The Holocene History of Lake Kivu (East Africa): New perspectives from new cores
2014-07
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The Holocene History of Lake Kivu (East Africa): New perspectives from new cores
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2014-07
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Lake Kivu lies at the heart of East Africa&lsquos rift lakes in a volcanically active region. Hydrothermal seeps impose a complex stratification regime with heated, high-salinity waters entering below 280 m water depth. Previous detailed studies of fossil diatoms and mineralogy of the sediment record suggest this hydrothermal activity began 5,000 years BP. Unfortunately, dating bulk organic matter of these original cores was problematic due to dissolved volcanogenic CO<sub>2</sub>. This study offers a new chronology and a detailed perspective on the limnologic history of Lake Kivu through investigation of carbonates and bulk organic matter from sediment cores recovered in 2012 and 2013. A Holocene history was compiled by <super>14</super>C dating of recovered terrestrial macro fossils from a deep, central basin core, and by <super>210</super>Pb geochronology of recent sediments from a near shore core. Water levels in Lake Kivu rose during the African Humid Period (AHP) pluvial from 12 ka to 5 ka. Authigenic CaCO<sub>3</sub> deposition began around 4.2 ka in the deep, main basin with all subsequent carbonate intervals composed of endogenic aragonite. A solute budget reveals that most of the Ca<super>2+</super> ion is supplied at depth via the hydrothermal seeps and suggests that this sub-lacustrine input was initiated just prior to onset of carbonate deposition. Stable isotopic analyses of δ<super>13</super>C<sub>aragonite</sub> and δ<super>13</super>C<sub>OM</sub> both indicate slight enrichment beyond the expected kinetic fractionation and above other East African lakes suggesting volcanogenic influence on water column DIC began around 4.2 ka. Some of the alternating intervals of carbonate deposition and cessation in the late-Holocene, and associated δ<super>18</super>O<sub>aragonite</sub> enrichment, coincide with records of drought from nearby Lake Edward, such as at the AHP termination, at 2 ka, and during the Little Ice Age. This suggests a climate overprint on the predominantly volcanogenic record of carbonate sedimentation in Lake Kivu.
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University of Minnesota M.S. thesis. July 2014. Major: Geological Sciences. Advisors:Thomas C. Johnson and Robert E. Hecky. 1 computer file (PDF); iv, 106 pages, appendices 1-4.
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