Earth's Weathering Continuum: Links between weathering, terrigenous marine sediments, and global biogeochemistry

Abstract

Weathering, the chemical transformations of rocks and sediments in water, globally redistributes elements and modulates global carbon cycling and ocean acid-base chemistry on geological timescales. Concepts and models of the global biogeochemical cycles have largely focused on rock weathering on land. Here, I systematically investigate the role of marine sediment weathering, i.e., chemical reactions between rock and soil-derived minerals, biological remains and seawater, in the global cycles of the elements and in the regulation of planetary conditions. Based on data compilations, statistical and mechanistic models, I quantify material fluxes from land to sea, systematically conceptualize the factors governing marine weathering dynamics, and derive chemical exchange fluxes between seawater and sediments. Marine weathering can either release or consume nutrients, carbon dioxide, major and trace elements at rates that vary by several orders of magnitude in different sedimentary environments. These dynamics are governed by terrestrial and marine sediment sources and by the biological and physical conditions of deposition. Shallow nearshore environments appear to play a prominent role that is unproportionally large compared to their spatial extent and particularly susceptible to environmental change. Consequently, weathering is most accurately thought of as a continuum of chemical reactions in a succession of environments, the relative distribution of which eventually determines the global net weathering flux and effects on ocean biogeochemistry and carbon cycling.