238 research outputs found
Spatio-temporal Functional Regression on Paleo-ecological Data
The influence of climate on biodiversity is an important ecological question.
Various theories try to link climate change to allelic richness and therefore
to predict the impact of global warming on genetic diversity. We model the
relationship between genetic diversity in the European beech forests and curves
of temperature and precipitation reconstructed from pollen databases. Our model
links the genetic measure to the climate curves through a linear functional
regression. The interaction in climate variables is assumed to be bilinear.
Since the data are georeferenced, our methodology accounts for the spatial
dependence among the observations. The practical issues of these extensions are
discussed
VariabilitĂ© des Ă©cosystĂšmes terrestres et du climat sur un cycle glaciaireâinterglaciaire
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High-resolution marine data and transient simulations support orbital forcing of ENSO amplitude since the mid-Holocene
Lack of constraint on spatial and long-term temporal variability of the El Niño southern Oscillation (ENSO) and its sensitivity to external forcing limit our ability to evaluate climate models and ENSO future projections. Current knowledge of Holocene ENSO variability derived from paleoclimate reconstructions does not separate the role of insolation forcing from internal climate variability. Using an updated synthesis of coral and bivalve monthly resolved records, we build composite records of seasonality and interannual variability in four regions of the tropical Pacific: Eastern Pacific (EP), Central Pacific (CP), Western Pacific (WP) and South West Pacific (SWP). An analysis of the uncertainties due to the sampling of chaotic multidecadal to centennial variability by short records allows for an objective comparison with transient simulations (mid-Holocene to present) performed using four different Earth System models. Sea surface temperature and pseudo-ÎŽ18O are used in model-data comparisons to assess the potential influence of hydroclimate change on records. We confirm the significance of the Holocene ENSO minimum (HEM) 3-6ka compared to low frequency unforced modulation of ENSO, with a reduction of ENSO variance of âŒ50 % in EP and âŒ80 % in CP. The approach suggests that the increasing trend of ENSO since 6ka can be attributed to insolation, while models underestimate ENSO sensitivity to orbital forcing by a factor of 4.7 compared to data, even when accounting for the large multidecadal variability. Precession-induced change in seasonal temperature range is positively linked to ENSO variance in EP and to a lesser extent in other regions, in both models and observations. Our regional approach yields insights into the past spatial expression of ENSO across the tropical Pacific. In the SWP, today under the influence of the South Pacific Convergence Zone (SPCZ), interannual variability was increased by âŒ200 % during the HEM, indicating that SPCZ variability is independent from ENSO on millennial time scales
VARIATIONS DEPUIS 10000 ANS DE LA REPARTITION ET DE LA PRODUCTIVITE DES FORETS D'ALTITUDE DANS LES ALPES ET LE JURA ET SIMULATION DES CHANGEMENTS FUTURS
Ce travail repose sur les charbons de bois enfouis dans les sols et les autres macrorestes ont Ă©tĂ© datĂ©s par 14C et identifiĂ©s botaniquement, et pour un site particulier (lac Cristol), sur les analyses de pollens, d'insectes, de macro-restes vĂ©gĂ©taux, charbons de bois et tronc d'arbres ont Ă©tĂ© combinĂ©s en une « approche multi-proxy » afin de mieux comprendre les variations de la forĂȘt de montagne en rĂ©ponse aux changements climatiques globaux et Ă l'activitĂ© anthropique. Les variations de la limite de la forĂȘt sont de plus de 500 m durant l'HolocĂšne. La pĂ©riode la plus chaude semble avoir Ă©tĂ© 9000-8000 ans cal B.P. (annĂ©es calendaires avant le prĂ©sent). Les hauts niveaux lacustres du dĂ©but et de la fin de l'HolocĂšne sont de natures en fait assez diffĂ©rentes. Au dĂ©but de l'HolocĂšne ils sont principalement dus Ă une Ă©vapotranspiration plus faible, et Ă la fin de l'HolocĂšne Ă des prĂ©cipitations plus Ă©levĂ©es. L'ensemble de ces informations a permis de tester un modĂšle de vĂ©gĂ©tation (Biome3) par une utilisation en mode inverse et Ă essayer de prĂ©dire l'Ă©volution de la vĂ©gĂ©tation. Un doublement de CO2 permet Ă la vĂ©gĂ©tation d'Ă©voluer vers des conditions plus tempĂ©rĂ©es. Une « forĂȘt mixte tempĂ©rĂ©e », pourra devenir une forĂȘt dĂ©cidue tempĂ©rĂ©e grĂące Ă des hivers nettement plus doux et Ă une meilleure efficacitĂ© dans l'utilisation de l'eau en Ă©tĂ©. Ces sites d'altitude ont connu une telle vĂ©gĂ©tation entre 9000 et 8000 ans cal B.P
The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period
Quaternary records provide an opportunity to examine the nature of the
vegetation and fire responses to rapid past climate changes comparable in
velocity and magnitude to those expected in the 21st-century. The best
documented examples of rapid climate change in the past are the warming events
associated with the DansgaardâOeschger (DâO) cycles during the last glacial
period, which were sufficiently large to have had a potential feedback through
changes in albedo and greenhouse gas emissions on climate. Previous
reconstructions of vegetation and fire changes during the DâO cycles used
independently constructed age models, making it difficult to compare the
changes between different sites and regions. Here, we present the ACER (Abrupt
Climate Changes and Environmental Responses) global database, which includes
93 pollen records from the last glacial period (73â15âŻka) with a temporal
resolution better than 1000âŻyears, 32 of which also provide charcoal records.
A harmonized and consistent chronology based on radiometric dating (14C,
234Uâ230Th, optically stimulated luminescence (OSL), 40Arâ39Ar-dated tephra
layers) has been constructed for 86 of these records, although in some cases
additional information was derived using common control points based on event
stratigraphy. The ACER database compiles metadata including geospatial and
dating information, pollen and charcoal counts, and pollen percentages of the
characteristic biomes and is archived in Microsoft AccessTM at
https://doi.org/10.1594/PANGAEA.870867
The origin and spread of olive cultivation in the Mediterranean Basin:The fossil pollen evidence
Olive (Olea europaea L.) was one of the most important fruit trees in the ancient Mediterranean region and a founder species of horticulture in the
Mediterranean Basin. Different views have been expressed regarding the geographical origins and timing of olive cultivation. Since genetic studies and
macro-botanical remains point in different directions, we turn to another proxy \u2013 the palynological evidence. This study uses pollen records to shed new
light on the history of olive cultivation and large-scale olive management. We employ a fossil pollen dataset composed of high-resolution pollen records
obtained across the Mediterranean Basin covering most of the Holocene. Human activity is indicated when Olea pollen percentages rise fairly suddenly,
are not accompanied by an increase of other Mediterranean sclerophyllous trees, and when the rise occurs in combination with consistent archaeological
and archaeobotanical evidence. Based on these criteria, our results show that the southern Levant served as the locus of primary olive cultivation as early
as ~6500 years BP (yBP), and that a later, early/mid 6th millennium BP cultivation process occurred in the Aegean (Crete) \u2013 whether as an independent
large-scale management event or as a result of knowledge and/or seedling transfer from the southern Levant. Thus, the early management of olive
trees corresponds to the establishment of the Mediterranean village economy and the completion of the \u2018secondary products revolution\u2019, rather than
urbanization or state formation. From these two areas of origin, the southern Levant and the Aegean olive cultivation spread across the Mediterranean,
with the beginning of olive horticulture in the northern Levant dated to ~4800 yBP. In Anatolia, large-scale olive horticulture was palynologically recorded
by ~3200 yBP, in mainland Italy at ~3400 yBP, and in the Iberian Peninsula at mid/late 3rd millennium BP
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High-resolution marine data and transient simulations support orbital forcing of ENSO amplitude since the mid-Holocene
Lack of constraint on spatial and long-term temporal variability of the El Niño southern Oscillation (ENSO) and its sensitivity to external forcing limit our ability to evaluate climate models and ENSO future projections. Current knowledge of Holocene ENSO variability derived from paleoclimate reconstructions does not separate the role of insolation forcing from internal climate variability. Using an updated synthesis of coral and bivalve monthly resolved records, we build composite records of seasonality and interannual variability in four regions of the tropical Pacific: Eastern Pacific (EP), Central Pacific (CP), Western Pacific (WP) and South West Pacific (SWP). An analysis of the uncertainties due to the sampling of chaotic multidecadal to centennial variability by short records allows for an objective comparison with transient simulations (mid-Holocene to present) performed using four different Earth System models. Sea surface temperature and pseudo-ÎŽ18O are used in model-data comparisons to assess the potential influence of hydroclimate change on records. We confirm the significance of the Holocene ENSO minimum (HEM) 3-6ka compared to low frequency unforced modulation of ENSO, with a reduction of ENSO variance of âŒ50 % in EP and âŒ80 % in CP. The approach suggests that the increasing trend of ENSO since 6ka can be attributed to insolation, while models underestimate ENSO sensitivity to orbital forcing by a factor of 4.7 compared to data, even when accounting for the large multidecadal variability. Precession-induced change in seasonal temperature range is positively linked to ENSO variance in EP and to a lesser extent in other regions, in both models and observations. Our regional approach yields insights into the past spatial expression of ENSO across the tropical Pacific. In the SWP, today under the influence of the South Pacific Convergence Zone (SPCZ), interannual variability was increased by âŒ200 % during the HEM, indicating that SPCZ variability is independent from ENSO on millennial time scales
Paleoclimats au nord de la Mediterranee orientale depuis 250 000 ans : analyse pollinique et stratigraphie isotopique de quatre carottes marines
SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
How the Asian subtropical area became evergreen since the Last Glacial Maximum
International audienc
Past climate changes and the role of refugia in the temperate Northern Hemisphere
International audienceClassical and cryptic glacial refugia plant species' potential range (fundamental niche) is delineated by a climate space that they often occupy only partially (realized niche). Generally, temperate plant species tend to occupy a wider geographical range when climate is warm and wet, and retract when climate is cold and dry. During the last glacial period, cold-tolerant herbs dominated the mid-to high-latitude landscape in both hemispheres and the range of most temperate tree species was reduced to discrete populations until the climate became warmer and wetter during the Holocene, which allowed them to expand
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