Plioprox: reconstructing continental temperatures during the Mid-Pliocene Warm Period using branched glycerol dialkyl glycerol tetraethers

Based on current climate models the Intergovernmental Panel on Climate Change (IPCC) predicts that the rising concentration of CO2 in the atmosphere, due to anthropogenic emissions, will have marked effects on regional and global climates1. In order to prepare for future climate scenarios, the earth system response to various forms of climatic forcing must be anticipated. For this purpose, it is necessary to investigate past geological periods that bear resemblance to current and projected climate conditions.
The Pliocene (ca 5.3 to 2.6 Myr) is the most recent geological interval that serves as an appropriate analogue to our current climate for two main reasons. Firstly, atmospheric CO2 levels are similar (400-450 ppmv) to present day levels. Secondly, continental configurations during the Pliocene were largely similar to those in the present day, rendering interpretations of past climate more applicable to present day scenarios. Temperatures in the Pliocene (especially the Mid-Pliocene Warm Period, ca 3.3 – 3 Myr) were roughly 2 to 3 °C higher than today2.
Comprehensive estimates of sea surface temperatures (SSTs) during the Mid-Pliocene Warm Period (MPWP) have been provided by the United States Geological Survey’s PRISM Group (Pliocene Research Interpretation and Synoptic Mapping)3. However, continental temperatures during the Pliocene remain poorly constrained. Herein, we propose to quantify continental temperatures and qualitatively describe humidity changes during the MPWP using terrestrial biomarkers extracted from near-coastal marine sediments.


Fig. 1. Global sea surface temperature anomalies for the Pliocene vs. present day conditions in August. Figure and data was obtained from the PRISM3 dataset and PRISM website4.

In this initial study, two cores, one from the North Sea Basin in North-Western Europe, and one from the Focsani Basin (Romania), will be analysed for their distribution of branched GDGTs. Branched GDGTs are membrane lipids of organisms living predominantly in soils whose relative distributions relate with the temperature and pH of the soil in which they are biosynthesized. The relationship between mean annual air temperature (MAAT) and the relative distributions of branched GDGTs is described by the MBT/CBT paleothermometer5. As the sampling sites are coastal, direct land-sea correlations with no dating error will be achieved by analysing alkenones in the same sediment and subsequently applying the Uk37’, TEX86, and long chain diol index (LDI) paleothermometers6,7,8.
Regional climate responses shall be interpreted in the framework of a global climate response. Results obtained from this analysis may then be used to restrain boundary conditions and increase confidence in climate models.