Diversity of Diatom and Carbon Isotope Characterization of Soil Organic Matter in Extreme Climate, Sikkim Himalaya, India

Analysis of spatial variation of diatom assemblages and characterization of carbon isotopic composition of surface soil/sediment samples along three high-altitude transects (Chopta, Lashar and Gurudongmar valleys) in North Sikkim, Higher Himalaya have been done to delineate the ecological information (modern analogue). We have studied the variation in the distribution of diatom species and stable carbon composition in three different valleys having variable climatic conditions ranging from sub-humid to semi-arid. The results reveal that the biotic components respond appreciably towards varying environmental conditions. The spatial distribution of diatoms in surface sediments seems to be controlled by physical parameters such as temperature, water and nutrient availability. The overall δ¹³C values vary from ‒25‰ to ‒29‰, suggesting a C₃-dominated vegetation in the region. Higher δ ¹³C values are observed in Gurudongmar samples that are characterized by less moisture and low temperature. The δ ¹³C values suggest that the source of organic matter in soil/sediment is contributed by open grasslands (C₃ grasses). The isotope values clearly demonstrate an increase in δ ¹³C values along with a progressive increase in elevation and decrease in precipitation. The present data will serve as an important archive for future correlations in palaeoclimatic studies.