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

Abstract

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 10.2-3.8ka and an expansion of forest cover. After 3.8ka 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±15mm respectively. Between 10.2 and 3.8ka MAT was about 19.4±0.5°C, while MAP was 1901±41.3mm. Between 3.8 and 1.2ka and onwards a slight increase in MAT (~0.3C°) was observed with further decrease in MAP to 1861±33.4mm. During pre and post LGM times, MAT was more or less similar in the Ziro Lake Basin which increased gradually after 3.8ka and was ~1.2C° higher than today. Prior to the LGM, MAP was higher than the present day by 94mm, between 10.2 and 3.8ka by 70mm and since 3.8ka onwards by ~30mm showing a tendency of gradual decline suggesting a consequent increase in dryness