Palaeoclimate investigations in Sri Lanka have been rarely attempted despite being located directly in the path of the Inter Tropical Convergence Zone. In this study, a 4.1-m undisturbed sediment core was retrieved from the Bolgoda Lake situated in the western coast of Sri Lanka, and influenced by the strong southwest monsoons. Mollusc shells in the core were dated, and the age-depth model indicated a depositional history extending from 2941 cal yr BP to the present. Grain size, major and trace elements, total organic C and N content and stable C and N isotopes were analysed in freeze-dried sediments to reconstruct the palaeoclimate changes.The multi-proxy records in the core revealed four distinct zones that show distinct variations in physical and chemical conditions in the lake associated with climate change. Zone 1 (2941 to 2390 cal yr BP; 385-252 cm) indicated the climate to be warm and humid with intense precipitation. The resulting high lake level helped in organic matter preservation in bottom sediments. Zone 2 (2390 to 1782 cal yr BP; 252-140 cm) indicated an unstable dry period associated with weak precipitation. Consequently, low lake level and intense degradation of organic matter occurred in this zone. Zone 3 (1782 to 1299 cal yr BP; 140-60 cm) indicated a 2 resurgence of intense monsoon along with warm and humid conditions. Zone 4 (1299 cal yr BP to present; 60-0 cm) indicated dry conditions with less intense monsoon, low lake level and extensive degradation of organic matter. Vascular plants were the predominant organic matter source into the lake during the late Holocene. In contrast, algal input was significant between 2390 cal yr BP and 2153 cal yr BP. The palaeoclimate evidences in this study showed an overall weakening trend of SW monsoon during the late Holocene, and this was consistent with changes happening in other locations as in southern and western India.

The catastrophic impact and unpredictability of the Indian Ocean Monsoon (IOM) over South Asia are evident from devastating floods, mudslides and droughts in one of the most densely populated regions of the globe. However, our understanding as to how the IOM has varied in the past, as well as its impact on local environments, remains limited. This is particularly the case for Sri Lanka, where erosional landscapes have limited the availability of well-stratified, high-resolution terrestrial archives. Here, we present novel data from an undisturbed sediment core retrieved from the coastal Bolgoda Lake. This includes the presentation of a revised Late Holocene age model as well as an innovative combination of pollen, source-specific biomarkers, and compound-specific stable carbon isotopes of n-alkanes to reconstruct the shifts in precipitation, salinity and vegetation cover. Our record documents variable climate between 3000 years and the present, with arid conditions c. 2334 and 2067 cal a BP. This extreme dry period was preceded and followed by more wet conditions. The high-resolution palaeoenvironmental reconstruction fills a major gap in our knowledge on the ramifications of IOM shifts across South Asia and provides insights during a time of major redistribution of dense human settlements across Sri Lanka.

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The South Asian Monsoon (SAM) brings precipitation crucial for agriculture across the densely populated region of South Asia. Identifying the key long-term drivers of the SAM is essential to improve the predictability of future monsoonal trends in the context of current global climate scenarios and increasingly frequent drought and flooding events in this part of the world. Here, we reconstruct ∼6000 years of climatic and environmental history of the South Asian summer monsoon-fed Bolgoda South Lake and the Horton Plains, and the winter monsoon-fed Panama lagoon, in Sri Lanka to better understand monsoonal operation over this island and its connection to broader climate systems. Multiple proxies (diagnostic biomarkers, hydrogen and carbon isotopes of individual n-alkane, grain size, and Zr/Rb elemental ratio) indicate a sub-millennial scale decreasing trend of summer monsoon rainfall in the wet zone of Sri Lanka alongside an increasing trend of winter monsoon rainfall in the dry zone during the last ∼6000 years. We also observed multi-centennial scale arid events in the Bolgoda South Lake and Horton Plains records at ∼3,500 and ∼1,000 cal years BP. Inverse monsoonal behavior during the mid- and late Holocene seems to be led by the southward migration of the mean latitudinal position of ITCZ, induced by varying solar energy distribution between the Northern and Southern hemispheres due to Earth’s processional cycle. Our observations are broadly supported by existing paleoclimatic records from the Indian sub-continent, but abrupt arid phases are asynchronous in the regional records. In addition, these short-term arid conditions do not show systematic correlations with the different modes of climate variables known to have teleconnections with the Indian Ocean monsoon.

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Investigation of Homo sapiens’ palaeogeographic expansion into African mountain environments are changing the understanding of our species’ adaptions to various extreme Pleistocene climates and habitats. Here, we present a vegetation and precipitation record from the Ha Makotoko rockshelter in western Lesotho, which extends from ~60,000 to 1,000 years ago. Stable carbon isotope ratios from plant wax biomarkers indicate a constant C3-dominated ecosystem up to about 5,000 years ago, followed by C4 grassland expansion due to increasing Holocene temperatures. Hydrogen isotope ratios indicate a drier, yet stable, Pleistocene and Early Holocene compared to a relatively wet Late Holocene. Although relatively cool and dry, the Pleistocene was ecologically reliable due to generally uniform precipitation amounts, which incentivized persistent habitation because of dependable freshwater reserves that supported rich terrestrial foods and provided prime locations for catching fish.