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Abstract. Sedimentary records of lipid biomarkers such as leaf wax n-alkanes are influenced by not only ecosystem turnover and physiological changes in plants but also earth surface processes integrating these signals into the sedimentary record, though the effect of these integration processes is not fully understood. To determine the depositional constraints on biomarker records in a high-altitude small catchment system, we collected both soil and stream sediments along a 1000 m altitude transect (1500–2500 m a.s.l.) in the Areguni Mountains, a subrange of the Lesser Caucasus Mountains in Armenia. We utilize a treeline at ∼ 2000 m a.s.l., which separates alpine meadow above from deciduous forest below, to assess the relative contribution of upstream biomarker transport to local vegetation input in the stream. We find that average chain length (ACL), hydrogen isotope (δD) and carbon isotope (δ13C) values of n-alkanes are significantly different in soils collected above and below the treeline. However, samples collected from the stream sediments do not integrate these signals quantitatively. As the stream drops below the treeline, the ACL, δD and δ13C values of n-alkanes preserved in streambed sediments reflect a bias toward n-alkanes sourced from trees. This suggests that either (1) there is minimal transportation of organic matter from the more open vegetation at higher elevations or (2) greater production of target biomarkers by trees and shrubs found at lower elevations results in overprinting of stream signals by local vegetation. Though these observations may preclude using n-alkanes to measure past treeline movement in these mountains, δD values of biomarkers in fluvial deposits in these settings are more likely to record local hydrological changes rather than reflect fractionation changes due to turnover in the upstream vegetation structure. 

A paleotopographic record of Taiwan shows ~2 km of surface uplift since ~1.3–1.5 Ma. 

We present the first paleotopographic reconstruction of Taiwan by measuring the hydrogen isotope composition of leaf waxes (δ²H_nC29) preserved in 3-Ma and younger sediments of the southern Coastal Range. Plant leaf waxes record the δ²H of precipitation during formation, which is related to elevation. Leaf waxes produced across the orogen are transported and deposited in adjacent sedimentary basins, providing deep-time records of the source elevation of detrital organic matter. δ²H_nC29exported from the southern Taiwan orogen decreased by more than 40‰ since ~1.3–1.5 Ma, indicating an increase of >2 kilometers in the organic source elevation. The increase in organic source elevation is best explained by rapid surface uplift of the southern Central Range at around ~1.3–1.5 Ma and indicates that this part of the orogen was characterized by maximum elevations of at least 3 km at this time. Further increase in organic source elevation from ~0.85 to ~0.3 Ma indicates continued topographic growth to modern elevations. 

Stable isotope paleoaltimetry is one of the most commonly used approaches for quantifying the paleoelevation history of an orogen yet this methodology is often limited to arid to semi-arid climates, mountain systems with a clear orographic rainshadow and terrestrial basins. We present a new approach to reconstructing past topography and relief that uses the catchment-integrated signature of organic molecular biomarkers to quantify the hypsometry of fluvially-exported biomass. Because terrestrially-produced biomolecules are synthesized over the full range of global climate conditions and can be preserved in both terrestrial and marine sediments, the geochemistry of fluvially-transported sedimentary biomarkers can provide a means of interrogating the evolution of topography for a range of environments and depositional settings, including those not well suited for a traditional isotope paleoaltimetry approach. We show an example from Taiwan, a rapidly eroding tropical mountain system that is characterized by high rates of biomass production and short organic residence time and discuss key factors that can influence molecular isotope signal production, transport and integration. Data show that in high relief catchments of Taiwan, river sediments can record integration of biomass produced throughout the catchment. Sedimentary biomarker δ 2 H n C29 in low elevation river deposition sites is generally offset from the δ 2 H n C29 value observed in local soils and consistent with an isotope composition of organics produced at the catchment mean elevation. We test the effect of distinct molecular production and erosion functions on the expected δ 2 H n C29 in river sediments and show that elevation-dependent differences in the production and erosion of biomarkers/sediment may yield only modest differences in the catchment-integrated isotopic signal. Relating fluvial biomarker isotope records to quantitative estimates of organic source elevations in other global orogens will likely pose numerous challenges, with a number of variables that influence molecular production and integration in a river system. We provide a discussion of important parameters that influence molecular biomarker isotope signatures in a mountain system and a framework for employing a molecular paleohypsometry approach to quantifying the evolution of other orogenic systems.