Holocene changes in precipitation seasonality in the western Mediterranean Basin: a multi-species approach using delta C-13 of archaeobotanical remains

Abstract

Precipitation has been of utmost importance in shaping the evolution of landscapes and human settlements in the Mediterranean. However, information on seasonal precipitation patterns through the Holocene is scarce. This study attempts to quantify the evolution of seasonal precipitation in the East Iberian Peninsula (5000 BC to AD 600) based on the carbon isotope composition (δ13C) of archaeobotanical remains. Data on Holm oak, Aleppo pine and small-grain cereals were combined, and precipitation was inferred from models relating present-day records to the δ13C of modern samples. Subsequently, charred grains were used as a proxy for ancient moisture during April–May, whereas oak and pine charcoals provided complementary rainfall estimates for September–December and January–August, respectively. The results reveal aridity changes throughout the Holocene in the western Mediterranean. Past spring–summer precipitation was consistently higher than at present. In contrast, autumn and early winter precipitation showed stronger fluctuations, particularly during the first millennium BC, and often exhibited values below those of the present. The high contribution of autumn precipitation to the annual water budget, typical of the present Mediterranean climate, was definitively established at the beginning of the current era. This study shows how a combination of species holding complementary environmental signals can contribute to a wider knowledge of local precipitation dynamics.

This work was partially supported by the DGI project CGL2009-13079-C02-01 and the ERC-Advanced grant 230561 (AGRIWESTMED). We acknowledge Ernestina Badal, Elena Grau and Yolanda Carrión for charcoal identification and P. Sopeña for technical assistance. M.A. has a PhD fellowship from the Spanish Ministry of Science and Innovation and J.P.F. is supported by a postdoctoral contract from the “Ramon y Cajal” programme (MCINN).