- Email: [email protected]
Pingo remnants as recorders of Late Weichselian climate and environmental change
Abstracts / Quaternary International 279-280 (2012) 121–232
203
in this area still remain elusive, because most published records do not reach back beyond the last interglacial. In this study, we present three orbitally resolved SST records from the southeast Pacific - from the subtropics (GeoB3388, 25 S 75 W, 1.1Myr), the subantarctic mid-latitudes (GeoB3327, 43 S 80 W, 0.5Myr) and high-latitudes (PS75/034, 54 S 80 W, 0.7Myr) respectively - reconstructed using the alkenone-derived proxy, UK’37. We found larger SST glacial/interglacial (G/I) amplitudes in the subantarctics (6 – 8 C) compared to the subtropics (3 – 4 C), with the most severe glacial occurring in MIS 12 (subtropics) and MIS 10 (subantarctic). There is a mismatch between the SST and benthic d18O in terms of the severity of glacial, where relatively warm SSTs are found (MIS 6 and 16) during times when the benthic d18O indicate severe glacial conditions. The varying glacial severity in SST appears to correlate with the eccentricity curve, suggesting that the forcing might have originated from the low latitudes. At mid- and high-latitudes, there is a progressive warming during several glacial intervals prior to the termination, resulting in an “inverted saw-tooth” pattern (gradual warming and rapid cooling). Interestingly, the high-latitudes SST record exhibits a striking resemblance with the EPICA temperature residual, i.e. the part of the Antarctic temperature variation that cannot be explained by the radiative forcing (Masson-Delmotte et al, 2010), implying that they might be modulated by a common forcing mechanism, and/or there is a substantial marine influence on the temperature evolution in the East Antarctica.
application of amino acid racemisation (ARR) as a geochronological tool has received considerable attention in other biominerals, only a few early studies have attempted to utilize AAR to date coral, attaining mixed results. However, due to recent advancements in preparative and analytical techniques, such as the isolation of an “intra-crystalline” amino acid fraction and the use of reverse-phase high-pressure liquid chromatography (RP-HPLC) with fluorescence detection, the efficacy of AAR dating has increased, and it is therefore appropriate to revisit AAR as a coralbased geochronological tool. Applying these latest methodological improvements, the potential of AAR to date coral over the past four centuries has recently been re-evaluated. In addition, skeletal samples of the scleractinian coral Acropora palmata collected from Rendezvous Hill and Christchurch Ridge (Barbados) were dated using the U-series chronometer to be of MIS 5 age ((80-130 ka) and older. The intra-crystalline protein fraction was then isolated from these samples, and the extent of protein degradation determined using RP-HPLC. We examine whether AAR can be used to distinguish between isotope stages (and substages) beyond MIS 5 where increased U-series open-system behaviour limits this chronometer. Finally, we evaluate the potential benefits and limitations of this alternative “cost-effective” dating technique.
RECONSTRUCTION OF ENVIRONMENTAL CHANGES BASED ON MSCLAND XRF-MEASUREMENTS OF QUATERNARY LACUSTRINE SEDIMENTS FROM BANYOLES LAKE, NORTHERN SPAIN
Wim Hoek. Department of Physical Geography, Faculty of Geosc, Netherlands
Nicole Höbig. RWTH Aachen University, Germany E-mail address: [email protected]
Lacustrine sediments were investigated in order to obtain high quality terrestrial archives for paleoclimatic reconstruction. Spatially focused on the Iberian Peninsula two sediment cores from Lake Banyoles (42 07’37’’ N; 2 45’20’’ E) in Northern Spain were sampled and analyzed. The drill site is located on the eastern shore of the lake, next to the neolithic site “La Draga“. The lake with an extent 1.2 km2 of and a maximum water depth of 46 m is situated 22 km east of Garrotxa volcanic field (or Olot volcanic field), whose explosive ash deposits provide excellent dating possibilities in this archive (last eruption around 11 ka BP). Sediment cores of almost 70 m length were scanned and partly complemented by cores of a second, parallel drilling. Geophysical and geochemical properties were measured using MSCL (Multi-Sensor Core Logger) and XRF (X-Ray Fluorescence). The MSCL detects color, magnetic susceptibility, gamma-density and p-wave velocity. The correlation of corelog data between the two cores was achieved by the CoreWall visualization system. Additionally, mineral composition of potential tephra layers was analyzed by smear slides to evaluate applicability for dating methods (e.g. U/Th-dating). The macroscopic core description shows high variability in sediment composition from coarse-grained beach and fine-grained lacustrine facies. Core logging parameters also reveal these changes. The non-destructive dataset will be correlated to other paleoclimate archives such as ice cores or marine deposits as well as the close-by travertines at Arbreda Cave, in order to establish a robust chronology for the Paleolithic-Neolithic climate changes. ESTABLISHING THE RELATIVE CHRONOLOGY OF RAISED REEF TERRACES ON BARBADOS USING AMINO ACID RACEMISATION IN FOSSILIZED ACROPORA PALMATA CORALS
THE ALLERØD-YOUNGER DRYAS TRANSITION IN LAKE SEDIMENTS FROM THE NETHERLANDS
E-mail address: [email protected]
A hypothesised extra-terrestrial impact over North America has been proposed as the trigger for the onset of the global Younger Dryas event. One of the lines of evidence for this impact is the presence of increased values of Iridium as reported from buried soil horizons (palaeosols) in North America and Belgium. The top of the palaeosol, or so-called Usselo layer has been recognised and dated frequently in the Netherlands and marks the transition from Allerød to Younger Dryas. However, soil horizons are often characterised by low sedimentation rates, leaching, and accumulation processes. Until the moment of burial, a soil surface is constantly exposed to cosmic radiation; therefore increased values of Iridium in a soil are not unlikely. If these elevated concentrations in Iridium were caused by an extra-terrestrial impact, the obvious place to look for truly increased values would not be a soil horizon, but a continuously accumulating system such as an isolated lake basin. We analysed two records obtained from selected lake deposits from the southern and northern Netherlands. Both lake sequences comprise the Allerød-Younger Dryas Transition and show no indications of hiatuses or oxidation caused by periods of low lake level during the transition. The transition is marked by clear changes in lithology and vegetation composition as indicated by palynology. This lithological change and the change in vegetation, which is characteristic for the onset of the Younger Dryas have both been 14C-dated at several locations in the Netherlands and yield an average age of 10,900 BP. Further age control was provided by the presence of both Laacher See Tephra and Vedde Ash in one of the sequences. Consecutive samples over the transition were analysed for the occurrence of Iridium and other elements. No elevated values of Iridium could be found and the values of the other elements measured indicated no disturbances in accumulation rates. PINGO REMNANTS AS RECORDERS OF LATE WEICHSELIAN CLIMATE AND ENVIRONMENTAL CHANGE
Annabel Hodge. Bristol University, United Kingdom
Wim Hoek. Department of Physical Geography, Faculty of Geosc, Netherlands
E-mail address: [email protected]
E-mail address: [email protected]
An accurate record of past sea-level provides a proxy for the timing and extent of Quaternary climate variability. As reef-building corals grow only in shallow water, absolute dating of fossilised specimens can provide a direct palaeo sea-level marker. Uranium-series (U-series) dating is commonly used to assign an absolute age to the fossil coral. However, as with all dating methods, U-series has its limitations; the procedure is relatively expensive and open-system remobilization of the U-series isotopes can compromise the reliability of the dates acquired. While the
Pingos are known from present day permafrost regions in Alaska, Canada and Siberia and occur under conditions with sufficient supply of groundwater, leading to the formation of ice lenses. In the Netherlands, the remains of hundreds of pingos have been recognised over the last decades. These pingos presumably originated as a result of hydrostatic pressure, under conditions of discontinuous permafrost during the Weichselian Pleniglacial. As temperature rose at the onset of the Lateglacial Interstadial (GI-1, round ca. 12,500 14C BP or 14,700 cal BP), permafrost most likely
204
Abstracts / Quaternary International 279-280 (2012) 121–232
started to disappear from that time onward resulting in the development of pingo remnants – isolated depressions with a diameter of 50 to 300 meters, either with or without a rampart. The presence of these pingo remnants vary in depth between 5 meters in the southern Netherlands to 20 meters in the northern Netherlands, indicating a minimum thickness of permafrost in the order of these values. Melting of the permafrost layer that was several meters thick presumably lasted several hundreds of years. Implications for the disappearance of permafrost during the Lateglacial in the Netherlands are given by the basal organic infilling of pingo remnants, dated to begin between 12,500 and 11,900 14C BP. The fills of the pingo remnants in the Netherlands form a unique record of environmental change since the last deglaciation containing for instance pollen, aeolian sand, chironomids, and tephra. A number of these depressions are filled with calcareous gyttja, implying that hydrostatic pressure and groundwater exfiltration continued after the decay of the ice-body. Others show distinct water level fluctuations and can be used to reconstruct changes in effective precipitation. The fills of clusters of pingo remnants that are situated closely together can be used to estimate local variation within and between basins. GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL ANALYSES OF POSSIBLY HUMAN-INDUCED LATE-HOLOCENE VALLEY FILLS IN THE CENTRAL APENNINES, ITALY Philipp Hoelzmann. Freie Universität Berlin, Germany E-mail address: [email protected]
We report on geoarchaeological, geomorphological and sedimentological investigations on the late-Holocene landscape evolution in several smallscaled catchments in the Sabinian Mountains, Italy. Basic morphometric analyses and automated landscape classifications were generated on the basis of digital elevation models and resulted in catchment-area specific morphometric characteristics such as asymmetric valleys, levelled plains, tectonic structures etc. In several subcatchments of the Turano River (Lazio, Central Apennines) up to 10 m thick alluvial valley fills were sampled continuously with a closed drilling system. Based on 14C dating sediment formation occurred mainly during the last 2000 years. Within this period phases of accumulation (fluvial and alluvial sedimentation) alternated with erosion (fluvial incision of terraces). The trigger-pulses have not been identified so far. Into consideration come:- Tectonic movements: such as time-transgressive tectonic uplift or subsidence and/or event controlled tectonics (e.g. earthquakes). - Climate change: alluvial phases in the Central Apennines correspond to glacier advances of the Grand-Sasso-Massif which correlate with intensified flood events of the Tiber and its delta propagation. Catastrophic flood events were also proven for various Mediterranean rivers between 2100 to 1600 cal a BP. - Human influence: anthropogenic alterations of the landsurface conditions (e.g. land-use, forest clearance) within the catchments may have led to intensified bed-load with sediment accumulation. This line of argument was proven for the northward situated supra-catchment of the Arno river since the Middle Ages. The evaluation of historical sources in combination with further geomorphological, stratigraphical, sedimentological and palynological studies serve as an approach to understand the timing and the involved processes that formed these young sediments. INTERGLACIAL GEOMORPHIC DYNAMICS DURING THE QUATERNARY: DOES GLACIAL EROSION DOMINATES INTERGLACIAL ADJUSTMENT? Thomas Hoffmann. University of Bonn, Germany E-mail address: [email protected]
High mountains are generally sculptured by glacial erosion that resulted in the formation of glacial cirques and U-shaped valleys with strongly oversteepened hillslopes and widespread glacial deposits. The abundance of glacial (erosion and depositional) landforms in high mountains has been attributed to very effective glacial erosion and sediment transfer. Furthermore, it has been argued that geomorphic activity remains increased after the retreat of valley glaciers at the transition between glacial and interglacial periods. Thus, geologists and geomorphologist
generally tend to look at glaciers as geomorphic agents that strongly enhance erosion and sediment fluxes. An important but overlooked aspect of glacial erosion is the affect of glacial erosion on the decoupling of headwater basins from main river systems. Strong glacial erosion results in flat valley bottoms and glacial over-deepenings, with reduced transport capacities of the interglacial rivers draining formerly glaciated headwaters. In this paper, we will present evidences of increased erosion but decreased sediment yields in glacial headwaters, which results from the transition of glacial to peri-/paraglacial process regimes. These evidences are derived from geomorphomteric analysis, numerical sediment flux models and sediment budget approaches of headwater basins with different degree of glacial erosion in the Kananaskis Valley (Canadian Rocky Mountains). Through the comparison of the duration and erosion rates of glacial and interglacial periods during the Quaternary, we will discuss the wider implications of the results with respect to the landform evolution of glaciated mountains during the Quaternary. WHEN WAS THE TAUPO ERUPTION? Alan G. Hogg. Waikato Radiocarbon Dating Laboratory, University, New Zealand E-mail address: [email protected]
Taupo volcano in northern New Zealand is the world's most frequently active and productive rhyolite volcano. The latest eruption was the extremely powerful Taupo eruption. It involved 5 phases of plinian/ultraplinian and phreatomagmatic fall activity; the climactic 6th phase generated violent emplacement of nonwelded (loose) Taupo ignimbrite from hot pyroclastic density currents moving 200-300 m/s radially away from vent for w80 km. The total bulk volume of eruptives is w105 km3. Taupo deposits provide a widespread marker bed of importance to paleoenvironmental studies because it pre-dates the earliest arrival of humans in NZ in wAD 1280. The Taupo eruption occurred in (austral) late summer-early autumn on the basis of fruit and seeds, and a lack of latewood on the final growth rings on logs, preserved in a buried forest at Pureora. The eruption year has been estimated from a range of evidence including calibration of multiple 14C dates from carbonized wood, leaves or seeds; putative, disputed historical observations of sunsets in Rome and China (wAD 186); an acid peak in Greenland ice-cores (AD 181 2); and wiggle-match dating. We report here a new 14C-wiggle match date for the eruption of AD 232 5 (95%). It was obtained by high-precision dating decadal blocks from a log (bark intact) of celery pine (Phyllocladus trichomanoides) killed by Taupo ignimbrite and preserved at Pureora. The 14C ages were wigglematched against two new calibration curves, one on NZ kauri and the other on Tasmanian huon pine. Both curves generated statistically-identical dates. A previous 14C-wiggle match date for the Taupo eruption of AD 232 15 by Sparks et al. (1995; revised to AD 233 13 in 2008), was fortuitously correct because these authors used Northern Hemisphere calibration curves without correcting for interhemispheric offset (assumed erroneously to be zero years), and because age assays were systematically too young by the same value as the offset (w40 years). ARE THE CHANGES OBSERVED IN THE THERMAL REGIME AND THE CHEMICAL PROPERTIES OF A HIGH ARCTIC LAKE RELATED TO PERMAFROST MELTING IN THE CATCHMENT? Trine M. Holm. University of Innsbruck, Austria E-mail address: [email protected]
High arctic lakes are highly responsive to climate change as they are strongly affected by changes in both the catchment (snow cover duration, permafrost melting), and in lake processes (thermal regimes, limnochemistry). In addition these remote ecosystems are currently altered by anthropogenic impacts, especially long range transport of nitrogen, which functions as nutrient in these systems. In order to study climate and anthropogenic impacts in the High Arctic, we obtained short and long sediment records from Kongressvatn, a lake located in Spitzbergen within a karst system. Limnochemical properties had been measured in the 1960ies and have been monitored since summer 2005. Over the last decades we observed distinct changes in the chemical properties, and the
203
in this area still remain elusive, because most published records do not reach back beyond the last interglacial. In this study, we present three orbitally resolved SST records from the southeast Pacific - from the subtropics (GeoB3388, 25 S 75 W, 1.1Myr), the subantarctic mid-latitudes (GeoB3327, 43 S 80 W, 0.5Myr) and high-latitudes (PS75/034, 54 S 80 W, 0.7Myr) respectively - reconstructed using the alkenone-derived proxy, UK’37. We found larger SST glacial/interglacial (G/I) amplitudes in the subantarctics (6 – 8 C) compared to the subtropics (3 – 4 C), with the most severe glacial occurring in MIS 12 (subtropics) and MIS 10 (subantarctic). There is a mismatch between the SST and benthic d18O in terms of the severity of glacial, where relatively warm SSTs are found (MIS 6 and 16) during times when the benthic d18O indicate severe glacial conditions. The varying glacial severity in SST appears to correlate with the eccentricity curve, suggesting that the forcing might have originated from the low latitudes. At mid- and high-latitudes, there is a progressive warming during several glacial intervals prior to the termination, resulting in an “inverted saw-tooth” pattern (gradual warming and rapid cooling). Interestingly, the high-latitudes SST record exhibits a striking resemblance with the EPICA temperature residual, i.e. the part of the Antarctic temperature variation that cannot be explained by the radiative forcing (Masson-Delmotte et al, 2010), implying that they might be modulated by a common forcing mechanism, and/or there is a substantial marine influence on the temperature evolution in the East Antarctica.
application of amino acid racemisation (ARR) as a geochronological tool has received considerable attention in other biominerals, only a few early studies have attempted to utilize AAR to date coral, attaining mixed results. However, due to recent advancements in preparative and analytical techniques, such as the isolation of an “intra-crystalline” amino acid fraction and the use of reverse-phase high-pressure liquid chromatography (RP-HPLC) with fluorescence detection, the efficacy of AAR dating has increased, and it is therefore appropriate to revisit AAR as a coralbased geochronological tool. Applying these latest methodological improvements, the potential of AAR to date coral over the past four centuries has recently been re-evaluated. In addition, skeletal samples of the scleractinian coral Acropora palmata collected from Rendezvous Hill and Christchurch Ridge (Barbados) were dated using the U-series chronometer to be of MIS 5 age ((80-130 ka) and older. The intra-crystalline protein fraction was then isolated from these samples, and the extent of protein degradation determined using RP-HPLC. We examine whether AAR can be used to distinguish between isotope stages (and substages) beyond MIS 5 where increased U-series open-system behaviour limits this chronometer. Finally, we evaluate the potential benefits and limitations of this alternative “cost-effective” dating technique.
RECONSTRUCTION OF ENVIRONMENTAL CHANGES BASED ON MSCLAND XRF-MEASUREMENTS OF QUATERNARY LACUSTRINE SEDIMENTS FROM BANYOLES LAKE, NORTHERN SPAIN
Wim Hoek. Department of Physical Geography, Faculty of Geosc, Netherlands
Nicole Höbig. RWTH Aachen University, Germany E-mail address: [email protected]
Lacustrine sediments were investigated in order to obtain high quality terrestrial archives for paleoclimatic reconstruction. Spatially focused on the Iberian Peninsula two sediment cores from Lake Banyoles (42 07’37’’ N; 2 45’20’’ E) in Northern Spain were sampled and analyzed. The drill site is located on the eastern shore of the lake, next to the neolithic site “La Draga“. The lake with an extent 1.2 km2 of and a maximum water depth of 46 m is situated 22 km east of Garrotxa volcanic field (or Olot volcanic field), whose explosive ash deposits provide excellent dating possibilities in this archive (last eruption around 11 ka BP). Sediment cores of almost 70 m length were scanned and partly complemented by cores of a second, parallel drilling. Geophysical and geochemical properties were measured using MSCL (Multi-Sensor Core Logger) and XRF (X-Ray Fluorescence). The MSCL detects color, magnetic susceptibility, gamma-density and p-wave velocity. The correlation of corelog data between the two cores was achieved by the CoreWall visualization system. Additionally, mineral composition of potential tephra layers was analyzed by smear slides to evaluate applicability for dating methods (e.g. U/Th-dating). The macroscopic core description shows high variability in sediment composition from coarse-grained beach and fine-grained lacustrine facies. Core logging parameters also reveal these changes. The non-destructive dataset will be correlated to other paleoclimate archives such as ice cores or marine deposits as well as the close-by travertines at Arbreda Cave, in order to establish a robust chronology for the Paleolithic-Neolithic climate changes. ESTABLISHING THE RELATIVE CHRONOLOGY OF RAISED REEF TERRACES ON BARBADOS USING AMINO ACID RACEMISATION IN FOSSILIZED ACROPORA PALMATA CORALS
THE ALLERØD-YOUNGER DRYAS TRANSITION IN LAKE SEDIMENTS FROM THE NETHERLANDS
E-mail address: [email protected]
A hypothesised extra-terrestrial impact over North America has been proposed as the trigger for the onset of the global Younger Dryas event. One of the lines of evidence for this impact is the presence of increased values of Iridium as reported from buried soil horizons (palaeosols) in North America and Belgium. The top of the palaeosol, or so-called Usselo layer has been recognised and dated frequently in the Netherlands and marks the transition from Allerød to Younger Dryas. However, soil horizons are often characterised by low sedimentation rates, leaching, and accumulation processes. Until the moment of burial, a soil surface is constantly exposed to cosmic radiation; therefore increased values of Iridium in a soil are not unlikely. If these elevated concentrations in Iridium were caused by an extra-terrestrial impact, the obvious place to look for truly increased values would not be a soil horizon, but a continuously accumulating system such as an isolated lake basin. We analysed two records obtained from selected lake deposits from the southern and northern Netherlands. Both lake sequences comprise the Allerød-Younger Dryas Transition and show no indications of hiatuses or oxidation caused by periods of low lake level during the transition. The transition is marked by clear changes in lithology and vegetation composition as indicated by palynology. This lithological change and the change in vegetation, which is characteristic for the onset of the Younger Dryas have both been 14C-dated at several locations in the Netherlands and yield an average age of 10,900 BP. Further age control was provided by the presence of both Laacher See Tephra and Vedde Ash in one of the sequences. Consecutive samples over the transition were analysed for the occurrence of Iridium and other elements. No elevated values of Iridium could be found and the values of the other elements measured indicated no disturbances in accumulation rates. PINGO REMNANTS AS RECORDERS OF LATE WEICHSELIAN CLIMATE AND ENVIRONMENTAL CHANGE
Annabel Hodge. Bristol University, United Kingdom
Wim Hoek. Department of Physical Geography, Faculty of Geosc, Netherlands
E-mail address: [email protected]
E-mail address: [email protected]
An accurate record of past sea-level provides a proxy for the timing and extent of Quaternary climate variability. As reef-building corals grow only in shallow water, absolute dating of fossilised specimens can provide a direct palaeo sea-level marker. Uranium-series (U-series) dating is commonly used to assign an absolute age to the fossil coral. However, as with all dating methods, U-series has its limitations; the procedure is relatively expensive and open-system remobilization of the U-series isotopes can compromise the reliability of the dates acquired. While the
Pingos are known from present day permafrost regions in Alaska, Canada and Siberia and occur under conditions with sufficient supply of groundwater, leading to the formation of ice lenses. In the Netherlands, the remains of hundreds of pingos have been recognised over the last decades. These pingos presumably originated as a result of hydrostatic pressure, under conditions of discontinuous permafrost during the Weichselian Pleniglacial. As temperature rose at the onset of the Lateglacial Interstadial (GI-1, round ca. 12,500 14C BP or 14,700 cal BP), permafrost most likely
204
Abstracts / Quaternary International 279-280 (2012) 121–232
started to disappear from that time onward resulting in the development of pingo remnants – isolated depressions with a diameter of 50 to 300 meters, either with or without a rampart. The presence of these pingo remnants vary in depth between 5 meters in the southern Netherlands to 20 meters in the northern Netherlands, indicating a minimum thickness of permafrost in the order of these values. Melting of the permafrost layer that was several meters thick presumably lasted several hundreds of years. Implications for the disappearance of permafrost during the Lateglacial in the Netherlands are given by the basal organic infilling of pingo remnants, dated to begin between 12,500 and 11,900 14C BP. The fills of the pingo remnants in the Netherlands form a unique record of environmental change since the last deglaciation containing for instance pollen, aeolian sand, chironomids, and tephra. A number of these depressions are filled with calcareous gyttja, implying that hydrostatic pressure and groundwater exfiltration continued after the decay of the ice-body. Others show distinct water level fluctuations and can be used to reconstruct changes in effective precipitation. The fills of clusters of pingo remnants that are situated closely together can be used to estimate local variation within and between basins. GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL ANALYSES OF POSSIBLY HUMAN-INDUCED LATE-HOLOCENE VALLEY FILLS IN THE CENTRAL APENNINES, ITALY Philipp Hoelzmann. Freie Universität Berlin, Germany E-mail address: [email protected]
We report on geoarchaeological, geomorphological and sedimentological investigations on the late-Holocene landscape evolution in several smallscaled catchments in the Sabinian Mountains, Italy. Basic morphometric analyses and automated landscape classifications were generated on the basis of digital elevation models and resulted in catchment-area specific morphometric characteristics such as asymmetric valleys, levelled plains, tectonic structures etc. In several subcatchments of the Turano River (Lazio, Central Apennines) up to 10 m thick alluvial valley fills were sampled continuously with a closed drilling system. Based on 14C dating sediment formation occurred mainly during the last 2000 years. Within this period phases of accumulation (fluvial and alluvial sedimentation) alternated with erosion (fluvial incision of terraces). The trigger-pulses have not been identified so far. Into consideration come:- Tectonic movements: such as time-transgressive tectonic uplift or subsidence and/or event controlled tectonics (e.g. earthquakes). - Climate change: alluvial phases in the Central Apennines correspond to glacier advances of the Grand-Sasso-Massif which correlate with intensified flood events of the Tiber and its delta propagation. Catastrophic flood events were also proven for various Mediterranean rivers between 2100 to 1600 cal a BP. - Human influence: anthropogenic alterations of the landsurface conditions (e.g. land-use, forest clearance) within the catchments may have led to intensified bed-load with sediment accumulation. This line of argument was proven for the northward situated supra-catchment of the Arno river since the Middle Ages. The evaluation of historical sources in combination with further geomorphological, stratigraphical, sedimentological and palynological studies serve as an approach to understand the timing and the involved processes that formed these young sediments. INTERGLACIAL GEOMORPHIC DYNAMICS DURING THE QUATERNARY: DOES GLACIAL EROSION DOMINATES INTERGLACIAL ADJUSTMENT? Thomas Hoffmann. University of Bonn, Germany E-mail address: [email protected]
High mountains are generally sculptured by glacial erosion that resulted in the formation of glacial cirques and U-shaped valleys with strongly oversteepened hillslopes and widespread glacial deposits. The abundance of glacial (erosion and depositional) landforms in high mountains has been attributed to very effective glacial erosion and sediment transfer. Furthermore, it has been argued that geomorphic activity remains increased after the retreat of valley glaciers at the transition between glacial and interglacial periods. Thus, geologists and geomorphologist
generally tend to look at glaciers as geomorphic agents that strongly enhance erosion and sediment fluxes. An important but overlooked aspect of glacial erosion is the affect of glacial erosion on the decoupling of headwater basins from main river systems. Strong glacial erosion results in flat valley bottoms and glacial over-deepenings, with reduced transport capacities of the interglacial rivers draining formerly glaciated headwaters. In this paper, we will present evidences of increased erosion but decreased sediment yields in glacial headwaters, which results from the transition of glacial to peri-/paraglacial process regimes. These evidences are derived from geomorphomteric analysis, numerical sediment flux models and sediment budget approaches of headwater basins with different degree of glacial erosion in the Kananaskis Valley (Canadian Rocky Mountains). Through the comparison of the duration and erosion rates of glacial and interglacial periods during the Quaternary, we will discuss the wider implications of the results with respect to the landform evolution of glaciated mountains during the Quaternary. WHEN WAS THE TAUPO ERUPTION? Alan G. Hogg. Waikato Radiocarbon Dating Laboratory, University, New Zealand E-mail address: [email protected]
Taupo volcano in northern New Zealand is the world's most frequently active and productive rhyolite volcano. The latest eruption was the extremely powerful Taupo eruption. It involved 5 phases of plinian/ultraplinian and phreatomagmatic fall activity; the climactic 6th phase generated violent emplacement of nonwelded (loose) Taupo ignimbrite from hot pyroclastic density currents moving 200-300 m/s radially away from vent for w80 km. The total bulk volume of eruptives is w105 km3. Taupo deposits provide a widespread marker bed of importance to paleoenvironmental studies because it pre-dates the earliest arrival of humans in NZ in wAD 1280. The Taupo eruption occurred in (austral) late summer-early autumn on the basis of fruit and seeds, and a lack of latewood on the final growth rings on logs, preserved in a buried forest at Pureora. The eruption year has been estimated from a range of evidence including calibration of multiple 14C dates from carbonized wood, leaves or seeds; putative, disputed historical observations of sunsets in Rome and China (wAD 186); an acid peak in Greenland ice-cores (AD 181 2); and wiggle-match dating. We report here a new 14C-wiggle match date for the eruption of AD 232 5 (95%). It was obtained by high-precision dating decadal blocks from a log (bark intact) of celery pine (Phyllocladus trichomanoides) killed by Taupo ignimbrite and preserved at Pureora. The 14C ages were wigglematched against two new calibration curves, one on NZ kauri and the other on Tasmanian huon pine. Both curves generated statistically-identical dates. A previous 14C-wiggle match date for the Taupo eruption of AD 232 15 by Sparks et al. (1995; revised to AD 233 13 in 2008), was fortuitously correct because these authors used Northern Hemisphere calibration curves without correcting for interhemispheric offset (assumed erroneously to be zero years), and because age assays were systematically too young by the same value as the offset (w40 years). ARE THE CHANGES OBSERVED IN THE THERMAL REGIME AND THE CHEMICAL PROPERTIES OF A HIGH ARCTIC LAKE RELATED TO PERMAFROST MELTING IN THE CATCHMENT? Trine M. Holm. University of Innsbruck, Austria E-mail address: [email protected]
High arctic lakes are highly responsive to climate change as they are strongly affected by changes in both the catchment (snow cover duration, permafrost melting), and in lake processes (thermal regimes, limnochemistry). In addition these remote ecosystems are currently altered by anthropogenic impacts, especially long range transport of nitrogen, which functions as nutrient in these systems. In order to study climate and anthropogenic impacts in the High Arctic, we obtained short and long sediment records from Kongressvatn, a lake located in Spitzbergen within a karst system. Limnochemical properties had been measured in the 1960ies and have been monitored since summer 2005. Over the last decades we observed distinct changes in the chemical properties, and the