Grantee Research Project Results
Chemical Weathering in the Himalayan Mountains of Northern Pakistan: Implications for the Global Carbon and Strontium CyclesEPA Grant Number: U915032
Title: Chemical Weathering in the Himalayan Mountains of Northern Pakistan: Implications for the Global Carbon and Strontium Cycles
Investigators: Jacobson, Andrew D.
Institution: Dartmouth College
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1996 through January 1, 1999
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Geochemistry , Ecological Indicators/Assessment/Restoration
The objective of this research project is to determine how the relative rate of carbonate versus silicate mineral weathering in the Himalayan Mountains varies as a function of time following the exposure of fresh rock surfaces by glacial erosion. The results have direct implications for linking silicate weathering rates to long-term fluctuations in the global carbon and strontium cycles.
The Raikhot watershed, located on the northern slope of the Nanga Parbat massif within the Himalayan Mountains of northern Pakistan, provides the ideal example of a predominantly silicate terrain interspersed with very minor amounts of carbonate minerals. Within the watershed, there is a series of glacial moraines ranging in age from approximately 500 to 50,000 years before present. Because all moraines experience identical climatic variables and only differ by their age of exposure, the formation of soils provides a mechanism to study how the relative importance of carbonate and silicate mineral dissolution varies as a function of time. Samples collected from the individual moraines were subjected to a sequential leach and digestion procedure designed to isolate and prepare the carbonate, silicate, and exchangeable fractions of the soil material for elemental and Sr isotope analyses. The carbonate and silicate fractions refer to the bulk chemistry of carbonate and silicate weathering endmembers, respectively. The exchangeable fraction refers to labile elements loosely adsorbed to mineral surfaces. Exchangeable elements identify the mineral provenance of the most dominant weathering endmember, and indicate how the relative influence of carbonate and silicate dissolution varies after the exposure of fresh rock surfaces.