Fig. 1: Location and stratigraphy of sapropel S5 and an exemplary MSI-based determination of SST via analysis of alkenones.

a, Map of the Mediterranean Sea; the map was generated by The Generic Mapping Tools software. Core M51/3-SL104 is indicated with a black circle. Discussed cores from the eastern Mediterranean with preserved sapropel S5 and alkenone-based SST reconstruction (LC21²¹, ODP Site 971²⁸, ODP Site 967²⁸, KS 205²⁸) are indicated with coloured circles. b, Sapropel S5 from core M51/3-SL104; sediment depth is presented in centimetres below seafloor (cmbsf). c–e, An illustrative example of MSI on a ~5 cm embedded subsample. c, Image of a slice on which MSI was performed, red rectangle indicates the area analysed. d, Spatial distribution of \({{U}}_{37}^{{{{\mathrm{K}}}}\prime }\)values obtained by MSI. Note that the scale is presented as x- and y-position spot, where each spot accounts for 200 µm. e, \({{U}}_{37}^{{{{\mathrm{K}}}}\prime }\) and calculated SST time series for the selected sample; data points represent SST derived from \({{U}}_{37}^{{{{\mathrm{K}}}}\prime }\) values calculated from the sum of alkenone intensities in one horizontal layer (only layers with >10 spots with successful detection of alkenones were considered). Depth is presented as y-position spots where each spot is 200 µm.