RESUMEN
Natural lakes are thought to be globally important sources of greenhouse gases (CO2, CH4, and N2O) to the atmosphere although nearly no data have been previously reported from Africa. We collected CO2, CH4, and N2O data in 24 African lakes that accounted for 49% of total lacustrine surface area of the African continent and covered a wide range of morphology and productivity. The surface water concentrations of dissolved CO2 were much lower than values attributed in current literature to tropical lakes and lower than in boreal systems because of a higher productivity. In contrast, surface water-dissolved CH4 concentrations were generally higher than in boreal systems. The lowest CO2 and the highest CH4 concentrations were observed in the more shallow and productive lakes. Emissions of CO2 may likely have been substantially overestimated by a factor between 9 and 18 in African lakes and between 6 and 26 in pan-tropical lakes.
RESUMEN
Robust reconstructions of paleoclimate and paleoenvironmental changes using stalagmite proxy records critically depend on detailed observations of the transfer function between the regional climate/environment, the karst aquifer hydrology, and finally the cave microclimate via monitoring, which is currently lacking in Madagascar. This paper reports the first monitoring study performed in Anjohibe Cave, in Mahajanga, NW Madagascar to understand the linkage between regional climatological changes and cave responses to such changes. In this research, we monitored (1) the drip water pH, TDS, EC, temperature, δ13CDIC, δ18Ow, δ2Hw, and elemental (Ca, Mg, Sr) composition, and (2) the cave atmosphere pCO2, relative humidity (RH) and temperature. Three significant findings were drawn from the results. First, the data show that air-to-air transfer is fast, and the internal parameters closely vary with the regional climatology. Second, rainfall to drip signal transfer is not immediate, and it can take few months to one season for the signals to be detected in the drip water due to the "epikarst storage effect". Lastly, CaCO3 precipitation is likely to occur during the winter-summer transition, during which prior carbonate precipitation was detected. Since the growth of speleothems is influenced by numerous cave-specific factors, this study, although preliminary, indicates that Anjohibe Cave drip waters are capable of registering changes in its surrounding environment. Such information is ultimately archived in speleothems to reconstruct paleoclimate and paleoenvironmental changes. Results from this research will be of high significance for those working on speleothems within Madagascar, and for those working on understanding the transfer of climatic variations to cave deposits.
RESUMEN
Madagascar and the Mascarene Islands of Mauritius and Rodrigues underwent catastrophic ecological and landscape transformations, which virtually eliminated their entire endemic vertebrate megafauna during the past millennium. These ecosystem changes have been alternately attributed to either human activities, climate change, or both, but parsing their relative importance, particularly in the case of Madagascar, has proven difficult. Here, we present a multimillennial (approximately the past 8000 years) reconstruction of the southwest Indian Ocean hydroclimate variability using speleothems from the island of Rodrigues, located â¼1600 km east of Madagascar. The record shows a recurring pattern of hydroclimate variability characterized by submillennial-scale drying trends, which were punctuated by decadal-to-multidecadal megadroughts, including during the late Holocene. Our data imply that the megafauna of the Mascarenes and Madagascar were resilient, enduring repeated past episodes of severe climate stress, but collapsed when a major increase in human activity occurred in the context of a prominent drying trend.