2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 9-11
Presentation Time: 11:00 AM


FISHER, Beth A., Department of Soil, Water and Climate, University of Minnesota Twin Cities, 1991 Upper Buford Cir, 439 Borlaug Hall, St Paul, MN 55108, YOO, Kyungsoo, Soil, Water, and Climate, University of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55108, AUFDENKAMPE, Anthony K., Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311 and NATER, Ed, Soil, Water, and Climate, University of Minnesota, 439 Borlaug Hall, 1991 Upper Buford Circle, Saint Paul, MN 55108, fisherba@umn.edu

Mineral surface area is a measurable landscape property that is a critical interface for biogeochemical interactions that span every discipline in the Critical Zone. This work quantifies the vertical and lateral generation and distribution of specific surface area (SSA) on a landscape scale using two 21-meter deep drill cores. The cores are located in Spring Brook, a first-order forested watershed in the Christina River Basin Critical Zone Observatory, which is underlain by greenschist bedrock in the Piedmont physiographic province. We positioned drill sites at the ridge and at an interfluve 11 meters lower in elevation to elucidate hillslope dynamics in the generation of SSA and the resulting coevolution of landscape and biogeochemical processes. We present a first ever landscape scale inventory of mineral surface area, revealing that the inventory of SSA reaches an asymptotic relationship with depth, and inflections in SSA inventory with depth provide an additional means to reveal significant weathering interfaces. The SSA inventory reveals a distinct change in rock physical properties at 3 meters below the ground surface and little or no surface area change below this 3 meter-deep interface, representing a very gradual transition from weathered to fresh bedrock. We identify that chemical weathering alters minerals to generate the shallow and drastic SSA change. Near-surface pedogenic and biotic processes are key drivers for the distinct surface area increase and mineralogical changes from the ground surface to 3 meters deep. However, organic matter occlusion of mineral surfaces in the first two meters of this interface is not a clear driving mechanism for mineral weathering in this landscape. We conclude that the primary controls on SSA production occur in the near-surface zone where a confluence of biogeochemical processes physically disrupt and chemically alter minerals.