Ocean oxygenation

Oxygen rise in subsurface ocean during the PETM

Our latest study shows an oxygen increase in the tropical subsurface ocean during the PETM, reconstructed by foraminifera-bound nitrogen isotopes (FB-δ15N) and a foraminiferal body size model (FS-pO2). Fossil body size modelling for benthic foraminifera implies deep ocean O2 loss. This hints at the role of oxygenation in maintaining marine habitability amidst climate stress. While deep-sea organisms faced extinction during the PETM, those near the surface were less affected, leading us to the question if O2 played a role in preventing mass extinction in pelagic ecosystems?

A well-ventilated Pacific during the warm Miocene

This study on I/Ca and FB-δ15N sheds light on how well-oxygenated the eastern equatorial Pacific was during the Middle Miocene Climate Optimum (>100 µmol/kg!) and looks at the timing and different thresholds of the expansion of the oxygen deficient zone (ODZ) during the Middle Miocene Climate Transition. We show strong evidence for a reduction in equatorial upwelling during the warm period and invigoration of upwelling during the cold period, which drives productivity, respiration and the extent of the ODZ.

Enhanced ocean oxygenation during Cenozoic warm periods

In this study, we discovered that oxygen-poor zones in the Pacific got a lot smaller during past periods of prolonged climate warming.

This was an unexpected finding, because a warmer ocean can hold less oxygen. What we found is that there may have been other factors overwhelming the solubility effect: Reduced equatorial upwelling and invigorated Southern Ocean overturning leading to a better ventilated ocean. Read the press release for this research article.

Foraminifera-Bound Nitrogen Isotopes

For the study on past nitrogen cycle we measure nitrogen isotopes on the organics that lies within the calcitic shell of planktic foraminifera, also known as "foraminifera-bound nitrogen isotopes". The nitrogen isotopes record the subsurface nitrate signal during the time of deposition, allowing us to determine the extent of earlier oxygen-deficient zones.

More sites and different time periods

Together with colleagues from Max Planck Institute for Chemistry and collaborators from around the world, we work on compiling more FB-δ15N records, spanning past global warming periods. A main focus currently lies on the Miocene Climate Optimum (MCO) and Middle Eocene Climate Optimum (MECO).