Soils as pacemakers and limiters of global silicate weathering

The weathering and erosion processes that produce and destroy regolith are widely recognized to be positively correlated across diverse landscapes. However, conceptual and numerical models predict some limits to this relationship that remain largely untested. Using new global data compilations of soil production and weathering rates from cosmogenic nuclides and silicate weathering fluxes from global rivers, we show that the weathering-erosion relationship is capped by certain 'speed limits'. We estimate a soil production speed limit of between 320 to 450 t km(-2) yr(-1) and the associated weathering rate speed limit of roughly 150 t km(-2) yr(-1). These limits appear to be valid for a range of lithologies, and also extend to mountain belts, where soil cover is not continuous and erosion rates outpace soil production. We argue that the presence of soil and regolith is a requirement for high weathering fluxes from a landscape, and that rapidly eroding, active mountain belts are not the most efficient sites for weathering. (c) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.