LATITUDINAL TRENDS IN MODERN FLUVIAL EROSIONAL EFFICIENCY ALONG THE ANDES

Abstract

Abstract Latitude is a dominant control on climate, influencing both temperature and precipitation, leading to potential gradients in erosional efficiency. Previous work focused on the latitudinal control of glacial erosion on topography; however, the expected latitudinal trend in erosional efficiency in the absence of glacial processes is unknown. We parameterize a suite of numerical models using uniform rock-uplift and climate from the Andes to explore how latitudinal patterns of rainfall could influence the efficiency of fluvial bedrock erosion. We use the CHILD landscape evolution model parameterized with storm duration, intensity and frequency statistics from NCEP/NCAR Reanalysis data along the Andes over 31 years to predict latitudinal trends in topography subject only to fluvial and hillslope erosion. Modeled elevations, as a metric for erosional efficiency, vary 2–30 fold depending on the erosional and hydrological model parameterization. Modeled elevation trends generated using stochastic storm generation vary significantly from those generated using mean annual precipitation (MAP). The variation suggests MAP may not capture the true erosional efficiency of the modern climate in some locations, but may in others, explaining the discrepancy of conclusions in previous studies. Erosional efficiency is greatest in the tropics (5–15°S) where high intensity and frequent storms occur and mid-latitudes (30–35°S) where less frequent but intense storms occur. Erosional efficiency is lowest in the subtropics (20 to 25°S) where low intensity and infrequent storms occur and upper-mid-latitudes (45–50°S) where low intensity and somewhat frequent storms occur. Erosional efficiency varies across the width of the orogen because of across-orogen effects. The results provide further evidence supporting climate's control on erosion processes and topography, highlighting the importance of stochastic storm distributions and suggesting that latitudinal controls on rainfall can explain some observed trends in topography. The modern latitudinal trend in topography is frequently used as an argument for a glacial buzzsaw; however, our results suggest more information on the pre-glacial distribution of topography is needed to justify such an argument since latitude dependent rainfall regimes may generate similar topographic trends.