A Multiple Tracer Approach to Tracking Changes in Terrestrial Organic Carbon Transported Across a Small Mountainous River Landscape Using Deuterated Tetramethylammonium Hydroxide Thermochemolysis

Cumulatively, organic carbon from sedimentary rocks, soils and vascular plants comprise the terrestrial organic carbon (TOC) pool. When sequestered in the marine sedimentary record TOC represents a global carbon sink for the greenhouse gas CO2 while its decomposition results in the release of CO2 and represents a carbon source. The regulation of atmospheric CO2 over geological timescales depend on the balance between these competing processes and is primarily controlled by the transfer of TOC to the marine environment. Although large rivers such as the Amazon were thought to transport the bulk of TOC to the ocean, more recent studies have focused on small mountainous rivers (SMRs) since these may cumulatively contribute just as much TOC to oceans worldwide. However, the fate of TOC expelled by SMRs is still highly debated but a necessary step in understanding the role of TOC in regulating the global carbon cycle.;The major challenge in determining the fate of TOC in marine environments is its complex mixture of organic compounds sourced from multiple OC pools (sedimentary rocks, soils, vascular plants etc.) and the vastly different analytical methods used to detect and track changes in source specific organic compounds - "biomarkers" - of TOC along the terrestrial-river-marine transport continuum. Therefore, there remains a need for broad-spectrum analytical tools that can be used across multiple geochemical matrices to effectively differentiate OC signatures between TOC (carbon sources), river suspended sediments (transition zone) and marine sediments (ocean carbon sink).;We present a modified "online" thermochemolysis method that utilizes deuterium-labeled tetra-methylammonium hydroxide (D-TMAH thermochemolysis) to characterize TOC biomarker abundance and distribution at various points along a well-studied and prototypical SMR system; the Waipaoa Sedimentary System (WSS) located on New Zealand's North Island. First, we outline the empirical approach used to optimize D-TMAH. Next, we evaluated this method by comparing its biomarker results to those from the more commonly used cupric oxide (CuO) oxidation for a small suite of plant tissues. Finally, we applied D-TMAH at our study site to map differences in the biomarker signature between TOC sources, suspended river sediments and marine surface sediments (0-2cm) from WSS.