Weak influences of climate and mineral supply rates on chemical erosion rates: Measurements along two altitudinal transects in the Idaho Batholith

Abstract

Chemical weathering promotes regolith production, physical erosion, nutrient supply, and drawdown of atmospheric CO2. Although mineral dissolution rates show dependences on temperature and moisture in theoretical models and laboratory experiments, effects of climate on chemical erosion rates in nature remain uncertain, in part because variations in physical erosion rates and lithology can obscure climatic signals in chemical erosion rate measurements. Here we present new estimates of millennial‐scale chemical and physical erosion rates along two altitudinal transects in the Idaho Batholith. Our measurements suggest that chemical erosion rates and the extent of regolith chemical alteration are insensitive to mean annual regolith temperature, even though the study sites span a wide range in temperatures (4.8°C–10.9°C). These data also suggest that rates of chemical erosion and the extent of regolith chemical alteration are weakly correlated with the annual duration of high regolith moisture conditions. Lastly, our measurements show that the sampled regoliths tend to grow more chemically weathered with increasing regolith residence time, implying that weathering at these sites is primarily limited by mineral dissolution kinetics rather than mineral supply rates to the regolith. The lack of strong control by mineral supply means that chemical erosion rates at these sites could potentially vary in response to climatic factors. Such climatically driven variation in chemical erosion rates is not obvious in our data, however. Instead, our measurements suggest that chemical erosion rates at these sites are insensitive to mean annual regolith temperature and only weakly dependent on the length of the wet season.