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Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 4979-4992, 2015
https://doi.org/10.5194/bg-12-4979-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 Aug 2015
Assessing the potential of amino acid 13C patterns as a carbon source tracer in marine sediments: effects of algal growth conditions and sedimentary diagenesis
T. Larsen1, L. T. Bach2, R. Salvatteci3, Y. V. Wang3, N. Andersen1, M. Ventura4, and M. D. McCarthy5 1Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
2Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany
3Institute of Geoscience, Department of Geology, Kiel University, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany
4Biogeodynamics and Biodiversity Group, Centre for Advanced Studies of Blanes (CEAB), Spanish Research Council (CSIC), 17300-Blanes, Catalonia, Spain
5Ocean Sciences Department, UC Santa Cruz, Santa Cruz, CA 95064, USA
Abstract. Burial of organic carbon in marine sediments has a profound influence in marine biogeochemical cycles and provides a sink for greenhouse gases such as CO2 and CH4. However, tracing organic carbon from primary production sources as well as its transformations in the sediment record remains challenging. Here we examine a novel but growing tool for tracing the biosynthetic origin of amino acid carbon skeletons, based on naturally occurring stable carbon isotope patterns in individual amino acids (δ13CAA). We focus on two important aspects for δ13CAA utility in sedimentary paleoarchives: first, the fidelity of source diagnostic of algal δ13CAA patterns across different oceanographic growth conditions, and second, the ability of δ13CAA patterns to record the degree of subsequent microbial amino acid synthesis after sedimentary burial. Using the marine diatom Thalassiosira weissflogii, we tested under controlled conditions how δ13CAA patterns respond to changing environmental conditions, including light, salinity, temperature, and pH. Our findings show that while differing oceanic growth conditions can change macromolecular cellular composition, δ13CAA isotopic patterns remain largely invariant. These results emphasize that δ13CAA patterns should accurately record biosynthetic sources across widely disparate oceanographic conditions. We also explored how δ13CAA patterns change as a function of age, total nitrogen and organic carbon content after burial, in a marine sediment core from a coastal upwelling area off Peru. Based on the four most informative amino acids for distinguishing between diatom and bacterial sources (i.e., isoleucine, lysine, leucine and tyrosine), bacterially derived amino acids ranged from 10 to 15 % in the sediment layers from the last 5000 years, and up to 35 % during the last glacial period. The greater bacterial contributions in older sediments indicate that bacterial activity and amino acid resynthesis progressed, approximately as a function of sediment age, to a substantially larger degree than suggested by changes in total organic nitrogen and carbon content. It is uncertain whether archaea may have contributed to sedimentary δ13CAA patterns we observe, and controlled culturing studies will be needed to investigate whether δ13CAA patterns can differentiate bacterial from archeal sources. Further research efforts are also needed to understand how closely δ13CAA patterns derived from hydrolyzable amino acids represent total sedimentary proteineincous material, and more broadly sedimentary organic nitrogen. Overall, however, both our culturing and sediment studies suggest that δ13CAA patterns in sediments will represent a novel proxy for understanding both primary production sources, and the direct bacterial role in the ultimate preservation of sedimentary organic matter.

Citation: Larsen, T., Bach, L. T., Salvatteci, R., Wang, Y. V., Andersen, N., Ventura, M., and McCarthy, M. D.: Assessing the potential of amino acid 13C patterns as a carbon source tracer in marine sediments: effects of algal growth conditions and sedimentary diagenesis, Biogeosciences, 12, 4979-4992, https://doi.org/10.5194/bg-12-4979-2015, 2015.
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Short summary
A tiny fraction of marine algae escapes decomposition and is buried in sediments. Since tools are needed to track the fate of algal organic carbon, we tested whether naturally occurring isotope variability among amino acids from algae and bacteria can be used as source diagnostic fingerprints. We found that isotope fingerprints track algal amino acid sources with high fidelity across different growth conditions, and that the fingerprints can be used to quantify bacterial amino acids in sediment.
A tiny fraction of marine algae escapes decomposition and is buried in sediments. Since tools...
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