Dr Parth Dharmendrabhai Shah

Past PhD research

Late Holocene climate reconstruction from Southern Arabia: A tale of monsoons, humans, and lakes

The Arabian Desert is considered climatic sensitive zone which is susceptible to changes subtle global atmospheric circulation. The unique geographical location of this region can provide an excellent opportunity to understand the interactions between the monsoons, zonal migrations of the Inter-Tropical Convergence Zone and regional environmental change. Lake sedimentary records from the southern Arabian Desert are scarce. Thus, documentation of the distinct climatic and environmental shifts based on these archives for the mid-late Holocene is of utmost importance. This project aims to provide the lacking high-resolution information on climate variability in the southern margins of the Arabian Peninsula through integration of a set of physical, chemical, and biological proxies carried out on two sites paleo-lake Gayal el Bazal and lake Karif Shawran.

Paleo-lake Gayal el Bazal is a karstic basin situated on the southern margin of the Arabian Desert, a climatic sensitive zone that responds to small-scale hydrological changes. A multi-proxy approach applied on a lacustrine sedimentary record from paleo-lake Gayal el Bazal provides a long, continuous, and high-resolution dataset inhibiting a broader understanding of environmental and climatic changes dating back to the last 1200 years. Variations in sediment lithology and sedimentology from the lake core suggest fluctuation in the precipitation regime during the late Holocene. We identified two globally recognized events from the sediment core retrieved from this lake (i) Medieval Climate Anomaly (MCA) and (ii) Little Ice Age (LIA). Moreover, we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution. Specifically, how paleo-lake Gayal elBazal responds to the changing hydro-climate conditions, including water-level, salinity, and productivity. The study reveals during the wet climatic conditions, there is an increase in the input of freshwater through ephemeral wadi influxes, which leads to an increase in the nutrient content of the lake. This process causes an upsurge in the lake productivity, as estimated by n-alkane proxies. As the lake level rises and macrophytes increase, there is a rise in the prevalence of swimmer ostracod species such as B. lineata and a decrease in chironomids production.

Lake Karif Shawran occupies a volcanic crater in close proximity to Arabian Sea. The lake is fed by seawater seepage, thereby providing optimal conditions for mangrove growth and algae blooms. A multi-proxy approach involving elemental concentration, TOC/TIC, grain size, ostracods analysis as well as biomarker (n-alkane) investigations was carried out on ~1 m long sediment core retrieved from the lake. The chronology presented here is based on four radiocarbon ages derived from ostracod shells that reach ~4400 yr BP. The results suggest alternating wet and dry intervals marked by lamina-scale alternations of aragonite and organic detritus layers, with wet periods coinciding with globally recognized events like the Medieval Climate Anomaly (MCA) and Roman Warming Period (RWP), and dry intervals coinciding with the Little Ice Age (LIA), Late Antique Little Ice Age (LALIA), and ‘4.2 ky event’. This study investigates the climate and cultural implication in the southern Arabian desert of Yemen by integrating a high-resolution paleoclimate record from Lake Karif Shawran with historical and archaeological data. The study also highlights the significant sensitivity of agriculture-based economies and socio-political unrest in kingdoms during the late Holocene period to climatic variations.

Overall, we have reconstructed the late Holocene in the southern Arabian desert, and discussed the impact of climate on the regional environment and lake system. Moreover, estimating the impact of climate on humans in the region by differentiating climatic signals from anthropogenic signals. The study provides key insights into the main driving forcing behind hydroclimatic changes in the region and sheds light on the role of the ITCZ vis-à-vis monsoonal dynamics. Additionally, it lays the foundation for better understanding long-term seasonal predictions for Southern Arabia.