in the south of Paramushir Island has enabled us to obtain the first continuous pollen record of climate and vegetation changes in the north of the Kurile archi� pelago during the Holocene. Series of radiocarbon datings of between 10 000 ± 40 and 2180 ± 40 years ago are evidence that the beginning of sediments accumulation, found after borehole development, is related to the Early Holocene. Diatom analysis has shown several stages in the lake development: raised bog on the border of the Pleistocene and Holocene, lagoon formation resulting from the sea level rise over 9-6 ky, and freshwa� ter lake formation 6 ky and up to the present. Climate warming during the period attributed to the boreal and Atlantic periods of the Holocene is reflected by the dominance of Pinus pumila and Alnus serrulata assem� blages in vegetation cover. Wide dune fields were formed in the Sea of Okhotsk and the Pacific shores of Para� mushir Island 5-4 ky. Strengthening of atmogenic processes is related to cooling of the climate and drying of some areas of the underwater slope. DOI: 10.1134/S1028334X1002011X

One of the most glowing representatives of the Kolyma flora [1], ''Pinus pumila'' (Pall.) Regel (Japanese stone pine), is a typical shrub in larch forests of the northern Okhotsk region, basins of the Kolyma and Indigirka rivers, and high-shrub tundra of the Chukchi Peninsula. It also forms a pine belt in mountains above the forest boundary, which gives way to the grass-underbrush mountain tundra and bald mountains. In the southern Chukchi Peninsula, ''Pinus pumila'' along with ''Duschekia fruticosa'' (Rupr.) Pouzar and ''Betula middendorffii'' Trautv. et C. A. Mey form trailing forests transitional between tundra and taiga [2]. Pinus pumila pollen, usually predominating in subfossil spore-and-pollen spectra of northeastern Siberia, is found as single grains or a subordinate component (up 2-3%, rarely 10%) in spectra of lacustrine deposits formed during the last glacial stage (isotope stage 2) in the Preboreal and Boreal times of the Holocene. Sometimes, its content increases to 15-22% in spectra of lacustrine deposits synchronous to the last glacial stage near the northern coast of the Sea of Okhotsk [3], evidently indicating the proximity of Japanese stone pine thickets.