1,295 research outputs found
Abrupt climate changes of the last deglaciation detected in a Western Mediterranean forest record
Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial
Greniers
Les sociétés berbères rurales n’ont pas un système unique de conservation des récoltes. Les lieux où sont entreposés et protégés les produits végétaux destinés à la consommation sont très divers. Le silo creusé dans le sol Le plus archaïque et le plus commun est le silo creusé dans le sol. Il s’imposait dans la zone semi-aride où règne l’élevage des ovins et où se pratique une céréaliculture risquée. L’existence d’une croûte pédologique près de la surface qui recouvre des sédiments meubles fa..
Greniers
Les sociétés berbères rurales n’ont pas un système unique de conservation des récoltes. Les lieux où sont entreposés et protégés les produits végétaux destinés à la consommation sont très divers. Le silo creusé dans le sol Le plus archaïque et le plus commun est le silo creusé dans le sol. Il s’imposait dans la zone semi-aride où règne l’élevage des ovins et où se pratique une céréaliculture risquée. L’existence d’une croûte pédologique près de la surface qui recouvre des sédiments meubles fa..
Greniers
Les sociétés berbères rurales n’ont pas un système unique de conservation des récoltes. Les lieux où sont entreposés et protégés les produits végétaux destinés à la consommation sont très divers. Le silo creusé dans le sol Le plus archaïque et le plus commun est le silo creusé dans le sol. Il s’imposait dans la zone semi-aride où règne l’élevage des ovins et où se pratique une céréaliculture risquée. L’existence d’une croûte pédologique près de la surface qui recouvre des sédiments meubles fa..
Phosphorylation of class I histocompatibility antigens in human B lymphocytes. Regulation by phorbol esters and insulin
Sur quelques propriétés pharmacodynamiques d’ECHINOPS SPINOSUS L.
Bost Jack, Ferrando Raymond, Peyron R., Marboux H. Sur quelques propriétés pharmacodynamiques d'Eckinops spinosus L. In: Bulletin de l'Académie Vétérinaire de France tome 107 n°2, 1954. pp. 87-93
Pollen-based temperature and precipitation changes in the Ohrid Basin (western Balkans) between 160 and 70 ka
Our study aims to reconstruct climate changes that occurred at Lake Ohrid
(south-western Balkan Peninsula), the oldest extant lake in Europe, between
160 and 70 ka (covering part of marine isotope stage 6, MIS 6; all of MIS 5;
and the beginning of MIS 4). A multi-method approach, including the “Modern
Analog Technique” and the “Weighted Averaging Partial Least-Squares Regression”, is
applied to the high-resolution pollen sequence of the DEEP site, collected
from the central part of Lake Ohrid, to provide quantitative estimates of
climate and bioclimate parameters. This allows us to document climatic change
during the key periods of MIS 6 and MIS 5 in southern Europe, a region where
accurate climate reconstructions are still lacking for this time interval.
Our results for the penultimate glacial show cold and dry conditions, while the onset of
the “last interglacial” is characterized by wet and warm conditions, with temperatures
higher than today (by ca. 2 ∘C). The Eemian also shows the well-known climatic
tri-partition in the Balkans, with an initial pre-temperate phase of abrupt warming
(128–121 ka), a central temperate phase with decreasing temperatures associated with
wet conditions (121–118 ka), followed by a post-temperate phase of progressive change
towards cold and dry conditions (118–112 ka).
After the Eemian, an alternation of four warm/wet periods with cold/dry
ones, likely related to the succession of Greenland stadials and cold events
known from the North Atlantic, occurred. The observed pattern is also
consistent with hydrological and isotopic data from the central
Mediterranean.
The Lake Ohrid climate reconstruction shows greater similarity with climate
patterns inferred from northern European pollen records than with southern
European ones, which is probably due to its intermediate position and the
mountainous setting. However, this hypothesis needs further testing as very
few climate reconstructions are available for southern Europe for this key
time period.</p
Using the past to constrain the future: how the palaeorecord can improve estimates of global warming
Climate sensitivity is defined as the change in global mean equilibrium
temperature after a doubling of atmospheric CO2 concentration and provides a
simple measure of global warming. An early estimate of climate sensitivity,
1.5-4.5{\deg}C, has changed little subsequently, including the latest
assessment by the Intergovernmental Panel on Climate Change.
The persistence of such large uncertainties in this simple measure casts
doubt on our understanding of the mechanisms of climate change and our ability
to predict the response of the climate system to future perturbations. This has
motivated continued attempts to constrain the range with climate data, alone or
in conjunction with models. The majority of studies use data from the
instrumental period (post-1850) but recent work has made use of information
about the large climate changes experienced in the geological past.
In this review, we first outline approaches that estimate climate sensitivity
using instrumental climate observations and then summarise attempts to use the
record of climate change on geological timescales. We examine the limitations
of these studies and suggest ways in which the power of the palaeoclimate
record could be better used to reduce uncertainties in our predictions of
climate sensitivity.Comment: The final, definitive version of this paper has been published in
Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All
rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso
European climate optimum and enhanced Greenland melt during the Last Interglacial
The Last Interglacial climatic optimum, ca. 128 ka, is the most recent climate interval signifi cantly warmer than present, providing an analogue (albeit imperfect) for ongoing global warming and the effects of Greenland Ice Sheet (GIS) melting on climate over the coming millennium. While some climate models predict an Atlantic meridional overturning circulation (AMOC) strengthening in response to GIS melting, others simulate weakening, leading to cooling in Europe. Here, we present evidence from new proxy-based paleoclimate and ocean circulation reconstructions that show that the strongest warming in western Europe coincided with maximum GIS meltwater runoff and a weaker AMOC early in the Last Interglacial. By performing a series of climate model sensitivity experiments, including enhanced GIS melting, we were able to simulate this confi guration of the Last Interglacial climate system and infer information on AMOC slowdown and related climate effects. These experiments suggest that GIS melt inhibited deep convection off the southern coast of Greenland, cooling local climate and reducing AMOC by ~24% of its present strength. However, GIS melt did not perturb overturning in the Nordic Seas, leaving heat transport to, and thereby temperatures in, Europe unaffected. © 2012 Geological Society of America
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