High-Resolution Paleoclimate Data

Wed, 23 Jul 2025, 16:00 CEST

Conveners: Julie Loisel & Denis-Didier Rousseau

The recent past witnessed developing and refining methods to obtain high-resolution climate data from proxies like ice cores, tree rings, and sediment layers and selecting two among those for this webinar was really challenging. In these presentations, two guest speakers will share research insights and novel methodological approaches that yield very-high-resolution paleoclimate time series. Helle Astrid Kjaer is an ice core specialist who developed the use of continuous flow analysis as a high-resolution, high-precision method to analyze impurities found in ice cores as proxies for past environmental changes. David Naafs applies state-of-the-art isotopic and organic mass spectrometry to the study of lipids and molecular fossils (biomarkers) derived from organisms found in marine and terrestrial natural archives to understand the processes and mechanisms that drive changes in climate and biogeochemistry.

Guest speakers:

• Helle Astrid Kjaer (University of Copenhagen, Denmark)
• David Naafs (University of Bristol, UK)

Sea ice and abrupt change – a land ice core perspective

Helle Astrid Kjaer

Ice cores provide an excellent high-resolution climate archive. Greenland ice cores reach back to the last interglacial period. Halogens, such as bromine and iodine measured in such ice cores are speculated to be an indicator for past sea ice extent. Bromine through so-called bromine explosions happening over first year sea ice and iodine through biological activity at the sea ice edge. Here we review halogen results from EGRIP, NEEM, Dye3 and RECAP ice cores to constrain sea ice-climate variations on various temporal scales.

Novel biomarker-based insights into the operation of the terrestrial methane cycle across the Cenozoic

David Naafs

Methane is an important greenhouse gas and wetlands are its largest natural source. There is much uncertainty about how the wetland methane cycle will respond to future climate change. Constraining its operation during past periods of climate change can provide insights into its response to warming and dynamics in a greenhouse world. However, the operation of the wetland methane cycle in the geological past is virtually unconstrained.

I will present data that for the first time shed light on the past operation of the wetland methane cycle across the Cenozoic. I will focus on rapid variations during the Holocene and last glacial, as well as long-term dynamics during the Cenozoic, including transient events (e.g. PETM).

The data show that the contribution of to the wetland bacterial pool has been remarkably stable through time, including across major climatic events. These results indicate that the terrestrial methane cycle is robust to long-term climatic perturbations and does not operate fundamentally different during greenhouse periods. However, during the deglaciation and Holocene as well as Eocene hyperthermals, the data indicate significant perturbations. This means that transient climate events have the potential to destabilize this key biogeochemical cycle, which suggests that the terrestrial methane cycle will be impacted by anthropogenic climate change.