Late Holocene climate changes in the southern Yemen region based on a high-resolution biomarkers and ostracods record from the paleo-lake Gayal el Bazal

Gayal el Bazal is a karstic paleo-lake situated on the southern margin of the Arabian Desert, a climatic sensitive zone that responds to small-scale hydrological changes modulated by the Indian Ocean monsoon system. High-resolution biomarker and ostracods assemblages obtained from a 3.25 m composite core from the lake provides insight into past environmental changes for the last 1200 years. Moreover, variations in the sediment lithology and geochemical proxies from the lake core suggests fluctuations related to the dominating precipitation regime. Through data amalgamation, we identified two globally recognized events: the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The study shows that the n-alkane homologues exhibited different distribution modes during these different climatic stages, indicative of variation in the sources of organic matter in response to changes in the regional hydrological conditions. The climate reconstruction based on the n-alkane proxies (P_aq, TAR) suggests a higher abundance of longer chain length carbons (C₂₇-C₃₅) derived from higher plants of the watershed during the MCA, indicating wetter conditions in the region. Furthermore, ostracods assemblage data also revealed Paracypretta amati abundance increases during the MCA and decreases during the LIA. The arid phase of LIA is also marked by gypsum formation and dust deposition and is consistent with evidence and theory for weakened summer monsoons during intervals of northern hemisphere cooling. Overall, this study aims to provide a better insight of the monsoon variability and to help to understand the role of northwards migrations of the Intertropical Convergence Zone (ITCZ) vis-à-vis monsoonal dynamics in the region.