The deglacial hemicycle

Absolute age relationships between (a) size reduction of continental ice sheets, (b) glacio-eustatic sea level rise, (c) temperature changes of the ocean surface, and (d) temperature changes on land show that the proper sequence is as follows: first, withdrawal of the ice sheets; second, warming of the land surface; and, third, warming of the ocean surface. At about 13,000 years only one-half of the ice surface remained. Significant warming of the land surface began about 14,000 years ago, although several short cold phases occurred after that time. The sudden warming of the ocean surface did not take place until between 12.000 and 11,000 years ago. This sequence of events shows that initial glacier retreat did not occur because of rising atmospheric temperature. On the other hand, it suggests that the nourishment of the major ice sheets was reduced below the equilibrium value, probably because the ocean surface was too cold to provide the necessary precipitation.