Silicate weathering in marine sediments: processes, governing factors, and role in global elemental cycles

Abstract

not-yet-known not-yet-known not-yet-known unknown Silicate weathering occurs across marine sediments with a spectrum of reaction balances and fluxes, influencing seawater chemistry and carbon cycling on long timescales. Fluxes range from net alkalinity and cation consumption (‘reverse’ weathering) to net alkalinity and cation release (‘forward’ weathering), varying across depositional environments and locally with depth and time. Here, we review the research history, mechanisms and biogeochemistry of silicate weathering in marine sediments. We then examine the distribution of marine sediment sources (reactants), depositional environments (biogeochemical, physical), and authigenic mineral suites (products) from the coast to the deep sea to assemble representative reaction balances and rate estimates. Permeable sediments, deltaic mobile muds, steady anoxic muds, deep-sea clays and carbonate oozes together constitute significant global fluxes with vastly different reaction balances, rates and sensitivities. These fluxes appear to net reduce alkalinity generation (~ - 30 %), but augment authigenic carbonate burial (~ + 10 %) associated with terrestrial silicate weathering today. A new set of modern oceanic budgets, embracing the coupling of Si, K, Mg, Ca, and alkalinity, suggests those cycles to be close to steady state (≤ + 25 % imbalance for Si and alkalinity) and ~ 20 – 50% faster. This continuum of weathering environments has evolved with magmatism and tectonics, climate and…