Climate change and human impact on the Song Hong (Red River) Delta, Vietnam, during the Holocene

On the basis of the results of palynological research on two cores from the Song Hong (Red River) delta in the sub-tropical zone of Asia, centennial- to millennial-scale climate changes and human impacts during the Holocene were clarified. Three cycles of cooling and warming were identified during the last 5000 yr: a cool and wet climate during 4530–3340 cal. yr BP, 2100–1540 cal. yr BP, and 620–130 cal. yr BP, a warm and dry climate during 3340–2100 cal. yr BP, 1540–620 cal. yr BP and the present warm climate. The first and last cooling events correspond to global Holocene cooling events, the Neoglacial Period and the Little Ice Age, respectively. Each persisted for 500–1000 yr, and they occurred at intervals of 1500–2000 yr. Pollen records also reflect human impacts on this area, which intensified after 3340 cal. yr BP when large quantities of cultivated Gramineae taxa, possibly including the main wet rice species, Oryza sativa, secondary forest, and other upland cultivated taxa appear in the record.