PhD defence: Earth’s Weathering Continuum

PhD Candidate: Gerrit Müller

Defence date: 27-11-2024
Time: 14:15
Institute: Utrecht University
Location: Academiegebouw, Domplein 29, Utrecht

PhD supervisors:
prof. dr. J.B.M. Middelburg
prof. dr. A. Sluijs

Title thesis: Earth’s Weathering Continuum


The chemical weathering of rocks, e.g., during soil formation, leads to a global scale redistribution of the chemical elements. Weathering on land typically releases nutrients otherwise trapped in rocks and transforms atmospheric carbon dioxide (CO2 dissolved in rain) to dissolved bicarbonate (HCO3-) at rates that appear to accelerate in a warming climate. Because CO2 has a warming effect on climate (‘greenhouse’ effect), weathering is thought to exert carbon-cycle feedback that stabilizes life-supporting Earth surface conditions on long, geological timescales. The relevant timescales depend on the material weathered: Limestone (carbonate minerals, mostly (Ca,Mg)CO3) weathers rapidly but its chemical effects are largely reversed by biological calcification (CaCO3 biomineralization) in the ocean after ~ 50,000 – 100,000 years. However, reorganisation of carbonate sources and sinks within the ocean can drive long-term effects. The bicarbonate released during weathering of silicate rocks (various Si-based minerals) is only partly offset by calcification, hence silicate weathering net sequesters atmospheric CO2, and it also adds salts and nutrients to the oceans. However, despite this relevance to seawater chemistry and Earth system regulation, the role of the weathering feedback and its relationship to biology, tectonics and climate remain enigmatic, impeding our understanding of past and future Earth system evolution. Traditionally, the weathering of continental and oceanic crusts is considered in biogeochemical cycles and Earth system models, but many biogeochemical budgets cannot yet consentaneously be balanced.