Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles

Throughout the Quaternary period, the Earth’s surface has been subject to large changes in temperature and precipitation associated with fluctuations between glacial and interglacial states that have affected biogeochemical cycling. However, the effect of these climate oscillations on weathering is debated, with climate modelling efforts using empirical relationships between measures of climate and weathering suggesting minimal changes in global weathering rates between these two climate states. The ratio of the cosmogenic isotope 10Be, which is produced in the atmosphere and deposited to the oceans and the land surface, to 9Be, which is introduced to the oceans by the riverine silicate weathering flux, can be used to track relative weathering fluxes. Here we apply this proxy to marine sediment beryllium records spanning the past two million years, and find no detectable shifts in inputs from global silicate weathering into the oceans. Using climate model simulations of the Last Glacial Maximum along with a model for silicate weathering, we find that there was large regional variability in runoff between glacial and interglacial periods, but that this regional variability was insufficient to shift global weathering fluxes. We suggest that this stability in weathering explains the observation that the removal of CO2from the atmosphere by silicate weathering has been in approximate balance with CO2degassing over the past 600,000 years.