Glaciation

Résumé

thumb|Représentation artistique de l'englacement lors du dernier maximum glaciaire (DMG) selon Ice age terrestrial carbon changes revisited de Thomas J. Crowley. Une glaciation (ou englaciation) est une période glaciaire ou ère glaciaire, c'est-à-dire à la fois une phase paléoclimatique froide et une période géologique de la Terre durant laquelle une partie importante des continents est englacée. L'histoire de la Terre est marquée par de nombreux épisodes glaciaires au cours de refroidissements climatiques. Le Quaternaire se caractérise par leur relative fréquence et leur régularité. Historique des recherches sur les glaciations Les glaciations ont d'abord été mises en évidence grâce à leurs manifestations géomorphologiques (moraines, blocs erratiques) dans les vallées alpines à la fin du . La glaciation de Würm, manifestation locale de la dernière période glaciaire, a été définie par Albrecht Penck et Eduard Brückner au début du , qui lui ont donné le nom d'un tributaire

Source officielle

https://fr.wikipedia.org/wiki/Glaciation

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, ,

Ring width (TRW) chronologies from Siberian (Pinus sibirica) and Scots (Pinus sylvestris) pine trees were sampled at Mukhrino - a large mire complex in central-western Siberia - to evaluate the impacts of hydroclimatic variability on tree growth over the last three centuries. For this purpose, we compared climate-growth correlation profiles from trees growing on peat soils with those growing on adjacent mineral soils. Tree growth at both peat and mineral soils was positively correlated to air temperature during the vegetation period. This finding can be explained by (i) the positive influence of temperature on plant physiological processes (i.e. growth control) during the growing season and (ii) the indirect impact of air temperatures on water table fluctuations. We observe also a strong link between TRW and the winter Palmer Drought Severity Index (PDSI), especially in Siberian pine, reflecting the isolating effect of snow and limited freezing damage in roots. Significant negative relations were, by contrast, observed between bog TRW chronologies and hydroclimatic indices during spring and summer; they are considered an expression of the negative impacts of high water levels and moist peat soils on root development. Some unusually old bog pines - exhibiting >500 growth rings - apparently colonized the site at the beginning of the Little Ice Age, and therefore seem to confirm that (i) peat conditions may have been drier in Siberia than in most other regions of western Europe during this period. At the same time, the bog trees also point to (ii) their strong dependence on surface conditions. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier Science Bv2017

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Autopolyploidy and post-glacial recolonization of Biscutella laevigata (Brassicaceae): molecular analysis and spatial modeling of gene dispersal in the western Alps

Régis Caloz, Stéphane Joost

Over the past five years there have been significant advances in both genetic and palaeoecological research on the ancestry of populations. The alternation of cold and warm stages during the Ice Ages has caused repeated geographic restriction and expansion of many organisms. The conference will examine the degree to which this may have affected the evolution of the organisms involved and their relationships, particularly the mechanisms and rates of changing selective processes. It will bring together geneticists, palaeoecologists, evolutionary biologists, geologists, taxonomists, archaeologists and biogeographers to contribute to an emerging synthesis on the evolutionary significance of the Ice Ages.

2004

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The effects of land use and climate change on the carbon cycle of Europe over the past 500 years

Jed Oliver Kaplan, Kristen Marie Krumhardt

The long residence time of carbon in forests and soils means that both the current state and future behavior of the terrestrial biosphere are influenced by past variability in climate and anthropogenic land use. Over the last half-millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO2 concentrations, and human induced deforestation and land abandonment. To quantify the importance of these processes, we performed a series of simulations with the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO2 concentrations. Although land use change was the major control on the carbon inventory of Europe over the last 500years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability led to temporary sequestration events of up to 3Pg, whereas increasing atmospheric CO2 concentrations during the 20th century led to an increase in carbon storage of up to 15Pg. Anthropogenic land use caused between 25Pg of carbon emissions and 5Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12Pg of carbon at the present day.

2012

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