Holocene hydro-climatic variability and multi-frequency analyses at Lake Sidi Ali (Morocco)

Abstract. The North African desert margin is considered one of the most sensitive areas to future climate changes. Improved knowledge about Holocene climatic variability and environmental responses on millennial to centennial scale will help to refine scenarios related to future climate changes. During the last two decades, the recovery and compilation of Holocene records from the subtropical North Atlantic and the Mediterranean realms have improved our knowledge about the millennial-scale variability of the Western Mediterranean palaeoclimate and the Saharan dust cycle. However, the understanding on periodicities as well as potential coupling and forcing mechanisms remains poor. To detect periodicities in Holocene climatic variability and geomorphological processes, we use a Holocene sediment record from Lake Sidi Ali in the semiarid to sub-humid Middle Atlas with a robust ²¹⁰Pb /¹³⁷Cs and pollen-concentrates-based ¹⁴C chronology. We use a high-resolution core scanning-XRF record, in order to distinguish between lake-internal (e.g., chemical precipitation) and lake-external (e.g., detrital input) processes. Redfit and Wavelet time series analyses reveal distinct periodicities of millennial to centennial scale. By a correlation analysis of extracted, highly significant, frequency analysis spectra, three XRF-based “Redfit Proxy Groups” (RPGs) which potentially reflect different hydro-climatic forcing mechanisms were derived. Subsequently, we integrated environmental and climatic proxies from the same core (Cedrus pollen abundance, magnetic susceptibility, δ¹⁸O and δ¹³C values of ostracod shells, grain-size endmembers and total organic carbon) and used their wavelet domain to improve the interpretation. Finally, we identified two main periodicity regimes that affected, on the one hand, the hydrological regime and, on the other hand, the lake productivity and catchment erosion dynamics. For RPG 1 (Ca, Sr, Ca/Ti, Sr/Ti), we identified 2 ky and 1 ky periodicities, which we interpret as precipitation/evaporation related proxies in the context of North Atlantic and solar forcing. For RPG 2 (Fe, Ti, K, Si/Ti), we observe 3.5 ky and 1.5 ky periodicities, which we interpret as driven by lake productivity or detrital input.