“Wrecking the rocks”: Continental weathering by groundwater

Abstract

Groundwater solute mass flux discharged from the continents to the oceans is between 56% and 63% of particulate sediment transport mass flux. Herein we utilized newly developed continental geospatial groundwater concentration estimates that were multiplied by groundwater volumetric recharge flux to provide a continental-scale discharge mass flux to the oceans of 7.3 Pg DS/yr (petagrams dissolved solutes per year). This mass flux was evaluated from six continental ecosystems: direct ocean discharge (0.28 Pg DS/yr), endorheic basins (0.59 Pg DS/yr), cold-wet exorheic basins (0.55 Pg DS/yr), cold-dry exorheic basins (1.1 Pg DS/yr), warm-dry exorheic basins (0.82 Pg DS/yr), and warm-wet exorheic basins (4.0 Pg DS/yr), thus providing insight into the role of rainfall and temperature on continental weathering and denudation. A new, robust molar silicate/carbonate ratio of 0.42 was calculated for weathering of continental rocks, which is important in the Urey model of climate change. We estimate that rock weathering accounts for ~50% of the total solute mass flux discharged from the continents, the remainder being from externally derived marine aerosols and organic-derived bicarbonate.