The occurrence of several large and abrupt climate changes dated to the last deglaciation, first clearly evidenced in Greenland ice cores, has also been confirmed by a variety of other proxies in lower-latitude Northern and Southern Hemispheric marine and terrestrial records. Despite much knowledge of the environmental changes that accompanied these events, an understanding of their causal mechanisms is hampered by the difficulty of determining the absolute ages of the different records. In order to better determine the phase relationships of these events at different locations, Genty et al. analyzed stalagmite records of δ13C isotopic distributions from several Northern Hemispheric locations, in France and Tunisia, and compared them with corresponding records from speleothems in China, New Zealand, and South Africa. The advantage of this approach is that stalagmites can be precisely dated, thereby establishing an accurate common chronology.
The data suggest that the Bølling-Allerød warm interval began synchronously in France, Tunisia, and China; that the Younger Dryas cold period also began concurrently at all of these sites; and that although the onset times were the same at widely separated sites in both hemispheres, the duration and intensity of transitions differed among sites. The authors also suggest a simple explanation for these changes, involving the gradual increase of insulation at high northern latitudes, due to orbital changes, and the resulting northward movement of the limits of sea ice there. — HJS
Quat. Sci. Rev. 25, 2118 (2006).