NAO control on the hydrology of Laguna Grande de Archidona (southern Spain) during the Iberian Roman Humid Period recorded by stable isotopes (δ18O and δD) of gypsum hydration water

The North Atlantic Oscillation (NAO) has a major effect on the modern precipitation patterns in the southern Iberian Peninsula and also controlled the hydroclimate of this region in the past [1,2]. The oxygen and hydrogen stable isotopes (δ¹⁸O and δD) of lake waters are sensitive to long-term changes in hydrological conditions (e.g. relative humidity, evaporation/outflow ratio, etc.). Here we reconstruct the δ¹⁸O and δD values of Laguna Grande de Archidona Lake (Málaga Province, southern Spain) from the stable isotopes of hydration water of gypsum (CaSO₄·2H₂O) [3] that precipitated and deposited in the lake from 2.7 to 1.4 ka BP.

The maximum δ¹⁸O and δD of values of the lake water (7.8‰ and 23.9‰, respectively) were recorded at 2.7 ka BP (~700 BCE), suggesting that relatively dry conditions prevailed during the Early Iron Age in southern Iberia. Subsequently, the δ¹⁸O and δD of the lake decreased to minimum values (3.0 and -2.2‰, respectively) at 2.4 ka BP, during the early stages of the Iberian Roman Humid Period (~600 BCE to ~400 CE). A relatively arid phase was also recorded at 2.2 ka BP, which preceded a wetter stage at 2.0 ka BP. A longer drier phase occurred later on, from 1.6 ka to 1.4 ka BP, coinciding with the decline of the Western Roman Empire (395-476 CE).

The comparison of our paleo-humidity proxy with long-term NAO index [4] shows that the lake water was isotopically enriched during periods of persistent NAO+ mode, suggesting drier and more evaporative conditions and probably lake level lowstands. In contrast, lower δ¹⁸O and δD of values of the lake water occurred during periods of NAO- configuration, resulting in wetter and less evaporative conditions and lake level highstands. In summary, our results indicate that the hydrologic balance of Laguna Grande de Archidona during the Iberian Roman Humid Period was controlled by the strength of the long-term NAO and that stable isotopes of gypsum hydration water are a powerful tool for paleo-hydrologic reconstructions.

 

 

[1] Toney et al. (2020), Quat. Sci. Rev. 106395; [2] Martín-Puertas et al. (2009), Quat. Res. 71, 108–120; [3] Gázquez et al. (2018), Earth Plan. Sci. Lett. 48, 177–188; [4] Faust et al., (2016), Earth Plan. Sci. Lett. 435, 84-93.

Acknowledgement

This study was supported by projects PY18-871 and Retos P20_00059 of the Junta de Andalucía, the project CGL2017-85415-R of the Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional FEDER and the project B-RNM-144-UGR18. Dr. Antonio García-Alix acknowledges the Ramón y Cajal fellowship, RYC-2015-18966. Dr. Fernando Gázquez acknowledges the Ramón y Cajal fellowship, RYC2020-029811-I.