E.M. van Zinderen Bakker (1907-2002) and the study of African Quaternary palaeoenvironments

摘要

The scientific contributions of E.M. van Zinderen Bakker (1907-2002) included the introduction of pollen analysis to Quaternary studies in South Africa. His palaeoecological theories evolved while performing palynological research in Southern Africa (the Maluti Mountains, Florisbad, Aliwal North, the Namib Desert), East Africa (Kalambo Falls, Mount Kenya, Cherangani Hills) and on the subantarctic islands (Marion and Prince Edward Islands). He was involved in the first radiocarbon dating from South Africa at Florisbad. Due to quantitative palynological studies he abandoned Wayland's (1929) Pluvial Theory that was generally accepted in the 1960s. He correlated observations of climate changes in Africa to data from marine borehole-cores and climatic fluctuations in the Northern Hemisphere. His observations led to the proposal that global temperature fluctuations are the primary cause of palaeoenvironmental changes. His studies culminated in a conceptual paleoecological model for the Last Glacial Maximum (LGM). Initially he based the model on symmetrical contraction of climatic belts about the equator that shifted the mid-latitude westerly wind system northward to increase the area receiving winter rainfall but later adjusted this by proposing a mechanism of westerly wind system intensification. He suggested that at this time grasslands had spread over wider areas in Southern Africa and that the tropical rain forests in the equatorial region fragmented. For interglacial periods he suggested that a southward shift of the Intertropical Convergence Zone (ITCZ) resulted in widespread humidity in the Congo Basin while large areas of the interior of Southern Africa became arid. Some of his ideas, especially his conceptual models of Quaternary vegetation and climate, are still relevant to the explanation of recent discoveries.