28 Mar 2022
28 Mar 2022
Status: this preprint is currently under review for the journal ESurf.

Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

Beth A. Fisher1, Kyungsoo Yoo2, Anthony K. Aufdenkampe3, Edward A. Nater2, Joshua M. Feinberg4, and Jonathan E. Nyquist5 Beth A. Fisher et al.
  • 1Biochemistry, Chemistry, and Geology, Minnesota State University, Mankato, Mankato, 56001, USA
  • 2Soil, Water and Climate, University of Minnesota, St. Paul, 55108, USA
  • 3LimnoTech, Oakdale, 55128
  • 4Earth & Environmental Sciences, University of Minnesota, Minneapolis, 55455, USA
  • 5Earth & Environmental Sciences, Temple University, Philadelphia, 19122, USA

Abstract. Mineral specific surface area (SSA) is generated as primary minerals weather and restructure into secondary phyllosilicate, oxide, and oxyhydroxide minerals. SSA is a measurable property that captures cumulative effects of many physical and chemical weathering processes in a single measurement and has meaningful implications to many soil processes, including water holding capacity and nutrient availability. Here we report our measurements of SSA and mineralogy of two 21-meter deep SSA profiles at two landscape positions, in which the emergence of a very small mass percent (0.8–2.7 %) of secondary oxide generated 36–81 % of the total SSA at both landscape positions. The SSA transition occurred at 3 meters and did not coincide with the morphological boundaries of soil to weathered rock or with the water table. The 3-meter boundaries coincide with the depth extent of secondary iron minerals and secondary phyllosilicates. Although elemental depletions in both profiles extend to 7 and 10 meters, secondary minerals were not detected below 3 meters. The 3-meter depth marks the emergence of secondary oxide minerals, and this boundary appears to be the depth extent of oxidation weathering reactions. Our results suggest that oxidation weathering reactions may be the primary limitation in the co-evolution of both secondary silicate and secondary oxide minerals.

Beth A. Fisher et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2022-9', Anonymous Referee #1, 17 May 2022
    • AC1: 'Reply on RC1', Beth Fisher, 17 Jul 2022
  • RC3: 'Comment on esurf-2022-9', Sétareh RAD, 16 Jun 2022
    • AC2: 'Reply on RC3', Beth Fisher, 17 Jul 2022

Beth A. Fisher et al.

Beth A. Fisher et al.


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Short summary
We measured surface area of minerals in two 21 m cores from soil to bedrock, to test hypotheses on formation of this critical soil property. A sharp continual increase in high-surface area secondary minerals extended from 3 m to the ground surface. Half of total surface area was from corroded iron minerals, which form with oxygen, even though iron was < 3 % of weathered rock. Other hypotheses cannot explain observations. Acid dissolution of rock started at 7 m but did not form new minerals.