Late Holocene climate dynamics in NW Iberian Peninsula: Exploring the Atlantic-Mediterranean interactions and paleoenvironmental impacts

The northwestern Iberian Peninsula is a climatically complex region influenced by both Atlantic and Mediterranean systems, making it a key area for studying past climate dynamics. Mountain lake ecosystems in this region are particularly sensitive to climate variability, serving as valuable archives of sedimentary records that document paleoenvironmental responses to major climatic phases. This study aims to reconstruct Late Holocene climate variability in northwestern Iberian Peninsula, with focus on clarifying the uncertainties regarding its timing and extent of climatic changes in this region. Accordingly, mountain lakes are highly sensitive to climatic fluctuations, serving as critical archives for reconstructing past climate dynamics with high temporal resolution

Lake Ocelo, an oligotrophic mountain lake at 1517 m a.s.l. in the Pena Trevinca Massif (Galicia), lies at the interface of Eurosiberian and Mediterranean bioclimatic regions. In April 2021, a sediment core (OCE21-3GA, 131 cm) was retrieved using a UWITEC® gravity corer. Radiocarbon dating, alongside concentration profiles of ²¹⁰Pb and ¹³⁷Cs, established an age-depth model indicating a sequence spanning approximately 2900 years. To identify and precisely date major environmental transitions over the last millennia (ca. 3 ka), a multidisciplinary approach was used, including sedimentological (facies analysis), geochemical (XRF, TOC, TN, biogenic silica, δ¹³C_ORG, δ¹⁵N_ORG analyses), and biological proxies (diatoms and pollen). Statistical analyses, including Principal Component Analysis (PCA), were applied to reconstruct environmental conditions.

The age of the main changes in sediment composition roughly correlate with documented Late Holocene climate centennial periods, providing evidence of regional responses to larger-scale climatic events. However, our findings also reveal a complex dynamic interplay between Atlantic and Mediterranean climatic influences. The shift from drier to wetter conditions during the Older Subatlantic (ca. 800-200 BCE) likely reflect the end of the 2.8 ka event, characterized by dry conditions in the northern hemisphere. The aridity of the Roman Warm Period (ca. 200 BCE-300 CE) suggests the onset and a northward shift of the Mediterranean bioregion. Wetter conditions during the Dark Ages (ca. 300-750 CE) indicate a subsequent Atlantic dominance, whereas the arid Medieval Climate Anomaly (ca. 750-1100 CE) reflects intensified Mediterranean influence, with temporal offsets compared to other Iberian records. The Little Ice Age (LIA; ca. 1300-1900 CE) exhibits significant hydroclimatic variability, subdivided into alternating wet and dry sub-phases: LIA-I (ca. 1300-1500 CE), LIA-II (ca. 1500-1700 CE), and LIA-III (ca. 1700-1900 CE). Diatom data suggest extended and prolonged lake ice cover conditions during the LIA in the lake, leading to stronger denitrification and prolonged stratification periods, with a marked anoxia in the lake bottom. The transition of the Medieval Climate Anomaly to Little Ice Age (ca. 1100-1300 CE) marks a shift to wetter conditions. Finally, the Industrial Era (ca. 1850 CE–present) is defined by warming trends, increased lake productivity, reduced detrital inputs, and human-induced impacts such as elevated atmospheric nitrogen deposition.

This work is supported by Grants PID2019-107424RB-I00 and PID2022-139775OB funded by MCIN/AEI/10.13039/501100011033, with the latter also co-funded by “ERDF A way of making Europe”. Xunta de Galicia also supports this work through project ED431F 2022/18 and ED431B 2024/03