Pitfalls of acid leaching method for determining organic and inorganic carbon contents in marine sediments
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Pitfalls of acid leaching method for determining organic and inorganic carbon contents in marine sediments Chen Ling1, Zhifei Liu1*, Jingwen Zhang1, Yulong Zhao1, Yanwei Zhang1, Adrian R. Fernandez1 1 State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
Received 13 December 2019; accepted 2 March 2020 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity, global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments. Key words: marine sediments, organic carbon, inorganic carbon, acid leaching method, limitation Citation: Ling Chen, Liu Zhifei, Zhang Jingwen, Zhao Yulong, Zhang Yanwei, Fernandez Adrian R.. 2020. Pitfalls of acid leaching method for determining organic and inorganic carbon contents in marine sediments. Acta Oceanologica Sinica, 39(8): 96–102, doi: 10.1007/s13131-020-1631-z
1 Introduction Preservation and migration of carbon in marine sediments are important processes for transferring carbon from an active surface cycle to a slower geological cycle (Keil, 2017). The marine biological pump, as an important part of the global carbon cycle, is the main mechanism for absorbing carbon from atmosphere through photosynthesis and sequestering it into the deep sea (Passow and Carlson, 2012). Carbon fixed by primary productivity is mainly transported to the deep sea by passive sinking (Castro et al., 2018). The sinking particles, the most suitable materials to study the sinking process, are mainly composed of biogenic and terrigenous components. The biogenic component mainly consists of calcareous shells (CaCO 3 ), siliceous shells (opal), and organic matter (Chen et al., 1998). The organic matter can be represented by organic carbon, while the CaCO3 can be calculated by inorganic carbon (Chen et al., 2015). As a result, it highlights the importance of a precise laboratory method to determine the carbon content in marine sediments (Sun et al., 2014). Total organic carbon (TOC) is the total amount of carbon in
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