Evidence for a regional warm bias in the Early Cretaceous TEX86 record.

• New Early Cretaceous South Atlantic TEX 86 samples and climate modelling. • Systematic differences in Cretaceous isoGDGT abundances. • Regional similarities to modern Mediterranean and Red Sea sediments. Regional TEX 86 -temperature calibration enables model-data congruence for OAE 1a. The Cretaceous Period (145-66 Ma) provides an opportunity to obtain insights into the adaptation of the climate system to increased atmospheric greenhouse gas concentrations. The organic paleothermometer TEX 86 is one of the few proxies available for reconstructing quantitative estimates of upper ocean temperatures of this time period. Here we show that the sedimentary TEX 86 signal in the Early Cretaceous North and South Atlantic shows systematic differences to other Cretaceous samples. In particular, the relative increase in the fractional abundances of the crenarchaeol isomer compared to crenarchaeol exhibits similarities with surface sediments from the modern Mediterranean and Red Sea. Dedicated climate model simulations suggest that the formation of warm and saline deep waters in the restricted North and South Atlantic may have influenced TEX 86 export dynamics leading to a warm bias in reconstructed upper ocean temperatures. Applying a regional calibration from the modern Mediterranean and Red Sea to corresponding TEX 86 data significantly improves the model-data fit for the Aptian Oceanic Anoxic Event 1a and the overall comparison with other temperature proxies for the Early Cretaceous. Our results demonstrate the need to consider regional and temporal changes of the TEX 86 -temperature relation for the reconstruction of deep-time ocean temperatures. [ABSTRACT FROM AUTHOR]