Speleothem evidence of late glacial and Early Holocene Preboreal and Boreal hydro-climate changes in western Mediterranean (Corchia Cave, Italy)

Abstract

This paper explores the rainfall variability across the western Mediterranean area from ca. 12 to 9 ka, and its climate teleconnection within the northern Hemisphere realm. A high-resolution stable isotope (δ¹⁸O, δ¹³C) and growth rate record from a Corchia Cave stalagmite (Apuan Alps, Central Italy) shows evidence of: 1) increased rainfall during the transition from the late Younger Dryas (YD) to the Holocene; and 2) two Early Holocene episodes of reduced rainfall during the so-called Preboreal and Boreal Oscillations (PBO and BO respectively). The YD to Holocene transition occurs at Corchia from 11.91^+0.10/_-0.11 to 11.33^+0.07/_-0.07 ka, in agreement with other Mediterranean records. The expression of PBO is constrained in Central Italy between 11.19^+0.09/_-0.08 and 11.04^+0.09/_-0.09 ka, while the BO from 10.42^+0.13/_-0.27 to 10.19^+0.27/_-0.24 ka, contemporaneous with a significant reduction of the Lago dell’ Accesa lake levels (Central Italy).

The new record suggests that the increase of rainfall at Corchia during the deglaciation is connected to the enhanced evaporation from a warming north Atlantic and the higher moisture amount across the Mediterranean delivered by the westerlies. Reduced rainfall is instead attested during PBO/BOs. The latter are often associated with fluxes of ice-sheet meltwaters into the Atlantic, which trigger a deficit in moisture availability resulting in lower humidity reaching the Mediterranean area. This work confirms that the PBO/BO relative aridity is restricted to the Mediterranean area, while mid-European records point to moister conditions within the same events. Thus, our results imply that future – even subtle - polar ice sheet instabilities, boosted by the ongoing climate crisis, might amplify the change of rainfall dynamics across the western Mediterranean, a hot-spot area for climatic change that is already experiencing an increasing number of drought years.