Plant Biomarker Isotopes and Catchment Integration of Organic Matter in Tropical, Rapidly Eroding Catchments of Eastern Taiwan: Implications for Paleotopography Reconstruction

Understanding the interplay of climate, surface processes, and tectonics is vital for understanding landscape evolution. Organic biomarker-based proxies have proved to be a powerful tool for understanding these complex feedbacks and are increasingly utilized to reconstruct past topographic change. One of the fundamental challenges to using biomarkers to understand landscape evolution is the uncertainty in the relationship between geochemical signatures of organic matter and surface processes. Here, we examine the geochemical signature of organic matter (n-alkanes) exported via the primary river networks in Taiwan, a region characterized by some of the highest rates of surface uplift, erosion, and carbon export on the globe. These are used to quantify the relationship between catchment processes and biomarker isotopes. Soil and river sediment samples were collected from river catchments that span the length of the eastern coast of Taiwan. Soil samples were collected in a vertical transect representing the elevation gradient. Corresponding river sediments were also collected at elevations comparable to those of the soil samples. The isotopic signatures of hydrogen (δD) in organic matter obtained at various elevations within a catchment reflects the integration of plant n alkanes in the sedimentary cycle. Data show a significant biomarker isotope gradient as a function of elevation and variable offset in biomarker δD between soil and river sediment pairs. Moreover, the distributions of n alkanes differ between catchments along the orogen, which implies different retention times of the terrestrial organic matter. These data are used to evaluate the factors that influence catchment integration of biomarker isotope signatures and implications for isotope reconstruction of past topography and climate change.