Triple oxygen isotope insight into terrestrial pyrite oxidation
Jordon Hemingway, Haley Olson, Alexandra V. Turchyn, Edward T. Tipper, M. J. Bickle, David T. Johnston
Abstract
Significance Pyrite is oxidized during weathering to form dissolved sulfate that is carried to the ocean by rivers. This process is thought to incorporate atmospheric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> -derived oxygen; geologically preserved sulfate has thus been proposed to directly trace past <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> isotope compositions. However, this mechanism has not been thoroughly tested in modern weathering environments. We show that dissolved sulfate in Himalayan rivers is predominantly derived from pyrite, yet its oxygen isotope compositions preclude direct <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> incorporation. Rather, alternative oxygen sources (e.g., reactive oxygen species) may be incorporated during oxidation, prompting reconsideration of the pyrite oxidation mechanism and the interpretation of geologically preserved sulfate as a direct <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> tracer.