Estimation of Marine Versus Terrigenous Organic Carbon in Sediments Off Southwestern Taiwan Using the Bromine to Total Organic Carbon Ratio as a Proxy

• Published in: Journal of geophysical research. Biogeosciences 2018-10, Vol.123 (10), p.3387-3402
• Main Authors: Kandasamy, Selvaraj, Lin, Baozhi, Lou, Jiann‐Yuh, Kao, Shuh‐Ji, Chen, Chen‐Tung Arthur, Mayer, Lawrence M.
• Format: Article
• Language: English
• Subjects: Bromine; Carbon; Carbon cycle; carbon isotope; Carbon isotopes; continental margin; Earth; Lake deposits; Lake sediments; Lakes; Marine sediments; Mountain regions; Mountainous areas; Organic carbon; Organic matter; Passive margins; Profiles; Ratios; River beds; Riverbeds; Rivers; Sediment; Sediments; Soil; southwestern Taiwan; Suspended sediments; Terrestrial environments; Total organic carbon; Winnowing
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2018JG004674

We measured bromine to total organic carbon (Br:TOC) ratios as an organic source indicator in terrestrial and marine settings of Taiwan, a tectonically active margin that differs from previously studied, passive margins. Terrestrial lake sediments, soils, and river bed and suspended sediments showed Br:TOC ratios ranging from 0.02 to 2.8 mg‐Br/g‐TOC. In ocean margin sediments, Br:TOC ratios ranged from terrigenous values up to 7.6 mg‐Br/g‐TOC. A two‐component Br:TOC mixing model for ocean margin sediments indicates roughly equal proportions of terrigenous and marine organic matter (FT and FM, respectively). Terrestrial δ13C values varied from −31.5 to −24.7‰, a range which is twice the difference between the isotopic terrigenous and marine end‐members used to calculate these proportions. FT and FM based on δ13C were similar to those using Br:TOC if averaged across all marine sediments but often differed at the level of individual samples. Depth profiles of amounts of these two forms of organic matter (OCterr and OCmar) using Br:TOC ratios show that OCmar burial is relatively constant while OCterr and hence TOC vary more strongly; this pattern suggests either episodic terrigenous carbon inputs or winnowing before burial. Variations in TOC:TN and δ13C are consistent with this control of TOC by terrigenous carbon. This study validates Br:TOC as a source indicator for terrigenous versus marine‐derived organic matter in sediments derived from mountainous areas in Oceania. As a single parameter source indicator it should have less error than δ13C due to less uncertainty of the terrestrial end‐member. Plain Language Summary Ocean margins account for most burial of organic matter in Earth's sediments. This burial affects global cycles such as carbon, nitrogen, and oxygen. Both land and sea contribute organic matter to these margin sediments, varying in extent in different places and times. Here we explore the use of bromine as an indicator of land versus sea contribution in Taiwan—representing the sediment‐rich, southwest Pacific region of Oceania. We compare the use of bromine with the more commonly used stable carbon isotope approach, finding that each provides 50:50 estimates of land versus sea sources at the scale of averages. Nevertheless, there is less agreement at the scale of individual samples, probably due to wide ranges of carbon isotope compositions in terrestrial end‐members. Key Points We report the first time Br measurements of terrestrial particula