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Abstract
While our understanding of climate systems continues to improve, it has also become clear that regional responses to global forcing, as well as the interaction of regional phenomena within global climate systems, are more complex than we have previously understood them to be. The complexity could be purely climatic, or it could be interfered with by anthropogenic influences. Climate reconstructions and simulations have suggested the need for more information from remote locations in the world, such as Africa and Madagascar, not only to complete gaps in our understanding of global atmospheric and oceanic circulation, but also to distinguish anthropogenic influences on climate from natural variability. This dissertation research has been an investigation of past climate and vegetation changes in northeastern Namibia and in northwestern Madagascar using proxies from stalagmites. Stalagmites, which are upward growing, pillar-like, and convex-up shape cave deposits, can preserve various signatures (18O, 13C, mineralogy, petrography, layer-specific width, macro-cavities distributions) that reflect environmental conditions at the time of their deposition. These proxies are powerful tools to reconstruct paleoclimate and paleoenvironmental changes.The main research question has focused around the dynamics of the Inter-Tropical Convergence Zone (ITCZ) and the climatic responses in these regions during the last two millennia and during the Holocene. The stalagmite records have revealed linkage to the ITCZ in accord with climate simulations, which suggest that the ITCZ migrates latitudinally toward a warmer hemisphere. More specifically, the ITCZ migrates southward/northward during globally cooler/warmer conditions. This migration could determine the length of summer months in the ITCZ-visited regions. The records from northwestern Madagascar have also helped better understand the timing when humans started to leave significant imprints on the landscape, and they revealed that climate in Madagascar was also sensitive to abrupt climate changes, such as the 8.2 ka event. These new climatic data from northeastern Namibia and northwestern Madagascar are useful to refine our understanding of the global circulation. They can also be useful to test for climate models that could be used to predict changes in future climate.