Late Holocene climate and environmental changes in Kamchatka inferred from subfossil chironomid record.

This study presents a reconstruction of the Late Holocene climate in Kamchatka based on chironomid remains from a 332 cm long composite sediment core recovered from Dvuyurtochnoe Lake (Two-Yurts Lake, TYL) in central Kamchatka. The oldest recovered sediments date to about 4500 cal years BP. Chironomid head capsules from TYL reflect a rich and diverse fauna. An unknown morphotype of Tanytarsini, Tanytarsus type klein, was found in the lake sediments. Our analysis reveals four chironomid assemblage zones reflecting four different climatic periods in the Late Holocene. Between 4500 and 4000 cal years BP, the chironomid composition indicates a high lake level, well-oxygenated lake water conditions and close to modern temperatures (w13 �C). From 4000 to 1000 cal years BP, two consecutive warm intervals were recorded, with the highest reconstructed temperature reaching 16.8 �C between 3700 and 2800 cal years BP. Cooling trend, started around 1100 cal years BP led to low temperatures during the last stage of the Holocene. Comparison with other regional studies has shown that termination of cooling at the beginning of late Holocene is relatively synchronous in central Kamchatka, South Kurile, Bering and Japanese Islands and take place around 3700 cal years BP. From ca 3700 cal years BP to the last millennium, a newly strengthened climate continentality accompanied by general warming trend with minor cool excursions led to apparent spatial heterogeneity of climatic patterns in the region. Some timing differences in climatic changes reconstructed from chironomid record of TYL sediments and late Holocene events reconstructed from other sites and other proxies might be linked to differences in local forcing mechanisms or caused by the different degree of dating precision, the different temporal resolution, and the different sensitive responses of climate proxies to the climate variations. Further high-resolution stratigraphic studies in this region are needed to understand the spatially complex pattern of climate change in Holocene in Kamchatka and the surrounding region.

Holocene vegetation dynamics and climate change in Kamchatka Peninsula, Russian Far East

We re-examined sixteen pollen records from non-volcanic areas in the Kamchatka Peninsula to reconstruct vegetation and climate changes during the Holocene. Pollen recordswere first summarized and evaluated for each of three main physiographic regions: (1)Western Lowland(WL), open to the Sea of Okhotsk (6 records); (2) Central Kamchatka Depression (CKD), bordered by mountains (4 records); and (3) Eastern Coast (EC), facing the Pacific Ocean (6 records), and then compared over the peninsula. The synthesized data suggest that the climate over Kamchatka was generally wet and mild before ca. 5.8 ka (1 ka=1000 cal. yrs BP) due to strong and prolonged maritime influence. The first forest maximumin the CKD started at ca. 8.9, indicating awarmer climate; however, forest spread along the both coasts was delayed until ca. 7 ka, suggesting a possible modulation of greater effective moisture on the coastal sites. Thewarmest period at ca. 7–5.8 ka is defined by the evidence of maximal forest extension overall the peninsula. During that time, birch (Betula) prevailed over alder (Alnus) in forest everywhere except in the EC. Since ca. 5.8 ka, divergent vegetation patterns became evident in northern vs. southern and coastal vs. interior sites that correspondwith a shift fromwarmer/maritime climate to cooler/continental climate. Also, greater climate variability accompanied the Neoglacial cooling since 5.8 ka. This climate cooling, indicated by drastic shrub expansion, advanced southward from the northern coasts (ca. 5.8 ka) to the central interior and coastal areas (ca. 5 ka) and then to the south (ca. 3.5 ka). Subsequent warming, suggested by the evidence of a second forest maximum, advanced westward from the EC (ca. 5.2 ka) to the CKD (ca. 3.2 ka) and then to the WL (ca. 1.9 ka). An advance of larch (Larix) in the CKD since ca. 3.2 ka points to increased climate continentality and larger seasonal variations. In contrast, alder forest spread after ca. 1.7 ka, reported only from the southern EC and CKD sites, indicates a mild, maritime-like climate that also agrees with the first apparent advance of spruce (Picea) in the interior. The latest cooling event, indicated by another shrub expansion, shows eastward trend: it occurred much earlier at the WL (ca. 2.4–1.6 ka) then at the EC (ca. 900–350 cal. yrs BP), and was less evident in the CKD. Instead, therewas a remarkable coniferous expansion during the last millennium when both larch and spruce invaded and replaced deciduous forests so that by ca. 450–320 cal. yrs BP, an extensive coniferous forest (“Coniferous Island”) appeared in the interior of Kamchatka. Since ca. 300 cal. yrs BP, spruce expanded most rapidly what broadly coincides with the beginning of the Little Ice Age

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

A pollen record, obtained from sediments of Lake Sokoch in mountain interior of the Kamchatka Peninsula, covers the last ca. 9600. years (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. 9600. year 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. 8000-7600. year 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 5100. year 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. 5100. year BP was pronounced as forests retreat while shrublands, meadows and bogs extended. An expansion of white birch forest since ca. 3500. year 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 1700. year 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. 1500. year BP suggests a short-term return of maritime-like conditions. Since ca. 1300. year 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

Sector collapses and large landslides on Late Pleistocene–Holocene volcanoes in Kamchatka, Russia

On Kamchatka, detailed geologic and geomorphologic mapping of young volcanic terrains and observations on historical eruptions reveal that landslides of various scales, from small (0.001 km3) to catastrophic (up to 20–30 km3), are widespread. Moreover, these processes are among the most effective and most rapid geomorphic agents. Of 30 recently active Kamchatka volcanoes, at least 18 have experienced sector collapses, some of them repetitively. The largest sector collapses identified so far on Kamchatka volcanoes, with volumes of 20–30 km3 of resulting debris-avalanche deposits, occurred at Shiveluch and Avachinsky volcanoes in the Late Pleistocene. During the last 10,000 yr the most voluminous sector collapses have occurred on extinct Kamen' (4–6 km3) and active Kambalny (5–10 km3) volcanoes. The largest number of repetitive debris avalanches (> 10 during just the Holocene) has occurred at Shiveluch volcano. Landslides from the volcanoes cut by ring-faults of the large collapse calderas were ubiquitous. Large failures have happened on both mafic and silicic volcanoes, mostly related to volcanic activity. Orientation of collapse craters is controlled by local tectonic stress fields rather than regional fault systems. Specific features of some debris avalanche deposits are toreva blocks — huge almost intact fragments of volcanic edifices involved in the failure; some have been erroneously mapped as individual volcanoes. One of the largest toreva blocks is Mt. Monastyr' — a ∼ 2 km3 piece of Avachinsky Somma involved in a major sector collapse 30–40 ka BP. Long-term forecast of sector collapses on Kliuchevskoi, Koriaksky, Young Cone of Avachinsky and some other volcanoes highlights the importance of closer studies of their structure and stability

Late Holocene diatom assemblages in a lake-sediment core from Central Kamchatka, Russia

Fossil diatom assemblages in a sediment core from a small lake in Central Kamchatka (Russia) were used to reconstruct palaeoenvironmental conditions of the late Holocene. The waterbody may be a kettle lake that formed on a moraine of the Two-Yurts Lake Valley, located on the eastern slope of the Central Kamchatka Mountain Chain. At present, it is a seepage lake with no surficial outflow. Fossil diatom assemblages show an almost constant ratio between planktonic and periphytic forms throughout the record. Downcore variations in the relative abundances of diatom species enabled division of the core into four diatom assemblage zones, mainly related to changes in abundances of Aulacoseira subarctica, Stephanodiscus minutulus, and Discostella pseudostelligera and several benthic species. Associated variations in the composition and content of organic matter are consistent with the diatom stratigraphy. The oldest recovered sediments date to about 3220 BC. They lie below a sedimentation hiatus and likely include reworked deposits from nearby Two-Yurts Lake. The initial lake stage between 870 and 400 BC was characterized by acidic shallow-water conditions. Between 400 BC and AD 1400, lacustrine conditions were established, with highest contributions from planktonic diatoms. The interval between AD 1400 and 1900 might reflect summer cooling during the Little Ice Age, indicated by diatoms that prefer strong turbulence, nutrient recycling and cooler summer conditions. The timing of palaeolimnological changes generally fits the pattern of neoglacial cooling during the late Holocene on Kamchatka and in the neighbouring Sea of Okhotsk, mainly driven by the prevailing modes of regional atmospheric circulation