Sea surface conditions during deposition of Mediterranean sapropel S5

Deposition of sapropels has been linked to increased outflow of the river Nile and precipitation over the Mediterranean basin, resulting in overall freshening of eastern Mediterranean surface waters. Still, the relative contribution of Nile water remains unclear. Tracing origin of the freshwater input and quantification of different sources relies on the ability to accurately reconstruct salinity, temperature and δ18Ow. Combined measurements of single-specimen foraminiferal Mg/Ca, Na/Ca and δ18O may allow reconstruction of these parameters. Culturing foraminifera at different salinities shows that the incorporation of Na into foraminiferal test carbonate reflects seawater salinity. Since temperatures derived from foraminiferal Mg/Ca are impacted by salinity we corrected these values using this novel salinity proxy. Corrected Mg/Ca temperatures were used to calculate δ18OW from single specimen δ18O analyses of the planktonic foraminifer G. ruber from Mediterranean sapropel S5 (~ 125 kyr BP). Post and pre-sapropel sea surface δ18Ow values fall on a different δ18Ow -salinity mixing line compared to the time of sapropel deposition. This change during sapropel formation can only be explained by Mediterranean surface water having a more "Atlantic" character due to reduced evaporation and enhanced precipitation. Mass balance considerations imply that Sapropel formation is not primarily related to increased Nile outflow but reduced evaporation and/or increased precipitation over the Mediterranean itself.