Stable (δ13C and δ15N) isotopes and magnetic susceptibility record of late Holocene climate change from a lake profile of the northeast Himalaya

This study aims at reconstructing paleovegetation history in the northeast Himalaya during the past 2700 yrs using a 100 cm long sedimentary section selected near Anini village, Dibang valley, Arunachal Pradesh (India). Stable carbon and nitrogen isotopic composition (delta C-13 and delta N-15); and total organic carbon (TOC) and total nitrogen (TN) content in organic matter as well as magnetic susceptibility were determined. Results obtained show a strong correlation between TOC-TN indicating similar source for organic matter. delta C-13 and TOC/TN ratio throughout the stratigraphic unit seems to be poorly correlated which suggests that the primary carbon isotope signatures are preserved in the sedimentary environment. Overall, delta C-13 values of the organic matter in the section vary in the range from-23.9 to-21.2 aEuro degrees which is typical of mixed C-3-C-4 plants.. A distinguishable increasing trend in delta C-13 during 2700 to 1300 yrs indicates change in vegetation pattern from C-3 to C-4 plants due to significant climate change from wetter to drier conditions. After 1300 yrs delta C-13 values decrease rapidly by 1.3aEuro degrees and suggest increasing abundance of C-3 plants in wetter climatic condition. The relatively small variation in delta C-13 values in the upper part of the section during 1200 yrs to present suggest a stable climatic condition.