ALBERT

Description: Investigation of the sedimentary record of pre-Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long-term evolution of the lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub-annual resolution for µ-XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large-scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14 C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ 18 O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500–750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ 18 O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150–300 a. Three short-term Lateglacial cold intervals, corresponding to Greenland isotope substages GI-1d, GI-1c2 and GI-1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd.

Description: This study investigated the Grabia River valley mire in central Poland to reconstruct its palaeoenvironmental conditions from the Younger Dryas to the present. We analysed sedimentological, biological and geochemical data from the palaeo-oxbow lake and valley mire to identify the principal hydrological trends, especially episodes of high water level. During the Lateglacial and Holocene, the Grabia River had a meandering channel, and its hydraulic parameters and the channel dimensions changed in response to climatic oscillations and vegetation development. We identified phases of high flood intensity and high groundwater level that correlate with regional and supraregional climatic events. The frequency and timing of palaeohydroclimatic oscillations show strong similarities to records from other sites in Poland and the rest of Europe. We show that various analytical methods, namely, pollen, plant macrofossils, Cladocera, Chironomidae, sedimentological, geochemical and radiocarbon data, can be effective tools for reconstructing past hydroclimatic changes in palaeo-oxbow lakes and investigating the effects of past climate changes on river environments. The high sensitivity of the biota, especially Cladocera, to changes in water level permits the reconstruction of palaeoecological changes, especially flood episodes that occurred in the river valley. In particular, the increase in the proportion of sediment-associated Cladocera and pelagic taxa was closely correlated with floods. Through comparisons with the palaeobiological data, geochemical data allowed the identification of humid phases within the fen associated with a rising groundwater table, direct fluvial activity (floods) and alluvial deposition. We also discuss the limitations of palaeohydrological reconstructions based on these proxies, especially on fossil aquatic invertebrates.

Description: The Holocene, Ahead of Print. 〈br/〉During the Holocene, multiple thermal changes commonly occurred in the northern hemisphere. They are well-recorded in lakes with minimum human impact from the Arctic Circle area. The development of these lakes reflects ecological and climatic changes occurring from the formation of the lakes until present-day times. All environmental fluctuations affect biodiversity and are reflected in the number and composition of species. The goals of this study were to detect the ecological changes in a small Finnish lake using pollen, Cladocera and geochemical analyses. The research area is located within the northern zone of boreal coniferous forest and is the most sparsely populated region of Finland. The lake is located in Kuusamo uplands, E Finland, near the polar circle and over 20 km from the Russian border. Indicators of cold water were found only during the initial stage, after the 8.2 ka event and then the temperature was higher. Trophy was high at the beginning of the lake development and then a significant increase in trophy was found after 2600 BP. The impact of human activity is hardly traceable in Arctic Circle Finland throughout the Holocene Thermal Maximum. During the late-Holocene (after 4200 yr cal. BP), this impact is still weak and, even as late as the 20th century, only a few traces of human activity are recorded. General conclusion is that long-term climatic shift has been the most important factor driving changes in the limnology of Lake Talvilampi.

Description: The Holocene, Ahead of Print. 〈br/〉During the Holocene, multiple thermal changes commonly occurred in the northern hemisphere. They are well-recorded in lakes with minimum human impact from the Arctic Circle area. The development of these lakes reflects ecological and climatic changes occurring from the formation of the lakes until present-day times. All environmental fluctuations affect biodiversity and are reflected in the number and composition of species. The goals of this study were to detect the ecological changes in a small Finnish lake using pollen, Cladocera and geochemical analyses. The research area is located within the northern zone of boreal coniferous forest and is the most sparsely populated region of Finland. The lake is located in Kuusamo uplands, E Finland, near the polar circle and over 20 km from the Russian border. Indicators of cold water were found only during the initial stage, after the 8.2 ka event and then the temperature was higher. Trophy was high at the beginning of the lake development and then a significant increase in trophy was found after 2600 BP. The impact of human activity is hardly traceable in Arctic Circle Finland throughout the Holocene Thermal Maximum. During the late-Holocene (after 4200 yr cal. BP), this impact is still weak and, even as late as the 20th century, only a few traces of human activity are recorded. General conclusion is that long-term climatic shift has been the most important factor driving changes in the limnology of Lake Talvilampi.