Ice in the Greenhouse

David De Vleeschouwer (Speaker)

Activiteit: Talk at an external academic organisation

Description

Without Earth’s natural greenhouse effect, life on our planet would not be possible in its current form. The intensity of the greenhouse effect, however, has varied significantly throughout geological history, in response to changes in the concentration of different greenhouse gasses in the atmosphere. These changes were so significant that, throughout Earth’s history, the planet’s climate has been alternating between two dominant climate states: the greenhouse Earth and the icehouse Earth. Generally, the greenhouse Earth is defined as a period during which no continental ice whatsoever existed on the planet. This view came under increasing pressure over the last years, especially since reconstructions of sea-level change during greenhouse periods could only be explained by glacioeustacy. Throughout my PhD research, I studied the warm greenhouse Earth conditions of the Devonian Period. Interestingly, the Late Devonian climate transitioned from an extreme greenhouse world (Frasnian) towards an icehouse world (late Famennian), coupled with decreasing atmospheric pCO2 values. During the seminar, I will approach the greenhouse climate of the Devonian, and the potential role of continental ice in this climate system, from two different angles. First, I will introduce the general state of the Devonian greenhouse climate system on the basis of paleoclimate simulations with the HadSM3 general circulation model (GCM) for Late Devonian (Frasnian) greenhouse boundary conditions. Interestingly, in a “median orbit” simulation, a large part of the Gondwanan continent freezes during austral winter. Negative average winter temperatures occur up to 45–50°S, but there is nevertheless only one single gridbox (at 85°S and 2000 meter altitude) where snow and ice survive the summer, and where it is thus possible to form a glacier or ice cap. Secondly, I will approach the topic of the seminar from a geologic point of view, by showing paleoclimate records from several globally-distributed Devonian sections. These paleoclimate records show increased spectral power at the frequency of obliquity. This is rather unexpected, as obliquity only has a very limited influence in the variations of incoming solar radiation at tropical latitudes. Hence, the observation of an obliquity imprint at the tropical paleolatitude of the study area suggests some sort of climatic teleconnection. A climatic teleconnection implies that climate variations at a certain place are related to climatic changes at large distances (typically thousands of kilometres). Continental ice sheets are an excellent example of an important agent in climatic teleconnections. At the end of the seminar, I will talk about my ongoing postdoctoral research that focusses on the evolution of Cenozoic climate at the orbital scale. I will present a newly-constructed megasplice, a 35 Myr-long benthic δ18O record that consists of twelve globally-distributed isotope records ‘spliced’ together. The megasplice provides a complete and high-resolution stratigraphic section of benthic δ18O over the last 35 Ma, with the advantage that individual precession and obliquity cycles are clearly delineated. I will exploit the megasplice to characterize different climate regimes, with different responses to astronomical forcing, mainly dependent on the state of the global cryosphere at the time of investigation.
Periode9 jun 2016
Gehouden opKorean Polar Research Institute, Korea, Republic of