Scleractinian corals increasingly are studied as geochemical archives of modern- and palaeoclimate, but microsampling for geochemical data is complicated by: 1) the microstructural complexity and spatial variability in skeletal growth in different coral genera; and 2) the rapidity and scale of diagenetic alteration that occurs in living coralla. Geochemical sampling techniques now have spatial resolution into the sub-micrometer to tens of micrometers range, and it is hoped that the spatial resolution can be translated to temporal resolution. This study investigated the effects on geochemical analyses imposed by microstructure and diagenesis in different live-collected coral genera representing somewhat different depositional environments. Suites of samples of four reef-building genera (Acropora, Pocillopora, Goniastrea and Porites) were collected from three adjacent environments in intertidal and subtidal positions near the reef edge at Heron Reef, Great Barrier Reef and studied by means of optical and scanning electron microscopy, combined with vibrational and energy dispersive spectroscopy. The first section of this study compares and documents the microstructure of the four coral genera. Each genus was found to have very different three-dimensional arrangements of microstructural elements, and a new general growth model was proposed for Acropora, to take into account differences in the timing of precipitation of trabeculae and thickening deposits. The results highlight the complexity and spatial variability of skeletal growth in different coral genera. Because microstructural patterns vary in different genera, direct observation of microstructural elements and growth lines are necessary to allow geochemical microsamples to be placed into series that represent temporal sequences with known degrees of time averaging. Coral growth rates (i.e., rates of extension) are discussed to determine the range of temporal relationships that exist between closely spaced skeletal microstructural elements. Such data are necessary in order for coral skeletogenesis to be understood and are critical for constraining microsampling strategies aimed at developing true time series geochemical data at very fine spatial and temporal scales. The second part of the study focused on early diagenetic alteration of the corals, which is an equally important concern for geochemical analysis. Early marine diagenesis was documented in the same live-collected samples of the four common reef-building coral genera. Samples show extensive early marine diagenesis where parts of the coralla less than three years old contain abundant macro- and microborings (sponges, algae, cyanobacteria and fungi) and significant amounts of aragonite, high-Mg calcite, low-Mg calcite and brucite [Mg(OH)2] cements. Many of the cements are associated with microendoliths and endobionts that inhabit recently abandoned parts of the skeleton. The cements are problematic for palaeoclimate reconstruction because geochemical proxies used for paleoclimate studies are meant to reflect ambient seawater chemistry and conditions, but the occurrence of brucite and low-Mg calcite demonstrates how far fluid chemistry in microenvironments within the corals has evolved from ambient seawater. Some Porites lobata specimens have had as much as 60% of the most recently deposited skeletal aragonite (i.e., the part of the skeleton that projects into the layer of living polyps) bored and replaced by low-Mg calcite cement. The low-Mg calcite cement has significantly different trace element ratios (Sr/Ca(mmol/mol) = 6.3 ± 1.4; Mg/Ca(mmol/mol) = 12.0 ± 5.1) than the host coral skeletal aragonite (Sr/Ca(mmol/mol) = 9.9 ± 1.3; Mg/Ca(mmol/mol) = 4.5 ± 2.3), thus providing a serious challenge for Sr/Ca or Mg/Ca based sea surface temperature calculations. This study illustrates that many diagenetic changes that can radically alter important geochemical characteristics of coral skeleton occur very early on the sea floor (i.e., while corals are still alive). Documented cements altered trace element inventories (e.g., Sr and Mg), thus, interfering with the use of those elements in palaeotemperature calculations. Hence, significant diagenetic changes that jeopardise palaeoclimate data do not require long-term diagenesis or meteoric exposure. Some of the diagenetic changes (e.g., calcite filled borings) occur at scales that are very difficult to detect short of visual inspection using SEM. Hence, vetting of coral samples with SEM is required before any sample is subjected to geochemical analysis.

This thesis refines and develops understanding of the ecological and climatic characteristics of early Middle Pleistocene (MIS 19-13, c. 780-430 ka) interglacial environments in Britain. This period is characterised by globally muted (i.e. low amplitude) glacial-interglacial cycles, which increased in amplitude c. 430 ka with the Mid-Brunhes Transition (MBT). However, the influence of these global climatic characteristics on climates and ecology at regional and local scales is yet to be fully understood. Local ecological processes, particularly disturbance processes, have also received limited attention in pre-Holocene interglacial settings, despite their likely importance for vegetation and habitat structure. Chapters 4, 5 and 6 present in-depth multi-proxy palaeoenvironmental studies from three early Middle Pleistocene sites: West Runton, Pakefield and Brooksby. A combination of Coleoptera, pollen, coprophilous fungal spores, microcharcoal and sedimentology is used to reconstruct local ecological attributes for each site. Multivariate analyses of these datasets indicate the importance of disturbance processes (herbivore activity, wildfire, hydrogeomorphic processes) in driving and maintaining local vegetation structure and habitat heterogeneity. This is explored further (in Chapter 8), emphasising the apparent importance of site-specific factors, rather than those shared between sites, in determining the relative influence of each disturbance factor. In Chapter 7, new approaches to the coleopteran Mutual Climatic Range (MCR) method are applied to a suite of coleopteran records from interglacial sites spanning the Middle and Late Pleistocene (c.712-126 ka, MIS 17-5e). Summer temperatures, winter temperatures and temperature seasonality are reconstructed, to test whether there is evidence for MBT expression in Northwest European thermoclimates. No evidence for this is found, and it is suggested (in Chapter 8) that MBT expression in this region may instead be reflected in hydroclimatic variables (e.g. enhanced annual precipitation). Finally, it is suggested that disturbance processes and potentially wetter climates were beneficial to contemporary Lower Palaeolithic populations in Northwest Europe.

No description available.

No / A laboratory-based experiment was carried out to examine the dissolution characteristics of testate amoebae (Protozoa: Rhizopoda) under acidic conditions. The results suggest a large degree of variability in the dissolution susceptibility of taxa and no straightforward distinction between the relative robustness of xenosomic and idiosomic test types. Individuals from the genus Euglypha have tests composed of thin-walled siliceous plates, which are prone to severe dissolution. Certain other taxa are relatively unaffected by low pH conditions, including Assulina muscorum, Amphitrema flavum and Trigonopyxis arcula type. Differential preservation of subfossil testate amoebae must be acknowledged as a particular problem for peat-based palaeoclimate studies.

No description available.

The objective of this research is to interpret high-resolution palaeo-proxy data sets to understand the Asian summer monsoon variability in the past. This was done by synthesizing published palaeo-records from the Asian monsoon region, model simulation comparisons, and analysing new lake sedimentary records from northeast Thailand. Palaeo-records and climate modeling indicate a strengthened summer monsoon over Mainland Southeast Asia during the Last Glacial Maximum (LGM), compared to dry conditions in other parts of the Asian monsoon region. This can be explained by the LGM sea level low stand, which exposed Sundaland and created a large land-sea thermal contrast. Sea level rise ~19 600 years before present (BP), reorganized the atmospheric circulation in the Pacific Ocean and weakened the summer monsoon between 20 000 and 19 000 years BP. Both the Mainland Southeast Asia and the East Asian monsoon hydroclimatic records point to an earlier Holocene onset of strengthened summer monsoon, compared to the Indian Ocean monsoon. The asynchronous evolution of the summer monsoon and a time lag of 1500 years between the East Asian and the Indian Ocean monsoon can be explained by the palaeogeography of Mainland Southeast Asia, which acted as a land bridge for the movement of the Intertropical Convergence Zone. The palaeo-proxy records from Lake Kumphawapi compare well to the other data sets and suggest a strengthened summer monsoon between 10 000 and 7000 years BP and a weakening of the summer monsoon thereafter. The data from Lake Pa Kho provides a picture of summer monsoon variability over 2000 years. A strengthened summer monsoon prevailed between BC 170-AD 370, AD 800-960 and since AD 1450, and was weaker about AD 370-800 and AD 1300-1450. The movement of the mean position of the Intertropical Convergence Zone explains shifts in summer monsoon intensity, but weakening of the summer monsoon between 960 and 1450 AD could be affected by changes in the Walker circulation. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript..</p>

<p>The main aim of this thesis was to contribute with detailed information of regional environmental change during the Holocene through studies of speleothems and their growth environments from two caves, Korallgrottan and Labyrintgrottan in northwestern Sweden, and a cellar vault in Uppsala. This was done through studies of stable isotopes and luminescence properties in the speleothems in combination with a detailed monitoring study in Korallgrottan.</p><p>The monitoring study suggests that stalagmites fed by stalactites with slow and stable drip rates from deep inside the cave may be suitable as palaeoclimate archives. Similarities between oxygen isotope signals of contemporary samples from Labyrintgrottan and Korallgrottan emphasize the potential of speleothems from Labyrintgrottan to also provide high resolution regional palaeoclimate information.</p><p>Except for a number of cold events stalagmite δ¹⁸O records from northern Scandinavia indicate that temperatures were warmer than today between 9500 and 6000 years ago. During this period the interval between 7800 and 6000 years ago seems to have been the warmest. The area above Labyrintgrottan was most likely covered by much denser vegetation than today at the time of stalagmite growth (9500-7500 years ago) and was, unlike today, probably situated below the local tree-limit between 9000 and 8000 years ago. The δ¹⁸O record of a stalagmite from Korallgrottan covering the last 4000 years agrees with the concept of a warmer period, the so called Medieval Warm Period, centred around AD1000 and a colder period, the so called Little Ice Age, somewhere between AD1000 and today.</p><p>Studies of luminescence properties in fast growing speleothems from Uppsala indicate that the variations in luminescence intensity are annual and that the annual lamiae of the luminescent record represent a flush of organic material.</p>

This thesis presents the results of contemporary limnological and palaeolimnological investigations of a series of crater lakes in order to reconstruct the palaeoenvironmental history of western Uganda, East Africa. The research examines questions of spatial and temporal heterogeneity of climate changes in the context of growing human impacts on the landscape over the last millennium. Sediment records from two lakes, Nyamogusingiri and Kyasanduka within the Queen Elizabeth National Park (QENP) were investigated to look at the long term records of climate and environmental change (spanning the last c. 1000 years). Five shorter cores across a land-use gradient were retrieved to assess the impact of human activity on the palaeoenvironmental record over the last ~150 years. High-resolution (sub-decadal), multiproxy analyses of lake sediment cores based on diatoms, bulk geochemistry (C/N and δ13C) and sedimentary variables (loss-on-ignition, magnetic properties and physical properties) provide independent lines of evidence that allow the reconstruction of past climate and environmental changes. This multiproxy approach provides a powerful means to reconstruct past environments, whilst the multi-lake approach assists in the identification and separation of local (e.g. catchment-scale modifications and groundwater influences) and regional effects (e.g. climatic changes). The results of a modern limnological survey of 24 lakes were used in conjunction with diatom surface sediment samples (and corresponding water chemistry) from 64 lakes across a natural conductivity gradient in western Uganda (reflecting a regional climatic gradient of effective moisture) to explore factors controlling diatom distribution. The relationships between water chemistry and diatom distributions were explored using canonical correspondence analysis (CCA) and partial CCA. Variance partitioning indicated that conductivity accounted for a significant and independent portion of this variation. A transfer function was developed for conductivity (r2jack = 0.74). Prediction errors, estimated using jack-knifing, are low for the conductivity model (0.256 log units). The final model was applied to the core sediment data.This study highlights the potential for diatom-based quantitative palaeoenvironmental reconstructions from the crater lakes in western Uganda. Sedimentary archives from the Ugandan crater lakes can provide high-resolution, annual to sub-decadal records of environmental change. Whilst all of the lakes studied here demonstrate an individualistic response to external (e.g. climatic) drivers, the broad patterns observed in Uganda and across East Africa suggest that the crater lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Warm Period (MWP; AD 1000-1200) and a relatively drier climate during the main phase of the Little Ice Age (LIA; c. AD 1500-1800); though lake levels in western Uganda do fluctuate, with a high stand c. AD 1575-1600). The general trends support the hypothesis of an east to west (wet to dry) gradient across East Africa during the LIA, however, the relationship breaks down and is more complex towards the end of the LIA (c. AD 1700-1750) when the inferred changes in lake levels at Nyamogusingiri and Kyasanduka are synchronous with changes observed at Lakes Naivasha (Kenya) and Victoria and diverge from local lake level records (from Edward, Kasenda and Wandakara). Significant changes in the lake ecosystems have occurred over the last 50-75 years, with major shifts in diatom assemblages to benthic-dominated systems and an inferred increase in nutrient levels. These changes are coincident with large sediment influx to the lakes, perhaps as a result of increasing human activity within many of the lake catchments.

Studies in paleoclimate are important because they give us knowledge about how the climate system works and puts the current climate change in necessary perspective. By studying (pre)historic periods we increase our knowledge not just about these periods, but also about the processes that are important for climatic variations and changes. This thesis deals mainly with the interaction between climate and vegetation. Vegetation changes can affect climate in many different ways. These effects can be divided into two main categories: biogeochemical and biogeophysical processes. This thesis studies the biogeophysical effects of vegetation changes on climate in climate models. Climate models are a necessary tool for investigating how climate responds to changes in the climate system, as well as for making predictions of future climate. The biogeophysical processes are strongly related to characteristics of the land surface. Vegetation changes alter the land surface’s albedo (ability to reflect incoming solar radiation), roughness and evapotranspiration (the sum of evaporation and tran-spiration), which in turn affects the energy fluxes between the land surface and the atmosphere and thereby the climate. It is not, however, evident in what way; denser vegetation (e.g. forest instead of grassland) gives decreased albedo, which results in higher temperature, but also increased evapotranspiration, which contrastingly results in lower temperature. Vegetation changes are in this thesis studied in four different (pre)historic periods: two very cold periods with no human influence (c. 44,000 and 21,000 years ago), one warm period with minor human influence (c. 6,000 years ago) and a cold period with substantial human influence (c. 200 years ago). In addition to that the present climate is studied. The combination of these periods gives an estimate of the effect of both natural and anthropogenic vegetation on climate in different climatic contexts. The results show that vegetation changes can change temperature with 1–3 °C depending on season and region. The response is not the same everywhere, but depends on local properties of the land surface. During the winter half of the year, the albedo effect is usually most important as the difference in albedo between forest and open land is very large. During the summer half of the year the evapotranspiration effect is usually most important as differences in albedo between different vegetation types are smaller. A prerequisite for differences in evapotranspiration is that there is sufficient amount of water available. In dry regions, evapotranspiration does not change much with changes in vegetation, which means that the albedo effect will dominate also in summer. The conclusion of these studies is that vegetation changes can have a considerable effect on climate, comparable to the effect of increasing amounts of greenhouse gases in scenarios of future climate. Thus, it is important to have an appropriate description of the vegetation in studies of past, present and future climate. This means that vegetation has the potential to work as a feedback mechanism to natural climatic variations, but also that man can alter climate by altering the vegetation. It also means that mankind may have influenced climate before we started to use fossil fuel. Consequently, vegetation changes can be used as a means to mitigate climate change locally. / Studiet av paleoklimat är viktigt för att det ger kunskap om hur klimatsystemet fungerar samt för att det sätter nuvarande klimatförändring i ett nödvändigt perspektiv. Genom att studera (för)historiska perioder ökar vi vår kunskap om dessa perioder, men också om vilka processer som har betydelse för klimatets variationer. Denna avhandling behandlar framförallt interaktionen mellan klimat och växtlighet. Förändringar i växtligheten kan påverka klimatet på flera olika sätt. Dessa kan delas in i två huvudgrupper: biogeokemiska och biogeofysikaliska processer. Denna avhandling studerar de biogeofysikaliska effekterna på klimatet i klimatmodeller. Klimatmodeller är ett nödvändigt verktyg för att studera hur klimatet svarar på förändringar i klimatsystemet, samt för att göra förutsägelser om framtidens klimat. De biogeofysikaliska processerna är förknippade med markytans egenskaper. Förändrad växtlighet förändrar markytans albedo (förmågan att reflektera inkommande soltrålning), skrovlighet och förmågan att transportera vatten från marken till atmosfären genom evapotranspiration (summan av avdunstning och transpiration), vilket i sin tur påverkar energiflödena mellan markytan och atmosfären. Dessa förändringar påverkar sedermera klimatet. Det är emellertid inte självklart på vilket sätt; tätare växtlighet (t.ex. skog i stället för äng) ger minskat albedo vilket ger högre temperatur, men också ökad evapotranspiration vilket däremot ger lägre temperatur. Växtlighetsförändringars påverkan på klimatet studeras i denna avhandling i fyra olika (för)historiska perioder: två väldigt kalla perioder utan mänsklig påverkan (ca 44 000 och 21 000 år sedan), en varm period med liten mänsklig påverkan (ca 6 000 år sedan) och en kall period med avsevärd mänsklig påverkan (ca 200 år sedan). I tillägg till det studeras också dagens klimat. Resultaten visar att förändringar i växtlighet lokalt kan ha en signifikant effekt på klimatet. Kombinationen av dessa perioder ger en uppskattning av effekten av både naturlig och antropogen växtlighet i olika klimatsammanhang. Förändrad växtlighet kan ändra temperaturen med 1-3 °C beroende på årstid och område. Responsen är inte densamma överallt utan beror på lokala egenskaper hos markytan. Under vinterhalvåret är oftast albedoeffekten viktigast eftersom skillnaden i albedo mellan skog och öppet landskap då är mycket stor. Under sommarhalvåret är evapotranspirationen oftast viktigast eftersom skillnaden i albedo mellan olika växtlighetstyper då oftast är små. En förutsättning för det är att det finns tillräckligt med vatten tillgängligt för evapotranspiration. I torra områden förändras evapotranspirationen inte särskilt mycket när växtligheten förändras, vilket gör att albedoeffekten dominerar även på sommaren.  Slutsatsen av dessa studier blir att förändrad växtlighet kan ha en betydande effekt på klimatet, jämförbar med den effekt som ökade halter av växthusgaser har i scenarier för framtida klimat. Alltså är det viktigt att ha en korrekt beskrivning av växtligheten i studier av (för)historiskt, nutida och framtida klimat. Det betyder att växtligheten har potentialen att fungera som en återkopplingsmekanism till naturliga klimatvariationer, men också att människan kan påverka klimatet genom att förändra växtligheten. Det betyder också att mänskligheten kan ha påverkat klimatet innan vi började använda fossilt bränsle. Följaktligen kan växtlighetsförändringar användas som ett sätt att lokalt begränsa klimatförändringar. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Sediment records of three European lakes were investigated in order to reconstruct the regional climate development during the Lateglacial and Holocene, to investigate the response of local ecosystems to climatic fluctuations and human impact and to relate regional peculiarities of past climate development to climatic changes on a larger spatial scale. The Lake Hańcza (NE Poland) sediment record was studied with a focus on reconstructing the early Holocene climate development and identifying possible differences to Western Europe. Following the initial Holocene climatic improvement, a further climatic improvement occurred between 10 000 and 9000 cal. a BP. Apparently, relatively cold and dry climate conditions persisted in NE Poland during the first ca. 1500 years of the Holocene, most likely due to a specific regional atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high-pressure cell above the remaining Scandinavian Ice Sheet (SIS) might have blocked the eastward propagation of warm and moist Westerlies and thus attenuated the early Holocene climatic amelioration in this region until the final decay of the SIS, a pattern different from climate development in Western Europe. The Lateglacial sediment record of Lake Mondsee (Upper Austria) was investigated in order to study the regional climate development and the environmental response to rapid climatic fluctuations. While the temperature rise and environmental response at the onset of the Holocene took place quasi-synchronously, major leads and lags in proxy responses characterize the onset of the Lateglacial Interstadial. In particular, the spread of coniferous woodlands and the reduction of detrital flux lagged the initial Lateglacial warming by ca. 500–750 years. Major cooling at the onset of the Younger Dryas took place synchronously with a change in vegetation, while the increase of detrital matter flux was delayed by about 150–300 years. Complex proxy responses are also detected for short-term Lateglacial climatic fluctuations. In summary, periods of abrupt climatic changes are characterized by complex and temporally variable proxy responses, mainly controlled by ecosystem inertia and the environmental preconditions. A second study on the Lake Mondsee sediment record focused on two small-scale climate deteriorations around 8200 and 9100 cal. a BP, which have been triggered by freshwater discharges to the North Atlantic, causing a shutdown of the Atlantic meridional overturning circulation (MOC). Combining microscopic varve counting and AMS 14C dating yielded a precise duration estimate (ca. 150 years) and absolute dating of the 8.2 ka cold event, both being in good agreement with results from other palaeoclimate records. Moreover, a sudden temperature overshoot after the 8.2 ka cold event was identified, also seen in other proxy records around the North Atlantic. This was most likely caused by enhanced resumption of the MOC, which also initiated substantial shifts of oceanic and atmospheric front systems. Although there is also evidence from other proxy records for pronounced recovery of the MOC and atmospheric circulation changes after the 9.1 ka cold event, no temperature overshoot is seen in the Lake Mondsee record, indicating the complex behaviour of the global climate system. The Holocene sediment record of Lake Iseo (northern Italy) was studied to shed light on regional earthquake activity and the influence of climate variability and anthropogenic impact on catchment erosion and detrital flux into the lake. Frequent small-scale detrital layers within the sediments reflect allochthonous sediment supply by extreme surface runoff events. During the early to mid-Holocene, increased detrital flux coincides with periods of cold and wet climate conditions, thus apparently being mainly controlled by climate variability. In contrast, intervals of high detrital flux during the late Holocene partly also correlate with phases of increased human impact, reflecting the complex influences on catchment erosion processes. Five large-scale event layers within the sediments, which are composed of mass-wasting deposits and turbidites, are supposed to have been triggered by strong local earthquakes. While the uppermost of these event layers is assigned to a documented adjacent earthquake in AD 1222, the four other layers are supposed to be related to previously undocumented prehistorical earthquakes. / Sedimente aus drei europäischen Seen wurden untersucht um die regionale Klimaentwicklung während des Spätglazials und Holozäns und die Reaktion der Ökosysteme auf Klimaschwankungen und menschlichen Einfluss zu rekonstruieren sowie die regionalen Besonderheiten der spätquartären Klimaveränderungen in einen überregionalen Kontext zu setzen. Die Sedimente des Jezioro Hańcza (Nordostpolen) wurden im Hinblick auf die frühholozäne Klimaentwicklung und die Identifikation möglicher Unterschiede gegenüber Westeuropa untersucht. Im Anschluss an die Erwärmung zu Beginn des Holozäns konnte eine weitere Verbesserung der Klimabedingungen zwischen 10 000 und 9000 Jahren vor heute nachgewiesen werden. Offensichtlich herrschten in Nordostpolen während der ersten 1500 Jahre des Holozäns noch relative kalte und trockene Klimabedingungen, höchstwahrscheinlich als Resultat besonderer regionaler atmosphärischer Zirkulationsverhältnisse. Eine antizyklonale Zirkulationszelle als Resultat eines Hochdruckgebiets über dem Rest des Skandinavischen Eisschilds verhinderte wahrscheinlich das Vordringen warmer und feuchter Luftmassen aus Westen und verursachte damit eine Abschwächung der frühholozänen Klimaverbesserung in dieser Region bis zum endgültigen Zerfall des Eisschilds, was grundsätzlich von der frühholozänen Klimaentwicklung in Westeuropa abweicht. Die spätglazialen Sedimente des Mondsees (Oberösterreich) wurden im Hinblick auf die regionale Klimaentwicklung und die Reaktion des Ökosystems auf abrupte Klimaschwankungen untersucht. Während die Erwärmung zu Beginn des Holozäns von einer zeitgleichen Reaktion des Ökosystems begleitet wurde, war die Reaktion des Ökosystems auf die Erwärmung zu Beginn des Spätglazials deutlich verzögert. Insbesondere die Ausbreitung von Nadelwäldern und die Reduktion des klastischen Eintrags folgten der spätglazialen Erwärmung erst mit einer Verzögerung von ca. 500–750 Jahren. Die Abkühlung zu Beginn der Jüngeren Dryas war durch eine deutliche Synchronizität zwischen Temperatur- und Vegetationsänderung gekennzeichnet, wohingegen der Anstieg des klastischen Eintrags erst 150–300 Jahre verzögert folgte. Eine komplexe Reaktion des Ökosystems zeigt sich auch während kurzfristiger spätglazialer Klimaschwankungen. Zusammenfassend lässt sich sagen, dass abrupte Klimaveränderungen durch komplexe und zeitlich variable Reaktionsmuster des Ökosystems gekennzeichnet sind, die hauptsächlich von dessen Klimasensitivität und den ökologischen Ausgangsbedingungen abhängen. Eine zweite Studie an den Sedimenten des Mondsees konzentrierte sich auf zwei Klimaschwankungen vor ca. 8200 und 9100 Jahren, für die Schmelzwassereintrag in den Nordatlantik und ein damit verbundenes Zusammenbrechen der thermohalinen Zirkulation als Ursache angesehen wird. Durch Warvenzählungen und 14C-Datierungen konnten sowohl die Dauer (ca. 150 Jahre) als auch das absolute Alter der Kältephase vor ca. 8200 Jahren zuverlässig bestimmt werden, welche in guter Übereinstimmung mit Resultaten aus anderen Paläoklimaarchiven stehen. Darüber hinaus wurde eine kurze Warmphase direkt im Anschluss an das Abkühlungsereignis identifiziert, die auch in anderen Klimaarchiven im nordatlantischen Raum nachweisbar ist. Diese wurde wahrscheinlich durch ein Wiedererstarken der thermohalinen Zirkulation verursacht, welches darüber hinaus eine Verschiebung ozeanischer und atmosphärischer Frontsysteme zur Folge hatte. Obwohl andere Klimaarchive auch nach dem Abkühlungsereignis vor ca. 9100 Jahren auf ein Wiedererstarken der thermohalinen Zirkulation hindeuten, finden sich in den Sedimenten des Mondsees keine Anzeichen für eine solche Wärmeperiode, was die Komplexität des globalen Klimasystems verdeutlicht. Die holozänen Sedimente des Lago d’Iseo (Norditalien) wurden im Hinblick auf die regionale Erdbebenaktivität und den Einfluss von Klima und Mensch auf Erosionsprozesse im Einzugsgebiet und den klastischen Eintrag in den See untersucht. Zahlreiche kleinere detritische Lagen in den Sedimenten spiegeln Eintrag durch extreme Oberflächenabflussereignisse wieder. Während des Früh- und Mittelholozäns zeigt sich eine deutliche Übereinstimmung zwischen erhöhtem klastischen Eintrag und kühleren und feuchteren Klimaverhältnissen, was auf einen dominanten Einfluss der natürlichen Klimavariabilität hindeutet. Im Gegensatz dazu zeigen Phasen erhöhten klastischen Eintrags während des Spätholozäns teilweise auch eine Korrelation mit erhöhter Siedlungsaktivität, was die Komplexität der Einflüsse auf Erosionsprozesse im Einzugsgebiet verdeutlicht. Darüber hinaus konnten auch fünf größere Ereignislagen nachgewiesen werden, welche durch Rutschmassen und Turbidite gekennzeichnet sind und für die lokale Erdbeben als Ursache vermutet werden. Die jüngste Ereignislage kann mit einem historisch dokumentierten proximalen Erdbeben im Jahr AD 1222 korreliert werden. Für die anderen vier Ereignislagen werden bisher undokumentierte prähistorische Erdbeben als Ursache angenommen.