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

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. δ13C values mostly reflect soil bioproductivity and vegetation density. During less humid periods these values reflect bedrock δ13C values, because of a semi-closed system and/or sulphuric acid-driven bedrock dissolution. δ18O changes were governed by the interplay of rainfall amount and moisture source. Disentangling these two effects was possible by comparing δ13C and δ18O values, whereby both isotopes co-vary during periods when δ18O was dominated by the amount effect. Changes in the relative proportion of Atlantic and Mediterranean moisture sources was the main control on δ18O at times when δ18O was decoupled from δ13C. δ18O variations during MIS 5 are synchronous with Greenland stadials (GS) and interstadials (GI) GS 26, GI 25, GI-GS 22, GI-GS 21. With the exception of GS 22, these climate oscillations did not affect soil bioproductivity, and δ18O mirrors the relative proportion of Atlantic and Mediterranean moisture sources. GS 22 was a prominent arid period in Sardinia, in accordance with other regional palaeoclimate archives. High soil bioproductivity is indicated by δ13C values for MIS 7e and MIS 7c-a; the latter interval was characterized by a 30 kyr-long time span of warm and humid conditions in Sardinia. Soil bioproductivity decreased markedly during MIS 7d and the climate became drier. The latter period, also constrained by δ18O data, lasted significantly shorter in Sardinia than in central Europe. As indicated by changes in δ13C and δ18O relationships, variations in moisture source are also recorded for MIS 7, with Mediterranean-dominated rainfall during MIS 7e and 7c followed by a shift toward Atlantic-dominated rainfall.