Holocene pollen record from Lake Sokoch, interior Kamchatka (Russia), and its paleobotanical and paleoclimatic interpretation

Abstract

A pollen record, obtained from sediments of Lake Sokoch in mountain interior of the Kamchatka Peninsula, covers the last ca. 9600years (all ages are given in calibrated years BP). Variations in local components, including pollen, spores and non-pollen palynomorphs, and related changes in sedimentation document the lake development from initially seepage and shallow basin to deeper lake during the mid Holocene and then to the hydrologically open system during the late Holocene. The studies of volcanic ashes from the lake sediment core show their complex depositional histories.Lake Sokoch occupies a former proglacial basin between two terminal moraines of the LGM time. The undated basal part of record before ca. 9600year BP, however, does not reflect properly cold conditions. At that time, although shrublands and tundra dominated, stone birch and white birch forests have already settled in surroundings; the presence of alder woodland indicates wet and maritime-like climate. The subsequent forest advance suggesting warmer conditions was interrupted by the ca. 8000–7600year BP spell of cooler climate. The following culmination of warmth is bracketed by the evidence of the first maximal forest extent between ca. 7400 and 5100year BP. During that time, dramatic retreat of alder forest suggests a turn from maritime-like to more continental climate conditions. The cool and wet pulse after ca. 5100year BP was pronounced as forests retreat while shrublands, meadows and bogs extended. An expansion of white birch forest since ca. 3500year BP reflected the onset of drier climate, strengthening continentality and seasonal contrast. The second maximum of forests dominated by both stone and white birches occurred between ca. 2200 and 1700year BP and indicated warming in association with relatively dry and increasingly continental climate. The following period was wetter and cooler, and minor outbreak of alder forest around ca. 1500year BP suggests a short-term return of maritime-like conditions. Since ca. 1300year BP forests retreated and replaced by shrublands, tundra and bogs, pointing to cool and wet climate and likely increased back continentality. A prominent re-advance of stone birch forest shown atop the record, most probably reflects recent warming trend.The reconstructed cool periods correlate well with Holocene glacial advances in neighboring mountain areas and with the tree ring and ice core records from the Central Kamchatka Depression. The Lake Sokoch pollen record, being consistent with the previously obtained regional paleoclimatic data, yet contributes new detailed information, especially for the late Holocene.