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International audience ; ZUSAMMENFASSUNG Dieser Artikel befasst sich mit den Pollendaten von einer neuen 9m tiefen Probebohrung in einem der Siimpfe des Sandynallah-Gebiets (11°26' N, 76°38'0. Hôhe 2200 m) im Nilgiri-Gebirge. Diese Berge im Sùdwesten Indiens unterliegen einem Sommer-Monsun-System. Man hat vierzehn konventionelle Kohlestoffdatierungen auf neun Roh-Sedimentproben erhalten. Die Datierungen des unteren Teils der Probebohrung reichen von 2000 bis 35 000 Jahre v.u.Z. Sie lassen eindeutig erkennen. dass der Beginn der Auffullung vor das letzte glaziale Maximum reicht. Die Pollen-Analyse wurde auf 65 Proben durchgefuhrt. Zahlreiche Zâhlungen fùhrten zur Identifizierung von 95 Pollen-Taxa, von denen 55 Baum- und Buschpollen sind, einige davon spezifisch WaId zugehôrig. In der Gesamtheit der Taxa repràsentieren die Pollen von Gramineae, Cyperaceae und anderen Sumpfpflanzen mehr als 80%. Die Glazialzeit zeichnet sich durch das Vorherrschen von C4-Gramineae aus, welche mit Artemisia und Apiaceae in Verbindung gebracht werden. Eine Phase mit Michelia (Magnoliaceae), ein Halb-Laubbaum der Hochwàlder, wird dem spâten Holozan um 3800 Jahre v.u.Z. zugeordnet. Das regelmassige Vorkommen anderer Wald-Taxa wie Olea, Ilex, Glochidion und Rapanea.wenn auch in geringen Mengen, in der gesamten Sequenz zeigt, dass ein Wald-Savanne-Mosaik in diesen Gebieten lange vor Einwirken des Menschen auf den WaId bestand. ; ABSTRACT This paper presents pollen data from the Nilgiri hills in South-West India subjected to the summer monsoon climatic regime. The sequence comes from a new 9-m core (A2) collected in one of the Sandynallah swamps (11°26'N, 76°38'E) at an elevation of 2200 m. Forteen conventional radiocarbon dates have been obtained from nine bulk samples. They clearly indicate that the lower part was deposited during the last glacial period and confirm previous information from this area. The oldest dates, 27,000 to 35,000 yr BP, measured at the Laboratoire souterrain de Modane (France), present consistent results. The lower part of the pollen sequence dates from the last glacial period (isotopic stage 3) before the last glacial maximum. The upper three metres were deposited during the last 5000 years. The record of the lower Holocene is apparently missing. Pollen analysis was undertaken on 65 samples.The pollen flora appears to be strongly dominated by grasses and swamp plants accounting for more than 80 % of the total counts. High counts were done which allow to recognize 95 distinct taxa among which 55 are attributed to tree forest elements. The glacial period is dominated by C4 grasses associated with a significant signal of Artemisia and Apiaceae. During the late Holocene a sharp peak of Michelia, a semi-deciduous tree of the montane forest among the Magnoliaceae is dated at around 3800 yr BP. Its association with other forest components such as Olea, Glochidion. Ilex and Rapanea favour the interpretation that a mosaic of grassland and forest existed in the Nilgiri hills since a few thousand years, well before human impact on forest. ; Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter en ligne.

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 Dansgaard-Oeschger (D-O) 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 D-O 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 (73-15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (C-14, U-234/Th-230, optically stimulated luminescence (OSL), Ar-40/Ar-39-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 Access (TM) at https://doi. org/10.1594/PANGAEA. 870867. ; Basque Government postdoctoral fellowship [POS_2015_1_0006]; ERC; QUEST-DESIRE (UK and France); INQUA International Focus Group ACER; INTIMATE-COST ; info:eu-repo/semantics/publishedVersion

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 Dansgaard–Oeschger (D–O) 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 D–O 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 (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-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. ; Basque Government postdoctoral fellowship [POS_2015_1_0006]; ERC; QUEST-DESIRE (UK and France); INQUA International Focus Group ACER; INTIMATE-COST ; Open Access Journal. ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.