PhD Candidate: Laura Pacho Sampedro

Defence date: 6-11-2024
Time: 14:15
Institute: Utrecht University
Location: Academiegebouw, Domplein 29, Utrecht

PhD supervisors:
prof. dr. Gert-Jan Reichart
dr. Lennart J. de Nooijer

Title thesis: Foraminiferal diversity and novel trace elements for carbonate system proxies

Abstract:

This thesis focuses on improving methods to reconstruct past environments and climates, an increasingly urgent task as climate change accelerates. By understanding past climates, we can better predict future conditions. One valuable tool in this process is the study of foraminifera, tiny marine organisms with calcium shells. Their fossils provide clues about past seawater conditions like temperature, salinity, and pH, as they incorporate different elements into their shells during formation.

The research explores how foraminifera form their shells, a process called biomineralization, to better interpret the chemical data from these fossils. A key finding is that there is significant variability in how different foraminifera build their shells. This biological diversity must be considered when using their geochemical signatures to reconstruct past conditions.

One notable result is the identification of potassium (K) as a promising new tool for climate reconstruction. Potassium levels in foraminifera shells, measured as the K/Ca ratio, are independent of seawater calcium levels, unlike other elements commonly used for reconstructions, such as magnesium and sodium. This makes potassium more reliable for tracking seawater conditions. The potassium content reflects processes like continental weathering, the breakdown of rocks on land that releases potassium into the ocean, which is then recorded in foraminiferal shells.

In conclusion, reconstructions of past climates using foraminifera can be improved, both by accounting for the biological impact on their shell chemistry and by investigating incorporation of elements previously ignored.