Sea level change during MIS 5a based on submerged speleothems from the eastern Adriatic Sea (Croatia)

Two stalagmites were collected from below sea level in U Vode Pit on the Krk Island, eastern Adriatic Sea, at elevations of -14.5 and -18.8 m. They exhibit a growth history indicating a double high sea-level stand during marine isotope stage (MIS) 5a (~ 87-77 ka). Thin layers of halite and gypsum were found to be associated with hiatuses in speleothem growth probably caused by sea water inundation during sea level highstands. These mineral deposits are likely to have been precipitated during a marine regression phases under evaporitic conditions. We constrain the age of the speleothem growth below and above growth hiatuses, and hence timing of possible marine incursions, using multi-collector inductively coupled mass-spectrometry (MC-ICPMS) U-Th techniques. Age estimates indicate that, during MIS 5a, relative sea level elevations were greater than - 14.5 m from ~ 87 to ~ 82 ka and -18.8 m from ~ 77 to ~ 64 ka, and constrained to be lower than -18.8 m from > 93 to ~ 90 ka, ~ 82 to ~ 77 ka and ~ 64 to ~ 54 ka, assuming no tectonic adjustment. However, present speleothem depths could indicate long term regional tectonics.