Late Quaternary climate variability and vegetation response in Ziro Lake Basin, Eastern Himalaya: A multiproxy approach

Pollen, phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmental and palaeoclimatic changes in Ziro Lake Basin, sub-Himalayan Arunachal Pradesh, India since pre-LGM time. Phytoliths record a minor change in grass/woodland cover and appear to be more sensitive than pollen grains to climate fluctuations. Both pollen and non-pollen palynomorph data suggest prevalence of a dense C3 species-dominated moist semi-evergreen forest in the area until the LGM which shows conformity with δ13C data. The phytolith assemblage indicates an alteration in forest cover with expansion of C4 grasses during the LGM. The study further indicates a climatic amelioration with intensification of south-west monsoon during 10.2–3.8 ka and an expansion of forest cover. After 3.8 ka there was a rising trend of dryness, shrinkage in forest cover, and a slight increase in C4 species while C3 plants dominated. Ecosystem variability also points towards a hydrological transformation in the area since pre-LGM time. Application of coexistence approach on pollen data reveals that prior to the LGM the mean annual temperature and mean annual precipitation were approximately 19.3 ± 0.001 °C and 1925 ± 15 mm respectively. Between 10.2 and 3.8 ka MAT was about 19.4 ± 0.5 °C, while MAP was 1901 ± 41.3 mm. Between 3.8 and 1.2 ka and onwards a slight increase in MAT (∼0.3C°) was observed with further decrease in MAP to 1861 ± 33.4 mm. During pre and post LGM times, MAT was more or less similar in the Ziro Lake Basin which increased gradually after 3.8 ka and was ∼1.2 C° higher than today. Prior to the LGM, MAP was higher than the present day by 94 mm, between 10.2 and 3.8 ka by 70 mm and since 3.8 ka onwards by ∼30 mm showing a tendency of gradual decline suggesting a consequent increase in dryness.