Towards reliable reconstructions of Pliocene terrestrial temperatures using branched glycerol dialkyl glycerol tetraethers

Abstract

The mid-Pliocene Warm Period (mPWP, 3.3-3.0 million years ago) is considered to be an analogue for the climate of the mid-21st century. Atmospheric CO2 concentrations, continental configurations, land elevations, and ocean bathymetry during the mPWP were similar to present. However, global temperatures were warmer by 2-4 °C indicating that current climate may not have achieved equilibrium. Continental temperature records are a big missing puzzle piece in our understanding of mPWP climate and in past climates in general, because there are very few climate proxies that reconstruct this parameter. In this PhD thesis, continental temperatures are reconstructed using so-called branched glycerol dialkyl glycerol tetraethers (brGDGTs) that are produced by bacteria in soils, where their molecular structure is correlated to mean air temperature (MAT). Hence, upon mobilization, transport, and deposition in coastal marine sediments, brGDGTs can be used to reconstruct MAT of the adjacent river catchment. However, their applicability as paleothermometer may be hampered by in situ production of brGDGTs in marine settings. Here, a method is presented to correct for marine-derived brGDGTs in coastal zones and applied to a sediment core from the Southern North Sea Basin. The obtained record shows that the temperature of the proto-Rhine Meuse catchment at that time (i.e. North Western Europe) was approximately 1-3 °C higher than present, which is comparable to mPWP temperatures reconstructed by climate modelling studies. Subsequent reconstruction of other climate parameters using the same sediments reveals that the evolution of marine and terrestrial climate of the Southern North Sea area was de-coupled during the mPWP.