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Jef Vandenberghe - One of the best experts on this subject based on the ideXlab platform.
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Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last Glacial-Interglacial Cycle
Quaternary International, 2011Co-Authors: Mirjam Vriend, Maarten A. Prins, Jan-pieter Buylaert, Jef VandenbergheAbstract:Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last Glacial-Interglacial Cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2-4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period. © 2010 Elsevier Ltd and INQUA
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Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last Glacial-Interglacial Cycle
Quaternary International, 2010Co-Authors: Mirjam Vriend, Maarten A. Prins, Jan-pieter Buylaert, Jef VandenbergheAbstract:Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last Glacial-Interglacial Cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2–4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period.
Mirjam Vriend - One of the best experts on this subject based on the ideXlab platform.
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Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last Glacial-Interglacial Cycle
Quaternary International, 2011Co-Authors: Mirjam Vriend, Maarten A. Prins, Jan-pieter Buylaert, Jef VandenbergheAbstract:Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last Glacial-Interglacial Cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2-4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period. © 2010 Elsevier Ltd and INQUA
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Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last Glacial-Interglacial Cycle
Quaternary International, 2010Co-Authors: Mirjam Vriend, Maarten A. Prins, Jan-pieter Buylaert, Jef VandenbergheAbstract:Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last Glacial-Interglacial Cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2–4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period.
Sylvie Charbit - One of the best experts on this subject based on the ideXlab platform.
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Interdependence of the growth of the Northern Hemisphere ice sheets during the last glaciation: the role of atmospheric circulation
Climate of the Past, 2014Co-Authors: P. Beghin, Sylvie Charbit, C. Dumas, M. Kageyama, D.m. Roche, C. RitzAbstract:The development of large continental-scale ice sheets over Canada and northern Europe during the last glacial Cycle likely modified the track of stationary waves and influenced the location of growing ice sheets through changes in accumulation and temperature patterns. Although they are often mentioned in the literature, these feedback mechanisms are poorly constrained and have never been studied throughout an entire Glacial-Interglacial Cycle. Using the climate model of intermediate complexity CLIMBER-2 coupled with the 3-D ice-sheet model GRISLI (GRenoble Ice Shelf and Land Ice model), we investigate the impact of stationary waves on the construction of past Northern Hemisphere ice sheets during the past glaciation. The stationary waves are not explicitly computed in the model but their effect on sea-level pressure is parameterized. We tested different parameterizations to study separately the effect of surface temperature (thermal forcing) and topography (orographic forcing) on sea-level pressure, and therefore on atmospheric circulation and ice-sheet surface mass balance. Our model results suggest that the response of ice sheets to thermal and/or orographic forcings is rather different. At the beginning of the glaciation, the orographic effect favors the growth of the Laurentide ice sheet, whereas Fennoscandia appears rather sensitive to the thermal effect. Using the ablation parameter-ization as a trigger to artificially modify the size of one ice sheet, the remote influence of one ice sheet on the other is also studied as a function of the stationary wave parameter-izations. The sensitivity of remote ice sheets is shown to be highly sensitive to the choice of these parameterizations with a larger response when orographic effect is accounted for. Results presented in this study suggest that the various spatial distributions of ice sheets could be partly explained by the feedback mechanisms occurring between ice sheets and atmospheric circulation.
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Investigating the evolution of major Northern Hemisphere ice sheets during the last Glacial-Interglacial Cycle
Climate of the Past Discussions, 2009Co-Authors: S. Bonelli, Masahiko Kageyama, Sylvie Charbit, M.-n. Woillez, G. Ramstein, C. Dumas, A. QuiquetAbstract:Abstract. A 2.5-dimensional climate model of intermediate complexity fully coupled with a 3-dimensional thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last Glacial-Interglacial Cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial Cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.
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Investigating the evolution of major Northern Hemisphere ice sheets during the last Glacial-Interglacial Cycle
Climate of the Past, 2009Co-Authors: S. Bonelli, Masahiko Kageyama, Sylvie Charbit, M.-n. Woillez, G. Ramstein, C. Dumas, A. QuiquetAbstract:A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREM-LINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last Glacial-Interglacial Cycle and to investigate the ice sheets responses to both insolation and atmospheric CO 2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial Cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×10 15 m 3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO 2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North Ameri-can ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ 18 O signals. In contrast, low insolation and low atmospheric CO 2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.
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Numerical reconstructions of the Northern Hemisphere ice sheets through the last Glacial-Interglacial Cycle
Climate of the Past, 2007Co-Authors: Sylvie Charbit, G. Philippon, Vincent Peyaud, Christian Ritz, Masahiko KageyamaAbstract:A 3-dimensional thermo-mechanical ice-sheet model is used to simulate the evolution of the Northern Hemisphere ice sheets through the last Glacial-Interglacial Cycle. The ice-sheet model is forced by the results from six different atmospheric general circulation models (AGCMs). The climate evolution over the period under study is reconstructed using two climate equilibrium simulations performed for the Last Glacial Maximum (LGM) and for the present-day periods and an interpolation through time between these snapshots using a glacial index calibrated against the GRIP d18O record. Since it is driven by the timing of the GRIP signal, the temporal evolution of the ice volume and the ice-covered area is approximately the same from one simulation to the other. However, both ice volume curves and spatial distributions of the ice sheets present some major differences from one AGCM forcing to the other. The origin of these differences, which are most visible in the maximum amplitude of the ice volume, is analyzed in terms of differences in climate forcing. This analysis allows for a partial evaluation of the ability of GCMs to simulate climates consistent with the reconstructions of past ice sheets. Although some models properly reproduce the advance or retreat of ice sheets in some specific areas, none of them is able to reproduce both North American or Eurasian ice complexes in full agreement with observed sea-level variations and geological data. These deviations can be attributed to shortcomings in the climate forcing and in the LGM ice-sheet reconstruction used as a boundary condition for GCM runs, but also to missing processes in the ice-sheet model itself.
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Numerical reconstructions of the Northern Hemisphere ice sheets through the last Glacial-Interglacial Cycle
Climate of the Past Discussions, 2006Co-Authors: Sylvie Charbit, G. Philippon, Vincent Peyaud, Christian Ritz, Masahiko KageyamaAbstract:A 3-dimensional thermo-mechanical ice-sheet model is used to simulate the evolution of the Northern hemisphere ice sheets through the last Glacial-Interglacial Cycle. The ice-sheet model is forced by the results from six different atmospheric general circulation models (AGCMs). Two climate snapshots simulations performed for the last glacial maximum (LGM) and for the present-day periods are interpolated through time using a glacial index calibrated against the GRIP d18O record to reconstruct the climate evolution over the period under study. Since it is driven by the timing of the GRIP signal, the temporal evolution of the ice volume and the ice-covered area is approximately the same from one simulation to the other. However, both ice volume curves and spatial distributions of the ice sheets present some major differences from one AGCM to the other. The origin of these differences, which are most visible in the maximum amplitude of the ice volume, is analyzed in terms of differences in climate forcing. The analysis of the results allows an evaluation of the ability of GCMs to simulate climates consistent with the reconstructions of past ice sheets to be evaluated. Although some models properly reproduce the advance or retreat of ice sheets in some specific areas, none of them is able to reproduce both North American or Eurasian ice complexes in full agreement with observed sea-level variations and geological data. These deviations can be attributed to shortcomings in the climate forcing and in the LGM ice-sheet reconstruction used as a boundary condition for GCM runs, but also to missing processes in the ice-sheet model itself.
Chenglong Deng - One of the best experts on this subject based on the ideXlab platform.
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Paleomagnetic and mineral magnetic investigation of the Baicaoyuan loess-paleosol sequence of the western Chinese Loess Plateau over the last Glacial-Interglacial Cycle and its geological implications
Geochemistry Geophysics Geosystems, 2008Co-Authors: Chenglong DengAbstract:Closely spaced paleomagnetic and mineral magnetic studies were conducted on the Baicaoyuan (BCY) loess-paleosol sequence since the last interglacial in the western Chinese Loess Plateau. The multiproxy records of mineral magnetic parameters clearly indicate loess-paleosol alternations with the fine structure of pedostratigraphy over the last Glacial-Interglacial Cycle. However, the paleomagnetic results reveal the absence of any short-lived geomagnetic excursions in the BCY section. This absence could be interpreted by two alternative mechanisms, such as magnetic overprinting and discontinuous sedimentation. The absence of the Mono Lake and Laschamp excursions in the loess unit L1 is probably due to the viscous overprinting of the remanence carried by coarse-grained magnetite of eolian origin and/or to the episodic nature of loess accumulation during the last glacial period. However, discontinuous sediment accumulation may more probably lead to the absence of the Blake excursion in the last interglacial soil S1 as well as of the Mono Lake and Laschamp excursions in the last glacial loess L1 at the BCY section. Together with previously published paleomagnetic results from other sections over the Loess Plateau, the findings probably further indicate the discontinuous nature of loess accumulation in the western Loess Plateau, where sedimentation of the last interglacial soil may be episodic at the timescale equivalent to the duration of the Blake geomagnetic excursion (4–6 ka), much longer than the timescale for episodic loess sedimentation in the last glacial loess of both the western and eastern Loess Plateau due to the reduced sediment accumulation rate compared to that during the last glacial period. Thus, sediments with relatively high sedimentation rate in some parts of the western Loess Plateau do not consistently guarantee the faithful recording of high-frequency geomagnetic variations.
Richard A. Staff - One of the best experts on this subject based on the ideXlab platform.
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the multiple chronological techniques applied to the lake suigetsu sg06 sediment core central japan
Boreas, 2013Co-Authors: Richard A. Staff, Takeshi Nakagawa, Achim Brauer, Gordon Schlolaut, Michael H Marshall, Henry F Lamb, Christopher Bronk Ramsey, Charlotte Bryant, Fiona Brock, Hiroyuki KitagawaAbstract:The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high-resolution, multi-proxy palaeoenvironmental data across the last glacial/interglacial Cycle. In order to maximize the potential of this archive, a well-constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree-ring) time scale, as derived using radiocarbon data from the uppermost (non-varved) portion of the core. This tie-point, defined as a distinct (flood) marker horizon in SG06 (event layer B-07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).
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sg06 a fully continuous and varved sediment core from lake suigetsu japan stratigraphy and potential for improving the radiocarbon calibration model and understanding of late quaternary climate changes
Quaternary Science Reviews, 2012Co-Authors: Takeshi Nakagawa, Achim Brauer, Katsuya Gotanda, Tsuyoshi Haraguchi, Toru Danhara, Hitoshi Yonenobu, Yusuke Yokoyama, Ryuji Tada, Keiji Takemura, Richard A. StaffAbstract:Abstract The high potential of the varved sediments of Lake Suigetsu, central Japan, to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades. However, this potential has not been fully realised since the only available long sediment core from the lake (‘SG93’) was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections. In the summer of 2006, a new sediment core (‘SG06’) was recovered from the lake. Four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely, without gaps between segments. This new record provides the ability to test existing atmospheric radiocarbon calibration models, as well as to assess the scale of inter-regional leads and lags in palaeoclimatic changes over the last Glacial–Interglacial Cycle. Multi-disciplinary analyses from SG06 are still ongoing, but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released, thereby allowing fully-informed critical evaluation of all subsequent releases of data based on the SG06 record. In this paper, we report key litho-stratigraphic information concerning the SG06 sediment core, highlighting changes in the clarity of annual laminations (varves) with depth, and possible implications for the mechanism of the climate change. We also discuss the potential of the SG06 record to meet the fundamental goals of the INQUA-INTIMATE project.