A long record of MIS 7 and MIS 5 climate and environment from a western Mediterranean speleothem (SW Sardinia, Italy)

摘要

Here we present the first record of Marine Isotope Stage (MIS) 7 from Sardinia, based on a U-Th-dated speleothem from Crovassa Azzurra cave, which also grew during MIS 5. Carbonate precipitation was continuous during MIS 7, while two multi-millennial hiatuses interrupted growth during MIS 5. These hiatuses occurred during times of unstable climate, but local karst-specific conditions are considered to have played an important role as well. delta C-13 values mostly reflect soil bioproductivity and vegetation density. During less humid periods these values reflect bedrock delta C-13 values, because of a semi-closed system and/or sulphuric acid-driven bedrock dissolution. delta O-18 changes were governed by the interplay of rainfall amount and moisture source. Disentangling these two effects was possible by comparing delta C-13 and delta O-18 values, whereby both isotopes co-vary during periods when delta O-18 was dominated by the amount effect. Changes in the relative proportion of Atlantic and Mediterranean moisture sources was the main control on delta O-18 at times when delta O-18 was decoupled from delta C-13.