Lukas Jonkers
Lukas Jonkers is a micropalaeontologist working at MARUM | Bremen University. His research combines observations on modern and past marine plankton with the aim to study changes in climate, biodiversity and their interactions. He primarily works with planktonic foraminifera, ubiquitous unicellular marine zooplankton with an exceptional fossil record. He studies their modern ecology to improve our capabilities to derive quantitative insights from the fossil record. Lukas applies this knowledge to investigate how the oceans and marine biodiversity change across a range of time scales including those that are not accessible from direct observations. He combines the generation of new data with meta-analysis and advocates open and reproducible science.
Macroecology meets palaeoceanography
The species composition of marine microfossils can be used to estimate past environmental conditions. This approach was pioneered in the late 1970 and played an important role in the first global climate reconstructions within the CLIMAP framework. These reconstructions were initially used as boundary conditions for palaeoclimate simulations, but over time (e.g. MARGO) served as benchmarks to evaluate climate model skill in simulating different climate states. However, such data-model comparison remains problematic because of uncertainties in the reconstructions and the simulations. Instead of relying on reconstructions, I here show an example of how marine microfossil assemblage composition can also inform climate modelling more directly by using the fundamental macroecological principle of distance decay: the decreasing community similarity with increasing environmental distance. Whereas modern planktonic foraminifera assemblages show a clear distance decay trend with increasing thermal distance, species assemblages from the last ice age show a different pattern when confronted with simulated glacial seawater temperatures. This inconsistency between the modern temperature dependence of plankton species turnover and the simulations arises because the simulations show globally rather uniform glacial cooling, whereas the species assemblages indicate stronger cooling in the subpolar North Atlantic, pointing at a potential issue with the representation of the glacial circulation in the simulations. The analysis thus shows how macroecology can be used on top of classical proxy-based reconstructions to robustly diagnose simulations of past climate. Future directions of how microfossil assemblages can be used to learn about past climate change and the other way around - understanding the response of marine biodiversity to climate change - will be discussed.
