Palaeoclimatology and Palaeoceanography from Laminated Sediments

Book excerpt: The magnitude and causes of decadal to century-scale changes in climate are major issues of global concern. The separation of anthropogenically driven change from natural 'baseline' variability within the atmosphere/ocean system is a prerequisite to identifying human impact on global climate. An understanding of past climate variability is therefore a key to predicting future climate change. The sedimentary record of the oceans, seas and lakes is produced by a series of depositional events that occur on seasonal timescales but can rarely be resolved due to mixing of the sediment by bottomdwelling organisms. Where they are preserved, laminated sediments act like tree rings to record these seasonal-scale processes, such as plankton blooms and floods, and provide a uniquely high-resolution record of environmental change. In addition, annually laminated or 'varved' sediment sequences act as geochronometers against which other timescales can be tested. Laminated sediments may therefore be used to develop records of interannual and decadal-scale variability which serve to test models of climate change. The authors cover a range of topics that include strategies for study and techniques of analysis. A series of case studies, dealing with a variety of lacustrine and marine records, illustrates the wide potential of laminated sediments as palaeoclimatic and palaeoceanographic indicators.