Monsoon Rains of the Late Pleistocene and Early Holocene: Patterns, Intensity and Possible Causes of Changes

Abstract

Field evidence for marked environmental changes in the regions subject to monsoon climate has long been available: ancient lake shorelines, fossil dunes, evaporites and Alpine moraines (Brooks 1926, Zeuner 1946). However, a clear picture of the spatial patterns of these features and an accurate radiocarbon-dated chronology of events has been lacking. Without information on the pattern and timing of events, it has been difficult to characterize and interpret these environmental changes in terms of circulation patterns and climate. Moreover, it has been difficult to test hypotheses that attempt to explain the changing monsoon climates. This paper summarizes recent studies that have provided sufficient information about the nature, location and timing of climatic events to facilitate reconstruction of the changes in monsoonal circulations and estimation of the magnitude of precipitation changes. The possible role of changes in the Earth’s orbital elements (obliquity, precession and eccentricity) in causing the observed climatic changes is examined. Some early ideas on the astronomical theory of climatic change, as it relates to tropical climates, are traced.