Royal Netherlands Institute for Sea Research
Royal Netherlands
Institute for Sea Research
Phone number
+31 (0)222 369 584
PhD student
Universiteit Utrecht
Jaap Sinninghe Damste

Caitlyn Witkowski

PhD student


  • 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


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 projects