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

Abstract

Abstract. The North African desert margin is considered one of the most sensitive areas to future climate changes, yet the periodicities, coupling mechanisms and external forcing of Holocene environmental variability remain poorly understood. To investigate millennial- to centennial-scale 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 hydroclimatic 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 and 1 kyr 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 and 1.5 kyr periodicities, which we interpret as driven by lake productivity or detrital input. Overall, our results show that Holocene environmental variability at Lake Sidi Ali was structured by two partly decoupled regimes: hydroclimatic variability linked to precipitation/evaporation changes and catchment-related variability linked to erosion, productivity and terrestrial sediment supply.