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RESEARCH

2023.06.29

Environmental study through chlorophylls and porphyrins

Chlorophylls are widely known pigments that collect light energy in photosynthesis. On Earth, more than one billion tons of chlorophyll are synthesized annually. Since they are molecule synthesized exclusively by photosynthetic organisms (i.e. plants), they retain information about the euphotic layer of Earth's surface environment. The biological and chemical aspects of the chlorophyll molecule have long been studied, and hence its synthesis and metabolism are now very well understood. With this strong background, chlorophylls have great potential as a tool for geoscience.

Chlorophylls are degraded by various chemical reactions and microbial activities after the death of plants, but some of them are preserved in sediments on the seafloor. Chlorophylls (and their degradation products) in sediments are valuable ‘biomarkers’ that tell us about past biological production, and their carbon and nitrogen isotope ratios provide rigorous information about the carbon and nitrogen cycles at the time of sediment formation. Interestingly, a variety of tetrapyrrole structures, the central ring of the chlorophyll molecule, are found in sediments (and sedimentary rocks) over even longer period of time. They are called ‘porphyrins’ and have sometimes been extracted from sediments more than one billion years old. Few other nitrogenous compounds have been preserved for such a long period of time, and their carbon and nitrogen isotope ratios remain as they were at the time of production. Porphyrins, along with the highly indicative nature of chlorophylls, the compounds from which they originated, provide a unique approach for understanding the ancient Earth's environment.

Our major publications on this topic

  • Isaji, Y., Yoshikawa, C., Ogawa, N.O., Matsumoto, K., Makabe, A., Ishikawa, N.F., Ogawa, H., Saito, H., Honda, M.C., and Ohkouchi, N. (2022) Nitrogen sources for phytoplankton in the eastern Indian Ocean determined from δ15N of chlorophyll a and divinylchlorophyll a. Geochemistry, Geophysics, Geosystems, 23, e2021GC010057. [Open Access]
  • Hallman, C., Grosjean, E., Shapiro, N., Kashiyama, Y., Chikaraishi, Y., Ohkouchi, N., and Summons, R.E. (2021) Redox-controlled ammonium storage and overturn in Ediacaran Oceans. Frontiers in Earth Science, 9:706144. [Open Access]
  • Isaji, Y., Ogawa, N.O., Takano, Y.,and Ohkouchi, N. (2020) Quantification and carbon and nitrogen isotopic measurements of heme B in environmental samples. Analytical Chemistry, 92, 11213-11222. [Abstract]
  • Isaji, Y., Ogawa, N.O., Boreham, C., Kashiyama, Y., and Ohkouchi, N. (2020) Evaluation of δ13C and δ15N uncertainties associated with the compound-specific isotopic analysis of geoporphyrins. Analytical Chemistry, 92, 3152-3160. [Abstract]
  • Gueneli, N., McKenna, A.M., Ohkouchi, N., Boreham, C., Beghin, J., Javaux, E.J., and Brocks, J.J. (2018) 1.1 billion years old porphyrins and their isotopic composition establish a marine ecosystem dominated by bacterial primary producers. Proceedings of the National Academy of Science, USA, 115, E6978-E6986. [Open Access]
  • Naeher, S., Suga, H., Ogawa, N.O., Schubert, C.J., Grice, K., and Ohkouchi, N. (2016) Compound-specific isotopic carbon and nitrogen isotopic compositions of chlorophyll a and its derivatives reveal the eutrophication history of Lake Zurich (Switzerland). Chemical Geology, 443, 210-219. [Abstract]
  • Ishikawa, N.F., Yamane, M., Suga, H., Ogawa, N.O., Yokoyama, Y., and Ohkouchi, N. (2015) Chlorophyll a specific Δ14C, δ13C, and δ15N values in stream periphyton: implications for aquatic food web studies. Biogeosciences, 12, 6182-6789. [Abstract]
  • Ohkouchi, N., and Takano, Y. (2014) Organic nitrogen: Sources, fates, and chemistry. Treatise on Geochemistry (Eds. Falkowski P and Freeman KH), 12, 251-289. [Abstract]
  • Kusch, S., Kashiyama, Y., Ogawa, N.O., Altabet, M., Butzin, M., Friedrich, J., Ohkouchi, N., and Mollenhauer, G. (2010) Implications for chloro- and pheopigment synthesis and preservation from combined compound-specific δ13C, δ15N, and Δ14C analysis. Biogeosciences, 7, 4105-4118. [Abstract]
  • Tyler, J., Kashiyama, Y., Ohkouchi, N., Ogawa, N.O., Yokoyama, Y., Chikaraishi, Y., Staff, R.A., Ikehara, M., Bronk Ramsey, C., Bryant, C., Brock, F., Gotanda, K., Haraguchi, T., Yonenobu, H., and Nakagawa, T. (2010) Tracking aquatic change using chlorin-specific carbon and nitrogen isotopes: The last glacial-interglacial transition at Lake Suigetsu, Japan. Geochemistry Geophysics Geosystems, 11, Q09010. [Open Access]
  • Ohkouchi, N., Nakajima, Y., Okada, H., Ogawa, N.O., Chikaraishi, Y., Suga, H., Sakai, S., and Kitazato, H. (2008) Carbon isotopic composition of tetrapyrrole nucleus in chloropigments from a saline meromictic lake: A mechanistic view for interpreting the isotopic signature of alkyl porphyrins in geological samples. Organic Geochemistry, 39, 521-531. [Abstract]
  • Kashiyama, Y., Miyashita, H., Ogawa, N.O., Chikaraishi, Y., Takano, Y., Suga, H., Toyofuku, T., Nomaki, H., Kitazato, H., Nagata, T., and Ohkouchi, N. (2008) Evidence of global chlorophyll d. Science, 321, 658. [Abstract]
  • Kashiyama, Y., Ogawa, N.O., Kuroda, J., Shiro, M., Nomoto, S., Tada, R., Kitazato, H., and Ohkouchi, N. (2008) Diazotrophic cyanobacteria as the major photoautotrophs during mid-Cretaceous Oceanic Anoxic Events: nitrogen and carbon isotopic evidence from sedimentary porphyrin. Organic Geochemistry, 39, 532-549. [Abstract]
  • Ohkouchi, N., Kashiyama, Y., Kuroda, J., Ogawa, N.O., and Kitazato, H. (2006) The importance of diazotrophic cyanobacteria as primary producers during Cretaceous Oceanic Anoxic Event 2. Biogeosciences, 3, 467-478. [Abstract]
  • Ohkouchi, N., Nakajima, Y., Okada, H., Ogawa, N.O., Suga, H., Oguri, K., Kitazato, H. (2005) Biogeochemical processes in the meromictic lake Kaiike: Implications from carbon and nitrogen isotopic compositions of photosynthetic pigments. Environmental Microbiology, 7, 1009-1016. [Abstract]