The terminations of the glacial cycles

The geography of the Earth at the end of the Tertiary, with the new arrangement of continents, oceans and the distribution of mountain ranges, especially since the opening of the Drake Strait and the closing of the Isthmus of Panama, favoured a global cooling trend that culminated in the Quaternary. In addition to the ice sheets of Antarctica and Greenland, glaciers during the Quaternary tended to expand, especially on the Northern Hemisphere continents and in the mountains. The expansion ended abruptly for short periods, of about 10 ka, during which these glaciers largely disappeared. These periods are called terminations and mark the end of different glacial cycles. In the first half of the Quaternary, terminations occurred every 41 ka, but in the last 800 ka, terminations have been delayed, whilst glaciers could extend over larger areas, occurring every 100 ka. The onset of the terminations and their dynamics remains a mystery, but it coincides with a series of processes, where it is difficult to know what the cause is and what is the effect. It appears that when the glaciers in the Northern Hemisphere reach their maximum extent, an increase in insolation in the mid-latitudes of the Northern Hemisphere causes the onset of global termination. Once termination has begun, a series of temperature changes take place, intense in the Northern Hemisphere and milder in the Southern Hemisphere, but with inverse trends, and in direct relation to changes in the intensity of the Atlantic Meridional Overturning Circulation (AMOC) and to latitudinal changes in atmospheric circulation. Despite these changes in temperature, CO2 in the atmosphere increases throughout the termination, albeit with varying intensity. Once the balance between the AMOC and the proportion of CO2 in the atmosphere is in equilibrium, the temperature stabilises and the termination ends, leading to the onset of an interglacial optimum. This occurs when the northern continental ice sheets have disappeared or have reduced their extension.