High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa

Maarten Blaauw, Bas van Geel, Iris Kristen, Birgit Plessen, Anna Lyaruu, Daniel R. Engstrom, Johannes van der Plicht, Dirk Verschuren

Research output: Contribution to journalArticlepeer-review

49 Scopus citations

Abstract

We dated a continuous, ∼22-m long sediment sequence from Lake Challa (Mt. Kilimanjaro area, Kenya/Tanzania) to produce a solid chronological framework for multi-proxy reconstructions of climate and environmental change in equatorial East Africa over the past 25,000 years. The age model is based on a total of 168 AMS 14C dates on bulk-organic matter, combined with a 210Pb chronology for recent sediments and corrected for a variable old-carbon age offset. This offset was estimated by i) pairing bulk-organic 14C dates with either 210Pb-derived time markers or 14C dates on grass charcoal, and ii) wiggle-matching high-density series of bulk-organic 14C dates. Variation in the old-carbon age offset through time is relatively modest, ranging from ∼450 yr during glacial and late glacial time to ∼200 yr during the early and mid-Holocene, and increasing again to ∼250 yr today. The screened and corrected 14C dates were calibrated sequentially, statistically constrained by their stratigraphical order. As a result their constrained calendar-age distributions are much narrower, and the calibrated dates more precise, than if each 14C date had been calibrated on its own. The smooth-spline age-depth model has 95% age uncertainty ranges of ∼50-230 yr during the Holocene and ∼250-550 yr in the glacial section of the record. The δ13C values of paired bulk-organic and grass-charcoal samples, and additional 14C dating on selected turbidite horizons, indicates that the old-carbon age offset in Lake Challa is caused by a variable contribution of old terrestrial organic matter eroded from soils, and controlled mainly by changes in vegetation cover within the crater basin.

Original languageEnglish (US)
Pages (from-to)3043-3059
Number of pages17
JournalQuaternary Science Reviews
Volume30
Issue number21-22
DOIs
StatePublished - Oct 1 2011
Externally publishedYes

Bibliographical note

Funding Information:
This research was sponsored by funding agencies in Belgium (FWO-Vlaanderen project FWO G.0641.05 ), Denmark (NERI) , Germany (DFG) and The Netherlands (NWO-ALW project 855.01.083 ) through the European Science Foundation (ESF) EuroCORES programme EuroCLIMATE. We thank M. van Hardenbroek for discussion, and David Williamson and an anonymous referee for their comments on a previous version of this manuscript.

Keywords

  • 14C age offsets
  • 14C chronology
  • Bayesian age-depth modelling
  • Equatorial East Africa

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