Jean MALEY | Université de Montpellier (original) (raw)
Papers by Jean MALEY
Suite à la publication récente d'une courbe des fluctuations du lac Naivasha en Afrique orien... more Suite à la publication récente d'une courbe des fluctuations du lac Naivasha en Afrique orientale au cours du dernier millénaire et de l'impact des changements climatiques sur les peuplades régionales (Verschuren & al., 2000), une comparaison a été tentée avec le lac Tchad (Figure). Une relation apparente semble exister entre les hauts niveaux lacustres du lac Naivasha qui correspondent régionalement à des phases climatiques plus humides, et les périodes de "prospérité" des sociétés humaines régionales, et l'inverse durant les bas niveaux du lac. Pour le bassin du Tchad, la "réponse" des populations régionales est nettement plus complexe, car suivant les périodes et leur localisation dans le bassin, cette réponse a été soit en phase, soit opposée avec les niveaux du lac.
Quaternary Research, 2017
During the warmer Holocene Period, two major climatic crises affected the Central African rainfor... more During the warmer Holocene Period, two major climatic crises affected the Central African rainforests. The first crisis, around 4000 cal yr BP, caused the contraction of the forest in favor of savanna expansion at its northern and southern periphery. The second crisis, around 2500 cal yr BP, resulted in major perturbation at the forest core, leading to forest disturbance and fragmentation with a rapid expansion of pioneer-type vegetation, and a marked erosional phase. The major driver of these two climatic crises appears to be rapid sea-surface temperature variations in the equatorial eastern Atlantic, which modified the regional atmospheric circulation. The change between ca. 2500 to 2000 cal yr BP led to a large increase in thunderstorm activity, which explains the phase of forest fragmentation. Ultimately, climatic data obtained recently show that the present-day major rise in thunderstorms and lightning activity in Central Africa could result from some kind of solar influence, a...
This study aims to assess the succession of vegetation-types over Central Africa during the last ... more This study aims to assess the succession of vegetation-types over Central Africa during the last two glacial/interglacial cycles. Analysis of core KZai 02, which contains pollen from the Zaire River watershed (9°N–13°S latitude), allows the investigation of long term patterns of plant ecosystem development and their climatic causes. Core KZai 02 (18.20 m long) was recovered from 6°24.20’S/9°54.10’E in the uppermost axial edifice of the Zaire deep sea fan. Chronology of this sedimentary archive was established using nannofossils and correlations of pollen and total organic carbon signals with the nearby core GeoB1008. Our pollen record indicates that (1) glacials (MIS 6, 4, 2), are marked by the development of afromontane (Podocarpus) forest at high altitude when central basin lowlands were occupied by Cyperaceae marshes and savannah; (2) during interglacials (MIS 1, 5) we identified the development of lowland forests, marked by successive expansion of pioneer, warm-temperate, rain forests, and mangrove indicating sea-level rise; (3) glacial-interglacial transitions (MIS 6/5, 2/1) display identical vegetation dynamics.
Journal of African Earth Sciences, 2016
Lake Chad sedimentation and environments during the late Miocene and Pliocene: new evidence from ... more Lake Chad sedimentation and environments during the late Miocene and Pliocene: new evidence from mineralogy and chemistry of the Bol core sediments
Journal of Volcanology and Geothermal Research
ABSTRACT
Suite à la publication récente d'une courbe des fluctuations du lac Naivasha en Afrique orien... more Suite à la publication récente d'une courbe des fluctuations du lac Naivasha en Afrique orientale au cours du dernier millénaire et de l'impact des changements climatiques sur les peuplades régionales (Verschuren & al., 2000), une comparaison a été tentée avec le lac Tchad (Figure). Une relation apparente semble exister entre les hauts niveaux lacustres du lac Naivasha qui correspondent régionalement à des phases climatiques plus humides, et les périodes de "prospérité" des sociétés humaines régionales, et l'inverse durant les bas niveaux du lac. Pour le bassin du Tchad, la "réponse" des populations régionales est nettement plus complexe, car suivant les périodes et leur localisation dans le bassin, cette réponse a été soit en phase, soit opposée avec les niveaux du lac.
Quaternary Research, 2017
During the warmer Holocene Period, two major climatic crises affected the Central African rainfor... more During the warmer Holocene Period, two major climatic crises affected the Central African rainforests. The first crisis, around 4000 cal yr BP, caused the contraction of the forest in favor of savanna expansion at its northern and southern periphery. The second crisis, around 2500 cal yr BP, resulted in major perturbation at the forest core, leading to forest disturbance and fragmentation with a rapid expansion of pioneer-type vegetation, and a marked erosional phase. The major driver of these two climatic crises appears to be rapid sea-surface temperature variations in the equatorial eastern Atlantic, which modified the regional atmospheric circulation. The change between ca. 2500 to 2000 cal yr BP led to a large increase in thunderstorm activity, which explains the phase of forest fragmentation. Ultimately, climatic data obtained recently show that the present-day major rise in thunderstorms and lightning activity in Central Africa could result from some kind of solar influence, a...
This study aims to assess the succession of vegetation-types over Central Africa during the last ... more This study aims to assess the succession of vegetation-types over Central Africa during the last two glacial/interglacial cycles. Analysis of core KZai 02, which contains pollen from the Zaire River watershed (9°N–13°S latitude), allows the investigation of long term patterns of plant ecosystem development and their climatic causes. Core KZai 02 (18.20 m long) was recovered from 6°24.20’S/9°54.10’E in the uppermost axial edifice of the Zaire deep sea fan. Chronology of this sedimentary archive was established using nannofossils and correlations of pollen and total organic carbon signals with the nearby core GeoB1008. Our pollen record indicates that (1) glacials (MIS 6, 4, 2), are marked by the development of afromontane (Podocarpus) forest at high altitude when central basin lowlands were occupied by Cyperaceae marshes and savannah; (2) during interglacials (MIS 1, 5) we identified the development of lowland forests, marked by successive expansion of pioneer, warm-temperate, rain forests, and mangrove indicating sea-level rise; (3) glacial-interglacial transitions (MIS 6/5, 2/1) display identical vegetation dynamics.
Journal of African Earth Sciences, 2016
Lake Chad sedimentation and environments during the late Miocene and Pliocene: new evidence from ... more Lake Chad sedimentation and environments during the late Miocene and Pliocene: new evidence from mineralogy and chemistry of the Bol core sediments
Journal of Volcanology and Geothermal Research
ABSTRACT