Palaeoecological records of the last glacial-interglacial cycle: Patterns and causes of change

For many years, detailed studies of past terrestrial environments have been largely tethered to the last 35,000 years — the period of reliable radio carbon dating. Conversely, studies of ocean records, which have traditionally provided longer but more generalised Quaternary stratigraphies and environmental reconstructions, have become more refined in temporal resolution. Records that span the last 21,000 years (the period since the Last Glacial Maximum),as well as longer time series offered by marine and a few terrestrial records, show the importance of climate variations occurring on orbital time scales.Long-term variations in the seasonal cycle of insolation, global ice volume, sea-surface temperature, and atmospheric CO2 affect regional climate and vegetation on all continents. Interest in climatic variations occurring on sub-orbital or millennial time scales has increased as a result of their clear display in paleoclimatic records from the North Atlantic region. Climatic instability during the glacial period is apparent in oxygen-isotope profiles from the Greenland ice cores (Dansgaard et al., 1993; Grootes et al.,1993), and twenty or so episodes of cold–warm cycles, so-called Dansgaard–Oeschger or D–O cycles, have been identified, each cycle lasting about 1500 years (Alley, 1998). The mechanisms by which millennial-scale variations originate and are transmitted from one region to another is a topic of considerable discussion within the paleoclimatic community, particularly as it has bearing on future climate stability.