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

摘要

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 δ~(13)C 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 δ~(13)C 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 (OC_(TERR) and OCMAR) using Br:TOC ratios show that OC_(MAR)burial is relatively constant while OC_(TERR)and hence TOC vary more strongly; this pattern suggests either episodic terrigenous carbon inputs or winnowing before burial. Variations in TOC:TN and δ~(13)C 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 δ~(13)C due to less uncertainty of the terrestrial end-member.