Sea-level during the penultimate interglacial period based on a submerged stalagmite from Argentarola Cave (Italy)

Accurate constraints are presented for the absolute age, duration and sea-level for the highstand corresponding to marine isotope stage (MIS) 7.1. Our work is based on a stalagmite collected in a currently submerged cave from Italy (Argentarola Cave). Flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms. Precise uranium–thorium (U–Th) ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during MIS 7.2 and MIS 6, the penultimate glacial period. In addition, the period of marine transgression is bracketed between 202 and 190 kyr BP, defining a MIS 7.1 duration of 11±2 kyr. Comparison with previous studies provides a new constraint on the sea-level during MIS 7.1 that has approximately remained between −18 and −9 m relative to present sea-level. The timing of the MIS 7.1 highstand is in full agreement with the SPECMAP chronology which contrasts with the growing body of evidence showing a significant phase difference for MIS 5.5. A tempting conclusion is that second order sea-level highstands such as MIS 7.1 may be purely driven by astronomical changes, in contrast with major terminations such as Termination II. Atmospheric CO2 levels may partly explain this contrast since the two sea-level transitions, (MIS 7.2–7.1 and MIS 6–5.5) are characterized by very different CO2 rises (20 vs 100 ppm).