Organic geochemical records from Lake Malawi (East Africa) of the last 700 years, part II: Biomarker evidence for recent changes in primary productivity

Isla S. Castañeda, Josef P. Werne, Thomas C. Johnson, Lindsay A. Powers

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36 Scopus citations

Abstract

Relatively few well-dated and high-resolution paleoclimate records of the past few centuries presently exist from tropical East Africa. Here, we examine the bulk and molecular geochemical records of two varved sediment cores from Lake Malawi, which together provide a continuous record of environmental variability in East Africa of the last 730years. We observe a number of changes in the aquatic ecosystem of Lake Malawi, which are likely attributed to both natural climatic forcing and anthropogenic activities. Biomarkers of dinoflagellates (dinosterol) and bacterivorous ciliates (tetrahymanol) display increased accumulation rates from ~1900AD to the present, while a simultaneous decrease in accumulation rates of diatom biomarkers (isololiolide/loliolide) is observed. Increased accumulation rates of retene, a compound derived from conifers, are also noted since ~1930AD and likely reflect increased soil erosion due to deforestation of the Lake Malawi watershed. Spectral analysis of the high-resolution TOC record indicates a periodicity of 204years, similar to the 206year cycle noted in 14C and 10Be records, suggesting a link between East African climate and solar forcing.

Original languageEnglish (US)
Pages (from-to)140-154
Number of pages15
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume303
Issue number1-4
DOIs
StatePublished - Apr 1 2011

Bibliographical note

Funding Information:
We wish to thank Yongsong Huang (Brown University) for providing n -alkane δ 13 C analyses, and David Hollander (University of South Florida) and William P. Patterson (University of Saskatchewan) for providing bulk 13 C analyses. We also wish to thank Sarah Grosshuesch (Large Lakes Observatory) and Marcelo Alexandre (Brown University) for analytical assistance. Stefan Schouten (Royal Netherlands Institute for Sea Research) and Simon Brassell (Indiana University) are thanked for assistance with compound identification. We thank Phil Meyers and an anonymous reviewer for comments that improved this manuscript. This material is based in part upon work supported by the National Science Foundation under Grant No. ATM-9709291 to T. Johnson. Additional support was provided by an award from the Research Corporation to J. Werne and fellowship support from the University of Minnesota and the Ford Foundation to I. Castañeda.

Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.

Keywords

  • Biomarker
  • C25 n-alkanol
  • Lake Malawi
  • Phytoplankton
  • Primary productivity

Continental Scientific Drilling Facility tags

  • M98

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