Chironomid-inferred Holocene temperature reconstruction in Basa de la Mora Lake (Central Pyrenees)

We present the first Holocene chironomid-based summer temperature reconstruction for the Iberian Peninsula. A sequence from the shallow mountain lake Basa de la Mora (1914 m a.s.l., Central Pyrenees) was analysed and the reconstruction was performed by means of a merged Norwegian–Swiss chironomid calibration dataset. The presence of a multiproxy study conducted in the same lake, as well as other available regional temperature estimations, allowed the comparison of our results with distinct local and regional records in order to disentangle different temperature and hydrological and seasonal patterns throughout the Holocene. The sampling resolution does not allow analysing rapid climatic oscillations, but provides insights into general Holocene trends. Overall, we found increasing temperatures at the onset of the Holocene, reaching the highest values during the Holocene Climatic Optimum (in our record ca. 7800 cal. yr BP). High temperatures were observed until ca. 6000 yr BP, when a decline of ca. 1.5ºC was inferred and the lowest temperature values throughout the sequence were reconstructed during the period 4200–2000 cal. yr BP coinciding with the first part of the late Holocene. Finally, an increasing trend in temperature values characterized the last two millennia, although we interpret this reconstructed temperature rise with caution as distinguishing between climatic and anthropogenic influences on the chironomid record in this youngest section of the Holocene is challenging.