The timing and causes of paleoenvironmental changes in Madagascar have been debated, specifically in respect to human activity following the settlement in the late Holocene. Here we present δ18O, δ13C, layer-bounding surfaces, layer-specific width, mineralogy, and distribution of macroholes from Stalagmite MA3 from Anjohibe Cave to provide a detailed understanding of the paleoenvironmental changes in northwestern Madagascar between 370 CE and 1300 CE. The stable isotope records of Stalagmite MA3 are compared with stable isotope records of Stalagmites ANJ94-5 and MA2. Detailed examination of the proxies suggests three distinct intervals of changes. (1) Prior to 795 CE, changes in vegetation seem to have responded to changes in monsoonal rainfall linked to the relative position of the ITCZ. The period between ca. 755 CE and 795 was the driest, and the Stalagmite MA3 record is consistent with sediment records (pollen and lithology) from Lake Mitsinjo, northwestern Madagascar, and with sediment records (fossil pollen and charcoal) from Sainte Luce, southeastern Madagascar. (2) Between 795 CE and 870, the environmental conditions became more favorable, when vegetation recovered from the driest interval. The new conditions must have been suitable for community development in the region as suggested by archaeological evidence around Lake Mitsinjo and the Boeny region, and the establishment of the stone town of Mahilaka. (3) After 870 CE, a gradational change in plant communities from C3 to C4 marks the record until around 1130 CE, after which vegetation was dominated by C4 plants. This change cannot be explained by climate alone, as there is no clear relationship in the climate-sensitive proxies. Instead, it could have been caused by “Tavy”, a variety of “swidden” agriculture practiced in the region.
Bibliographical noteFunding Information:
This research was supported by a grant from the National Natural Science Foundation of China Grant (NSFC 41230524) to Hai Cheng and by a grant from NOAA (#NA56GP0323) to David Burney and L. Bruce Railsback. We thank David Burney for organizing fieldwork at Anjohibe Cave in 1994, also supported by NOAA, that led to the collection of the stalagmites by Dr. Brook discussed in this paper. We thank Paul A. Schroeder, supervisor of the XRD lab of the department of Geology, for providing access to X-ray diffraction analysis. We also thank the government and people of Madagascar, particularly local guides in Anjohibe, for their assistance in making this work possible. We thank the Cenozoic Research Group, a Malagasy-American collaboration sanctioned by the Service de Pal?ontologie and the Mus?e d'Art et d'Arch?ologie of the Universit? d'Antananarivo for fieldwork assistance and sample collection. We thank Dr. Rakotondrazafy Michel and Dr. Madison Razanatseheno from the Department of Geology of the University of Antananarivo Madagascar for helping acquiring useful documents that are only available at the libraries in Antananarivo. Similarly, we thank Mr. Bruno Rakotoarivelo, from the National Office of Environment (Office National pour l'Environment, ONE), in Antananarivo, Madagascar for his assistance in acquiring information about climate and vegetation of the Mariarano region. We also thank Dr. Stephen Burns of the Department of Geosciences of the University of Massachusetts for sharing the data of Burns et al. (2016) with us. Finally, we thank the Schlumberger Foundation, Faculty for the Future, and the University of Georgia for supporting N.R. Voarintsoa's research.
- Ecosystem changes
- Human activities
- Northwestern Madagascar