Search

Your search keyword '"PAST 800,000 YEARS"' showing total 6 results
Start Over Descriptor "PAST 800,000 YEARS" Database OpenAIRE
6 results on '"PAST 800,000 YEARS"'

1. Timing and nature of AMOC recovery across Termination 2 and magnitude of deglacial CO2 change

Author

Deaney, Emily L, Barker, Stephen, Van de Flierdt, Tina, and Natural Environment Research Council (NERC)

Subjects
GC, Science & Technology, PAST 800,000 YEARS, OCEAN CIRCULATION CHANGES, Science, PENULTIMATE DEGLACIATION, Article, Multidisciplinary Sciences, LAST INTERGLACIAL PERIOD, BIPOLAR SEESAW, GLACIAL CYCLES, CLIMATE VARIABILITY, MD Multidisciplinary, Science & Technology - Other Topics, OVERTURNING CIRCULATION, ATMOSPHERIC CO2, DEEP-SEA
Abstract

Large amplitude variations in atmospheric CO2 were associated with glacial terminations of the Late Pleistocene. Here we provide multiple lines of evidence suggesting that the ∼20 p.p.m.v. overshoot in CO2 at the end of Termination 2 (T2) ∼129 ka was associated with an abrupt (≤400 year) deepening of Atlantic Meridional Overturning Circulation (AMOC). In contrast to Termination 1 (T1), which was interrupted by the Bølling-Allerød (B-A), AMOC recovery did not occur until the very end of T2, and was characterized by pronounced formation of deep waters in the NW Atlantic. Considering the variable influences of ocean circulation change on atmospheric CO2, we suggest that the net change in CO2 across the last 2 terminations was approximately equal if the transient effects of deglacial oscillations in ocean circulation are taken into account., Differences in the sequence and timing of ocean circulation changes across glacial terminations could affect the magnitude of deglacial atmospheric CO2 rise. Here, the authors argue that late ocean circulation recovery during the penultimate deglaciation (T2) led to a larger rise in CO2 compared with T1.

Published
2017

2. Ultra-high resolution pollen record from the northern Andes reveals rapid shifts in montane climates within the last two glacial cycles

Author

W. Westerhoff, L. Contreras, J. van der Plicht, Henry Hooghiemstra, A. Betancourt, M. Vriend, Martin Ziegler, Juan Carlos Berrio, Sergio Gaviria, D. Ortega, O. Rangel, S. L. Weber, E. Tuenter, M. van der Linden, Catalina Giraldo, N. González, B. van Geel, T. van der Hammen, Jef Vandenberghe, J. H. F. Jansen, Gustavo Sarmiento, M.H.M. Groot, Martin Konert, R. G. Bogotá, Lucas Joost Lourens, Isotope Research, Paleoecology and Landscape Ecology (IBED, FNWI), Earth and Climate, and Climate Change and Landscape Dynamics

Subjects
Marine isotope stage, 010506 paleontology, Arboreal locomotion, 010504 meteorology & atmospheric sciences, PAST 800,000 YEARS, Aardwetenschappen, Stratigraphy, lcsh:Environmental protection, TIME-SERIES, INTERMEDIATE COMPLEXITY, Forcing (mathematics), medicine.disease_cause, GREENLAND ICE, 01 natural sciences, Isotopes of oxygen, 000 YEARS, lcsh:Environmental pollution, Pollen, GRIP ICE CORE, medicine, lcsh:TD169-171.8, Glacial period, lcsh:Environmental sciences, 0105 earth and related environmental sciences, lcsh:GE1-350, Global and Planetary Change, OCEAN-ATMOSPHERE SYSTEM, PAST 800, Elevation, Paleontology, Vegetation, 15. Life on land, MILLENNIAL-SCALE, TEMPERATURE-VARIATIONS, 13. Climate action, Climatology, EASTERN-CORDILLERA, lcsh:TD172-193.5, TRANSIENT SIMULATION, Geology
Abstract

Here we developed a composite pollen-based record of altitudinal vegetation changes from Lake Fúquene (5° N) in Colombia at 2540 m elevation. We quantitatively calibrated Arboreal Pollen percentages (AP%) into mean annual temperature (MAT) changes with an unprecedented ~60-year resolution over the past 284 000 years. An age model for the AP% record was constructed using frequency analysis in the depth domain and tuning of the distinct obliquity-related variations to the latest marine oxygen isotope stacked record. The reconstructed MAT record largely concurs with the ~100 and 41-kyr (obliquity) paced glacial cycles and is superimposed by extreme changes of up to 7 to 10° Celsius within a few hundred years at the major glacial terminations and during marine isotope stage 3, suggesting an unprecedented North Atlantic – equatorial link. Using intermediate complexity transient climate modelling experiments, we demonstrate that ice volume and greenhouse gasses are the major forcing agents causing the orbital-related MAT changes, while direct precession-induced insolation changes had no significant impact on the high mountain vegetation during the last two glacial cycles.

Published
2011
Full Text
View/download PDF

3. Exposure dating outwash gravels to determine the age of the greatest Patagonian glaciations

Author

Tibor J. Dunai, Sheng Xu, Nicholas R. J. Hulton, and Andrew S. Hein

Subjects
MAXIMUM, geography, geography.geographical_feature_category, Early Pleistocene, PAST 800,000 YEARS, SOUTHERNMOST SOUTH-AMERICA, Climate change, Geology, ARGENTINE PATAGONIA, Paleontology, Moraine, CHRONOLOGY, Outwash plain, Glacial period, Ice sheet, Quaternary, PRODUCTION-RATES, Geomorphology, Chronology
Abstract

The relict moraines in Argentine Patagonia archive major expansions of the Patagonian Ice Sheet throughout the Quaternary, and are one of the few terrestrial climate proxies in the middle latitudes of the Southern Hemisphere that extends beyond the last glacial cycle. Determining their individual ages has proved challenging but has important implications for our understanding of terrestrial climate change in southern South America over the duration of the Quaternary. Here, for the first time, we demonstrate that sediment on outwash terraces can be directly dated to determine the timing of early-middle Quaternary glacial advances in southern South America. Cosmogenic Be-10 and Al-26 surface exposure ages were obtained from outwash gravels associated with two of the oldest glacial sequences in the Lago Pueyrredon valley (47.5 degrees S), Argentina. The outermost Gorra de Poivre glacial sequence marks the greatest extent of the Patagonian Ice Sheet. A cobble from this surface gives Be-10 and Al-26 surface exposure ages of ca. 1.2 Ma, consistent with bracketing Ar-40/Ar-39 age constraints obtained elsewhere in Patagonia. This is the first time early Pleistocene glacial surfaces have been directly dated in Patagonia. Cobbles on a younger Canadon de Caracoles outwash terrace give exposure ages of ca. 600 ka, while 4 of 5 boulders on an associated moraine give exposure ages that are significantly younger. If the demonstrated stability of outwash terraces in the valley is common throughout the region, it will be possible to extend Patagonian glacial chronologies as far back as the early Pleistocene.

Published
2011
Full Text
View/download PDF

4. The role of Southern Ocean processes in orbital and millennial CO2 variations - A synthesis

Author

Fischer H, Schmitt J., Luthi D., Stocker T.F., Tschumi T., Parekh P., Joos F., Kohler P., and Barbante C. et al

Subjects
C ICE CORE, LAST GLACIAL MAXIMUM, PAST 800,000 YEARS, SEA-SALT AEROSOL, ATMOSPHERIC CARBON-DIOXIDE
Abstract

Recent progress in the reconstruction of atmospheric CO2 records from Antarctic ice cores has allowed for the documentation of natural CO2 variations on orbital time scales over the last up to 800,000 years and for the resolution of millennial CO2 variations during the last glacial cycle in unprecedented detail. This has shown that atmospheric CO2 varied within natural bounds of approximately 170-300 ppmv but never reached recent CO2 concentrations caused by anthropogenic CO2. emissions. In addition, the natural atmospheric CO2 concentrations show an extraordinary correlation with Southern Ocean climate changes, pointing to a significant (direct or indirect) influence of climatic and environmental changes in the Southern Ocean region on atmospheric CO2 concentrations. Here, we compile recent ice core and marine sediment records of atmospheric CO2, temperature and environmental changes in the Southern Ocean region, as well as carbon cycle model experiments, in order to quantify the effect of potential Southern Ocean processes on atmospheric CO2 related to these orbital and millennial changes. This shows that physical and biological changes in the SO are able to explain substantial parts of the glacial/interglacial CO2 change, but that none of the single processes is able to explain this change by itself. In particular, changes in the Southern Ocean related to changes in the surface buoyancy flux, which in return is controlled by the waxing and waning of sea ice may favorably explain the high correlation Of CO2 and Antarctic temperature on orbital and millennial time scales. In contrast, the changes of the position and strength of the westerly wind field were most likely too small to explain the observed changes in atmospheric CO2 or may even have increased atmospheric CO2 in the glacial. Also iron fertilization of the marine biota in the Southern Ocean contributes to a glacial drawdown Of CO2 but turns out to be limited by other factors than the total dust input such as bioavailability of iron or macronutrient supply.

Published
2010

5. A major glacial-interglacial change in aeolian dust composition inferred from Rare Earth Elements in Antarctic ice

Author

Paolo Cescon, J. R. Petit, Anna Wegner, Carlo Barbante, Barbara Delmonte, Michael Kriews, Vania Gaspari, Urs Ruth, Hubertus Fischer, Patrick De Deckker, Paolo Gabrielli, Claude F. Boutron, Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Institute for the Dynamics of Environmental Processes-CNR, University of Ca’ Foscari [Venice, Italy], School of Earth Sciences and Byrd Polar Research Center, Ohio State University [Columbus] (OSU), Department of Bentho-pelagic processes, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), CLIPS, Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Dipartimento di Scienze dell'Ambiente e del Territorio (DISAT), Università degli Studi di Milano [Milano] (UNIMI), Research School of Earth Sciences [Canberra] (RSES), Australian National University (ANU), Physics Institute [Bern], University of Bern, Oeschger Centre for Climate Change Research (OCCR), Department of Environmental Sciences, Consorzio per l'Attuazione del Programma Nazionale delle Ricerche in Antartide, under projects on Environmental Contamination and Glaciology, Institut Universitaire de France, the Agence de l'Environnement et de la Maîtrise de l'Energie, the Institut National des Sciences de l'Univers and the Université Joseph Fourier of Grenoble, contribution number 1387 of the Byrd Polar Research Center, European Project: 39423,FP6-SUSTDEV,EPICA-MIS, Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Università degli studi di Milano [Milano], Gabrielli, P, Wegner, A, Petit, J, Delmonte, B, De Deckker, P, Gaspari, V, Fischer, H, Ruth, U, Kriews, M, Boutron, C, Cescon, P, Barbante, C, Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Università degli Studi di Milano = University of Milan (UNIMI)

Subjects
Archeology, 010504 meteorology & atmospheric sciences, PAST 800,000 YEARS, Atmospheric circulation, Earth science, GEO/04 - GEOGRAFIA FISICA E GEOMORFOLOGIA, 010502 geochemistry & geophysics, 01 natural sciences, Ice core, CLIMATIC CYCLES, GEO/08 - GEOCHIMICA E VULCANOLOGIA, Glacial period, [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology, Ecology, Evolution, Behavior and Systematics, Holocene, 0105 earth and related environmental sciences, Global and Planetary Change, EAST ANTARCTICA, HEAVY-METAL ANALYSIS, Geology, Particulates, 13. Climate action, Interglacial, Period (geology), Aeolian processes, Rare Earth Elements, ice cores, antarctica, Physical geography, DOME-C
Abstract

International audience; We present the first Rare Earth Elements (REE) concentration record determined in 294 sections of an Antarctic ice core (EPICA Dome C), covering a period from 2.9 to 33.7 kyr BP. REE allow a detailed quantitative evaluation of aeolian dust composition because of the large number of variables (i.e. 14 elements). REE concentrations match the particulate dust concentration profile over this period and show a homogeneous crustal-like composition during the last glacial stage (LGS), with only a slight enrichment in medium REE. This signature is consistent with the persistent fallout of a mixture of dust from heterogeneous sources located in different areas or within the same region (e.g. South America). Starting at not, vert, similar15 kyr BP, there was a major change in dust composition, the variable character of which persisted throughout the Holocene. This varying signature may highlight the alternation of single dust contributions from different sources during the Holocene. We observe that the frequent changes in REE composition at the onset of the Holocene (10-13.5 kyr BP) are linked to dust size and in turn to wind strength and/or the path of the atmospheric trajectory. This may indicate that atmospheric circulation dictated the composition of the dust fallout to East Antarctica at that time. Although the dust concentrations remained fairly low, a notable return towards more glacial dust characteristics is recorded between 7.5 and 8.3 kyr BP. This happened concomitantly with a widespread cold event around 8 kyr BP that was 400-600 years long and suggests a moderate reactivation of the dust emission from the same potential source areas of the LGS.

Published
2010
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results