HR: 1340h
AN: H43C-0378    [Abstracts]
TI: Surface Area Production: The Impact of Glacial Erosion on Chemical Weathering Fluxes
AU: * Anderson, S P
EM: suzanne.anderson@colorado.edu
AF: INSTAAR and Dept. of Geography, University of Colorado, Boulder, CO 80309-0450 United States
AU: Cacy, C
EM: cynthia.cacy@colorado.edu
AF: INSTAAR and Environ. Studies Prog., University of Colorado, Boulder, CO 80309-0450 United States
AB: Glacial erosion produces high sediment yields characterized by a large fraction of fine-grained material. As a consequence, the mineral surface area production due to glacial erosion is extraordinarily high, resulting in a high potential for chemical weathering. The clay and silt-sized fractions comprise as much as 80% of glacial till and, for typical glacial sediment yields, represent on order 10$^{3}$ km$^{2}$ mineral surface area production per km$^{2}$ of glacier per year. Despite this production of fresh mineral surface area, silicate chemical weathering fluxes from glaciers are lower than found in other environments. Here, we demonstrate that the measured silicate weathering flux from a small Alaskan glacier can be predicted from the measured sediment yield, grain size distribution, and mineralogy. We use published mineral weathering rate constants, adjusted for 0\degC conditions found at glacier beds. The success of this calculation shows that silicate-weathering fluxes from glaciers are directly related to mineral surface area production, and that they are low due to depression of the mineral weathering rate constants by low temperatures. A corollary of this calculation is that deposition of fine-grained glacial erosion products in environments conducive to chemical weathering should enhance chemical weathering fluxes. We explore this idea by estimating weathering fluxes from loess deposited in forested regions downstream from active glaciers. Loess is a small fraction of the total glacial sediment yield, but it should be highly reactive owing to its surface area. If, as we expect, weathering fluxes are high from loess-mantled regions, this shows that weathering rates are linked with the products of erosion, rather than the process of physical erosion.
DE: 1815 Erosion and sedimentation
DE: 1827 Glaciology (1863)
DE: 1886 Weathering (1625)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting