Effect of rock uplift and Milankovitch timescale variations in precipitation and vegetation cover on catchment erosion rates

Abstract

Catchment erosion and sedimentation are influenced by variations in the rates of rock uplift (tectonics) and periodic fluctuations in climate and vegetation cover. This study focuses on quantifying the effects of changing climate and vegetation on erosion and sedimentation over distinct climate-vegetation settings by applying the Landlab-SPACE landscape evolution model. As catchment evolution is subjected to tectonic and climate forcings at millennial to million-year timescales, the simulations are performed for different tectonic scenarios and periodicities in climate-vegetation change. We present a series of generalized experiments that explore the sensitivity of catchment hillslope and fluvial erosion as well as sedimentation for different rock uplift rates (0.05, 0.1, 0.2g€¯mmg€¯a-1) and Milankovitch climate periodicities (23, 41, and 100g€¯kyr). Model inputs were parameterized for two different climate and vegetation conditions at two sites in the Chilean Coastal Cordillera at g1/426g g€¯S (arid and sparsely vegetated) and g1/433g g€¯S (Mediterranean). For each setting, steady-state topographies were produced for each uplift rate before introducing periodic variations in precipitation and vegetation cover. Following this, the sensitivity of these landscapes was analyzed for 3g€¯Myr in a transient state. Results suggest that regardless of the uplift rate, transients in precipitation and vegetation cover resulted in transients in erosion rates in the direction of change in precipitation and vegetation. The transients in sedimentation were observed to be in the opposite direction of change in the precipitation and vegetation cover, with phase lags of g1/41.5-2.5g€¯kyr. These phase lags can be attributed to the changes in plant functional type (PFT) distribution induced by the changes in climate and the regolith production rate. These effects are most pronounced over longer-period changes (100g€¯kyr) and higher rock uplift rates (0.2g€¯mmg€¯yr-1). This holds true for both the vegetation and climate settings considered. Furthermore, transient changes in catchment erosion due to varying vegetation and precipitation were between g1/435g€¯% and 110g€¯% of the background (rock uplift) rate and would be measurable with commonly used techniques (e.g., sediment flux histories, cosmogenic nuclides). Taken together, we find that vegetation-dependent erosion and sedimentation are influenced by Milankovitch timescale changes in climate but that these transient changes are superimposed upon tectonically driven rates of rock uplift.