Stable isotope record of Eemian seasonal temperature from MIS 5e tufa stromatolite; Somme Basin, Northern France

In many modern to sub-fossil deposits tufa formations, very well crystallised deposits called stromatolites are preserved. These are often strongly laminated deposits, the laminae linked to seasonal climatic and environmental variations. Where found in fossil tufas such deposits have huge potential as high resolution archives of Pleistocene climate. One of the first investigations of this type has been performed on a 2.5 cm-radius stromatolite from the Eemian sequence of Caours (Somme Basin, Northern France), where precise observations in thin section have been combined with intra-lamina δ18O and δ13C analyses. Independent interpretations of petrographical and geochemical data are strongly coherent and demonstrate a clear seasonal signal. Moreover, as δ18O is temperature dependent, we have quantified likely maximum water temperature variations between summer and winter at Caours. A small mismatch between the δ18O derived temperature values and the typical modern range is observed, which may reflect a real difference between modern and Eemian temperature seasonality. This study supports previous investigations performed on a laminated tufa from central Greece and clearly confirms the potential of tufa stromatolites as records of seasonal climatic information and for the quantification of riverine water temperature variations.