Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: New constraints from laminae analysis and radiocarbon age modeling

Timothy M. Shanahan, J. Warren Beck, Jonathan T. Overpeck, Nicholas P. McKay, Jeffrey S. Pigati, John A. Peck, Christopher A. Scholz, Clifford W. Heil, John King

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

The Lake Bosumtwi sediment record represents one of the longest and highest-resolution terrestrial records of paleoclimate change available from sub-Saharan Africa. Here we report a new sediment age model framework for the last ~. 45. cal kyr of sedimentation using a combination of high-resolution radiocarbon dating, Bayesian age-depth modeling and lamination counting. Our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities, radiocarbon uncertainties of at least a few hundred years are unavoidable. Age model uncertainties are smallest during the Holocene (205. yr) and the glacial (360. yr) but are large at the base of the record (1660. yr), due to a combination of decreasing sample density, larger calibration uncertainties and increases in radiocarbon age scatter. For portions of the chronology older than ~. 35. cal kyr, additional considerations, such as the use of a low-blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon. A comparison of radiocarbon age model results and lamination counts over the time interval ~. 15-30. cal kyr agree with an overall discrepancy of ~. 10% and display similar changes in sedimentation rate, supporting the annual nature of sediment laminations in the early part of the record. Changes in sedimentation rates reconstructed from the age-depth model indicate that intervals of enhanced sediment delivery occurred at 16-19, 24 and 29-31. cal kyr, broadly synchronous with reconstructed drought episodes elsewhere in northern West Africa and potentially, with changes in Atlantic meridional heat transport during North Atlantic Heinrich events. These data suggest that millennial-scale drought events in the West African monsoon region were latitudinally extensive, reaching within several hundred kilometers of the Guinea coast. This is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt, and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt, decreased convection, or both.

Original languageEnglish (US)
Pages (from-to)49-60
Number of pages12
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume361-362
DOIs
StatePublished - Nov 15 2012

Bibliographical note

Funding Information:
We thank the people of Abono, Ghana and the other towns surrounding Lake Bosumtwi for their assistance during fieldwork as well as the researchers in the Arizona AMS Facility for their help in preparing and analyzing radiocarbon samples. The research was funded in part by National Science Foundation grants EAR0601998 , ATM0401908 , ATM0214525 , and ATM0096232 .

Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.

Keywords

  • Age model
  • Lake
  • Paleoclimate
  • Radiocarbon
  • West Africa

Continental Scientific Drilling Facility tags

  • GLAD6

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