Beschreibung: A detailed Holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from NE Germany (Lake Tiefer See) and central N Poland (Lake Czechowskie). A total of thirteen tephras and cryptotephras of Icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies. Out of these, three cryptotephras (Askja-AD1875, Askja-S and H€asseldalen) were identified in both records, thus allowing a detailed synchronization of developing high-resolution palaeoenvironmental proxy data. The early Holocene Saksunarvatn Ash layer and the middle Holocene Lairg-B and Hekla-4 cryptotephras in Lake Tiefer See are further important anchor points for the comparison with other high-resolution palaeoclimate records in Central and Northern Europe. Tentative correlations of cryptotephras have been made with a historical basaltic Grimsv€otn eruption (~AD890 e AD856) and three late Holocene rhyolitic eruptions, including the 2.1 ka Glen Garry and two unknown high-silicic cryptotephras of probably Icelandic provenance (~1.9 cal ka BP).

Beschreibung: Silicic Icelandic magmas are widely believed to contain low to moderate H2O content prior to degassing, and that their high explosivity mostly results from the interaction of the magmas with ice or meteoric water. Here we report the compositions of glass inclusions (SiO2=57–72 wt%, K2O=1.3–2.6 wt%) in Fe-rich olivines (Fo2–42) from the largest Holocene eruptions of Hekla volcano (H3 and H4) on Iceland, which preserved quenched melts with very high primary H2O contents (3.3–6.2 wt%). The silicic Hekla melts originate primarily by extensive (∼90%) crystal fractionation of H2O-poor (∼0.6 wt%) basalts and represent an end member in the systematics of terrestrial magmas because they originate at low fO2 (ΔQFM ∼−0.1 to −0.4) and have as high H2O contents as significantly more oxidized island-arc magmas (ΔQFM≥1). This demonstrates that H2O and ΔQFM do not correlate in silicic magmas from different tectonic settings, and that fO2, not H2O content, shows a major difference between silicic ocean-island (e.g., Icelandic) and island-arc magmas. Analysis of available experimental data suggests that high H2O activity and low fO2 expand the field of olivine stability in silicic melts. Low fO2 and low MgO content could also suppress crystallization of amphibole. On the basis of these results we propose that an anhydrous mineral assemblage bearing Fe-rich olivine in evolved volcanic and Skaergaard-type intrusive rocks does not imply low H2O in magmas prior to degassing but, in contrast to the commonly held view, is an indicator of H2O-rich silicic parental magmas crystallized at low fO2. Finally, the high H2O content in magma was a major driving force of the largest explosive eruptions of Hekla volcano and must be at least as important for driving silicic explosive volcanism on Iceland as magma–ice interaction.

Beschreibung: 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.

Beschreibung: Distal volcanic tephras in soil sections and lake sediments in the Dvuh-yurtochnoe (Two-Yurts) lake area, central Kamchatka, were investigated in order to provide a chronological framework for the reconstruction of late Quaternary landscape development. Mineralogical and geochemical data point to sources from 5 volcanoes. Ten tephra layers were identified and correlated to known eruptive events. The ages were corroborated by radiocarbon dating of the soil sections around Two-Yurts lake. These findings allow the reconstruction of regional paleoenvironmental change, recorded in the soil sections around Two-Yurts lake. During the Last Glacial Maximum (LGM) time, the area was affected by glacial advances that produced the glacial moraines at the eastern outlet of the lake. A large landslide, ca. 15,000–18,000 14C BP, dammed the valley and led to formation of Two-Yurts lake. Several more landslide events can be recognized in the Holocene, and one affected Two-Yurts lake ca. 3000 14C BP. This event produced a “tsunami”, documented by poorly sorted deposits with rounded pebbles in the onshore sections around the lake. In contrast to the soil sections, tephras buried in the “soupy” lacustrine sediments of Two-Yurts lake are not well preserved and show inconsistent age-depth relationships compared to those suggested by radiocarbon dating, due to sinking through the lake sediments. Nevertheless, tephrochronological data revealed the strong impact of terrestrial landslides on lake sedimentation.

Beschreibung: Paleoecological records from two Holocene peat bogs in northern Germany are linked by two microscopic volcanic ash layers, correlated by petrology and geochemistry to explosive volcanism on Iceland. The younger “Microlite tephra” cannot be correlated to any known eruption, while the older tephra layer is identified as a deposit of the Hekla 3 eruption. The tephra layers are dated by an age–depth regression of accelerator mass spectrometry 14C ages that have been calibrated and combined in probability distributions. This procedure gives an age of 730–664 cal yr B.C. for the “Microlite tephra” event and 1087–1006 cal yr B.C. for the Hekla 3 event. Accordingly, the tephra layers were deposited during the late Bronze Age. At this time, human settlement slowly increased pressure on the environment, as indicated by changes in woodland pollen composition at the two bogs. The tephra-marker horizons further show that the palynologically defined transition from the Subboreal to the Subatlantic Period is synchronous in the investigated area. However, the macroscopic visible marker in peat, the change from fibrous to sapric peat, the “Schwarztorf-Weißtorf-Kontakt,” is asynchronous. Bog vegetation did not immediately react in unison to a climatic change at this pollen zone boundary; instead, the timing of vegetation change depended on the location within the bog.

Beschreibung: 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.

Beschreibung: In the sediments of both of the investigated lakes, the tephra from the Mercato-Ottaviano eruption (Vesuvius, southern Italy) (ca. 7900 B.P.) could be identified. The palynological investigations show that from ca. 9000-7200 B.P. (8000-6000 cal B.C.) deciduous oak forests predominated, with only a few representatives of Mediterranean vegetation. At the transition to the central European Atlantic Period those forests changed to an open vegetation type, dominated byJuniperus andPhillyrea. At about 5500 B.P. (4400 cal B.C.), theJuniperus-Phillyrea vegetation was replaced byQuercus ilex woodland that still occurs on the island of Mljet today and is considered to be the natural vegetation of the Dalmatian coastland. The associated vegetation of theQ. ilex forests changed several times. At the beginning of theQ. ilex period,Juniperus values were still high, but soon they decreased andErica spread. In more recent times theQ. ilex forests were partially replaced by plantations ofPinus halcpensis. Indicators of human impact are sparse throughout the pollen record. Clear evidence for human influence exists only from ca. 3100 B.P. (1300 cal B.C.) whenJuglans andPinus halepensis were introduced to the area. Later,Olea andSecale cultivation can be suggested and further spreading ofJuniperus indicates use of the land as pasture.