Small mountain lakes are natural archives for understanding long‐term natural and anthropogenic impact on the environment. This study focused on long‐term (last ca. 13 000 years) vegetation changes ...and sedimentary processes in the catchment area of Lake Planina pri jezeru (1430 m a.s.l.) by using mineralogical, geochemical and palynological methods. Palynological results suggest that regional vegetation between 12 900 and 11 700 cal a bp was a herbaceous–forest tundra (Pinus, Artemisia, Poaceae). Climate warming at the beginning of the Holocene (ca. 11 700 cal a bp) caused the transition from a wetland (Cyperaceae) to an eutrophic lake with alternating anoxic (pyrite) and oxic conditions (gypsum). In addition, the surrounding area became forested (Picea, Larix, Ulmus). Fagus expanded at 10 200 cal a bp and Abies at 8200 cal a bp. Between 7500 and 4300 cal a bp, human impact on the environment was barely noticeable and mostly limited to grazing. During 4300–430 cal a bp human impact became more evident and gradually increased. The greatest influence was observed from 430 cal a bp onwards, when excessive exploitation of the surrounding area (logging and grazing) severely eutrophicated the lake.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Microfacies analyses and X-ray fluorescence scanning (μ-XRF) at sub-mm resolution were conducted on the varved Mid- to Late Holocene interval of two sediment profiles from pre-alpine Lake Ammersee ...(southern Germany). The coring sites are located in a proximal (AS10prox) and distal (AS10dist) position towards the main tributary River Ammer, in 1.8 km distance from each other. To shed light on sediment distribution within the lake, particular emphasis was (1) the detection of intercalated detrital layers and their micro-sedimentological features, and (2) intra-basin correlation of these event deposits. Detrital layers were dated by microscopic varve counting, verified by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils.
Since ∼5500 varve years (vyr) BP, in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles. Based on their microfacies, geochemistry, and proximal-distal deposition pattern, detrital layers were interpreted as River Ammer flood deposits. Earlier studies on flood layer seasonality have proven that flood layer deposition occurs predominantly during spring and summer, the flood season at Lake Ammersee. Most prominent features of the record are the onset of regular flood layer deposition at ∼5500 vyr BP in AS10prox and ∼2800 vyr BP in AS10dist as well as three major increases in mean flood layer thickness at ∼5500, 2800, and 400 vyr BP. Integrating information from both sediment profiles allowed to interpret these changes in terms of shifts towards higher mean flood intensity. Proposed triggering mechanisms are gradual reduction in Northern Hemisphere orbital summer forcing and superimposed centennial-scale solar activity minima. Likely responses to this forcing are enhanced equator-to-pole temperature gradients and changes in synoptic-scale atmospheric circulation. The consequences for the Ammersee region are more intense cyclones leading to extremer rainfall and flood events in spring and summer.
► We present a 5500-year record comprising 1573 flood layers in varved lake sediments. ► Microfacies data from two sediment profiles enabled deciphering depositional processes. ► Shifts towards higher flood intensity occurred at ∼5500, 2800, and 400 varve years BP. ► Proposed triggers are gradual reduction in NH orbital summer forcing and solar activity minima.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A 450 year spring‐summer flood layer time series at seasonal resolution has been established from the varved sediment record of Lake Ammersee (southern Germany), applying a novel methodological ...approach. The main results are (1) the attainment of a precise chronology by microscopic varve counting, (2) the identification of detrital layers representing flood‐triggered fluxes of catchment material into the lake, and (3) the recognition of the seasonality of these flood layers from their microstratigraphic position within a varve. Tracing flood layers in a proximal and a distal core and correlating them by application of the precise chronology provided information on the depositional processes. Comparing the seasonal flood layer record with daily runoff data of the inflowing River Ammer for the period from 1926 to 1999 allowed the definition of an approximate threshold in flood magnitude above which the formation of flood layers becomes very likely. Moreover, it was possible for the first time to estimate the “completeness” of the flood layer time series and to recognize that mainly floods in spring and summer, representing the main flood seasons in this region, are well preserved in the sediment archive. Their frequency distribution over the entire 450 year time series is not stationary but reveals maxima for colder periods of the Little Ice Age when solar activity was reduced. The observed spring‐summer flood layer frequency further shows trends similar to those of the occurrence of flood‐prone weather regimes since A.D. 1881, probably suggesting a causal link between solar variability and changes in midlatitude atmospheric circulation patterns.
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BFBNIB, CEKLJ, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Oxygen-isotope ratios of precipitation ($\delta^{18}$O$_p$) inferred from deep-lake ostracods from the Ammersee (southern Germany) provide a climate record with decadal resolution. The record in ...detail shows many of the rapid climate shifts seen in central Greenland ice cores between 15,000 and 5000 years before the present (B.P.). Negative excursions in the estimated $\delta^{18}$O$_p$ from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the North Atlantic. Deviating millennial-scale trends, however, indicate that climate gradients between Europe and Greenland changed systematically, reflecting a gradual rearrangement of North Atlantic circulation during deglaciation.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Here we present a palynological and sedimentological record from a 96-cm sediment core covering the last 13 ka aiming to document palaeoecological changes in the central South Caucasus driven by ...climate and/or human impact. The core was retrieved from Lake Paravani (2073 m asl, 41°27′N, 43°48′E), located in the steppic grasslands of South Caucasus in the Samsari-Javakheti volcanic plateau. The geomorphological features observed on the plateau, including moraine deposits, suggest the presence of local glaciers reaching the lake level during the Last Glacial periods. Based on sediment and pollen data, three palaeoecological phases have been identified. The first phase spanning the Younger Dryas and the Early Holocene, corresponds to a steppic environment with a limited lake productivity driven by a cold and particularly dry climate. According to the Age–depth model, this phase ends near 8500 cal BP with the decline of Chenopodiaceae. The second phase starts with an important expansion of trees at 8300 cal years BP. The delayed afforestation recorded in Lake Paravani is a pattern that has now been recognised widely through the Black Sea region's more continental areas. As soon as the climatic and edaphic conditions were favourable, the main deciduous and coniferous trees expanded concurrently due to the proximity of glacial forest refugia located in western Caucasus. This second phase marked by a climatic optimum is also characterized by an increase in lake productivity. The third phase starts at 2000–3000 cal BP and corresponds to the decline of forests on the plateau and the expansion of herbaceous formations, leading to the present-day steppic environment. This deforestation phase is driven by the deterioration of the climate conditions and human impact.
•First palaeoecological study of Lake Paravani, the largest lake in Georgia (Caucasus).•Multi-proxy analyses, including pollen and sedimentology (MS, grain-size analysis and XRD).•Dating of volcanic features to provide a time-frame for the geomorphology of the Lake Paravani area.•Reconstruction of 12.5 ka of unique vegetation evolution & dynamics.•The influences of glacial forest refugia and the local environment are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Sediments of Lake Paravani, the largest natural lake in the South Caucasus, were analysed to reconstruct the millennial history of the environment. Pollen analysis, previously undertaken on the first ...core retrieved in the middle of the lake, revealed a vegetation history for the last 12 millennia. As part of the present study, a new core was taken from the north-western part of the lake. Pollen analysis was performed on this new core with the same methodology as for the previous one. A sedimentological and geochemical analysis was also conducted on both cores in order to gain an understanding of the dynamics of erosion in the catchment area in response to landscape modifications. The results show that the sediment deposits within Lake Paravani yield rather complex and puzzle-like palaeoecological records. Despite the differences between the two records, correlations have been made that are supported by the 14C dates. By combining all of the data from both cores, it was finally possible to reconstruct the puzzle of the environmental history recounted by the Lake Paravani sediments. This reconstructed history is composed of four main phases: 1. A steppic environment marked by pronounced erosion processes from 12 000 to 10 000 cal. BP; 2. A transition phase characterized by the expansion of grasses (Poaceae) from 10 000 to 9-8 000 cal. BP; 3. A more forested phase from 9-8 000 to 2 000 cal. BP, during which the erosion fluxes decreased; and 4. A decline in tree cover probably due to human activities over the last 2 millennia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The carbon isotopic composition (delta.sup.13 C) of such carbonates ...depends on the delta.sup.13 C of dissolved inorganic carbon (DIC). Their oxygen isotopic composition (delta.sup.18 O) is controlled by the delta.sup.18 O of the lake water and by water temperature during carbonate precipitation. Lake water delta.sup.18 O, in turn, reflects the delta.sup.18 O of atmospheric precipitation in the catchment area, water residence time and mixing, and evaporation. A paleoclimatic interpretation of carbonate isotope records requires a site-specific calibration based on an understanding of these local conditions.
The sedimentary processes in the deep basin of large peri‐Alpine lakes have not been studied much on long timescales due to high coring complexity of such lake systems. In 2018, a 15.5 m long ...sediment section was retrieved from the deep basin of Lake Iseo (Italy) at 251 m water depth. A seismic survey associated with a multi‐proxy approach using sedimentological and geochemical analyses, reveals that event deposits correspond to 61.4% of the total sedimentation during the last 2000 years. The great heterogeneity of textures, colours and grain‐size distribution between the different types of event layers can be explained by the high number of potential sources of sediment in this large lake system. By combining a proxy of sediment sources with proxies of transport processes, flood events were distinguished from destabilizations of the slopes and the main delta. The three thickest mass wasting deposits correspond to major regional earthquakes events of 1222 ce, 1117 ce and around 700 ce. From a thorough comparison with regional climatic fluctuations and human activities in the watershed, it appears that periods of high sediment remobilization can be linked to a preceding increase in erosion in the watershed mainly under human forcing. Hence, even in large catchments, human activities play a key role on erosion processes and on sediment availability, disrupting the recording of extreme events in lacustrine archive.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Rotational sense does matter! Left and right circularly polarised laser light can be used to achieve different ionisation yields when applying multiphoton ionisation to chiral ketones (see picture). ...So a new type of enantioselective laser mass spectrometry becomes possible which also gives information on the involved electronic transitions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Hüls, M., Milecka, K., Namiotko, T., Plessen, B., von Grafenstein, U. & DecLakes participants 2010: Multi‐proxy evidence for ...early to mid‐Holocene environmental and climatic changes in northeastern Poland. Boreas, 10.1111/j.1502‐3885.2010.00159.x. ISSN 0300‐9483.
We investigated the sedimentary record of Lake Hańcza (northeastern Poland) using a multi‐proxy approach, focusing on early to mid‐Holocene climatic and environmental changes. AMS 14C dating of terrestrial macrofossils and sedimentation rate estimates from occasional varve thickness measurements were used to establish a chronology. The onset of the Holocene at c. 11 600 cal. a BP is marked by the decline of Lateglacial shrub vegetation and a shift from clastic‐detrital deposition to an autochthonous sedimentation dominated by biochemical calcite precipitation. Between 10 000 and 9000 cal. a BP, a further environmental and climatic improvement is indicated by the spread of deciduous forests, an increase in lake organic matter and a 1.7‰ rise in the oxygen isotope ratios of both endogenic calcite and ostracod valves. Rising δ18O values were probably caused by a combination of hydrological and climatic factors. The persistence of relatively cold and dry climate conditions in northeastern Poland during the first one and a half millennia of the Holocene could be related to a regional eastern European atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high‐pressure cell above the retreating Scandinavian Ice Sheet might have blocked the influence of warm and moist Westerlies and attenuated the early Holocene climatic amelioration in the Lake Hańcza region until the final decay of the ice sheet.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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