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

Abstract

Sediment samples from a 50-m-long core representing ~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 87Sr/86Sr and εNd vary signifi cantly 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 refl ect 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 87Sr/86Sr and εNd depth profi les further confi rm this hypothesis. The isotope profi les 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 signifi cant infl uence of climate on erosion in the Himalaya.