Royal Netherlands Institute for Sea Research
Guest researcher
Universiteit Utrecht
Jaap Sinninghe Damste
  • Developing organic geochemical proxies for reconstructing Phanerozoic CO2
  • Exploring potential CO2 biomarkers in naturally-occurring high-CO2 environments
  • Validating isotopic fractionation in phytoplankton through multi-proxy analysis

Caitlyn Witkowski

Guest researcher


Research Interests

My research interests are to better understand the environment through the use of organic geochemical techniques. The goal of my PhD, more specifically, is to explore past atmospheric concentrations of carbon dioxide (pCO2).

pCO2 is central for the biosphere, carbon cycle, and climate. To better understand pCO2 for today and tomorrow, the history of pCO2 needs to be better understood. Secular trends of pCO2 often rely on compiling many different proxies in order to average the conflicting estimations and to extend records. Thus, a single well-constrained proxy that spans the Phanerozoic may strengthen and support the current pCO2 reconstructions.

One of the most robust pCO2 proxies is photosynthetic carbon isotopic fractionation (Ɛp), which occurs during CO2-fixation when the enzyme Rubisco uses lighter carbon (12C) from the environment's CO2 before they use the heavier carbon (13C), making the photoautotroph isotopically lighter than the environment.  Ɛp is generally applied to species-specific compounds which have an evolution-limited record (e.g. alkenones limited ca. 50 Ma). To extend the use of Ɛp, we explore the general phytoplankton biomarkers like phytane.

Phytane is a diagenetic product of all phytoplankton, making it spatially and temporally ubiquitous in the geologic record. To develop and validate its potential as a pCO2 proxy, we explored phytane in modern environments, in a multi-proxy case study, and in a Phanerozoic reconstruction.

Collecting seawater filters, plankton net filters, and sediment samples at Shikine Island, Japan



Comparing CO2 vents sites, collecting seawater filters, plankton net filters, and sediment samples at Vulcano Island, Italy




Linked news

Thursday 09 January 2020
Reconstructing past atmospheric CO2 levels to better understand climate change
Carbon dioxide plays a critical role in global climate and is of growing concern with the continuous rise of CO2. Past Earth is used to better understand the precise relationship between CO2 and climate (aka climate sensitivity), but reconstructing…
Wednesday 28 November 2018
Fossiele algen onthullen 500 miljoen jaar klimaatverandering
Om betere voorspellingen te doen over het klimaat in de toekomst, kijken geologen terug in het verre verleden naar de samenhang tussen veranderende CO2-concentraties en het klimaat. Wetenschappers van het Koninklijk Nederlands Instituut voor…

NIOZ publications

  • 2019
    Hollis, C.J.; Dunkley Jones, T.; Anagnostou, E.; Bijl, P.K.; Cramwinckel, M.J.; Cui, Y.; Dickens, G.R.; Edgar, K.M.; Eley, Y.; Evans, D.; Foster, G.L.; Frieling, J.; Inglis, G.N.; Kennedy, E.M.; Kozdon, R.; Lauretano, V.; Lear, C.H.; Littler, K.; Lourens, L.; Meckler, A.N.; Naafs, B.D.A.; Pälike, H.; Pancost, R.D.; Pearson, P.N.; Röhl, U.; Royer, D.L.; Salzmann, U.; Schubert, B.A.; Seebeck, H.; Sluijs, A.; Speijer, R.P.; Stassen, P.; Tierney, J.E.; Tripati, A.K.; Wade, B.S.; Westerhold, T.; Witkowski, C.R.; Zachos, J.C.; Zhang, Y.G.; Huber, M.; Lunt, D.J. (2019). The DeepMIP contribution to PMIP4: methodologies for selection, compilation and analysis of latest Paleocene and early Eocene climate proxy data, incorporating version 0.1 of the DeepMIP database. Geosci. Model Dev. 12(7): 3149-3206.
    Witkowski, C.R.; Agostini, S.; Harvey, B.P.; van der Meer, M.T.J.; Sinninghe Damsté, J.S.; Schouten, S. (2019). Validation of carbon isotope fractionation in algal lipids as a pCO2 proxy using a natural CO2 seep (Shikine Island, Japan). Biogeosciences 16(22): 4451-4461.
  • 2018
    Witkowski, C.R.; Weijers, J.W.H.; Blais, B.; Schouten, S.; Sinninghe Damsté, J.S. (2018). Molecular fossils from phytoplankton reveal secular Pco2 trend over the Phanerozoic. Science Advances 4(11): eaat4556.