A promising approach to advance proxy-based pCO2 reconstructions
Carbon continuously moves between the atmosphere, oceans, land, and Earth's crust through natural processes such as erosion and plant growth. These shifts influence atmospheric CO₂ levels over time, making it crucial to study past changes in marine carbon chemistry better understand the global carbon cycle. Szabina Karancz has focused her PhD research project on foraminifera- and alkenone-based proxies to reconstruct marine inorganic carbon systems and atmospheric CO₂ levels. On 31 March, she will defend her PhD Thesis at Utrecht University.
The amount of carbon in the atmosphere, in the oceans, on land and in the earth’s crust, is not static. Rather, carbon moves between these compartments by erosion (taking up CO2 from the atmosphere and transport to sea), plant growth (fixing carbon as biomass), etc. Relative contributions of these processes change over time and thereby result in rising or declining atmospheric CO2 levels. Understanding the dynamics of this so-called global carbon cycle requires studying past changes in marine carbon chemistry, as this is by far the largest reservoir of active carbon. The six components of the carbon system are pCO2, [CO32-], [HCO3-], pH, dissolved inorganic carbon, and total alkalinity, which tend to co-vary in nature and are therefore difficult to reconstruct separately. During her research Karancz investigated investigates foraminifera- and alkenone-based proxies using various approaches and assesses their application potential in reconstructions of the marine inorganic carbon system and thereby, atmospheric CO2 levels.
Boron isotopic composition of calcitic shells of foraminifera and the carbon isotopic composition of alkenones belong to the most commonly applied CO2-proxies. They are applied here to reconstruct past seawater carbon chemistry and air-sea interactions in the Benguela and Canary Current Upwelling regions during the last glacial-interglacial cycle. In addition, sulfur and boron concentrations in (foraminiferal) calcite are explored as novel tools to reconstruct marine inorganic carbon parameters. Karancz concludes "My research demonstrates that investigating cooperative incorporation of elements into calcite along with alternative incorporation pathways in the form of ion-pairs offers a promising approach to advance proxy-based pCO2 reconstructions.
The PhD defence ceremony will take place on 31 March 2025 at 14.15, in the Academy Building of Utrecht University.