Introduction

Lake sediments are natural archives of environmental information. Material settling on a lake bed may have originated from the atmosphere, the surrounding catchment or the lake itself, and samples of accumulated sediment may be examined in a variety of ways to reconstruct past environmental conditions. Since 1975, the sediments from over 100 different lakes world-wide have been analysed for their magnetic properties. This chapter is a review of the approaches which have been developed to interpret magnetic measurements and a summary of the environmental information which has been gained from magnetic records in different contexts – recent pollution, human and climate impact on hydrological processe and climate change. The focus is on the Holocene period but records which span glacial–interglacial timescales are briefly considered.

Lough Neagh revisited

When presented with a pollen diagram (Fig. 7.1) from Holocene lake sediments which displayed the same features as the sediment's record of magnetic susceptibility, a sediment property for which at the time little was known, there were alternative responses. A bizarre but unimportant coincidence? Or a correlation suggesting new insight, which demanded a closer look? In choosing the latter response, Frank Oldfield and Roy Thompson triggered not only new interest in the magnetic properties of environmental materials but also led a path of discovery along which completely novel applications of using magnetic measurements rapidly appeared.