Decoding last interglacial sea-level variations in the western Mediterranean using speleothem encrustations from coastal caves in Mallorca and Sardinia:A field data - model comparison

摘要

U-Th ages of phreatic overgrowths on speleothems in coastal caves of the Western Mediterranean record high sea level positions during marine isotope stage (MIS) 5e of the last interglacial. While relative sea level (RSL) on the southeastern coast of Mallorca stood ～2.6 m above present sea level (apsl) during MIS 5e, it stood ～4.3 m apsl at this time in northwestern Sardinia. The difference between the two sites during MIS 5e and the deviation from the eustatic sea level trend during the Holocene was investigated using the numerical code SELEN. The offset between the eustatic curve and those pertaining to the two sites principally reflect the vertical deformations and geoidal variations in response to meltwater loading. As Sardinia is closer to the center of the Mediterranean basin, the hydro-isostatic component of RSL is enhanced here compared to Mallorca, which.results in a modeled offset of ～60 cm between the two sites. This result is qualitatively useful as it provides a partial reconciliation for the site differences. However, the need for refinement in the model is also recognized, as it does not match the observation based on U-Th dating of speleothem overgrowths in Mallorca that sea level there has remained stable for the past 2800 years. Overall, the results of the study first suggest that both sites largely track the eustatic sea level curve, and second suggest that glacial isostatic adjustment is a viable mechanism to reconcile some, if not most, of the relatively small elevation difference of MIS 5e sea level observed at Mallorca and Sardinia, although minor tectonic adjustments cannot be ruled out in explaining some low-amplitude local variations.