The Oligocene (33.9–23.03 million years ago) is an important epoch of the Cenozoic because it marks an early modern ‘icehouse’ climate with the formation of large ice sheets in the Antarctic. Previous studies have concerned the Oligocene climate. However, there has been little in the way of direct Oligocene model-proxy comparison on a continental scale.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and University of Bristol have compiled a database of 149 Oligocene macro-fossil floras across the mid-high latitudes of Eurasia.
They quantitatively reconstructed paleoclimate data using the Coexistence Approach for 114 floras, and combined this with 35 published paleoclimate records. Their aim was to explore both temporal and spatial climate variability through Eurasia in the Oligocene.
They then presented a comparison against a set of paleoclimate model simulations with differing boundary conditions (CO2 and paleogeography) using the UK Met Office GCM (General Circulation Model), HadCM3L.
The reconstructed paleoclimates indicate a typical humid subtropical climate with distinct seasonality during the Oligocene. Geographic change played an important role in shaping climate patterns of Eurasia. There was a spatial heterogeneity of climate change patterns between the Early and Late Oligocene.
They compared the fossil data with a range of different HadCM3L simulations of the Oligocene with differing boundary conditions. The results suggest that fossil and modelling results are generally spatial consistent but have some distinct disparities.
The findings suggest that models generate higher temperature seasonality and lower precipitation than fossil proxy reconstructions.
Further analysis indicates that different CO2 concentration and topographic representations of Eurasia may be responsible for the differences in the model-data comparisons.