Natural Environmental Change: The Last 3 Million Years

By A. M. Mannion | Go to book overview

9

Environmental change in low latitudes (30°N and 30 S)

9.1

Introduction

Traditionally, most research on environmental change has focused on middle- and high-latitude regions. This is because such regions were directly affected by glacial and/or periglacial processes, as discussed in Chapters 7 and 8. Moreover, the absence of glaciation from all but the highest regions of low latitudes has led to the belief that such regions had remained largely unaltered throughout the last 3×106 years. The advent of palaeoenvironmental information from ocean sediments, beginning in the 1950s, scotched this myth as theories of global-scale change began to be formulated. The recognition that global temperatures were depressed by c. 10°C during the ice ages, prompted questions about the nature and direction of environmental change in extraglacial regions, especially within the tropics.

Have the world’s deserts always enjoyed their present distribution, and have their boundaries shifted as climatic change has occurred? How have the world’s most productive vegetation communities, notably tropical forests, been affected by temperature depression and elevation? These are just some of the questions that palaeoenvironmental research in low latitudes has addressed.

The evidence for environmental change during the last 3×106 years derives from a range of archives, as it does in middle and high latitudes. Evidence from ocean cores provides the longest and most complete record of environmental change (Chapter 4) in low latitudes. However, there are a number of long lacustrine sequences that provide evidence of changing conditions on the continents. The longest of these is from Funza, near Bogotá in Colombia, which extends back to the Pliocene period (Section 5.3.1). Glaciers, such as Huascarán in the Peruvian Andes, also provide palaeoenvironmental information, though peat and mire deposits are the most common sources of data on environmental change. In particular, pollen analysis of such deposits is making a major contribution to the elucidation of environmental change.

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