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Late-Holocene climate and vegetation dynamics in eastern Lesotho highlands

Norström, Elin, Bringensparr, Caroline, Fitchett, Jennifer M, Grab, Stefan W, Rydberg, Johan, Kylander, Malin
C3 plants, aquatic organisms, calcium, carbon, chemical analysis, climate, highlands, hydrology, latitude, sediments, temperature, vegetation, wetlands, Lesotho
The eastern Lesotho highlands are of considerable hydrological importance to southern Africa as a so-called ‘water tower’ for the surrounding region. Here, we contribute proxy-data inferring climate and vegetation changes over the past 1600 years, assessing in parallel inorganic and organic chemical analyses on a sediment core from Ladybird wetland, eastern Lesotho. Several proxies were used to determine changes in local vegetation dynamics, productivity, hydrology (δ¹³ C, δ¹⁵ N, C/N, TOC) and the input and source of the detrital components (Ca/Ti, CIA). The first part of the multi-proxy record (AD 400–800) shows stable terrestrial conditions and low detrital input, followed by higher variability in almost all proxies between ca. AD 900 and 1200. The δ¹³ C record infers a higher proportion of C₄ vegetation, tentatively associated with higher temperatures during this phase, coeval with the Medieval Climate Anomaly (MCA). After AD 1200, local conditions change gradually from purely terrestrial, towards the typical wetland environment prevailing today. A higher proportion of C₃ plants and possibly an increase in aquatic organisms within the organic matrix corresponds with decreasing detrital input, suggesting locally high available moisture in this part of Lesotho during the Little Ice Age (LIA). Although age-model constraints impedes a robust regional comparison, the inferred climate variability is discussed as a tentative response to enhanced mid-latitude cyclonic activity during LIA, and the variable MCA climate conditions as indirectly dictated by changes in solar activity.