- Email: [email protected]
Multi-centennial annually-resolved integrated marine and terrestrial reconstruction of North Atlantic climate
400
Abstracts / Quaternary International 279-280 (2012) 346–461
presented. In the second part of the paper, the role of Eyserheide and neighbouring Magdalenian open-air sites in regional settlement systems is discussed, focusing on several characteristics (location in the landscape, raw material and tool composition, core types, etc.) and arguing against an simple, overall interpretation of these sites as quarry-workshop sites or flint exploitation sites. EARLY HOLOCENE COOLING IN THE SOUTHERN OCEAN CAUSED BY LAURENTIDE ICESHEET DEGLACIATION Hans Renssen. VU University, Netherlands E-mail address: [email protected]
We studied the impact of Laurentide Icesheet (LIS) deglaciation on the early Holocene climate at Southern Hemisphere high latitudes by performing three transient simulations with the LOVECLIM global climate model of the coupled atmosphere-ocean-vegetation system. In these simulations, we quantify separately the effects of the background meltwater fluxes and the changes in topography and surface albedo. In LOVECLIM, the melt-water flux into the North Atlantic produces considerable weakening of the Atlantic Meridional Overturning circulation, associated with absence of Labrador Sea deep convection. As a result, northward heat transport by the Atlantic Ocean is reduced by 28%. North Atlantic Deep Water (NADW) is cooled due to reduced temperatures over the source region of this water mass. In the Southern Ocean, upwelling of this cool NADW leads to reduced surface temperatures (by 1 to 2 C) between 9 and 7 ka BP relative to a simulation without LIS deglaciation. Poleward of the polar front, this advective teleconnection between both hemispheres overwhelms the impact of the ‘classical’ bipolar seesaw mechanism. Our model results provide an explanation for the relatively cool climate between 9 and 7 ka BP suggested by several proxy records from Southern Hemisphere high latitudes. We can hypothesize that similar hemispheric connections existed during earlier terminations. MODELLING SPATIAL AND TEMPORAL VARIATION IN THE HOLOCENE CLIMATIC OPTIMUM ACROSS THE GLOBE Hans Renssen. VU University, Netherlands E-mail address: [email protected]
Proxy records provide evidence for substantial spatial variations in the timing and magnitude of the Holocene climate optimum around the World. We have performed several experiments with the LOVECLIM global atmosphere-ocean-vegetation model to analyze these variations and their dependence on various forcings. In these experiments, we consider the influence of variations in orbital parameters and atmospheric greenhouse gases and the early-Holocene deglaciation of the Laurentide Icesheet (LIS). Considering the LIS deglaciation, we quantified separately the impacts of the background melt-water fluxes and the changes in topography and surface albedo. We present modelled global maps showing the spatial variation in timing (in thousand years BP) of the Holocene climatic optimum and the magnitude of the climatic anomaly. In addition, also the seasonal dependence of the climatic signal is analysed that is mainly related to the nature of the orbital forcing. The model results are compared with proxy-based reconstructions of Holocene temperatures. RE-THINKING TEMPORAL TRENDS OF DEGLACIAL AND HOLOCENE PEATLAND INITIATION INFERRED FROM LARGE COMPILATIONS OF 14C DATES Alberto Reyes. University of Alberta, Canada E-mail address: [email protected]
Chronologies of deglacial and Holocene peatland initiation are typically based on compiled basal peat radiocarbon dates and frequency histograms of binned calibrated age ranges. However, such compilations are problematic because poor quality radiocarbon dates are commonly included and because frequency histograms of binned age ranges introduce chronological artefacts that bias the record of peatland initiation. Using a previously published compilation of 274 basal radiocarbon dates from
Alaska as a case study, we show that nearly half the dates are not suitable for reconstructing peatland initiation, and that the temporal structure of peatland initiation is sensitive to sampling biases and radiocarbon calibration methods. We present revised chronologies of peatland initiation for Alaska and the circumpolar Arctic based on summed probability distributions of calibrated radiocarbon dates. These revised chronologies suggest that northern peatland initiation lagged abrupt increases in atmospheric methane concentration at the start of the Bølling-Allerød interstadial and the end of the Younger Dryas chronozone, thus indicating that northern peatlands were not the primary drivers of the rapid increases in atmospheric methane concentration. Our results show that subtle methodological changes in the synthesis of basal radiocarbon ages lead to substantially different interpretations of temporal trends in peatland initiation, with direct implications for the role of peatlands in the global carbon cycle. ESTIMATING SOUTH GREENLAND ICE SHEET RETREAT DURING PLEISTOCENE INTERGLACIALS USING RADIOGENIC ISOTOPE TRACERS IN MELTWATER AND MARINE CORE SEDIMENTS Alberto Reyes. University of Wisconsin-Madison, United States E-mail address: [email protected]
There is little direct terrestrial field evidence that constrains the extent of the Greenland Ice Sheet during Pleistocene interglacials, particularly beyond the last interglacial, when numerical model simulations of past ice sheet extent diverge widely. Another approach for assessing the magnitude of the Greenland Ice Sheet deglaciations, and its associated contributions to sea-level change, is to exploit the geochemical signatures of terrigenous sediment recovered from marine sediment cores. This approach requires characterization of different bedrock sources that can be compared with sediment core records. We present the results of geochemical analyses of 40 stream sediment samples from across southwest Greenland that provide geochemical end-members from which to assess sediment sources. Distinct differences in the age and crustal evolution of major southern Greenland bedrock terranes are largely mirrored in the Sr-Nd-Pb isotope composition of sediment in meltwater streams draining the ice sheet. Suspended sediment discharged from the southern Greenland Ice Sheet during deglaciation is transported via the Western Boundary Undercurrent and East Greenland Current to the Eirik Drift, where several long (>400 ka), well-dated marine sediment cores have been collected. With the new end-member constraints presented here, we will assess the extent of the southern Greenland Ice Sheet during Marine Isotope Stage 11, when southern Greenland may have been completely deglaciated. MULTI-CENTENNIAL ANNUALLY-RESOLVED INTEGRATED MARINE AND TERRESTRIAL RECONSTRUCTION OF NORTH ATLANTIC CLIMATE David J. Reynolds. Bangor University, United Kingdom E-mail address: [email protected]
The internal growth increment series contained within the shell valves of long-lived marine bivalve molluscs (sclerochronology) constitute climate series analogous to dendrochronology. We present analysis of two independently-constructed chronologies from northwest Scotland, one derived from the tree-ring widths of coastal Scots Pine (Pinus sylvestris L.) and the first sclerochronology constructed from the internal growth increments of the dog cockle, Glycymeris glycymeris L. The two chronologies correlate significantly over the AD 1870-2006 period (r¼0.418, p<0.0005). Spatial correlation models have been used to assess the correlations between each chronology and sea surface (SST) and air temperatures (data from HadISST1 and CRU TS3 gridded timeseries respectively). Significant positive correlations were identified between the Glycymeris series and mean March-August North Atlantic Current (NAC) SSTs over the period AD 1870 – AD 2006 (r ¼ 0.391, p < 0.0005) demonstrating a clear linkage between the NAC and Glycymeris growth increments; there is also a significant positive correlation between the Pinus series and mean June-August east Atlantic SST values (r ¼ 0.288, p < 0.0005). The Glycymeris series correlates significantly with mean
Abstracts / Quaternary International 279-280 (2012) 346–461
November-April north European air temperatures (r ¼ 0.367, p < 0.0005) for the period AD1902-2006. The Pinus chronology is less strongly correlated yet still demonstrates a significant relationship with mean June air temperatures (r ¼ 0.201 p < 0.03). Calibration-verification and scaling approaches were then used to reconstruct sea surface and air temperatures based on composite sea surface and air temperature series constructed using data from HAdISST1 and CRU TS3 datasets respectively for geographical areas identified as statistically significant using spatial correlation techniques. We are therefore able to present the first statistically robust annually resolved marine-terrestrial integrated reconstructions of North Atlantic Climate.
401
respect to the size of the glacier) will result in a significant glacial response (e.g. advance or cessation of retreat). However, rock avalanche debris that arrives on a glacier is likely to be recycled into moraines. This rock avalanche debris has specific sedimentary characteristics and in particular contains agglomerations of angular sediments. These agglomerations are produced under high stress conditions during rock avalanche emplacement and are easily detected through SEM examination. These agglomerations are not present in sediments produced in lower stress environments and are diagnostic of the presence of rock avalanche material in moraines. OSL DATING OF GEOMORPHIC AND NEOTECTONIC CONTEXTS
TWO HUNDRED YEARS OF DUST EMISSION IN WESTERN NORTH AMERICA, 1850-2050
Ed Rhodes. University of California, United States E-mail address: [email protected]
Richard Reynolds. U.S. Geological Survey, United States E-mail address: [email protected]
Contemporary dust emission within North America is important as an indicator of landscape change and ecosystem health, as well as for its effects on human health and snowpack-melt rates. Studies of dust emission in American drylands focus on interactions among geologic processes and settings; vegetation dynamics; hydrology; climate; and human activities. The influences of these interactions are illustrated from dustemission monitoring of shrublands, grasslands with different grazing histories, alluvial settings, wildfire areas, and dry lakes. Dust from some of these settings moves into populated areas and mountain snowpack, raising concerns about air quality and reliable water supplies. The influences of changing climate and land uses on dust emissions can be partly addressed through understanding past responses of dust generation to these factors along with modeling future climate, soil moisture, hydrology, vegetation change, and land use. Sediments in high-altitude lakes adjacent to western deserts reveal enormous influences of human activities on dust composition and flux in western North America during the past 150 years. Long-term vegetation datasets show that many plants, which protect soil from wind erosion, decrease during hot, dry periods, and both field measurements and modeling studies show increased dust production as a result. During the next forty years, a warmer American West with higher rates of evapotranspiration, coupled with continued human disturbance, would likely result in more dust emission relative to recent decades. Increased intensity of precipitation events may also lead to increased emissions. On shorter time frames, we may anticipate future locations of dust emissions from drought-prediction maps. We can also expect dust emission from new sources on the basis of land-management policies. For example, the planned drops in water level at inland Salton Sea will likely lead to more dust, with potential health effects on nearby communities. ROCK AVALANCHES IN GLACIAL ENVIRONMENT: EFFECTS ON GLACIERS AND THE IDENTIFICATION OF THESE DEPOSITS Natalya Reznichenko. University of Canterbury, New Zealand E-mail address: [email protected]
In recent decades there has been recognition of the importance of rock avalanches to glaciers. Specifically rock avalanche debris on a glacier surface changes glacial mass balance by insolating the ice from the atmosphere. Herein, we present the results of investigations into the influence of supraglacially emplaced rock avalanche deposits on glacier behaviour and develop a method to distinguish rock avalanche sediments in glacial moraines. Initial work involved physical experiments on the role of debris in insulating ice from ablation. These studies revealed the importance of the diurnal cycle to the insulation process and highlighted the role of permeability of rock avalanche sediments in controlling the rate of ablation (Reznichenko et al., 2010). Field investigations using Ground Penetrating Radar determined rock avalanche effects on ice thickness on modern rock avalanche deposits on New Zealand glaciers. The results demonstrate that ice platforms build up under the rock avalanche deposits. These results confirm that thick rock avalanche deposits make mass balance more positive by reducing ablation underneath the debris. It is likely that only larger rock avalanche events (with
In Optically Stimulated Luminescence (OSL), the dating signal is reset when mineral grains are exposed to light or heat, and gradually rebuilds during subsequent burial by interaction with ionising radiation. Quartz and feldspar provide useful OSL signals that are reset by only seconds of light exposure. Age estimates ranging from under 1 year to around 200,000 years can be determined for a wide range of sedimentary contexts, including dunes, marine deposits, fluvial and glacial environments. Recent developments provide the framework for low temperature thermochronometric applications on timescales comparable with rapid climate fluctuations. In this presentation, we explore the range of applications from geomorphic and neotectonic contexts using OSL. We examine technical limitations, and provide a framework for overcoming current difficulties experienced in several specific regions and contexts. We will focus on OSL dating applications to glacigenic and fluvial records, along with use of the technique in tectonic and paleoseismic contexts. In many ways, these represent the most challenging environments for OSL. Rapid high energy deposition is associated with incomplete signal zeroing, and mineral characteristics in these environments can make it difficult to derive precise age estimates. We will review a range of strategies that are available to help overcome these limitations. TOWARDS A SYNCHRONOUS GSCHNITZ GLACIER STADIAL (HEINRICH EVENT 1) ACROSS THE ALPS Adriano Ribolini. University of Pisa, Italy E-mail address: [email protected]
One of the most important post LGM cold climatic oscillation is that of the Heinrich Event 1 (HE1), during which a variation in North Atlantic Ocean circulation caused a significant decrease of sea surface temperature that was accompanied by a general increase of sea-ice surface area (Hemming, 2004; McManus, 2004). In the Alps, the HE1 manifested itself as a general readvance of the Alpine glaciers known as the Gschnitz stadial. According to palaeo-glacial models developed from reconstructed Gschnitz glaciers and their ELA, this stadial has been attributed to the severest cold climatic conditions of the Lateglacial period in the Alps, in agreement to the climatic importance of the HE1 (Kerschner et al., 1999). However, and somewhat surprising given its relevant palaeo-climatic implications, this stadial has been relatively understudied in the Alps, and the actual extension of the Alpine Gschnitz glaciers and exact chronology is largely unknown. Here, we present the results of our geomorphological study of the Gesso Valley, in the Maritime Alps (SW Alps), where we have been able to identify, date and reconstruct the extent of the Gschnitz stadial. 10Be cosmogenic dating of Ponte Murato (PM) moraine constrains the first clear glacier readvance experienced by the main Gesso Glacier during the retreat that followed the LGM. The obtained age of 16,820 510 Ka (average) marks the first date of this stadial in the whole Western sector of the Alps. Both this age and the ELA corresponding to the reconstructed Gesso glacier at PM appear to be consistent with other Gschnitz moraines ages and relative ELAs in other sectors of the Alps (van Husen, 2004; IvyOchs et al., 2006). This suggests that the global climatic HE1 had a synchronized and comparable glacial effect throughout the entire
Abstracts / Quaternary International 279-280 (2012) 346–461
presented. In the second part of the paper, the role of Eyserheide and neighbouring Magdalenian open-air sites in regional settlement systems is discussed, focusing on several characteristics (location in the landscape, raw material and tool composition, core types, etc.) and arguing against an simple, overall interpretation of these sites as quarry-workshop sites or flint exploitation sites. EARLY HOLOCENE COOLING IN THE SOUTHERN OCEAN CAUSED BY LAURENTIDE ICESHEET DEGLACIATION Hans Renssen. VU University, Netherlands E-mail address: [email protected]
We studied the impact of Laurentide Icesheet (LIS) deglaciation on the early Holocene climate at Southern Hemisphere high latitudes by performing three transient simulations with the LOVECLIM global climate model of the coupled atmosphere-ocean-vegetation system. In these simulations, we quantify separately the effects of the background meltwater fluxes and the changes in topography and surface albedo. In LOVECLIM, the melt-water flux into the North Atlantic produces considerable weakening of the Atlantic Meridional Overturning circulation, associated with absence of Labrador Sea deep convection. As a result, northward heat transport by the Atlantic Ocean is reduced by 28%. North Atlantic Deep Water (NADW) is cooled due to reduced temperatures over the source region of this water mass. In the Southern Ocean, upwelling of this cool NADW leads to reduced surface temperatures (by 1 to 2 C) between 9 and 7 ka BP relative to a simulation without LIS deglaciation. Poleward of the polar front, this advective teleconnection between both hemispheres overwhelms the impact of the ‘classical’ bipolar seesaw mechanism. Our model results provide an explanation for the relatively cool climate between 9 and 7 ka BP suggested by several proxy records from Southern Hemisphere high latitudes. We can hypothesize that similar hemispheric connections existed during earlier terminations. MODELLING SPATIAL AND TEMPORAL VARIATION IN THE HOLOCENE CLIMATIC OPTIMUM ACROSS THE GLOBE Hans Renssen. VU University, Netherlands E-mail address: [email protected]
Proxy records provide evidence for substantial spatial variations in the timing and magnitude of the Holocene climate optimum around the World. We have performed several experiments with the LOVECLIM global atmosphere-ocean-vegetation model to analyze these variations and their dependence on various forcings. In these experiments, we consider the influence of variations in orbital parameters and atmospheric greenhouse gases and the early-Holocene deglaciation of the Laurentide Icesheet (LIS). Considering the LIS deglaciation, we quantified separately the impacts of the background melt-water fluxes and the changes in topography and surface albedo. We present modelled global maps showing the spatial variation in timing (in thousand years BP) of the Holocene climatic optimum and the magnitude of the climatic anomaly. In addition, also the seasonal dependence of the climatic signal is analysed that is mainly related to the nature of the orbital forcing. The model results are compared with proxy-based reconstructions of Holocene temperatures. RE-THINKING TEMPORAL TRENDS OF DEGLACIAL AND HOLOCENE PEATLAND INITIATION INFERRED FROM LARGE COMPILATIONS OF 14C DATES Alberto Reyes. University of Alberta, Canada E-mail address: [email protected]
Chronologies of deglacial and Holocene peatland initiation are typically based on compiled basal peat radiocarbon dates and frequency histograms of binned calibrated age ranges. However, such compilations are problematic because poor quality radiocarbon dates are commonly included and because frequency histograms of binned age ranges introduce chronological artefacts that bias the record of peatland initiation. Using a previously published compilation of 274 basal radiocarbon dates from
Alaska as a case study, we show that nearly half the dates are not suitable for reconstructing peatland initiation, and that the temporal structure of peatland initiation is sensitive to sampling biases and radiocarbon calibration methods. We present revised chronologies of peatland initiation for Alaska and the circumpolar Arctic based on summed probability distributions of calibrated radiocarbon dates. These revised chronologies suggest that northern peatland initiation lagged abrupt increases in atmospheric methane concentration at the start of the Bølling-Allerød interstadial and the end of the Younger Dryas chronozone, thus indicating that northern peatlands were not the primary drivers of the rapid increases in atmospheric methane concentration. Our results show that subtle methodological changes in the synthesis of basal radiocarbon ages lead to substantially different interpretations of temporal trends in peatland initiation, with direct implications for the role of peatlands in the global carbon cycle. ESTIMATING SOUTH GREENLAND ICE SHEET RETREAT DURING PLEISTOCENE INTERGLACIALS USING RADIOGENIC ISOTOPE TRACERS IN MELTWATER AND MARINE CORE SEDIMENTS Alberto Reyes. University of Wisconsin-Madison, United States E-mail address: [email protected]
There is little direct terrestrial field evidence that constrains the extent of the Greenland Ice Sheet during Pleistocene interglacials, particularly beyond the last interglacial, when numerical model simulations of past ice sheet extent diverge widely. Another approach for assessing the magnitude of the Greenland Ice Sheet deglaciations, and its associated contributions to sea-level change, is to exploit the geochemical signatures of terrigenous sediment recovered from marine sediment cores. This approach requires characterization of different bedrock sources that can be compared with sediment core records. We present the results of geochemical analyses of 40 stream sediment samples from across southwest Greenland that provide geochemical end-members from which to assess sediment sources. Distinct differences in the age and crustal evolution of major southern Greenland bedrock terranes are largely mirrored in the Sr-Nd-Pb isotope composition of sediment in meltwater streams draining the ice sheet. Suspended sediment discharged from the southern Greenland Ice Sheet during deglaciation is transported via the Western Boundary Undercurrent and East Greenland Current to the Eirik Drift, where several long (>400 ka), well-dated marine sediment cores have been collected. With the new end-member constraints presented here, we will assess the extent of the southern Greenland Ice Sheet during Marine Isotope Stage 11, when southern Greenland may have been completely deglaciated. MULTI-CENTENNIAL ANNUALLY-RESOLVED INTEGRATED MARINE AND TERRESTRIAL RECONSTRUCTION OF NORTH ATLANTIC CLIMATE David J. Reynolds. Bangor University, United Kingdom E-mail address: [email protected]
The internal growth increment series contained within the shell valves of long-lived marine bivalve molluscs (sclerochronology) constitute climate series analogous to dendrochronology. We present analysis of two independently-constructed chronologies from northwest Scotland, one derived from the tree-ring widths of coastal Scots Pine (Pinus sylvestris L.) and the first sclerochronology constructed from the internal growth increments of the dog cockle, Glycymeris glycymeris L. The two chronologies correlate significantly over the AD 1870-2006 period (r¼0.418, p<0.0005). Spatial correlation models have been used to assess the correlations between each chronology and sea surface (SST) and air temperatures (data from HadISST1 and CRU TS3 gridded timeseries respectively). Significant positive correlations were identified between the Glycymeris series and mean March-August North Atlantic Current (NAC) SSTs over the period AD 1870 – AD 2006 (r ¼ 0.391, p < 0.0005) demonstrating a clear linkage between the NAC and Glycymeris growth increments; there is also a significant positive correlation between the Pinus series and mean June-August east Atlantic SST values (r ¼ 0.288, p < 0.0005). The Glycymeris series correlates significantly with mean
Abstracts / Quaternary International 279-280 (2012) 346–461
November-April north European air temperatures (r ¼ 0.367, p < 0.0005) for the period AD1902-2006. The Pinus chronology is less strongly correlated yet still demonstrates a significant relationship with mean June air temperatures (r ¼ 0.201 p < 0.03). Calibration-verification and scaling approaches were then used to reconstruct sea surface and air temperatures based on composite sea surface and air temperature series constructed using data from HAdISST1 and CRU TS3 datasets respectively for geographical areas identified as statistically significant using spatial correlation techniques. We are therefore able to present the first statistically robust annually resolved marine-terrestrial integrated reconstructions of North Atlantic Climate.
401
respect to the size of the glacier) will result in a significant glacial response (e.g. advance or cessation of retreat). However, rock avalanche debris that arrives on a glacier is likely to be recycled into moraines. This rock avalanche debris has specific sedimentary characteristics and in particular contains agglomerations of angular sediments. These agglomerations are produced under high stress conditions during rock avalanche emplacement and are easily detected through SEM examination. These agglomerations are not present in sediments produced in lower stress environments and are diagnostic of the presence of rock avalanche material in moraines. OSL DATING OF GEOMORPHIC AND NEOTECTONIC CONTEXTS
TWO HUNDRED YEARS OF DUST EMISSION IN WESTERN NORTH AMERICA, 1850-2050
Ed Rhodes. University of California, United States E-mail address: [email protected]
Richard Reynolds. U.S. Geological Survey, United States E-mail address: [email protected]
Contemporary dust emission within North America is important as an indicator of landscape change and ecosystem health, as well as for its effects on human health and snowpack-melt rates. Studies of dust emission in American drylands focus on interactions among geologic processes and settings; vegetation dynamics; hydrology; climate; and human activities. The influences of these interactions are illustrated from dustemission monitoring of shrublands, grasslands with different grazing histories, alluvial settings, wildfire areas, and dry lakes. Dust from some of these settings moves into populated areas and mountain snowpack, raising concerns about air quality and reliable water supplies. The influences of changing climate and land uses on dust emissions can be partly addressed through understanding past responses of dust generation to these factors along with modeling future climate, soil moisture, hydrology, vegetation change, and land use. Sediments in high-altitude lakes adjacent to western deserts reveal enormous influences of human activities on dust composition and flux in western North America during the past 150 years. Long-term vegetation datasets show that many plants, which protect soil from wind erosion, decrease during hot, dry periods, and both field measurements and modeling studies show increased dust production as a result. During the next forty years, a warmer American West with higher rates of evapotranspiration, coupled with continued human disturbance, would likely result in more dust emission relative to recent decades. Increased intensity of precipitation events may also lead to increased emissions. On shorter time frames, we may anticipate future locations of dust emissions from drought-prediction maps. We can also expect dust emission from new sources on the basis of land-management policies. For example, the planned drops in water level at inland Salton Sea will likely lead to more dust, with potential health effects on nearby communities. ROCK AVALANCHES IN GLACIAL ENVIRONMENT: EFFECTS ON GLACIERS AND THE IDENTIFICATION OF THESE DEPOSITS Natalya Reznichenko. University of Canterbury, New Zealand E-mail address: [email protected]
In recent decades there has been recognition of the importance of rock avalanches to glaciers. Specifically rock avalanche debris on a glacier surface changes glacial mass balance by insolating the ice from the atmosphere. Herein, we present the results of investigations into the influence of supraglacially emplaced rock avalanche deposits on glacier behaviour and develop a method to distinguish rock avalanche sediments in glacial moraines. Initial work involved physical experiments on the role of debris in insulating ice from ablation. These studies revealed the importance of the diurnal cycle to the insulation process and highlighted the role of permeability of rock avalanche sediments in controlling the rate of ablation (Reznichenko et al., 2010). Field investigations using Ground Penetrating Radar determined rock avalanche effects on ice thickness on modern rock avalanche deposits on New Zealand glaciers. The results demonstrate that ice platforms build up under the rock avalanche deposits. These results confirm that thick rock avalanche deposits make mass balance more positive by reducing ablation underneath the debris. It is likely that only larger rock avalanche events (with
In Optically Stimulated Luminescence (OSL), the dating signal is reset when mineral grains are exposed to light or heat, and gradually rebuilds during subsequent burial by interaction with ionising radiation. Quartz and feldspar provide useful OSL signals that are reset by only seconds of light exposure. Age estimates ranging from under 1 year to around 200,000 years can be determined for a wide range of sedimentary contexts, including dunes, marine deposits, fluvial and glacial environments. Recent developments provide the framework for low temperature thermochronometric applications on timescales comparable with rapid climate fluctuations. In this presentation, we explore the range of applications from geomorphic and neotectonic contexts using OSL. We examine technical limitations, and provide a framework for overcoming current difficulties experienced in several specific regions and contexts. We will focus on OSL dating applications to glacigenic and fluvial records, along with use of the technique in tectonic and paleoseismic contexts. In many ways, these represent the most challenging environments for OSL. Rapid high energy deposition is associated with incomplete signal zeroing, and mineral characteristics in these environments can make it difficult to derive precise age estimates. We will review a range of strategies that are available to help overcome these limitations. TOWARDS A SYNCHRONOUS GSCHNITZ GLACIER STADIAL (HEINRICH EVENT 1) ACROSS THE ALPS Adriano Ribolini. University of Pisa, Italy E-mail address: [email protected]
One of the most important post LGM cold climatic oscillation is that of the Heinrich Event 1 (HE1), during which a variation in North Atlantic Ocean circulation caused a significant decrease of sea surface temperature that was accompanied by a general increase of sea-ice surface area (Hemming, 2004; McManus, 2004). In the Alps, the HE1 manifested itself as a general readvance of the Alpine glaciers known as the Gschnitz stadial. According to palaeo-glacial models developed from reconstructed Gschnitz glaciers and their ELA, this stadial has been attributed to the severest cold climatic conditions of the Lateglacial period in the Alps, in agreement to the climatic importance of the HE1 (Kerschner et al., 1999). However, and somewhat surprising given its relevant palaeo-climatic implications, this stadial has been relatively understudied in the Alps, and the actual extension of the Alpine Gschnitz glaciers and exact chronology is largely unknown. Here, we present the results of our geomorphological study of the Gesso Valley, in the Maritime Alps (SW Alps), where we have been able to identify, date and reconstruct the extent of the Gschnitz stadial. 10Be cosmogenic dating of Ponte Murato (PM) moraine constrains the first clear glacier readvance experienced by the main Gesso Glacier during the retreat that followed the LGM. The obtained age of 16,820 510 Ka (average) marks the first date of this stadial in the whole Western sector of the Alps. Both this age and the ELA corresponding to the reconstructed Gesso glacier at PM appear to be consistent with other Gschnitz moraines ages and relative ELAs in other sectors of the Alps (van Husen, 2004; IvyOchs et al., 2006). This suggests that the global climatic HE1 had a synchronized and comparable glacial effect throughout the entire