Climate control on erosion distribution over the Himalaya during the past ∼100 ka

Sediment samples from a 50-m-long core representing similar to 100 ka of deposition, taken from the Ganga Plain on the campus of the Indian Institute of Technology, Kanpur, were analyzed for Sr and Nd isotope compositions. Both Sr-87/Sr-86 and epsilon(Nd) vary significantly with depth in the core, 0.72701-0.76708 and -14.4 to -16.6, respectively, within the range for silicate rocks of the Higher and the Lesser Himalaya. The variations in the isotope compositions reflect variations in the mixing proportion of sediments from the Higher and Lesser Himalaya, the two major sediment sources to the Ganga. The opposite trends in Sr-87/Sr-86 and epsilon(Nd) depth profiles further confirm this hypothesis. The isotope profiles exhibit two major excursions, ca. 20 ka and ca. 70 ka ago, coinciding with periods of precipitation minima and larger glacial cover. These excursions are the result of a decrease in the proportion of sediment from the Higher Himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation. This study highlights the significant influence of climate on erosion in the Himalaya.