Atmospheric Controls on Precipitation Isotopes and Hydroclimate in High-elevation Regions in Eastern Africa Since the Last Glacial Maximum
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Date
2021Author
Garelick, Sloane
James M. Russel, James M
Dee, Sylvia
Verschuren, Dirk
Olago, Daniel O
Type
ArticleLanguage
enMetadata
Show full item recordAbstract
Tropical Africa experienced large changes in hydroclimatic conditions since the Last Glacial Maximum
(LGM), ∼26.5 to 19 thousand years (ka or kyr) ago. The hydrogen isotopic composition of fossil leaf
waxes (δD wax ), assumed to record past variations in the hydrogen isotopic composition of precipitation
(δD precip ), is increasingly being used to study past hydroclimatic change in Africa, and are commonly
interpreted to reflect variation in the amount of precipitation through time (i.e., the amount effect).
Although there are now many such δD precip records from tropical Africa, there are few robust δD precip
records from easternmost equatorial Africa of sufficient length and resolution to evaluate the mechanisms
governing hydroclimate variation during and since the LGM. We produced a new δD precip record based on
analyses of δD wax in sediment cores collected from Lake Rutundu, situated at an elevation of 3,078 meters
above sea level (m asl) on Mt. Kenya. This record displays large variations in δD precip corresponding with
known climate events over the past 25 kyr, including D-enrichment during the Heinrich 1 stadial (H1)
and the Younger Dryas (YD), and D-depletion during the Holocene portion of the African Humid Period
(AHP). We also observe D-depletion during the LGM relative to the late Holocene, which, considering
the amount effect, could be interpreted to imply that LGM climate conditions were wetter than today.
However, because other hydroclimate proxies at this site indicate a drier LGM climate at Lake Rutundu,
and since precipitation isotopes at this high-elevation site are likely influenced by different processes
than at low elevations, we used a single-column Rayleigh distillation model to evaluate temperature
and altitude-related effects on high-elevation δD precip . This revealed that a change in the temperature
lapse rate exerts strong control on δD precip in this high-elevation setting, and that a steeper lapse rate
could explain the observed D-depletion during the LGM at our site. Comparison of the Lake Rutundu
δD precip record with other leaf-wax based δD precip records from East Africa indicates that changes in the
meridional precipitation gradient associated with the mean annual position and intensity of the tropical
rain belt, in turn driven by precessional insolation forcing, were likely a primary control on East African
hydroclimate over the past 25 kyr, thereby contributing to overall regional drying during the LGM.
Citation
Garelick S, Russell JM, Dee S, Verschuren D, Olago DO. "Atmospheric controls on precipitation isotopes and hydroclimate in high-elevation regions in Eastern Africa since the Last Glacial Maximum.". 2021;567:116984.Publisher
University of Nairobi
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Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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